Page 365 - Injection Molding Advanced Troubleshooting Guide

37.3 Pin Push Troubleshooting 361

37.3.3.3„ Machine: Velocity to Pressure Transition
An often-overlooked factor that can lead to pin push is how well the machine trans-
fers from first-stage velocity control to second-stage pressure control. There are
many cases where this transition is not responsive and instead of immediately
reaching the desired pressure the machine will overshoot. Figure 37.2 shows a
process monitoring screenshot where the machine injection pressure spikes way
above set point. The cavity pressure curve shows the resulting spike in actual
cavity pressure. This type of poor transfer can lead to over-packed parts that in
turn lead to pin push.

Figure 37.2 Process monitoring showing overshoot at velocity to pressure transfer

37.3.4„ Pin Push Troubleshooting Material Issues

Some potential material-related causes of pin push may be:
ƒ Release agent
ƒ Moisture content
ƒ Fillers

37.3.4.1„ Material: Release Agent
The majority of molding materials have some form of lubricants and/or release
agents to improve their moldability. There are many cases where the same mate-
rial comes in an enhanced release formulation that may work better for a given