PL · engineering plastic
Polycarbonate PC (unfilled and 20% GF)
Tough and transparent, and it machines without cracking if the tooling is sharp and the depth of cut is light. It stress-cracks in the presence of some solvents, which is a process constraint.
Quoting this material
- Typical lead time
- 7–14 working days
- Condition
- Extruded sheet, rod or moulded stock
- Achievable finish
- Ra 0.8 µm typical · Ra 0.2 µm (flame or vapour polished) best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Tough and transparent, and it machines without cracking if the tooling is sharp and the depth of cut is light. It stress-cracks in the presence of some solvents, which is a process constraint.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 65 | MPa |
| Modulus of elasticity | 2.4 | GPa |
| Hardness | M70 | Rockwell |
| Continuous service temperature | 115 | °C |
| Thermal conductivity | 0.20 | W/m·K |
| Density | 1.20 | g/cm³ |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Extruded sheet, rod or moulded stock
Heat treatment
No heat treatment, but stress relieving is used before machining a complex part from sheet - residual stress from extrusion is what makes a polycarbonate part craze weeks later.
Achievable surface finish
Ra 0.8 µm
Ra 0.2 µm (flame or vapour polished)
Machined polycarbonate can be brought to optical clarity by flame or vapour polishing, which is a separate process after the machining.
Tooling and cutting parameters
Cutting speed
- 200–500 m/min (sharp uncoated carbide)
Feed
- 0.10–0.30 mm/rev turning · 0.10–0.25 mm/tooth milling
Tooling
- Sharp uncoated carbide, high rake; a dull cutter will craze the surface
Coolant
- Air blast; avoid solvent-based coolants entirely
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Machine guards and windows
- Display and fascia panels
- Lighting covers and lenses
- Electrical enclosures
- Medical equipment housings
DFM notes for this grade
- Solvent stress cracking is the classic failure: a machined edge left in contact with a solvent-based cleaner or adhesive will craze and crack, so the machining and the cleaning agent have to be chosen together
- Where optical clarity is needed, the machining is only a shaping operation - flame or vapour polishing produces the surface, and it is a separate process with its own cost
- Annealing before machining a complicated part avoids the crazing that appears weeks after a part appears finished
Questions buyers ask
- Why did my polycarbonate part craze after a few weeks?
- Almost always residual stress plus a chemical. Polycarbonate is notch and stress sensitive: a machined edge carrying stress from the stock, exposed to a solvent or an alkaline cleaner, crazes at the surface and then cracks. Annealing before machining breaks that chain.
- Can machined polycarbonate be made optically clear?
- Yes, by flame or vapour polishing after the machining - the machined surface is opaque by comparison. It is a separate operation with real skill in it, and the machining has to leave enough material for the polishing to remove.
Grades we would quote instead
PSU (Polysulfone)
6/10A transparent, sterilisable high-temperature plastic that machines cleanly.
PEI (Ultem)
5/10A hard, stiff, amber-coloured plastic that machines like a tough wood: clean chips, crisp edges and good dimensional stability.
POM-C (Acetal Copolymer)
8/10The best-machining plastic in this catalogue: it produces clean chips, holds a tolerance without drama and takes a fine finish.