In order to create a production mold for any products, the producer or designer need to find the materials that exist in the market. There are various types of materials including metal and non-metal group such as carbon steel, alloy steel, stainless steel, or aluminum alloy. Choosing the right materials for the mold is an important issue that need to be considered. In addition, the lifetime of the mold depends highly on the types and quality of the steel.
In general, plastic injection mold need to be pressure resistant since the injection process have high pressure along with tensile stress, compressive stress, friction power, and high temperature impact. The designers need to be aware of these factors and choose the appropriate types of steel for different parts of the mold.
For example, metal stamping dies mainly used cast iron as moldbase to decrease cost in production since grade steel could be expensive and effect to the material cost. In making a huge size mold or dies, pure grade steel could be expensive and ineffective. Therefore, the designer could design some part with lower grade steel or cast iron to save the cost of production while everything still works fine.
In order to cast iron, the producer would heat treated the material, and let it cool down and form as desired. After that, the producer would heat it again to let it release stress to reduce the problem from unstable shape of metal while further using. After that, the producer would use those materials to further process as desired shape through machining or through casting.
Mild Steels is considered as low carbon steel which the carbon percentage of the materials would be less than 0.25% of the total weight. Mild steels could be cheap, easy to shape or machine since it has low level of hardness. In addition, it could also be weld easily. This type of steel could use to make the structure of the mold in the part that are not quite important. The grade that often use would be SS40 and SS41. The disadvantage of this type of steel is that it could not quench to increase the hardness property.
Case hardening steels often been used to make part of the injection mold. The grade steel in this category could be AISI P2 or P4. The mold could further carburize at the surface until it reaches the hardness at 58-62 HRC, while the internal of the mold still have the hardness of 25-35 HRC. These properties could assist the mold to resist to corrosion during the high-pressure operation. In addition, the hardness surface could assist polishing stage to be easier. However, there are disadvantages from the carburize stages such as the sizing of the materials which could bend from the changing of temperature during the carburizing process. Therefore, the designer needs to calculate the allowance to ensure that the materials could be further use.
Medium carbon steels that usually use in the mold industry would be S45C or S50C grade. These molds would usually use to make the moldbase structure such as spacer block, or retaining plate. Moreover, this type of steel could use to make the A or B plate itself for the mold that have low volume. This type of steel would have the carbon property of around 0.6-1.4% and the hardness of around 65-68 HRC after carburize. This type of steel has quite good impact resistant due to the hardness and property. However, the heat resistant of the steel is not quite good so it should be use only with parts that have low volume and short production lots.
Plastic mold steel is the most common types of steel that been used for plastic mold production. This type of steel has been pre-hardened to reach the hardness of around 28-40 HRC. The property of the steel is suitable for further machining and polishing. The hardness level of this type of steel could be further use in operation without carburizing which could avoid from the change in sizing of the steel. However, the designer and operator need to be aware of the residual stress from the machining process which could also change the sizing and shape of the steel. The common plastic mold grade steel that been use in the market would consists of AISI P21, P20, and P20S while the S indicates the mixture of Sulphur into the steel to allow better result in machining. This type of steel often uses as the insert or the critical part of the mold since the pricing of this group of steel is high compare to others.
At Jaje, we do experience in making mold for more than 2 centuries. Throughout the past, we do get trusted from customers from both locally and internationally. If there are any projects that related to mold, production, or manufacturing, we are more than welcome to co-develop the products along with our customers in order to suit with the usage of the customers, proper quality and also within the budget. Please do not hesitate to contact us at jajemold@gmail.com
