Choosing heat-resistant plastics for CNC components means balancing temperature limits with cost and machinability. With decades of experience machining high-temp plastics for aerospace and automotive applications, small material decisions dramatically impact both performance and production efficiency.
Answer Section: Heat-resistant plastics range from 135°C (PC) to 400°C (PI). PEEK (250°C), PTFE (260°C), and PEI (200°C) offer different balances of thermal performance, chemical resistance, and CNC machinability based on application requirements.
Learn how temperature ratings impact performance, choose cost-effective heat-resistant plastics, and design for successful CNC machining.
Table of Contents
What Temperature Range Can Heat-Resistant Plastics Handle?
Heat-resistant plastics range from PC at 135°C to PI at 400°C continuous service. PEEK (250°C), PTFE (260°C), and PEI (200°C) represent the most commonly machined high-temperature options per ASTM D648 testing standards.
Heat-Resistant Plastic Temperature Ranges:
- PI (Polyimide): 350-400°C — Aerospace, extreme environments
- PTFE (Teflon): 260°C — Chemical processing, seals
- PEEK: 250°C — Medical devices, automotive
- PEI/PPS: 200°C — Electronics, under-hood components
- PSI (Polysulfone): 180-187°C — Moderate heat applications
- PC (Polycarbonate): 135°C — General housings, cost-sensitive
- Nylon/PA: Up to 300°C — Varies by grade
We routinely machine PI components for aerospace customers requiring 350°C+ continuous service, achieving ±0.02 mm tolerances using ceramic tooling and controlled feeds per AS9100 documentation requirements. PEEK medical parts typically operate at 200-250°C sterilization cycles, while PTFE’s 260°C capability suits chemical processing applications despite requiring specialized machining strategies.
Temperature ratings follow ASTM D648 and ISO 75 continuous service standards, not short-term exposure limits. Automotive under-hood applications typically require 150-200°C capability per SAE J1885 standards, making PEI ideal for radiator components. Electronics rarely exceed 135°C operational temperatures, where PC provides cost-effective performance.
Design Takeaway: Specify continuous operating temperature per ASTM D648/ISO 75 standards, not peak exposure limits. Reserve PI (400°C) for genuine extreme-heat applications; use PEEK (250°C) or PEI (200°C) for cost optimization without compromising thermal reliability.
How Do I Choose the Right Heat-Resistant Plastic for My Application?
Match material to critical requirements: PEEK for medical/aerospace requiring strength + heat, PTFE for chemical processing needing universal compatibility, PEI for electronics requiring dielectric properties, PPS for automotive fluid resistance.
Selection Criteria by Priority:
- Operating Temperature: Continuous service rating per ASTM D648/ISO 75
- Chemical Exposure: Specific acids, solvents, oils requiring resistance
- Mechanical Load: Tensile strength (20-80 MPa range) and impact requirements
- Electrical Properties: Dielectric strength per ASTM D149 for electronics
- Regulatory Compliance: UL94, FDA CFR 177, FAR 25.853 as required
PEEK dominates medical implants requiring FDA CFR 177 compliance plus 250°C sterilization and 80 MPa tensile strength — a combination unmatched by alternatives. PTFE excels in chemical pump seals where 260°C rating and universal solvent compatibility outweigh its limited 20 MPa strength.
PEI provides optimal cost-performance for electronics housings needing 200°C capability, 15-17 kV/mm dielectric strength per ASTM D149, and UL94 V-0 flame ratings. PPS handles automotive under-hood applications requiring SAE J200 oil/coolant resistance alongside 200°C thermal performance.
Multiple properties often drive selection — aerospace components need both temperature resistance and strength-to-weight ratios per FAR 25.853, while medical devices require heat resistance plus USP Class VI biocompatibility testing.
Design Takeaway: Rank operating requirements by criticality — temperature, chemical exposure, mechanical loads, electrical needs. Select the most cost-effective material meeting all critical standards rather than over-specifying for non-critical properties.
Which Applications Work Best for Each Heat-Resistant Plastic?
Automotive uses PEI/PPS for under-hood components, aerospace relies on PEEK/PI for structural parts, electronics prefer PEI/PC for housings, and chemical processing requires PTFE for seals and valve components.
Application-Specific Material Matching:
- Automotive Engine Bay: PEI, PPS — SAE J200 fluid resistance, 150-200°C
- Aerospace Structural: PEEK, PI — FAR 25.853 compliance, extreme temperatures
- Electronics Housings: PEI, PC — UL94 flame ratings, dielectric properties
- Chemical Processing: PTFE — Universal chemical compatibility, 260°C
- Medical Devices: PEEK — FDA compliance, sterilization capability
- Industrial Equipment: PPS — Chemical resistance, dimensional stability
Automotive radiator tanks typically use PPS for ethylene glycol resistance at 180°C continuous service per SAE J1885, maintaining structural integrity through thermal cycling. We machine valve covers from PEI that hold ±0.1 mm tolerances on mounting surfaces despite engine bay temperature fluctuations.
Electronics applications favor PEI for power components generating 150-200°C heat while meeting UL94 V-0 requirements, while PC handles general housings under 135°C cost-effectively. Chemical processing pumps use PTFE seals for universal solvent compatibility, though mechanical support is required due to limited strength.
Medical sterilization demands drive PEEK selection for surgical instruments requiring repeated 250°C autoclave cycles with FDA CFR 177 compliance. Aerospace applications specify PI for jet engine components where 350°C+ capability and FAR 25.853 flame resistance are mandatory.
