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Common Plastics for CNC Machining: A Guide to Temperature Resistance, Thermal Conductivity, and Fire Resistance

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Common Plastics for CNC Machining: A Guide to Temperature Resistance, Thermal Conductivity, and Fire Resistance

Introduction

When selecting plastic materials for CNC machining, in addition to considering mechanical strength, understanding their thermal and fire resistance properties is crucial. These properties directly impact the stability, safety, and lifespan of the part in its final application. This article will analyze the key thermal performance indicators of each material based on the physical property tables of common engineering plastics.

Detailed Explanation of Thermal and Fire Resistance Properties of Common Plastics

  • ABS

ABS has a continuous temperature resistance of approximately 80°C. Its thermal conductivity is 0.17 W/m·K, making it a good thermal insulator. As an amorphous plastic, it has no distinct melting point; its glass transition temperature (softening point) is approximately 105°C. Standard ABS is UL 94 HB rated.

  • ABS-94V0

This is a flame-retardant ABS with a UL 94 V-0 fire rating. To achieve flame retardancy, the continuous temperature rating is slightly reduced to 75°C.

  • PC (Polycarbonate)

PC has excellent temperature resistance and can be used in environments below 120°C for extended periods. Its thermal conductivity is 0.20 W/m·K, and its glass transition temperature is approximately 145–150°C.

  • ABS+PC (Composite)

This composite combines the properties of both materials, offering a continuous temperature resistance of up to 100°C and a glass transition temperature between 105–150°C. It has a UL 94 HB fire rating.

  • PA6/PA66 (Nylon)

PA6 and PA66 are common nylon materials with continuous temperature resistances of 85°C and 80–95°C, respectively. They are crystalline plastics with melting points of 220°C and 255°C, respectively. Their standard fire rating is UL 94 HB.

  • Bakelite

As a thermosetting plastic, Bakelite has excellent heat resistance, with a continuous temperature resistance of 130–155°C. It does not melt and carbonizes directly when heated to extreme temperatures.

  • POM (Plasticized Metal)

POM has a continuous temperature resistance of 100°C and a melting point of approximately 162–165°C. Its thermal conductivity is 0.31 W/m·K, and its fire rating is UL 94 HB.

  • Glass Fiber Reinforced Plastic (e.g., PA6+30%GF, PC+30%GF)

Adding glass fiber significantly improves the material’s heat resistance. For example, PA6+30%GF has a continuous temperature resistance of up to 135°C, while PC+30%GF reaches 130°C. Fire resistance is also improved, with PC+GF achieving V-1/V-2 ratings.

  • PMMA (Acrylic)

PMMA has a continuous temperature resistance of approximately 80–85°C, with a glass transition temperature of around 100–105°C. It has a UL 94 HB fire rating.

  • PEEK (Polyetheretherketone)

PEEK is a top-tier, high-performance engineering plastic with an ultra-high continuous temperature resistance of 240°C and a melting point of 343°C. It also has a UL 94 V-0 fire rating.

  • FR4 (Fiberglass Epoxy)

This is a thermoset composite material commonly used as a substrate for circuit boards. It offers excellent temperature resistance, with a continuous operating temperature of approximately 110–130°C. The “FR” in its name stands for flame retardant, and it must meet the UL 94 V-0 fire rating.

Key Terms

  • Continuous temperature resistance refers to the highest temperature at which a material can maintain its physical properties and stability despite prolonged exposure to heat.
  • Thermal conductivity (W/m·K): A measure of a material’s ability to conduct heat. The lower the value, the better the material’s thermal insulation properties.
  • Melting point (Tm) / Glass transition temperature (Tg): Tg is the temperature at which amorphous plastics (such as ABS and PC) begin to soften; Tm is the temperature at which crystalline plastics (such as PA6 and POM) melt into a liquid state.
  • Fire rating (UL 94): A flammability test standard for plastics developed by the US UL Corporation. The ratings, from lowest to highest, are as follows:
  • HB: Horizontal burning. Burns slowly and is the lowest flame retardant rating.
  • V-2: Vertical burning. Extinguishes within 30 seconds; dripping of burning materials is permitted.
  • V-1: Vertical burning. Extinguishes within 30 seconds; dripping of burning materials is not permitted.
  • V-0: Vertical burning. Extinguishes within 10 seconds; dripping of burning materials is not permitted. This is the most commonly used high flame retardant rating.

Conclusion

Correctly understanding a material’s thermal properties is fundamental to ensuring component safety and reliability. For example, materials used in electronic device housings typically require V-0 flame resistance, while parts operating in high-temperature environments require materials with higher continuous temperature resistance, such as PEEK or Bakelite. If you have any questions about material selection, please feel free to contact our expert team.