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Injection Molding Sticking Issues

From a tooling view point, surface finish is the first thing to look at with sticking issues. Different materials react differently to finishes. The draw polish (320 paper) in this case to the half that is sticking and free of sharp edges, cutter marks and EDM. Mirror finishes can contribute to sticking also, I have removed many mirror finishes to eliminate sticking issues. A very fine glass bead blast can also help in some cases.

On the core half where you want it to stick, surface finish is also a big factor. Outside of adding undercuts (which can cause flaking and visual issues) you can blast the side walls with AO (Aluminum Oxide), pretty cheap. Start with 320 AO (pretty fine) not aggressive and provides a mat finished that the material will stick too. You can keep dropping down 220, 180, 120, 80 AO, the lower the number the more aggressive the finish which will add a fine simple/texture for bite. Need to have adequate ejection also. There are other tricks to adding fine textures that will bite more than undercuts which can cause flaking and visual issues.

These are some cheap things to try before getting more involved with modifying the injection mold with added mechanics, coatings or adding cooling. Assuming you have covered the processing side.

Troubleshooting the problem this way. First eliminate thing which cause the part to stick. Look for undercuts, insufficient draft, vacuum, texture, etc. Then provide draw polish. If there is still a problem you should then provide positive pull on the moveable. If the other side is clear of problems very small undercuts should suffice. In an extreme case you can shorten KO pins and undercut. The vestage can be cut or broken off.

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