Preface

The range of industries utilizing drilling is wide and includes machining and manufacturing, oil and gas, construction, mining, and so on. The success of drilling operations depends on many factors and much progress has been made in this regard. This book presents the latest scientific and engineering achievements in drilling. It covers new and creative methods of performing this operation, applications of drilling, and process optimization methods to enhance the efficiency and productivity of drilling while lowering associated costs and time. I hope researchers, engineers, and scientists reading this book will find it useful in enhancing the quality of their work and research.

The research presented in this book is that of scientists and engineers from various countries around the world. I am thankful to all the contributors for their work. I would also like to thank Mr. Muhammad Aamir who assisted me in the review process, and Ms. Sara Gojević-Zrnić and the staff at IntechOpen for their continuous support in seeing this book through to publication. Lastly, I give special thanks to my wife, Mahtab Moradi, for her encouragement and support while I was editing this book.

> **Dr. Majid Tolouei-Rad** School of Engineering, Edith Cowan University, Perth, Australia

**1**

**Chapter 1**

Technology

to generate holes on the hard materials.

**1. Introduction**

drilling operations.

quality [4, 5].

very common.

Introductory Chapter: Drilling

Drilling technology has been widely used in many industries such as manufacturing,

mining, oil and gas, and construction. In manufacturing industries, drilling processes are not limited to conventional methods where a physical contact is made between the cutting tool and the solid material. Non-conventional drilling processes use forms of energy such as electrical, chemical, electrochemical, thermal and heat,

Among all drilling processes, conventional drilling with twist drill bits is the first operation attracting extensive attention of researchers. Therefore, the fact that majority of today's products incorporate holes generated by drilling operations cannot be ignored. In various industries, drilling is one of the essential operations, where the joint's life can be critically affected by the quality of the drilled holes. Drilling is often considered the final machining operation during assembly of components, where an efficient drilling process provides superior quality of drilled holes to ensure high strength and high efficiency [1]. A low-quality drilled hole can result in cracks within the structure, which ultimately reduce their service lifetime and add extra costs for maintenance [2]. This is why the drilling process is acknowledged as a more challenging issue during assembly and is the most common, frequent and necessary processing craft in various industries. Therefore, both academia and industries are highly motivated for research on the applications of

However, the drilling process required the use of right cutting tools together with appropriate cutting parameters, such as cutting speed or spindle speed, feed rate, and a reliable machine tool setup, to ensure high quality holes in terms of low surface roughness, cylindricity, circularity, perpendicularity and less formation of burrs [3]. Therefore, the drilling process can be explicitly understood by proper selection and optimization of process parameters without compromising productivity and hole

Drilling operations form the largest portion of machining operations in manufacturing industries; therefore, conventional and CNC machines do not give a high production rate where production volumes are huge. In contrast, special purpose machines can provide very high production rates for performing drilling and drilling-related operations including tapping and reaming. The production rates of these machines are many times higher than conventional and CNC machines. In addition, the quality and uniformity of production are superior compared to conventional methods. **Figure 1** shows a two-station special-purpose machine used to perform drilling and tapping operations. The production rate increases as the number of workstations increases, since the machine can perform multiple operations simultaneously. Special purpose machines with 8, 10, and 12 workstations are

*Majid Tolouei-Rad and Muhammad Aamir*

### **Chapter 1**

## Introductory Chapter: Drilling Technology

*Majid Tolouei-Rad and Muhammad Aamir*

### **1. Introduction**

Drilling technology has been widely used in many industries such as manufacturing, mining, oil and gas, and construction. In manufacturing industries, drilling processes are not limited to conventional methods where a physical contact is made between the cutting tool and the solid material. Non-conventional drilling processes use forms of energy such as electrical, chemical, electrochemical, thermal and heat, to generate holes on the hard materials.

Among all drilling processes, conventional drilling with twist drill bits is the first operation attracting extensive attention of researchers. Therefore, the fact that majority of today's products incorporate holes generated by drilling operations cannot be ignored. In various industries, drilling is one of the essential operations, where the joint's life can be critically affected by the quality of the drilled holes. Drilling is often considered the final machining operation during assembly of components, where an efficient drilling process provides superior quality of drilled holes to ensure high strength and high efficiency [1]. A low-quality drilled hole can result in cracks within the structure, which ultimately reduce their service lifetime and add extra costs for maintenance [2]. This is why the drilling process is acknowledged as a more challenging issue during assembly and is the most common, frequent and necessary processing craft in various industries. Therefore, both academia and industries are highly motivated for research on the applications of drilling operations.

However, the drilling process required the use of right cutting tools together with appropriate cutting parameters, such as cutting speed or spindle speed, feed rate, and a reliable machine tool setup, to ensure high quality holes in terms of low surface roughness, cylindricity, circularity, perpendicularity and less formation of burrs [3]. Therefore, the drilling process can be explicitly understood by proper selection and optimization of process parameters without compromising productivity and hole quality [4, 5].

Drilling operations form the largest portion of machining operations in manufacturing industries; therefore, conventional and CNC machines do not give a high production rate where production volumes are huge. In contrast, special purpose machines can provide very high production rates for performing drilling and drilling-related operations including tapping and reaming. The production rates of these machines are many times higher than conventional and CNC machines. In addition, the quality and uniformity of production are superior compared to conventional methods. **Figure 1** shows a two-station special-purpose machine used to perform drilling and tapping operations. The production rate increases as the number of workstations increases, since the machine can perform multiple operations simultaneously. Special purpose machines with 8, 10, and 12 workstations are very common.

A significant 59% cost reduction is reported in the literature when a specialpurpose machine is used in place of a CNC machine, and the cost reduction is an impressive 95.5% when compared to a conventional machine [6]. Although these machines are capable of improving the quality and quantity of the parts produced compared to conventional machines, the utilization of this technology is not proportional to its benefits [6]. This, to a large extent, is attributed to the lack of a solid foundation for feasibility analysis of utilization of these machines. To tackle this, extensive research has been performed by contemporary researchers and models are developed for feasibility analysis of the utilization of such machines; both technically and economically [7–9]. The models developed can assist engineers

**3**

**Author details**

Majid Tolouei-Rad\* and Muhammad Aamir

provided the original work is properly cited.

\*Address all correspondence to<EMAIL_ADDRESS>
The authors declare no conflict of interest.

School of Engineering, Edith Cowan University, Joondalup, WA, Australia

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Introductory Chapter: Drilling Technology DOI: http://dx.doi.org/10.5772/intechopen.97648*

compared to other alternatives.

three holes simultaneously.

fragmented chips [13].

**Conflict of interest**

and manufacturing firms in deciding when this technology gives superior results

Another essential accessory for the drilling operation is the poly-drill head, which can increase production by creating many holes simultaneously [10]. Poly-drill heads are used for drilling and drilling-related operations. As these can perform multiple operations simultaneously, then the overall machining time is reduced significantly, resulting in a huge improved productivity [11, 12]. Poly-drill heads are of fixed and adjustable types, and the number of spindles could vary from two to more than 10. In the adjustable type, the position of the spindles can change providing varied center-to-center distances of the holes within a range. Poly-drills could be used on the conventional drill presses, milling machines, CNC machines, and special-purpose machines. **Figure 2** shows a threespindle poly-drill head mounted on a conventional milling machine for drilling

Poly drill head also ensures advantages like less rejection of parts by providing better accuracy, less operator fatigue and time saved in the operation.

A significant 59% cost reduction is reported in the literature when a specialpurpose machine is used in place of a CNC machine, and the cost reduction is an impressive 95.5% when compared to a conventional machine [6]. Although these machines are capable of improving the quality and quantity of the parts produced compared to conventional machines, the utilization of this technology is not proportional to its benefits [6]. This, to a large extent, is attributed to the lack of a solid foundation for feasibility analysis of utilization of these machines. To tackle this, extensive research has been performed by contemporary researchers and models are developed for feasibility analysis of the utilization of such machines; both technically and economically [7–9]. The models developed can assist engineers

*A poly-drill head with three adjustable spindles mounted on conventional milling machine.*

*Flex drill: A special purpose machine used for performing drilling and tapping operations [6].*

and manufacturing firms in deciding when this technology gives superior results compared to other alternatives.

Another essential accessory for the drilling operation is the poly-drill head, which can increase production by creating many holes simultaneously [10]. Poly-drill heads are used for drilling and drilling-related operations. As these can perform multiple operations simultaneously, then the overall machining time is reduced significantly, resulting in a huge improved productivity [11, 12]. Poly-drill heads are of fixed and adjustable types, and the number of spindles could vary from two to more than 10. In the adjustable type, the position of the spindles can change providing varied center-to-center distances of the holes within a range. Poly-drills could be used on the conventional drill presses, milling machines, CNC machines, and special-purpose machines. **Figure 2** shows a threespindle poly-drill head mounted on a conventional milling machine for drilling three holes simultaneously.

Poly drill head also ensures advantages like less rejection of parts by providing better accuracy, less operator fatigue and time saved in the operation. A poly drill head or multi-spindle drill head performed better than the one-shot drilling process by giving a better hole quality, less tool wear, and producing small and fragmented chips [13].

### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Majid Tolouei-Rad\* and Muhammad Aamir School of Engineering, Edith Cowan University, Joondalup, WA, Australia

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Aamir M, Giasin K, Tolouei-Rad M, Vafadar A. A review: drilling performance and hole quality of aluminium alloys for aerospace applications. Journal of Materials Research and Technology. 2020;9(6):12484-500.

[2] Aamir M, Tolouei-Rad M, Giasin K, Nosrati A. Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review. The International Journal of Advanced Manufacturing Technology. 2019; 105(5-6):2289-308.

[3] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Feasibility of tool configuration and the effect of tool material, and tool geometry in multihole simultaneous drilling of Al2024. The International Journal of Advanced Manufacturing Technology. 2020;111(3):861-79.

[4] Karataş MA, Gökkaya H. A review on machinability of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composite materials. Defence Technology. 2018;In Press.

[5] Aamir M, Tu S, Tolouei-Rad M, Giasin K, Vafadar A. Optimization and modeling of process parameters in multi-hole simultaneous drilling using taguchi method and fuzzy logic approach. Materials. 2020;13(3):680.

[6] Tolouei-Rad M. Intelligent analysis of utilization of special purpose machines for drilling operations. Intelligent Systems, Prof Vladimir M Koleshko (Ed), ISBN: 978-953-51-0054-6, InTech, Available from: http://wwwintechopen com/books/intelligent-systems/ intelligent-analysis-of-utilization-ofspecial-purposemachines-for-drillingoperations. Croatia2012. p. 297-320.

[7] Vafadar A, Tolouei-Rad M, Hayward K. An integrated model to use drilling modular machine tools. The International Journal of Advanced Manufacturing Technology. 2019; 102(5):2387-97.

[8] Vafadar A, Tolouei-Rad M, Hayward K, Abhary K. Technical feasibility analysis of utilizing special purpose machine tools. Journal of Manufacturing Systems. 2016;39:53-62.

[9] Vafadar A, Hayward K, Tolouei-Rad M. Drilling reconfigurable machine tool selection and process parameters optimization as a function of product demand. Journal of Manufacturing Systems. 2017;45:58-69.

[10] Tolouei-Rad M, Aamir M. Analysis of the Performance of Drilling Operations for Improving Productivity. In: Tolouei-Rad M, editor. Drilling. London, UK: IntechOpen, Available from: https://www.intechopen.com/ online-first/analysis-of-theperformance-of-drilling-operations-forimproving-productivity; 2021.

[11] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Machinability of Al2024, Al6061, and Al5083 alloys using multihole simultaneous drilling approach. Journal of Materials Research and Technology. 2020;9(5):10991-1002.

[12] Aamir M, Tolouei-Rad M, Vafadar A, Raja MNA, Giasin K. Performance Analysis of Multi-Spindle Drilling of Al2024 with TiN and TiCN Coated Drills Using Experimental and Artificial Neural Networks Technique. Applied Sciences. 2020;10(23):8633.

[13] Aamir M, Tu S, Giasin K, Tolouei-Rad M. Multi-hole simultaneous drilling of aluminium alloy: A preliminary study and evaluation against one-shot drilling process. Journal of Materials Research and Technology. 2020;9(3):3994-4006.

**5**

**Chapter 2**

**Abstract**

Productivity

investigated and discussed.

the fabrication of various industrial parts [3].

**1. Introduction**

Analysis of the Performance of

*Majid Tolouei-Rad and Muhammad Aamir*

Drilling Operations for Improving

Drilling is a vital machining process for many industries. Automotive and aerospace industries are among those industries which produce millions of holes where productivity, quality, and precision of drilled holes plays a vital role in their success. Therefore, a proper selection of machine tools and equipment, cutting tools and parameters is detrimental in achieving the required dimensional accuracy and surface roughness. This subsequently helps industries achieving success and improving the service life of their products. This chapter provides an introduction to the drilling process in manufacturing industries which helps improve the quality and productivity of drilling operations on metallic materials. It explains the advantages of using multi-spindle heads to improve the productivity and quality of drilled holes. An analysis of the holes produced by a multi-spindle head on aluminum alloys Al2024, Al6061, and Al5083 is presented in comparison to traditional single shot drilling. Also the effects of using uncoated carbide and high speed steel tools for producing high-quality holes in the formation of built-up edges and burrs are

**Keywords:** drilling, cutting tools, hole quality, productivity, multi-spindle head

industries. Therefore, the analysis and improvement of this process are of great importance in increasing productivity and competitiveness, where many existing studies reported on the optimization and improvement of this process [1, 2]. There are many machines that perform drilling operations including dedicated drilling machines, lathes, milling machines, machining centers and special purpose machines. The drilling process is extensively and heavily used in industries, accounting for a large portion of overall machining time and costs. Therefore, drilling has a significant economic role in industries, where it hugely contributes to

Hole-making processes using drilling operations have been the focus of many research studies, where a lot of development and progress has been made. However, as technology has progressed and newer tools and equipment have been introduced, further research is required to improve the productivity and efficiency of this important operation, which forms the core of activities in many industries [4, 5].

