Over Molding – Enhance Your Product

Stebro Mold is a leader in custom plastic overmolding. Overmolding is a injection molding process which a single part is created using two or more different materials in combination, it is a tyep of multi-material molding. Using two separate injection molds on the injection molding machines, two materials are bonded together during the overmolding process to form plastic parts and components with unique visual or ergonomic appeal. Traditionally, overmolding starts with injection molding a hard plastic resin that has a higher metling point. Then, once that part is cooled, another plastic resin (usually a soft material such as TPE, TPU or TPV) is injection molded over the first part. Sometimes called elastomeric overmolding, elastomer overmolding. Small touches of overmolded soft touch plasic can make a big impact on product value. Getting it right depends on the strength of the bond between hard and soft plastic, each material must be carefully selected to ensure a chemical compatibility, as well as a thermal compatibility.

With overmolding, you can improve the functionality, look, and bond strength of your product while saving time and reducing costs.

Ready to try our Over Molding service?

You can design the product and we can build it to your specs, just provide us the engineering drawings and we can go from there. Our experienced engineering and tooling teams work with you to make sure your parts and tools are designed properly to account for shrink and other variables when overmolding. If you’re wondering if your interconnect product can benefit from over molding, contact us. We’ll be honest and discuss whether over molding is even right for you.

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Overmolding Service From Part Design to Final Delivery

Overmolding Part Design

Overmolding Mold Design

Overmolding Mold Manufacturing

Overmolding Manufacturing

Overmolding Part Design Considerations

Overmolding is not without its limitations. Several factors must be weighed before determining if it is the best solution as below:

  • One main consideration is that the two materials must be compatible, chemically and thermally.
  • Since we have to put the first piece into the injection molding for overmolding, the first parts have to withstand the temperature needed to melt the second material.
  • The wall thickness of the substrate and overmold should be as uniform as possible to obtain the best molding cycle time. Wall thickness between 1.5MM to 3MM generally provide the best bonding.
  • Keeping 0.5MM minimum in corners reduces localized stresses.
  • For the thick TPE sections, 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.
  • Transitions between wall thickness should be gradual to reduce flow problems, such as back fills and gas traps.
  • The TPE/TPU/TPV should be less thick than the substrate to prevent warpage, especially critical for long, flat geometries.
  • Design in a mechanical interlock when possible

Overmold design considerations

  • Start with small TPE injection gates to obtain best TPE fill with minimum cosmetic gate vestige. Large gates should be avoided.
  • Gates should be located at the thickest TPE wall section.
  • Thought should be given to proper component ejection from the tool to minimize marks on the soft elastomer surface.
  • It is critical that adequate cooling is provided to the TPE cavity through proper mold cooling techniques to minimize cycle time.

Advantage and Application of Over Molding

Overmolding Advantages

  • Reduce secondary operation, assembly and labor costs
  • Improved physical and mechanical performance
  • Improved product integrity, reliability, and safety
  • Enhance design flexibility and multi-material components
  • Improve the touch feel
  • Enhance fit and sealing

Overmolding Application

Overmolded plastics find a wide range of application in multiple industries. Plastic over plastic, rubber over plastic, plastic over metal and rubber over metal are typical overmolding application. Some of the most common applications of overmolding include:

  • Electrical components
  • Automotive parts
  • Brackets and handles
  • Sports and Leisure Equipment
  • Plastic or metal parts with a soft grip handle
  • Plastic housing for various electrical devices
  • Custom handle grips for mobile industrial equipment
  • Plastic components for Medical Devices and Medical instruments
  • Small components like control knobs and buttons for various types of appliances
  • Outdoor Power Equipment Products such as hand tools or garden tools

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