How to choose the best Plastic Injection Mold Tool Material?

Selection of the best Injection molding tool material for injection mold core and cavity is very critical. It has an impact on injection mold cost, tool life, and quality of the injection-molded plastic part. 

This article covers various injection molding tool materials for core and cavity and how to select the best tool steel?

Factors affecting the selection of injection mold tool Material

You should consider the following points to select the best injection molding tool material for a given injection molded plastic part.

  1. Injection-molded part Surface finish.
  2. Production Volumes (Tool Life)
  3. Plastic Material Properties.
  4. Expected cycle time.
  5. Part Geometry

Types of Injection Mold Material

We can classify injection molding Tool materials into the following two categories.

  1. Heat treating or hardening tool steel
  2. Pre-hardened tool steel
1. Heat Treating or Hardening Tool Steel

Hardening tool steel materials for injection molding require hardening or heat treatment operation after cutting mold core and cavity. Hardening tool steel materials are available in the following grades.

  • H-13 mold steel
  • Stavax mold steel
  • Ramax Heat treating tool steel
  • S7 mold steel
  • Stainless tool steel.

Let’s discuss the above injection molding tool steel materials in more detail.

H-13 Mold Steel

H13 is a type of through hardening tool steel. It has excellent hot tensile properties, wear resistance, toughness, and resists tempering at high operating temperatures.

  • After hardening, H-13 tool steel’s typical hardness range is approx. 44 to 48 RC.
  • Welding and nitriding are also possible on H-13 tool steel.

Click this link to know more about H-13 tool steel properties.

H-13 tool steel is used to manufacture high production volume injection molds. For example, the H-13 material mold insert can give more than 1 million injection cycles with 33% glass-filled nylon injection molding material. Therefore H-13 tool steel is recommended for manufacturing injection mold for abrasive materials.

Stavax mold Steel

Stavax is through-hardened stainless steel material with good corrosion resistance, polish-ability, and wear resistance. Photo-etching and welding are possible on Stavax tool steel. Recommended Stavax through hardness range is 45 – 54 HRC. Click this link to know more about Stavax mold steel.

Using Stavax tool steel has the following advantages.

  • Lower mold maintenance costs. 
  • The surface of the cavities maintains their original finish over extended running periods. 
  • Injection Molds can be stored and operated in humid conditions. 
  • Water cooling channels are not affected by corrosion. As a result, heat transfer characteristics and cooling efficiency are constant throughout the mold life.

Because of the above advantages, Stavax tool steel material has application in high production volumes injection mold (core, cavities, and stripper rings). It is also suitable for molding corrosive materials such as PVC and abrasive-filled materials. 

Because of good polish-ability, Stavax tool steel material is also suitable for injection molding of optical parts such as clear glass.

Ramax Heat Treating Mold Steel

Ramax (heat-treated tool steel material) is through-hardened stainless steel with good corrosion resistance. It is available in uniform hardness of 38HRC. 

Welding is also possible on ramax tool steel with the required expertise. Click this link for more details in Ramax mold steel.

Ramax heat-treating mold steel has application to manufacture a mold for low to medium polished injection-molded plastic parts.

S7 mold Steel

S7 is a very durable, impact-resistant tool steel material with the following properties.

  • Hardening up to 56 RC is possible.
  • Air or oil hardening is possible
  • Shock resisting tool steel offering a unique combination of toughness and wear resistance.
  • High-accuracy machining is possible.

S7 tool steel is primarily used in applications where we require shock and impact resistance such as slides, lifters, etc. Click this link for more details on the S7 mold steel material.

Stainless Steel

Stainless steel is a post-hardened tool steel with a hardness range of 50-52 Rc. It is a low-cost post hardened tool steel and has an application to manufacture low production volume molds.

2. Pre-hardened Mold Steel For Injection Molding

Pre-hardened tool steel materials have an application to manufacture relatively medium production volume injection molds. The pre-hardened tool steel does not require heat treatment after machining operation. Therefore you can save mold manufacturing time. 

Following are the widely used pre-hardened steels for injection mold tool manufacturing.

  1. P20 mold steel
  2. NAK 80
  3. NAK 55
P20 Mold Steel

P-20 is pre-hardened mold steel is available in the hardness range of 28-32 Rc. It has applications to manufacturing medium production volume molds with surface finish up to SPI B-2. 

P20 tool steel has the following properties.

  • Good polishability.
  • Photo-etching properties. 
  • Hard chromium plating is feasible for mold reconditioning purposes.
  • P20 steel is electroless nickel plated for extra corrosion resistance.
  • Welding is feasible for repair.
  • It can be flame hardened or nitrided for extra resistance to wear and erosion. A nitride surface also increases the corrosion resistance.

Read this article for more details on P-20 tool steel.

NAK 80 Mold Steel

NAK-80 is Pre-hardened tool steel, available in uniform through the hardness of approximately 40 HRC. It is super clean, vacuum-arc remelted steel with uniform grain structure, uniform hardness, and excellent dimensional stability. When welded, NAK 80 leaves no witness lines after re-aging.

NAK-80 material machines up to 20% faster than 30 HRC P20 mold steels. It also does not require stress relief even after heavy machining.

NAK-80 tool steel has application to manufacture medium production volume molds with a critical diamond finish. For example, Clear lens molds.

NAK 55 Mold Steel

NAK 55 is pre-hardened mold steel with a uniform microstructure. It is available in the hardness range of 38-42 HRC. 

NAK 55 Machines up to 30 to 40 % faster than P20 mold steels. It had good weldability and EDM properties.

We will continue updating more information on injection mold tool steel. Add your comments, suggestions, or questions on the selection of injection mold materials in the comment box.

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