Drilling is the most commonly performed machining operation in manufacturing

**Chapter 2**

## Analysis of the Performance of Drilling Operations for Improving Productivity

*Majid Tolouei-Rad and Muhammad Aamir*

### **Abstract**

Drilling is a vital machining process for many industries. Automotive and aerospace industries are among those industries which produce millions of holes where productivity, quality, and precision of drilled holes plays a vital role in their success. Therefore, a proper selection of machine tools and equipment, cutting tools and parameters is detrimental in achieving the required dimensional accuracy and surface roughness. This subsequently helps industries achieving success and improving the service life of their products. This chapter provides an introduction to the drilling process in manufacturing industries which helps improve the quality and productivity of drilling operations on metallic materials. It explains the advantages of using multi-spindle heads to improve the productivity and quality of drilled holes. An analysis of the holes produced by a multi-spindle head on aluminum alloys Al2024, Al6061, and Al5083 is presented in comparison to traditional single shot drilling. Also the effects of using uncoated carbide and high speed steel tools for producing high-quality holes in the formation of built-up edges and burrs are investigated and discussed.

 Introduction**

Drilling is the most commonly performed machining operation in manufacturing industries. Therefore, the analysis and improvement of this process are of great importance in increasing productivity and competitiveness, where many existing studies reported on the optimization and improvement of this process [1, 2]. There are many machines that perform drilling operations including dedicated drilling machines, lathes, milling machines, machining centers and special purpose machines. The drilling process is extensively and heavily used in industries, accounting for a large portion of overall machining time and costs. Therefore, drilling has a significant economic role in industries, where it hugely contributes to the fabrication of various industrial parts [3].

Hole-making processes using drilling operations have been the focus of many research studies, where a lot of development and progress has been made. However, as technology has progressed and newer tools and equipment have been introduced, further research is required to improve the productivity and efficiency of this important operation, which forms the core of activities in many industries [4, 5].

**4**

*Drilling Technology*

**References**

2020;9(6):12484-500.

105(5-6):2289-308.

[1] Aamir M, Giasin K, Tolouei-Rad M, Vafadar A. A review: drilling performance and hole quality of aluminium alloys for aerospace applications. Journal of Materials Research and Technology.

drilling modular machine tools. The International Journal of Advanced Manufacturing Technology. 2019;

[8] Vafadar A, Tolouei-Rad M, Hayward K, Abhary K. Technical feasibility analysis of utilizing special purpose machine tools. Journal of Manufacturing Systems. 2016;39:53-62.

[9] Vafadar A, Hayward K,

of product demand. Journal of

of the Performance of Drilling

online-first/analysis-of-the-

improving-productivity; 2021.

[12] Aamir M, Tolouei-Rad M, Vafadar A, Raja MNA, Giasin K. Performance Analysis of Multi-Spindle Drilling of Al2024 with TiN and TiCN Coated Drills Using Experimental and Artificial Neural Networks Technique. Applied Sciences. 2020;10(23):8633.

[13] Aamir M, Tu S, Giasin K,

drilling of aluminium alloy: A preliminary study and evaluation against one-shot drilling process. Journal of Materials Research and Technology. 2020;9(3):3994-4006.

Tolouei-Rad M. Multi-hole simultaneous

Tolouei-Rad M. Drilling reconfigurable machine tool selection and process parameters optimization as a function

Manufacturing Systems. 2017;45:58-69.

[10] Tolouei-Rad M, Aamir M. Analysis

Operations for Improving Productivity. In: Tolouei-Rad M, editor. Drilling. London, UK: IntechOpen, Available from: https://www.intechopen.com/

performance-of-drilling-operations-for-

[11] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Machinability of Al2024, Al6061, and Al5083 alloys using multihole simultaneous drilling approach. Journal of Materials Research and Technology. 2020;9(5):10991-1002.

102(5):2387-97.

[2] Aamir M, Tolouei-Rad M, Giasin K, Nosrati A. Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review. The International Journal of Advanced Manufacturing Technology. 2019;

[3] Aamir M, Tolouei-Rad M, Giasin K,

[4] Karataş MA, Gökkaya H. A review on machinability of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composite materials. Defence Technology. 2018;In Press.

[5] Aamir M, Tu S, Tolouei-Rad M, Giasin K, Vafadar A. Optimization and modeling of process parameters in multi-hole simultaneous drilling using taguchi method and fuzzy logic approach. Materials. 2020;13(3):680.

[6] Tolouei-Rad M. Intelligent analysis of utilization of special purpose machines for drilling operations. Intelligent Systems, Prof Vladimir M Koleshko (Ed), ISBN: 978-953-51-0054-6, InTech, Available from: http://wwwintechopen com/books/intelligent-systems/ intelligent-analysis-of-utilization-ofspecial-purposemachines-for-drillingoperations. Croatia2012. p. 297-320.

[7] Vafadar A, Tolouei-Rad M,

Hayward K. An integrated model to use

Vafadar A. Feasibility of tool configuration and the effect of tool material, and tool geometry in multihole simultaneous drilling of Al2024. The International Journal of Advanced

Manufacturing Technology.

2020;111(3):861-79.

For example, the heat exchangers of nuclear energy centrals require up to 16,000 holes in a single exchanger for assembly with refrigeration tubes [6]. Other examples include the automotive industry, where the drilling process forms up to 40% of total material removed [7], or the aerospace industry where millions of holes are required for joining various parts of aircraft fuselage [8]. It is estimated that 750,000 holes are required in a single wing of an Airbus A380, with 1.5–3 million holes as the requirements for producing a typical commercial aircraft [7]. Furthermore, over a million rivets are needed for large ships [9] where drilling is the primary process. Therefore, a proper selection of machine tools and equipment, cutting tools and parameters is essential in achieving required productivity, dimensional accuracy, and surface roughness. This subsequently helps industries achieve success and improve the service life of their products.

### **2. The drilling process**

In the drilling process, holes are created when a cylindrical tool rotates against a workpiece, where a tool called a drill bit is used as shown in **Figure 1** [10, 11]. The drilling operation process involves three stages: the start and centering stage, the full drilling stage and the breakthrough stage [12]. In the first stage, the exact position of the hole is required, whereas the second stage leads to the full engagement of the drill bit, whilst the last stage includes passing the drill through the underside of the workpiece, where the operation stops [13].

A hole in the drilling process can be created in many forms, including blind and through holes, as shown in **Figure 2**. Blind holes are drilled to a certain depth whilst through-holes refer to the condition when the drill bit passes through the material and exits the workpiece on the other side [13].

Generally, a depth to diameter ratio of 5:1 or greater is commonly performed by twist drills, where this ratio may be doubled when using high-performance twist drills equipped with through-tool coolant systems. This ratio can be increased to roughly 20:1 when using special deep hole drilling tools equipped with through-tool coolant systems. Whilst this chapter focuses on the use of twist drills, it is worthnoting that a depth to diameter ratio of 100:1 or more is achievable in gun-drilling machines with through-tool coolant systems. Unlike conventional drilling operations, within gun-drilling machines both the cutting tool and workpiece rotate in opposite directions and at different rotational speeds, which significantly improves the straightness of the deep hole that is generated [14].

**7**

*Analysis of the Performance of Drilling Operations for Improving Productivity*

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

**3. Cutting conditions in drilling process**

*Drilling process: (a) blind holes (b) through holes [10].*

where *v* is the cutting speed in m/min,

cutting tool in mm, and *n* is the spindle speed in rev/min.

multiplied by the spindle speed. Hence, feed rate can be found as.

**3.1 Spindle speed and cutting speed**

ing operation is computed by.

**Figure 2.**

**3.2 Feed and feed rate**

spindle speed in rev/min.

**3.3 Material removal rate**

obtained by [15].

rate, and machining time, as discussed in this section below.

To a large extent, cutting conditions determine the success of any drilling operation. Basic cutting conditions include cutting speed, feed rate, material removal

The spindle speed is the rotational speed measured in rev/min, calculated using

*dn*

π

In a drilling process feed is specified in mm/rev. The feed rate, which is the linear

travel rate in mm/min, can be adjusted by a convenient system when the feed is

where *<sup>r</sup> f* is the feed rate in mm/min, *f* is the feed in mm/rev, and *n* is the

The material removal rate can be considered as an index for the determination of the efficiency of a machining process. In a drilling process, material removal is

<sup>=</sup> <sup>1000</sup> (1)

*<sup>r</sup> f fn* = (2)

= 3.14, *d* is the diameter of the

π

a tachometer during the drilling process. The spindle speed is used to compute desired cutting speed, defined as the distance travelled by each cutting edge on the surface of the workpiece when cutting material. Therefore, cutting speed in a drill-

*v*

**Figure 1.** *Standard twist drill nomenclature [11].*

*Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

**Figure 2.**

*Drilling Technology*

service life of their products.

**2. The drilling process**

the workpiece, where the operation stops [13].

and exits the workpiece on the other side [13].

the straightness of the deep hole that is generated [14].

For example, the heat exchangers of nuclear energy centrals require up to 16,000 holes in a single exchanger for assembly with refrigeration tubes [6]. Other examples include the automotive industry, where the drilling process forms up to 40% of total material removed [7], or the aerospace industry where millions of holes are required for joining various parts of aircraft fuselage [8]. It is estimated that 750,000 holes are required in a single wing of an Airbus A380, with 1.5–3 million holes as the requirements for producing a typical commercial aircraft [7]. Furthermore, over a million rivets are needed for large ships [9] where drilling is the primary process. Therefore, a proper selection of machine tools and equipment, cutting tools and parameters is essential in achieving required productivity, dimensional accuracy, and surface roughness. This subsequently helps industries achieve success and improve the

In the drilling process, holes are created when a cylindrical tool rotates against a workpiece, where a tool called a drill bit is used as shown in **Figure 1** [10, 11]. The drilling operation process involves three stages: the start and centering stage, the full drilling stage and the breakthrough stage [12]. In the first stage, the exact position of the hole is required, whereas the second stage leads to the full engagement of the drill bit, whilst the last stage includes passing the drill through the underside of

A hole in the drilling process can be created in many forms, including blind and through holes, as shown in **Figure 2**. Blind holes are drilled to a certain depth whilst through-holes refer to the condition when the drill bit passes through the material

Generally, a depth to diameter ratio of 5:1 or greater is commonly performed by twist drills, where this ratio may be doubled when using high-performance twist drills equipped with through-tool coolant systems. This ratio can be increased to roughly 20:1 when using special deep hole drilling tools equipped with through-tool coolant systems. Whilst this chapter focuses on the use of twist drills, it is worthnoting that a depth to diameter ratio of 100:1 or more is achievable in gun-drilling machines with through-tool coolant systems. Unlike conventional drilling operations, within gun-drilling machines both the cutting tool and workpiece rotate in opposite directions and at different rotational speeds, which significantly improves

**6**

**Figure 1.**

*Standard twist drill nomenclature [11].*

*Drilling process: (a) blind holes (b) through holes [10].*

### **3. Cutting conditions in drilling process**

To a large extent, cutting conditions determine the success of any drilling operation. Basic cutting conditions include cutting speed, feed rate, material removal rate, and machining time, as discussed in this section below.

### **3.1 Spindle speed and cutting speed**

The spindle speed is the rotational speed measured in rev/min, calculated using a tachometer during the drilling process. The spindle speed is used to compute desired cutting speed, defined as the distance travelled by each cutting edge on the surface of the workpiece when cutting material. Therefore, cutting speed in a drilling operation is computed by.

$$v = \frac{\pi dn}{1000} \tag{1}$$

where *v* is the cutting speed in m/min, π = 3.14, *d* is the diameter of the cutting tool in mm, and *n* is the spindle speed in rev/min.

### **3.2 Feed and feed rate**

In a drilling process feed is specified in mm/rev. The feed rate, which is the linear travel rate in mm/min, can be adjusted by a convenient system when the feed is multiplied by the spindle speed. Hence, feed rate can be found as.

$$f\_r = f \mathbf{n} \tag{2}$$

where *<sup>r</sup> f* is the feed rate in mm/min, *f* is the feed in mm/rev, and *n* is the spindle speed in rev/min.

### **3.3 Material removal rate**

The material removal rate can be considered as an index for the determination of the efficiency of a machining process. In a drilling process, material removal is obtained by [15].

$$\mathbf{M}\_{rr} = \left(\frac{\pi}{4}\right) d^2 f\_r \tag{3}$$

where *Mrr* is the material removal rate in mm3 , *d* is the diameter of the drill in mm, and *<sup>r</sup> f* is the feed rate in mm/min.

### **3.4 Drilling time**

Drilling time is the time a tool is engaged from the beginning of chip production to the end for uninterrupted machining. Any pause during this process, either planned or unplanned, is not included in this time. The drilling time in minutes for through holes can be determined by [15].

$$T\_m = \frac{L}{f\_r} \tag{4}$$

where *T*m is drilling time in minutes, *L* is the distance travelled by the cutting tool in mm, and *<sup>r</sup> f* is the feed rate in mm/min.

