How to choose the right steel for your injection mold is a critical factor in getting 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 first get clear on what we are asking. And then we need to consider the plastic material, expected output, production cycle, standard components, appearance requirements, 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 is used for the injection molding process?
If you expect to make a 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 the pre-project but will also 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 a longer production cycle. If you use mold steel with low hardness, although you can save money in a short time, you may need to spend much more on mold maintenance.
For injection molding materials that have greater abrasion, such as glass-filled material, we need to consider how to reduce the wear and corrosion of the cavity unless the expected output is very low. However, for the most common glass-filled materials, wear-resistant steel can reduce thermal conductivity, which requires a better cooling system.
For corrosive plastics (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 a 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 a 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 number of alloy components is very small (the mass of most components is less than 0.10%; some are even less), this 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, can withstand higher loads in the injection molding process, and prolong their 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, and 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-molded steels. Apart from some other differences, the main difference between cold-worked and hot-worked steel is heat resistance. Cold work steel is suitable 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 commonly used mold steels for injection mold making
1. NAK55
The hardness of NAK55 is between 37 and 43 HRC, with no heat treatment, high hardness, good wear resistance and pressure resistance, uniform hardness, and good machinability. It is suitable for making high-precision mold processing and is commonly used in manufacturing high-precision mirror molds, such as cameras, makeup instruments, transparent covers, etc., suitable for injection mold materials such as PMMA, PC, and PS.
2. NAK80
In pre-hardened plastic mold steel, the hardness can reach 32 ~ 43 HRC. This kind of material does not need heat treatment and has good polishing, machinability, and erosion resistance. It is often used to make products with high appearance requirements. Such as an ear thermometer shell, a TV filter plate, a 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 or 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 and 32 HRC, 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 a hardness between 290 and 300 HB, excellent corrosion resistance, polishing, and machinability, and 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 30-33 HRC. Its corrosion resistance and strength are far superior to those of 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 molds, and is often used for knife tools.
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 and erodible plastics.
LUSHI not only has deep know-how about the characteristics of the materials but also provides the right materials according to the customer's needs, which is conducive to the control of project costs and the perfect completion of mold manufacturing.