Aluminum vs. Steel Plastic Injection Molds

Special Tool and Engineering, Inc. has over twenty years of experience making plastic injection molds. We produce injected plastic components used in industries such as automotive, consumer goods and defense. Our in-house tooling experts utilize aluminum to construct custom plastic injection molds for many reasons. Take a look at the pros and cons of aluminum vs. steel injection molds:

Strength and Durability

Processes that depend on the strength and lifespan of plastic injection molds benefit most from steel tooling. Longer production runs can be hard on molds, and the durability and strength afforded by steel are unparalleled by any other material. Steel is also a clear forerunner in corrosion resistance and thermal stability. It can stand up to more aggressive materials that require high injection temperatures and pressure.


When considering cost, the size and run time of the project determine which material comes out on top. Aluminum is less expensive as a raw material, and for that reason, it outperforms steel for making plastic injection molds. The cost per manufactured part yields a less clear frontrunner. Steel achieves a lower cost per part on larger runs, due to its superior longevity and durability. Essentially, as run time extends, the cost-per-part advantage increases for steel.

Run Time

Time is money. The run time for your component affects your bottom line, and materials that support faster production benefit your operations, overall. Cooling time takes a high percentage of overall run time and is an important variable. Because aluminum achieves a higher rate of heat dissipation, it heats and cools up to seven times more quickly. This factor significantly shortens overall turnaround times.

Aluminum’s superior heat dissipation also allows the plastic injection molds to uniformly heat and cool. Non-uniform temperature fluctuations can cause product defects such as burn marks, bubbles or voids. Fewer defects mean lower rejection rates and more cost advantages.

Run Volume

As alluded to above, the production volume of your job determines whether steel or aluminum will perform more efficiently. Aluminum offers a lower material investment, and that cost benefit holds for most batches under a hundred thousand. For molds that must endure multiple production runs or volumes in the hundreds of thousands or millions, aluminum may lose integrity over time. The higher initial investment in steel for making plastic injection molds pays off for large volumes.

Component Complexity

Steel plastic injection molds generally outperform aluminum for complex product designs. Steel is more durable for products with varying wall thicknesses, tighter angles or other intricate elements. Aluminum may lose stability eventually if used for thin-walled or high-precision molds. In addition, steel molds offer more post-run finishing options than aluminum.

Abrasion Tolerance

If your injection formula uses abrasive additives, steel outperforms aluminum. Injection materials containing additives such as glass have the potential to scratch or chip aluminum. The mold may not fail, but Special Tool has found that any mold damage can affect the intended product finish and require additional post-run treatments. While aluminum-based plastic injection molds are softer and more susceptible to damage, that same quality makes them more receptive to modifications or minor repairs than steel molds.

Special Tool and Engineering, Inc. appreciates the advantages of both steel and aluminum for injection-mold production. Steel comes out on top for higher-volume runs, abrasive injection formulas or intricate configurations. Aluminum plastic injection molds are less susceptible to manufacturing defects, require less heating and cooling time and generally perform very well for shorter runs. At Special Tool & Engineering, we specialize in quality custom aluminum plastic injection molds.

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