Page 362 - Injection Molding Advanced Troubleshooting Guide

358 37 Pin Push

37.3.1.5„ Molding Process: Cooling Time
The length of time that a part spends in the mold cooling will potentially impact
pin push in two different ways:
1. Excess cooling time may lead to increased shrink and the part may stick to the
ejector half of the mold leading to pin push during ejection.

2. If cooling time is too short the parts will be ejected in a state that cannot resist
deformation from the force of ejection, which can lead to pin push.
Check the part ejection temperature and if it is running higher than the heat de-
flection temperature (HDT) of the material the cooling should be increased to allow
more heat energy to be removed from the parts prior to ejection. If the parts are
ejecting at a cool temperature try to reduce cooling time to determine if pin push
is improved. Whenever cooling or overall cycle time is changed be sure to verify
dimensions and any other key parameters.

37.3.2„ Pin Push Troubleshooting Mold Issues

Some potential mold-related concerns are:
ƒ Sticking
ƒ Lack of ejection
ƒ Lack of draft
ƒ Cavity balance

37.3.2.1„ Mold: Sticking

If the molded part sticks on the ejector half of the mold, pin push may be a result-
ing defect. Because the part is sticking, the force that is applied from the ejector
pins can cause pin push defects.
Some of the key things to examine for possible sticking causes include:
1. Undercuts on the ejector side of the mold
These undercuts could be a rolled parting line edge or other damage to the mold
steel. Also examine if pullers have been ground in the ejector, which may be too
deep, which can lead to sticking. If any of the above is causing sticking, address
the issue in the steel.

2. Texture on the ejector side of the mold
If there is texture on the ejector half of the mold, it must have an appropriate
amount of draft to allow the texture to fall away from the mold surface.

3. Machining/cutter marks left on ejector half of mold