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An Introduction to Building Molds

Mold building is both an art and a science. In this area of our website, we look at the mold-building process, which starts by understanding and defining the project’s objectives. We explore some basic elements of design, materials and mold specifications. And at each step, we look at the some of the many considerations that come into play when creating a successful mold.

Start with the Project Objectives

Building a mold for injection molding requires an in-depth knowledge of the project. Thoroughly understanding the unique goals of each project will help ensure the mold accomplishes those goals.

Factors to consider when building a mold include:

What type of plastic is being molded?
There are countless types of plastic materials available. In raw form, they are called resins. Some resins have very abrasive qualities. Others require high temperatures or very high pressures to perform correctly. These factors will influence the mold design.

How many parts will the mold produce?
Choosing the correct steel is critical to the success of a mold, and the choice often depends on the number of parts the mold will produce. That’s why better-quality steels are the best choice for higher-volume molds. When building a high-volume mold, the choice to save money by using cheap material will likely lead to expensive repairs or even replacement. For lower volume or test projects (such as creating prototypes), a less expensive, pre-hardened steel or even aluminum will likely accomplish your goals. But a mold that produces a million shots will require a higher grade of steel. The volume also dictates the number of cavities required. Molds with more cavities also require higher grades of steel.

How detailed is the part?
The design of the part is vital in creating a successful mold. A mold producing a detailed part or a moving part will be more complicated and will have different requirements than a mold that produces a simple part. Features that make molds more complicated include whether the mold has long cores where it is not possible to cool, whether the mold has thin steel areas that are subject to cracking, and whether the mold has shutoffs that could wear and cause flash (excessive material on the part where the mold separates).

How long do you have to build the mold?
It takes many labor and machine hours to produce a quality injection mold. Even simple molds can take hundreds of hours to build and usually require the skills of journeyman toolmakers with a minimum of 5 years experience. The length of time varies greatly, depending on the class and requirements of the tool. A simple prototype tool may take four weeks to build, while a complicated tool with a longer life expectancy may take eight weeks. Each project is unique.

The answers to these questions will help the mold-making team recommend the best type of mold, material and design.


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