Overmolding
Overmolding is the process of injection molding two or more materials together. This can be done with two different types of material, such as plastic and metal, or it can be done with two different colors of the same type of material.
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Types of Overmolding Process
Overmolding can be used to improve the strength, durability, and aesthetics of a plastic part. It can also be used to add functionality to a part, such as adding a grippy surface or creating a water-tight seal.
Plastic Over Plastic
A second layer of plastic is added to the core part. This can be used to improve the strength or aesthetics of the part.
Rubber Over Plastic
A layer of rubber is added to the core part. This can be used to improve the grip of the part or create a water-tight seal.
Plastic Over Metal
A layer of plastic is added to a metal core. This can be used to improve the durability or aesthetics of the part.
Rubber Over Metal
A layer of rubber is added to a metal core. This can be used to improve the durability or grip of the part.
What is Overmolding Process?
Overmolding technology enables many functions and features, such as abrasion, molding, corrosion resistance, insulation, and so on.
1. Molding Core Part
The first step is to create the core part using injection molding. This part will be the innermost layer of the overmolded part.
2. Create Overmold Layer
A second mold is created that is slightly larger than the first mold. This second mold will be used to create the overmold layer.
3. Assembly
Molten plastic is then injected into the second mold. This plastic will flow around the core part, and fill the entire mold.
4. Cooling & Demould
Once the overmold layer has cooled and hardened, it can be removed from the mold. The overmolded part will now have two layers of plastic!
How does overmoling work?
The overmolding process begins with a mold that has two halves. The first half of the mold is filled with the first material, and the second half is filled with the second material. The two materials are then injected into each other, bonding them together.
The basic items used for Over Molding have been classified into two types – the first one being the substrate, and the second one being the Over Molding material. The substrate may be composed of glass, plastic, metal, or rubber. Whereas the other item is commonly thermoplastic. When these two are combined, their adjoining can be the cause of a mechanical interlock or a chemical bond between the two. Either way, the parts create a new object, for example, scissors, cellphones, drill machines, etc.
Using Overmolding technology reduces the assembly process and manufacturing cost, improves product quality and performance, enhances the appearance and molding, and improves competition for the product.
Overmolding Plastics
ABS
Acrylonitrile Butadiene Styrene resin is a milky white solid with a certain degree of toughness, with a density of about 1.04~1.06 g/cm3. It has strong corrosion resistance to acids, alkalis, and salts, and it can also tolerate organic solvents to a certain extent. ABS is a resin that has good mechanical toughness, wide temperature range, good dimensional stability, chemical resistance, electrical insulation properties and it’s easy to manufacture.
- Common applications: Enclosures
Nylon 6
Nylon 6, also known as PA6, polyamide 6, is a polymer compound. Except for its low melting point and wide process temperature range, its chemical and physical properties are very similar to nylon 66. Among all nylon grades, nylon 6 has the lowest modulus.
- Common applications: Enclosures
Nylon 66
Polyhexamethylene adipamide, commonly known as nylon-66, is a thermoplastic resin. The performance of nylon 6-6 is better than nylon 6, and the price is not as expensive as nylon 4-6. Its abrasion resistance is the best among all nylons, and its mechanical strength, hardness, and rigidity are very high. Can be used as engineering plastics and making synthetic fibers.
- Common applications: Enclosures
Nylon 11
The density of nylon PA11 is 1.04g/cm3, the melting point is 185℃, the water absorption is 0.1-0.4℅, and the tensile strength is 47-58MPa. It has the advantages of low water absorption, good oil resistance, low-temperature resistance, and easy processing. Widely used in our lives due to its good cost performance.
- Common applications: Enclosures
PBT
Polybutylene terephthalate (PBT), a milky white semi-crystalline thermoplastic polyester, is one of the five major engineering plastics. It has high heat resistance. Not resistant to strong acids and alkalis, resistant to organic solvents, flammable, and decomposes at high temperatures. It is widely used in the fields of automobiles, machinery, and equipment, precision instrument parts, etc.
- Common applications: Enclosures
PC
Polycarbonate is a high molecular weight polymer containing carbonate groups in the molecular chain. It is a tough thermoplastic resin with flame retardancy. Antioxidant. It has excellent impact strength, transparency, and optical properties, mechanical properties, and can be molded to tight tolerances. PC has a wide range of applications, and there are a variety of compounds to choose from.
- Common applications: Enclosures
PE
The full name is Polyethylene, which is the simplest polymer organic compound and the most widely used polymer material. According to the density, there are 2 types of PE: LDPE and HDPE. It has good inherent lubricity and is easy to process. It should be noted that it is very soft and cannot be used at a temperature much higher than 150.
