Page 356 - Injection Molding Advanced Troubleshooting Guide
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352 36 Part Sticking on Ejector
an ejector plate on a 300-ton with one knock-out bar will likely lead to plate-cock-
ing problems.
36.3.3.3 Machine: Robot Handling
When a robot removes a part from a mold there can be problems getting the part
free from the mold. Two potential causes of sticking that relate to the robot are:
1. The robot pushes the part back onto lifters and locks the part onto the lifters.
2. The robot does not pull straight back away from the mold resulting in part detail
getting trapped on the mold.
Carefully watch the robot as it makes its movements while extracting a part. Un-
usual movements can highlight a step in the robot program that can be optimized.
Adding additional grippers, gripper fingers, or standoffs to the end of arm tooling
may stabilize the part and allow for improved handling.
36.3.4 Part Sticking on Ejector Troubleshooting Material Issues
Potential material causes of sticking include:
Material type
Moisture content
Release agents
Viscosity
36.3.4.1 Material: Material Type
Some materials will be more prone to sticking in the mold including:
TPU
Polyesters
Polycarbonate
It is critical for all materials to build the mold with the appropriate draft angles for
the intended material. Check the recommended draft of the material supplier for
both shrink on and shrink away conditions.
With TPU and polyesters any process-related condition that degrades the material
will magnify the sticking concern. Many times with these types of materials the
process can be running and all of a sudden the ejector pins punch through the part
indicating that the material has gotten wet! With both TPU and polyesters make
sure that the machine is thoroughly purged with dry material before injecting the
material into the mold.
