Injection Molding Optimization Process

Optimized Parameter Settings

Presented below is the optimized parameter settings sheet for the main body mold for the cookie. It took us a few iterations on the BOY injection molder to arrive at these settings. We initially had too high of a shot size and still had excess plastic left in the screw. After a few iterations, we got that shot size down to 39.5mm which was ideal for our case and allowed our part to come out with no defects/flash/etc.. We were also able to take the cooling time down from around 30 seconds down to 20 seconds while still maintaining good part quality and minimum shrinkage. After several iterations of 10 or so parts, we arrived at the below sheet which will guide us as we do our final production runs.

Process Optimization Outcome

One major issue resulting from initial injection molding runs concerned the press fit interface between our cookie body and frosting parts.

Here we were able to press the two together right after the body part came out of the machine when it was still flexible, but also really hot. After nearly burning our hands, we decided that this assembly process was not optimal.

The primary cause of this issue was that the inner diameter of the cookie body part (shown above in white) was too small, such that the frosting part (blue) outer diameter could not fit inside. This mishap was potentially caused by differences in shrinkage or misaligned dimensions in the mold. To fix this issue, we needed to re-machine the cookie body core mold to allow for an increased diameter on the cookie body part.

The secondary cause of this issue was that the height of the press fit walls on the frosting part were too short, giving us too little length of engagement at the press fit interface. To fix this, we deepened and widened this wall on the frosting core mold to allow for a longer, stronger press fit connection.