PL · 10 grades
Engineering Plastics
Insulating, chemical-resistant and light - until the part gets hot.
Engineering plastics cover electrical insulation, chemical service, low-friction and light-weight jobs that metal solves badly. They machine beautifully on the right setup, and badly on the wrong one: they clamp out of shape, they hold heat at the cut, and the swarf will not break. PEEK and PPS handle temperature and chemicals, POM and nylon handle wear, and PTFE handles chemistry at the cost of creep.
What this family does well, and where it bites
- Machined from extruded or compression-moulded stock; the stock grade matters
- Clamping pressure distorts the part - vacuum or soft jaws, light clamping
- Sharp, polished, high-rake tooling and generous clearance, or the plastic smears
- Thermal expansion is 5–10× steel, so tolerances have to be quoted at a temperature
Industries served
- Medical
- Semiconductor
- Food Processing
- Chemical Processing
- Electrical & Power
Engineering Plastics grades we machine
Each grade page carries the properties as supplied, what heat treatment does or does not do to it, the achievable surface finish, starting cutting parameters and the DFM notes that matter for that specific grade.
PEEK
5/1085–95 Shore D (M99 Rockwell) · 100 MPa
Machines cleanly for a plastic but it holds heat at the cut and the swarf will not break.
POM-C (Acetal Copolymer)
8/1084 Shore D (M94 Rockwell) · 68 MPa
The best-machining plastic in this catalogue: it produces clean chips, holds a tolerance without drama and takes a fine finish.
PTFE
7/1055 Shore D · 23–30 MPa
Soft and easy to cut, but it deforms under clamping pressure and creeps after machining, so holding a tolerance is harder than the cutting suggests.
Nylon 6/6 (PA66)
6/1080 Shore D · 80 MPa
Machines well when dry, but it absorbs moisture from the air and grows - which is the opposite of what most machined parts are expected to do.
UHMW-PE
6/1062 Shore D · 22 MPa
Cuts easily but badly: it is soft, it moves under clamping and it produces a continuous string of swarf that has to be managed.
PVDF
6/1078 Shore D · 50 MPa
Machines like a hard, slightly brittle plastic: clean chips, decent finish, and it holds a dimension far better than PTFE.
PEI (Ultem)
5/1085 Shore D (M109 Rockwell) · 105 MPa
A hard, stiff, amber-coloured plastic that machines like a tough wood: clean chips, crisp edges and good dimensional stability.
PPS
5/1085 Shore D · 75 MPa
Hard, brittle and dimensionally stable.
Polycarbonate (PC)
6/10M70 Rockwell · 65 MPa
Tough and transparent, and it machines without cracking if the tooling is sharp and the depth of cut is light.
PSU (Polysulfone)
6/10M69 Rockwell · 70 MPa
A transparent, sterilisable high-temperature plastic that machines cleanly.
Questions buyers ask
- Why are PEEK parts so expensive compared to aluminium?
- The stock costs more than aluminium by a factor of ten or more, and it is often bought as small-diameter rod or plate with a lot of waste. Machining time is not the issue - the material is. On a small medical component the raw material can be 70% of the price.
- Can you hold a tight tolerance in plastic?
- We will quote one, but understand what it means. Plastics move 5–10× more than steel for the same temperature change, and machined-in stress relaxes over days. A ±0.02 mm tolerance on PEEK is realistic on a feature being measured at 20 °C right after machining; it is not realistic on the same part sitting in a 40 °C enclosure a month later.