Most molds are made of hardened or pre-hardened steel. Hardened steel (post-process heat treatment) has better wear resistance and longer service life than pre-hardened steel. Although steel molds are more expensive than molds made from other materials such as aluminum, they are more durable and support higher productivity before they need to be replaced.
Design engineers must consider the hardness of the steel and the brittleness of the steel. Harder steel is more brittle and therefore not suitable for use in mold parts that are subject to lateral loads or impacts, as it cracks if it bends. Formed glass fill materials also require the use of harder steel because the glass fill material will wear the mold prematurely; wear can also be a heavy runner system and gate.
Due to the rapid cooling characteristics of aluminum, it is sometimes used in molds. It also reduces the time required to make a mold because it is easier to machine than steel, providing faster turnaround and production cycles. However, because it is softer than steel, even hardened aluminum is more difficult to weld, difficult to maintain, and wears faster – making it ideal for prototyping and short-term operation. Depending on the product and mold design, the hybrid mold can sometimes be made of steel, but aluminum is used for heat transfer in low wear areas.
Aluminum is not a good choice for complex parts or hard glass filled plastics due to premature wear. Copper alloys are sometimes used as a substitute for aluminum when rapid heat dissipation is required.
Both steel and aluminum molds can be coated with special materials to improve wear resistance and reduce friction, especially when forming FRP. Common coatings are nickel boron alloy and nickel polytetrafluoroethylene (thickness 0.0002 ~ 0.0004 inches).
Aluminum vs Steel Molds: What are the Differences?
What are the differences between aluminum vs steel molds?
Tooling costs
Time to manufacture
Cost per part
Sustainability and durability
Heating and cooling times
Suitability for advanced resins
Suitability for complex designs
Modifications and repair
You have a great idea for a new plastic product, so you choose to make new molds with your injection molding partner. Chances are, your plastic mold maker can make the tooling you need — but offers it in either steel or aluminum. But what are the differences between aluminum vs steel molds, and which one should you choose?
Under different circumstances, steel may be the better choice for your plastic project and vice versa. Here are a few things to consider to help you make the right choice:
Tooling Costs
Aluminum tends to be cheaper, and your molding partner may quote as little as half the price for their aluminum compared to their steel molds. This is because of scarcity and manufacturing methods. Overall, steel is an expensive material. Aluminum molds can be made much more easily compared to steel, as it is malleable and readily available.
All other factors equal, aluminum gives you a lower tool investment compared to steel. However, the overall value and return on investment of your mold can vary greatly — so the initial price should not be the only thing you consider when picking between an aluminum mold or steel mold.
As aluminum molds are made much more easily than steel ones, they take less time to manufacture overall. Compared to steel molds (which generally take a month or two to produce) aluminum molds can be ready in as little time as three to four weeks.
However, the time it takes to manufacture your specific mold will rely on several factors, including inserts, special features, and part complexity.
Cost Per Part
When it comes to cost per part, this heavily depends on your intended product run — so there is no consistent winner in this category.
For shorter runs, going with lower upfront costs will help you recoup costs per part more easily. In this case, aluminum molds’ lower costs are ideal.
But, if you intend to use your mold for high volume runs (think in the hundred thousand to the millions range), then this is where you’ll see a better payoff with bigger initial investments. In this case, steel is the ideal choice, and you’ll see that the cost per part will decrease over time.
In this area, it’s important to determine how much and how often you will use your mold to get the best advantages in this area.