So yes, we watched some movies and TV in the 80’s. Mr. Miyagi’s advice in the movie The Karate Kid came to mind the other day when we were talking shop here at PlastiCert. “Better learn balance. Balance is key. Balance good, karate good. Everything good. Balance bad, better pack up, go home. Understand?” He was driving home to his student that first you have to attain balance, and things will fall into place. Then you have to work to maintain it, or things will fall apart.
We were talking about it in the context of mold design and multi-cavity orientation. Whether designing multiple cavities of the same part or a number of different cavities in a “family” mold, the melt flow needs to be balanced or the plastic filling the mold will encounter difficulties. While some cavities will fill correctly, others may encounter short shots, or possibly over packing (flash). A problem since multi-cavity molding came about, it has been dealt with from all angles. From the basic design of runners and gates, to mold accessories that help achieve balance through manipulating temperatures and flow.
If you are designing a component or group of components to be injection molded such that they will be in the same multi-cavity mold, know that component complexity aside, just having multiple cavities induces complexity.
The moral of this story is if you are looking at a multi-cavity mold design; work with your mold shop as up front as possible. Make sure that the injection molder (if a separate entity from the mold shop) is on board and in agreement with the cavitation and runner design having achieved balance. An optimum scenario would involve having the mold designer and injection molding under the same roof to help alleviate the over-the-wall syndrome. Remember, balance is good, parts are good!