Over-molding is a common molding process typically used to manufacture complex parts. It plays a vital role in different industries, including electronics, medical, automotive, and aerospace. So what is over-molding? How does it work?
I. What Is Over-molding?
Over-molding needs to put the material into the packing tank at a high temperature to melt, and then inject the melted material into the mold through the internal screw to finalize the mold. Over-molding is characterized by the ability to produce two kinds of products of different materials at one time. It will first shoot a relatively hard rubber and plastic skeleton, and then immediately move to another mold, and inject soft elastomer to cover, which is called cladding injection. The steps sound simple but completing them is not easy, need to be equipped with a special machine, as well as a more complex mold to achieve. Although over-molding requires a higher initial input cost than injection molding, the advantages and characteristics of over-molding can bring greater profits in the market.
II. What is The Benefit of Over-molding?
(1) Good user experience and good shape
Over-molding can combine two different materials to make the product easier to use. For example, the handle of a toothbrush can be coated with a soft material over a rigid frame to provide a better tactile and anti-slip effect. Even if the color of the raw materials is different, the over-molding will not mix, and the design of the product’s appearance is more flexible.
(2) Simplify the manufacturing process, and improve efficiency
Generally injection machine usually only has a packing slot, while the over-molding machine has more than two, when the injected product is combined with more than two kinds of materials, generally, the semi-finished product needs to move to the second machine. But specialized over-molding machines condense these processes in one machine. Because the whole manufacturing will complete in one machine, the process is automatic. And the biggest advantage is that the automatic process can assembly mistakes, further greatly improving production efficiency.
(3) Stronger quality
For complicated electronic accessories, over-molding can isolate important parts of the product from air and water and even prevent the influence of electricity and heat, so that electronic products can operate in the most stable environment. Compared with the traditional manual assembly parts, the automated over-molded products have better fineness and tightness.
III. What Raw Material Can Be Applied in Over-molding?
·Common hard materials
- PE plastic
PE plastic is composed of polyethylene, which is the most common plastic in our daily life. Plastic bags and opaque plastic containers are almost all products of PE plastic. PE plastic is so widely used because its nature is very stable, has heat resistance, corrosion resistance, and high hardness but low friction, and it can meet most use occasions, so it becomes one of the common materials in over-molding.
- ABS plastic
The characteristics of ABS plastics are mainly determined by three chemical substances, acrylonitrile, butadiene, and styrene. By increasing the proportion of specific substances, the corresponding performance can be improved. For example, ABS plastics with a high acrylonitrile ratio are quite heat-resistant and can be used in products such as hair dryers or irons. A little more butadiene can be used in helmets that need to be crash-resistant. And a higher proportion of styrene can create thinner ABS products, such as mobile phone protection cases. ABS plastic with high adjustability can be used in a wide range of fields, from automobiles, and aerospace to daily necessities.
(3) PA plastic
PA plastic is made of polyamide, but perhaps more commonly known as “nylon”. PA plastic has high hardness, heat resistance, and electrical insulation, so it is often used to produce industrial products and daily household appliances
·Common soft materials
(1) Silicone rubber
Silicone rubber is soft, non-toxic, and can withstand temperatures from 220°C to -40°C, making it ideal for containers, conveyor covers, and related contact products for the food processing industry. The waterproof and electrical insulation of silicone rubber makes it popular in electronic products. It can not only block contact between internal and external products but also improve the service life of electronic products.
- TPU material
TPU, also known as thermoplastic polyurethane, has excellent wear resistance, weather resistance, oil resistance, and elasticity. TPU is also a very good material for over-molding, which can protect the gaps between components from external substances and improve product life. Its property makes it easy for the user to hold the handle without slipping.
- TPR material
TPR is called a thermoplastic rubber elastomer. Among many thermoplastic elastomers, TPR owns unique softness. It can also be combined with other additives to improve the hardness or tensile strength. This material has a high degree of environmental protection, so it is one of the most eye-catching over-molding materials.
IIII. What Are The Applications of Over-molding?
(1) Automotive Industry
The car is equipped with many devices that need to combine multiple materials, such as control Windows, sound, screen, and other panels. This kind of equipment often needs to overcome the situation of high temperature and high ultraviolet, so the use of sunfast and high-temperature resistant material is necessary, such as ABS plastic combined with silicone rubber is very suitable. For the automobile industry,over-molding can improve the precision of the work at the same time, and further reduce the cost.
Medical products can be roughly summarized into two categories, the first is consumable products, including tubes, syringes, aseptic packaging, etc. Take the piston of the injection needle as an example, the part of the push rod is made of PE plastic with low cost and stability, combined with a soft rubber pad, which can save the time of manual assembly and reduce the cost of disposable consumables. The second is implanting medical organs, such as artificial blood vessels and artificial joints. In addition to non-toxic and accurate size as the main consideration, most of these devices need to combine a variety of materials to function, so over-molding can be the best solution.
(3) Electronics industry
There are a lot of small parts in electronic equipment. The traditional production mode is to produce a large number of parts through molding and then manually assemble them. However, as the parts of electronic products become more and more precise with the increasing number of small parts, the advantages of over-molding are more and more critical, including reducing the process, improving the dimensional accuracy, the tightness higher than the artificial bonding, etc.,
Over-molding is one of the injection methods, although the capital of the early investment is higher, it also needs more mold professionals than the general injection molding to design high-quality products, but in terms of long-term investment is the most affordable choice for composite material products. We support one-stop customized services from design prototypes to manufacturing. We also acquire multiple molding:
·Silicone injection molding
·Silicone compression molding
·Custom silicone molding