Insert Molding- All You Need to Know

Molding is the process of turning raw plastic into a shape or form that is the desired finished product. Every kind of product demands a different molding technique, and among them, overmolding process and insert molding design types are considered the best molding techniques in the market.

The conventional plastic manufacturing process involves melting or softening the plastic at considerably high temperatures and then using different techniques to mold them into shapes that make them a useful finished product.

Molding is used in making virtually any molded component out of plastic following design considerations for plastic overmolding. A plastic chair or anything made out of plastic is basically made using molding techniques. 

In this blog post, we will discuss insert molding various design aspects related to the technique in detail. The aim of this post is to discuss the most common and encouraged molding technique in the world (insert molding), its working methodology, design considerations, benefits and applications in various sectors. 

How Does Insert Molding Work?

So, what is insert molding?

Insert molding works on similar basic principles as plastic injection molding. Molten resins are injected into a plastic mold that is designed to suit the geometric requirements of the part. The plastic resins are injected into the mold and allowed to solidify. They are then removed/ejected from the insert mold. 

The only difference here is that the metal is inserted into the molten resin before the mold closes. This way, the plastic covers the product completely and the entire main product is engulfed in the plastic with no cracks and even wall thickness. 

The inserted product can be simple such as a blade or a tube or it can be very complex like a metal insert for a complex machine.

The reason insert molding is preferred is that it is not an attachment of many plastic parts through screws to develop a cover for the product. The product is completely inside the covering and the cover is naturally formed around the product by a mechanical bond. It provides a soft grip and good quality product design by using CNC machining.

Various plastic injection molding companies make the use of vertical injection molding presses for the process. This allows them to use gravity to position and maintain the insert while the mold is closed. 

Additionally, vertical insert molding machines have multiple bottom mold halves within a single cavity half. Different bottom halves can be loaded at different times. Hence when one bottom half is in the process of molding with the cavity half, the other bottom can be loaded with resins. 

In a screw-based assortment with threaded insert, which happens in other kinds of molding, there is a high risk of wear and tear.

This plastic injection molding process is used because it has a more reliable structure and it increases the strength of the product by many folds. It is also preferred because the process is cheaper and is easy for 3D modeling.

Any other form of molding alternative to inserting costs more because the other processes require many sub-processes such as soldering, adhesives, connectors, threaded insert, and screws.

Insert molding does not require any of these processes and the product comes out stronger and more reliable due to sound design for manufacturability.

Design Guidelines:

Insert molding design guideline is beneficial for product manufacturing in many ways. The design guidelines for insert moulding are similar to those of conventionally molded parts. Maintaining consistency in wall thickness, adding draft for ejecting the part, etc are the regularly used guidelines. 

However, certain unique considerations need to be accounted for when thinking about insert moulding. Since injection moulding inserts are placed within the mold, it is important to carefully consider the position of the insert. Keeping them in place while the molding is in the process is also important. Additional features like designing the undercut can improve the insert strength. 

Here we have listed a few ways in which molding design needs to be executed in a specific manner.

The Machinery: 

The process requires advanced molding machines for product development. 

These vertical machines are designed for doing the plastic molding process through insert injection molding and have a set of design guidelines that need to be followed by the engineering team. 

The machines have an exceptionally tight tolerance as that makes sure that the information of the plastic arts is accurate in plastic injection molding. Even a small misalignment in millimeters can end up causing failure for the product. 

The Inserts: 

There are different types of inserts used in the design engineering of molded component. The metal insert in the plastic molding is usually made of brass, stainless steel or usual steel. 

These molds have threaded surfaces so that they will have improved adhesion to the product. 

The molds are placed in the machine vertically either by hand or through the CNC machining. The vertical position is to make sure that the mold stays in place during over molding and insert molding with the help of gravity. 

Now the molten plastic is poured into the mold and the mold is closed.

Inserts are used for various types of processes like Injection Moulding, Compression molding, GRP molding, SMC/DMC molding, Extrusion Blow Molding, Structural foam, Rotational molding, etc.  

Thread Options: 

Different thread options are available for the insert mold production. 

Thread options are ways for the manufacturer to place pipes, screws or anything else into the mold at the specified location. It could also mean a mold for the screw to be inserted into. 

The aim is to ensure that the mold does not make the product insert. As the product needs to be connected to external conduits in many ways, the mold will allow the product to stay functional and useful.

Insert Molding Materials:

There are many kinds of materials used in an insert molding operation. 

The molding material  or the plastic resin is chosen based on the mold, the material of the product and other factors like chemical bonding, additive manufacturing, mechanical bond, and the wall thickness of the finished 3D print product.

The main focus is to ensure that the mold will be viable and sustainable through the process of molding.

1. Thermoplastics:

These are plastic molding process materials that are considered eco-friendly because they can be used multiple times. 

They are resistant to chemicals and are a good option for ensuring variance and sheen in the molding process. 

These are the main types of thermoplastic materials available in the market:

          a. Polyethylene: 

This thermoplastic polymer is chemical resistant and also has high toughness, dielectric and impermeability characteristics. 

The usual polyethylene thermoplastics in the market are HDPE, MDPE, and LDPE. 

They are considered lightweight thermoplastic materials.

          b. Polystyrene:

These are lightweight and clear plastics that have a low melting point. 

