There are many criteria that must be considered while selecting tool steel for mold cavities. Some of these include the type of molding material, expected volume, maintenance, and cost of the tool. Hot Work steel tool steel is known for its capacity to withstand high abrasion, pressure, and temperature conditions.
For the tool manufacturers, maintenance is an important aspect and not the cost of the tool itself, because it affects the productivity of the tool where it is used. There is a positive and negative side to each aspect. For example, if your requirement is hardened tool steel, then the cost of the tool might be more, but it will require less maintenance, so if you calculate the actual cost, it will be less. However, the main drawback of the hardened steel is its less thermal conductivity. So, if you select soft steel with higher thermal conductivity, the initial cost will be less, but the maintenance cost will increase. So, tool manufacturers should be cautious about selecting material. Sometimes it is an ideal option to apply a coating to the material, to get the properties of hardened steel, it can certainly offer cost-benefit. However, if the coating gets damaged, then replacing it with a new coating would not be an economical option since it will require extra cost and time. However such coated steel can offer more thermal conductivity compared to hardened steel.
You must know what you want to mold and the selection of material depends on it.
For the abrasive and Glass material, the corrosion issue must be addressed. Also for the Glass material, lower thermal conductivity is required.
PVC is corrosive material, and stainless steel is an ideal option. However, if you use cheaper options compared to stainless steel then you must implement procedures to prevent corrosion.
If you are expecting high-quality finishing, lens-grade tool steels should be used.
If molding material doesn’t have corrosive or abrasive content, like glass fibers, P-20 Steel is an ideal option. But if you need production in higher quantity with small-sized tools, then hardened tool steel is an ideal option, because it offers longer tool life and needs less maintenance.
If you want production in less quantity then aluminum is a good option, but maintenance is an issue for using aluminum. Also, nowadays, there are different aluminum versions, with different properties, so you should know which type of aluminum is best for you. If aluminum is used for developing prototypes only and the actual tool uses different tool steel, then production results might differ because aluminum is a good thermal conductor, and actual tool steel used might not offer similar thermal conductivity. Since aluminum is a soft material, extra efforts are required to make it tough. You have to be careful to prevent any cavity damage.
Tool steel P-20 is also widely used, its hardness is 28-30 RC and it is also available in hardness of 38-40 RC. P-20 is a popular choice when you need high-quality finishing.
S-7 is popular if you need high-volume parts and high tolerance. It is long-lasting and impact-resistant.
Stainless steel is used for medical tooling since it offers excellent polished cavities.
H-13 is an ideal material for abrasive material. Mostly, for reducing the possibility of stress cracks, above 50 RC, cavities are not hardened.
For the hardened steel tool, there are issues with cracked cavities. This can happen if RC hardness is extremely high or it can be due to bad design or due to a sharp edge on the tool.