Over-molding is a manufacturing process that combines two different types of plastic together to create a single part. Typically, this involves the use of a hard plastic and a softer plastic (often rubberized). Alternatively, this method can be used to bind two hard plastics together that are different colors. Overall, this is a process that takes various materials with different properties and combines them into a single molded component.
The over-molding process is accomplished through the use of two separate injection molds. To begin, the substrate, which is the first shot (and usually a rigid plastic), is made using the first injection tool. The rigid part is then removed and placed into a separate injection mold tool where the second shot, or over-mold, is molded over the first part. In most cases, mechanical bonds are designed into the part to allow the over-mold to stick to the substrate. These mechanical bonds are formed by creating areas in the substrate (first shot) where the second shot (over-mold) would flow into during the over-molding process.
Over-molding is a value-added technology that is used to provide additional functionality and decoration to parts. It is most often used for its durability for the creation of ruggedized products. It can also be utilized for decoration to provide benefits such as increased aesthetics and functionality. Over-molding can give a product a soft, rubberized feel, making it much more comfortable to handle compared to hard plastic. It also allows for hard edges to be smoothed over and rounded. The main functionality benefit of over-molding is the ruggedized and non-slip surface that it creates, which keeps products safe in extreme environments. Additional benefits include the reduction of unwanted vibrations or noise, increased protection against liquids, and additional brand identity opportunities.
As a technology utilized throughout a variety of industries, such as aerospace, over-molding is an excellent option for customers who are interested in soft-touch handles, grips, etc., or multi-colored buttons, switches, or knobs for their products. Additionally, this process is a great option for sealing or gaskets on parts. Over-molding a gasket on a plastic substrate bonds the gasket material to the substrate, which helps to prevent moisture ingression, as opposed to using a rubber or die-cut gasket that is pressed/held together by screws
Common applications for over-molding within the aerospace industry include aircraft seating, lavatories, stowage bin latches, handles, and user interface switches. Instead of having to create two different parts that then require additional assembly to fasten them together, over-molding allows for multiple parts to be formed into a single part at once. Since the second shot is molded over the first substrate, the bond created between the two is much stronger and more durable, as well as results in a clean design. The key advantages that aerospace applications take away from over-molding include:
- Decreased weight
- Increased strength and durability
- Enhanced industrial design
- Elimination of additional manufacturing and assembly steps
- Reduced manufacturing and assembly time
Since this process involves the use of two separate tools, it is a great method for lower volume programs, but is inefficient for high-volume projects. If you’re looking for a high-volume over-molded part, a better technology to employ would be two-shot molding, which uses a single two-shot mold.