New Prototyping Skills: Casting

Hey everyone, sorry for the lack of updates! It’s been a busy few weeks to say the least, with final presentations, midterm exhibitions, and the inevitable travel I needed for a recovery afterwards! But the exciting news is, I have lots of juicy posts to update you.

This post is mostly for my Industrial Design/Architecture/Artist friends and anyone else who is interested in metal casting. I had the great opportunity to cast some pieces out of bronze for one of my classes here at TU/e. I had never cast before (and neither had the other 7 people that were present at the casting) so it was quite a new experience. The casting was done at Beeldenstorm, which in Dutch roughly means “statue form.” It is a metal/casting shop (and they also do plastic) on the Technical University campus. It is a resource for many more people than just students, though!

I’m going to describe the steps and also include some cool photos. Nothing like recounting the process of fiery, extremely hot, molten metal being poured into sand molds…am I right?

Steps To Casting via Green Sand Mold

  1. Make an initial model impression. First off, you must set your models into a section of reddish sand to make the first half of the mold. This step is pretty simple. You press your models in and pack in some sand around the sides so that all of your details are included in the mold.ImageImage
  2. Mix sand with chemicals to pour onto impression and make side 1 of your mold. After packing in your red sand, the group (it takes several people for this because the process must be quick) mixes a bucket of sand with two different chemicals. You must mix one chemical at a time, and you also have to flip the sand in the bucket so that each chemical mixes evenly. As soon as the mixing is complete, you have to pour the sand onto your model impression, because the sand sets quickly. The sand quickly begins to turn green, and hardens, which is essential to making your mold correctly. Also, we had to mix 2 buckets of sand for each side (for the bigger molds) which meant that we had to quickly mix 2 buckets in a row, because the layers couldn’t harden at different times. If they did, the mold would be an incorrect consistency. After patting down the poured sand, you place some sort of object on top (we used a piece of scrap wood) so you can check the color of the sand to see whether the mold is ready to flip over and repeat this process.ImageImageImage
  3. When side 1 of the sand mold has hardened, it’s time to flip it over and repeat step 2. The hardening process takes about an hour to an hour and a half, so we just took a break outdoors during the process. Before flipping, you must check whether the green color is deep enough and thus the sand is hard enough to withstand being flipped to the other side. After flipping & carefully removing the side supports for the model, you must remove the excess red sand so that you can make an impression of that side of the models. This is a delicate process. You need to remove as much of the red sand as you can, so that the sand covers all of your models’ details.ImageImage
  4. Repeat step 2 and wait for the entire mold to harden. Once the new side of the mold has hardened, you must carefully pry the two sides apart so that you can remove the models (ours were made of MDF wood) from the inside as well as draw the channels for the metal to run through. The prying apart was also a delicate process, because the sand mold could easily break apart and hours of work could be ruined, so one of the professionals performed this part for us. He also drew the channels for our mold, which seems simple enough but there is an important infrastructure to it. Image
  5. Once the channels are carved properly, it’s time to spray the mold down to make it firesafe! (This part is fun.) The spray smells awful but the fireproofing part is awesome. After you take your two sides outside and spray the mold-side thoroughly, one of the Beeldenstorm employees took each side of the mold over to the oven, and lit it on fire. You then wait for the sprayed part’s fire to go out. Then it’s time to clamp the two sides together, and pour the metal through the channels!ImageImage
  6. Clamp the mold and watch the professional pour molten metal (bronze or aluminum) through it! This part is pretty simple and makes for some great pictures. Unless of course you want to actually be one of the guys that gets paid to pour this extremely hot stuff- I imagine that process is a bit more difficult.ImageImage
  7. Wait for the metal to cool (about 20 minutes) and take apart your mold to remove your new casted object! This process was much shorter than I thought it’d be. Turns out, metal cools pretty quickly! As soon as the metal is removed, you put it in water to speed up the cooling process so that it is touchable. The metal piece looks a bit less-than-attractive because of the metal channels attached to it, but once this piece is fully cooled you can start cutting and shaping it! We waited to finish the next step after the weekend because of the metal shop’s hours.ImageImageImageImageImage
  8. Shape using tools- cutters/polishers, etc. This step is the most artistic and hand-crafted part of the process. Unfortunately, I don’t have photos due to time constraints we were under, but the process was very similar to wood-shaping (just more time intensive). We also had to wear more protective material, because it turns out that when you’re removing metal, the hot shavings that fly out everywhere really sting when they hit your skin. Who knew? We had to wear faceguards, ear protection, thick gloves, and clothes that cover your entire arms/legs/chest areas. The final result? Two pieces of bronze cutlery, designed to fit the terms repulsive + inappropriate. One piece of the set was required to be “sufficient” while the other was deemed “excessive.” Check out the final product!Image