How Are Injection Molds Made for Plastic Manufacturing?

Injection mold manufacturing process：

The process of injection mold making involves more than machining cavities out of metal.

Developing a mold design by evaluating the part and project requirements

Fabricating and precision machining of the mold by journey person tool builders.

Debugging and trialing the mold for accuracy

Developing the injection molding process parameters and validations

 Developing the mold design and DFM support

Mold Designers and engineers review the essential aspects of the mold-making process. At the initial step, evaluating the 2D or 3D models can provide valuable insights into the part geometries and production requirements. These part features will determine the mold design, if actions are required, the type of gate to use, the gate location, the ejector system, the mold steels, the cooling features, the runner system, and more.

This design also considers the necessary draft angles for easy ejection and minimizes the risk of part damage. Furthermore, the resin material needs to be addressed for shrinkage allowance, as different materials have different shrinkage levels after cooling.

It is vital to consider cooling when designing and building molds. This includes adding venting and cooling channels to the mold design. Venting allows air pockets to escape during plastic processing, reducing the risk of air pockets and accelerating the cooling of the material. Cooling channels are designed into the mold, and optimizing the cooling time helps reduce the manufacturing cycle time.

Mold flow or mold analysis looks at how the injection molten plastic would travel through the injection mold, handle the molding process, cool, and eject the part. This process is done during the design phase to ensure the part fills completely and evenly. It eliminates problems in the design phase before cutting steel to build the mold.

Mold Building Materials and Surface Finishes

Mold building materials are essential. There is a difference between hardened tool steels and soft metals, even though soft metals will reduce the tool cost and make it cheaper than hard steels, which don’t withstand many production cycles. So steel is determined by part features and production volumes to ensure the mold's wear resistance and durability.

Polishing and texturing are steps necessary to give the finished part the desired appearance, feel, or effects beyond what the resin raw material will provide.

Mold Building and Trialing

Skilled journeyperson tool makers and CNC machinists produce the injection mold from the mold design. They use skill, CNC mills, EDM mills, Wire EDM, and more to make the fine precision cuts needed to build a quality injection mold. This is important when creating products with complex geometries and design features.

When all the components are fabricated, the mold is assembled.

A process engineer performs trial runs. These trial runs are done to:

Ensure there are no problems or part defects

Confirm part features, colors, etc., to meet customer requirements

Develop the process parameters for reliable and repeatable manufacturing

Once the injection mold is complete, the validation protocols have been met, and the customer has approved it, the mold is ready to launch into full production.