Design Takeaway: Match material to the most demanding application requirement and relevant standards. Avoid over-specifying premium materials when standard options meet actual operating conditions and regulatory requirements.
What Factors Affect Heat-Resistant Plastic CNC Costs?
Material costs range from approximately $3-5/lb (PC) to $40-80/lb (PEEK), while machining complexity typically adds 40-100% labor time for premium materials requiring specialized tooling.
Cost Factors by Impact Level:
- Raw Material: PC ($3-5/lb) < PEI ($8-12/lb) < PEEK ($40-80/lb) typical
- Machining Time: PEEK/PI typically require 40-100% longer cycle times
- Tooling Cost: Ceramic tools for PI cost approximately 3-5x standard carbide
- Setup Complexity: Specialized fixturing for thin walls, temperature-sensitive materials
- Quality Requirements: Tighter tolerances increase inspection and cycle time
- Volume: Low quantities eliminate material purchasing advantages
PEEK medical parts typically cost 8-12x more than equivalent PC electronics housings due to both material premium and machining complexity requirements. PI aerospace components require ceramic tooling with approximately 50-part tool life versus 200+ parts for carbide tools in PEI applications.
Machining parameters vary significantly — PC machines at standard speeds/feeds, while PEEK typically requires 50% reduced parameters to prevent thermal damage and maintain surface finish. PTFE demands frequent tool changes due to material buildup, increasing labor costs despite faster cutting capabilities.
Volume economics matter significantly — 100-piece PEEK production runs spread setup costs effectively, while single prototypes bear full fixturing and programming overhead. Material minimums often force small quantities to purchase excess stock, inflating per-piece costs.
Design Takeaway: Balance material performance against total manufacturing cost including machining complexity. PEI often provides optimal cost-performance for moderate heat applications, while PEEK premiums are justified only when performance requirements exceed alternatives’ capabilities.
What Design Rules Ensure Successful Heat-Resistant Plastic Machining?
Maintain 1.5mm minimum wall thickness for rigidity, use 0.5mm minimum corner radii, and allow thermal expansion 2-5x higher than metals. Design for plastic behavior, not metal equivalents.
Critical Design Guidelines:
- Wall Thickness: 1.5-2.0mm minimum for dimensional stability during machining
- Corner Radii: 0.5mm minimum to prevent stress concentration and cracking
- Hole Tolerances: ±0.05mm standard, ±0.02mm achievable for precision features
- Thermal Clearances: Allow 50-150 μm/m/°C expansion per ISO 11359
- Surface Finish: Ra 0.4-1.6 μm achievable with diamond tooling
- Draft Angles: 0.5-1.0° recommended for deep pockets and complex geometry
Thin-walled sections under 1.0mm typically deflect during machining, causing dimensional errors and poor surface finish. We maintain 1.5mm minimum walls in PEEK housings to consistently achieve ±0.02 mm tolerances while preventing chatter and tool breakage during production.
Heat-resistant plastics expand 50-150 μm/m/°C per ISO 11359 testing versus 12-25 μm/m/°C for aluminum alloys, requiring assembly clearance adjustments. PTFE’s approximately 100 μm/m/°C expansion necessitates sliding fits rather than interference fits in high-temperature applications.
Fixturing requires soft-jaw or vacuum workholding techniques to prevent stress-induced cracking during machining. Standard mechanical clamping can introduce residual stresses causing post-machining warpage. Surface finishes of Ra 0.4 μm are consistently achievable using diamond-tipped tools with optimized cutting parameters.
Design Takeaway: Design for plastic material behavior — higher thermal expansion, lower stiffness, stress sensitivity. Consult your CNC partner during design reviews to optimize geometry for both performance and manufacturability before finalizing technical drawings.
Conclusion
Heat-resistant plastic selection balances operating temperature (135-400°C), chemical exposure, and mechanical requirements against material and machining costs. PEI provides optimal cost-performance for most applications under 200°C, while PEEK and PI justify premiums for extreme environments requiring superior strength or temperature resistance. Always design for plastic thermal expansion and stress sensitivity rather than metal equivalents. Contact us to explore manufacturing solutions tailored to your heat-resistant plastic component requirements.
Frequently Asked Questions
If operating temperatures exceed 100°C continuously or 120°C intermittently, standard plastics will deform or degrade. Heat-resistant options start at PC (135°C) and scale up based on thermal requirements.
Yes, ±0.02mm is achievable in PEEK and PEI with proper fixturing. Maintain 1.5mm minimum walls and 0.5mm corner radii for optimal results. PTFE requires special techniques due to deformation tendencies.
Material costs range 2-15x standard plastics: PEI costs $8-12/lb vs $2-3/lb ABS, while PEEK reaches $40-80/lb. Machining complexity adds 40-100% labor time for premium materials.
Over-specifying temperature ratings, inadequate thermal expansion allowances, or stress concentration from sharp corners. Design for continuous service temperatures per ASTM D648, not peak exposure limits.
PEI and PPS excel in 150-200°C engine bay environments with oil/coolant resistance per SAE J200. PPS offers better chemical resistance, while PEI provides superior dimensional stability.
PEEK handles 250°C with 80 MPa strength for extreme applications, while PEI provides 200°C capability at 1/3 the cost. Choose PEI unless you specifically need PEEK’s superior temperature or strength performance.
