What is Insert Molding? | Insert Molding Vs. Overmolding | Types of Inserts | Insert Molding Materials

insert molding

What is Insert Molding?

Insert molding is an injection molding process that utilizes encapsulation of a component in the plastic part. The process consists of two necessary steps. Firstly, a finished component is inserted into the mold before the molding process actually takes place.

Secondly, the molten plastic material is poured into the mold; it takes part’s shape and joints with the previously added part.

The added part is as simple as a knife, tube, handles a female threaded insert to create a hard thread in the plastic part. Complex parts also exist, but it’s fine as the insert molding process comes with immense possibilities. The added comment can be anything from plastic handles to electrical components.

Insert molding is prevalent in the mainstream because of such a variety of potential applications and significant cost-cutting. It eliminates any need to run secondary operations like soldering, welding, connectors, and adhesives.

The Importance of Insert Molding process – 

the importance of insert molding

As discussed before, insert molding comes with various applications and can be crucial for any manufacturing company to improve production without hampering the quality and cutting production costs simultaneously.

Insert molding can be attributed to cost-cutting and high productivity. It eliminates your need to run a secondary process, giving you supreme flexibility to manufacture different products.

Another factor that makes insert molding quite useful is its ability to make reliable and strong products.

Fascinating Read – What is Ultrasonic Welding | Ultrasonic Welding for Injection Molded Parts | Common Welding Problems and Solutions | Ultrasonic Welding Advantages

 Insert molding vs. Overmolding 

Insert Molding vs Overmolding

On the surface, Insert Molding and overmolding seem to be very similar to each other, but there are some subtle differences between them.

Contrary to insert molding, overmolding is a two-step process where a plastic component is molded over an already molded part to produce a single component.

On the other hand, Insert molding does the same thing, but only in one step. The difference lies in the way the final product is made. Here, the insert and molten material are located into the mold to form the final combined product.

One more fundamental difference is that insert molding is not bounded by plastic, including metals with different products.

Overmolding is usually utilized to produce products with great textures, shapes, and colors, predominantly made for shelf appeal.  Insert molding is used to create more rigid products.

Types of Inserts – 

types of insert molding

Inserts are objects which are used for fastening and assembling plastic parts with their counterparts. Sometimes even two inserts are used in a single part for smooth function. Below is the list of the most widely used inserts.

  • Male threads
  • Female threads
  • Electrical contacts
  • Spring-loaded clips
  • Dowel Pins

Types of Insert Molding Applications –

  • Manual Insert Application
  • Automatic Insert Application

Manual Insert Application:

Manual insert operations are pretty common with low-volume productions. An operator is hired to mold and insert during the molding process.

Hiring labor is essential for manual insert operations, especially with low-volume productions. Manual labor gives the advantage of having detailed inspections of production quality, neatness, assembly, and kitting. However, the same method is not practical for high-volume productions as it will add to production costs and inefficiency.

Automatic Insert Application:

As the name suggests, automatic insert applications will utilize robots to insert and mold the molding process’s parts. Automatic inserts are highly reliable for high-volume production as they will help reduce per part cost because of the robot’s speed and accuracy.

The same reduction of costs can be passed on to the customer. Robots are, without a doubt, faster than manual labor that will drastically reduce your production cost per hour.

Considering quality control, people might have the wrong idea that manual labor has an advantage over robots as they can inspect every part on their own. However, that’s not true (at least up to some extent).

There are robotics systems available in the market equipped with magnetic sensors to ensure that the inserts have been properly molded. Moreover, integrated vision systems are also present in some robotic machines that can check on quality standards.

Interesting Read – Compression Molding Process – A Detailed Guide

Insert Molding Materials – 

insert molding materials

A variety of thermoplastic polymers can be utilized in insert molding, depending on your requirements. Therefore, the materials which I will mention below will have different properties and applications depending on the final product.

#1 Thermoplastics – 

Thermoplastics are the most popular polymer group whose services are provided by mostly all the big manufacturing companies. They have a wide range of applications and are environment friendly as they can be reheated and reysed several times.

Thermoplastic materials include nylon, polyethylene, polycarbonate, Polypropylene, etc.

#2 Thermosets – 

Thermoset materials are quite similar to thermoplastics, except that they can’t be recycled or melted after curing. The three-dimensional network of bonds present in thermosets makes them more challenging and thereby stronger than thermoplastics.

The most used thermoplastics are epoxy and phenolic.

#3 Elastomers – 

Elastomers are a blend of rubber and synthetic polymers. Unlike, thermosets elastomers are recyclable, known for their resilience and flexibility. They are mostly used in home and automotive applications.

Engaging Read – What is Blow Molding? | Guide to Blow Molding Process | Blow Molding Advantages | Blow Molding Disadvantages

Part Designs For Insert Molding – 

What is insert molding? It is a manufacturing method that also follows a particular process. Below is the part design for insert molding.

The insert:

The insert is the most important part, and it should resist high temperature and high pressure.

The Insert Location:

Inserts are completely relied on plastic to hold them in place. Keeping in mind the insert’s function and how pressure will be applied at every corer is very important.

The Cost:

If if you’re running or going to run or hire someone else to run the process and you’re price sensitive, consulting with an injection molder about the cost attributes inserts will add is a must.

The Mold:

Designing a good quality mold is essential as it will be critical in holding the insert in one place.


Depending on your scenario, doing an in-depth cost analysis of your needs should be manually operated or automated with robots.

FAQs – 

1. Why is metal insert used in the plastic components?

Ans. It is useful in metal to plastic conversion to make plastic parts more structured. There’s a paradigm shift going on in the market to replace plastic with metal. That will help in lower weight, eliminate corrosion, reducing production costs. Insert molding is essential for retaining the important metal elements in a plastic part.

2. What is the difference between metal injection molding and casting?

Ans. There are many differences between die casting and injection molding. However, the most subtle and noticeable difference between them is that die casting uses some metal, often aluminum alloy, as a raw material; on the other hand, injection molding uses plastics or polymers.

3. What are the different types of injection molding variations?

Ans. Below are the most common injection molding variations:

  • Cube Molding
  • Insert molding
  • overmolding
  • Gas-assisted injection molding
  • Microinjection molding
  • Reaction injection molding
  • Thin-walled injection molding
  • Liquid silicon rubber injection molding
  • Metal injection molding

4. What is overmolded rubber?

Ans. Over-molded rubber is usually a substrate joined on the top of a plastic part. The substrate used TPE or TPU typically.

Suggested Read – 

How is Plastic made? A Simple and Detailed Explanation.

Plexiglass Vs. Acrylic | What are the Differences and Similarities?

UHMW Vs. Delrin: Which one is the Best?

What is a Plastic Mold? | Parts of Plastic Mold | Applications of Plastic Mold

Final Thoughts – 

Thus, were my thoughts and views on the insert molding process. I have done my best to keep it brief and mentioned every important factor. Insert molding

Feel free to share your reviews in the comment box.

Have a wonderful day 🙂

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