Overmolding vs. Insert Molding What’s the difference?

What Is Overmolding?

Overmolding is a multi-step injection molding process where two or more components are molded over top of one another. Overmolding is sometimes referred to as two-shot molding because it is a two-step process.

First, a base component (otherwise known as a substrate) is molded and allowed to cure. Overmolded substrates are often made of plastic. Then, a second layer is molded directly on top of the first to create a single solid piece. Overmolding is commonly used to manufacture plastic parts that feature a rubber handle. The two-shot process of overmolding a toothbrush, for example, consists of forming a base layer for the plastic handle and a top layer of rubber (to make the toothbrush less slippery to hold).

Why Choose Overmolding?

Overmolding is a versatile process that has numerous benefits:
  1. Increased Material Flexibility – Overmolding allows designers to leverage the benefits of multiple types of materials to create complex parts with different properties, add visual complexity, or add haptics.
  2. No Adhesives Required – Overmolding allows different materials to be fused in the mold, thus eliminating the need for glues or other permanent bonding methods. This increases the part’s overall durability and reduces assembly costs.  
  3. Embedded Seals – Overmolding offers the option of molding soft seals into parts. An example would be an electronics enclosure that needs to be IP rated. Usually, the part will have a groove into which an o-ring can be installed later. However, it is far more cost-efficient and robust to permanently mold the seal as an integral component. 
What Is Insert Molding?

Insert molding is another form of injection molding where a secondary part is formed over a substrate. The differentiating factor between insert molding and overmolding is that insert molding is performed with a pre-existing substrate (base or inner component). A prefabricated part (often produced in a completely different facility or procured from another company) is inserted into a mold, and then a secondary layer is formed around it.

Insert molding is often used to add a plastic layer on top of a metal one, for example, to add a plastic handle to a metal screwdriver. You can also use insert molding to manufacture insulated pipes, wiring, and other similar products, or embed electronics into plastics.

Why Choose Insert Molding?

Insert molding is a versatile process that has numerous benefits, some of which are listed below.

  1. Reduced Assembly Cost – An injection molding machine can create thousands of parts per day. Such economies of scale can significantly reduce the cost of the individual parts. In a typical CNC machined, sheet metal, or additive manufactured part, any required assembly can be a major bottleneck. Insert molding can be used to eliminate assembly and thus maximize cost savings.
  2. Part Performance – In general, plastic parts are less robust than their metal counterparts. However, plastic offers other benefits such as reduced cost, superior design flexibility, and lighter weight. Combining both metal and plastic materials into one part can capitalize on the benefits of both. Metal inserts can be used where strength and stiffness are required and the remainder of the part can be made of plastic to reduce weight. Moreover, plastic parts do not fare well against wear and tear and metal inserts add an element of durability to parts to withstand any kind of cyclical loading.
If you want to know more about the two technologies or need to choose the best one for your parts, welcome to visit our injection molding service page.

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