5 Axis CNC Machinable Materials

Aluminum is the first material we suggest for most 5-axis work. It cuts fast, holds tight tolerances, and the tool load stays low, so a 4,000 mm part can be roughed and finished in one setup without thermal drift becoming a problem. We keep 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 in the material list.

Grade matters more than people expect. 6061-T6 gives a good balance of strength and weldability, and it anodizes cleanly. 7075 machines well and takes a mirror finish, but it is less corrosion resistant and costs more. 2024 has higher fatigue strength and is common in aerospace brackets, though it needs a protective finish. ADC12 is a die-casting alloy; we machine it when a casting needs secondary features.

Watch thin walls. Aluminum deflects under cutting force, and a 0.5 mm wall on a 5-axis contour will sing unless the toolpath is adjusted. The fix is usually a lighter radial engagement rather than a slower feed. Tell us the wall thickness at quoting and we plan the strategy around it.

Aluminum is a poor fit when the part sees continuous abrasion or high temperature. Above roughly 150 °C it loses strength quickly. For those cases we move to steel or titanium.

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  Good fitHousings, brackets, manifolds, heat sinks, prototype frames
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  Less idealHigh-wear surfaces, parts running above 150 °C

Titanium is where 5-axis pays for itself. TA1, TA2 and TC4 (Ti-6Al-4V) are all in our list, and complex impeller or medical geometry that would need three fixtures on a 3-axis machine can be cut in one continuous pass. The trade-off is heat. Titanium conducts heat poorly, so the cutter takes the temperature instead of the chip. We run lower surface speeds, higher coolant pressure, and sharp uncoated or AlTiN tools.

TC4 gives roughly twice the strength of 6061 at about 60% of the weight of steel. It also galls, which means threads and sliding surfaces need attention. Use thread milling rather than tapping for anything under M6, and specify a finish on wear faces.

Stainless steel covers 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH (SUS630). 303 is the free-machining grade and the easiest to run. 304 and 316 are tougher, work-harden quickly, and need a constant feed so the tool never rubs. 17-4PH machines in the annealed condition and then ages to high strength, which suits pump shafts and valve bodies.

Carbon steel rounds out the group: 1018, 1045, 4130, 4140, 4340, A36 and tool steel. These are inexpensive and strong, and they cut predictably. The catch is corrosion. Unless the part is painted, plated or black oxided, plain carbon steel will rust in service.

With any of these three families, the 5-axis advantage is fewer setups. Every re-clamp on a hard material adds error and handling time, and a single continuous toolpath removes both.

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  TitaniumAerospace, medical, motorsport. Slow speeds, heavy coolant
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  StainlessFood, chemical, marine. Control work hardening
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  Carbon steelShafts, plates, fixtures. Needs a protective finish

Plastics cut on the same 5-axis centers, but the rules change. Thermal expansion is high, so a part checked hot will not match the drawing when it cools. We rough, let the part rest, then finish. On a long part this is the difference between a good tolerance and a rejected one.

Polycarbonate (PC) is tough and transparent. It is used for guards, light covers and manifolds. It scratches easily and stress-cracks around sharp internal corners, so radii matter. POM (acetal) is the most predictable plastic we machine. It holds ±0.05 mm on a well-supported part, has low friction, and is a natural fit for gears, bushings and valve bodies.

Nylon (PA) is strong and abrasion resistant but absorbs moisture, which changes dimensions after machining. If a nylon part has a tight tolerance, specify it dry and expect movement. PP is chemical resistant and cheap, good for tanks, lids and fluid parts, but it is soft and gummy; sharp tools and climb milling keep the edge clean.

PTFE has the lowest friction and the widest chemical resistance of the group. It also creeps under load and expands a lot with heat, so it suits seals, insulators and lab hardware rather than structural parts. We also run ABS, PMMA, PEEK, HDPE and carbon fibre when the application calls for it.

PEEK sits at the top of the plastic range. It keeps strength near 250 °C and survives steam and many solvents. It is also expensive and abrasive to tooling, so we only recommend it when the temperature or chemical load rules out cheaper options.

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  POMGears, bushings, precision mechanical parts
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  PCTransparent covers, guards, impact parts
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  PAWear strips, rollers. Expect moisture movement
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  PTFESeals, insulators, chemical hardware

Start with mechanical load. If the part carries a structural load, the yield strength decides the family before anything else. Aluminum covers most brackets and housings. Steel and titanium cover the rest. Plastics are for low-load parts, wear surfaces and electrical insulation.

Then look at the environment. Temperature, moisture, chemicals and UV each remove options. A part that sees salt spray should not be 7075 without a coating. A part that sees steam should not be nylon. PTFE and PEEK handle chemical exposure that would destroy most metals.

Machinability is the third check, and it drives cost more than material price does. Titanium stock costs more than aluminum and takes several times longer to cut. A 316L part with deep pockets may need more spindle time than a 4140 part of the same shape. When the design allows, a small geometry change can cut cycle time significantly.

Surface finish is the fourth. If the drawing calls for Ra 0.2–0.8 μm, that is achievable on aluminum and on many plastics with the right toolpath, but it adds a finishing pass. On titanium it is slow. Ask whether the finish is functional or cosmetic; cosmetic finishes on non-critical faces often cost more than they return.

Finally, cost and quantity. For one prototype, pick the material that machines easiest and meets the load. For a 10,000-part run, it is worth revisiting the choice, because a cheaper alloy that cuts 20% faster can beat a premium alloy that needs extra operations. We machine from one part to full production runs with no minimum order quantity.

If two materials both pass the checks, run the cheaper one first and test it. A prototype is the least expensive place to find out that a substitution works.

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  LoadStrength and stiffness decide the family
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  EnvironmentHeat, moisture, chemicals, UV
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  MachinabilityCycle time usually outweighs stock price
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  FinishFunctional versus cosmetic surfaces
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  QuantityRevisit the choice at production volume

High-speed machining changes what is practical. With light radial cuts and high spindle speeds, hardened steel and titanium become more economical because the tool stays cool and the chips clear. It also reduces the force on thin aluminum walls, which is why we use it on large, lightly supported parts. We hold ±0.005 mm (±0.0002 in) on qualifying features across our 16 simultaneous 5-axis centers.

Adaptive toolpaths matter for hard materials. Instead of a fixed stepover, the control adjusts engagement to keep the load constant. On 17-4PH or TC4 this extends tool life and avoids the sudden load spike that breaks a small end mill in a deep pocket. On plastics, the same approach controls heat, which is the main cause of poor edges.

Multi-tool setups let one program rough, semi-finish, drill and finish without an operator touching the part. On a 5-axis center with a Ø400 mm rotary table, that means features on five faces can be reached in one cycle. Fewer setups means less stacked tolerance.

We also combine processes when it saves a step. A printed prototype can be machined on critical faces to hold a tolerance the printer cannot reach. A casting can be machined on its mounting faces and bores to bring it into spec. Both routes are useful when the geometry is complex and the volume is low.

Surface finishing is part of the material decision, not an afterthought. Anodizing, plating, powder coating, black oxide, bead blasting, brushing and polishing all behave differently by substrate. Laser marking needs a minimum character height of 1.5 mm to stay legible.

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  16 five-axis centersSimultaneous cutting on complex geometry
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  Max part size4,000 mm, travel up to 4,000 × 400 × 150 mm
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  Inspection100% before shipment, reports on request