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A Marriage of Necessity: Two-Shot Molded Plastic Medical Devices

January 27, 2021

Medical devices, perhaps more than any other products made from plastic injection molding, are inherently complex. There are the stringent low-tolerances, for one thing. But there’s also the design of many of the devices themselves. Often times, these designs call for two-shot injection molding, which can make items comprised of two different pieces, in one seamless process that “marries” the parts together.

Plastic Injection Molded Medical Device

Let’s say you’re producing a medical device (like an insulin delivery device) that might contain a thermoplastic elastomer (a kind of rubbery-plastic) and a true thermoplastic resin. Here’s how it works:

  • plastic resin pellets are heated and liquified, then injected into a mold
  • the cooled part is conveyed to a second mold where (in this case) the thermoplastic elastomer is injected
  • the two parts form a strong bond on the molecular level
  • the finished piece (in this case, an insulin delivery device) is ejected and the process repeats

What are the advantages of two-shot injection molding for medical devices?

1. Cost Effective

Because two-shot injection molding only uses one cycle instead of two, it costs less for any given production run and necessitates fewer employees.

2. Enhanced Product Quality

Two-shot injection molding improves product quality in these ways:

  • Provides for the tightest seal possible when thermoplastics and thermoplastic elastomers materials are utilized in the same part
  • Improved ergonomics: because the process allows for the use of “soft touch surfaces” made up of thermoplastic elastomers, the resulting items are easier for surgeons and patients to hold
  • Can greatly reduce defects, when compared to over-molding or more conventional molding processes
  • Empowers manufacturers to create more complicated designs using multiple materials that can’t be effectively combined utilizing other methods
  • The bond created is exceptionally strong, creating a product that is more durable, more reliable and with a longer life

3. Versatility

While two-shot injection molding is ideal for medical devices, it’s also optimal for:

  • automotive interior parts
  • tools
  • toys

Bottom line: two-shot injection molding allows manufacturers to combine a variety of materials and colors to produce a final product that is both strong and attractive.



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