PEEK can be machined to tight tolerances in China, but only by shops that control heat from the first roughing pass through final inspection. Still, there is a real need to understand why so many suppliers get PEEK wrong, what their mistakes cost you, and how to read a PEEK quote before you commit a program to it.
Which PEEK Grade Does Your Part Actually Need?
Grade selection drives everything downstream: tooling, cycle time, achievable tolerance, and price. Most buyers specify “PEEK” and leave the choice to the supplier, which is how carbon-filled material ends up in a part that needed electrical insulation.
The three grades below cover most industrial work. Figures come from published Victrex datasheets for injection-molded test specimens, so treat them as comparison values rather than guarantees for your finished part.
| Property (23°C unless noted) | Unfilled PEEK (450G) | GF30 (450GL30) | CF30 (450CA30) |
|---|---|---|---|
| Density (g/cm³) | 1.30 | 1.51 | 1.40 |
| Tensile modulus (MPa) | 4,000 | 11,500 | 28,000 |
| Tensile stress (MPa) | 98 (yield) | 179 (break) | 265 (break) |
| Deflection temperature at 1.8 MPa (°C) | 152 | 328 | 336 |
| Expansion along flow, below 143°C (ppm/K) | 45 | 18 | 5 |
| Thermal conductivity (W/m/K) | 0.29 | 0.30 | 0.95 |
| Water absorption, saturation (%) | 0.45 | 0.30 | 0.30 |
| Volume resistivity (Ω·cm) | 1 × 1016 | 1 × 1016 | 1 × 105 |
| Machining behavior | Easiest; sharp carbide | Abrasive; carbide or PCD | Most abrasive; PCD preferred |
| Typical fit (approved sectors) | Insulating fixtures, seals, food and pharma equipment parts | Stiff structural parts, valve seats, wafer-handling hardware | High-load wear parts where conductivity is acceptable |
Source: Victrex technical datasheets for PEEK 450G, 450GL30, and 450CA30 (March 2026 revision). PCD means polycrystalline diamond.
Two rows deserve a second look.
Deflection temperature. Unfilled PEEK deflects at 152°C under a 1.8 MPa load, not at the 260°C figure buyers remember from marketing pages. Glass fiber lifts that to 328°C. Where your part carries load at temperature, unfilled PEEK can fail long before you expected it to – and the Victrex 450G datasheet states the number plainly.
Volume resistivity. Carbon fiber takes PEEK from roughly 1016 to 105 ohm-centimeters, a drop of 11 orders of magnitude. That is no longer an insulator. Specify CF30 for a test socket body, and you’ve built a short circuit with excellent dimensional stability.
Why Do Most Shops Machine PEEK Badly?
PEEK doesn’t fight the tool the way a nickel superalloy does. It fails quietly instead, and the failure often surfaces weeks after the parts ship. Three mechanisms account for most of it.
Heat with nowhere to go
Unfilled PEEK conducts heat at 0.29 W/m/K. Aluminum sits near 150 W/m/K, roughly 500 times higher. Every joule the tool generates stays close to the cut, because the workpiece simply cannot carry it away.
A peer-reviewed micromilling study measured the result directly. Researchers dry-milled PEEK at 60,000 rpm with a 1 mm cutter and a 1 mm/s feed. They recorded cutting-zone temperatures near 253°C, far above the glass transition and within sight of the 343°C melting point. The same study found burr heights on PEEK reaching 350 micrometers, against under 50 micrometers on acrylic under matched conditions.
Above glass transition, PEEK stops cutting and starts smearing. Chips fuse instead of breaking, edges tear, and the surface you paid for disappears.
The feed rate paradox
Now the counterintuitive part, and it’s where careful-sounding suppliers go wrong. That study found cutting-zone temperature falling as feed rate rose at high spindle speeds. Slower, gentler passes ran hotter, not cooler.
Shops that “take it easy” on PEEK are cooking it. Chips are the primary heat-removal mechanism, so starving the chip load leaves the energy in your part. Burned, sintered chips appeared at low feed rates and high temperatures, exactly where a cautious operator would expect to be safest.
