A Short Guide to the Injection Molding Process

By | May 30, 2017

Numerous breakthroughs have made the process of injection molding more predictable and cost-effective. When workers learn about the process with Paulson Training Programs and they apply that knowledge to real-world scenarios, the industry continues to move forward. Several factors are crucial to the process of injection molding, such as:

  • Melt temperatures
  • Barrel and nozzle temperatures
  • Flow rates

  • Screw back and plastic pressure

  • Cooling times and rates

These factors are discussed in detail in the sections below.

Melt Temperatures

Plastic melt temperatures are a combination of various settings and factors such as barrel, mold and nozzle temperature. The latter two are related to the flowability of the plastic that’s being moved through the mold, and the mold’s temperature is directly related to the capability of the plastic to flow through and cool during the process. Barrel temperatures are an important consideration as well. When they’re set too high, flash and overflow can occur; when they’re set too low, melt lines, unfilled parts, and ripples in finished products can result.

Nozzle Temperature

It is important for the nozzle temperature to be lower than the barrel temperature. If it’s too high, melted plastic will drool through the nozzle. If the temperature is too low, the plastic may decompose. Materials can block the nozzle, causing the creation of poor-quality components.

Plastic Flow Rate

The flow rate needs to be able to support the ability to inject heated plastic into the mold as fast as possible until it is 95-99% full. Flow rates determine the plastic’s viscosity as it goes into the mold’s cavity. When the hold pressure is too high, flash and overflow can result, and pressure that’s too low can cause void issues.

Timing and Cooling Rates

The cooling rate is the difference between the melt and the mold temperatures, which are established by using manufacturer-recommended materials and customer-requested temperatures. Cooling time may be established based on mold and part designs as well as the materials used. To fine-tune cooling times, companies must consider customers’ expectations, part appearance, requested size and desired properties.

With knowledge and experience, injection molding companies can advance deliverables while supporting quality production and timely delivery. Thanks to training programs, companies can focus on ethics, safety, quality control and reliability.