Arc XV: November 2013

Optimizing the Ring Parameters

After the molds were completely machined, we moved on to shoot out a few test parts from the injection molding machine. We did 4 iterations with different parameters to determine which parameters we would use for the final production run.

Test 1:

The very first trial piece had a very noticeable weld line (not obvious from the picture, but it can be seen right across the "#1" marker) as well some considerable dishing around the center triangle. The cause for both defects was a shortage of injection pressure as well as injection speed. The weld lines form because the plastic cools and hardens before the streams of molten material are able to fuse together properly. The dishing is caused by a lack of material towards the center of the ring because plastic is not being packed sufficiently before cooling takes place.

First Trial

Test 2:

For this trial, we increased the injection speed profile to get rid of the huge weld line formed during the first trial run. It was effective in that the weld line is not so obvious but it can be seen and felt with a little more close attention. Dishing was still a problem.

Second Trial

Test 3:

For this trial, we increased the injection pressure to address the dishing in the center of the ring. By bumping up the pressure, we allow more molten plastic to be packed into the mold before it gets a chance to cool therefore the mold will be filled with plastic and no dishing will appear. It worked to a certain degree in that it improved the dishing problem, but we still could do better.

Third Trial

Test 4:

At this point, we were not able to increase the injection pressure any further but what we did was increased the stroke speed so that material could flow in a bit faster. This solution improved the dishing problem significantly but there still was some left. Unfortunately that was all that we could optimize for and overall we have agreed to use the latest set of parameters during our production runs.