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Steel vs. Aluminum Molds: What’s Right for Your Small Plastic Parts Project?

[fa icon="calendar"] Apr 25, 2017 10:19:51 AM / by Jon Gelston


Historically, small plastic part injection molding has been performed primarily with steel molds. There are many advantages to steel, including:

  • Longer life. Steel molds are capable of producing millions of high-quality parts. Hardened grades of steel can improve longevity, particularly with abrasive materials.
  • Durable for complex features. Complex or delicate features can have a difficult time withstanding the forces involved in molding. Steel has an excellent balance of machinability, strength, and cost.
  • Lower per-part cost long term. Steel tools can have lower maintenance costs, which increases uptime and reduces operational cost.
  • More finishing options. Some surface finishes can only be produced with steel molds.

For these reasons and others, steel tooling will always play a prominent role in small part plastic injection molding. However, steel is not your only option. In many scenarios, aluminum molds may be the right choice. But before we go there, you might be used to the "old" rules of why people selected aluminum, such as:

  • Perceived faster development time. It used to be that aluminum was machined much faster than steel, but advances in cutters and machining technology have narrowed this gap. Now, producing a steel vs. aluminum tool often requires the same amount of time.
  • Perceived lower manufacturing costs. Though the cost of raw aluminum and steel may differ, the cost of blank mold bases is similar, particularly since aluminum tool bases need to be larger than steel. Coupled with the fact that machining times may be similar, the cost gap between steel and aluminum has narrowed, too.

There are still some advantages to aluminum including:

  • Improved heat dissipation. Aluminum molds cool much faster than their steel counterparts.  For some materials, this may enable faster cycle times, which reduces production cost.
  • Inexpensive changes. Not only are aluminum molds easier to produce, they are easier to modify in some circumstances. This can be a huge benefit when you are looking to validate a design.

Breaking Down the Decision

Many companies that are pondering a small parts plastic injection molding project start by considering if aluminum is a viable option for them. When that’s the case, there are four key questions to ask:

  1. Can aluminum stand up to the material we’re using? For example, glass-filled nylon is a material that is best used with a hardened steel mold while something like polypropylene will work fine with an aluminum mold.
  2. What color? Many grades of untreated aluminum oxidize, which can leave hints of black marks on a white or clear part at startup.
  3. What volumes will we run with this mold? If the number is higher than 100,000, aluminum probably is not the way to go.
  4. Is there complicated part geometry? If the answer is “Yes,” you may need to use a steel mold.

Helping Companies Choose the Right Mold for their Small Plastic Parts Projects

At our small plastic parts manufacturing company north of Denver, we work closely with our customers to be sure they know their options when it comes to steel vs. aluminum tooling. While we use a project-specific sourcing approach and don’t produce molds ourselves, we have decades of experience helping customers choose the type of mold that’s right for their project.

If you’ve got questions about the right tooling for your needs, we’re happy to share our insights. Give us a call or stop by and visit us in Longmont, Colorado. We are the fastest-growing plastic injection molding company in the Denver area.


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Topics: Plastic Injection Molding Tooling

Jon Gelston

Written by Jon Gelston