Stress that machining releases
Extruded PEEK stock carries internal stress from its own manufacture. Ensinger, a major producer of machinable plastic stock, states plainly that dimensionally precise parts require stress-annealed material. Machining heat otherwise releases that stress and warps the component.
Semi-crystalline thermoplastics can post-shrink by roughly 1 to 2.5% after heat exposure above the glass transition. On a 100 mm feature, that’s millimeters of movement, not microns. Asymmetric parts and one-sided stock removal warp hardest.
What Does Competent PEEK Machining Look Like?
Competent PEEK machining in China looks exactly like competent PEEK machining anywhere. Every control below exists to hold the cutting zone below the glass transition, then release stress before it can distort a finished dimension. None of it is exotic. All of it is discipline, applied the same way on part one and part 10,000.
Sharp tools, changed on schedule
Blunt edges generate heat instead of chips, so tool condition is a thermal control, not a cost line. Unfilled PEEK cuts cleanly with sharp carbide. Glass- and carbon-filled grades are abrasive, and Ensinger recommends carbide or polycrystalline diamond tooling with regular wear checks for reinforced plastics.
Carbon fiber shortens tool life sharply. We budget those tool changes into filled-grade quotes rather than discovering the cost mid-run.
Feeds that keep chips moving
Our feeds keep chip load high enough that heat leaves with the material. Deep holes get peck cycles, since drilling more than two diameters deep traps heat with no route out.
Compressed air clears chips and cools the cut without wetting the part. Dry or air-cooled machining also avoids leaving coolant residue on components bound for clean process environments.
Annealing before finishing, not after
Rough machining releases stress and moves the part. Anneal at that point, then take the finishing cut to the final dimension.
Reverse the order and you anneal a finished part into a scrapped one. Cut sequences get planned to balance material removal across the part because uneven removal is what drives warp.
Inspection that catches drift
We inspect PEEK on coordinate measuring machines (CMM) with full traceability at controlled temperatures. PEEK expands about 45 ppm/K below glass transition, so a 10-degree swing on the inspection floor moves a 100 mm dimension by roughly 45 micrometers.
Measure warm parts, and you’ll pass work that fails at the customer. Letting components equalize before final measurement costs minutes and saves returns.
Five questions that separate real PEEK capability from hopeful capability
Ask any prospective supplier these before you place a program. The answers take two minutes and tell you more than a certificate wall.
1. Which grade are you quoting, and why? A supplier who answers “PEEK” without naming unfilled, glass-filled, or carbon-filled hasn’t thought about your service conditions.
2. Was the stock stress-relieved before machining? If they don’t know, the answer is effectively no.
3. Where does annealing sit in your process order? Between roughing and finishing is correct. After finishing is a warning sign.
4. What tooling do you run on filled grades? Standard carbide on carbon-filled PEEK means tool wear will drift your dimensions across the batch.
5. At what temperature do you inspect? Uncontrolled inspection temperature makes tight plastic tolerances meaningless.
Where Are Machined PEEK Parts Used?
PEEK earns its price where a cheaper polymer fails on temperature, chemistry, or dimensional drift. Four sectors account for most of the industrial PEEK CNC work we quote in China.
Semiconductor equipment
Wafer-handling fixtures, carriers, guides, and test socket bodies all lean on the same property set. Semiconductor-grade PEEK has to stay dimensionally stable through thermal cycling, resist process chemistry, insulate electrically, and shed few particles. Test sockets hold contact arrays in position while devices sit hot, so hole position matters more than headline strength.
Taiwan’s specialist shops share this same semiconductor ecosystem, and our China vs. Taiwan CNC machining comparison covers how the two fit together on a split program.
Grade selection matters more here than in any other sector we serve. Our semiconductor CNC machining work runs unfilled and glass-filled PEEK where parts must insulate and reserves carbon-filled grades for structural components where conductivity is acceptable.
