A common defect found in injection molding is Distortion. Distortion is when the molded part is not an exact replica of the cavity as some parts are deformed, bowed, or distorted. We will go through some likely causes and solutions to this defect. Luckily it is a defect that is usually easy to process out if the conditions of the mold are in line.
Machine: Most times when the machine or the process is the cause of the distortion it means that the part is being ejected while it is still too hot. In this case the processor can look at several different factors to try and solve the issue. You could increase the cooling time to give the part more time to hold shape during the cooling process. Reducing the melt temperature can help if you can still process the part fully at the lower temperature and that could reduce the cooling time needed for the part to cure. Reducing the mold temperatures could work if the mold is too hot for the plastic to cool.
Mold: As is the case with some other molding defects, there are definitely times where the mold could also be the cause of the issue. Some likely causes are; Undercuts in the mold are too deep. In this case the depth of the undercut should be reduced, and radii included wherever possible. There could also be an issue with the ejector pins as the mold could have been designed with the ejector pins being too small or too few in number for the part. There could also be uneven movement of the ejection mechanism. Lastly, the polished surface could have a poor surface finish in which case you would want to polish the surfaces of the mold that need it.
In either case, once you recognize the cause of the defect, you can make easy adjustments and be back running good parts in no time.
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