Page 353 - Injection Molding Advanced Troubleshooting Guide
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36.3 Part Sticking on Ejector Trouble shooting 349
If other factors do not seem to influence the sticking problem try adjusting melt
temperature to determine impact. If changing melt temperature make sure to re-
check gate seal and final part dimensions.
36.3.2 Part Sticking on Ejector Troubleshooting Mold Issues
There are many mold-related issues that can cause part sticking on ejector includ-
ing:
Surface finish
Lack of ejection
Lack of draft
Buildup
Slides or lifters
Damage, erosion, or burrs
Lack of cooling
36.3.2.1 Mold: Surface Finish
Finish on the ejector half of the mold is often overlooked and as a result sticking
can be a major problem. In many cases molds will have EDM or machining marks
left on the ejector half of the mold that prohibit ejection. Normally a 320 draw pol-
ish will provide good release properties from the mold. In many cases too much
polish can lead to sticking issues, but a good draw polish is often the key to provid-
ing release. Be sure to examine molded parts with a flashlight to look for EDM or
machining marks on all details.
36.3.2.2 Mold: Lack of Ejection
If a mold is designed without adequate ejection the part will stick to the ejector
side of the mold. Ejection must be incorporated during mold design and must be
balanced with cooling requirements as well as designed support pillars.
Where possible it is often advantageous to increase the size of the ejector pin to
provide more ejection surface area as well as avoid pin deflection from thinner
pins. Use of straight lifters can allow for increased surface area for the ejection
force to be distributed against. Ensuring adequate ejection will help eliminate
sticking, pin push, and even improve cycle times.
36.3.2.3 Mold: Lack of Draft
Every material has specific requirements for draft angles to provide release from a
mold. Draft needs to be incorporated into the design of the part and the mold to
