Insert Injection Molding

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By Jeremy Losek, Sep 14th, 2021

Insert Molding — Plastic Injection Molding

Threaded insert molded into plastic

What is Insert Injection Molding?

Insert molding is a process that starts with placing metal, ceramic, or plastic parts into the plastic injection mold. After those parts have been properly placed, the mold is filled with molten plastic in the regular injection molding process. Once the plastic has cooled, the inserted parts are now firmly bound to, and integrated into, the plastic parts. There are many options for inserts that can be placed into the mold.  Threaded bushings, wires, batteries, and warning labels are a few examples.

Why Should I Use Insert Molding?

One of the biggest reasons to use insert injection molding is the overall cost savings. While it will cost more during the production run for the inserts to be added, there is significant savings by not having the part handled a second time to manually install the inserts. The other benefit is that the inserts are more structurally stable then if they were inserted post-molding.

Consider a plastic part that requires multiple threaded bushings integrated into it. If these bushings weren’t insert molded during the plastic injection molding process, the bushings would have to be added by some other method, such as heat staking (thermoplastic staking), in an additional post-molding process. This secondary process would add time and cost to the molding project.

Metal Insert Molding

One last benefit to consider is the amount of weight you can save with insert molding. For instance, if you were considering creating your part completely out of metal because it required machined metal screw holes, you could save significant weight by injection molding your part out of plastic and inserting threaded metal bushings (assuming your design would allow this change in material). This is very important in industries where weight reduction is a priority, like in the automotive and aerospace industries.

Are There Special Considerations for Insert Molding?


Whether you are using metal, ceramic, or plastic inserts, one of the biggest considerations is that you have enough material to support your inserts. Having too thin of walls will lead to the insert breaking away from the rest of the part. This can happen during production or during the use of the part. You need to make sure there is enough plastic material to house the insert properly.


This consideration is more of an issue when using plastic inserts. You will want to make sure that the inserts you are using in the mold can safely be exposed to the temperature required to melt the plastic injection material without deforming your inserts. If your inserts can’t handle the temperature required to melt the plastic material, you will want to see if a different plastic material with a higher melting point to be safely used in your part.


The other consideration for insert molding is whether or not your inserts can handle the pressure. The amount of pressure generated during the plastic injection molding process is very intense. You need to make sure that the inserts can withstand this pressure without cracking or deforming.

Insert Injection Molding Process

Insert molding (a.k.a. insert moulding) is similar to injection molding and utilizes the same type of machine. During the process of insert molding, plastic resin pellets are heated until they melt. The melted liquid plastic is introduced, under pressure (injected), into a mold. The mold may be made up of any metal such as steel or aluminum. The molten form is then allowed to cool down and set into a solid form. The plastic material thus formed is then retrieved out of the mold.

Insert molding also utilizes similar materials as the injection molding process. The only exception is metal elements that may be added prior mold completion.

Insert Molding Applications

There are many applications to insert molding. Such applications include:

  • Auto industry components
  • Industrial equipment components
  • Medical devices
  • Couplings
  • Threaded fasteners
  • Electrical parts

ICOMold can help you with your insert molding needs.

Insert Molding vs Overmolding

On the surface, these two techniques look very similar. Insert molding generally takes a small part and encapsulates it within the plastic resin, like embedding a threaded bushing. Overmolding, on the other hand, is the process of plastic injection molding a layer of plastic over the top of another, different material, piece of plastic. An example of this is the housing for a portable drill. The main body of the housing is the first run (substrate) of injection molding, then the softer grips and handles are overmolded onto the main body.

How Long Does an Injection Mold Last?

Our injection molds will typically last well over 100,000 cycles. Moreover, ICOMold offers a lifetime warranty for these injection molds. As long as we continue to make the parts for you, we will maintain and refurbish the tool as needed at our own cost.

Process for Insert Molding — Plastic Injection Molding

ICOMold’s online quoting system and mold frame sharing technology enables us to simplify and shorten both the quoting and tooling manufacturing process for plastic injection molding. 

  1. Load your 3D CAD file to get your mold and part quote.
  2. Add your requirements for inserts in the comments, and your project manager will contact you.
  3. Upon order confirmation, ICOMold starts the mold and part order process.
  4. Tooling design review by ICOMold engineers.
  5. Upon design approval, ICOMold begins building your injection mold.
  6. Customer examines samples for approval.
  7. Part production begins.

Insert Mold — Injection Molding Highlights

  • Fast mold and part quote (inserts must be quoted offline by a project manager)
  • Low cost, high quality and fast turnaround 
  • Mold frame sharing technology
  • Online project management
  • Trouble-free part modifications  
  • Any commercially available material and surface finish

Go to our plastic injection and CNC machining case studies page to see how we helped customers on their projects.

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Injection Molding for US Companies