Overmolding

Plastic injection involves many similar but different processes, such as the overmolding process, often discussed in conjunction with insert molding, and commonly confused as two plastic injection techniques. Strictly speaking, overmolding refers to the injection process of two different plastic materials; insert molding is considered a subcategory of overmolding, specifically referring to the plastic injection process of embedding metal into plastic. However, some manufacturers loosely refer to the process of encapsulating plastic material on a substrate as overmolding. This article will introduce the overmolding process with precise definitions.

 

 

What is the Overmolding Process?

Overmolding refers to a series of manufacturing processes involving two or more plastic materials seamlessly combined into a single part or product through injection molding. The first step in overmolding typically involves solidifying the plastic base material. Subsequently, another layer is molded on top of the first layer to form a product. A typical product produced using overmolding is like the handle of a toothbrush, where the main body of the toothbrush is first formed by plastic injection to create the base layer, followed by covering it with a silicone layer to complete the handle, providing different colors and hardness, offering a more comfortable grip.

 

What Are the Differences Between Overmolding and Insert Molding?

Insert molding refers to a single manufacturing process involving the insertion of components into molded parts, commonly metal components embedded in plastic during the injection process, followed by direct solidification of the plastic material, with both parts combined on the same body.

 

To further distinguish the product characteristics between overmolding and insert molding—overmolding typically provides products with more comfortable grip, aesthetics, and shock absorption effects; insert molding can enhance product structural strength, increase product design flexibility, and combine different materials. In general, these two processes are often used simultaneously in the same product. For example: Western tableware. The plastic handle adopts the overmolding process, while the hardware parts use insert molding to insert metal parts into the plastic handle.

 

 

  

 

 

Layana's Overmolding Process

Layana has over 20 years of experience in overmolding processes. Its in-house plastic injection equipment includes 11 vertical plastic injection machines ranging from 35 to 250 tons and 4 horizontal plastic injection machines ranging from 60 to 200 tons, providing overmolding services for small, medium, and precision parts. Layana is an certified IATF 16949 factory that can provide diverse technologies such precision stamping and plastic injection services. Below are examples of products overmolded by Layana:

 

Item	Item	Materials
Beverage Machine Components		TPU ISOTHANE 1055D
Cutlery		ABS (Food-grade plastic resins)
The Case of Smart Door Lock		UL94V-0 PC with 10% masterbatch

 

 

The Advantages of Utilizing Overmolding Technique

• Overmolding can enhance the product's waterproof performance, shock resistance, durability, and aesthetics.
• As the product is directly molded through plastic injection, overmolding process eliminates assembly steps and adhesive usage, reducing production processes, costs, and time.
• The plastic material used in overmolding allows product designers to create more creative and unique products with greater design freedom, using different plastic materials and colors as deemed appropriate.

 

The Applications of Overmolding Technique

  

The application of encapsulation molding is not only common in products related to handles, but also extends to, but is not limited to:

• Hand Tools: For hand tool products, the plastic handle is often molded onto the metal part using an insert molding technique, followed by molding the second layer of overmolding, providing better comfort, anti-slip effects, and different colored appearances.
• Automotive Components: Overmolding technology can be used in the production of automotive components. These components need to have characteristics such as high strength, wear resistance, and waterproofing, or provide a better user experience, such as door handles and steering wheel covers. By using encapsulation molding technology, different materials can be combined to meet these requirements and improve the overall product quality.
• Electronic Products: Overmolding technology is also used in the production of parts such as casings, connectors, and switches for electronic products. These products need to have good sealing and waterproof performance to protect internal electronic components from damage while providing an aesthetically pleasing appearance.
• Household Goods Industry: For example, in the production of dinnerware, Layana has experience in independently developing dinnerware products using overmolding technology, creating dinnerware with spotted patterns, eliminating assembly costs, and avoiding concerns about detachment and food safety associated with the use of adhesives.

 

Layana's Capabilities of Overmolding

Layana introduces dual-alloy material pipes to facilitate smooth mass production of insert molding, providing customers with the highest quality service from precision injection molds, continuous stamping molds, mold processing, injection molding, stamped part processing to product assembly. The overmolded parts are suitable for medical devices, automotive precision components, electronic components, connector parts, sensor system parts, etc.

 

 

 

 

The Common Materials Used in Overmolding

There are many plastic materials available for use in overmolding, each with its own characteristics and suitable scenarios. Plastic materials suitable for overmolding include, but are not limited to:

 

Common Materials Used in Encapsulation Molding
Thermoplastic Elastomer (TPE)	TPE has excellent elasticity and flexibility, providing a good tactile feel and slip resistance. This makes TPE an ideal choice for many daily necessities, such as handles and buttons.
Silicone Gel	Silicone gel is resistant to high temperatures, chemicals, and has good insulating properties. It is widely used in automotive components, electronic products, and medical devices.
Polycarbonate (PC)	PC has excellent impact resistance and transparency, as well as outstanding weather resistance and fire resistance. Therefore, PC is commonly used to manufacture products that require high-strength protection, such as safety glasses and phone cases.
Nylon	Nylon is a high-strength, wear-resistant material commonly used in the production of industrial parts, sports equipment, and automotive components.
Polypropylene (PP)	Polypropylene (PP) is a lightweight, chemically resistant, and high-temperature plastic material. It finds extensive applications in the fields of packaging, household goods, and medical instruments.

 

 

 

The Considerations in Overmolding Process

1. Before employing the encapsulation molding technique, one must contemplate the suitability of the plastic materials in use. Especially, the inner layer material needs to have a forming temperature higher than the outer base material to prevent the inner plastic from melting during the second injection. Thus, it is imperative to ascertain the compatibility of materials' tolerances before selecting the inner and outer layer materials.
2. The adhesive properties between the base material and encapsulation material depend on confirming the compatibility of the two plastic materials. Otherwise, after overmolding, there might be occurrences of material peeling. To ameliorate the situation of material peeling, consideration may be given to the incorporation of metal inserts, namely, the insert molding technique, to reinforce the bonding strength of the two plastic materials.

 

 

The Relevant Information of Overmolding Process

The overmolding process, depending on the different procedures, further extends into various sub-techniques. Additionally, there are other molding techniques such as plastic injection molding and insert molding that can be referenced:

 

• Insert Molding: Integrating metal into the plastic injection molding process.
• Two-Shot Molding: By means of mechanism inversion, mold design, and other methods, allowing components to undergo encapsulation molding with two successive injections within the same mold set.
• Coinjection: Simultaneously injecting two or more different materials for molding.