Page 236 - Injection Molding Advanced Troubleshooting Guide

24.3 Cracking Troubleshooting 227

pact onto a chute. If a part is robotically picked it can be damaged by the end-of-
arm tooling as well as by being dropped from too high of a height. A key portion of
STOP troubleshooting is Observation, which includes listening for strange noises.

24.3.1.6„ Molding Process: Operator
Cracking is a defect that can be caused by how an operator is handling a part. If
operators are dropping the part or banging it around they could actually cause the
part to crack or break. Normally if an operator is causing the part to break the
design has an inherent weakness that should be addressed. If a part is so weak
that simply handling it causes damage it should be examined for improvement
opportunities.
Also when dealing with operators, make sure that there are clear work instruc-
tions available and that they are being followed. It can be difficult to track a prob-
lem if every operator is treating the parts differently.
Another possible impact that an operator can have on parts is to chemically con-
taminate the molded part. An operator could try to improve the part by wiping
with a cleaner. Various materials will react to solvents and cleaners and may show
crazing or an environmental stress cracking from the chemical exposure. It is pos-
sible that someone trying to help could jeopardize the integrity of the molded part.

24.3.1.7„ Molding Process: Mold Breakaway Speed
If a part has a tendency to stick in the cover half of the mold fast mold breakaway
speeds can damage the part. There will be cases where running a slower break-
away speed will help to release the part from the cover. The downside of slowing
down breakaway speed is that the cycle time will be increased. This can also be a
factor when the crack is occurring near a slide driven by a horn pin.
Notice that the interaction with the mold must be carefully evaluated when dealing
with breakaway problems. See tooling concerns below for details, and do not pro-
cess around a tooling issue!

24.3.1.8„ Molding Process: Gate Seal
There can be cases where molding a part with gate seal freezes in excess stress
near the gate. Especially if the cracking is occurring near the gate it may be worth
trying to mold some parts without gate seal to see if there is an over-packing high-
stress condition contributing to the cracking. Try running without gate seal to see
if the cracking problem is improved.