Zhongde (Beijing) Machinery Equipment., Ltd.

ZHONGDECustomizing | Manufacturing


Custom Overmolding Insert Injection Molding Services

Zhongde, a reputable plastic and rubber injection molding company in China, provides insert and overmolding services and produces unique multi-material parts. 

Both over-molding and insert molding injection processes by Zhongde, a reliable injection molding supplier, involve putting two types of materials together to make one part. And the inserts can be threaded metal inserts. Overmolding is a two steps process that one to create the substrate and one for the oversold that goes on top of it. China insert molding is a slightly faster process as it takes only one step that the two materials are molded at the same time.

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Overmolding & Insert Molding
Overmolding vs Insert Molding

What Materials are Used in Injection Moulding

In addition to the general materials listed below, Zhongde, a reliable custom rubber injection molding company, can also modify the materials according to the special needs of customers. Our professional engineers will adjust the raw material formula to meet the unique conditions of use. Our production materials of custom over-molding and insert molding range from thermoplastic to elastomer-rubber, as well as metal and silicone. We've broken down the differences and similarities between the two processes. Let us help you decide which process is right for your project.

Overmolding vs Insert Molding

Overmolding is a process where a single part is created using two or more different materials in combination. Traditonally, overmolding starts with injection molding a hard plastic resin that has a higher melting point. Once that part is cooled, another material is injection molded over the first part, resulting in a single, finished product.

Insert molding combines metal and plastic injection molding service into one single part. It allows plastic to bond to insert pieces, mostly brass or stainless steel metal component, which go inside a mold cavity. There are many options for insert that can be placed into the mold. A few of examples are warming labels, threaded bushings, wires, batteries, etc.

Insert and Overmolded Plastic Injection

  • ABS | Acrylonitrile Butadiene Styrene

  • PA 6 | Polyamide 6, Nylon 6

  • PA 6/6 | Polyamide 6/6, Nylon 6/6

  • POM | Acetal Polyoxymethylene, Delrin

  • PP | Polypropylene

  • PE | Polyethylene

  • LDPE | Low-Density Polyethylene

  • HDPE | High-Density Polyethylene

  • UHMWPE |Ultrahigh Molecular Weight Polyethylene

  • PTFE  | Polytetrafluoroethylene

  • PEEK | Polyether Ether Ketone

  • PC | Polycarbonate

  • PMMA | Polymethyl Methacrylate, Acrylic

  • PS | Polystyrene

  • PVC | Polyvinyl Chloride (Shore D)

  • PU | Polyurethane

Rubber Overmolding & Insert Molding

  • NR | Natural Rubber

  • NBR | Nitrile Rubber

  • SBR | Styrene-butadiene Rubber

  • HNBR | Hydrogenated Nitrile

  • CR | Neoprene Rubber

  • VMQ | Silicone

  • LSR | Liquid Silicone Rubber

  • FVMQ | Fluorosilicone

  • FKM | Fluorocarbon

  • FFKM | Perfluorocarbon Rubber

  • EPDM | Ethylene-Propylene Diene Monomer Rubber

  • IR | Polyisoprene Rubber

  • IIR | Butyl Rubber

Metal Overmolding and Injection Molding with Metal Inserts

  • Aluminum

  • Stainless Steel

  • Carbon Steel

  • Copper

  • Brass

Overmolding VS Insert Molding Type

Machining TypesCase Display
Bonding the resin to the metalBonding-the-Resin-to-the-Metal.jpg
Metal insert into the resinMetal-Insert-into-the-Resin.jpg
Rubber onto plasticRubber-onto-Plastic.jpg

Size of Molding Over & Insert Injection Molding

Below table shows the size of Overmolding & Insert Molding parts we usually make. If you need a larger size, we can also help you achieve it.


Additives of Overmolding & Insert Molding Injection



UV absorbers

Absorb UV radiation, slowing down the degradation of the material when used outdoors.

Flame retardants

Prevent ignition and inhibits spread of fire.


Increase flexibility and promotes plasticity, reducing brittleness of the material.


Used to color plastics.

Carbon fibers

Increase strength, toughness, and rigidity of the material at the expense of making the material more brittle.

Glass fibers

Increase strength, toughness, and rigidity of the material at the expense of making the material more brittle. It is more flexible than carbon fibers.

Surface Finishing of Overmolding & Inserts Injection Molding

For product designers and engineers, surface finish on molded parts is an important design consideraton. Most polish and texture is appled directly to the mold itself and trasferred to the parts during the injection molding process. Following are serveral surface finish options for molded parts.




The mold is smoothed and then polished with a diamond buff, resulting in parts with a mirror-like finish.


The mold is smoothed with fine grit sandpaper, resulting in parts with a fine surface finish.


The mold is smoothed using fine stone powder, removing all machining marks.

Textured finish

The mold is first smoothed with fine stone powder and then sandblasted, resulting in a textured surface.

As-machined finish

The mold is finished to the machinist's discretion. Tool marks may be visible.

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