13. Molding and casting

Due Wednesday May 20 2020


individual assignment:
1. design a mold around the stock and tooling that you’ll be using,
2. mill it (rough cut + (at least) three-axis finish cut),
3. and use it to cast parts

group assignment:
1. review the safety data sheets for each of your molding and casting materials,
2. then make and compare test casts with each of them

My plan to complete the assignment

  1. CAD: Design a vacuum forming pattern in Onshape
  2. CAM: Generate tool paths (gcode) with FreeCAD
  3. Mill foam to create vacuum pattern
  4. Vacuum form parts


I decided to vacuum form this half-dome topper to add to the face shield I have been manufacturing for the Illinois PPE Network. This half-dome topper will allow protection from splashes that may go over the top of the shield. I already had the fame parametrically designed in Onshape, so it didn’t take long to design half-dome topper I wanted to vacuum form.

Next I used the Boolean function of Onshape to subtract the half-dome topper from a tool block. Next I used various extrudes to cut away the cavity side of the tool block leaving the core tool block. The core tool block is the part I need to make the vacuum form pattern.


I wanted to try out FreeCAD CAM to mill my mold from foam a X-Carve milling machine. This video to help get me started with creating tool paths in FreeCAD: FreeCAD- The Powerful Path Workbench for CNC Machining and Gcode|JOKO ENGINEERING| I used the FreeCAD Path Workbench to Generate tool-paths to use on our x-carve milling machine. I will use the gcode from FreeCAD and it’s GRBL post processor to generate g-code to run our fab labs x-carve milling machine.

Mill Foam

I will post the results of milling the foam vacuum form pattern here. I will use 2” thick XPS foam board glued together with gorilla glue as milling stock.

3D Printed Vacuum Mold

Before milling I 3D Printed a prototype of the mold on a Flashforge Guider 2 3D printer. The Flashforge Guider 2 has a very large build envelope of 280x250x300mm (11x9.8x11.8 inch) allowing it to print the mold in one piece.

The mold printed well in about 11 hours.
I then designed a vacuum port for the mold. Holes will be drilled into the 3D print just under the flange of the port. The porous nature of 3D printing will allow air to be pulled through the surface of the mold. PETG sheet will be clamped in a wood frame, heated and then lowered onto the mold, then vacuum will be applied. The slumping of the PETG combined with the vacuum should be enough to form the PETG into the desired half-dome topper shape.

Vacuum Form

I will post the results of vacuum forming here.

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