Overmolding: Chemical and Mechanical Bonding

Learn more about overmolding in our free webinar we’re hosting with RTP Company on Tuesday, Nov. 15 at 1 p.m. CT. REGISTER TODAY!

Overmolding is not a new manufacturing technology, but there is still some confusion about how to design for the two-part process. One of the largest areas to consider? Bonding. A number of materials can be used to overmold components together, but without a chemical bond or mechanical interlock, some overmolded parts won’t stand the test of time.

Chemical Bonding
This bonding process involves two chemically compatible materials that are molded together to form a strong bond with each other. It’s important to note that not all materials play well with one another.

The compatibility chart below indicate whether a chemical or mechanical bond is recommended for key thermoplastic and thermoset materials.

mechanical bonding

Three types of mechanical bonding techniques.

Mechanical Interlocking
What happens when your materials are not compatible, the desired bonding strength cannot be achieved, or you want to ensure your materials don’t peel apart from repeated use? This is where designing a mechanical interlock, which physically holds the overmolded material to the substrate, makes sense. There are many ways to design these into parts (see example), so discuss the options with your manufacturer.


Learn more about overmolding in our free webinar we’re hosting with RTP Company on Tuesday, Nov. 15 at 1 p.m. CT. REGISTER TODAY!

If you have further questions regarding rapid overmolding at Proto Labs, contact one of our application engineers at 877.479.3680 or customerservice@protolabs.com.

WEBINAR: How to Choose the Right Thermoplastic with PolyOne

With thousands of thermoplastics on the market, selecting the right material for a run of injection-molded parts can be intimidating. To help make the process more manageable, we’re teaming up with the plastics industry leader, PolyOne, to host a webinar with tips on choosing the right thermoplastic material for your application.

TITLE: Thermoplastics: How to choose the right material for your application
PRESENTER: Jeremy Bland, Technical Dev. Engineer, PolyOne
DATE: Thursday, September 22 at 1 p.m. CDT
REGISTER: Click here to sign up

The presentation will include the following:

  • Factors in thermoplastic material selection
  • Overview of common thermoplastics including the effects of additives
  • An open Q&A session

Busy that day and can’t make it? Not a problem. You can still register and we’ll send a link to a recording that can be watched on-demand. As usual, feel free to forward to a colleague know if you think he or she will be interested in attending.

TIPS WITH TONY: Flame-Retardant Thermoplastics and UL Classifications

UL 94 is a plastics flammability standard released by the Underwriters Laboratories (USA). The standard classifies plastics according to how they burn in various orientations and part thicknesses from the lowest flame-retardant to most flame-retardant in six different classifications.

UL 94 Rating

Definition of Rating


                                          Slow burning on a horizontal part.


                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of flammable plastic.


                                          Burning stops within 30 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.


                                          Burning stops within 10 seconds on a vertical                                             part allowing for drops of plastic that are not                                               inflames.


                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed but may                                               burn through the part.


                                          Burning stops within 60 seconds on a vertical                                             part with no drops of plastic allowed and                                                     cannot burn through the part.

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On-Demand Webinar: Choosing the Right Rapid Manufacturing Method

We recently hosted a 30-minute webinar on: Choosing the Right Rapid Manufacturing Method for Plastic Parts. If you missed it, no worries. You can still watch it on-demand HERE.

What did you miss?
We discussed the benefits of rapid manufacturing for plastic components and how to select the correct manufacturing process:

  • 3D printing, machining and molding processes and specifications
  • Material selection and properties for each process
  • Advanced molding materials like thermally conductive plastic and liquid silicone rubber

Top 3 Questions Asked
How long will you keep a mold and do you inform the customer if you’re going to get rid of it?
We’ll store the mold for one year from the last order unless it is requested to keep in storage, and we’ll notify the customer of inactivity to if they would like the mold disposed of or retained in storage.

Is there any limit on volume for injection-molded parts?
No, you can get injection-molded parts in quantities of 25 to 10,000+ with several molds even surpassing 100,000 parts. We have the ability for single and multi-cavity molds dependent on size and complexity.

Can Proto Labs be used for light pipe assemblies in PC, PMMA and silicone?
Yes, we have molded countless parts in those materials for light pipe assemblies. Mold finish should be polished to a SPI-A2 with special attention made to the mold build for ejector pin location, gate location and parting lines.

Stay Tuned
Look for additional technical webinars throughout the year on various 3D printing, CNC machining or injection molding topics. The next webinar will discus how to navigate through Proto Labs’ design for manufacturability (DFM) feedback.

THE SHORT LIST: 5 Med-Friendly Materials

Developing medical devices or health care components? Here’s five good material options to consider.

PEEK, PEI (Ultem) and PPSU (Radel). Attributes: High temperature resistance, creep resistance and works well for applications that require sterilization.

Polycarbonates (Makrolon and LEXAN HP1). Attributes: Good clarity with clear and translucent applications, good impact resistant, and durability.

Medical-grade LSR.

Medical-grade liquid silicone rubber (QP1-250). Attributes: Thermal, electrical and chemical resistance, biocompatibility, and is suitable for skin contact.

Titanium (Ti 6-4). Attributes: Lightweight, temperature and corrosion resistant 3D printed metal used with direct metal laser sintering (DMLS) process to produce fully functional medical components.

WaterShed XC 11122.

WaterShed XC 11122. Attributes: ABS-like material used to 3D print clear microfluidic parts with sterolithography (SL) process. Resistance to water and humidity, and good for lens and flow-visualization models.

For more information on materials, check out our complete selection at protolabs.com, and to learn more about using rapid manufacturing to develop health care and medical products, read our white paper: Prototyping and Low-Volume Production for Medical Applications.