Plastics injection molding components, when they are built the right way, have three big advantages over metal parts—they cost less, are lighter weight, and don’t corrode.
Yet it seems some companies that have tried the switch eventually go back to metal, citing two major problems: 1) inconsistent processing and 2) inconsistent dimensions.
When parts are converted from metal to plastic overmolding the processing of the parts has to be done very consistently to maintain the tight tolerances. That can be a challenge for many vendors. Even the slightest changes in factors such as temperature, pressure, melt flow index of material, dryness of material, and machine processing parameters can impact consistency. Perhaps most critically, it is important to see what is happening inside the mold as the parts are being molded using pressure transducers (sensors) and other sophisticated measuring equipment.
Without the ability to properly monitor these factors there will be ongoing quality issues with the processing, parts, and tolerances; it also makes the root cause for any failure very difficult to determine. That’s why it is critical to have a robust quality system in place that oversees the process (this is also something customers increasingly expect and demand).
When vendors cannot meet tolerances consistently with plastic parts, this creates additional costs in reworking parts (machining), quality costs to sort or even re-call parts from the field, increased scrutiny from regulatory agencies, and possibly even lawsuits for failures in the field.
It only takes one bad experience with plastic parts to drive a company back to metal. For a successful metal-to-plastic conversion, select an experienced vendor. High-quality tools, proper internal controls on machines, quality systems, and highly skilled engineers are essential to deliver the same kind of quality and tight tolerances that can be produced with metal.