# Injection Molding Factory Tour

### Shenzhen Adventure Day 4

This was fun! At the injection molder they had a massive pile of not being run molds

and about 20 machines which were cranking out parts. We got to see our mold for the class pried apart which was cool.

Molds are super complicated; I didn’t have an appreciation for how hard they are to make before.

Here’s a run down:

• Tolerances are ridiculous. They need to be airtight metal with no gaskets so that the plastics don’t leak
• For nice looking parts, the molds need to be basically mirror finish.

• Molds can be made from Aluminium for lower cost but they basically don’t do it in China because Steel is cheap enough there.
• A mold will run about $5000-$10000 USD for a reasonably sized design, and can do about 500,000 casts. This is mostly the price of the steel
• You can modify your mold by welding on a block of steel and then re-carving out the features
• Designs with overhangs or other features are much more complicated to build because the mod needs to essentially unfold itself to be able to release a part
• A mold has a couple key properties, the points where the pins push the cast out and the fill points. Based on these, the finished product will have different flows of plastic through it which could cause different knit points (where two flows meet) or flow lines (artifacts of the plastic’s path). The points where the pins push out are those raised disks you sometimes see on plastic objects.