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Trusting Plastics Again

Posted by Ben Harrison on Feb 17, 2012 12:30:00 PM
Ben Harrison

There are lots of good reasons for changing from metal to plastic components—the big three are cost reduction, lighter weight, and zero corrosion.

Yet it seems a fair number of 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 there is typically not much relaxing on the tolerances—that means the processing of the parts has to be done very consistently. That can be a challenge for vendors. Consistency is impacted by a number of factors that have to be carefully monitored, such as melt flow index of material, dryness of material, machine processing parameters, maintenance of the machines, and most importantly, being able to see what is happening inside of the mold as the parts are being molded with the use of pressure transducers (sensors) also known as Scientific Molding.

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 failures very difficult to determine. That’s why it is ultra-important to have the appropriate monitors in place and run a robust quality system to oversee the process. 

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, 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. Proper internal controls on machines and quality systems are essential. Tool construction/quality also plays a bigger role than many people realize—there will always be less rework to get the dimensions within spec with high-quality tools (and the tools will last longer).

When metal to plastic is done correctly, there are some big advantages:

Lower cost to produce

  • No secondary process to prevent oxidation
  • May be able to eliminate some assembly
  • Plastic is generally less expensive than metal
  • May be able to eliminate costly machining operations
  • Lighter weight means lower shipping charges
  • No painting needed, molded in color/graphics

Lighter weight

  • Less fatigue on a person if it is carried
  • Might make a product go faster

The key to a successful metal-to-plastics conversion is understanding the limitations of the process, materials, and tools before committing to a project. At Kaysun we will evaluate a project in detail and determine if it is a good candidate for conversion based on several key factors, including required tolerances, materials, specific part design/configuration, and initial mold flow/analysis. Contact a Kaysun engineer now to see if your program would benefit from a metal-to-plastics conversion.

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