Laszeray Technology

How Does the Injection Molding Process Work?

Injection molding is a manufacturing process compatible with almost any kind of plastic resin. It can yield parts in various sizes and levels of complexity, making custom injection molding possible. Production volumes can range from short runs to millions of components. Injection molding is one of the most common forms of manufacturing, but few people truly understand the injection molding process.

How Does Injection Molding Work?

When selecting a plastic or resin, one must determine the intended purpose of the injection molded part, its use, and function. Strength, melt flow, and cooling time are other factors manufacturers must consider. The chosen material is melted inside a specialized machine and injected into a mold shaped like the finished part.

While in the mold, the material cools and solidifies. Relatively small, thin parts can harden within a few seconds, but larger, thicker components can take 30 minutes or longer.1 Cooling can take up more than 50% of cycle time.2 In plastic injection molding, a cycle includes:

  • Mold closing/clamping: Each half of the mold, designed so the part can be removed without being damaged, is secured with a hydraulic press or motor.
  • Injection: Over a few seconds, the resin is fed into the machine, heated, and melted. It becomes molten in the barrel, from where it’s injected quickly into the mold.
  • Cooling: The plastic must fully cool to ensure its integrity and stability. In general, cooling time is proportional to the thickness of the wall, squared.
  • Ejection: The mold is quickly opened. As air fills the vacuum, parts may shrink. The mold’s draft angle must permit all part surfaces to be reachable, to avoid damage, while ejector pins in the mold’s core half aid removal.

Types of Injection Molding

For customers who rely on fast injection molding, Laszeray Technology, LLC may apply one of a few processes. Two-shot injection molding is a process in which one material is injected into a mold and another compatible material is delivered via secondary injection. This reduces product runs and labor, strengthens bonds between materials, and eliminates the need for additional assembly.

With insert molding, plastic parts can be formed around one another or other non-plastic parts and inserts, which may be metal or non-metal materials. Over molding is used to combine two or more molded parts into one product. First, the base layer is molded. Then additional layers of plastic are molded over and around the original part. This process is often used during custom injection molding.


Additional processes can be integrated with injection molding. Robot Part Handling is when robots transfer, feed, or remove parts or tools from machines, increasing speed and improving precision and safety. Automated/Robotic Part Trimming is a process in which a router bit (attached to a high-speed spindle on the robot) is driven into a part or used to clear away material at the edges.

Trust Laszeray Technology, LLC for Custom Injection Molding

Thanks to a state-of-the-art 62,000-square-foot facility and professionals experienced with the injection molding process and custom injection mold tool design, we’re able to manufacture nearly any type of molded component, in any quantity. Customers also rely on our Eastman Tritan™ co-polyester molding expertise. For more information on our custom injection molding services and to discuss your requirements, call us today at 440-582-8430.

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