Material Machinability & Formability Ratings

Machinability (rated relative to free-machining brass C360 at 100%) and formability (qualitative) for common metals. Higher machinability means faster cutting and longer tool life; higher formability means easier bending and drawing. The two rarely move together, so a material that machines cleanly may form poorly, and the ratings help match the metal to the dominant process.

How to read these ratings

Machinability is given as a percentage of free-machining brass C360, the long-standing industry benchmark set at 100%. A metal at 70% machines at roughly 70% of the speed or tool life of C360 under comparable conditions, so lower numbers mean slower cuts and more frequent tool changes. Formability is qualitative, from excellent down to poor, and tracks how readily a metal bends, draws, or stamps before it cracks. Each row also carries a note on the temper, the tooling demand, or the typical use, because the same alloy changes behavior with heat treatment. Read the two columns together: a material chosen for machining still has to survive any forming step, and a material chosen for forming still has to machine to tolerance.

Machinability, from easy to hard

Easy end: brass and aluminum

At the easy end, free-machining brass C360 sets the 100% benchmark and clears chips cleanly, which is why it is the standard for screw-machine work. Aluminum 6061-T6 and 7075-T6 both rate near 100% and machine fast with good finish, though 7075 is the stronger of the two. Aluminum 5052-H32 sits around 90% and machines well while also being the formable aluminum.

Mid range: carbon and stainless steels

Carbon steels 1018 and 1045 rate near 70 to 75%; 1018 is the common low-carbon machining steel and 1045 the medium-carbon choice for shafts and gears. Stainless 304 and 316 drop to about 45% because they work-harden under the cut and need sharp tooling and coolant.

Hard end: copper, titanium, and Inconel

The hard end is copper C110 near 20% (soft but gummy), titanium Ti-6Al-4V at 20 to 30% (low thermal conductivity traps heat at the edge), and Inconel 718 at 10 to 20% (work-hardens rapidly). For these last metals, expect slow speeds, heavy cuts, carbide tooling, and high tool wear.

Formability, bending and drawing

Aluminum family

Formability runs almost the opposite direction in some cases. Aluminum 5052-H32 is the formable aluminum and bends to tight radii with low springback; 6061-T6 needs overbending to offset 5 to 10 degrees of springback; 7075-T6 should not be bent at all because it cracks at the line.

Stainless, copper, and carbon steel

Annealed stainless 304 and 316 form and draw excellently despite machining poorly, and they spring back more than mild steel. Copper C110 is outstanding for drawing and spinning even though it machines badly. Carbon steel 1018 forms well in thin gauges; 1045 is moderate.

Poor end and the forming rule

At the poor end, titanium forms only with simple bends in the annealed condition because of high springback, and Inconel resists forming throughout. The rule is that softer, lower-strength tempers form better, and high-strength tempers trade formability for strength.

The machinability-versus-formability trade

The trade by material

The clearest pattern in the table is the trade between the two. Brass C360 machines best but is only moderately formable. Aluminum 5052 forms best of the aluminums but machines slightly behind 6061 and 7075. Stainless forms and draws well but machines slowly. Copper draws beautifully but machines poorly.

Picking and working around the trade

The practical takeaway is to pick the material for the operation that dominates the part: a turned fitting points to brass or 6061; a deep-drawn shell points to stainless or copper; a bent bracket points to 5052 or mild steel; a high-strength aerospace part points to 7075 or titanium and accepts the machining cost. When a part needs both heavy machining and significant forming, split the temper or the material so neither operation is fighting the metal. A common workaround is to form a part in a soft temper and then heat-treat it to the harder, stronger condition, which captures the formability of the soft state and the strength of the hardened one.

Limitations

The ratings are typical industry values relative to the C360 benchmark, not a certified speed for a specific machine, tool, or coolant setup. Real machinability moves with temper, tool geometry, feed and speed, rigidity, and lubrication, and a capable shop can improve a poor rating with the right setup. Formability shifts with temper, gauge, bend direction relative to grain, and die design. Confirm the behavior for the specific temper and process with the shop, and test a coupon for any new material or forming limit, before locking a specification.