Which Tool Steel Is Right for Your Plastic Injection Mold

Home Which Tool Steel Is Right for Your Plastic Injection Mold

Creating the right mold for your injection molding process can save you from a lot of losses and pain down the road. This is why injection mold manufacturers that deal with injection molding pay a lot of attention to the mold creation process. There are certain steel tools that have to be used to ensure the mold comes out just right.

We are going to look at the right tool steel that you have to use for plastic injection mold design for all your injection molding processes. We will also compare the different alternatives that one can use. Therefore, if you have been thinking of creating your injection mold, then stick around to know exactly what you need.

Why Steel?




There are so many metals that can be used for creating molds, but steel is the one that’s preferred by most injection molding factories. So why exactly is this the case? What properties does steel have that make it ideal? The following are some of the reasons why you should also go for it.

  • Steel is very hard and has the strength to cut through other lesser metals easily without losing any part of itself. This makes it the ideal tooling option when it comes to fashioning out the right mold of your injection processes.
  • Steel is widely available and can be found easily. This makes it easy to make all types of tools that can be used to make big and small molds for injection molding. In case of any damage or wear and tear, they can be replaced quickly and easily.
  • Steel has high resistance to heat and can handle high temperatures which are common in injection processes and the making of molds. For the tool steel to cut out parts of the workpiece, there’s a lot of heat and pressure involved and it has to hold its ground for it to work.
  • Steel comes in many variations, each with its own attributes as far as hardness is concerned. This increases flexibility and versatility as you can have different types for different roles, all you would need to do is simply switch them out when changing the task. This level of flexibility cannot be found when using other types of metals.

Commonly Used Tool Steels

There are a number of tool steel types that are specifically used for making injection molds. All of them possess particular sets of attributes that make them ideal for this kind of work above all the other options that may be available. These include the following.

P-20 Pre-Hardened Tool Steel

P-20 Steel



This is commonly known as an all-purpose steel and is one of the hardest versions of steel. It is a very solid performer that can be used for the following roles in the making of the injection mold crate.

  • It can be cast and immediately put into service within a very short time.
  • There’s never any need for further heat-treatment. Once the right shapes are configured it is ready to roll. 
  • It is very versatile and it can be switched for many roles, from holding workpieces to being used as the cutting tool.

However, the steel has some challenges like the inability to meet the minimum ASTM-A681 standards. This means that this type of steel is best suited for plastic materials that are not abrasive or lack any abrasive elements like glass fibers as that will leave dents on them.  Uncoated P-20 has also been observed to lack the ability to be used for mass production and repeatable processes that go on for very long.

S-7 Pre-Hardened Tool Steel

S-7 Steel



This is a tool steel type that has very high tolerances for high temperatures and is the most ideal for making molds that are destined to work for long hours dealing with high temperatures for mass production. The following are some of the upsides of using this as a tooling option.

  • Stability when dealing with high temperatures
  • High resistance to softening when pressure and temperature are raised
  • It has excellent wear properties that ensure it can be used on hard surfaces without losing much of itself. This is handy when it comes to preventing the galling in lifters and slides.
  • Has a high shock and impact resistance.

H-13 Tool Steel

H-13 Steel



This is best for making molds that are suited for high volume production. The type that can run for days onitsown without any dent being registered in any part. It is hard enough to even deal with materials that are abrasive. The following are some of the features you should expect from this robust tool.

  • It is versatile enough to work in different extreme conditions, including both cold and hot works
  • It has  a high resistance to thermal fatigue and this ensures that no cracks or chipping happen when the temperatures fluctuate from hot to cold
  • It has great machinability and strength which increases its durability.

The only drawback to the H-13 steel tool is the corrosion that eventually happens due to overuse, especially when it is exposed to chemicals in the injection molding materials. It is also weak against most forms of moisture.

420 Stainless Steel

420 Stainless Steel



This is specially made steel that contains about 13% chromium, making it a very high-quality tooling option for anyone looking to make a reliable injection mold crate. It also has a high carbon content that imparts some very desirable attributes that most of the others lack. The following are the attributes that make it the ideal tooling option.

  • It has the best corrosion resistance, the best on this list. This makes it the best-suited tooling option to deal with highly abrasive materials.
  • It has good edge retention and excellent wear resistance.
  • It has one of the highest hardness when compared to all the other versions of stainless steel. The durability is off the charts and it can handle a prolonged injection molding process without as much as sustaining a scratch.

The only drawback to this element is the fact that the mechanical and tempering properties are greatly reduced when they are exposed to temperatures that far exceed the relevant parameters. They will not melt in the process but their efficiency becomes impacted negatively.

Other Alternatives

Besides steel, there are a number of metallic alternatives that can be used for tooling purposes. This ranges from aluminum which is best known for being lightweight and easily available. The on;y drawback when compared to steel is that it is not as hard and can be affected by high temperatures. 

Steel carbon is also another great option but the cost can be high due to the carbon presence. It simply doesn’t make much financial sense to have a tool that expensive just to make a normal mold crate. The tool you chose to go with should be guided by a number of factors that are directly related to the type of injection molding you intend to carry out.

Another option that is rarely used is Titanium, one of the hardest metals on the planet. The biggest drawback to going with this option is the high cost of extracting and fashioning it into a cutting tool. 


Getting the right tool for your mold could be the difference between having a successful injection molding and one that is fraught with complications. This is why it is important that you take your time when it comes to selecting the tool. For more information on how to make a plastic mold prototype and the entire mold-making process, check out our website and have all your questions and concerns answered by our team of experts.

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