How to choice the right Plastic mold material

Selecting the right plastic mold material is crucial for performance, durability, and cost-efficiency. Key factors include polishing performance, thermal stability, machinability, surface hardness, wear and corrosion resistance, and budget. Common choices range from P20 and NAK80 for polishability, H13 and S136 for heat resistance, to D2 and 1.2379 for wear-heavy parts. Material decisions should be based on the application, production volume, and surface requirements, supported by mold flow analysis and prototype testing.

How to choice the right Plastic mold material

1. Polishing Performance

Requirements:

Low surface roughness (Ra ≤ 0.025μm for optical components).

Microstructure: Fine-grained, homogeneous steel (e.g., P20, 718H).

Avoid impurities (sulfur < 0.005%, phosphorus < 0.01%).

Suitable Materials:

P20 (AISI): Pre-hardened to 28-36 HRC, ideal for general-purpose molds.

NAK80 (JIS): Mirror-polishable to Ra ≤ 0.01μm, used for transparent parts.

2. Thermal Stability

Key Properties:

Low thermal expansion coefficient (e.g., 10-12 × 10⁻⁶/°C for H13).

Minimal distortion during heat treatment (≤ 0.05% dimensional change).

High tempering resistance (retains hardness up to 550°C).

Materials:

H13 (AISI): Chromium-molybdenum steel for high-temperature applications (e.g., hot runners).

S136 (ASSAB): Corrosion-resistant with low thermal expansion, suitable for acidic plastics.

3. Machinability

Factors:

Pre-hardened steels (30-40 HRC) reduce post-machining distortion.

Sulfur addition (e.g., P20+S) improves chip formation but may reduce polishability.

Optimized Materials:

718HH (ASSAB): Pre-hardened to 33-38 HRC, balances machinability and polishability.

Moldmax HH (ATI): Beryllium-copper alloy for high thermal conductivity and ease of machining.

4. Surface Hardnes And Wear Resistance

· Requirements:

· Hardness: 50-60 HRC for high-wear areas (e.g., gates, slides).

· Surface treatments: Nitriding, chrome plating, or PVD coatings (e.g., TiN).

· Materials:

· D2 (AISI): High-carbon, high-chromium steel (60-62 HRC) for inserts subject to abrasion.

· 1.2379 (DIN): Cold-work tool steel with excellent wear resistance for ejector pins.

5. Corrosion Resistance

· For Hygroscopic or Corrosive Plastics (PVC, PC):

· Stainless steels (e.g., 420SS, S136) with ≥13% chromium.

· Aluminum alloys (e.g., 7075-T6) for low-volume production.

6. Cost vs. Performance

Example Specifications

Mobile Phone Housing Mold:

· Cavity: S136 (stainless, polished to mirror finish).

· Core: 718H (pre-hardened for machinability).

· Ejector Pins: 1.2379 (wear-resistant).

Automotive Headlight Lens Mold:

Cavity: NAK80 (superior polishability).

Cooling Channels: Copper alloy inserts (enhanced thermal conductivity).

Proper material selection ensures mold longevity, dimensional stability, and cost-effective production. Always validate choices with mold flow analysis and prototype testing.