Injection mold tooling utilizes a variety of different materials depending on the given application. Some tools may experience considerable heat, pressure, and abrasion during the molding process and must have a long lifetime to survive millions of mold cycles, while others are merely meant for prototyping or bridge tooling. Selecting the correct tooling material is crucial for delivering on the expectations of the function and lifetime. The best tools are ones that are designed for the specific application that the customer needs, and selecting the correct tool steels is a crucial first step in the process.
Listed below are some of the most common tool steels—P20, H13, S7, 420 stainless steel, D2, 4140, and copper alloys. Each material has its own advantages, disadvantages, and use cases, all of which are outlined in this guide.
P20 is a pre-hardened mold steel and is one of the first steels listed in any plastics engineering textbook because of its versatility and relatively easy processing ability. It’s part of the P-series mold steels, which are chromium-molybdenum-based low-carbon tool steels.
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Best Used For: Low to medium-volume production with plastics that don’t require high wear resistance.
P20 is the best tool steel for a first-iteration product, and it will likely be used with a mold that has 1-4 cavities, a single face, and a cold runner. The most common plastic materials molded in P20 would be polypropylene, polyethylene, and materials in those families.
ZunKai’s metal 3D printed P20 mold inserts used for prototyping a medical device component
H13 tool steel is a chromium-molybdenum-vanadium steel. It is the workhorse of the tooling industry. Known for its excellent toughness, wear resistance, and thermal fatigue resistance, H13 is commonly used for high-volume tooling and the molding of any abrasive plastics. H13 is a member of the H (Hot working) family of tool steels.
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Best Used For: High-volume molding of engineering, abrasive, or high-temperature plastics and tools that must endure high-temperature fluctuations.
H13 is the go-to steel for high-volume applications. It is the logical step up from a P20 or aluminum tool. If the tool is going to run millions of cycles or the part is made from a high-temperature or filled plastic, this is the correct steel to choose.
For a deeper dive into the properties and applications of H13 tool steel,explore our dedicated blog post on the topic.
ZunKai metal 3D printed H13 slide molding 35% glass filled PEEK at 720° F
S7 is a tool steel known for its unique combination of toughness, impact resistance, and high strength. It has the ability to fit both cold and hot work applications, making it a uniquely versatile steel. S7 is a member of the S (Shock resisting) family of tool steels.
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Best Used For: Mold components requiring high impact resistance and durability, such as slides and large mold components.
S7 steel is best used for cavities, cores, slides, or other mold components requiring a great finish, impact resistance, and toughness. It is not a steel you would make an entire face or mold base out of, but it is a great option for components in a high-volume tool.
420 stainless steel is a martensitic stainless steel with great wear and corrosion resistance and top-notch polishability. Its ability to effectively add texturing and mirror finishing makes it a very good choice for a variety of high-value applications.
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Best Used For: Ideal for molds used in corrosive environments or for products requiring a high-quality surface finish.
420 stainless steel is a great choice for high-value applications like the medical industry, consumer electronics, and automotive markets. Due to its high cost, it is difficult to justify building every mold out of 420; however, it is often the best option when molding very corrosive materials or in lens applications.
Copper alloys like beryllium copper exhibit superior thermal conductivity to the more common tool steels. These alloys are primarily used in the molding industry to reduce cycle times on high-volume tools.
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Best Used For: Perfect for molds requiring fast heat transfer and high-quality surface finishes, such as those in the electronics industry.
Copper alloy cores are often seen in the industry on high-volume tools with very short cycle times. Because of the ease of machining, complex core designs can be achieved. This makes it a viable choice for a core on a high-volume tool where the thermal conductivity can be taken advantage of, but this is almost exclusively reserved for commodity-level plastics. Tools molding polypropylene and the family of polyethylenes are where you would most commonly see copper alloy inserts.
D2 tool steel is a high-carbon, high-chromium tool steel known for its high wear and abrasion resistance. D2 is a cold work steel, characterized by high stability and the resistance to deformation at high temperatures.
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Best Used For: D2 is ideal for molds that require high wear resistance, particularly for processing abrasive materials. It’s less suitable for high-impact or high-temperature applications.
D2 is a great choice for many applications outside traditional injection mold tooling like dies, cutting tools, and punches. D2 would be reserved for high-wear applications like MIM or highly filled polymers for injection molding.
4140 alloy steel is a chromium-molybdenum medium-carbon steel that exhibits high toughness and good fatigue strength. With a good balance of wear resistance, strength, and toughness, this steel can be relatively versatile in its applications. Heating treatment is often required to achieve the properties desired for mold tools.
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Best Used For: 4140 alloy steel is ideal for molds that require a balance of strength, toughness, and wear resistance. It’s especially suitable for molds that do not encounter highly abrasive materials or extreme temperatures.
4140 Alloy Steel can be thought of as a competitor to P20, winning out in applications where impact resistance and cost are key drivers. However, P20 would be the better choice if the application requires a better surface finish or dimensional stability in high heat. For commodity plastics in low to medium volumes, 4140 can be a great alternative to P20 and a good way to cut down on the cost of a tool.
The tool steel that you choose for each mold needs to be selected with great care and attention to detail. Spending the time upfront on the application development and understanding the exact expectations is crucial. P20, H13, S7, 420 SS, and copper alloys each have their place in the tooling world, with many pros and cons. Understanding each of these materials and the application of the tool allows the mold builder to ensure efficiency, durability, and cost-effectiveness for every one of their projects.
Here at ZunKai, we utilize H13 and P20 tool steels, which have the properties needed for molding even the most demanding plastics. Our tool steels are compatible with existing shop operations, have the durability needed for volume production, and remain stable during standard toolmaking operations like machining and EDM. Read more about our tool steels here.