- Common applications: Enclosures
PEI
Polyetherimide (PEI for short) is an amorphous high-temperature super engineering plastic, and its cost is relatively low compared with other high-temperature materials. It has the best high-temperature resistance and dimensional stability, as well as chemical resistance, flame retardancy, electrical properties, high strength, high rigidity, etc. The performance is similar to polycarbonate, but it can work at higher temperatures.
- Common applications: Enclosures
LDPE
Low-density polyethylene, also known as high-pressure polyethylene (LDPE), is milky white, odorless, odorless, non-toxic, and waxy particles with a matt surface. It has good electrical insulation, transparency, easy processing, and certain air permeability. And has strong extensibility and flexibility, making it have excellent impact strength. This is offset by the permanent deformation after the impact.
- Common applications: Enclosures
HDPE
High-density polyethylene (HDPE) is a white powder or granular product. Non-toxic and odorless, the use temperature can reach 100℃. It does not have the impact strength of LDPE, but it is more elastic. Surface hardness, tensile strength, rigidity, and other mechanical strength are higher than LDPE, close to PP, tougher than PP, but the surface finish is not as good as PP.
- Common applications: Enclosures
PET
Polyethylene terephthalate (PET), milky white or light yellow, is a highly crystalline polymer with a smooth and shiny surface. It is non-toxic, tasteless, and has good hygiene and safety, and can be directly used for food packaging. It has excellent physical and mechanical properties in a wide temperature range, and the long-term use temperature can reach 120°C. But it is difficult to mold to very close tolerances.
- Common applications: Enclosures
PP
Polypropylene is abbreviated as PP, which is a colorless, odorless, non-toxic, translucent solid substance. The density is about 0.89～0.91g/cm3, and the operating temperature range is -30～140℃. It is difficult to mold to very close tolerances. Widely used in the production of clothing, medical equipment, automobiles, bicycles, parts, pipelines, chemical containers, etc.
- Common applications: Enclosures
PPA
Polyphthalamide is a kind of synthetic resin with high hardness, high strength, good chemical resistance, and low cost. Due to the excellent physical, thermal, and electrical properties of PPA, especially the moderate cost, it has a wide range of applications. Although the use and introduction of PPA are relatively late, its good design data is still very useful.
- Common applications: Enclosures
PPS
Polyphenylene Sulfide is a new type of high-performance thermoplastic resin, which has the advantages of high mechanical strength, high-temperature resistance, chemical resistance, flame resistance, good thermal stability, and excellent electrical properties. It is widely used in the fields of electronics, automobiles, machinery, and chemicals.
- Common applications: Enclosures
PMMA(Acrylic)
PMMA, also known as acrylic, is a tough, highly transparent material with excellent resistance to ultraviolet radiation and weather resistance. It can be colored, shaped, cut, drilled, and shaped. With its beautiful appearance, it has a wide range of applications in the construction industry.
- Common applications: Enclosures
POM
POM is a crystalline plastic, a density of 1.42g/cm3. It has good rigidity, it is an engineering plastic with excellent comprehensive properties. POM has exhaust problems at high temperatures and is brittle at low temperatures. Glass filled, add lubrication grade available, no flame retardant grade.
- Common applications: Enclosures
PEEK
Peek (polyetheretherketone) is a kind of special engineering plastic with high-temperature resistance, self-lubrication, easy processing, and high mechanical strength, and other excellent properties. It can be manufactured and processed into various mechanical parts, such as automobile gears, oil screens, gear shift start plates; Aircraft engine parts, automatic washing machine runner, medical equipment parts, etc.
- Common applications: Enclosures
HIPS
HIPS(High Impact Polystyrene) is a bright and pure amorphous plastic. It has the advantages of easy processing, rigidity, dimensional stability, and transparency, but its low impact strength limits its application. It has a lower modulus, better elongation, and is much more brittle than crystalline styrene.
- Common applications: Enclosures
PSU
PSU is a relatively low-cost high-temperature amorphous material. It is transparent and has good radiation stability and heat resistance. Can be used at temperatures up to 300 degrees Fahrenheit. Widely used in medical equipment, machinery industry, electronic appliances, and other fields.
- Common applications: Enclosures
PU
PU(Polyurethane) is an extremely elastic, wear-resistant, and tear-resistant elastic material that can be used in ether and ester-based formulations. These different formulations cover a very wide range of hardness and density.
- Common applications: Enclosures
TPE
TPE(Thermoplastic Elastomer), also known as artificial rubber or synthetic rubber. It is a kind of elastomer that has the elasticity of rubber at normal temperatures and can be plasticized and molded at high temperatures. It contains thermoplastic and elastomer properties, which makes the product very easy to use in the manufacture of various products. Standard thermoplastic processing equipment and techniques can be used for processing and molding, such as extrusion, injection, blow molding, etc.
