The question becomes not if injection molding tool steel matters, but which is the best choice for your project.
P-20 Pre-Hardened Tool Steel (28-30 RC)
Widely known as the general purpose tool steel for injection molding, P-20 is a solid performer that:
Can be cast and put directly into service
Typically does not require further heat treating
Is versatile &#; it&#;s common for P-20 to be used in prototypes and holder blocks in addition to tooling
For all of its advantages, P-20 also has some challenges including not being able to meet ASTM-A681 minimums. Chiefly, it is best used with plastics that do not contain abrasives like glass fibers. There are also concerns around volume; P-20 that is not coated or surface-hardened will not stand up to high-volume production.
S-7 Pre-Hardened Tool Steel (56 RC)
If your injection molding project requires tight tolerances and high volumes, S-7 is the pre-hardened tool steel of choice.
There are few, if any, downsides to S-7, and the upsides are considerable:
Stability during heat treating, and resistance to softening at high temperatures
Excellent wear properties, which are especially important when preventing galling in slides and lifters
Good impact and shock resistance
H-13 Tool Steel
High-volume runs of plastic parts that contain abrasive materials are no match for H-13. This robust tool steel offers:
Versatility in hot work and cold work applications
Resistance to thermal fatigue cracking
Excellent strength and machinability
Eventually, H-13 tooling surfaces will become susceptible to corrosion brought about by chemically enhanced plastics, moisture, humidity and cooling water contamination.
420 Stainless Steel
Link to Jiebao
Containing 13% chromium, 420 stainless steel is a high-quality tool steel that&#;s preferred for custom injection molding. The high carbon content provides:
Maximum corrosion resistance when fully hardened
Excellent wear resistance and edge retention
The highest hardness among all stainless steel grades
420 stainless steel is relatively easy to machine unless hardened above 30 HRC. Also, if used in temperatures that exceed the relevant tempering temperature, mechanical properties are reduced.
Specialty Tool Materials
The design and manufacture of steel tools are a considerable piece of a project&#;s budget. While a worthy investment, there are certain situations wherein tools designed using specialty materials may be appropriate.
Tools made from specialty materials with high thermal conductivities can reduce overall production costs by about 25% compared to standard steel tools. If you&#;re interested in speeding up the cooling process of your next project, consider using tools made from specialty materials with high thermal conductivity, like MoldMAX®, aluminum or tungsten carbide.
Injection molding tool steel is a carefully measured consideration in any custom injection molding project. Working with an experienced molder like Kaysun will provide balance in materials selection and give you the most value for your tooling dollar. Explore how to maximize your options in our white paper, 5 Key Considerations when Comparing Tooling Quotes.
Plastics Manufacturing Resources, a FORGE partner, connects companies to a wide range of plastics manufacturing options, from injection and blow molding to additive manufacturing, thermoforming and more. In this Tools of the Trade, they discuss the options for tool steels for injection molds. There are many options to consider, depending on your needs. If you&#;re on the journey to injection molding, this information can help you plan your process.
In this article, we will provide a general introduction and guide to understanding common tool steels for injection molds. In this article, we are going to discuss the most common steels used when building injection molds. Each of the materials have pros and cons. One that works well for one application doesn&#;t necessarily mean it will work well for another. There is no simple formula to make this determination. Instead, several factors contribute to the ultimate choice of steel.
1) What is the annual volume and life expectancy of the part? A part that only requires parts per year, will have different steel requirements than a part that runs millions of parts per year.
2) What polymer have you chosen for your part? If the material is a filled resin (glass/carbon etc.), those materials are abrasive and will require steel that has good wear properties. High-temperature materials will also require steels that tolerate the required higher processing temperatures.
The most common choices are Aluminum, P-20, H-13, S-7, and 420 SS. When matched properly with the application, each of these materials will perform well. However, if you opt for aluminum based on its affordability and you are running a glass-filled material, that tool is not going to yield thousands of parts. While the price point may be attractive up front, you may need further investment to produce more parts due to wear and dimensional issues. Here is a brief description of each:
Aluminum is a common choice for low-volume applications and prototyping. It is best suited for unfilled commodity or engineering-type resins. Generous tolerances fit best with this steel choice. Because it is a less dense steel, it machines much faster than hardened steel thereby reducing machining time, lead times as well as reduced labor costs. While it is low cost, it will not offer you longevity. This is a true prototype/low-volume choice.
P-20 is a semi-hardened tool steel. This is a step up from aluminum and is usually worth the minor increase in cost. P-20 is going to give you a longer life and will perform well with abrasive materials (glass and/or carbon filled). For some applications, P-20 is enough for the entire life of the program. As a general rule, P-20 is good for volumes up to 50,000. When given the option to build a first-stage tool before production, P-20 is a good choice. It can then serve as a backup tool if an unforeseen issue comes up with the production tool.
H-13 is a hardened steel. Prior to heat treat it machines well. It works well in high-volume applications and can last dimensionally for over 1 million shots. H-13 is also a choice when it comes to highly filled (abrasive) materials. It also works well for materials that require high tool temperatures like polyamide-imide (PAI), polyaryletherketones (PAEK/PEEK), and Liquid Crystal Polymer (LCP). It is also a good option for optical quality type parts that require high polish and/or a mirror-like finish.
S-7 is a pre-hardened tool steel. This steel is suited for both high volumes and tight tolerances. It can stand up to abrasive filled materials and can be welded successfully. In addition, S-7 polishes well to a high luster making it a good choice for aesthetics including glossy finishes.
420 SS is a grade of stainless steel. Its hardness is excellent in maintaining tight tolerances and has high wear resistance with abrasive materials. 420SS is a good choice for PVC and it performs well in mildly corrosive environments.
Interested in learning more? Here is a link to a great resource on mold making. https://moldmakingresource.com/injection-mold-tool-steel/
Here is a matrix that you can reference as you head down the design and product development path:
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