Making the Right Choice in Materials

Posted by Kaysun Corporation on Aug 12, 2015 2:25:09 PM

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What You Need to Know About Materials in Complex Injection Molding

With the freedom to create new features – and cost-effectively achieve process efficiencies – it’s evident why many design engineers lean toward parts and products that require complex injection molding.

What isn’t always clear, however, is what goes into it. That’s probably why it’s called “complex” injection molding, which involves more than a few considerations especially at the beginning of the process. Among them is the material used to make the actual mold, in addition to the plastic materials for the part. Here are pointers to keep in mind when working through it with a molder.

Mold design: choosing the right stuff

Since almost everything is riding on the tool, it stands to reason that the mold be built with the right stuff.

A place to begin is with production volume. If it’s a small or finite run, it’s fine for the mold to be made of an inexpensive material like aluminum. It is relatively inexpensive and easily machined, but it won’t last. Conversely, greater production volumes call for hardened steel.

Mold complexity and volume together are another key factor. Soft steels are acceptable for simple, single-cavity prototype molds that are often equated with smaller runs. Beyond that, it becomes increasingly important to select the proper steel for complex, multi-cavity molds since they typically require the need to satisfy greater production volumes.

And what would a project be without taking into account costs? Again, materials of the mold play a significant role.

In general, the harder the steel, the more effort and expenditure that will go into it – and the higher the cost. On the plus side, however, harder steel molds last considerably longer and return higher-quality parts with greater consistency. The same can’t be said for softer metals, such as P20 steel and aluminum, which can be easily machined for less cost.

Corrosion resistance also needs to be taken into account. Stainless steel, for example, is always a good choice since it resists corrosion, pitting, and wear, while also supporting smooth finishes. On a related note, careful consideration must be given to the materials injected into the mold that have a high degree of acidity, such as resins in the PVC family, or additives like flame retardants.

Questions to consider in part materials

No less crucial than the mold and what goes into it is the plastic materials used in the project. It’s why the molder should always start the process by asking essential questions. Just some of the issues to discuss include:

  • What is the physical load? The impact expectations of the part must be determined to ensure it will stand up to the conditions of everyday fatigue.
  • What is the mechanical function? The polymer chosen must be right for the rigors of the application to ensure success.
  • What are thermal conditions? To be vetted up front is whether the polymers must be chosen to endure fluctuating and extreme temperatures.
  • What is the exposure to chemicals? The ability to hold up to extreme environments, such as those in the medical, automotive fields and other industries, will influence a host of decisions about proper materials.
  • Will dissimilar materials be used? If the answer is yes and it dictates multi-shot technology or overmolding, both the materials and the processes need to be thoroughly vetted.
  • Does the part require high-heat resins? These materials are more difficult to work with mainly due to their higher melting points, driving the need for careful deliberation about everything from safety to the molding process used.

Making informed decisions

Design engineers and OEMs who develop parts and products that require complex injection molding are making the right choice because the outcome is invariably better quality and production efficiencies.

So don't hesitate to design something that requires complex molding. And certainly don’t hesitate to learn more about it through our white paper, “Complex Injection Molding for Competitive Advantage.” It contains plenty of insights to guide the process.

Topics: Plastics / Resins