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By Jeremy Losek, Aug 30th, 2022

What Metal is Used for Injection Molds?

Injection molding is a manufacturing process that uses a metal mold to manufacture large numbers of plastic parts. ICOMold by Fathom uses only high-strength steel when making plastic injection molds. Steel molds have several advantages over aluminum molds. Steel molds consistently produce a higher quality product when compared to aluminum molds. Steel molds are built to last — up to ten times longer than aluminum molds. Steel molds may have a higher up-front price but they can save significant time and money down the road.

Can You Use Aluminum for Injection Molding?

Aluminum can be used to make molds for the injection molding process. Aluminum is an affordable material that is easy to work with and has many applications. However, aluminum molds, while slightly cheaper to produce, are considered inferior to steel molds. ICOMold by Fathom uses only high-strength steel to manufacture injection molds.

Aluminum cannot be used as the injection molded material. The manufacturing process of metal injection molding does exist, however, aluminum cannot be injected molded. ICOMold by Fathom specializes in injection molding custom plastic parts. ICOMold can also manufacture custom metal parts with Computer Numerical Control (CNC) machining. As part of the Fathom manufacturing network, ICOMold will work to match customers to manufacturers in order to meet their specific aluminum machining needs.

How Long Do Aluminum Injection Molds Last?

An aluminum injection mold will last 3,000 to 10,000 cycles. Each cycle represents the mold closing, the mold being filled, the mold opening, and the part being ejected. If the mold has a single cavity, customers can expect to get up to 10,000 parts from an aluminum mold.

Steel molds are much more durable and can last up to 100,000 cycles or more. While aluminum molds may be cheaper to machine, the steel mold will last ten times as long – producing parts long after the aluminum mold has been scrapped and replaced several times. The cost of machining a new aluminum mold after every 10,000 cycles will add up quickly.

Steel Molds Can Make Complex Parts

Aluminum injection molds cannot be used for complex parts. Aluminum is a softer metal that can only be used for simple injection molded designs. Designs with complex geometry will need to be made with a steel mold. The steel is better able to handle complex designs and any thin walls in the design. Aluminum molds cannot handle thin walls or complex geometry because the metal is not as structurally strong as steel and will deform during the molding process. This is a universal limitation for all mold makers – not unique to the ICOMold by Fathom manufacturing process.

More Surface Finish Options with Steel Injection Molds

Steel molds offer more options for surface finishes. The high-density nature of steel allows more texture selections. Custom, tall, or deep details in the tooling can be achieved by adding steel inserts. The number of surface finishes possible with an aluminum mold is limited and custom finishes are not available. The difference in available surface finishes is based on the mold material. This limitation affects all mold makers, not just ICOMold.

steel injection mold

Ease of Design Modifications – Steel Molds vs Aluminum

Steel molds can be modified and repaired after initial tooling. Aluminum molds cannot be changed or repaired if there is a problem with the initial design. Steel molds can be modified with welding. If a part re-design requires less plastic in an area, and therefore, more steel in that area of the injection mold tooling, the steel mold can be modified. This is not the case with aluminum. Consider using a steel mold if there is any chance your part may undergo design revisions that will require modifications. Steel molds can also be repaired in some instances. This will save customers thousands of dollars by simply repairing the mold instead of machining a new mold. The ability to repair a mold will depend on the tooling. Not all steel molds will be able to be repaired.

Less Flash with Steel Molds

Flash is what happens when the plastic injection material seeps into the mold seams during the injection process. The excess material will need to be removed in post-processing. This post-processing can be expensive depending on the amount of flash and the work required to remove it. Aluminum molds for injection molding are prone to flash. Aluminum is a soft metal and is therefore easier to deform and allow the injected material to leak out of the machined cavity. Steel is a harder material, which reduces the chance for flash. Steel molds will not deform as easily as an aluminum mold.

Steel Molds Will Produce Higher Part Volumes

Aluminum molds have a limited manufacturing life span. Aluminum is a soft metal and cannot with stand the repeated pressure and temperature of the injection molding process. Aluminum molds will produce 3,000 to 10,000 cycles before needing to be replaced. Steel molds are more resilient and will produce 30,000 to 100,000 cycles before needing to be replaced or repaired.

Steel Molds Can Handle Aggressive Materials

Injection molded material can impact the life expectancy of the tool. Aggressive materials like ASA/glass-filled Nylon and Ultem can reduce the lifespan of injection molds. Steel injection molds can be hardened through heat treatment to become extremely durable. The heat treatment will allow steel molds to handle the aggressive material without issue. Aluminum molds for injection molding cannot be hardened and will not be able to handle the high injection pressure and temperature required when injecting these aggressive materials.

Durability – Steel Molds vs Aluminum Molds

An aluminum mold will hold up for short part runs and is an ideal choice for small orders. However, steel molds are more durable and suited for extended manufacturing runs. Aluminum molds do not have the corrosion resistance or thermal stability found in steel molds. Steel molds are also better able to resist the constant wear and tear of the injection molding process. These characteristics allow the steel injection molds to achieve higher production cycles and withstand non-conformities in the product. Aluminum molds must be anodized or plated with nickel to reach the same level of hardness as steel molds. Anodizing and plating will increase the tooling cost and negate the benefit of using the less expensive aluminum to machine the mold.

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