What is injection molding?
Injection molding is process tailored for producing large volumes of parts. Compared to other manufacturing technologies—like CNC machining and 3D printing—it requires an upfront, capital investment into tooling. But individual piece-part price will be substantially less when compared to other means of manufacturing plastic parts. This cost structure makes it an affordable solution for production runs.
It's most often used for the manufacturing plastic parts at scale due to its low material waste and low cost per part. It’s an ideal manufacturing process for industries like medical devices, consumer products, and automotive to name a few.
How does injection molding work?
Once an injection molding design is finalized the first step is to create the tooling.
The plastic part production begins by loading resin pellets. The temperature of the barrel is raised until the pellets reach a molten state and are then compressed.
Finally, the molten plastic is injected into the metal tool which then feeds into the mold cavity. The part cools down, solidifies, and is ejected from the tool.
What are injection molding tools made from?
Usually it is made from a metal block of steel or aluminum. A CNC mill carves out the negative space of the plastic part.
What types of injection molding are available?
The 4 most common are:
- Thermoplastic injection molding - the most common type of molding. It injects resin into the mold where the material cools to form the final part.
- Liquid silicone rubber molding - a thermoset material and a chemical reaction creates the plastic part.
- Overmolding - used to manufacture plastic parts with two or more materials. You’ll often find this on parts to improve grip by adding rubber to the handle.
- Insert molding - an insert component is placed into the mold before resin enters. The material is then injected and flows around the insert, typically metal, to form the final part. This is frequently used for parts that require metal threads.
What resins are available?
Different materials should be used based on the specific needs including properties like chemical, heat or UV resistance. Common materials include:
- ABS: It’s reasonably priced, strong and is easy to work with.
- Acetal: A strong material with good lubricity.
- LCP: A strong material that works well especially for thin parts.
- Nylon: Affordable, strong, and wear resistant but is susceptible to shrink and warp.
- Polycarbonate: Tolerates higher temperatures and more durable than a typical ABS but lower moldability.
- Acrylic: An affordable option for clear parts although it can be brittle.
- Polypropylene: A cheap material and good when cosmetics and rigidity aren’t a priority.
- Polyethylene: High and low density options. Is durable and chemical resistant.
- Polystyrene: A hard thermoplastic that is cheap and clear.