6 Tips for Processing Aluminum Alloys on CNC Machines

Not every aluminum behaves the same way. 6061-T6 is the default for brackets, housings and fixtures because it welds, anodizes and machines predictably. 7075 offers roughly twice the yield strength of 6061, which suits aerospace ribs and mold cores, but it is less weldable and costs more per kilogram.

The softer grades cause most of the trouble. 5052 and 5083 are gummy, so they build up on the cutting edge and tear instead of shearing. Use them for sheet metal work or welded tanks, not for tight-tolerance turned parts. ADC12 is a die-casting alloy; it is not a good choice for machined structural components.

Before quoting, we check the drawing against the grade. A part with thin walls and a 7075 callout may need more passes and a different workholding plan than the same part in 6061. Getting that settled early avoids a mid-run change.

One more point on temper. 6061-T6 machines cleanly, but annealed 6061-O is soft and tends to smear. When the drawing only says aluminum, ask which temper.

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  6061-T6General machining, anodizing, moderate strength
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  7075-T6High strength, aerospace and mold work, harder on tools
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  5052 / 5083Sheet, welded assemblies, gummy on the lathe
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  2024-T4Fatigue resistance, poor corrosion resistance without coating

Aluminum needs sharp edges and plenty of rake. A polished, uncoated 2-flute or 3-flute carbide end mill works for most pockets and profiles. The high helix angle pulls chips up and away, which matters in deep cavities where recutting causes built-up edge.

Coatings are a mixed bag. TiAlN and similar hard coatings resist heat but have a higher friction coefficient against aluminum, so they can drag and weld. Diamond-like carbon (DLC) or ZrN run cooler on aluminum. If the job is short, an uncoated polished tool is often the better call.

For drilling, use a 118° or 130° point with a split point and polished flutes. Standard jobber drills grab and pull when they break through thin sections. A stub drill on a rigid setup gives a cleaner hole and less exit burr.

Reamers and taps deserve attention too. Spiral-flute taps cut aluminum without packing the flutes, while straight-flute taps tend to clog. Form taps work well in 6061 but need a slightly larger pilot hole.

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  2–3 flutesGood chip room for roughing and profiling
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  High helixBetter evacuation in deep pockets
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  Polished flutesReduces built-up edge on gummy grades
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  Avoid TiAlNHigher friction against aluminum

Aluminum conducts heat away from the cut, so the tool stays cooler than it would in steel. That lets you run surface speeds of 300 to 500 m/min with carbide, and spindle speeds that would burn a steel tool. The limit is usually the machine, not the material.

Chip load matters more than spindle speed. A light chip rubs the edge and work-hardens the surface. Aim for a chip load that produces a thick, curled chip, then adjust feed to keep it consistent. If the chip looks like dust, the feed is too low.

Coolant choice depends on the operation. Flood coolant handles deep pockets and keeps chips moving. Mist or air blast works for open profiling where coolant would pool. For finishing passes, a light mist can leave a better surface than a heavy flood.

Watch for chatter on thin walls. It shows up as a rippled surface and a squealing sound. Reducing radial engagement and increasing feed per tooth often fixes it better than slowing the spindle.

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  300–500 m/minTypical surface speed with carbide
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  Thick chipsSign of a healthy feed rate
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  Dusty chipsFeed too low, edge will rub
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  Light radial cutReduces chatter on thin walls

Aluminum moves when you remove material. A block that is flat in the vise can bow after roughing as internal stress releases. Rough, stress-relieve, then finish is the reliable sequence for tight parts.

For thin plates, vacuum chucks or dedicated soft jaws spread the clamping force. Three-point clamping on a thin wall will distort it, and the finished part springs back when you unclamp. Support underneath and clamp lightly.

Five-axis work benefits from a single setup. A trunnion or a Ø400 mm rotary table lets you reach five faces without re-fixturing, which removes stacking error. That matters on parts with bores that must stay concentric.

On long parts, support the overhang. A 4,000 mm travel machine can hold a long extrusion, but without a steady or tailstock the middle will deflect. Check the setup before blaming the tool.

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  Rough then finishLets internal stress release before the final pass
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  Soft jawsSpread clamping force on thin sections
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  Single setupFive-axis reduces stacking error
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  Support overhangsPrevents mid-span deflection on long parts

Aluminum makes a lot of chips fast. If they stay in the cut, the tool recuts them, heat rises and the finish goes dull. Deep pockets and blind holes are where this shows up first.

Through-spindle coolant or high-pressure air clears the cut. When neither is available, program a peck cycle or a retract move to break the chip and let it fall. A short dwell at the bottom of a pocket can help, but it also rubs the edge.

Chip size is a clue. Long stringy chips tangle around the tool and scratch the finished wall. Adjusting feed and speed to break them into short curls solves most of it. If the chip is fine powder, the feed is too low.

For deep holes, drill in steps and clear the flutes. A peck drill cycle with a full retract keeps the hole straight and stops the drill from packing.

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  Through-coolantBest for deep pockets and blind holes
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  Peck cycleBreaks chips and clears flutes
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  Short curlsSign of good feed and speed
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  Stringy chipsTangling risk, adjust feed

A sharp tool and a light finishing pass give the best surface. Worn tools leave a haze that no amount of polishing removes evenly. Change the tool before the finish pass on visible faces.

Bead blasting evens out tool marks and prepares the surface for anodizing. Brushing gives a directional grain. Polishing reaches a mirror finish but can round edges if it is overdone. Pick the finish before the last cut, because the machining allowance depends on it.

Anodizing adds a thin oxide layer that grows into the part. Hardcoat anodizing can build 25 to 50 μm, which changes the size of a bore or a shaft. Leave stock for it on critical diameters.

Deburring by hand is fine for a prototype. For production runs, a chamfer tool in the program does the work consistently and removes the risk of a sharp edge reaching the customer.

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  Fresh toolUse a new cutter for the finish pass
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  Bead blastEvens marks before anodizing
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  Hardcoat anodizeBuilds 25–50 μm, plan the stock
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  Chamfer in programConsistent deburring on production runs