Understanding Polymer Manufacturing: Injection Molding

Injection Molding Parts

In this series of “Understanding Polymer Manufacturing,” we will dive into different processes in which AxisNorth has experience. In each of these processes, AxisNorth has developed strong relationships with highly vetted suppliers over years of working together. The first question we will answer in this series is “What is injection molding?”


Injection Molding

Injection molding is the process of molding polymer components into a predefined mold state. Injection-molded plastic parts are used in endless applications. It is known as one of the most versatile plastic-forming processes. Versatility is not the only reason for injection molding’s popularity. Three other major factors that we have noticed to be important include.

  • Relatively low cost per unit: creating a mold is the most expensive part of the process. A single injection molded tool can run from $5,000 to $150,000, depending on the complexity of the mold and the number of cavities. On average a single injection molded piece costs between $.03 to $.15.
  • Efficiency: The typical cycle time for each injection molded part ranges from 3 seconds to 3 minutes. For large estimated annual usages (EAU) this quick cycle time allows parts to be produced equally as fast. Unlike processes such as rotomolding where cycle times can be upwards of 45 minutes. Injection molding allows for quick output.
  • Consistency: Injection molded polymer materials can withhold tolerances down to thousandths of an inch. This precision allows highly complex pieces to be produced without any noticeable difference to the human eye.

Materials Used in Injection Molding

Injection molding utilizes a wide variety of materials. Some of the more popular materials include acrylonitrile butadiene styrene (ABS), nylon polyamide (PA), polycarbonate (PC), polypropylene (PP), and polyethylene (PE). But these are not the only plastic materials used, there are many different types of injection molded materials that are enlisted for differing applications. Determining the right material to use is paramount to creating good injection molded parts, utilizing the expertise of the manufacturer of your choice for the process will be crucial to the success of your project. Also, the experts at the manufacturer will ask the proper questions which will help determine what material will fit your application properly. All in all, be sure that you know the proper material for your application.

How does Injection Molding Work?

There are multiple different steps in the injection molding process. We have covered the importance and different materials utilized. Now we must talk about how the sausage gets made. We have broken it down into 4 steps.

  • Melting and screwing material: Injection molding equipment are highly complex machines, but the process within the machines is easy to understand. First raw material is dumped into a large hopper at one end of the machine. The material is then fed into a large screw in the machine (called the barrel) which pushes it towards the mold. While traveling down the barrel of the machine material is heated into a molten plastic. Allowing it to conform to the mold when it reaches the end of the barrel.
  • Injecting material into the mold: Reaching the end of the barrel the molten material is injected into the mold. Molten material fills each crevasse of the mold to create the shape of the desired component.
  • Cooling time: Molten material is captured in the mold then it begins to cool. During this time the mold stays clamped shut and allows the material to cool. This process is known as holding time and varies between parts. As we talked about earlier with cycle times. Cycle time is the process that has large variances of time. We see anywhere from 3 seconds to 3 minutes for holding time to be complete. Holding time makes certain that the component is properly formed and won’t change drastically after it is removed from the mold.
  • Ejection of the molded component: Lastly the mold splits apart and allows the molded component to fall out. When the component is ejected from the mold it will need to be finished by hand whether it’s trimming excess material or assembly components needed to complete the part.

Injection Molding at AxisNorth

AxisNorth is a single source for everything plastic and rubber. Meaning, when you come to us, we will help source the proper process. Coordinate the manufacturing effort. Bring in bulk quantities to store in our warehouse. Provide logistic services to ship the materials we store and lastly, we can complete in-house assembly on components that are required. Over thirty years of experience in the polymer industry has allowed us to build strong relationships with injection molding suppliers and develop our own expertise to best assist you on your next injection molded project. Before you start your next injection molded project come to AxisNorth and let’s work on your solution together!