Material and hardness matrix for cutting tool selection
Exactalloy · Updated
Use the workpiece material group and its measured hardness to narrow the tool family, coating and starting cutting data. Always confirm the actual hardness rather than relying on a nominal grade.
Why nominal hardness is not enough
The same designation can be supplied in very different conditions, and hardness strongly affects tool life and the risk of chipping. Record the measured hardness of the actual batch and state it in the enquiry so the specification can be checked against it.
- State the standard and grade, for example 45# steel, 304 stainless, 6061 aluminium, Ti-6Al-4V.
- Give the measured hardness (HRC or HB) rather than an assumed value.
- Mention pre-hardened, quenched or annealed condition.
Speed ranges by material group
The following are starting points for coated fine-grain carbide only. Machine rigidity, holder runout, coolant and engagement all shift the usable window, so treat them as a first trial rather than a guaranteed setting.
- Carbon and alloy steel: 120–200 m/min, 0.03–0.08 mm/tooth.
- Stainless steel: 80–150 m/min, 0.02–0.06 mm/tooth.
- Hardened steel above HRC 55: 60–120 m/min, 0.01–0.03 mm/tooth.
- Aluminium: 300–800 m/min, 0.05–0.15 mm/tooth.
- Titanium alloys: low surface speed with high-pressure coolant and light radial engagement.
Hardness bands and tool family
Hardness bands are a first filter for the tool family. Use them to shortlist, then confirm with the operation and feature drawing.
- Below HRC 45: general-purpose series.
- HRC 45–55: high-hardness four-flute series.
- HRC 55–65: dedicated high-hardness series.
- Above HRC 65: consider CBN or grinding rather than a coated carbide cutter.
Difficult materials and the practical countermeasures
Difficult materials usually fail through heat and work hardening rather than through hardness alone. Change the strategy as well as the tool.
- Titanium: dynamic milling with shallow radial and deep axial passes so the chip carries heat away.
- Nickel alloys: climb milling, low surface speed, high-pressure coolant, no dwelling in cut.
- CFRP: climb milling, high speed, low chip load to avoid delamination and fibre pull-out.
- Graphite: high speed, light cut, with effective dust extraction.