Insert Molding Service

Unlike molds that use secondary injection molding to produce the final part, insert molding usually consists of a preformed part (usually metal) loaded into the mold and then encased in plastic to create an improved function or mechanical property.

One method of molding using inserts is threaded inserts, which enhance the mechanical properties of the plastic parts’ ability to fasten together, especially during repeated assembly. Bushings and sleeves are another good way to improve the durability of parts for fitting parts that require higher wear resistance due to moving parts.

What is Insert Molding?

Insert injection molding is forming or molding plastic parts around other non-plastic parts or inserts. The components inserted are usually simple objects, such as threads or rods, but in some cases, the inserts can be as complex as a battery or motor.

In addition, insert molding combines multiple combinations of metal and plastic or materials and components into a single unit. The process uses engineering plastics to improve wear resistance, tensile strength, weight reduction, and metallic materials to improve strength and electrical conductivity.

Insert molding involves injecting plastic around a pre-placed insert to form a strong, durable, and permanent bond between the molded plastic and the insert. During production, inserts are placed in empty mold cavities, filled with molten thermoplastic, and cooled to form solid parts.

Cost-effective, accurate, and consistent insert molding for small to high-volume production.


Basic Guide of Plastic Overmolding

Unlock the potential of your encapsulation molding project with the following injection molding design considerations, including mold details, available materials and colors, and finishing and post-processing options

Design Guide of Insert Molding

Right Substrate

The initial component or substrate is the foundation of the overmolded product. The substrate must be able to withstand the overmolding process, and its shape must be compatible with the overmolding material. Common substrate materials include metals, plastics, and composites.

Parting Line

The parting line is the point where the two materials meet. The parting line should be located in a non-critical area of the final product to minimize any visible lines or parting marks.

Wall Thickness

Maintaining uniform wall thickness throughout the part is important to ensure consistent strength and prevent warping or sink marks. Varying wall thickness can cause uneven cooling during the molding process, leading to defects.

Ensure that the wall thickness of the substrate and the thickness of the cladding die are uniform from the beginning of the process. The 0.060″ to 0.120″ (1.5 mm to 3 mm) wall thickness will ensure good adhesion in most cladding applications.


Sharp corners can cause stress concentrations that weaken the part and make it more prone to failure. It’s better to use rounded corners or fillets to distribute stress and strengthen the part.

Draft Angles

Draft angles are angled surfaces that allow the part to be easily ejected from the mold. A minimum draft angle of 1 degree is recommended to ensure smooth ejection and avoid damage to the part.


The gate is the location where the molten material enters the mold. Gates should be located in areas where the overmolded material will flow uniformly and bond well to the substrate. Common gate locations include the edge of the part, the center of the part, or the end of the part.

TEBATE’s Capabilities of Insert Molding

Maximum Part Size

  • 800 x 800 x 400 mm
  • 31.5 x 31.5 x 15.7 in

Minimum Part Size

  • 5 x 5 x 5 mm
  • 0.2 x 0.2 x 0.2 in


  • Standard tolerance:  ±0.005″ (0.127mm)
  • Best achievable tolerance:  ±0.001″ (0.025mm)

Delivery Time

  • As low as 2 weeks for T1 samples
  • After T1 sample approval, lead time for < 10,000 parts is as low as 1 week

Tool validation

  • Standard process is to produce a small set of T1 samples for approval before initiating full production

Maximum Press Size

  • 1200T


  • 1Pcs

Mold Information

Rapid processing

Mold with steel cavity and core, injection life of 5,000 to 10,000 times

Usually processed within 2 weeks.

Production tooling

Steel tool with a projectile life of up to 1 million cycles

Can integrate side pull or CAM action

It is usually completed within 3 weeks

Multi-cavity or set mold

Multiple identical cavities or parts series are machined into a single tool

Allowing more parts to be produced per injection minimizes unit cost

Insertion Parts

Inserts are placed in a mold and molded around it to extend tool life for key features

Allows you to mold inserts, such as spiral coils, into your design

Plastic Materials of Insert Molding

Most Common Materials

Additives and fiber

Additives and fiber

Acrylonitrile Butadiene Styrene (ABS)

Nylon (PA 6, PA66, PA12)

UV absorbers

Polyethylene (PE)

Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS)

Flame retardants

Polypropylene (PP)

Polyurethane (PU)


Polycarbonate (PC)

High Density Polyethylene (HDPE)


Low Density Polyethylene (LDPE)

Glass fibers

Polystyrene (PS)

Polyvinyl chloride (PVC)

POM (Acetal/Delrin)

Polyethylene Terephthalate (PET)

Thermoplastic Elastomer (TPE)

Insert Materials

Most Common Materials




Stainless Steel


Aluminum 6061


Aluminum 7075

Surface Finishes of Overmolding 


Surface Roughness Grade


Pantone color matching

A1 – A3

Pad printing

RAL color matching

B1 – B3

C1 – C3

D1 – D3

More Design and Manufacturing Guidelines

1. The blade should be round, or have round knurls, and should not have sharp corners. A bottom cut should be provided to improve pull strength.

2. Inserts should protrude at least 0.4 mm (0.016 in) from the die cavity. The moulding depth below should be at least 1/6 of the insert diameter to avoid shrinkage (see image above right).

3. The boss diameter shall be 1.5 times the diameter of the blade, with a diameter greater than 12.9 mm (0.5 in; See above left), except for blades. For the latter, the boss wall should be derived taking into account the overall part thickness and the specific material grade. Keep the metal plug-in small relative to the plastic surrounding it.

4. Toughened grades of resin should be considered. These have higher elongation and greater resistance to cracking than standard grades.

5. Inserts should be preheated before forming. This minimizes post-die shrinkage, pre-expansion inserts, and improves weld strength.

6. Conduct a thorough end-use test plan to detect problems during the prototype development phase. The test should include temperature cycles within the range to which the application may be exposed.