One of the most versatile design practices in plastic injection moulding is known as overmoulding. This is a multi-step process that combines two or more moulded components, one over the top of the other to form a more complex component. The process of overmoulding design is also called two-shot moulding, due to the fact that it takes two stages to complete. Here is a short overmoulding design guide to cover some of the basics.
What is overmoulding used for
Overmoulding design is used for a wide range of applications across many different sectors. It is a common manufacturing process used when there is a need to create a plastic item that has a rubber handle, such as a toothbrush for example. The plastic brush offers excellent hygiene properties, while the rubber handle makes the item easier to hold while. Other applications include surgical instruments made from plastic overmoulded with rubber for the exact same reasons as the toothbrush.
Many hardware tools are manufactured using overmoulding design and techniques, including screwdrivers, pliers, hammers and pocket knives. Household items made using an overmoulding design include mirrors, kettles, pens, plastic food containers, cookware and multi-port chargers. Then, the automotive industry uses the technique for making car trims for bumpers, wheels, door sides and interior finishes. These are often overmoulded with metals or metal plating for added strength.
How does overmoulding design work?
Plastic overmoulding design involves a number of key actions. First of all, the base component is melted, moulded and allowed to cure. This is often made from a plastic substrate, due to its versatility, high tensile strength and durability to withstand the overmoulding design process. Next, a second layer of plastic substrate, or a different type of material, is moulded directly on top of the first one. This creates a single, solid part that can be extracted from the moulding machine and allowed to harden and cool.
A range of plastics can be used for the overmoulding, including ABS (acrylonitrile butadiene styrene), nylon (polyamide), PE (polythene), PMMA (acrylic) and SI (silicone). These plastics all have very different properties that suit different applications. They all have high strength, good hygienic properties and are easy to shape, and colour to match highly precise specifications.
Why choose overmoulding design?
Overmoulding design allows you to manufacture products that have more than one finish , colour or type of material. It generally takes less time than other methods to create a comparable product. This also saves costs and employee hours.. It also does away with the need for more complex product assembly processes, resulting in a more durable design. It is especially effective for the prototype stage of product development as you can create highly precise components in smaller numbers. It is also highly effective for parts that will not need to be taken apart again once assembled.
Overmoulding can come with higher up-front costs for materials, however and the machines can be more complicated to set up. This means you need to watch out for overmoulding shrinkage issues and other injection moulding defects.
Plastic overmoulding tips
Your plastic injection moulding team will be able to advise you on the most effective overmoulding design and techniques to create the results you are looking for. There are various indicators to watch out for when assessing the quality of an overmoulded design. In particular, uniform overmoulding wall thickness is important to achieve in order to ensure stability in the final product. The overmould material’s thickness should be the same or higher than the substrate and its melting temperature needs to be lower. Check the parting line optimisation too, for added integrity and signs of a high quality finish.
