Which Tool Steel Is Right For Your Plastic Injection Mold?

It is not always to easy to know which tool steel is the right one for your plastic injection mold. Not only that, but choosing the wrong one can spell disaster for all your hard work! More than one core or cavity has cracked or worn out long before its time, due to the wrong choice of tool steel.

What are some points to consider in choosing tool steel?

• Will the mold run at a high temperature?
• How important is the surface finish? 
• How many pieces do you expect to get from the mold?
• What kind of material will be injected into the mold?
• Is the mold highly detailed?
• How do you plan on machining it? 
• How critical are the dimensional tolerances?
• Are there moving parts, such as slides and lifters? 
• Will the hardened steel be coated?
• Will the mold be etched or chemically treated?
• What about the thermal conductivity during the molding operation?
• What type of molding will you be doing? This could be thermoplastic, thermosetting, two color molding, overmolding, insert molding, blow molding or compression molding. There are even more types of molding such as extrusion, vacuum molding and RIM molding.

What are the most common steels used in mold making?

That depends your needs. There are basically two types of tool steel used in injection moldmaking. Of course, there are always exceptions. These two types are: Through hardened steels and pre-hardened steels.

Through Hardened Tool Steels

Pre-Hardened Tool Steels

Some low-production molds are even made of aluminum, such as the high grade QC-7. Then there are tool steel castings, cast epoxy/steel blends, berylium copper, and other materials.

A good tool steel supplier is an important part of your overall success.

Once you develop a good working relationship with your supplier, respect that because he is very critical to your success. It is not wise to bargain hunt for the cheapest steel around; you will be penny-wise and pound foolish. The steel represents only about 5% of the total cost of a mold anyway!

Your supplier will have the experience and knowledge to guide you and keep you informed when a new steel is developed, or a process comes along that can benefit you. Plus, they have the heat-treating information you need, suggestions on which steel is appropriate, which steels should be used in combination, etc.

Should you do heat-treatment in house?

If you have enough volume or your operation is far away from a heat treater, yes. Otherwise, you can get great service from local heat-treaters who are expert at what they do and will have a very fast turn-around. Your parts will be cleaner, the heat-treatment more reliable and the cost is generally lower than the expense of a furnace and the utilities to keep it up and running.