Shrinkage

A concept for a heated mold.

Injection molded and sand cast parts require a high rate of flow and the maintenance of temperatures above the glass transition to fill their molds. If the material cools before the mold is filled, shrink cavities and distortions of the part can occur. The most common way to deal with this is to keep parts small, with thin walls and oriented such that the material doesn’t have far to travel. Might there be a way around this? Could it be possible to heat the walls of the mold to maintain high internal temperatures until the material has filled the mold entirely? I don’t have a foundry to try this myself, but I would love to see someone experiment with heating a sand mold while casting aluminum to see if it reduces or eliminates problems with shrink cavities. Any additional control that we can get over the cooling process can only help, right?

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General Machining Tips

I’m by no means a good machinist. I get along OK, and I can perform most of the tasks that I need to on my own; but I still need a lot of help to get things done and done well. I’m quite thankful to Steve, the machinist here at CC, for teaching me through this semester and helping me to fabricate the parts needed for my arm project and I hope to learn much more from him. With that in mind, I thought that it might be helpful for other beginning machinists to have a resource for basic machining techniques that are not very complicated so they can get started. The best resource I’ve found is by far the video series on prototype machining provided by MIT here, but I hope I can help with some other tips and tricks I’ve found useful. Continue reading

Primitive Toolmaking

As I’ve worked on my robot arm project over the last semester, I’ve spent a lot of time in the machine shop fabricating parts. I think it’s incredibly fascinating that it is possible to create tools which have such high precision and rigidity that we can hold +/- .0005″ tolerances! Even more incredible is that these tools, by necessity, were originally created from less accurate ones.

With that in mind, I’ve become very interested in how this is done. What processes are necessary to go from having no metal tools whatsoever to a full-fledged industrial machine shop? We have the technologies developed, and I feel it would be possible to use the knowledge that we’ve accumulated over centuries to quickly undergo that journey again. I think this would be an incredibly useful survival skill, and extremely practical to boot.

So what would the steps of this process be? You’ll have to forgive me any omissions, I’m only just beginning to think about this. From my view, this would be the ordering:

  1. Ceramics. These are necessary to create crucibles, and containers for the manufacture of many types of tools which can be used to fabricate other tools. Simple knives, chisels, files, and bricks are necessary for the next phases.
  2. Charcoal manufacture. Using bricks from the development of ceramics, which could be cured in a dried-brick kiln, one would create charcoal for fueling the furnace needed to melt metals.
  3. Smelting/Casting. Once sufficient stores of charcoal are made, and crucibles are available, the melting of metal (I’m not including mining ore here) begins. Some careful innovation with regards to which tools can be used to lift the crucible will be necessary, but the first tool made with this process can be a crucible tool, which will make things significantly safer!
  4. Refinement of tools. Using abrasives such as fine grit sand and naturally occurring minerals, castings can be refined into more useful tools.
  5. Metallurgy. Using the crucible, furnace, and charcoal, it would be possible to manufacture the necessary components for a blast furnace which could be used to make steels. These steels would be very useful for creating more robust tools.
  6. Machining. Now, with the blast furnace steel, better tools, and castings, basic machine tools can be made (David Gingery style). A lathe would be first; and used to manufacture the parts for a shaper, both of which can be used to make a mill.

Once the mill is done, you’re all set! You have all of the components of a basic machine shop, and the capability to manufacture more as you see fit. This is what I estimate the progression would be, with each step building on the ones previous. If anyone has any experience doing this, I’d love to hear about it!