If you’re designing a product with a metal component, insert molding offers a cost-effective way to create a one-piece part. The process involves placing a preformed metal insert (like threaded inserts, electrical components, or other metal reinforcements) into an injection mold. Molten plastic is then injected around the insert, encapsulating it and creating a unified part. Inserts can be made of a variety of materials, including metals like brass and stainless steel, as well as ceramics and other plastics.
In addition to reducing costs, insert molding allows for increased part reliability. As the metal is firmly held in thermoplastic, it prevents loosening, faulty terminations, misalignment, and other design issues. It also improves the design’s resistance to shock and vibration.
Insert molding is ideal for products that require a durable yet lightweight construction, such as connectors, dash panels, electric sockets and wires, dials, remote control coverings, handles, and surgical implements. It can be used in conjunction with other molded parts to reduce stress on joined components, or to add a decorative element to the finished part.
The key to success with insert molding is careful design. The metal inserts must be strong enough to withstand the intense heat and pressure of the injection molding process. A metal-overmolding specialist can help you determine which type of metal to use for the best results. You’ll also need to consider the dimensions of your plastic overmold and the design of your inserts. Inserts with threaded holes, for example, must be designed to allow the threads to properly close after the molding process.
Typically, inserts must be a separate fabrication from the molded part, which increases the time and expense of production. This can be avoided by incorporating the insert into the initial design of the part, or by using a multi-material molding process that utilizes both injection and compression molding technologies to simultaneously form the overmold and the metal insert.
Injection molding experts can also provide guidance when designing a part for insert molding. Typical moldability guidelines, such as adding draft to aid in the release of the molded part and maintaining consistent wall thickness, apply equally well to insert molded parts. In addition, a design for manufacturability (DFM) review is essential when designing a part for insert molding to ensure that the part can be produced with inserts of varying sizes and shapes, and that the inserts are positioned where they’re needed in the final molded product.
Robotic systems can also lower production costs by removing the need for a human operator to load the inserts into the injection mold. This translates into cost savings that can be passed onto the customer. Additionally, these systems can handle multiple jobs at once, which leads to higher productivity and a lower per-part price.