The insert molding process is one of the most cost-effective manufacturing processes used by manufacturers. It eliminates post-molding assembly and separate parts installation, saving production time and reducing motion waste. It also reduces component weight and size and seamlessly improves the strength of parts by combining the physical strength of metal inserts with plastic resin.
What is an insert molded part?
An insert molded part is a preformed, often metal, part that’s loaded into a custom mold with space for additional plastic to be injected around it. This process allows the creation of a single-part assembly that is stronger, more durable and less expensive than multiple component parts assembled with adhesives or mechanical fasteners.
Insert molding is ideal for integrating parts that are difficult to machine or create in a single shot. For example, it’s a great choice for components that require threaded areas like a bolt-on cover on an electronics housing unit, medical instrument case or plastic air or hydraulic manifold. It’s also a great solution for a plastic door handle or knob that screws into a threaded stud, or a plastic water bottle that has a threaded lid.
The advantage of insert molding is that the molten plastic surrounding the metal encapsulates it, providing a strong, rigid bond that resists vibration and shock. It also helps prevent design issues like loosening and misalignment. It can also significantly enhance the overall reliability of a part by increasing its tolerance for temperature and pressure.
It’s important to select the correct type of metal for your insert based on the material requirements for the project. For instance, the insertion point should be able to withstand the high temperatures and pressures of the injection molding process. It’s also a good idea to choose a metal with a low coefficient of friction for the application. This will ensure that the insert remains in place and isn’t damaged during injection or subsequent assembly.
Inserts are usually made of metal or other materials with a high melting point. They can be hand-loaded or robotically into the customized mold before a stream of molten plastic is injected over them to create the final part. The most common metals include stiff, engineering-grade plastics such as Delrin and nylon, but some parts are made of more elastic liquid silicone rubber (LSR). At Protolabs, where all our quick-turn molds are aluminum, hand-loading inserts into a tool that’s been heated to several hundred degrees takes a bit of skill. If you’re not careful, you can burn your fingers.
Insert molded parts are available in a wide range of shapes and sizes, including some that can’t be produced with other manufacturing methods. It’s a popular option for industries that need to produce lightweight automotive components and trucking equipment in order to meet fuel economy standards. It’s also an excellent choice for medical devices, where precision and durability are critical. The process also enables designers to incorporate features that aren’t feasible with a traditional metal fabrication method.