It should be noted that the drill bit should travel the distance *L* (see **Figure 2**), which consists of the desired depth of the hole plus an allowance for the tool point angle, *A*, given by.

$$A = \frac{d}{2}\tan\left(90 - \frac{\theta}{2}\right) \tag{5}$$

**9**

**Figure 3.**

*Analysis of the Performance of Drilling Operations for Improving Productivity*

**5. Multi-spindle drilling for productivity improvement**

Multi-spindle drilling is used in manufacturing industries to improve productivity as they can drill many holes simultaneously, which reduces machining time significantly. The multi-spindle or poly-drill head gives high center-to-center accuracy and in many instances eliminates the need for the use of drilling jigs, and this further decreases drilling time and cost. Therefore, in today's competitive market, it is essential to produce a large number of products at the right time with high quality and at minimum cost, where the use of a multi-spindle drill head is one way to fulfil this goal. A multi-spindle drill head can simultaneously drill from two to ten or more holes on the same plane [20]. The multi-spindle drill head produces a number of holes of similar quality in the most economical way, providing a high

Multi-spindle drilling technology is used to increase productivity whilst reducing machining time in working conditions where a large number of closely-spaced holes need to be drilled. A good example of this is the manufacturing of aircraft fuselage and construction of metal bridges, where a large number of riveting holes are required. **Figure 3** shows a section of the Golden Gate Bridge which has been constructed using a large number of rivets. It is estimated that approximately

Multi-spindle or poly-drill heads are mounted on a machine tool to perform many operations simultaneously [23]. Multi-spindle drill heads are either fixed or flexible. The tool positions in fixed multi-spindle drill heads cannot change. Whereas in the flexible type the positions of tools can be adjusted as needed within a particular range [24]. **Figure 4** shows an adjustable 3-spindle drill head [25]. The importance of using this poly drill head instead of using a single drill bit is the possibility of producing high quality drilled holes, the elimination of a drilling jig for maintaining a high center-to-center tolerance, fewer rejections, reducing

*Thousands of rivets are used in the structure of the Golden Gate Bridge, San Francisco, United States.*

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

level of automation with a small investment [21].

600,000 rivets are used in this structure [22].

where *A* is the allowance in mm, *d* is the diameter of the drill in mm, and θ is the tool point angle in degrees.

### **4. Aluminium alloys**

Aluminium and its alloys are very attractive to many manufacturing industries due to its unique combinations of properties with outstanding engineering applications across various industries [16, 17]. Aluminium has low density, reasonably high strength, high ductility, high thermal and electrical conductivities, good oxidation and corrosion resistance, easy to manufacture and has a relatively low cost [18].

The high strength-to-weight ratio of aluminium alloys makes them suitable for wide use in marine, automotive and aerospace industries [19]. The various grades of aluminium alloys used in the aviation industry can be found in reference [5]. Aluminium and its alloys are also used in home appliances, construction industries, electrical, electronic, packaging industries, etc. [16, 19].

Aluminium alloys are divided into workable alloys and cast alloys. Alloys of aluminium that undergo hot or cold mechanical working processes are termed as workable alloys, while those whose shape is obtained by the casting process are known as cast alloys [19].

Aluminium alloys are generally considered more machinable than ferrous alloys; however, their ductile nature results in high machining forces, poor surface roughness and difficult control of chips, whereas those with hard particles can cause high tool wear [19].

*Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

### **5. Multi-spindle drilling for productivity improvement**

Multi-spindle drilling is used in manufacturing industries to improve productivity as they can drill many holes simultaneously, which reduces machining time significantly. The multi-spindle or poly-drill head gives high center-to-center accuracy and in many instances eliminates the need for the use of drilling jigs, and this further decreases drilling time and cost. Therefore, in today's competitive market, it is essential to produce a large number of products at the right time with high quality and at minimum cost, where the use of a multi-spindle drill head is one way to fulfil this goal. A multi-spindle drill head can simultaneously drill from two to ten or more holes on the same plane [20]. The multi-spindle drill head produces a number of holes of similar quality in the most economical way, providing a high level of automation with a small investment [21].

Multi-spindle drilling technology is used to increase productivity whilst reducing machining time in working conditions where a large number of closely-spaced holes need to be drilled. A good example of this is the manufacturing of aircraft fuselage and construction of metal bridges, where a large number of riveting holes are required. **Figure 3** shows a section of the Golden Gate Bridge which has been constructed using a large number of rivets. It is estimated that approximately 600,000 rivets are used in this structure [22].

Multi-spindle or poly-drill heads are mounted on a machine tool to perform many operations simultaneously [23]. Multi-spindle drill heads are either fixed or flexible. The tool positions in fixed multi-spindle drill heads cannot change. Whereas in the flexible type the positions of tools can be adjusted as needed within a particular range [24]. **Figure 4** shows an adjustable 3-spindle drill head [25]. The importance of using this poly drill head instead of using a single drill bit is the possibility of producing high quality drilled holes, the elimination of a drilling jig for maintaining a high center-to-center tolerance, fewer rejections, reducing

**Figure 3.** *Thousands of rivets are used in the structure of the Golden Gate Bridge, San Francisco, United States.*

*Drilling Technology*

**3.4 Drilling time**

angle, *A*, given by.

the tool point angle in degrees.

**4. Aluminium alloys**

known as cast alloys [19].

low cost [18].

tool wear [19].

*M df rr <sup>r</sup>* π =

Drilling time is the time a tool is engaged from the beginning of chip production to the end for uninterrupted machining. Any pause during this process, either planned or unplanned, is not included in this time. The drilling time in minutes for

*m*

*<sup>L</sup> <sup>T</sup>*

where *T*m is drilling time in minutes, *L* is the distance travelled by the cutting

It should be noted that the drill bit should travel the distance *L* (see **Figure 2**), which consists of the desired depth of the hole plus an allowance for the tool point

*<sup>d</sup> <sup>A</sup>*

where *A* is the allowance in mm, *d* is the diameter of the drill in mm, and

Aluminium and its alloys are very attractive to many manufacturing industries due to its unique combinations of properties with outstanding engineering applications across various industries [16, 17]. Aluminium has low density, reasonably high strength, high ductility, high thermal and electrical conductivities, good oxidation and corrosion resistance, easy to manufacture and has a relatively

The high strength-to-weight ratio of aluminium alloys makes them suitable for wide use in marine, automotive and aerospace industries [19]. The various grades of aluminium alloys used in the aviation industry can be found in reference [5]. Aluminium and its alloys are also used in home appliances, construction industries,

Aluminium alloys are divided into workable alloys and cast alloys. Alloys of aluminium that undergo hot or cold mechanical working processes are termed as workable alloys, while those whose shape is obtained by the casting process are

Aluminium alloys are generally considered more machinable than ferrous alloys; however, their ductile nature results in high machining forces, poor surface roughness and difficult control of chips, whereas those with hard particles can cause high

electrical, electronic, packaging industries, etc. [16, 19].

 = − tan 90

θ

*r*

where *Mrr* is the material removal rate in mm3

mm, and *<sup>r</sup> f* is the feed rate in mm/min.

through holes can be determined by [15].

tool in mm, and *<sup>r</sup> f* is the feed rate in mm/min.

2

<sup>4</sup> (3)

*<sup>f</sup>* <sup>=</sup> (4)

2 2 (5)

θis

, *d* is the diameter of the drill in

**8**

**Figure 4.** *An adjustable 3-spindle drill head [25].*

machining time, increasing profit rate and less operator fatigue [26]. Therefore, it is worth noting that the use of multi-spindle drilling is an excellent choice to improve productivity and reduce machining time for manufacturing industries requiring the production of a large number of holes with stringent tolerances. Therefore, the advantages of using the multi-spindle head are listed below [23]:

### **5.1 Cutting mechanisms in the drilling of aluminium**

In the machining process, when a tool penetrates inside a metal workpiece, it produces an internal shearing action in the metal where the metal becomes severely stressed. This causes the metal to be plastically deformed and flow in the form of chips when the ultimate shear strength of the metal is exceeded [27]. In the drilling process, the thrust force is the perpendicular force to the workpiece during its translational motion while the torque comes from the machine spindle to rotate the tool during drilling operation. Other forces in drilling are not important as they are small compared to the thrust force [28]. It should be noted that high cutting forces affect hole quality and tool life [29]. Forces generated in the drilling of metals are uniform where uncut chip thickness is constant [30].

**11**

*Analysis of the Performance of Drilling Operations for Improving Productivity*

generation which is the result of an increase in cutting speed [35].

finish and providing higher operator safety [27].

based on silicon contents in aluminium alloys [39].

**alloys**

Further, in machining ductile materials like aluminium, there is a chance of producing continuous chips due to the plastic deformation of its ductile nature. Other factors that contribute to the formation of continuous chips are high cutting speed, sharp cutting edge, etc. Continuous chips are not easy to handle and dispose of, where they can get tangled around the tool and pose safety issues to the operator. Additionally, when a tool face is in contact for a long time, it results in more frictional heat and affects machining. Therefore, discontinuous and segmented chips produce less friction between the tool and chip; hence, resulting in a better surface

**5.2 Cutting tool and spindle adjustment in multi-spindle drilling of aluminium**

As mentioned earlier, the best performance in a drilling process is obtained when using appropriate cutting tools, where the correct process conditions are used to reduce the level of damage as much as possible [27]. The most commonly used drill bit is the twist drill, as shown in **Figure 1**, which represents the industrial standard [36]. The important features of the twist drill include the point angle, clearance angle, chisel edge angle, drill diameter, web thickness, the rake angle, etc. The rake angle in drills is specified as the helix angle [13]. The high point angle and large helix angle are recommended for better hole quality and less tool wear [37]. The large point angle also contributes to producing thinner chips during the machining of aluminium alloys [38]. However, the point angle should be selected

Experimental studies performed in references [31, 40] have shown that tools used for multi-spindle drilling give less formation of built-up edges as compared to the single drilling process of aluminum alloy Al5083 due to differences in chip size when uncoated High-Speed Steel (HSS) drills with a point angle of 118° and size of 6 mm were used. The experiments were conducted using a conventional milling machine for both single drilling and multi-spindle drilling processes, and the same drilling parameters and conditions were applied. For the multi-spindle drilling

Multi-spindle drilling experiments were further extended and uncoated HSS drills were tested on aluminium alloy Al2024 and compared with uncoated carbide drills with a point angle of 140° and a diameter of 6 mm. Apart from aluminum alloy Al2024, the 6 mm uncoated carbide drills were also used for multi-spindle drilling of aluminium alloys Al5083 and Al6061. In addition, 6 mm uncoated carbide drills were used to compare different center-to-center tool distances of the spindle in the multi-spindle drilling process. Further, a comparison of 6 mm and 10 mm uncoated

process, a SUNHER poly-drill head, as shown in **Figure 5**, was used.

carbide drills with the same point angle of 140° were also made [41, 42].

Experimental studies have shown that thrust force generated in multi-spindle drilling is higher than that obtained in one-shot single drilling processes of aluminum alloy Al5083 [31]. The higher thrust force occurs due to the combination of more than one tool operating simultaneously in one go. However, the results of experiments have concluded that the average of all the tools' thrust force per tool in multi-spindle drilling was slightly lower than the thrust force resulting from single drilling [31]. In addition to thrust force, another important parameter in a drilling process is the increase in cutting temperature [32]. A higher cutting temperature increases the ductility of the material which results in the formation of long chips, which negatively affects the hole quality [33]. A high temperature may also increase the chemical interaction between aluminium and the tool coating that is responsible for inter-atomic diffusion [34]. The cutting temperature increases due to heat

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

### *Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

Experimental studies have shown that thrust force generated in multi-spindle drilling is higher than that obtained in one-shot single drilling processes of aluminum alloy Al5083 [31]. The higher thrust force occurs due to the combination of more than one tool operating simultaneously in one go. However, the results of experiments have concluded that the average of all the tools' thrust force per tool in multi-spindle drilling was slightly lower than the thrust force resulting from single drilling [31]. In addition to thrust force, another important parameter in a drilling process is the increase in cutting temperature [32]. A higher cutting temperature increases the ductility of the material which results in the formation of long chips, which negatively affects the hole quality [33]. A high temperature may also increase the chemical interaction between aluminium and the tool coating that is responsible for inter-atomic diffusion [34]. The cutting temperature increases due to heat generation which is the result of an increase in cutting speed [35].

Further, in machining ductile materials like aluminium, there is a chance of producing continuous chips due to the plastic deformation of its ductile nature. Other factors that contribute to the formation of continuous chips are high cutting speed, sharp cutting edge, etc. Continuous chips are not easy to handle and dispose of, where they can get tangled around the tool and pose safety issues to the operator. Additionally, when a tool face is in contact for a long time, it results in more frictional heat and affects machining. Therefore, discontinuous and segmented chips produce less friction between the tool and chip; hence, resulting in a better surface finish and providing higher operator safety [27].

### **5.2 Cutting tool and spindle adjustment in multi-spindle drilling of aluminium alloys**

As mentioned earlier, the best performance in a drilling process is obtained when using appropriate cutting tools, where the correct process conditions are used to reduce the level of damage as much as possible [27]. The most commonly used drill bit is the twist drill, as shown in **Figure 1**, which represents the industrial standard [36]. The important features of the twist drill include the point angle, clearance angle, chisel edge angle, drill diameter, web thickness, the rake angle, etc. The rake angle in drills is specified as the helix angle [13]. The high point angle and large helix angle are recommended for better hole quality and less tool wear [37]. The large point angle also contributes to producing thinner chips during the machining of aluminium alloys [38]. However, the point angle should be selected based on silicon contents in aluminium alloys [39].

