Overmolding: What You Need to Know

Without overmolding, cell phones, steering wheels, kitchen implements and other items you touch every day wouldn’t be the same. We’ve put together a comprehensive introduction to the process so you can determine if overmolding is an ideal choice for your next parts.

By Aaron Lichtig · June 11, 2018

What is Overmolding?

Simply put, overmolding lets you combine multiple materials into one part. One material, usually a thermoplastic elastomer (TPE/TPV), is molded onto a second material, which is often a rigid plastic. Think about your toothbrush handle where the single piece has both rigid and rubbery components. It’s a great way to make plastic parts perform and look better.

The Many Benefits of Overmolding

Overmolding can improve product performance in a number of ways. It can help enhance product:

  • Safety: It can be used to create a non-slip grip for precision devices such as medical instruments.
  • Ergonomics: The second layer can make grips more comfortable on any parts that people hold or grasp.
  • Functionality: Rubber-like TPEs/TPVs on the exterior of plastic parts can help the piece resist water or absorb sound. The TPE/TPV layer can also serve as electrical insulation.
  • Longevity: Overmolding can help keep dust and water out of plastic components, making them last longer.

In addition to providing functional improvements, overmolding also helps products look better. TPE and other materials can be colorful or glossy and you can also put logos, pictures, and patterns on it. It’s a great way to add a special touch to pieces that need it.

Overmolding Part Design Quick Tips

  • Wall thicknesses between 0.060" to 0.120" (1.5 mm-3 mm) generally provide the best bonding.
  • Keeping radii between 0.020" or 0.5mm minimum in corners reduces localized stresses.
  • If the part requires the use of thick TPE sections, they should be cored out to minimize shrinkage problems, reduce the part weight and lower cycle time.
  • Avoid deep or un-ventable blind pockets or ribs in your design.
  • Use gradual transitions between wall thickness to reduce or avoid problems with flow (back fills, gas traps, etc.)
  • The TPE/TPV should be less thick than the substrate to prevent warpage, especially if the part is flat, long, or both.
  • Overmolding needs mechanical or chemical bonding to the substrate, so your material choices should enable this.

Can I Prototype an Overmolded Part?

Absolutely! Our PolyJet multi-material option allows you to prototype overmolded parts. This can give you the look and feel of the part with the ability to rapidly iterate. Most PolyJet orders take between 1-3 business days to ship after order. If you need something even higher fidelity but are not quite ready for injection mold we recommend urethane casting which can bridge to about 50 units with end use look, feel, and function.

Get an Overmolding Design Review & Quote With Xometry

Xometry now offers overmolding as part of its injection molding capabilities. For a free overmolding design review and quote, click here to upload your CAD files to our site. Make sure to mention overmolding in the comments. Our expert team of injection molders will get back to you within 24 hours.

If you want to learn more about injection molding, download our design guide here. You can also reach our team via:

Email: support@xometry.com 

Phone: (240) 252-1138 

Online: xometry.com/support offers live chat, FAQs, and other helpful articles.

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