Introduction to Injection Molding

The same exact part can be produced with a variety of manufacturing methods. This can vary based on desired material, part complexity, quantity, etc. If you have a part that you plan on producing in mass quantities, and do not plan on making many changes, then injection molding could very well be the manufacturing method for you!

Injection molding uses melted plastic, pushed into an aluminum or steel mold to bring your design to life. There is a wide variation of plastics used in this process. Some common choices are polypropylene, polycarbonate, nylon, and ABS, with many more available. Before proceeding with injection molding, it is essential that you ensure that this method aligns with your intentions, because while parts (when produced in mass quantities) are relatively inexpensive, the initial start-up costs can be very high. Just the cost of producing a mold is often thousands of dollars and can even run upwards of $100,000.

As much of the cost comes from the initial tooling costs, it is essential that your design is just the way you desire before proceeding. This is often achieved by producing low cost prototypes with the use of 3D printing, allowing you to have a physical representation of your part before approving the mold. Once you approve your part, you will move on to the production of your mold, and then production of your product.

Once your mold is created it is attached to the plastic injection machine. Plastic pellets of the material of your choice are then loaded into a hopper and can be mixed to a color of your choice. These pellets are melted down and a ram screw then forces this melted plastic into your mold. Meanwhile, water runs through channels in your mold to help decrease the cooling time. Once the part is sufficiently cooled, the mold opens, and ejector pins eject the part from the mold. The surface finish of your part at this stage directly depends on the surface finish of the mold. Keep in mind, you can decrease initial tooling costs by accepting a lower surface finish, and if desired, you can use secondary processes to help improve your surface finish which may save money.

There are many considerations to keep in mind when it comes to injection molding. A few important ones are as follows; avoid any thick sections of material and add ribs to add strength and rigidity. Avoid any sharp corners as this can result in weaker parts. Provide a smooth transition between two different wall thicknesses. Lastly, a draft angle should be applied to all vertical walls. This should be at least 2° and up to 5° for taller features.

A great number of factors have to be taken into consideration when designing a part for injection molding. Thanks for reading, for any inquiries or contracting services, please don't hesitate to reach out to us!