How to choose the right injection mold material?

The selection of the right materials for injection mold processing has a crucial impact on injection molding, affecting production efficiency, cost, and the quality of plastic products. This blog comprehensively explores the criteria for selecting mold materials and provides a detailed explanation of the interactions between different materials and mold materials. These insights will help manufacturers and designers make informed decisions and optimize their injection molding production.

Injection molds must be made of materials that can withstand high pressure and high temperature during the injection molding process, and must also be compatible with the type of plastic that needs to be injected. The correct selection of mold materials not only affects the lifespan of the mold, but also impacts the aesthetics and structural integrity of the final product.

The selection of appropriate injection mold materials requires consideration of the following key factors:

Thermal conductivity: High thermal conductivity is crucial as it helps reduce cycle time by rapidly cooling the mold, which is essential for maintaining production efficiency.

Wear resistance: Mold materials must resist wear caused by the continuous flow of plastic, especially those filled with abrasive materials

Corrosion resistance: Some plastics may release corrosive substances. Under these conditions, the mold material should be selected to withstand corrosive environments to prevent degradation.

Cost effectiveness: Material cost is an important factor, especially in large-scale production where the cost of parts needs to be minimized.

Machinability: Materials that are easy to process can significantly reduce the time and cost associated with mold manufacturing.

Common injection mold materials

Several metal materials commonly used in the manufacture of injection molds, each with its unique properties and advantages

steel products:

Mold steel: The type of mold steel usually varies according to its purpose and performance characteristics, rather than a fixed model. Different types of mold steel have different characteristics and uses. Some common types of mold steel include:

- P20 steel: P20 is a universal plastic injection mold steel with good cutting performance, wear resistance, and heat resistance. It is typically used for producing large and complex plastic parts.

- H13 steel: H13 is a hot work mold steel with excellent heat resistance and wear resistance, suitable for die-casting and injection molding in high-temperature environments.

- S136 steel: S136 is a stainless steel mold steel with good corrosion resistance and oxidation resistance, commonly used in the production of transparent plastic products and medical devices.

- 718 steel: 718 is a heat-resistant plastic mold steel suitable for producing high-temperature plastic products, such as automotive parts and home appliance casings.

Stainless steel: favored due to its excellent corrosion resistance, particularly suitable for medical applications or when using corrosive plastics. Common stainless steels used for injection molds include:

- SUS420J2: It has good hardness and wear resistance, suitable for manufacturing general injection molds.

- SUS304: It has excellent corrosion resistance and is suitable for plastic products with high production requirements and good surface quality

- SUS316: It has higher corrosion resistance and is commonly used in the production of plastic products with higher requirements, such as medical devices and food containers.

- NAK80: It has good wear resistance and corrosion resistance, and is suitable for producing precision plastic products such as optical and electronic components.

Aluminum alloy: Aluminum alloy materials have the characteristics of lightweight and good thermal conductivity, and are suitable for rapid prototyping manufacturing, small batch production, and injection mold manufacturing that requires good processing performance. Common aluminum materials used for injection molds include:

- 7075 aluminum alloy: With excellent strength and hardness, it is suitable for producing plastic products that require higher wear resistance and heat resistance.

- 6061 aluminum alloy: It has good processability and strength, and is commonly used to manufacture injection molds with low to moderate complexity

- 2024 aluminum alloy: has high strength and cutting performance, suitable for manufacturing high-speed injection molds.

Beryllium copper alloy: Used in specific mold areas that require superior thermal conductivity or high dimensional stability, this material also has strength and hardness.

Understanding the way mold materials interact with specific types of plastics can guide the material selection process. Here are several commonly used engineering thermoplastic properties for your reference:

1. Acrylic ester (PMMA): commonly known as acrylic, requires precise temperature control during the molding process. Mold steel is usually used because they can maintain a stable temperature.

2. Acrylonitrile Butadiene Styrene (ABS): ABS is wear-resistant and requires molds made of wear-resistant materials, such as hardened steel, to resist wear.

3. Nylon (polyamide, PA): Nylon is hygroscopic and corrosive; Therefore, stainless steel molds are commonly used to prevent mold corrosion.

4. Polycarbonate (PC): PC has strong toughness and requires high-temperature molds. Prioritize the selection of mold steel with good thermal stability.

5. Polyethylene (PE) and polypropylene (PP): These two materials have low wear resistance and can be produced in short cycles using aluminum or pre hardened steel.

6. Polyoxymethylene (POM): POM is known for its rigidity and can be processed in steel molds that can withstand its high processing temperatures.

7. Polystyrene (PS): Due to its excellent cooling performance, brittle PS forms well in aluminum molds.

8. Thermoplastic elastomers (TPE) and thermoplastic polyurethanes (TPU): These materials require molds that can handle their elasticity and viscosity, typically using steel molds with specialized coatings for easy demolding.