Basic Principles of Mold Steel Selection

Selecting the right mold steel is critical for ensuring the quality, durability, and cost-effectiveness of plastic injection molds. Here are three basic principles to guide mold steel selection:

1. Match Steel Properties to Product Requirements

The steel's mechanical and physical properties must align with the specific needs of the molded product:

• High hardness and wear resistance for high-volume production or when using abrasive plastics (e.g., glass-filled).

• Toughness and impact resistance for complex molds or those with thin or deep cores.

• Thermal conductivity for efficient cooling and cycle time reduction.

• Corrosion resistance for molding corrosive materials like PVC or in humid environments.

Examples:

• P20 steel for general-purpose plastic parts.

• H13 steel for high-temperature resistance and durability.

• S136 or 420 stainless steel for high-gloss, transparent, or corrosive applications.

2. Consider Cost-Performance Balance

Optimize the steel grade to meet performance needs without unnecessary cost:

• For low-volume or prototype molds, lower-cost steels (e.g., pre-hardened steels like P20) may suffice.

• For mass production, hardened and wear-resistant steels are worth the higher upfront cost due to longer tool life.

Tip: Always evaluate the total cost of ownership — not just the steel price, but also machining, heat treatment, and maintenance costs.

3. Ensure Machinability and Processability

The chosen steel should be suitable for manufacturing processes:

• Good machinability reduces tooling and machining time.

• Dimensional stability after heat treatment prevents deformation.

• Polishability and etchability matter for surface texture or appearance-critical parts.

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