01
Parts come off the machine bowed
Extruded HDPE bar and plate carry internal stress. Cut one face and the part curls before finishing. We rough, stress-relieve and re-clamp, so the last pass still removes a light, even chip.
Plastic Machining
Precision CNC Machining HDPE for Chemical, Electrical and Wear Parts
HDPE machines clean and fast, but it moves when you cut it. We hold ±0.005 mm on stress-relieved stock using sharp tooling, air blast cooling and light finishing passes. One prototype or 10,000 parts.
±0.005 mm toleranceNo minimum orderRa 0.8–1.6 μm12-hour quote127 CNC machinesISO 9001:2015
±0.005 mmAchievable tolerance on HDPE
127High-precision CNC machines
16Simultaneous 5-axis centers
4,000 mmMaximum processing size
When HDPE fights back
Four problems engineers bring to us with HDPE parts
The material is not hard to cut. It is hard to cut accurately twice.
02
Walls melt instead of cutting
HDPE has low thermal conductivity, so heat stays at the edge. A dull tool or a stopped feed smears the surface and leaves a hairy finish that no secondary operation fixes. Sharp carbide and air blast keep the cut clean.
03
Hold dimensions drift overnight
The part measures 0.05 mm oversize in the morning and on size in the afternoon. Thermal expansion near 100–200 × 10⁻⁶ per °C explains most of it. We machine in a temperature-stable shop and let parts settle before final inspection.
04
Bolt holes creep under load
HDPE cold-flows. Threads alone loosen, and a clamped joint loses preload. We spec through-bolts with washers, coarse pitch threads or brass inserts, and we tell you when a design should be metal instead.
How we machine it
Tooling, cooling and clamping built around HDPE
Three decisions control whether an HDPE part holds tolerance: cutter geometry, heat removal and how the blank is held.
Cutting strategy
Sharp tooling, high spindle speed, no dwell
HDPE chips best when the tool shears rather than rubs. We run polished single-flute or two-flute carbide end mills with high rake angles, spindle speeds well above what the same cutter would use in aluminum, and feeds that keep the edge loaded.
Air blast carries chips out of the pocket. Coolant is optional and often unnecessary, but trapped chips are not: they recut, generate heat and weld to the wall. A vacuum shoe on the finish pass keeps the surface free of shavings.
- 1CutterPolished flutes, high rake, sharp corner radius
- 2HeatAir blast first, coolant only when the geometry traps heat
- 3Finish passLight depth of cut, continuous feed, no pause in the corner
Setup and inspection
Soft jaws, light clamping, settled measurement
HDPE deforms under clamp pressure. We hold thin plates in soft jaws or vacuum fixtures, set clamping force low, and support the floor of thin pockets with a sacrificial backup so the wall cannot flex inward during the cut.
Inspection happens after the part returns to room temperature. Measuring a warm part guarantees a false reading. For long parts we check straightness on a surface plate and record the number, so you can see what the material did rather than trusting a single caliper reading.
- 1WorkholdingSoft jaws, vacuum chucks, low clamp pressure
- 2Thin wallsBackup support and step-down passes to limit deflection
- 3MeasurementInspect at room temperature, report on request
Material fit
Is HDPE the right plastic for this part?
A quick read on where HDPE wins and where it should be replaced.
| Requirement | HDPE | Better choice |
|---|---|---|
| Chemical resistance | Strong against acids and bases | HDPE |
| Electrical insulation | Good, low moisture uptake | HDPE |
| Sliding wear, low load | Works, low friction | HDPE or POM |
| Stiffness and load bearing | Low modulus, cold flows | POM, PA or aluminum |
| Service above 80 °C | Softens, loses strength | PEEK or PTFE |
| Optical clarity | Opaque, waxy surface | PC or PMMA |
| Tight thread strength | Threads strip easily | Brass insert in HDPE |
| Dimensional stability | High thermal expansion | POM or aluminum |
What we run
Machining and finishing services for HDPE parts
One supplier from blank to finished, inspected part.
01
3-axis CNC milling
Plates, manifolds, covers and insulators with pockets, slots and drilled patterns. 27 machines available for plastic work.
02
4-axis and 5-axis machining
Angled ports, contoured ducts and multi-face parts in one setup. 16 simultaneous 5-axis centers cut handling error out of the tolerance stack.
03
CNC turning and mill-turn
Bushings, rollers, spacers and flanged fittings. 16 mill-turn centers combine turning and milling without a second fixture.
04
Rapid prototyping
One-off HDPE parts for fit checks and flow testing, machined from stock instead of tooled, so the geometry can change between revisions.
05
Surface finishing
Bead blasting, tumbling, brushing and polishing to control surface texture. Laser marking available down to 1.5 mm character height.
06
Assembly and inspection
Insert installation, hardware fitting and 100% inspection before shipment, with dimensional reports on request.
