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By far, most of the plastic parts that you see around you today were manufactured by injection molding. Injection molding manufacturing has the ability to economically mass-produce plastic parts by the thousands and the hundreds-of-thousands. That makes it the number one go-to for the manufacturing process for many designers and business owners. 

Injection Molding – Basics

Injection molding is a formative style of manufacturing. It is accomplished by forcing melted plastic into a mold. When the material cools and starts to harden, the part is ejected and more melted material is again forced into the mold. 

The time it takes for the material to harden enough to be ejected is the main factor in the time length of each cycle. But an advantage of injection molding over other types of manufacturing is the ability to produce more than one part at a time. Depending on the size and complexity of the part being produced, the mold can be made to produce multiple parts per cycle. 

A variety of plastics are available to be used to make your part. Different types of plastics provide their own characteristics to your needs. Some will provide a hard, ridged product, others will produce one that is soft and flexible. Fibers and coatings can be added to provide durability, abrasion resistance, and flame retardance. 

What are the benefits of injection molding?

Economical high-volume production: Once the mold is produced and the production machine is set up, manufacturing parts is exceptionally quick when compared to other manufacturing processes. A typical injection molding cycle ranges from 15 to 60 seconds. The time largely depends on the size and complexity of the part. CNC machining and 3D printing may take minutes or hours to produce the same part. Since in many cases multiple parts can be produced at the same time, hundreds of thousands of identical units can be manufactured per hour. This high-production output rate makes injection molding the most cost-effective manufacturing process of identical plastic products.

Produces detailed features with tight tolerances: Injection molding can produce parts with tolerances compatible to that of CNC machining and 3D printing. The advantage is that it can do it at a high rate of output. CNC machining and 3D printing do not come close. The melted plastic in an injection mold is subjected to extreme pressure. This extreme pressure allows the mold to produce highly complex and intricate details and geometries. Again, it can do this repetitively and economically at a high rate of speed.

Wide-range of materials and additives available: Almost all thermoplastics can be used for injection molding. In addition, some thermosets and silicones also can be used. Injection molding allows different types of plastics to be used simultaneously. Different plastics add to the properties desired in a part. Glass, fibers, rubber, minerals, and flame retardants can all be added to the plastic to modify its properties. The variety of plastics and enhancing additives gives your part the desired stiffness, flexibility, strength, and impact resistance. You are given much variety of material choices to reach your required design standards.

What are the limitations of injection molding?

The main limitations of injection molding revolve around the mold itself. Ranging in price from $5,000 to $100,000, molds are very costly to make. So, there is a high startup cost. For this reason, injection molding is not recommended for production runs of less than 500 units.

If you need to make a design adjustment to mold, it is neither easy or cheap. You may even have to pay for new mold to be made. To keep from having to make costly mold design changes, follow these three steps:

Have a part prototype made with CNC machining or 3D printing. Check the part for end-use and have any necessary design changes made.

Use 3D printing to produce a low-production run mold. It will be able to make a few thousand parts. Verify the usability of the parts being made.

Have a high-volume steel mold in production.