Polycarbonate (PC) – CNC Machining

Polycarbonate is used for CNC machined components that require impact resistance, transparency, and tight dimensional control without brittle failure.

Its machining behavior is strongly influenced by heat buildup, making cutting parameters and chip evacuation critical to avoid melting or edge smearing.

At ShvaveyMetal, polycarbonate CNC machining strategies are defined around thermal management, sharp tooling, and finishing passes that preserve optical and dimensional quality.

Polycarbonate (PC) is an amorphous thermoplastic known for its high impact strength, transparency, and dimensional stability across a wide temperature range.

It is commonly selected over acrylic when toughness and resistance to cracking under load are primary design requirements.

Mechanical Properties (Typical)

Property Typical Value Units
Density ~1.20 g/cm³
Tensile Strength ~60–70 MPa
Yield Strength ~55–65 MPa
Elongation at Break ~90–120 %
Elastic Modulus ~2.3 GPa
Impact Strength (Izod) Very high (no break) —

Mechanical properties vary with grade, additives, and processing history.

Thermal & Physical Properties

Property Typical Value Units
Glass Transition Temperature (Tg) ~147 °C
Continuous Service Temperature ~115–125 °C
Thermal Conductivity ~0.19 W/m·K
Coefficient of Thermal Expansion ~65–70 µm/m·K

These properties make thermal control during CNC machining critical to dimensional accuracy and surface quality.

Chemical Resistance (General)

Substance Category Resistance Level
Water / Aqueous Solutions Excellent
Alcohols Good
Oils and Greases Good
Acids (Dilute) Fair to Good
Solvents (Aromatic, Ketones) Poor

Chemical resistance depends on exposure time, temperature, and internal stress state.

Polycarbonate machining behavior is dominated by its low thermal conductivity and tendency to soften rather than fracture under excess heat.

Key machining characteristics include:

  • Risk of edge melting or smearing if surface speed is too high
  • Continuous chip formation requiring effective chip evacuation
  • Good surface finish achievable with sharp tools and controlled feeds
  • Sensitivity to dwell marks and tool rubbing during finishing
  • Internal stress sensitivity if excessive heat is introduced

Machining is typically performed dry or with air blast, using sharp carbide tools and conservative cutting parameters.

Benefit Description
High Impact Resistance Withstands shock and mechanical abuse
Optical Transparency Suitable for clear and light-transmitting components
Dimensional Stability Maintains geometry under moderate thermal variation
Tough, Non-Brittle Behavior Reduced risk of cracking during machining and use
Broad Grade Availability Available in clear, UV-stabilized, and filled variants

Polycarbonate is commonly used for CNC machined components such as:

  • Transparent covers, windows, and guards
  • Optical housings and protective enclosures
  • Medical and laboratory device components
  • Electrical and electronic insulation parts
  • Prototypes requiring toughness and visual inspection

Application suitability depends on optical requirements, thermal exposure, and chemical environment.

Variant General Characteristics
Clear Polycarbonate High transparency and impact resistance
UV-Stabilized Polycarbonate Improved outdoor and UV resistance
Glass-Filled Polycarbonate Higher stiffness with reduced impact strength
Flame-Retardant Grades Enhanced fire performance for electrical use

Machining parameters may vary significantly between unfilled and glass-filled grades.

  • Avoid sharp internal corners that concentrate stress
  • Allow for higher thermal expansion compared to metals
  • Specify surface finish requirements clearly for optical areas
  • Minimize heat input during finishing to prevent haze or distortion
  • Select the appropriate grade early in the design process

Proper alignment between design intent and machining strategy is critical for high-quality PC components.

FAQ

How is polycarbonate CNC machined without cracking?

Polycarbonate is notch-sensitive and prone to stress cracking. Sharp tooling with polished flutes, controlled heat generation, generous internal radii instead of sharp corners, and verified coolant compatibility are all essential. Many incompatible fluids initiate crazing, so cutting fluids and cleaning agents must be confirmed before production.

Can coated or profiled polycarbonate sheet be machined?

Yes, though coated material requires additional care. Hard or abrasion-resistant coatings are brittle and can chip at cut edges, so sharp tooling, light finishing passes and appropriate support are needed. Protective masking should generally be left in place during machining to prevent surface damage.

What tolerances can be held when machining polycarbonate sheet?

Reasonable tolerances are achievable, but polycarbonate's thermal expansion and tendency to relieve internal stress limit precision compared with acetal or PEI. Large sheet components in particular may move after machining. Stress-relieved stock, staged material removal and stable inspection conditions all improve dimensional consistency.

What are machined polycarbonate components used for?

Typical uses include machine guards, inspection windows, light covers, electrical insulators, fixtures, prototype housings and transparent enclosures. It is selected where a part must be transparent, impact resistant and dimensionally stable, and where the brittleness of acrylic would present a safety risk.

Should polycarbonate be annealed before or after machining?

Both are used. Annealing stock before machining relieves manufacturing stress and reduces cracking during cutting. Annealing after machining relieves residual machining stress and improves long term stability. For critical or highly stressed parts, annealing at both stages is common practice.


Why Machine Polycarbonate at ShvaveyMetal

ShvaveyMetal machines polycarbonate using CNC processes optimized for heat control, surface integrity, and dimensional repeatability.

This approach supports reliable production of clear and structural PC components across prototype and low-to-medium volume manufacturing programs.