- Common applications: Enclosures
TPU
Thermoplastic polyurethane (TPU) is an elastic material with good oil resistance, grease resistance, and wear resistance. It is also a mature environmental protection material. It is widely used in medical and health, electronic appliances, industry, and sports.
- Common applications: Enclosures
Notes On Material Selection
Property
Influence
Adhesion
Some materials stick together when they are overmolded, while others do not. Perfect combination is the ideal situation.
Temperature
Since it is overmolded on plastic, the substrate must not deform under the heat and pressure of the molding process.
Tensile property
Most materials of overmolding will have several properties related to tensile strength, elongation, tensile modulus, and so on.
Compression Properties
It may be important for your overmoling project to know how much parts can be compressed without permanent damage.
Friction Coefficient
Friction is the force required to cross one surface over another, The surface texture of the mold is a factor too.
Hardness
Hardness property is the ability of the material to resist indentation, hardness of different materials vary greatly.
Flexural properties
The bending resistance of a material is the bending modulus. This attribute is the second factor in the “feel” of materials.
Thickness
From a design point of view, the thickness of the material will change the effectiveness of the material properties.
Overmolding is a popular manufacturing process, By overmolding, different materials can be glued together to create a variety of shapes, sizes and colors and improve the grip of the product.
Car moldings
Most automobile companies utilize this process to enhance the appearance of their car. They are installed at the hinges, insides of the door, bumper, and below the windshields.These car trims become easily customized with the help of Over Molding, and that is why every other brand flaunts the difference in their cars. It may create diverse designs, shapes, and colors within and outside the vehicle for superior functioning.
Hardware and Mechanical Tools
Hardware tools have the ability to function on the hardest surfaces, and inaccuracy at any point can result in a fatal injury to the user. When a substrate of rubber or glass material is interlocked around the hardware tool, it becomes easy to handle them as wanted. Not only does it give a better grip on the tool, but also helps to absorb the shocks and vibrations created by them.
Kitchenware & Utensils
The kitchen is one of those places that are used extensively throughout the day. All of them have smooth handles and curved edges to avoid injury and appear extensive. During the process, it is kept in notice that the substrate and the Overmolding material should not affect the food ingredients by any means, and should be safe because it comes in direct contact with hands and the food items.
Typical Household Goods
Starting right from your toothbrush, extending to the TV remotes, wipers, chargers, shampoo, and deodorant bottles, everything is using Overmolding. We use these items on a regular basis, and seldom do we consider that they are adjoined with various different elements at once to carry out the operations with ease.
Navigation Devices
With the help of overmolding, the GPS gets to be protected inside a handy structure that has smooth edges and a rigid. Overmolding also prevents the machine from any exposure to harmful elements that could disrupt the proper functioning of this device. The substrate and the thermoplastic are fixed with a mechanical interlocking to keep the body of the device in place.
Medical industry
The tools used widely by doctors, surgeons, and their medical teams are made precisely using Overmolding. Their task is a crucial one and requires apt products that prove to be handy, comfortable, and sustainable.
For examplexs: Needles, dilators, syringes, injections, patient monitors, scissors, etc.
Advantages of Overmoding Servcies
There are a handful of reasons for its preference over the other molding processes. After closely evaluating each one of them, we’ve come up with some of the most impressive advantages of Overmolding for the plastic manufacturing industry.
Performance of parts improved
The overall performance is hence increased because the user has better control of the tool due to the addition of a rubber substrate.
Reduces cost of parts
As this method is a single cycle process, This increases their production rate, and the customers receive the final item faster!
Excellent shock absorption
Overmolding is used to provide plastic resins on the product. the user may feel a reduced shock and vibration when the products is used.
Elegant structure and design
Elegant structure is a very important factor in product competitiveness, because it immediately catches the eye of the buyers.
Plastic Injection Overmolding FAQs
Overmolding is a process where two or more different materials are molded together to create a single product.
In the case of plastic overmolding, one of the materials is typically a plastic. The other material can be another plastic, metal, rubber, or even glass.
The primary difference between them is that, in overmolding, the plastic material is injected directly onto a molded part or assembly; in insert molding, the plastic is first injected into a cavity and then the finished piece is inserted into another injection-molded part.
Overmolding can reduce production costs. While standard injection molding can combine multiple parts into a single multi-cavity mold, secondary molding can produce individual parts made of different materials without assembly. Mold production is more complex, but it eliminates the repetitive cost of assembling thousands of parts.
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