The selection of plastic injection mold steels is a critical decision that can significantly impact the quality, performance, and cost of the molded parts. A mold maker must consider various factors when selecting the steel, such as material properties, tooling requirements, production volumes, and budget constraints. In this blog, we will explore the different types of steel used in plastic injection molding, their properties, and how to make an informed selection.

Types of Mold Steels

There are three main types of mold steels used in plastic injection molding: pre-hardened steel, hardened steel, and stainless steel. Each type has its unique properties, advantages, and disadvantages, and the selection largely depends on the molding application.

1. Pre-hardened Steel

Pre-hardened steel is the most common type of mold steel used in plastic injection molding. It has a consistent hardness and uniformity throughout the steel, making it easy to machine and polish. Pre-hardened steel is also cost-effective and readily available, making it an ideal choice for high-volume production runs. This type of steel is typically used for molds that produce low to medium complexity parts with simple shapes and texture requirements.

2. Hardened Steel

Hardened steel is a high-speed tool steel that is heat-treated to achieve a high level of hardness and wear resistance. This type of steel is ideal for molds that produce complex parts with fine details, such as threads, logos, and textures. Hardened steel can withstand high temperatures and pressures during molding and has excellent wear resistance, making it suitable for high-volume production runs. However, hardened steel is more expensive than pre-hardened steel and requires specialized tools and techniques for machining and polishing.

3. Stainless Steel

Stainless steel is a non-corrosive and high-temperature resistant material that is suitable for molds that produce medical and food-grade parts. It is also commonly used for molds that produce transparent or thin-wall parts that require a high level of surface finish. Stainless steel molds are expensive compared to pre-hardened and hardened steel but provide long-term durability and low maintenance.

Properties of Mold Steels

The selection of mold steels is largely dependent on the material properties that are required for the molded parts. The following are some of the critical properties that a mold maker should consider:

1. Hardness

The hardness of the steel determines its wear resistance and durability. A hard steel can withstand high temperatures and pressures during molding without deforming or cracking. However, harder steels are more challenging to machine and polish.

2. Machinability

The machinability of the steel determines how easy it is to machine and polish. A steel with good machinability will reduce tooling costs and increase production efficiency.

3. Corrosion Resistance

The corrosion resistance of the steel is critical for molds that produce food and medical-grade parts. Stainless steel is an excellent choice for such molds since it is non-corrosive and can withstand harsh chemicals and cleaning agents.

4. Wear Resistance

The wear resistance of the steel used in mold production is an important factor that affects the lifespan of the mold. Molds are exposed to high levels of wear and tear during production, especially when producing large quantities of parts. The steel used in mold production must be able to withstand this wear and tear to ensure that the mold remains functional for a longer period. Steel with high wear resistance is preferred for mold production because it can withstand the high levels of friction that occur during the molding process.

5. Thermal Conductivity

The thermal conductivity of the steel is crucial for molds that require cooling during molding. A steel with high thermal conductivity will facilitate faster cooling and reduce cycle times.

How to Select the Right Mold Steel

Now that we have explored the different types of mold steels and their properties, here are some factors that a mold maker should consider when selecting the right mold steel:

1. Part Requirements

The mold steel selection largely depends on the requirements of the molded parts. If the parts have complex geometries with fine details, a hardened steel would be a suitable choice. If the parts require a fine surface finish, stainless steel would be ideal.

2. Production Volume

The production volume is a crucial factor in mold steel selection. If the production volume is high, a pre-hardened steel mold would be the most cost-effective option. If the volume is low or the parts require a high level of details, a hardened steel mold would be appropriate.

3. Budget

The budget is a critical consideration in mold steel selection. Pre-hardened steel molds are an affordable option, while hardened steel and stainless steel molds are more expensive. The mold maker should strike a balance between the quality of the steel and the budget constraints.

Conclusion

The selection of mold steel is a critical decision that can significantly impact the quality, performance, and cost of the molded parts. Mold makers must consider various factors when selecting the steel, such as part requirements, production volume, and budget constraints. By making an informed selection, they can produce high-quality parts that meet the expectations of the customer while minimizing production costs.