Experimental studies performed in references [31, 40] have shown that tools used for multi-spindle drilling give less formation of built-up edges as compared to the single drilling process of aluminum alloy Al5083 due to differences in chip size when uncoated High-Speed Steel (HSS) drills with a point angle of 118° and size of 6 mm were used. The experiments were conducted using a conventional milling machine for both single drilling and multi-spindle drilling processes, and the same drilling parameters and conditions were applied. For the multi-spindle drilling process, a SUNHER poly-drill head, as shown in **Figure 5**, was used.

Multi-spindle drilling experiments were further extended and uncoated HSS drills were tested on aluminium alloy Al2024 and compared with uncoated carbide drills with a point angle of 140° and a diameter of 6 mm. Apart from aluminum alloy Al2024, the 6 mm uncoated carbide drills were also used for multi-spindle drilling of aluminium alloys Al5083 and Al6061. In addition, 6 mm uncoated carbide drills were used to compare different center-to-center tool distances of the spindle in the multi-spindle drilling process. Further, a comparison of 6 mm and 10 mm uncoated carbide drills with the same point angle of 140° were also made [41, 42].

 Therefore, it is worth noting that the use of multi-spindle drilling is an excellent choice to improve productivity and reduce machining time for manufacturing industries requiring the production of a large number of holes with stringent tolerances. Therefore, the advantages of using the multi-spindle head are listed below [23]:

• The increase in productivity at a higher rate

• The performance of multiple operations in one cycle

• The multi-spindle drilling ensures positional accuracy

• Elimination or reduction of the need for drilling jigs

• Less quality control rejections

• Easy to install and use anywhere

• Easy to operate and low maintenance

• Simple in construction and robust in design

**5.1 Cutting mechanisms in the drilling of aluminium**

uniform where uncut chip thickness is constant [30].

In the machining process, when a tool penetrates inside a metal workpiece, it produces an internal shearing action in the metal where the metal becomes severely stressed. This causes the metal to be plastically deformed and flow in the form of chips when the ultimate shear strength of the metal is exceeded [27]. In the drilling process, the thrust force is the perpendicular force to the workpiece during its translational motion while the torque comes from the machine spindle to rotate the tool during drilling operation. Other forces in drilling are not important as they are small compared to the thrust force [28]. It should be noted that high cutting forces affect hole quality and tool life [29]. Forces generated in the drilling of metals are

• The time for one hole is the time for multiple numbers of holes

**10**

### **Figure 5.**

*The 3-spindle Suhner multi-spindle drill head mounted on conventional milling machine (Courtesy: Edith Cowan University, Australia).*

In general, the uncoated carbide drill has been recommended in multi-spindle drilling of aluminium as compared to the uncoated HSS drills due to the high built-up edge formation because of its moderate strength, as shown in **Figure 6**. The drill diameter did not show any significant changes in affecting the hole quality; however, the larger drill size covered a larger cross-sectional area that resulted in a higher thrust force and producing larger chips. Therefore, for the smaller drill size, an easier chip breaking and evacuation was resulted. Furthermore, the larger point angle of 140° - compared to 118° - provided a better hole quality but did not contribute to changing the size or shape of the chips.

The tool conditions from **Figure 6** also shows that when drilling aluminium alloy Al5083, a large built-up edge was formed, which was expected due to low silicon contents, where this is in agreement with research conducted by Akyüz [43] in which alloys with low silicon contents produce a high built-up edge. Additionally, the low hardness value of the material used in this operation might be another cause of high formation of the built-up edge because alloys with low hardness values have a high tendency towards the formation of built-up edges [44].

Multi-spindle drilling is useful in its easy adjustment of tools. Depending on the type and use, the tools of a multi-spindle head can be adjusted to any position without affecting the results, which not only increases productivity at a high rate but also produces high-quality holes. This is performed at the same time, whereas only a single hole is produced in one-shot single drilling process without a compromise on the hole quality.

### **5.3 Quality assessment of drilled holes in multi-spindle drilling of aluminium**

In any drilling process, it is important to ensure that damage-free and precise holes are produced to avoid rejection of parts [45]. For example, poor hole quality has been observed in 60% of aircraft components [5], which is of course a

**13**

**Figure 6.**

*spindle drill head.*

*Tool conditions after performing the drilling operation on different types of aluminium alloys using the multi-*

*Analysis of the Performance of Drilling Operations for Improving Productivity*

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

*Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

**Figure 6.**

*Tool conditions after performing the drilling operation on different types of aluminium alloys using the multispindle drill head.*

*Drilling Technology*

In general, the uncoated carbide drill has been recommended in multi-spindle

*The 3-spindle Suhner multi-spindle drill head mounted on conventional milling machine (Courtesy: Edith*

The tool conditions from **Figure 6** also shows that when drilling aluminium alloy Al5083, a large built-up edge was formed, which was expected due to low silicon contents, where this is in agreement with research conducted by Akyüz [43] in which alloys with low silicon contents produce a high built-up edge. Additionally, the low hardness value of the material used in this operation might be another cause of high formation of the built-up edge because alloys with low hardness values have

Multi-spindle drilling is useful in its easy adjustment of tools. Depending on the type and use, the tools of a multi-spindle head can be adjusted to any position without affecting the results, which not only increases productivity at a high rate but also produces high-quality holes. This is performed at the same time, whereas only a single hole is produced in one-shot single drilling process without a compromise on

**5.3 Quality assessment of drilled holes in multi-spindle drilling of aluminium**

In any drilling process, it is important to ensure that damage-free and precise holes are produced to avoid rejection of parts [45]. For example, poor hole quality has been observed in 60% of aircraft components [5], which is of course a

drilling of aluminium as compared to the uncoated HSS drills due to the high built-up edge formation because of its moderate strength, as shown in **Figure 6**. The drill diameter did not show any significant changes in affecting the hole quality; however, the larger drill size covered a larger cross-sectional area that resulted in a higher thrust force and producing larger chips. Therefore, for the smaller drill size, an easier chip breaking and evacuation was resulted. Furthermore, the larger point angle of 140° - compared to 118° - provided a better hole quality but did not

contribute to changing the size or shape of the chips.

a high tendency towards the formation of built-up edges [44].

**12**

the hole quality.

**Figure 5.**

*Cowan University, Australia).*

challenging problem. Hence, there is a need to control the number of rejected parts by overcoming problems related to the drilling process, especially the quality of drilled-holes [45]. A poor quality hole can create regions of concentrated stress that increase the chances of formation of fatigue cracks, which reduces the reliability of products [46]. Desirable hole quality in drilling operations can be achieved by proper selection of drilling process parameters, appropriate cutting tools, and machine setup [47].

In the experimental study by Aamir et al. [31], a single drilling process was compared with multi-spindle simultaneous drilling of aluminium alloy Al5083 using uncoated HSS tools. The drill diameter was 6 mm and the point angle was 118°. All drilling experiments were conducted using the same cutting parameters and in a dry environment. The hole quality produced by multi-spindle drilling was better than those obtained in a single-spindle drilling process. The holes drilled by the multi-spindle head had a lower surface roughness and fewer burrs around the holes. This was expected due to differences in chip formation.

Hole quality in a drilling process is also affected by the chemical composition and mechanical properties of aluminium alloys. An experimental study in multispindle drilling of aluminium alloys Al5083, Al6061, and Al2024 by Aamir et al. [42] concluded that regardless of drilling parameters, low surface roughness was obtained in aluminium alloy Al6061 due to its high silicon content. Literature has shown that alloys with high silicon content result in low surface roughness irrespective of drilling parameters [43, 48]. Furthermore, the reason for high surface roughness of aluminium alloy Al5083 might be due to the poor machinability and low hardness [44].

Aamir et al. [42] observed that less burrs formed around the hole edges of aluminium alloy Al2024 due to its good machinability compared with the aluminium alloys Al6061 and Al5083. Further, the less ductile nature of aluminium alloy Al6061 - in comparison with aluminium alloy Al5083 - resulted in the low formation of burrs. Hence, high ductility and poor machinability properties led to the formation of more burrs in aluminium alloy Al5083 [49]. Additionally, uncoated HSS drills produced low-quality holes by giving high surface roughness and more formation of burrs around the edges of holes due to the high built-up edges because of its moderate strength. Moreover, a larger point angle of 140° - compared to 118° and a smaller diameter of 6 mm - in comparison to a drill size of 10 mm – have been recommended for multi-hole simultaneous drilling of aluminium alloys. However, the drill diameter did not show any significant effect on hole quality including the surface roughness and burrs [41]. **Figure 7** shows the quality of holes in terms of burr formation in multi-spindle drilling of aluminium alloys.

Regardless of drilling parameters, the workpiece materials and different tools, the surface roughness increases with increasing the cutting speed and feed rate. The likely reasons for high surface roughness at high cutting speeds might include the increase in workpiece deformation due to rise in temperature and the chances of high vibrations exerted by the tools [7, 47]. The high cutting speed and feed rate are responsible for the formation of burrs that reduces the hole quality. However, the high impact is due to the feed rate because stable, jerk-free and slow insertions of drills are possible with low feed rates which form thin chips; hence, the hole quality is less affected [50]. Further, according to Costa et al. [51], any factor that causes the generation of high thrust force results in more formation of burrs, and the high feed rate increases thrust force. Additionally, due to less formation of burrs, the tool entry side of the holes was found to be better than those on the tool exit side. This is likely due to the different mechanism of burr formation at the entry and exit sides of the holes. According to Zhu et al. [52], the tearing occurs as a bending action followed by clean shearing or lateral extrusion causing entrance burrs while exit

**15**

**6. Conclusions**

**Figure 7.**

*spindle head.*

*Analysis of the Performance of Drilling Operations for Improving Productivity*

burrs formed as a result of plastic deformation of the materials. Besides this, low temperature and thrust force are the reasons for small burrs on the entry side of the

*Hole quality in terms of burr formation in multi-spindle drilling of aluminium alloys using the multi-*

Many industries, such as automotive and aerospace, produce millions of holes per day where productivity, quality, and precision of drilled holes plays a vital role in their success. Multi-spindle drilling is capable of producing more drilled-holes with higher rates, which makes it advantageous in high-volume production with uniform qualities, simultaneous machining, and most importantly reducing the drilling time which is one of the important factors in achieving greater productivity.

hole which can be removed by chamfering [53].

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

*Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

### **Figure 7.**

*Drilling Technology*

machine setup [47].

low hardness [44].

challenging problem. Hence, there is a need to control the number of rejected parts by overcoming problems related to the drilling process, especially the quality of drilled-holes [45]. A poor quality hole can create regions of concentrated stress that increase the chances of formation of fatigue cracks, which reduces the reliability of products [46]. Desirable hole quality in drilling operations can be achieved by proper selection of drilling process parameters, appropriate cutting tools, and

In the experimental study by Aamir et al. [31], a single drilling process was compared with multi-spindle simultaneous drilling of aluminium alloy Al5083 using uncoated HSS tools. The drill diameter was 6 mm and the point angle was 118°. All drilling experiments were conducted using the same cutting parameters and in a dry environment. The hole quality produced by multi-spindle drilling was better than those obtained in a single-spindle drilling process. The holes drilled by the multi-spindle head had a lower surface roughness and fewer burrs around the

Hole quality in a drilling process is also affected by the chemical composition and mechanical properties of aluminium alloys. An experimental study in multispindle drilling of aluminium alloys Al5083, Al6061, and Al2024 by Aamir et al. [42] concluded that regardless of drilling parameters, low surface roughness was obtained in aluminium alloy Al6061 due to its high silicon content. Literature has shown that alloys with high silicon content result in low surface roughness irrespective of drilling parameters [43, 48]. Furthermore, the reason for high surface roughness of aluminium alloy Al5083 might be due to the poor machinability and

Aamir et al. [42] observed that less burrs formed around the hole edges of aluminium alloy Al2024 due to its good machinability compared with the aluminium alloys Al6061 and Al5083. Further, the less ductile nature of aluminium alloy Al6061 - in comparison with aluminium alloy Al5083 - resulted in the low formation of burrs. Hence, high ductility and poor machinability properties led to the formation of more burrs in aluminium alloy Al5083 [49]. Additionally, uncoated HSS drills produced low-quality holes by giving high surface roughness and more formation of burrs around the edges of holes due to the high built-up edges because of its moderate strength. Moreover, a larger point angle of 140° - compared to 118° and a smaller diameter of 6 mm - in comparison to a drill size of 10 mm – have been recommended for multi-hole simultaneous drilling of aluminium alloys. However, the drill diameter did not show any significant effect on hole quality including the surface roughness and burrs [41]. **Figure 7** shows the quality of holes in terms of

Regardless of drilling parameters, the workpiece materials and different tools, the surface roughness increases with increasing the cutting speed and feed rate. The likely reasons for high surface roughness at high cutting speeds might include the increase in workpiece deformation due to rise in temperature and the chances of high vibrations exerted by the tools [7, 47]. The high cutting speed and feed rate are responsible for the formation of burrs that reduces the hole quality. However, the high impact is due to the feed rate because stable, jerk-free and slow insertions of drills are possible with low feed rates which form thin chips; hence, the hole quality is less affected [50]. Further, according to Costa et al. [51], any factor that causes the generation of high thrust force results in more formation of burrs, and the high feed rate increases thrust force. Additionally, due to less formation of burrs, the tool entry side of the holes was found to be better than those on the tool exit side. This is likely due to the different mechanism of burr formation at the entry and exit sides of the holes. According to Zhu et al. [52], the tearing occurs as a bending action followed by clean shearing or lateral extrusion causing entrance burrs while exit

holes. This was expected due to differences in chip formation.

burr formation in multi-spindle drilling of aluminium alloys.

