Let’s cut to the chase… here are the “Big Five”:
- Part design.
- Material.
- Mold design.
- Construction.
- Molding machine.
Those are the five most vital factors in the plastic injection molding process, according to experts. They all have to be optimized vis-a’-vis each other, or you can run into big problems. In many cases, these experts say, a mistake made by one person is passed along to the next person, and on down the line, until the problem — or problems — are incorporated into the final product. 
While any plastic injection-molded product can be compromised by mistakes, it seems that plastic medical devices and automotive parts are the ones where the same problems appear repeatedly. Most of the time, the errors are not process-related. They occur as a result of non-efficient tool design or bad construction. It is difficult, but vital, to examine the part design and determine if it just won’t work as a plastic-injection molded piece. Perhaps a section is just too thin. Perhaps a gate needs to be located at a different place so the molten plastic can flow through it more easily. Perhaps it’s a venting issue.
Then there is the material selection: if you need a tolerance of ±0.001 inches on a five-inch plastic part, you shouldn’t choose polyethylene or polypropylene. You need a material that will shrink much less than these two.
Today, there is software to help companies utilize scientific molding and perform proof-of-concept experiments. Some experts even call it scientific processing, because it involves more than just the mold itself.
If there is one take-away lesson here it’s that that the application of scientific molding and proof-of-concept principles will improve part quality, reduce scrap, and boost profitability. Companies should adopt these processes not to wow their customers, or ingratiate themselves with the stockholders, but because it’s simply the right thing to do.