A brief meeting between all those involved with your molded part can save you time and money.
Over-the-wall engineering – All in their own cubicles: lack of communication
Benefits of concurrent engineering in injection molding
A few months ago, a customer of mine called me to go look at an issue he was having with a part being molded in a brand-new mold. It was a two-shot part, with TPE overmolded on to a PP substrate. The issue was that the PP substrate had voids in it, reducing the strength of the part. Injecting the TPE would result in filling the voids, bottoming out the screw, and potentially lead to short shots.
I was told it was a 30% glass filled PP. I looked at the gate, and thought it was too small for a glass-filled plastic. Then as I glanced at the hopper and looked at the sight glass, I noticed that there were no pellets in there, as the material was LFT (long fiber thermoplastic). The machine screw had a GP screw with a high compression ratio, which would destroy the glass fibers and sometimes segregate the melt from the glass.
At this point I knew that this was not only going to be a time-consuming challenge, but that it was also going to be an expensive deal to get to the final molded part with the required quality.
A few things had to change. Modifications would have to be made to the mold. The machine would need a different screw and barrel assembly. This would require not only time, but also money. Further, there would be a learning curve to figure out how to process such a material since there was no prior knowledge base in the company.
This was a situation where cross-functional meetings and prior discussions could have saved the company time and money. Prior knowledge could have produced the parts on time, with the required quality, and within the allotted budget.
Another customer of mine was told by someone that it is possible in an overmolding operation to make the same overmolded plastic in the same shot stick to one area of the substrate and not the other. Imagine a 10 by 10-inch plate with TPE overmolded all over, but the TPE did not have to bond to ten small squares on the surface. This was a very critical part for an assembly and they had almost completed the design. They were going to send it to a moldmaker to make the expensive two-shot mold. At this point, no molder had been contacted—just the moldmaker in Asia who was going to build the mold. It would have been an unfortunate and expensive failure.
Simply put, concurrent engineering is involving representatives from every department in the project at the earliest stage. This should be followed with subsequent meetings where the project details and any changes should be reviewed by the team to understand the impact it may have on their own individual departments. This way, when the product designer mentions that the material is a LFT, the