Optimizing Injection Molding Parameters (other parts)

Previously, we talked specifically about the process through which we optimized the Bugs Bunny mold. In this post, we will run through the same process for all of our other parts. As before, we had to vary and experiment with many different parameters such as the cooling time, feed stroke length, injection speed profile, and injection hold pressure profile. In this post, we will focus on the path we took to optimize the Bugs Bunny mold.

Nathan, setting up the mold to make the rings

ORANGE RING

1. We wanted to minimize shrinkage, so we increased the cooling time to 15 seconds.
2. We decided that 15 seconds was too long, so we reduced it to 10 seconds. The fit was better, but still a little too tight. Our measurements at this stage were 2.235" for the outer diameter and 2.206" for the inner diameter.
3. We decreased the cooling time to 5 seconds, but the runner got stuck in the mold resulting in a deformed part. 
4. We increased the cooling time up to 7 seconds.
5. We increased the cooling time up to 8 seconds. This allowed for the right fit in the body, so we kept the cooling time the same. However, the ring was not uniform in thickness throughout the body, so we had to shim the part.
6. We shimmed the part with one piece of paper under the cavity for part 6.
7. We added another piece of paper for part 7 and 8. 
8. For part 9, we shifted the molds to get better centering by adjusting how the screws were tightened on the machine. 

Orange Ring finalized parameters

Measuring the thickness of the ring at different points of the ring

 RED RING

1. First, we adjusted the set screw feed stroke down to 0.9 because we were seeing some flash in the parts.
2. Next, we measured the radial thickness of the ring at different points and found that one side of the ring was consistently thicker than the other, which meant that the mold was off center. To fix this, we loosened the bolts holding the molds in place, pushed and held the mold in the compensation direction, and tightened the bolts again.
3. #2 didn't work, so we turned the brass pins holding down to 0.235 in diameter to give us more tolerance to shift the mold around.
4. We added dowel pins to prevent our part from getting stuck.
5. The mold was still off center, so we shifted the mold a little more.
6. Finally, we changed the cooling time from 8 seconds to 10 seconds to reduce shrinkage.

Red Ring Finalized Parameter

All the rings from our optimization!