**14**

*Hole quality in terms of burr formation in multi-spindle drilling of aluminium alloys using the multispindle head.*

burrs formed as a result of plastic deformation of the materials. Besides this, low temperature and thrust force are the reasons for small burrs on the entry side of the hole which can be removed by chamfering [53].

### **6. Conclusions**

Many industries, such as automotive and aerospace, produce millions of holes per day where productivity, quality, and precision of drilled holes plays a vital role in their success. Multi-spindle drilling is capable of producing more drilled-holes with higher rates, which makes it advantageous in high-volume production with uniform qualities, simultaneous machining, and most importantly reducing the drilling time which is one of the important factors in achieving greater productivity.

### *Drilling Technology*

Therefore, the production of a large number of closely-spaced holes simultaneously by using a poly-drill or multi-spindle drill head results in achieving higher productivity and quality. This approach not only enhances the competitiveness of the process but also results in cost reduction and uniformity of generated holes.

Further, it can be concluded that hole quality is affected by drilling parameters and properties of the workpiece. Alloys of aluminium with high silicon contents show lower values of surface roughness while those with low hardness and poor machinability provide poor hole quality. The experiments also show that uncoated carbide tools are more suitable compared to uncoated HSS for producing high-quality holes, resulting in the formation of less built-up edges when drilling aluminium alloys. Moreover, the aluminium alloy Al2024 produced better results in terms of hole quality due to its good machinability compared with aluminum alloys Al6061 and Al5083.

### **Acknowledgements**

The authors would like to thank Edith Cowan University, Australia for the awarded (ECU-HDR) higher degree research scholarship and for providing support on this research.

### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Majid Tolouei-Rad\* and Muhammad Aamir School of Engineering, Edith Cowan University, Joondalup, WA, Australia

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**17**

*Analysis of the Performance of Drilling Operations for Improving Productivity*

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*DOI: http://dx.doi.org/10.5772/intechopen.96497*

Tolouei-Rad M. Drilling reconfigurable machine tool selection and process parameters optimization as a function

Manufacturing Systems. 2017;45:58-69.

[2] Tolouei-Rad M, Shah A. Development of a methodology for processing of drilling operations. International Journal of Industrial and Manufacturing Engineering. 2012;6(12):2660-2664.

optimization of burr height in drilling of Al-7075 using Taguchi method and response surface methodology. The International Journal of Advanced Manufacturing Technology. 2010;49(9-12):911-923.

[4] Aamir M, Tolouei-Rad M, Giasin K,

[5] Aamir M, Giasin K, Tolouei-Rad M,

Nosrati A. Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review. The International Journal of Advanced Manufacturing Technology.

2019;105(5-6):2289-2308.

Vafadar A. A review: drilling performance and hole quality of aluminium alloys for aerospace applications. Journal of Materials Research and Technology. 2020;9(6):12484-12500.

[6] De Lacalle LL, Fernández A, Olvera D, Lamikiz A, Rodríguez C, Elias A. Monitoring deep twist drilling for a rapid manufacturing of light highstrength parts. Mechanical systems and signal processing. 2011;25(7):2745-2752.

[7] Giasin K, Hodzic A, Phadnis V, Ayvar-Soberanis S. Assessment of cutting forces and hole quality in drilling Al2024 aluminium alloy: experimental and finite element study. The International Journal of Advanced Manufacturing Technology.

2016;87(5-8):2041-2061.

[1] Vafadar A, Hayward K,

**References**

of product demand. Journal of

[3] Kilickap E. Modeling and

*Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

### **References**

*Drilling Technology*

and Al5083.

**Acknowledgements**

**Conflict of interest**

on this research.

**16**

**Author details**

Majid Tolouei-Rad\* and Muhammad Aamir

provided the original work is properly cited.

\*Address all correspondence to<EMAIL_ADDRESS>
The authors declare no conflict of interest.

School of Engineering, Edith Cowan University, Joondalup, WA, Australia

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Therefore, the production of a large number of closely-spaced holes simultaneously by using a poly-drill or multi-spindle drill head results in achieving higher productivity and quality. This approach not only enhances the competitiveness of the process but also results in cost reduction and uniformity of generated holes.

Further, it can be concluded that hole quality is affected by drilling parameters and properties of the workpiece. Alloys of aluminium with high silicon contents show lower values of surface roughness while those with low hardness and poor machinability provide poor hole quality. The experiments also show that uncoated carbide tools are more suitable compared to uncoated HSS for producing high-quality holes, resulting in the formation of less built-up edges when drilling aluminium alloys. Moreover, the aluminium alloy Al2024 produced better results in terms of hole quality due to its good machinability compared with aluminum alloys Al6061

The authors would like to thank Edith Cowan University, Australia for the awarded (ECU-HDR) higher degree research scholarship and for providing support [1] Vafadar A, Hayward K, Tolouei-Rad M. Drilling reconfigurable machine tool selection and process parameters optimization as a function of product demand. Journal of Manufacturing Systems. 2017;45:58-69.

[2] Tolouei-Rad M, Shah A. Development of a methodology for processing of drilling operations. International Journal of Industrial and Manufacturing Engineering. 2012;6(12):2660-2664.

[3] Kilickap E. Modeling and optimization of burr height in drilling of Al-7075 using Taguchi method and response surface methodology. The International Journal of Advanced Manufacturing Technology. 2010;49(9-12):911-923.

[4] Aamir M, Tolouei-Rad M, Giasin K, Nosrati A. Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review. The International Journal of Advanced Manufacturing Technology. 2019;105(5-6):2289-2308.

[5] Aamir M, Giasin K, Tolouei-Rad M, Vafadar A. A review: drilling performance and hole quality of aluminium alloys for aerospace applications. Journal of Materials Research and Technology. 2020;9(6):12484-12500.

[6] De Lacalle LL, Fernández A, Olvera D, Lamikiz A, Rodríguez C, Elias A. Monitoring deep twist drilling for a rapid manufacturing of light highstrength parts. Mechanical systems and signal processing. 2011;25(7):2745-2752.

[7] Giasin K, Hodzic A, Phadnis V, Ayvar-Soberanis S. Assessment of cutting forces and hole quality in drilling Al2024 aluminium alloy: experimental and finite element study. The International Journal of Advanced Manufacturing Technology. 2016;87(5-8):2041-2061.

[8] Rivero A, Aramendi G, Herranz S, de Lacalle LL. An experimental investigation of the effect of coatings and cutting parameters on the dry drilling performance of aluminium alloys. The International Journal of Advanced Manufacturing Technology. 2006;28(1-2):1-11.

[9] Felkins K, Leigh H, Jankovic A. The royal mail ship Titanic: Did a metallurgical failure cause a night to remember? JOM Journal of the Minerals, Metals and Materials Society. 1998;50(1):12-18.

[10] Groover M. Fundamental of modern manufacturing: Materials,Processes, andSystems. USA: John Wiley & Sons, Inc; 2004.

[11] Oberg E. Machinery's Handbook 29th Edition-Full Book: Industrial Press; 2012.

[12] Tönshoff H, Spintig W, König W, Neises A. Machining of holes developments in drilling technology. CIRP annals. 1994;43(2):551-561.

[13] Sharif S, Rahim EA, Sasahara H. Machinability of titanium alloys in drilling. Titanium Alloys-Towards Achieving Enhanced Properties for Diversified Applications. 32012. p. 117-137.

[14] Systems UDHD. What is Gun Drilling? 2020. Available from: https://unisig.com/information-andresources/what-is-deep-hole-drilling/ what-is-gun-drilling/.

[15] Girsang IP, Dhupia JS. Machine Tools for Machining. In: Nee AYC, editor. Handbook of Manufacturing Engineering and Technology. London: Springer London; 2015. p. 811-865.

[16] David J. Aluminum and Aluminum alloys. Alloying: Understanding the

basics. ASM International, Ohio; 2001. p. 351-416.

[17] Aamir M, Tolouei-Rad M, Vafadar A, Raja MNA, Giasin K. Performance Analysis of Multi-Spindle Drilling of Al2024 with TiN and TiCN Coated Drills Using Experimental and Artificial Neural Networks Technique. Applied Sciences. 2020;10(23):8633.

[18] Campbell FC. Aluminum. Elements of Metallurgy and Engineering Alloys: ASM International; 2008. p. 487-508.

[19] Santos MC, Machado AR, Sales WF, Barrozo MA, Ezugwu EO. Machining of aluminum alloys: a review. The International Journal of Advanced Manufacturing Technology. 2016;86(9-12):3067-3080.

[20] Tolouei-Rad M. An intelligent approach to high quantity automated machining. Journal of Achievements in Materials and Manufacturing Engineering. 2011;47(2):195-204.

[21] Tolouei-Rad M. Intelligent analysis of utilization of special purpose machines for drilling operations. Intelligent Systems, Prof Vladimir M Koleshko (Ed), ISBN: 978-953-51-0054-6, InTech, Available from: http://wwwintechopencom/ books/intelligent-systems/ intelligent-analysis-of-utilization-ofspecial-purposemachines-for-drillingoperations. Croatia2012. p. 297-320.

[22] Golden Gate Bridge HaTD. Frequently Asked Questions about the Golden Gate Bridge: How many rivets are in each tower of the Golden Gate Bridge 2020. Available from: https://www.goldengate.org/bridge/ history-research/statistics-data/faqs/.

[23] Tam BN, Van Dich T. Research, Design and Develop a prototype of Multi-Spindle Drilling Head. Journal of Science & Technology. 2018;127:029-034.

[24] Tolouei-Rad M. An efficient algorithm for automatic machining sequence planning in milling operations. International Journal of Production Research. 2003;41(17):4115-4131.

[25] Tolouei-Rad M, Zolfaghari S. Productivity improvement using Special-Purpose Modular machine tools. International Journal of Manufacturing Research. 2009;4(2):219-235.

[26] Vafadar A, Tolouei-Rad M, Hayward K, Abhary K. Technical feasibility analysis of utilizing special purpose machine tools. Journal of Manufacturing Systems. 2016;39:53-62.

[27] Sobri SA, Heinemann R, Whitehead D. Carbon Fibre Reinforced Polymer (CFRP) Composites: Machining Aspects and Opportunities for Manufacturing Industries. Composite Materials: Applications in Engineering, Biomedicine and Food Science. Cham: Springer International Publishing; 2020. p. 35-65.

[28] Tyagi R. Processing Techniques and Tribological Behavior of Composite Materials: IGI Global; 2015.

[29] Xu J, Mkaddem A, El Mansori M. Recent advances in drilling hybrid FRP/ Ti composite: a state-of-the-art review. Composite Structures. 2016;135:316-338.

[30] Sheikh-Ahmad JY. Machining of polymer composites: Springer; 2009.

[31] Aamir M, Tu S, Giasin K, Tolouei-Rad M. Multi-hole simultaneous drilling of aluminium alloy: A preliminary study and evaluation against one-shot drilling process. Journal of Materials Research and Technology. 2020;9(3):3994-4006.

[32] Kelly J, Cotterell M. Minimal lubrication machining of aluminium alloys. Journal of Materials Processing Technology. 2002;120(1-3):327-334.

**19**

*Analysis of the Performance of Drilling Operations for Improving Productivity*

Al2024. The International Journal of Advanced Manufacturing Technology.

[42] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Machinability of Al2024, Al6061, and Al5083 alloys using multihole simultaneous drilling approach. Journal of Materials Research and Technology. 2020;9(5):10991-11002.

[43] Akyüz B. Effect of silicon content on machinability of AL-SI alloys. Advances in Science and Technology Research Journal. 2016;10(31):51--57.

[44] Ratnam M. Factors affecting surface roughness in finish turning. In: Comprehensive materials finishing.

Elsevier. 2017;1(1):1-25.

2010;31(2):976-980.

[45] Arul S, Vijayaraghavan L,

Malhotra S, Krishnamurthy R. The effect of vibratory drilling on hole quality in polymeric composites. International Journal of Machine Tools and Manufacture. 2006;46(3-4):252-259.

[46] Liu J, Xu H, Zhai H, Yue Z. Effect of detail design on fatigue performance of fastener hole. Materials & Design.

[47] Kurt M, Kaynak Y, Bagci E. Evaluation of drilled hole quality in Al 2024 alloy. The International Journal of Advanced Manufacturing Technology.

[48] Kamiya M, Yakou T, Sasaki T, Nagatsuma YJMt. Effect of Si content on turning machinability of Al-Si binary alloy castings. 2008:0801280304-.

[49] Committee AH. Metals Handbook: Vol. 2, Properties and selection– nonferrous alloys and pure metals. American Society for Metals, Metals

[50] Uddin M, Basak A, Pramanik A, Singh S, Krolczyk GM, Prakash C. Evaluating hole quality in drilling of Al 6061 alloys. Materials. 2018;11(12):2443.

2008;37(11-12):1051-1060.

Park, OH. 1978.

2020;111(3):861-879.

*DOI: http://dx.doi.org/10.5772/intechopen.96497*

[33] Ozcatalbas Y. Chip and built-up edge formation in the machining of in situ Al4C3–Al composite. Materials &

design. 2003;24(3):215-221.

2009;27(3):535-544.

2000;24(4):371-376.

[34] Roy P, Sarangi S, Ghosh A,

Chattopadhyay A. Machinability study of pure aluminium and Al–12% Si alloys against uncoated and coated carbide inserts. International Journal of Refractory Metals and Hard Materials.

