Insert Molding

What is Insert Molding?

Insert molding is the process of encapsulating a non-plastic insert or component into molten resin, with the purpose of producing a single unit or part. Oftentimes, the molding insert is a simple item such as a rod, a thread, or a knife blade, but it can also be a complex part such as a motor or a battery. There are many situations that call for reinforcing the mechanical properties of plastic parts through such manufacturing methods.


The main use of plastic insert molding is to create a strong and reliable molded part with a very low investment of money and time. This process helps to reduce assembly and labor costs. Also, it allows manufacturers to benefit from increased design flexibility without having to compromise on the structural integrity of the part. The reduced labor cost and the excellent quality control makes the insert molding process one of the best and least expensive methods to manufacture lightweight and compact parts that are reliable, durable, and fully functional.


The plastic insert molding process calls for very high accuracy to ensure that the resulting plastic parts are properly formed. Even a slight misalignment can completely ruin the outcome, hence the need for very tight quality control procedures. In fact, the injection molding process is closely tied into the interface between the machine and mold tooling. There are high-precision machines that can meet even the most demanding requirements in terms of precision and reliability that only insert molding can manage.

What is Overmolding?

Overmolding is a two shot molding process that consists of molding a plastic layer around and over a previously molded part. The outcome of this plastic insert molding process is a single component, an encapsulated piece that accounts for a single finished product.


A form of plastic insert molding, overmolding is used to combine at least two materials to create one object part or design is injection molding, which is the most common process used for overmolding. It is commonly referred to as the double injection molding process. More recently, some 3D printing technologies are being used to overmold objects of the two or sometimes more materials. One material is commonly known as the substrate. It is either partially or fully covered by a second material or materials referred to as the overmolded material. The substrate material can be just about anything from metal to plastic or glass.


The overmolded material is often rubber or thermoplastic. Overmolding can be used as a double injection molding process, and often results in either a chemically bonded part or the materials are mechanically interlocked. Overmolding offers several benefits to the insert molding process. One, in particular, is that it can eliminate secondary operations when building parts, thereby reducing manufacturing costs. It is often used to deliver a specific feel to a product such as softening edges or delivering a more pleasant feel or giving users a firm but soft grip. In simple terms, the double injection molding, or overmolding process, works in this manner.

Important Points to Remember Regarding Molding Inserts

The molding inserts require special attention, as not all parts may be suitable for the insert molding process. These inserts need to be able to withstand the insert molding process. This means that they have to meet strict requirements in terms of temperature and pressure resistance.


A successful plastic insert molding process shouldn't alter the structure or the shape of the insert in any way. In insert molding, the shape of the molding inserts is also extremely important. First of all, manufacturers should explore the means to hold and locate these inserts during the molding process. Second of all, the insert has to have undercuts or bosses, in order to provide better retention strength with the molded plastic.

Injection Overmolding

The injection molding process involves substrate parts being molded first. The molded parts are then placed into a different mold where the second material or materials are injected via plastic insert molding. This object is removed from the mold, and you have an overmolded part.

The 3D printing technology is typically jetting, where two or more materials are jetted concurrently onto the part during the layer by the layer build process. The types of products that are overmolded include tool hand grips like screw drivers, scissors, and medical products such as cannula, needles, tubing, and catheters. 

Primary Difference Between Insert Molding and Overmolding

The difference between insert molding and overmolding are the number of steps required to achieve the end result, and the resulting item itself. Overmolding can be used as a double injection molding process, while insert molding is commonly one shot. Products that are obtained through overmolding (double injection molding process) have a very long life and often retain good safety features.

Two-Shot Molding

The Two Shot injection molding process, also referred to as double injection molding, is widely recognized as a complex manufacturing process that involves the use of two separate materials to produce a molded product. Two-shot molding (often referred to as double injection molding) is still a part of the insert molding family and deals delicately with the molding insert.


Two Shot insert molding is effective, evolving, and definitely an innovative manufacturing approach employed by industries to manufacture complicated components, primarily from two distinct (usually plastic) materials, which are far too complicated as well as uneconomical to produce using conventional molding processes.

Generally, this manufacturing process is carried out on a machine specially designed and built to carry out a double injection in a single cycle. The first stage involves injecting the one type of plastic into a mold. On completion of this insert molding process, the machine rotates the plastic mold automatically before injecting another type of plastic through into the mold.


Two-shot plastic insert molding creates a powerful molecular bond by optimizing the co-polymerization of the two substrates (one of which is usually hard while the other is soft). The ability to create a molded unit from two different types of materials in one process is the biggest advantage to insert molding as a double injection molding process.

What Are the Parts of a Mold?

Before addressing the components of a mold, we must first understand what mold type is required for insert molding. The term "mold" generally refers to two halves of steel but can be composed of aluminum, tool steel copper, and other alloys. The many crucial components of any mold include bushings, pins, injectors, mold bases, guides, and alignment tools that guide the plastic during the insert molding procedure.

Insert Molded Componenets
Overmolded Plastic Pieces

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