In plastic molding, a number of manufacturing techniques are employed. Two prominent methods – two-shot and overmolding – are practical processes that offer strategic advantages for manufacturers. In this post, we will examine the two-shot and overmolding manufacturing processes – what each entail, as well as their advantages for plastic manufacturers. 

Two-Shot Molding

Two-shot molding, also known as double shot molding, is a process by which molded parts are produced using two different materials. This method is used to manufacture complex parts and involves molding plastic around a pre-formed metal or plastic insert.   Specifically, the process occurs on one machine capable of two injections in a single cycle. To produce the main piece of the product, the machine injects one material into a mold through a nozzle. The mold then rotates and the second injection of a different material, and through a different nozzle, follows to form the next piece. The two pieces are compatible, and their resins bond together to create a multi-resin, molded part. Once the process is complete, the part cools and is ejected from the mold.  Two-shot molding is well-suited for more complicated products, especially those produced in high volumes. For parts that require multiple materials, various plastic colors, specialty designs, graphics, and finishes, two-shot molding is an ideal solution.  Some key advantages of the two-shot method include:

  • Lower unit cost
  • Minimal waste and cost resulting from assembly defects 
  • Superior product quality and integrity 
  • Minimal need for manual processes, such as handling and secondary assembly 

Overmolding

Aptly named, through the overmolding process, an additional layer of material is applied over an existing part or piece. Overmolding is commonly used to produce parts, as well as pieces and sub-sections of parts. It is especially useful in the development of prototypes and is often used to add color, texture or crucial components to the surface of a piece.  Specifically, the process involves placing the first piece into an injection molding tool and shooting the overmold material into or around the piece. The overmold materials solidify and bond to the initial piece to form a single part.  Overmolding offers versatility in terms of the materials manufacturers can utilize, as virtually any type of plastic or resin overmolding can be used with a metal piece. Overmolding plastics with another plastic piece carries more limitations, so it is important to ensure that the materials are compatible before beginning the overmold process.  Some other valuable benefits of overmolding include:

  • 1.Flexibility in design
  • 2.Minimal need for manual processes, such as handling and secondary assembly
  • 3.Reduced costs related to assembly and labor 
  • 4.Enhanced part strength and structural integrity 

Conclusion 

Both two-shot molding and overmolding represent advanced manufacturing processes in injection molding. These methods provide manufacturers with options for complex parts and products that require multiple and different materials, finishes/surface treatments and components. 
However, the tolerances involved are tight and very specific – requiring superior attention to detail and a high level of technical expertise. For these reasons, two-shot molding and overmolding are difficult processes to master and often intimidating for manufacturers. But that does not mean the benefit of these advanced manufacturing methods is unattainable for manufacturers. By partnering with a company that specializes in these processes, organizations across the manufacturing spectrum can realize the benefits of overmolding and two-shot molding.

Your One-Stop-Shop 

New Berlin Plastics offers a host of custom injection molding services and solutions, including: 

  • Scientific Injection Molding
  • Part design assistance
  • Design-for-manufacturing services
  • Resin selection assistance
  • Mold design
  • Tool maintenance

Customers benefit from a variety of press sizes – ranging from 4 to 1200 tons – which gives New Berlin Plastics the ability to manufacture parts of varying sizes and complexity. Our tightly controlled scientific injection molding practices raise our services to the highest level of precision and allow us to create parts – simple or complex – in a repeatable and dependable way.

Learn More 

To learn more about our multi-shot molding capabilities, contact us today