[35] Yousefi R, Ichida Y. A study on ultra–high-speed cutting of aluminium alloy:: Formation of welded metal on the secondary cutting edge of the tool and its effects on the quality of finished surface. Precision engineering.

[36] Panchagnula KK, Palaniyandi K. Drilling on fiber reinforced polymer/ nanopolymer composite laminates: a review. Journal of materials research and technology. 2018;7(2):180-189.

[37] Nouari M, List G, Girot F, Coupard D. Experimental analysis and optimisation of tool wear in dry machining of aluminium alloys. Wear.

2003;255(7-12):1359-1368.

press; 2005.

Elsevier; 2011. 412 p.

[38] Stephenson DA, Agapiou JS. Metal cutting theory and practice: CRC

[39] Davim JP. Modern machining technology: A practical guide. UK:

[40] Aamir M, Tu S, Tolouei-Rad M, Giasin K, Vafadar A. Optimization and modeling of process parameters in multi-hole simultaneous drilling using taguchi method and fuzzy logic approach. Materials. 2020;13(3):680.

[41] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Feasibility of tool configuration and the effect of tool material, and tool geometry in multi-hole simultaneous drilling of *Analysis of the Performance of Drilling Operations for Improving Productivity DOI: http://dx.doi.org/10.5772/intechopen.96497*

[33] Ozcatalbas Y. Chip and built-up edge formation in the machining of in situ Al4C3–Al composite. Materials & design. 2003;24(3):215-221.

*Drilling Technology*

p. 351-416.

basics. ASM International, Ohio; 2001.

[24] Tolouei-Rad M. An efficient algorithm for automatic machining sequence planning in milling operations. International Journal of Production Research. 2003;41(17):4115-4131.

[25] Tolouei-Rad M, Zolfaghari S. Productivity improvement using

Research. 2009;4(2):219-235.

[26] Vafadar A, Tolouei-Rad M, Hayward K, Abhary K. Technical feasibility analysis of utilizing special purpose machine tools. Journal of Manufacturing Systems. 2016;39:53-62.

[27] Sobri SA, Heinemann R,

Polymer (CFRP) Composites:

for Manufacturing Industries. Composite Materials: Applications in Engineering, Biomedicine and Food Science. Cham: Springer International

Publishing; 2020. p. 35-65.

Materials: IGI Global; 2015.

Whitehead D. Carbon Fibre Reinforced

Machining Aspects and Opportunities

[28] Tyagi R. Processing Techniques and Tribological Behavior of Composite

[29] Xu J, Mkaddem A, El Mansori M. Recent advances in drilling hybrid FRP/ Ti composite: a state-of-the-art review. Composite Structures. 2016;135:316-338.

[30] Sheikh-Ahmad JY. Machining of polymer composites: Springer; 2009.

Tolouei-Rad M. Multi-hole simultaneous

[31] Aamir M, Tu S, Giasin K,

drilling of aluminium alloy: A preliminary study and evaluation against one-shot drilling process. Journal of Materials Research and Technology. 2020;9(3):3994-4006.

[32] Kelly J, Cotterell M. Minimal lubrication machining of aluminium alloys. Journal of Materials Processing Technology. 2002;120(1-3):327-334.

Special-Purpose Modular machine tools. International Journal of Manufacturing

[18] Campbell FC. Aluminum. Elements of Metallurgy and Engineering Alloys: ASM International; 2008. p. 487-508.

[19] Santos MC, Machado AR, Sales WF, Barrozo MA, Ezugwu EO. Machining of aluminum alloys: a review. The International Journal of Advanced Manufacturing Technology. 2016;86(9-12):3067-3080.

[20] Tolouei-Rad M. An intelligent approach to high quantity automated machining. Journal of Achievements in Materials and Manufacturing Engineering. 2011;47(2):195-204.

[21] Tolouei-Rad M. Intelligent analysis of utilization of special purpose machines for drilling operations. Intelligent Systems, Prof Vladimir M Koleshko (Ed), ISBN: 978-953-51-0054-6, InTech, Available from: http://wwwintechopencom/

books/intelligent-systems/

[22] Golden Gate Bridge HaTD. Frequently Asked Questions about the Golden Gate Bridge: How many rivets are in each tower of the Golden Gate Bridge 2020. Available from: https://www.goldengate.org/bridge/ history-research/statistics-data/faqs/.

[23] Tam BN, Van Dich T. Research, Design and Develop a prototype of Multi-Spindle Drilling Head. Journal of Science & Technology.

intelligent-analysis-of-utilization-ofspecial-purposemachines-for-drillingoperations. Croatia2012. p. 297-320.

[17] Aamir M, Tolouei-Rad M, Vafadar A, Raja MNA, Giasin K. Performance Analysis of Multi-Spindle Drilling of Al2024 with TiN and TiCN Coated Drills Using Experimental and Artificial Neural Networks Technique. Applied Sciences. 2020;10(23):8633.

**18**

2018;127:029-034.

[34] Roy P, Sarangi S, Ghosh A, Chattopadhyay A. Machinability study of pure aluminium and Al–12% Si alloys against uncoated and coated carbide inserts. International Journal of Refractory Metals and Hard Materials. 2009;27(3):535-544.

[35] Yousefi R, Ichida Y. A study on ultra–high-speed cutting of aluminium alloy:: Formation of welded metal on the secondary cutting edge of the tool and its effects on the quality of finished surface. Precision engineering. 2000;24(4):371-376.

[36] Panchagnula KK, Palaniyandi K. Drilling on fiber reinforced polymer/ nanopolymer composite laminates: a review. Journal of materials research and technology. 2018;7(2):180-189.

[37] Nouari M, List G, Girot F, Coupard D. Experimental analysis and optimisation of tool wear in dry machining of aluminium alloys. Wear. 2003;255(7-12):1359-1368.

[38] Stephenson DA, Agapiou JS. Metal cutting theory and practice: CRC press; 2005.

[39] Davim JP. Modern machining technology: A practical guide. UK: Elsevier; 2011. 412 p.

[40] Aamir M, Tu S, Tolouei-Rad M, Giasin K, Vafadar A. Optimization and modeling of process parameters in multi-hole simultaneous drilling using taguchi method and fuzzy logic approach. Materials. 2020;13(3):680.

[41] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Feasibility of tool configuration and the effect of tool material, and tool geometry in multi-hole simultaneous drilling of Al2024. The International Journal of Advanced Manufacturing Technology. 2020;111(3):861-879.

[42] Aamir M, Tolouei-Rad M, Giasin K, Vafadar A. Machinability of Al2024, Al6061, and Al5083 alloys using multihole simultaneous drilling approach. Journal of Materials Research and Technology. 2020;9(5):10991-11002.

[43] Akyüz B. Effect of silicon content on machinability of AL-SI alloys. Advances in Science and Technology Research Journal. 2016;10(31):51--57.

[44] Ratnam M. Factors affecting surface roughness in finish turning. In: Comprehensive materials finishing. Elsevier. 2017;1(1):1-25.

[45] Arul S, Vijayaraghavan L, Malhotra S, Krishnamurthy R. The effect of vibratory drilling on hole quality in polymeric composites. International Journal of Machine Tools and Manufacture. 2006;46(3-4):252-259.

[46] Liu J, Xu H, Zhai H, Yue Z. Effect of detail design on fatigue performance of fastener hole. Materials & Design. 2010;31(2):976-980.

[47] Kurt M, Kaynak Y, Bagci E. Evaluation of drilled hole quality in Al 2024 alloy. The International Journal of Advanced Manufacturing Technology. 2008;37(11-12):1051-1060.

[48] Kamiya M, Yakou T, Sasaki T, Nagatsuma YJMt. Effect of Si content on turning machinability of Al-Si binary alloy castings. 2008:0801280304-.

[49] Committee AH. Metals Handbook: Vol. 2, Properties and selection– nonferrous alloys and pure metals. American Society for Metals, Metals Park, OH. 1978.

[50] Uddin M, Basak A, Pramanik A, Singh S, Krolczyk GM, Prakash C. Evaluating hole quality in drilling of Al 6061 alloys. Materials. 2018;11(12):2443.

### *Drilling Technology*

[51] Costa ES, Silva MBd, Machado AR. Burr produced on the drilling process as a function of tool wear and lubricantcoolant conditions. Journal of the Brazilian Society of Mechanical Sciences and Engineering. 2009;31(1):57-63.

**Chapter 3**

**Abstract**

*Jesus M. Orona-Hinojos*

knew as blue arc drilling technology.

challenge for engineers and technologists today.

**1. Introduction**

measured in mm<sup>3</sup>

**21**

Innovative Double Cathode

ECM + EDM Blue Arc Drilling

Electrical discharge machining is a machining method generally used for machining hard metals, those that would be high cost or have poor performance to machine with other techniques using, e.g., lathes, drills, or conventional machining. Therefore, also known as thermal processes like EDM, Plasma or Laser cutting can be used in drilling operations with poor metallurgical quality on cutting edge and will be necessary complement with other processes such as electrochemical machining (ECM). Both ECM and EDM processes use electrical current under direct-current (DC) voltage to electrically power the material removal rate (MRR) from the workpiece. However in ECM, an electrically conductive liquid or electrolyte is circulated between the electrode(s) and the workpiece for permitting electrochemical dissolution of the workpiece material. While the EDM process, a nonconductive liquid or dielectric is circulated between the cathode and workpiece to permit electrical discharges in the gap there between for removing the workpiece material. Both are principle too different, EC using an electrical conductive and ED using a dielectric medium. But exist a way that can to do a combination of Pulsed EC + ED Simultaneous and allowing the coexist both process, in a semidielectric medium, where both condition exist in the same time, therefore in this hybrid is possible create a tooling device dual cathode for drilling process with promissory advantages fast hole for this innovative hybrid ECDM Simultaneous, this hybrid it's

**Keywords:** Drilling, EDM and ECM process, Double Cathode, Hybrid ECDM

a maximum in the material removal rate (MMR), mainly due to conditions of electrochemical and physical equilibrium respectively. These processes defined as electrical discharge machining (EDM) and electrochemical machining (ECM) have high adaptability to make some variants of assisted hybrid systems that allow the acceleration of mass transport to improve considerably the metal removal rate

Is known that ECM and EDM are machining processes that each one has reached

combined with other variants such as the use of abrasive materials (G), ultrasound (US), laser projection (LB), and hydrodynamic magnetic force (HMF) that scientific community has reported in the last decades, then the integration is a possible

/min. Then those processes present important advantages when

Configuration for Hybrid

[52] Zhu Z, Guo K, Sun J, Li J, Liu Y, Zheng Y, et al. Evaluation of novel tool geometries in dry drilling aluminium 2024-T351/titanium Ti6Al4V stack. Journal of Materials Processing Technology. 2018;259:270-281.

[53] Shanmughasundaram P, Subramanian R. Study of parametric optimization of burr formation in step drilling of eutectic Al–Si alloy–Gr composites. Journal of Materials Research and Technology. 2014;3(2):150-157.

### **Chapter 3**

*Drilling Technology*

[51] Costa ES, Silva MBd, Machado AR. Burr produced on the drilling process as a function of tool wear and lubricantcoolant conditions. Journal of the Brazilian Society of Mechanical Sciences and Engineering. 2009;31(1):57-63.

[52] Zhu Z, Guo K, Sun J, Li J, Liu Y, Zheng Y, et al. Evaluation of novel tool geometries in dry drilling aluminium 2024-T351/titanium Ti6Al4V stack. Journal of Materials Processing Technology. 2018;259:270-281.

Subramanian R. Study of parametric optimization of burr formation in step drilling of eutectic Al–Si alloy–Gr composites. Journal of Materials Research and Technology. 2014;3(2):150-157.

[53] Shanmughasundaram P,

**20**

## Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling

*Jesus M. Orona-Hinojos*

### **Abstract**

Electrical discharge machining is a machining method generally used for machining hard metals, those that would be high cost or have poor performance to machine with other techniques using, e.g., lathes, drills, or conventional machining. Therefore, also known as thermal processes like EDM, Plasma or Laser cutting can be used in drilling operations with poor metallurgical quality on cutting edge and will be necessary complement with other processes such as electrochemical machining (ECM). Both ECM and EDM processes use electrical current under direct-current (DC) voltage to electrically power the material removal rate (MRR) from the workpiece. However in ECM, an electrically conductive liquid or electrolyte is circulated between the electrode(s) and the workpiece for permitting electrochemical dissolution of the workpiece material. While the EDM process, a nonconductive liquid or dielectric is circulated between the cathode and workpiece to permit electrical discharges in the gap there between for removing the workpiece material. Both are principle too different, EC using an electrical conductive and ED using a dielectric medium. But exist a way that can to do a combination of Pulsed EC + ED Simultaneous and allowing the coexist both process, in a semidielectric medium, where both condition exist in the same time, therefore in this hybrid is possible create a tooling device dual cathode for drilling process with promissory advantages fast hole for this innovative hybrid ECDM Simultaneous, this hybrid it's knew as blue arc drilling technology.

**Keywords:** Drilling, EDM and ECM process, Double Cathode, Hybrid ECDM

### **1. Introduction**

Is known that ECM and EDM are machining processes that each one has reached a maximum in the material removal rate (MMR), mainly due to conditions of electrochemical and physical equilibrium respectively. These processes defined as electrical discharge machining (EDM) and electrochemical machining (ECM) have high adaptability to make some variants of assisted hybrid systems that allow the acceleration of mass transport to improve considerably the metal removal rate measured in mm<sup>3</sup> /min. Then those processes present important advantages when combined with other variants such as the use of abrasive materials (G), ultrasound (US), laser projection (LB), and hydrodynamic magnetic force (HMF) that scientific community has reported in the last decades, then the integration is a possible challenge for engineers and technologists today.

