Page 343 - Injection Molding Advanced Troubleshooting Guide

35.3 Part Sticking on Cover Troubleshooting 339

Confirm that the melt temperature meets the recommended settings of the mate-
rial supplier. If the melt temperature is running high verify that settings that
impact melt temperature are correct including:
ƒ Barrel temperatures
ƒ Back pressure
ƒ Screw recovery speed

35.3.1.3„ Molding Process: Mold Temperature
The actual steel temperature of the mold can lead to sticking concerns. If the mold
temperature is too high the material may not shrink enough to effectively release
from cover details. High mold temperatures also lead to less pressure drop across
the cavity and allow the part to be packed out more effectively potentially leading
to sticking to the cover. Normally if mold temperatures are too cold sticking prob-
lems will be more likely to occur on the ejector side of the mold.
There may be cases where the cooling capabilities of the mold must be improved to
prevent sticking (see Chapter 14 on mold cooling).

35.3.1.4„ Molding Process: Mold Open Breakaway Speed

If the initial mold open speed is excessively fast sometimes the part will have more
tendency to stick to the cover side of the mold. There are cases where there is a
vacuum between the part and the mold and a slower speed will allow the vacuum
to break. Also fast breakaway speeds can cause a part to become angled onto mold
details and lead to sticking.
If the part is sticking to the cover try a reduced breakaway speed to determine if
the sticking improves. If it does improve the problem, utilize the STOP process to
work through any root causes that may be resulting from the mold itself such as
undercuts. Slowing the breakaway speed may end up as processing around an-
other root cause.

35.3.2„ Part Sticking on Cover Troubleshooting Mold Issues

There are many potential mold-related causes of part sticking including:
ƒ Mold damage
ƒ Lack of draft
ƒ Surface finish
ƒ Vacuum
ƒ Cavity balance
ƒ Buildup
ƒ Ejector half detail