7 Essential CNC Materials Every Engineer Must Know Before Machining

Aluminum is the default for prototypes and low-volume housings because it cuts fast and holds tight tolerances without much fuss. The workhorse is 6061-T6. It welds, anodizes cleanly, and machines at high spindle speeds. For brackets, heat sinks, and fixture plates, 6061 is usually the right answer and rarely the wrong one.

When you need strength, step up to 7075-T6. Its tensile strength sits in the range of mild steel while weighing roughly a third as much, which is why it appears in aerospace ribs and high-performance automotive parts. The trade is machinability: 7075 is less forgiving, tool wear climbs, and thin walls distort if you push the feed.

Not every aluminum is friendly. Soft, gummy grades such as 1100 or 5052 build up on the cutting edge, smear the surface, and tear during tapping. If a part needs a mirror finish or a fine thread, 1100 is the wrong call. Chip evacuation matters more than the tool path on deep pockets, because recut chips scratch the wall you just finished.

Anodizing changes the decision too. Hardcoat adds roughly 50% of its thickness to the surface, so a 20 μm coating on a Ø10 mm pin moves the diameter. Call out pre-plate dimensions on the drawing, not post-plate ones.

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  Choose 6061-T6 forbrackets, housings, heat sinks, most prototypes
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  Choose 7075-T6 forhigh-load ribs, aerospace fittings, wear plates
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  Avoid soft grades forfine threads, cosmetic faces, thin walls

Stainless steel work-hardens the moment the tool rubs instead of cuts. A dull edge, a light feed, or a pause in the cut all raise the local hardness and turn the next pass into a fight. The result is smearing, galling, and threads that tear out. Rigid setups and sharp tooling are not optional here; they are the process.

Grade choice follows the environment. 303 machines best and is fine for bushings and fittings that see mild corrosion. 304 and 316 cover food, medical, and marine service, with 316L preferred when welds are involved. For wear, 17-4PH (SUS630) offers high strength after precipitation hardening, and 440C suits bearings and valve seats where hardness drives the design.

Carbon steel is cheaper and easier to cut, which makes it the right choice when corrosion is not a factor. Grades like 1018 and 1045 turn and mill predictably. Alloy steels 4130, 4140, and 4340 add through-hardening depth for shafts, gears, and load-bearing links. A36 is structural plate steel, not a precision alloy, so do not expect tight flatness from it.

Heat is the shared enemy. Stainless distorts when the cut zone overheats, and hardened steel moves when stress relief is skipped between roughing and finishing. On long shafts we rough, stress-relieve, then finish. Skipping that step shows up as a bend you cannot measure until the part is off the machine.

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  303 / 304 / 316Lfittings, food and medical hardware, marine parts
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  17-4PH, 440Chigh-strength and wear-critical components
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  4130 / 4140 / 4340shafts, gears, load-bearing links
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  1018 / 1045general turned parts, no corrosion exposure

Copper and brass conduct heat away from the cut faster than any steel, which sounds helpful until the tool cannot shed its own heat. C36000 free-cutting brass machines cleanly and is the standard for fittings and connectors. C101 and C110 are the electrical grades, and they are gummy, so expect stringy chips and a shorter tool life. Beryllium copper is a different animal: it machines to high strength and conductivity but the dust is a health hazard, so it needs controlled handling and documented cleanup.

Titanium, typically TC4 (Ti-6Al-4V), gives an excellent strength-to-weight ratio and resists corrosion in seawater and body fluids. It also conducts heat poorly, so the cutting edge absorbs almost all of it. Speeds stay low, coolant flow stays high, and the tool never dwells in the cut. Thin titanium sections deflect under cutting force, which makes workholding as important as the cutter.

Magnesium AZ31B and AZ91D are the lightest structural option here, and they machine faster than aluminum. The catch is fire risk. Fine chips ignite, so chip control, dedicated tooling, and never letting fines accumulate are part of the job, not housekeeping. If your part does not need the last few grams saved, aluminum is the lower-risk choice.

Copper alloys and titanium both punish the wrong finish spec. Polishing titanium to a mirror takes more time than the machining itself, and bead blasting is often the better cosmetic answer.

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  C36000 brassfittings, valve bodies, connectors
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  TC4 titaniumaerospace brackets, medical implants, marine hardware
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  AZ31B magnesiumweight-critical housings, with strict chip control

Plastics machine faster than any metal, but they move after the cut. POM is dimensionally stable, low friction, and the usual pick for gears, bushings, and sliding parts. PEEK holds strength at high temperature and resists chemicals, which suits medical and semiconductor fixtures. ABS, PC, PMMA, PA, PP, and HDPE cover the lower-cost end of the range.

The trap is thermal expansion. A plastic part measured at the machine at 25 °C can be a different size in a 40 °C enclosure or a cold room. For long parts, tolerance should be quoted with a reference temperature, or the design should tolerate the growth. Coolant choice matters too: some plastics craze or absorb moisture, and PA is hygroscopic enough to change size across a season.

Sharp tools, high rake angles, and generous clearance keep plastics from melting or chipping. Deep holes need peck cycles because chips weld to the flutes. Carbon fibre behaves differently again: it is abrasive, so tooling wears fast and dust extraction is mandatory.

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  POMgears, bushings, sliding wear parts
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  PEEKhigh-temperature and chemical-resistant fixtures
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  Carbon fibrelightweight panels; abrasive, needs extraction

Tolerance is a system, not a number. The machine, the tool, the fixture, and the thermal state of the part all sit inside that number. Our 127 high-precision CNC machines include 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum processing size reaches 4,000 mm, and travel ranges run from 500 × 310 × 200 mm compact work up to a 4,000 × 400 × 150 mm envelope.

For hard materials we rough, let the part cool, then finish. For thin walls we use adaptive tool paths that keep radial engagement steady instead of burying the cutter. For plastics we keep fixtures soft and clamp loads low, because a plastic part will take a permanent set from a clamp screw. Five-axis work lets us reach deep pockets and angled features in one setup, which removes the re-fixturing error that stacks up on multi-setup parts.

Inspection closes the loop. Every order goes through raw material check, in-process monitoring, and final inspection, with 100% inspection before shipment and reports on request. Finish targets range from Ra 1.6–3.2 μm as machined down to Ra 0.2–0.8 μm where a sealing face or bearing bore calls for it.

We work from one prototype to 10,000+ part runs with no minimum order quantity. If a material choice is going to raise your cost or risk, we say so during DFM review rather than after the first article.

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  Rough, cool, finishfor stainless, titanium, and hardened steel
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  Adaptive tool pathsfor thin walls and deep pockets
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  Soft fixturingfor plastics and thin-walled aluminum