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How to choice the right Plastic mold material

2025-06-25

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.

This is the table of contents for this article

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How to choice the right Plastic mold material
1. Polishing Performance
2. Thermal Stability
3. Machinability
4. Surface Hardnes And Wear Resistance
5. Corrosion Resistance
6. Cost vs. Performance
Example Specifications

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

Material Category	Typical Applications	Cost Range (USD/kg)
Aluminum	Prototyping, low-volume molds	$5-15
Pre-hardened Steel	Consumer products, general molds	$8-25
Stainless Steel	Medical, food-contact applications	$15-40
High-performance Steel	Optical lenses, precision components	$30-80

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.

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FAQ

FAQs

Can Bost customize modified plastics with special properties?

Yes! We offer modification services such as reinforcement, flame retardancy, conductivity, wear resistance, and UV resistance, for example:
• Adding carbon fiber to enhance stiffness
• Reducing the coefficient of friction through PTFE modification
• Customizing food-grade or medical-grade certified materials

What is the minimum order quantity (MOQ)? Do you support small-batch trial production?

The MOQ for standard products is ≥100kg. We support small-batch trial production (as low as 20kg) and provide mold testing reports and performance data feedback.

How do I select the appropriate engineering plastic grade for my product?

Selection should be based on parameters such as load conditions (e.g., pressure/friction), temperature range, medium contact (e.g., oil/acid), and regulatory requirements (e.g., FDA/RoHS). Our engineers can provide free material selection consulting and sample testing.

What is the delivery lead time? Do you offer global logistics?

Standard products: 5–15 working days; custom modifications: 2–4 weeks. We support global air/sea freight and provide export customs clearance documents (including REACH/UL certifications).

What are the core advantages of Bost engineering plastics compared to ordinary plastics?

Bost engineering plastics feature ultra-high mechanical strength, high-temperature resistance (-50°C to 300°C), chemical corrosion resistance, and wear resistance. Compared to ordinary plastics, their service life is extended by 3 to 8 times, making them suitable for replacing metals in harsh environments.