Page 123 - Injection Molding Advanced Troubleshooting Guide

12.8 Artificial Balance 109

12.8.1„ Family Molds

Family molds are molds that have cavities that are different in size, shape, and
volume. Often a customer will prefer to bundle cavities in a mold to save tooling
costs. The practice of bundling cavities in a family mold will result in cavity imbal-
ance. If cavities have different volumes the fill time between them will be different,
which will result in different plastic conditions in each of the cavities.
A family mold will always be unbalanced even when using flow analysis software
to try to create a uniform fill to all cavities. Even when fill time is the same for all
cavities the pack rate, gate seal time, and cooling can still all vary between the
cavities.
The best solution is to avoid running family molds. If family molds cannot be
avoided, understand that the process window will suffer. Expect problems with di-
mensions between cavities as well as situations where some cavities short out and
others flash. Family molds will always be a compromise between cost and quality,
and in the long run the cost of quality may offset the initial savings in mold cost.

References
[1] Beaumont J. “Runner and Gating Design Handbook”, 2nd Ed., (2007) Hanser, Munich.
[2] Beaumont Technologies Inc. 1524 E.10th st. Erie, PA 16511 Tel (814)899-6390
http://www.beaumontinc.com.
[3] RJG Inc. Master Molder Manual.