Capability
HDPE machining scope and limits
| Item | Range | Notes |
|---|---|---|
| Tolerance | ±0.005 mm | On stable features after settling |
| Surface finish | Ra 0.8–1.6 μm | As-machined Ra 1.6–3.2 μm |
| Maximum part size | 4,000 mm | Long travel up to 4,000 × 400 × 150 mm |
| Minimum order | One part | Prototype to 10,000+ runs |
| Lead time | 3–5 days | Production can start within 24 hours |
| Thickness limit | From 1.5 mm | Thin walls need backup support |
| Inspection | 100% before shipment | Reports on request |
| Confidentiality | NDA on request | Secure uploads |
Why GreatLight
What we bring to a plastic machining job
15Y
Plastic cutting experience
Founded in 2011, we have machined plastics long enough to know which grades behave and which fight the tool. HDPE sits in the easy group when the setup is right.
±0.005
Tolerance we commit to
On stable HDPE features, ±0.005 mm is achievable. We say so up front when a drawing asks for more than the material can hold.
127
Machines under one roof
Milling, turning, mill-turn and 5-axis capacity in three plants across 7,600 m². A plastic job does not wait behind a metal backlog.
12h
Quote and DFM review
Send a model and get pricing plus a manufacturability read within 12 hours. We flag thin walls, sharp internal corners and thread choices before cutting.
24h
Production start
Once the drawing is frozen, machining can begin within 24 hours. Parts typically ship in 3–5 days.
100%
Inspection before shipment
Raw material check, in-process monitoring and final inspection. Nothing leaves without a dimensional check. Reports on request.
7,600 m²Manufacturing space
150Technicians on staff
99.99%Qualification rate
3Wholly-owned plants
Where HDPE parts go
Sectors that specify machined HDPE
Chemical and industrial equipment
Tank liners, pump housings, valve bodies and wear strips. The sector needs chemical resistance and flat sealing faces.
- Chemical resistant
- Flat sealing faces
- Up to 4,000 mm
New energy and battery lines
Insulating plates, spacers and non-conductive fixtures for cell handling and test rigs.
- Electrical insulation
- Low moisture uptake
- No metal contamination
Food and water handling
Guides, star wheels, chute liners and cutting boards where low moisture absorption and easy cleaning matter.
- Low water absorption
- Washable surface
- Ra 0.8–1.6 μm
Automation and robotics
Lightweight end-effector plates, guards and jigs that must not scratch or short nearby electronics.
- Light weight
- Non-marking
- ±0.005 mm
FAQs
Questions engineers ask about machining HDPE
What tolerance can you actually hold on HDPE?
On a stable feature that has settled at room temperature, ±0.005 mm is realistic. Long unsupported walls and large flat plates are harder because the material expands and contracts with the shop temperature.
If a drawing calls for tighter than the material allows, we say so before machining rather than shipping a part that will not repeat.
Why does my HDPE part warp after machining?
Extruded stock carries internal stress from the extrusion process. Removing material on one side releases that stress unevenly and the part bows.
The fix is sequencing: rough both sides, let the part relax, then take light finishing passes. We also remove equal amounts from opposing faces where the geometry allows.
Should I use coolant when cutting HDPE?
Air blast handles most jobs. It clears chips and limits heat without the cleanup that coolant brings to a porous plastic.
Coolant helps in deep pockets and small-diameter holes where chips pack and heat has nowhere to go. In those cases we use it deliberately, not by default.
Can you tap threads directly in HDPE?
Yes, but threads in HDPE are for light duty. They strip under repeated assembly or sustained load because the material cold-flows.
For anything that gets opened more than a few times, we recommend a brass insert or a through-bolt with a washer. We will tell you which one suits the wall thickness.
What is the thinnest wall you can machine?
Around 1.5 mm on a supported wall. Below that, clamp pressure and cutting force deflect the material and the dimension drifts.
We support thin floors with a sacrificial backup and take shallow step-down passes. If the design needs a 0.8 mm wall, a different plastic or a molded part is usually the better route.
How does HDPE compare with POM or PEEK for machining?
HDPE is softer, cheaper and more chemical resistant. It machines faster and wears tools less than POM or PEEK.
POM holds tolerance better and carries load without creeping. PEEK handles high temperature and keeps strength. Pick HDPE when chemical resistance and cost drive the decision, not stiffness.
Can you machine HDPE sheet up to 4,000 mm long?
Yes. Our long-travel machines handle up to 4,000 × 400 × 150 mm, and other cells cover 750 × 1,150 × 550 mm plus smaller envelopes.
Long parts need special attention to straightness. We check them on a surface plate after the material returns to room temperature.
Do you have a minimum order quantity for HDPE parts?
No minimum. We run one prototype or a 10,000-part production batch on the same process.
Uploads are treated as confidential and an NDA is available on request if the drawing is sensitive.
Send us the HDPE drawing
Upload a model and get a price plus a manufacturability review within 12 hours. We will flag anything the material cannot hold before the first chip is cut.
12-hour quote100% inspectionNo minimum orderNDA on request
