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).
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.
Time To Manufacture
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.
Sustainability And Durability
Both aluminum and steel are durable metals — these options can easily withstand thousands of shots with little to no issue. However, it must be said that steel far outperforms aluminum when it comes to durability.
If you plan on running just a small quantity of injection molded parts per year, then aluminum may be the best choice. As we mentioned, aluminum molds are the best cost-per-part option for lower production volumes.
Likewise, steel is ideal for large volumes of injection molded parts for years. This is because it is one of the most durable and strong materials for injection molding tooling — allowing it to reliably produce parts into millions of pieces. It even reliably lasts for decades, given the proper maintenance. In these cases, steel molds are an unparalleled choice.
Heating And Cooling Times
Both aluminum and steel have good heating and cooling times. But, aluminum is the better conductor and has a higher rate of heat dissipation than steel. This means that heating and cooling times with aluminum molds are greatly reduced — making their overall cycle times much shorter. Thus, aluminum molds may be able to produce your plastic parts more quickly.
Suitability For Advanced Resins
While both options are suitable for a broad range of resins, steel has the advantage here — especially when it comes to working with more complex or advanced resin formulations.
This is something you want to consider when using specialty resins, or formulations including glass, fiber, metal inserts, and other additives. Steel is the better choice because it is much less malleable than aluminum, and therefore can withstand the addition of other materials. Aluminum molds, on the other hand, run the risk of scratching and other damage from these additives, causing cosmetic defects and imperfections in your plastic product.
Before choosing how to make your mold, be sure to review the compatibility of the mold material and your resin of choice.
Suitability For Complex Designs
Aside from resin selection, you should also take your design in mind when choosing which metal to have your molds made from. Generally, aluminum molds are not suited for more complex designs. This is because aluminum cannot reliably hold complex shapes and tight tolerances for a long period — especially when production is high volume.
On the other hand, steel molds utilize such intricate designs — even having the capacity to accommodate designs with multiple cavities and inserts. Steel, being so stiff and strong, can hold this complex shape for much longer than an aluminum can, allowing you to produce your desired design to exact specifications.
Modifications And Repair
When it comes to modifications, steel molds can accommodate them much easier than aluminum molds can. So, aluminum molds are not recommended for parts that may go through many changes or design revisions in the long run.
However, when it comes to repairs, steel molds can be difficult and costly to repair. This is mostly due to their extreme hardness, and in most cases, a new mold may have to be manufactured to replace the defective one. Aluminum molds are more receptive to repair, which can be done much faster and cheaper compared to steel molds.
Key Takeaway
As you can see, the choice between aluminum vs steel molds comes down to the specifications of your part and the project itself. You should consider part design, the volume you want to produce, the materials you intend to use, and more factors to find which kind of mold is best for your product.
When considering plastic injection molding for their components, businesses have a variety of choices that must be made. An experienced plastic injection molding company will be able to guide you through determining which material, molding method, and 3D printing alternatives are most suited to the requirements of the component being formed. Choosing whether steel molds or aluminum molds are the optimal material for the mold itself is an additional subject that may be brought up. It should come as no surprise to manufacturers familiar with metals that the two most common metals used to construct tools have their benefits and drawbacks.
When deciding between the two types of molds, companies must look at how their molded parts are used and their production needs, including the parts’ sophistication, finish, and longevity. Both types of molds are often used in injection molding.
First when processing thermoplastics (injection molding) the plastic is heated to become a liquid that can flow into and fill the mold. There are basically 2 functions of the mold when injection molding plastics.:
One is to cool the plastic and freeze it in the shape of the cavity of the mold. Since Aluminum has a thermal conductivity of about 15 times that of steel, Al does this job significantly better and faster than steel. And since cooling time determines the cycle time there is a significant economic advantage to that faster cooling.
However, the second function of the mold is to resist the wear of injecting the plastic at very high (shear) rates. Although most plastics are not very abrasive, some can be and all will be at the very high shear rates of injection. In addition, there can be very significant wear and tear from moving the mold in and out of the press and storing it. The result is that an Aluminum mold may only last a week in production before needing to be replaced while a steel mold may last a year with similar use and abuse.
Although quality of the finished part from both can initially be equivalent, the wear on the tool is especially important if there is a texture or other critical function of the part because this would tend to wear noticeably on the Al tool.
So Aluminum is often used for prototyping or for low volume parts but any high volume production will use steel.
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.