Molding and Casting

This week assignment is about molding, casting and use of compounds. So, we have to design a 3D mold, machine it and cast parts from it.

Keeping in mind my final project, I designed a mold for a smd dispenser, building on the work done in the previous session.

Dispenser's 3D design

First I export, to postscript, the smd solder mask (tStop) using Eagle's Cam Processor, I considered 15 mils of clearence over the pad size, this for prevent jamming of components in the dispenser. Then open the file with Corel, redraw the space for each component and export to dxf.

Importing the dxf file with Rhino to design the dispenser in 3D.

Mold Design

For the mold design I've include the dispenser model in a solid receptable, this is very important to prepare the urethane mold. In the following figure you can see the mold assembled and their parts.


PCB Milling

Then we mil with MDX-20, both the base of the mold and the dispenser. For the base we use a 3mm tool and for the dispenser I made a tool change to 0.8mm.

Milling the dispenser with a 0.8mm tool


After milling we were ready for preparing the mold, for this I used a two component urethane rubber compound. Miixing in equal parts the components and pouring in the mold with a uniform flow to minimize entrapped air. The rubber cured 12 hours and then I demolded with any difficulty. Following I prepared the cement for the model.

Final comments

This has been a very interesting assigment, letting us now about new capabilities of MDX-20 as well as materials and processes for molding, very important for my final project.