The evidence on the growth of these removal speeds regain the interest of the industrial sector, being the advanced hybrid machining processes (HMP) like to EDCM technology that allows them will be competitive on some parameters versus Laser or Plasma thermal cutting with high material removal rate, but with a severe heat-affected zone (HAZ), between 1000 to 1600 μm. While in non-contact cutting processes EDM and ECM the HAZ is minimized below 40 μm. However, in terms of material removed, the ECM has speeds of the order of 100 to 250 mm<sup>3</sup> /min, depending on the work material and current density among other parameters. EDM process, the removal speed is between 300 to 600 mm<sup>3</sup> /min, depending on the discharge power and duty cycle [1].

from the EDM process, 6.5% from units sold in ECM, and just over 15% for "Water-

machines (CMM). Laser/plasma cutting tools and EDM are the processes of greater demand; it is a market that has not yet reached maturity with a growth of 7.8% per

To improve the application of the cutting process by electro-discharge EDM, it has been proposed to assist it with PEC pulsed electrochemistry, this class of processes is known as hybrid ECDM (Electrochemical discharge machining) or ECSM (Electro-chemical spark machining) as reported [8]. There are two categories of hybrid machining processes (HMP) as shown in **Figure 1**. Relationships of binary and ternary hybrids are based on their physical nature to carry energy (mechanical, chemical, and thermal). The first category of HMP's is that all its constituent processes are directly involved in the removal of material. The second category of assisted HMP's is made up of processes in which the only one of the constituent processes directly remove the material, while the others are only assisting the removal process, changing the machining conditions in an appropriate direction, improving the machining conditions. Some processes such as plastic flow, mechanical abrasion, heating, melting, evaporation, dissolution, manage to change the physicochemical conditions of the material of the workpiece during a machining

The application characteristics of hybrid processes are considerably different from the corresponding characteristics of the "constituent" processes when these are applied separately. For example, it is established that the productivity of ECM electrochemical machining, when assisted with EDM electric discharge, is 10 to 50

The pulsed electrochemical machining (PECM) on a simultaneous pulsed train of discharge plasma EDM, on the surface of a workpiece is named simultaneous ED + PEC drilling. Combination electro discharge and chemical machining in lowresistivity deionized water, has been investigated in the last decade to obtain a high

**2. Hybrid simultaneous ED/PEC drilling using double cathode**

material removal rate (MRR) and transfer energy to the workpiece [12].

Jet" cutting technologies, and 11.5% remaining in coordinate measurement

*Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling*

annum CAGR (Compound Annual Growth Rate).

*DOI: http://dx.doi.org/10.5772/intechopen.97547*

process [9].

**Figure 1.**

**23**

*Advanced Hybrid Machining Processes (HMP) El -Hofy [1].*

times higher [10, 11].

Variants to the recently published non-contact machining processes [2, 3] open up new lines of innovation in the use of hybrid high-speed EDM technology in drilling and grinding for: (i) Multi-manufacturing of complex precision 3D with additive-laser. (ii) Manufacture of alloys high strength with friction-free finishes (Ra < 400 nm). An EDM electro-discharge erosion process, also known as Blasting BEAM (Blasting Erosion Arc Machining) [4] is reported, with MRR of the order of 11,000 mm<sup>3</sup> /min in Inconel 1718, obtained experimentally.

General Electric Inc. in 2011 showed evidence of technological development of machining for high-speed blades with hybrid EDM in low thermal impact named Blue Arc Machining a device with registration US2010/0126877 A1. GE's laboratory in China achieves MRR in the order of 3,500 to 5,000 mm<sup>3</sup> /min.

On the other hand, leading global companies in thermal cutting processes such as TRUMPF Inc. unveiled in 2011, a hybrid Laser/EDM Drilling Cell, with removal capacities of 30,000 to 35,000 mm<sup>3</sup> /min, depending on the type of part to be manufactured "light-alloy", "medium-alloy" or "duty-alloy" component patent registration EP1988/0299143 A1 [5]. In other words, conventional laser and plasma thermal processes are also reaching their removal speed limit and are evolving into special hybrids.

A couple of decades ago, advanced materials and cutting precision were intended for components of the aerospace and aeronautical sector, which for safety were manufactured piece by the piece it's known as "aircraft-components", and the manufacturing precision allowed by electro-machining ECM and electrical discharge EDM, presented a good solution, because an aircraft is currently assembled between 2 to 8 months, depending on the size and the commercial nature, that means, assembly of 300 to 1000 Aircrafts per year. While the global automotive sector manufactures 80 a million vehicles per year, according to 2018 records referred to in OICA International Organization of Motor Vehicle Manufacturers [6]. This is where new high-performance materials challenge manufacturing processes as "cutting, forming-stamping, bonding and machining" play an important role. Consequently, manufacturing engineers are challenged to find viable highly innovative solutions.

The simultaneous hybrid ED + EC technologies not exist yet commercially for industrial use, being in development the machining by electrical discharge assisted with simultaneous electrochemical pulses ED + PEC or named Pulsed ECDM, the first of thermal nature of plasma-ionic type and the second electro ionic of chemical nature; is possible will be offered in this decade by the original equipment manufacturing houses (OEMs), for industrial applications.

A recent study called "Special Machine Tool Market by Research" [7], reveals that approximately 78,000 units were sold of special machine tools for the manufacturing of the cell-laser type, plasma cutting machines, EDM cutting machines, cutting machines ECM, Water-Jet Cutting machines, and CMM (Coordinate Measuring Machines), for a world market size with revenues of 9.6 billion dollars. Of which 22% of these units are made up of laser/plasma cutting, 45% are

### *Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling DOI: http://dx.doi.org/10.5772/intechopen.97547*

from the EDM process, 6.5% from units sold in ECM, and just over 15% for "Water-Jet" cutting technologies, and 11.5% remaining in coordinate measurement machines (CMM). Laser/plasma cutting tools and EDM are the processes of greater demand; it is a market that has not yet reached maturity with a growth of 7.8% per annum CAGR (Compound Annual Growth Rate).

To improve the application of the cutting process by electro-discharge EDM, it has been proposed to assist it with PEC pulsed electrochemistry, this class of processes is known as hybrid ECDM (Electrochemical discharge machining) or ECSM (Electro-chemical spark machining) as reported [8]. There are two categories of hybrid machining processes (HMP) as shown in **Figure 1**. Relationships of binary and ternary hybrids are based on their physical nature to carry energy (mechanical, chemical, and thermal). The first category of HMP's is that all its constituent processes are directly involved in the removal of material. The second category of assisted HMP's is made up of processes in which the only one of the constituent processes directly remove the material, while the others are only assisting the removal process, changing the machining conditions in an appropriate direction, improving the machining conditions. Some processes such as plastic flow, mechanical abrasion, heating, melting, evaporation, dissolution, manage to change the physicochemical conditions of the material of the workpiece during a machining process [9].

The application characteristics of hybrid processes are considerably different from the corresponding characteristics of the "constituent" processes when these are applied separately. For example, it is established that the productivity of ECM electrochemical machining, when assisted with EDM electric discharge, is 10 to 50 times higher [10, 11].

### **2. Hybrid simultaneous ED/PEC drilling using double cathode**

The pulsed electrochemical machining (PECM) on a simultaneous pulsed train of discharge plasma EDM, on the surface of a workpiece is named simultaneous ED + PEC drilling. Combination electro discharge and chemical machining in lowresistivity deionized water, has been investigated in the last decade to obtain a high material removal rate (MRR) and transfer energy to the workpiece [12].

**Figure 1.** *Advanced Hybrid Machining Processes (HMP) El -Hofy [1].*

The evidence on the growth of these removal speeds regain the interest of the industrial sector, being the advanced hybrid machining processes (HMP) like to EDCM technology that allows them will be competitive on some parameters versus Laser or Plasma thermal cutting with high material removal rate, but with a severe heat-affected zone (HAZ), between 1000 to 1600 μm. While in non-contact cutting processes EDM and ECM the HAZ is minimized below 40 μm. However, in terms of

depending on the work material and current density among other parameters. EDM

Variants to the recently published non-contact machining processes [2, 3] open up new lines of innovation in the use of hybrid high-speed EDM technology in drilling and grinding for: (i) Multi-manufacturing of complex precision 3D with additive-laser. (ii) Manufacture of alloys high strength with friction-free finishes (Ra < 400 nm). An EDM electro-discharge erosion process, also known as Blasting BEAM (Blasting Erosion Arc Machining) [4] is reported, with MRR of the order of

General Electric Inc. in 2011 showed evidence of technological development of machining for high-speed blades with hybrid EDM in low thermal impact named Blue Arc Machining a device with registration US2010/0126877 A1. GE's laboratory

On the other hand, leading global companies in thermal cutting processes such as TRUMPF Inc. unveiled in 2011, a hybrid Laser/EDM Drilling Cell, with removal

manufactured "light-alloy", "medium-alloy" or "duty-alloy" component patent registration EP1988/0299143 A1 [5]. In other words, conventional laser and plasma thermal processes are also reaching their removal speed limit and are evolving into

A couple of decades ago, advanced materials and cutting precision were intended for components of the aerospace and aeronautical sector, which for safety were manufactured piece by the piece it's known as "aircraft-components", and the manufacturing precision allowed by electro-machining ECM and electrical discharge EDM, presented a good solution, because an aircraft is currently assembled between 2 to 8 months, depending on the size and the commercial nature, that means, assembly of 300 to 1000 Aircrafts per year. While the global automotive sector manufactures 80 a million vehicles per year, according to 2018 records referred to in OICA International Organization of Motor Vehicle Manufacturers [6]. This is where new high-performance materials challenge manufacturing processes as "cutting, forming-stamping, bonding and machining" play an important role. Consequently, manufacturing engineers are challenged to find viable highly inno-

The simultaneous hybrid ED + EC technologies not exist yet commercially for industrial use, being in development the machining by electrical discharge assisted with simultaneous electrochemical pulses ED + PEC or named Pulsed ECDM, the first of thermal nature of plasma-ionic type and the second electro ionic of chemical

A recent study called "Special Machine Tool Market by Research" [7], reveals

nature; is possible will be offered in this decade by the original equipment

that approximately 78,000 units were sold of special machine tools for the manufacturing of the cell-laser type, plasma cutting machines, EDM cutting machines, cutting machines ECM, Water-Jet Cutting machines, and CMM (Coordinate Measuring Machines), for a world market size with revenues of 9.6 billion dollars. Of which 22% of these units are made up of laser/plasma cutting, 45% are

manufacturing houses (OEMs), for industrial applications.

/min,

/min, depending on the

/min.

/min, depending on the type of part to be

material removed, the ECM has speeds of the order of 100 to 250 mm<sup>3</sup>

/min in Inconel 1718, obtained experimentally.

in China achieves MRR in the order of 3,500 to 5,000 mm<sup>3</sup>

process, the removal speed is between 300 to 600 mm<sup>3</sup>

discharge power and duty cycle [1].

capacities of 30,000 to 35,000 mm<sup>3</sup>

11,000 mm<sup>3</sup>

*Drilling Technology*

special hybrids.

vative solutions.

**22**

### **2.1 Configuration double cathode for hybrid S-ED/PEC drilling**

The configuration of a hybrid S-ED/PEC process in a semi-dielectric medium comes from a base EDM system, as a scheme is shown in **Figure 2**. The EDM equipment was complemented with two feed inputs: (i) dielectric deionized water (DW) and (ii) low resistivity deionized water (LR-DW), thus causing simultaneous EDM and ECM operating conditions in different regions of a Dual Cathode system. For EDM it is possible to use a graphite electrode in the form of an external head (first cathode), and for ECM an electrode composed of a set of 12 pins mounted on a bronze ring inside the graphite head, the external electrode presents an arrangement of channels that allows movement of the semi-electrical fluid and ionic transfer, these electrodes are arranged in such a way that they connect with an arrow that allows a rotation between 1200 to 1600 rpm, the head is electrically isolated and both samples have electrical continuity fed by a VDC source external pulsed.

They conducted a study on W-EDM for the machining of high-quality heattreated alloy steels. They reported that the HAZ and the solidified layer reach 25 μm. Meanwhile, heat-affected zone with a white layer of approximately 10 μm with high hardness are reported [15]. On the other hand, the novel material removal process of high efficiency by blast erosion arc machining (BEAM), has an extremely higher material removal rate in relation to traditional EDM. However, the thickness of the HAZ caused by BEAM is close to 200 μm. Although it is known that the depth of the HAZ and the re-solidified layer is proportional to the amount of energy used.

*Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling*

*DOI: http://dx.doi.org/10.5772/intechopen.97547*

Machining by S-ED /PEC, under dielectric conditions of low resistivity results in a phenomenon of physic-chemical activation, on the surface of the material that allows an exchange of advantages of the constituent that substantially improve the removal of material at high speeds with minimal thermal impact. Although, the contributions of the ED and PEC processes are not fully explained in the literature. In this research work, a mathematical model for ED/EC simultaneous drilling is proposed to determine the removal rate and the proportion of energy transferred to the workpiece under a new theoretical model, as well as to minimize the white layer effect to determine the contribution of each process in drilling holes in a High Strength Steels (HSS).

