This invention relates to the swage mounting of a magnetic head-carrying suspension assembly to an actuator arm in a magnetic disk storage device for a computer. In particular, the present invention relates to a method and apparatus for forming a swaged connection between components under very controlled conditions and for testing the applied torque required to cause failure in such swaged connection.
A magnetic storage disk is "read from" or "written to" by means of a magnetic head mounted at the end of a suspension assembly that includes a spring, or load beam component that biases the head against the disc by means of its pre-load, or "gram load". The suspension assembly is in turn attached to a rigid, pivoting actuator arm which serves to precisely position the magnetic head over the many tracks of the disk corresponding to locations where digital information may be recorded. In order to meet the demand for higher-capacity drives, drive manufacturers utilize both sides of the magnetic disk, and also use multiple disks at the same time. Each side of each disk is served by its own magnetic head /suspension/actuator arm assembly. Each attachment of a suspension assembly to an actuator arm in the drive represents a potential for failure, and it is therefore important to make the mountings as reliable as possible.
"Swaging" is one method for mounting a suspension assembly to its corresponding actuator arm. In the swaging process, a precisely dimensioned and contoured boss protruding from a swage plate that is welded to the loadbeam of the suspension assembly, and surrounding a hole formed therein called the boss inside diameter is inserted into a precisely dimensioned hole formed in the actuator arm. A combination of small precision metal balls are forced through the boss inside diameter which causes the boss material to be displaced so as to expand against the walls of the actuator arm hole and thereby join the suspension/head assembly to the actuator arm in a strong friction bond. The balls may be forced through in either direction thereby exerting either a tensioning or compressive force on the boss. Many factors influence the integrity of the resulting swaged connection including, the force used to clamp the components together, the swage force required to drive the ball through the components, and the speed and acceleration with which the ball is driven through. These same variables of the swaging process can affect the change in suspension gram load caused by swaging. Such swage mount has a very low profile, allowing the separate disks to be placed closer together, reducing the overall size of the disk drive unit.
Manufacturers need to know that the swaged connection is strong enough to prevent the head/suspension assembly from "twisting out", causing head misalignment errors in following the tracks of the magnetic disk. Tolerances for twist-out torque are set by manufacturers for all head/suspension assemblies used in their disk drives. This is usually done with a destructive test, measuring the torque required to twist out sample head/suspension assemblies using hand-operated tools, offering little in the way of accuracy of measurement and reliability of method. What is needed is a method and apparatus that will allow swaged connections to be formed under very controlled conditions and then to be tested by the application of precisely-controlled torques, to yield accurate displacement data of the head/suspension assembly. Precise failure information can thereby be gathered to allow manufacturing processes to produce better, stronger disk drive head suspensions, resulting in better disk drive performance and lower failure rate.