Just as important as getting a good consistent part, it is also important to not get molding defects. These will happen from time to time. Good preventive measures can help prevent most molding defects. Defects will arise and have to be dealt with. There are a number of types of defects, but the most common are:


Quick overview of molding defects



Contamination is in my mind the number one molding defect. It can be caused by mixed materials, degraded material or grease from the mold itself.

 

Flash is a defect that appears when parting lines get damaged or the plastic pressure is too much for the clamping pressure to with stand and material leaks into the parting lines. Though correctable, flash is difficult to content with.











Short shots or underloads as they are sometimes called are places on the part that do not fill in completely. These can be caused by gases from the plastic being trapped in the cavity or the full shot of material didn't get injected into the mold creating a nozzle leak. The process may not be developed correctly causing an unbalanced fill between cavities.