The combination of two phenomena, known as: (i) electro-thermal discharge and, (ii) electro-ionic dissolution, in simultaneous ED/PEC, increases the speed of material removal through chemical and physical activation of the metal surface, due to the exchange of advantages. A conceptual scheme of the removal mechanism for drilling by EDM and comparatively by S-ED/PEC is presented in **Figures 3** and **4**. The initial surface condition for *ti*¼<sup>0</sup> ¼ 0, the volume elimination is VR = 0, as presented in **Figure 3(a)** for ED. After the first discharge condition *ti*þ<sup>1</sup> ¼ *ton*,*ED* the volume *VR*<sup>1</sup> ¼ *VRs* (elimination of volume by sparks), as indicated in **Figure 3(b)**. It is known that for every spark produced for EDM, this generate high roughness. In **Figures 3(c)** and **(d)**, the second discharge condition is *ti*þ<sup>2</sup> ¼ 2*ton*,*ED*, and the second volume is defined as: *VR*<sup>2</sup> ¼ *φVRs*, where the fraction φ <1, *VR*<sup>2</sup> <*VR*<sup>1</sup> and

On the other hand, the simultaneous ED / PEC drilling for the ED condition reveals that the surface initially for *ti*¼<sup>0</sup> ¼ 0, and VR = 0, as shown in **Figure 4(a)**. After the first discharge for the first time stage Δ*ton*,*ED*, the volume removal is *VRs*<sup>1</sup> ¼ *VRs* as **Figure 4(b)**. In the second stage *ti*þ<sup>2</sup> ¼ Δ*ton*,*EC* there is a change in the elimination of EC by dissolution of the Fe + 2 ion, then the volume *VR*<sup>2</sup> <sup>¼</sup> *VRd* as **Figure 4(c)** and **(d)**, with a lower surface roughness. Then, the value of the volume fraction is finally φ = 1, and therefore *VRs*<sup>2</sup> ¼ *VRs*1, for each S-ED/PEC cycle. Following the EC condition, the surface shows better behavior due to the amount of material removed by the electric discharge process. This lower degree of roughness is produced by ion exchange during the electrochemical dissolution stage of the workpiece.

*Diagram for EDM removal mechanism. (a) Initial discharge, (b) EDM first cycle VRs*1*, (c) EDM second cycle*

the volume release is not equal to the first download.

**Figure 3.**

**25**

*and (d) Surface removal VRs*<sup>2</sup> ¼ *VRs*<sup>1</sup> *for φ <1 [16].*

In this configuration, a fluid can be fed in two ways. The EDM case feeds: a central inlet deionized water flow V1, through the system of cathodes arranged in a shape concentric with the head of the system. The head speed parameter Vz in the "z" axis constant at 0.5 0.05 μm/s, up to a penetration height of 3 mm (H). On the other hand, stop the S-ED/PEC process, the equipment is configured using an ii) external input flow to the electrode with deionized water of low resistivity LR-DW and it is switched with the second flow V2 to the interior changing the deionized water DW by low resistivity water 0.5 MΩcm LR-DW. Sodium bromide salt (NaBr) in 1.23 ppm TDS was used to adjust the resistivity to 0.5 to 2.5 0.01 MΩcm. NaBr has the ability to solvate ions and, therefore, show a constant electrical conductivity behavior for high temperatures reported by [13].

### **2.2 Theoretical model S-ED/PEC**

The main characteristic of the proposed S-ED/ PEC (Simultaneous Electro Discharge/Pulsed Electrochemical), allows a significant increase in the efficiency of MRR, and a significant reduction in surface roughness, thus providing a better surface finish. It is well known that the EDM process contributes significantly to MRR, as it produces deep layer of heat affected zone (HAZ). While that the main contribution of ECM process as consequence of combining, is the removal HAZ layers allowed roughness less than 2.5 μm (Ra), as reported Levy GN and Maggi F (1990) [14].

**Figure 2.**

*Experimental scheme of (a) EDM River 300 Cell - Instrumented, (b) ED / PEC open circuit voltage pulsed signal [15].*

### *Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling DOI: http://dx.doi.org/10.5772/intechopen.97547*

They conducted a study on W-EDM for the machining of high-quality heattreated alloy steels. They reported that the HAZ and the solidified layer reach 25 μm. Meanwhile, heat-affected zone with a white layer of approximately 10 μm with high hardness are reported [15]. On the other hand, the novel material removal process of high efficiency by blast erosion arc machining (BEAM), has an extremely higher material removal rate in relation to traditional EDM. However, the thickness of the HAZ caused by BEAM is close to 200 μm. Although it is known that the depth of the HAZ and the re-solidified layer is proportional to the amount of energy used.

Machining by S-ED /PEC, under dielectric conditions of low resistivity results in a phenomenon of physic-chemical activation, on the surface of the material that allows an exchange of advantages of the constituent that substantially improve the removal of material at high speeds with minimal thermal impact. Although, the contributions of the ED and PEC processes are not fully explained in the literature. In this research work, a mathematical model for ED/EC simultaneous drilling is proposed to determine the removal rate and the proportion of energy transferred to the workpiece under a new theoretical model, as well as to minimize the white layer effect to determine the contribution of each process in drilling holes in a High Strength Steels (HSS).

The combination of two phenomena, known as: (i) electro-thermal discharge and, (ii) electro-ionic dissolution, in simultaneous ED/PEC, increases the speed of material removal through chemical and physical activation of the metal surface, due to the exchange of advantages. A conceptual scheme of the removal mechanism for drilling by EDM and comparatively by S-ED/PEC is presented in **Figures 3** and **4**. The initial surface condition for *ti*¼<sup>0</sup> ¼ 0, the volume elimination is VR = 0, as presented in **Figure 3(a)** for ED. After the first discharge condition *ti*þ<sup>1</sup> ¼ *ton*,*ED* the volume *VR*<sup>1</sup> ¼ *VRs* (elimination of volume by sparks), as indicated in **Figure 3(b)**. It is known that for every spark produced for EDM, this generate high roughness. In **Figures 3(c)** and **(d)**, the second discharge condition is *ti*þ<sup>2</sup> ¼ 2*ton*,*ED*, and the second volume is defined as: *VR*<sup>2</sup> ¼ *φVRs*, where the fraction φ <1, *VR*<sup>2</sup> <*VR*<sup>1</sup> and the volume release is not equal to the first download.

On the other hand, the simultaneous ED / PEC drilling for the ED condition reveals that the surface initially for *ti*¼<sup>0</sup> ¼ 0, and VR = 0, as shown in **Figure 4(a)**. After the first discharge for the first time stage Δ*ton*,*ED*, the volume removal is *VRs*<sup>1</sup> ¼ *VRs* as **Figure 4(b)**. In the second stage *ti*þ<sup>2</sup> ¼ Δ*ton*,*EC* there is a change in the elimination of EC by dissolution of the Fe + 2 ion, then the volume *VR*<sup>2</sup> <sup>¼</sup> *VRd* as **Figure 4(c)** and **(d)**, with a lower surface roughness. Then, the value of the volume fraction is finally φ = 1, and therefore *VRs*<sup>2</sup> ¼ *VRs*1, for each S-ED/PEC cycle. Following the EC condition, the surface shows better behavior due to the amount of material removed by the electric discharge process. This lower degree of roughness is produced by ion exchange during the electrochemical dissolution stage of the workpiece.

### **Figure 3.**

*Diagram for EDM removal mechanism. (a) Initial discharge, (b) EDM first cycle VRs*1*, (c) EDM second cycle and (d) Surface removal VRs*<sup>2</sup> ¼ *VRs*<sup>1</sup> *for φ <1 [16].*

**2.1 Configuration double cathode for hybrid S-ED/PEC drilling**

behavior for high temperatures reported by [13].

**2.2 Theoretical model S-ED/PEC**

(1990) [14].

*Drilling Technology*

**Figure 2.**

*signal [15].*

**24**

The configuration of a hybrid S-ED/PEC process in a semi-dielectric medium comes from a base EDM system, as a scheme is shown in **Figure 2**. The EDM equipment was complemented with two feed inputs: (i) dielectric deionized water (DW) and (ii) low resistivity deionized water (LR-DW), thus causing simultaneous EDM and ECM operating conditions in different regions of a Dual Cathode system. For EDM it is possible to use a graphite electrode in the form of an external head (first cathode), and for ECM an electrode composed of a set of 12 pins mounted on a bronze ring inside the graphite head, the external electrode presents an arrangement of channels that allows movement of the semi-electrical fluid and ionic transfer, these electrodes are arranged in such a way that they connect with an arrow that allows a rotation between 1200 to 1600 rpm, the head is electrically isolated and both samples have electrical continuity fed by a VDC source external pulsed. In this configuration, a fluid can be fed in two ways. The EDM case feeds: a central inlet deionized water flow V1, through the system of cathodes arranged in a shape concentric with the head of the system. The head speed parameter Vz in the "z" axis constant at 0.5 0.05 μm/s, up to a penetration height of 3 mm (H). On the other hand, stop the S-ED/PEC process, the equipment is configured using an ii) external input flow to the electrode with deionized water of low resistivity LR-DW and it is switched with the second flow V2 to the interior changing the deionized water DW by low resistivity water 0.5 MΩcm LR-DW. Sodium bromide salt (NaBr) in 1.23 ppm TDS was used to adjust the resistivity to 0.5 to 2.5 0.01 MΩcm. NaBr has the ability to solvate ions and, therefore, show a constant electrical conductivity

The main characteristic of the proposed S-ED/ PEC (Simultaneous Electro Discharge/Pulsed Electrochemical), allows a significant increase in the efficiency of MRR, and a significant reduction in surface roughness, thus providing a better surface finish. It is well known that the EDM process contributes significantly to MRR, as it produces deep layer of heat affected zone (HAZ). While that the main contribution of ECM process as consequence of combining, is the removal HAZ layers allowed roughness less than 2.5 μm (Ra), as reported Levy GN and Maggi F

*Experimental scheme of (a) EDM River 300 Cell - Instrumented, (b) ED / PEC open circuit voltage pulsed*

Substituting the respective expressions of Eq. (1), in Eq. (2), the resulting volume of material extracted during S-ED/PEC drilling could be calculated by means of Eq. (3), where *MRRhyb* is the velocity volume elimination *MRRhyb*, and *Ks*, *Kd* are the machinability constants of the ED and EC subsystems, respectively.

*Innovative Double Cathode Configuration for Hybrid ECM + EDM Blue Arc Drilling*

*Ks* ∗ *Es*ð Þ*t* � �

þ 1 *tc*

Considering *Rm* (μm) as the average radius of the tool and δ (μm) is the thick-

The amount of energy for each subsystem, *Es*ð Þ*t* and *Ed*ð Þ*t* , for a hybrid S-ED/ PEC condition is represented by the terms of Eq. (3), which can be solved using an experimental pulsed electrical signal. It is known that the expression *Es*ð Þ*t* for EDM

> ð*ton* 0

*Va* ∗ *io*,*Fe* ∗ *exp ηFe* ∗ *β*�<sup>1</sup>

Where *Va* is the anodic voltage (volts) and *IF* is the Faraday current (A) that can

*io*,*Fe* is the ion-exchange current (A) and *<sup>η</sup>Fe* <sup>¼</sup> *<sup>ϕ</sup><sup>a</sup>*,*Fe* � *<sup>ϕ</sup>*<sup>0</sup> � � is the overpotential (volts) where *ϕ<sup>a</sup>*,*Fe* is the anodic potential and *ϕ*<sup>0</sup> is the equilibrium potential of the

TAFEL anodic constant. The value of *β<sup>a</sup>*,*Fe* can be estimated assuming the following values. A symmetry coefficient of polarization *α* is equivalent to ½, ideal gas

It is possible to determine the fraction contributions of each process for the S-ED/PEC hybrid, where *ψ<sup>s</sup>* (9) is the contribution of the ED fraction and *ψ<sup>d</sup>* (10) is

exchange number *z* for iron case Fe ➔ Fe+2 + 2e, *z* = 2, and *T* is the interphase temperature assumed Temperature of room. Then, this can be estimated as *β*�<sup>1</sup> = 31*:*97 *mV* as was reported by Winston [17], for a cell S-ED/PEC.

*Es* ¼

While *Ed*ð Þ*t* for ECM it is possible to represent it by Eq. (7) [16].

*Ed* ¼

be determined using TAFEL Eq. (8).

constant *R* = 8.314 JK�<sup>1</sup> mol�<sup>1</sup>

**27**

ð*ton* 0

redox reaction with a value of �510 mV for Fe ➔ Fe+2 + 2e.

Was considered the argument *<sup>β</sup><sup>a</sup>*,*Fe* <sup>¼</sup> *RT*

**2.4 Simultaneous ED/PEC electro-ionic model**

*Kd* ∗ *Ed*ð Þ*t* � � � � *AT* (3)

*AT* ¼ 2*π* ∗ *Rm* ∗ *δ* (4)

*Ie* ∗*Vs dt* (5)

*<sup>a</sup>*,*Fe* � �*dt* (7)

) represent the

, the electron

*Ie* ¼ *f <sup>e</sup>* ∗ *Ip* (6)

*IF* <sup>¼</sup> *io*,*Fe* <sup>∗</sup> *<sup>e</sup>* <sup>∝</sup>*zf* ð Þ *RT* <sup>∗</sup> *<sup>η</sup>Fedt* (8)

*<sup>α</sup>zF* where *<sup>β</sup><sup>a</sup>*,*Fe* (Volts�<sup>1</sup>

, Faraday's constant *F* =96487 C mol�<sup>1</sup>

) is the cross-sectional area of the tubular electrode and is

*MRRhyb* <sup>¼</sup> <sup>1</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.97547*

For which, *AT* (mm2

represented by Eq. (4).

can be defined by Eq. (5).

ness of the tool.

Where:

*tc*

### **Figure 4.**