Prototype Injection Molding

What is Plastic Injection Molding?

Plastic injection molding is the process used to create the plastic parts that are used in most of the products you use every day. Plastics are used in a wide range of applications, from simple buttons to complex implantable medical devices visible under x-ray and everything in between. This is why plastic resin manufacturers offer over 60,000 grades of plastic. Plastics are well suited for manufacturing due to their relatively low cost per part, part consistency, and ability to fabricate large numbers of parts quickly.

The basic principle of injection molding hasn’t changed substantially since it was first patented in 1872. Over the last 150 years, innovations have involved the addition of electronic control and automation of the molding process. Plastic injection molding consists of two essential parts: an injection unit and a clamping unit. The injection unit is where the plastic resin is added to the machine, and heat is applied to change the plastic resin to a flowable liquid state. The clamping unit contains the mold.

The mold is a machined assembly that contains the part detail to be molded. Once the mold is split into two sections, it allows the clamping unit to open and close the mold as needed. In order to mold a part, the clamping unit closes the mold, and the injection unit pushes the liquid plastic into the mold. The plastic quickly cools. The clamping unit opens the mold, and the part is ejected. The process then repeats.

Machine Fabricating a Prototype Mold for a Client

Prototype Injection Molding Process

When developing a new product, it is typically necessary to fabricate a prototype injection mold to perform functional testing of the product. There are a couple of key reasons engineers utilize a prototype injection mold rather than a production mold. A production mold typically takes 2-3 months to fabricate. It would be a very long time to wait for parts. Prototype molds can be fabricated in as little as one week, allowing engineers to proceed more quickly with testing.

Typically, engineers discover during testing that their part design needs changes in order to meet product requirements. In that case, a mold iteration is needed. Prototype molds are faster and easier to iterate due to the softer metals that are used. Iterations are typically completed within a few days. Production molds are made out of hard steel. While mold iterations are possible in production molds, they tend to affect the mold’s life negatively. Ideally, the part design is finalized when the production mold is fabricated, and no iterations are needed. This allows the production mold to meet the full life cycle and optimize the investment.

Protoshop Team Member Working With Arburg Allrounder Injection Molding Machine - Injection Molding Process Graphic

What Types of Materials are Used?

Materials that are compatible with injection molding are known as thermoplastics. Within thermoplastics, there are approximately 70 different types. Commonly known types include polycarbonate, polypropylene, nylon, etc. Each thermoplastic type has a set of unique characteristics and usage scenarios that distinguishes itself from other types. Material selection for a part can be challenging because the engineer must be familiar with the 70 different types and know which type to select for the particular application.

For example, polycarbonate would be an ideal type to select if a part requires transparency and high strength. Once the type is selected, the next step would be to select a particular grade of material. Websites such as matweb.com and ulprospector.com are helpful plastic resin databases that make it possible to select a particular grade.

Continuing to use the polycarbonate example previously discussed, we find that there are over 6000 grades of polycarbonate available. Selection of a particular grade requires a review of the part design and its product requirements such as mechanical, cost, tolerances, environmental conditions, assembly, sterilization, regulatory, aesthetics, and any special requirements.

For example, this polycarbonate part may be a relatively thin wall part requiring a high melt flow grade. It could also be a medical part requiring gamma sterilization, requiring an additive to prevent color shift. These requirements can be searched on matweb.com and ulprospector.com to compile a list of the grades that meet those requirements. The final step would be to contact the distributors of those material grades for pricing and availability, then place an order for the selected grade of polycarbonate.

Arburg Molding Machines

Protoshop uses only Arburg injection molding machines, a high-quality brand built in Lossburg, Germany commonly used in production injection molding.  Our goal is to replicate production molding as closely as possible and using a production quality injection molding machine is critical.  Testing and development using a high quality prototype part that closely replicates production makes transfer to manufacturing an exercise rather than a step involving risk.

Arburger Allrounder 370E 600-170 EDrive Injection Molding Machine
Complex Part Design Image - Complex Geometry

Complex Part Geometry is Our Specialty

We specialize in challenging molding applications.  We have successfully designed and fabricated thousands of prototype molds and don’t reject complex part geometry like other prototype molders.  If a part is moldable, we can do it.