Page 233 - Injection Molding Advanced Troubleshooting Guide

224 24 Cracking

„ „24.2„ Cracking Troubleshooting Chart

Table 24.1 shows the cracking troubleshooting chart.

Table 24.1 Cracking Troubleshooting Chart
Molding Process Mold Machine Material
high second-stage pressure undercuts overheating moisture content
melt temperature sharp corners lack of process control contamination
residence time in barrel lack of draft regrind
ejection lifter or slide corners manufacturing issues
part removal molecular weight
operator wrong material
mold breakaway speed
gate seal

„ „24.3„ Cracking Troubleshooting

Cracking is a defect that can often come from post-molding conditions. When trou-
bleshooting cracking it is important to understand when the cracking is occurring.
Also with cracking, careful examination of the part design may highlight areas
with sharp corners that are acting as stress risers and initiating the crack; there-
fore look for opportunities to add radius to these areas.

24.3.1„ Cracking Troubleshooting Molding Process Issues

Cracking can be caused by several process settings as well as post-molding condi-
tions. Some of the key factors to investigate for cracking include:
ƒ Second-stage pressure
ƒ Melt temperature
ƒ Residence time in barrel
ƒ Ejection
ƒ Part removal
ƒ Operator
ƒ Post-mold operations