Page 465 - Injection Molding Advanced Troubleshooting Guide
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46.3 Warp Troubleshooting 465
Closely watch the robot to determine if the part is being damaged from the robot
end of arm. There are cases where the robot actually pushes excessively hard
against the part while picking and causes deflection of the part. Watch the robot to
see if it is moving straight back away from the mold because sometimes a robot
program will have a step that causes an indirect move that results in the part hang-
ing up on the mold and becoming distorted. See Section 46.3.3.2 for more infor-
mation on robot handling.
Case Study: Post-Mold Handling
In this case a small polypropylene automotive trim piece was being molded.
The operator would occasionally find a couple of warped pieces as they
inspected parts. Using the STOP method and Observing the parts after
molding highlighted that parts were catching on the conveyor and becoming
warped from the force of the conveyor pushing against them. The location
on the conveyor where the parts were getting trapped was shielded and the
warped parts were completely eliminated.
46.3.2 Warp Troubleshooting Mold Issues
Mold-related warp causes include:
Sticking
Cooling issues
Cavity imbalance
Gating
46.3.2.1 Mold: Sticking
If a part is sticking in the mold the part may distort when ejected. Parts that stick
will require additional force to remove from the mold, which in turn may lead to
distortion that appears to be warp.
Verify that the part is not sticking to the cover or the ejector half of the mold. Often
cracking noises will accompany sticking parts. If the noise is heard during mold
open, the part is likely sticking to the cover, but if the noise occurs during ejection
then the part is sticking to the ejector half.
A great way to verify that a part is not sticking is to run a cycle in semi-auto and
stop the cycle prior to ejection. Examine how the part sits on the steel of the ejector
half of the mold. A part that has lifted away from the ejector steel can indicate that
the part stuck in the cover half of the mold. Also try to manually remove a part
from the ejectors and lifters because many times it is possible to feel where the