Oil and gas
Downhole seals, back-up rings, and bushings meet heat, pressure, and aggressive fluids at once. PEEK holds shape where elastomers extrude and where cheaper thermoplastics soften.
Filled grades usually win here, since creep resistance under sustained load matters far more than electrical behavior.
Chemical processing
Pump seals, valve seats, bushings, and wear rings run against chemistry that attacks metals. PEEK resists most acids, bases, and solvents at temperature, which extends service intervals and cuts unplanned downtime.
Glass-filled and wear-grade materials handle the load-bearing versions. Unfilled PEEK suits lower-load parts where purity is the priority.
Food and pharmaceutical equipment
Equipment components such as guides, scrapers, bushings, and fittings need steam-sterilization tolerance and clean surfaces. Dry machining helps because it leaves no coolant residue to explain to an auditor.
Unfilled PEEK is the usual starting point, with glass-filled grades stepping in where stiffness matters more than absolute purity.
What Does PEEK Machining Cost, and Why?
PEEK parts cost several times the equivalent part in aluminum, and the split between material and process surprises most buyers. Four drivers account for the premium.
1. Raw material. PEEK stock costs many times more per kilogram than commodity engineering plastics such as nylon or acetal. Filled grades cost more again.
2. Stock utilization. Machining from solid turns most of the billet into chips, and PEEK chips carry no meaningful scrap value.
3. Tool consumption. Filled grades chew through carbide fast. Diamond tooling costs more upfront and repays that only across volume.
4. Process time. Annealing cycles run for hours and occupy oven capacity. That time lands on your lead time and your invoice.
Nesting parts efficiently and choosing the smallest viable stock size cuts material waste more than any other lever. We flag those opportunities during the design for manufacturability (DFM) review, before the first cut.
At XTJ CNC, we run prototypes in as fast as five days, with typical lead times of five to seven days, and we hold no minimum order quantity. Prototype one part, prove the grade, and then scale.
Send us your drawing and the service conditions: temperature, load, chemistry, and whether the part has to insulate. We’ll come back with a grade recommendation, a realistic tolerance set, and a quote that accounts for annealing time instead of hiding it.
FAQs on PEEK CNC Machining in China
Can a supplier in China hold tight tolerances on PEEK parts?
Yes, within limits, the polymer sets rather than the machine. Our general machining capability reaches ±0.003 mm on metals. PEEK tolerances run wider and stay part-dependent because PEEK expands about four times more than steel per degree.
Achievable tolerances depend on feature size, wall thickness, grade, and whether inspection happens at a controlled temperature. Send the drawing, and we’ll tell you which callouts are realistic and which need relaxing before anyone quotes.
Does every PEEK part need annealing?
No. Annealing is a stress-relief step needed when tolerances are tight, walls are thin or asymmetric, or heavy stock removal happens on one side of the part.
Simple, chunky, loosely toleranced components often skip it entirely. We decide per part during DFM review, since unnecessary annealing adds days and cost while improving nothing.
When does injection molding beat machining for PEEK?
Machine at low and moderate volumes; mold once geometry is frozen and annual volumes justify tooling. PEEK molds at melt temperatures near 380°C and need hot tooling, so mold amortization only works across serious quantities.
Machining also stays correct when you need grade flexibility, tight tolerances on isolated features, or design changes between batches.
What surface finish is achievable on machined PEEK?
Unfilled PEEK takes a clean as-machined finish readily, and better finishes come from sharp tooling and heat control rather than secondary operations. Filled grades expose fiber ends at the surface and finish rougher at identical parameters.
Tell us the functional requirement, whether sealing, sliding, or cosmetic, and we’ll set parameters against that instead of chasing a roughness number.
Why do PEEK parts change size after delivery?
Residual stress relaxing over time is the usual cause, and heat accelerates it. Parts cut from unannealed stock, or annealed after finishing rather than before, drift as that stress equalizes. Moisture plays a smaller role than it does with nylon, since PEEK absorbs under half a percent at saturation. Ask your supplier whether the stock was stress-relieved and where annealing sat in the process order.
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