Injection Molding Troubleshooting - Warpage

Warpage is a typical defect for an injection molded parts, it is related to many factors, some of them can be resolved by injection molding design, or injection parameter setting, some don't, actually most of the warpage issues caused by the part design itself.


Assembly drawings of a plant pod product


Front and back view of the lid and housing part

These are lid and housing parts of a plant pot product, the resin was designated as PP, a very high shrinkage factor and good melt flow resin, both of the part structure design and resin selection suggest the measurement/deformation of these parts are very difficult to control. Typically, a flat board shape part like this are very easy to get wrapped (lid/tray is not completed a flat board, but they don't have many features), both lid and tray has the possibility to get deformation, Lid part is most concerned. Adding some feature ribs can ease the deformation, also injection mold cooling design affect the deformation, injection molding parameter is also related with this, longer packing time (remain the parts in the mold for longer time) will help to ease deformation.

A mistake have been made that the engineer has not insisted on part design change before making injection mold, so here is the T1 samples result, both the lid and housing are seriously twisted.


The injection molded parts twisted seriously


The tray part bends inward


Adding as many ribs as possible so the features have a hold on each other to maintain the shape


Rib added on bottom side did improve the twisting horizontally


Here is another example with or without ribs design

These samples show an idea how the rib affects the deformation, all information reserved by ACO Mold.