Making molds!

We’ve noticed a few teams would make molds for thing on their robot. We were wondering how they created them. What was the process and can we get a tutorial!

Brandon Holley posted some decent information here:

This website would also be very helpful.

or leave some bread in a damp place…:rolleyes:

Seriously: The smooth-on site is awesome, buy one of their starter kits and play around. It can get expensive to make big molds, but the starter kit is around $35 and you can make a bunch of cool stuff with it, and more importantly understand the process.

Also, if inexpensive is important, get some plaster of paris and make molds for wax (or, use wax to make molds for plaster). Using flexible silicone has its advantages, but cost isn’t one of them. Plaster is cheap and reliable.

Is there an easy way to take a 3D CAD file, turn it into a 3D CAD file of the inverse of the object to make a mold, and then 3D print a mold, then pour urethane or something to cast the object from? Can you cast urethane directly in an ABS or a PLA mold?

Also, I’m lost on how to invert a CAD model to be basically a block with the negative of an object.

There’s a tab in SolidWorks called Mold Tools. Start with the tool called Parting Lines, and move to the right with tools in sequence until you get your mold.

Anyone have experience doing this in Inventor?

You can use the “Combine” command in the modeling tool bar to add, subtract, or intersect one body from another.

Create a mold body such as a rectangular block. Import another part with the Derive command, and select the option to maintain it as a separate body. Move it as needed with the Move Bodies command. Select Combine, indicate the base body (block) and the tool body (part) and indicate cut/subtract. Should cut the tool body volume from the base body.

PS edit: I do not see a way to rotate/reorient the part body after importing it into the mold file. Only translation moves. It may be necessary to make sure the mold body and part body are already in the proper orientation respectively.

If someone has experience in making molds and can make a video tutorial for FRC either in solidworks or inventor they’d be my hero. (I’ve looked tutorial for how to do this they were very confusing and not very helpful)

Hmmm, well I’m not doing anything tomorrow…

I might just do that. However, I don’t really know much about the urethane casting process. I can teach how to use the tools in Solidworks, but I don’t know if there are special considerations that need to be accounted for in the mold design, (Besides adding draft, eliminating undercuts and such, I’ve designed an injection mold before.)

Although there are many types of urethane, generally it is a pourable 2-part compound that is somewhat viscous, a little thinner than honey, but thicker than pancake syrup. It warms a little while curing, and shrinks a little especially in thicker casts.

Both ABS and PLA have enough temperature resistance to take a direct casting of most urethane. Surface finish may be less than desirable, and mold release agent is mandatory.

Make your assembly and save it. Next open a new .ipt and choose the derive component from the import panel. It will import you assembly and the you change the + to - on the part you want to delete/erase and the new derived part will be your mold.

Mr. B

Off topic:

That was a good one.
And of course, the image below (I’ve saved it cause I need to use it so often :D)

Screen Shot 2013-12-18 at 8.01.04 PM.png

Screen Shot 2013-12-18 at 8.01.04 PM.png

Thank you too all who have answered. We are currently 3d printing a wheel for our FTC team and they will be making a urethane mold from it. I will try to keep you up to date on it. If you have any suggestions or any comments or tips please ask or comment. I’m learning so much from this and I’m sure someone else is too. So thank you

Freeman Supply has a free DVD you can request, which shows molding and casting techniques using some of their products.

Smooth-On and Tap Plastics have You Tube channels demonstrating applications of their molding and casting products.

Here’s our attempt at cast urethane tread a couple of seasons ago. The mold was 3D printed in ABS (in 4 pieces). The resultant “flashing” was minor and easily removed with a razor blade. We used a 2-part 50A durometer urethane from Eager Polymers (Part # EP-1150). The surface finish was adequate, but you can improve it with a little sanding and acetone.