They are acid and base resistant and are commonly used for everyday mainstream products like consumer products and medical devices etc.

          c. Nylon: 

This is a strong and sturdy plastic type that can resist chemicals as well as abrasions. 

It has such a high melting point that it can even replace metal in various applications. 

That makes it a highly desired material in heavy products that are used in manufacturing and extraction.

2. Thermosets:

Thermosets have a close resemblance to thermoplastics but they cannot be recycled in any way and are not too eco-friendly. 

Here are a few kinds of thermosets that can be used in product manufacturing like medical devices that are made with stainless steel.

          a. Phenolic: 

The plastic has high chemical resistance to halogenated solvents and is usually IL 94V 0 approved. 

They are used in highly specialized operations when certain restrictions apply.

          b. Epoxy: 

They become permanently hard after processing and have no melting point. This makes them very suitable for challenging uses. 

They have the best adhesion as well as high resistance to heat and chemicals.

3. Elastomers:

The synthetic and natural polymers like rubber are included in the elastomer category. 

These polymers are of significance due to their elasticity and recyclability. 

They are very eco-friendly materials and are ideal for home appliances and automotive product manufacturing.

          a. Natural Rubber: 

Natural rubber is durable and highly flexible.

It is used in tire making and various other household appliance manufacturing. 

          b. Polyurethane: 

Polyurethane has exceptional abrasion resistance, and wear and tear tolerance. 

This plastic is highly elastic and it is also impact resistant. The material is long lasting and has a high-temperature tolerance.

Insert Molding vs Conventional Plastic Injection Molding

One of the most needed features during the process of plastic injection moulding is to fasten two parts together. It is hence required to add more than one metal insert into the plastic part. 

However, most plastic materials that we know often lack the mechanical properties to fasten the two parts effectively. Threads within the plastic part can wear and tear very fast and will not create effective fastening of the two parts. This often results in failed/poor quality parts. 

Metal inserts, however, enhance the properties of plastics and ensure efficient fastening of the two parts. 

Injection molding is hence the process of injecting one or more plastic resins (molten state) to create a finished part. 

Coming down to the next process, what is overmolding?

Overmolding, on the other hand, is a process that involves molding a plastic layer over a previously molded part. Overmolded plastics are hence produced in a two-step process. 

Insert molding technology brings forth the advantage of joining two separate parts to form a single product in a single step. 

Benefits of the Insert molding process

As stated earlier, the insert molding process is used in developing parts that are stronger and sturdier than the other options. Here is how this plastic molding process (insert molding) is a better and more efficient option for your molding needs:

  • The materials in the insert molding design are chosen specifically for the product application. This ensures that the material is going to be suited for all types of products, commercial or domestic.
  • The process of insert molding is cheaper and cost-efficient as compared to other processes of molding. Since insert molding is a one step process, there is an overall reduction in the assembly and labor costs. 
  • Insert molded components are free from failures, misalignment, loose halves, etc. This makes the process is also considered much more reliable and trusted than other methods because it does not require any assembly processes. 
  • Insert molding offers design flexibility and the ability to create uniquely shaped parts that are used in various commercial and industrial applications. 
  • The entire product is made of one sheet of plastic.
  • Insert molding design is also used to manufacture domestic appliances that are found in homes.
  • The insert mold allows the product to develop shape and have a good exterior finish.
  • The insert mold products can be developed decoratively and can be used to manufacture products that are used for semi-decorative purposes.

 Insert molding applications

As mentioned in the earlier sections, insert molding is a highly advanced technology in the field of plastic injection molding. Additionally, it is considered more efficient as compared to conventional processes. 

Insert moulding process is not just favored for the reduced assembly and labor costs but also improves the functionality of the parts by reducing the weight and size, and enhancing the strength and structure. 

This is perhaps the reason why insert molding finds its utility in a wide range of industries like the automotive sector, consumer goods, medical industry, electronics, aerospace, etc. 

From medical instruments like tube valves, needle hubs to knobs for electrical appliances, controls, electrical components, assemblies, etc, insert molding is an in-demand technology. 

Insert molding technology is also used to develop compact products because it is developed in comparatively smaller machinery. So the final product is compact in size. The products in overmolding are much larger in size and manufacturing through overmolding requires longer periods of time.

Injection molding types are best used for smaller products that are focused on commercial uses that require soft grip, additive manufacturing, and laser sintering. 

The products that are used in heavy machinery are conventionally developed through overmolding as this process of mold tooling makes the product highly strong and sturdy.

Insert molding also keeps the product long-lasting and of high quality, but not on an industrial level, as this requires a certain design for manufacturability. 

Plastic insert molding is also conducted at home and small garages but the overmold process requires proper manufacturing location like a plastics manufacturing company for product development and design engineering.

Final words:

In conclusion, insert molding design as a process is better than other forms of molding. 

Mainly because other forms of molding are older technology and insert molding design is the latest technology available. 

When it came out, it was considered a breakthrough and it has been around for a while.

Insert molding design is the best way to ensure that the product that is manufactured is lightweight. 

Most manufacturers and designers agree that insert molding is one of the most efficient plastic injection molding technologies. It offers the ability to work with a wide range of materials and create complex part geometries. 

The cost savings and the improved designs lead to efficient manufacturability and customer satisfaction too. 

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