Injection Molding Troubleshooting Tips
Tip #1: Understanding the Defect
One of the most important considerations when troubleshooting an injection molding defect is to understand exactly what the defect is. Sometimes molding personnel will incorrectly identify the defect; for example, they may describe the defect as “splay” when it may actually be a cold slug or blush mark. This can obviously lead you in the wrong direction in your troubleshooting process as processing changes to eliminate splay would be very different than the changes used to eliminate a cold slug or blush mark.
Once the defect is correctly identified you’ll want to identify the potential causes of that defect. You’ll want to consider the material, the machine / equipment / mold and the process settings.
In the case of gate blush, for example, potential material causes might be too high of viscosity (low melt flow index), over dried material (in the case of nylon), nucleated grade vs. non-nucleated grade, or effects due to colorant or other additives, reinforcements or fillers.
Potential causes related to the machine or equipment might be too small of gate size or sharp edges where the gate meets the cavity, or valve gates that are not seating properly.
Potential causes related to the process settings could be too fast of injection speed or too low of melt or mold temperatures.
Once you understand the potential causes of the defect, you should first look at changing / modifying the most likely cause of the defect or the easiest things to change. For gate blush you might first look at changing the injection speed and melt/mold temperatures before switching the material grade or making modifications to the tooling / gates. If the most logical and easiest changes don’t eliminate the defect then you may have to move onto the other potential causes such as modifying gate size or adding a radius to the gate.
Entec Polymers Technical Service Team