N-Group Aluminium & Non-Ferrous Machining Guide: Al, Copper, Brass

Aluminium and non-ferrous metals are ISO 513's group N (insert colour: green) — aluminium alloys, copper, brass and bronze. They are generally soft, light, conductive, machine fast and are relatively easy to cut, which is group N's big advantage; but the trouble lies in that softness: they readily form built-up edge (BUE) and stick to the cutting edge. In addition, high-silicon die-cast aluminium has abrasive silicon hard points, and aluminium should not use Al-bearing coatings (strong affinity, sticking). This guide covers the non-ferrous types, their grades and tool-selection direction; for the overview see "ISO Workpiece Material Classification."

Non-ferrous types and machinability

In practice aluminium alloys are the most common: wrought aluminium (6061/7075) is soft and sticky — the focus is BUE control; high-silicon die-cast (ADC12) is abrasive, best with PCD/diamond coating. Brass cuts well with good chipping; pure copper is very sticky and hard to chip; beryllium copper dust is toxic and must be controlled.

Three machining keys for aluminium & non-ferrous

Tool grade and coating direction

Aluminium alloys mainly use uncoated polished carbide (high rake, high helix, polished flutes); for high-volume or high-silicon die-cast aluminium use PCD/diamond coating; copper and brass use a sharp, high-rake carbide. Avoid Al-bearing coatings on aluminium. For full grade and coating selection, see "Cutting Tool Material Classification."

Key cutting strategy

Turning: why aluminium and copper stick to the tool

Aluminium turns easily at high cutting speed. The trouble is sticking and built-up edge: the melting point is low, so once the temperature rises the chip welds onto the edge.

For pure copper and brass edge forms see Turning Copper and Brittle Materials: Washer Tools, Chip-Breaking and Chip-Curling Corrugated Edges; for choosing positive or negative inserts see Insert Angle Guide: Negative, 7° & 11° Positive Inserts; for spindle-speed conversion see Turning Machining Formulas: Speed, Feed & Surface Roughness.

Milling: how many flutes for aluminium, and why polished edges

Aluminium cuts easily and runs at high cutting speed, so it makes a lot of chips per minute. The first limit in aluminium milling is usually chip evacuation, not tool wear. Chips that cannot get out stick back on the edge as built-up edge.

For flute count and helix see End Mill Flute Count and Helix Angle: How to Choose; for wrought versus cast aluminium see Dry Milling by Material: Cast Iron, Steel, Aluminium and Stainless Strategies. Speed and feed conversions are in End Mill Cutting Conditions Guide.

Drilling: why aluminium sticks and packs the flutes

Aluminium cuts easily, but two problems grow when drilling: aluminium welding to the edge, and loose, bulky chips packing the hole. Blind holes show it most.

In blind holes you do not want chips broken too fine: they pile at the bottom and push the drill off line. For speed conversions see Drilling Parameters Guide; for point grinds see Drill Point Types by Material and Hole.

Tapping: why aluminium sticks to the tap and the thread comes out small

Aluminium has a low melting point and is soft and sticky, so a cutting tap tends to pick up metal, and the thread can shrink after tapping. The good news is that aluminium, copper and brass are ductile, so most of them can be tapped with a form tap, which makes no chips.

Die-cast aluminium takes the low end of the speed range (about 15-25 m/min), and a form tap needs about 2-3 times the torque of a cutting tap. For choosing between the two see Cutting Tap vs Forming Tap; for form-tap hole sizes see Form Tap Drill Size Chart; for high-silicon die castings a nitrided tap is an option, see Tap Surface Treatment Guide.