to choose the right mold steel is important for injection tool
by Lushi-Molding  | April 12st. 2020  |  Tags: Injection Molding Tool

What should you consider when choosing the mold steel

How to choose the right steel for your injection mold is the critical factor to get the best parts that we need. Many variables are involved here and should be seriously considered. Before we try to answer this question, we should firstly get clear what we are making for. And then we need to consider the plastic material, expected output, production cycle, standard components, appearance requirement, expected mold costs, and also the post-maintenance costs. Only after comprehensive consideration of these factors can we truly know the mold materials we need.

What kind of plastic using for injection molding process

If you expect to make large output of parts, such as 1 million shots, you need a very wear-resistant and high-hardness mold steel which will increase your mold cost in pre-project, but it will reduce your maintenance cost in the long term, which is also a big expense. However, the thermal conductivity of hardened steel is low. If you do not pay special attention to the design of the cooling system in the mold, it will affect the cooling time with longer production cycle. If you use mold steel with low hardness, although you can save your cost in short time, but it maybe need much more cost on the mold maintenance.

For injection molding materials that have greater abrasion, such as glass-filled material, then we need to consider how to reduce the wear and corrosion of cavity unless the expected output is very low. However, for the most common glass-filled materials, wear-resistant steel can reduce thermal conductivity, which need better cooling system.

For corrosive plastic (such as PVC), stainless steel is a good choice. If injection molded parts require a high surface finish, mold steel with lens grade specifications should be considered to produce the high gloss surface. For injection molding materials that are not abrasive or corrosive, you can choose a cheaper injection mold steel, such as P20. If the desired production capacity is very low, then you can choose rapid tool using aluminum.

Classification of tool steel

Alloy tool steel and non-alloy tool steel

Tool steel can basically be divided into alloy steel and non-alloy steel. If the amount of alloy components is very small (the mass of most components is less than 0.10% some are even less), which is usually called non-alloy steel. The difference between alloy steel and non-alloy tool steels is that alloy steels have a much higher hardness and can withstand higher loads in the injection molding process and prolong the service life. At the same time, it can also withstand higher operating temperatures.

The alloy composition in alloy tool steel can be adjusted according to the required performance of the steel. Some alloy elements are added to the tool steel. Common ones are chromium, vanadium, manganese, molybdenum, nickel, tungsten, cobalt.

The carbon content of non-alloy tool steel is generally higher usually between 0.5% and 1.5%. Although the carbon content of stainless steel is usually less than 0.1%.

Cold work tool steel and hot work tool steel

The difference between cold-worked and hot-worked steels only exists in alloy mold steels. Apart from some other differences, the main difference between cold-worked and hot-worked steel is heat resistance. Cold work steel is suitable just for up to 200 ° C, while hot work steel can withstand twice the working temperature (up to 400 ° C). For higher temperatures, only high-speed steel (up to 600 ° C) is used.

10 common used mold steel for the injection mold making

10 common used mold steel for the injection mold making

1. NAK55

The hardness of NAK55 is between 37 ~ 43HRC, no heat treatment, high hardness, good wear resistance and pressure resistance, uniform hardness and good machinability, suitable for high-precision mold processing, commonly used in manufacturing high-precision mirror molds, such as cameras, Makeup instruments or transparent cover, etc. suitable for injection mold materials such as PMMA, PC and PS.

2. NAK80

Pre-hardened plastic mold steel, the hardness can reach 32 ~ 43HRC. This kind of material does not need heat treatment and has good polishing and machinability, erosion-resistance. It is often used to make products with high appearance requirements. Such as ear thermometer shell, TV filter plate, cosmetics box, etc., suitable for plastic products such as ABS, GPPS, PS, PC and AS.

3. 718H

718H material is pre-hardened plastic mold steel without hardening and tempering treatment. It is often used in long-life plastic injection molds, such as home appliance parts and computer housing molds. The working life is longer than P20 steel and has good polishing. It is widely used in injection molds, blow molds and extrusion molds and is suitable for the production of plastics such as PS, PE, PP and ABS.

4. P20

P20 material is one of the most commonly used plastic mold steels, with a hardness between 28 ~ 32HRC, which can be eroded by electricity and has good polishing. It is often used in toy molds and is suitable for PP and PE plastics.

5. S136

S136 steel has hardness between 290 ~ 300HB, has excellent corrosion resistance, polishing and machinability, no need for heat treatment. It is suitable for making molds used in weak acids and humid environments, especially for high-volume transparent plastic parts, such as CDs and optical instruments. It is preferred to manufacture transparent products of PVC, PP, EP, PC, PMMA and other materials.

6. 420SS

420SS steel is stainless steel with high hardness, good polishing and corrosion resistance. The hardness is 30-33HRC. Its corrosion resistance and strength are far more than other materials. Commonly used for corrosive materials, suitable for mass production molds.

7. H13

H13 material contains tungsten and has higher temperature resistance. It is suitable for die-casting alloy mold materials, such as aluminum, magnesium, zinc, and copper alloy die-casting mold and is often used for knife tool.

8. 8407

8407 material is alloy tool steel with chromium, molybdenum and vanadium. It is better than the general H13 material and has good fatigue strength and thermal stress fatigue performance. It is often used in die casting molds, forging molds and extrusion molds.

9. S7

S7 material is composed of chromium-molybdenum alloy, which has high impact resistance and toughness, good processing and heat treatment performance, and is suitable for molds such as knife dies and punches.

10. M300

The M300 material is well processed and polished after heat treatment. The chromium content is up to 16%. It has excellent corrosion resistance and is very suitable for PVC materials. It can be polished into a mirror surface. It is suitable for transparent plastic and erodible plastics.

Lushi-Molding not only have good expertise on the characteristics of the materials, but also provide the right materials according to customer's needs, which is conducive to the control of project costs and the perfect completion of mold manufacturing.


More Infos Please Contact Us:

Email: jonas@lushimold.com
Jonas Zhan
Mobil:+86 18818587045

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Injection Molding Tool

Plastic Injection Molding

Molding Technology

Mold Design

Injection Molding Process

Additive Manufacturing

Plastic Materials

Industrial applications

Chinese Tooling

Industry 4.0


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