Overmolding is a process whereby one product is made using two or more materials. Typically, the (TPE) is often molded over another material. In this article, we look at overmolding materials and overmolding in general.
The base material is commonly referred to as the substrate, and the overmold materials entirely or partially cover it during the manufacturing process. In connection to that, over-molding is categorized into three main types. They include:
- Insert Molding
This procedure is popularly used to mold soft elastomers over rigid plastics. Insert molding is the most affordable form of overmolding. Ordinarily, the base material is placed in the injection mold and covered with a hot molding material resulting in an assembled product. The elastomer must be sufficiently subjected to some heat.
- Two-shot Molding
As the name suggests, the two-shot molding is an overmolding technique that needs two injection molding machines. The hard components are inserted into the molding machine, and the elastomer is added.
The substrate is heated to a gel or semi-solid state. It’s then transferred to the second machine, and the process is repeated. The molds should feature the intended shape of the final product. It’s should also promote mechanical bonding.
Co-injection Molding
Although both the hard component and the elastomer are forced into one mold in co-injection, you must ensure the materials are compatible. The process is also carefully monitored.
Compared to the first two methods, co-injection is more costly and difficult to control. But since both elastomers are in a completely molten state, the bond created is robust, resulting in high-quality products.
Overmolding Materials
In overmolding, there are endless combinations of substrates and over-molded materials. Adhesion and compatibility are the most critical factors to look at when selecting the pairs. It’s also vital to control the thickness of the over-molded material.
The materials used during the process must be thermally and chemically compatible. Metals substrates are compatible with any plastic mold, but you may encounter challenges incompatibility when overmolding plastic with plastic.
If the materials aren’t compatible, you’ll end up with a deformed or inferior quality product. Fortunately, you can implement mechanical bonding features if chemical bonding isn’t possible.
Some of the materials used in overmolding include:
- HDPE(high-density polyethylene)
- ABS(acrylonitrile butadiene styrene)
- PEEK( polyetheretherketone)
- PEI(polyetherimide)
- POM (Acetal Copolymer)
Choosing the appropriate overmolding material is crucial to producing high-quality products that will remain competitive in the market. Since the possible material combinations are innumerable, you may be overwhelmed with what to use.
In this case, it’s advisable to seek the opinion of a resin expert. The specialist will advise you on the bonding compatibilities, inherent properties, cost, regulatory compliance, and appearance, including other critical aspects.
Besides, you can rely on information from the overmolding materials manufacturers; they usually provide compatibility charts.
Final Thoughts- Why Overmolding
Overmolding helps manufacturers to add a soft-touch exterior to products. This aspect improves the feel or grip besides providing appealing designs to attract customers.
The procedure also helps to come up with products that can withstand vibration, UV light, and offer electrical insulation.
These factors increase the usability and durability of the products. Overmolding enhances customer satisfaction and lowers production costs.
