DefinitionMachinability is a measure of how easily a material can be cut to shape, judged by tool life, cutting forces and power, surface finish, chip disposal and material-removal rate, and is usually expressed as a rating relative to B1112 steel at 1.00 (100%).
Explained
What does machinability mean?
Machinability is not a single physical property like density. It describes how a material behaves in a particular machining operation, with particular tooling and cutting conditions. A material machines well when it gives:
- longer tool life;
- lower cutting forces and power;
- a better surface finish;
- easier chip disposal;
- a higher material-removal rate.
It is linked to, but not the same as, a material's mechanical properties. High hardness wears tools by abrasion. High strength raises cutting forces, energy and temperature. High ductility makes the metal tear rather than shear as the chip forms, which causes chip-disposal problems and a poor finish. That is why a hard, strong titanium alloy (rated about 0.2) is slow to machine, while soft aluminum (about 2.00) is quick.
Machinability ratings of common metals
Ratings compare each material with B1112 steel at 1.00. A rating above 1.00 means better machinability than the reference.
| Material | Typical hardness (Brinell) | Machinability rating |
|---|---|---|
| B1112 steel (reference) | 180–220 | 1.00 |
| Aluminum, soft | — | 2.00 |
| Aluminum, hard | — | 1.25 |
| Medium-carbon steels | 140–210 | 0.65 |
| High-carbon steels | 180–230 | 0.55 |
| Low-carbon steels | 130–170 | 0.50 |
| Cast iron | 60–230 | 0.40–0.70 |
| Alloy steels | 170–230 | 0.25–1.5 |
| Titanium alloys | 220–280 | 0.2 |
These are group averages. The exact figure for a grade depends on its composition, temper and hardness, and on the operation being rated.
Plastics are not rated on this scale. Most do not need cutting fluid; choosing the correct speeds and feeds is what matters most.
How machinability affects cost and design
- Low machinability costs time. Materials with low machinability take longer to cut and cost more per part, so the choice of alloy can move a quote as much as the geometry does.
- Choose the easiest material that meets the requirement. Where strength, weight and corrosion allow it, an aluminum alloy such as 6061 or a brass such as C360 will usually be quicker to produce than stainless steel or titanium.
- Tight tolerances magnify the difference. Closer tolerances and finer finishes already add cost; on a hard-to-machine alloy they add more.
- Ask before you commit. Material, tolerance and finish are easier to change at the design review than after the first parts are cut.
At NICE Rapid, the engineering review at the start of every CNC machining project checks the design for machinability and confirms the material, tolerance and finish before programming begins.
Frequently asked questions
What is machinability?
Machinability is how easily a material can be machined. A material with good machinability gives longer tool life, lower cutting forces, a better surface finish, easier chip disposal and a higher material-removal rate, which means shorter cycle times and lower cost.
How is machinability measured?
It is usually given as a rating relative to a reference steel, B1112, which is set at 1.00 (100%). A material rated 2.00 rates twice as well as the reference; one rated 0.2, like many titanium alloys, is much harder to cut.
Which metals have the best machinability?
Among common engineering metals, aluminum alloys rate highest, at about 1.25 to 2.00 relative to B1112 steel. Carbon and alloy steels mostly fall between 0.25 and 1.5, and titanium alloys sit around 0.2.
Key takeaways
- Machinability describes how easily a material can be cut to shape, considering tool life, cutting forces, surface finish, chip disposal and material-removal rate.
- Machinability ratings compare materials to B1112 steel, which is set at 1.00 (100%).
- Higher ratings mean faster, cheaper machining; soft aluminum is about 2.00, while titanium alloys are around 0.2.
- Hardness, strength and ductility influence machining difficulty: harder and stronger materials wear tools and raise forces, while ductile materials can produce poor chip control.
- Selecting the easiest material that meets design requirements and reviewing tolerances early can reduce machining time and cost.
Example
Related terms
References
- Economics and Product Design Considerations — Michigan State University, ME 477 (P. Kwon)
- Standard Operating Procedures for Manual Milling Machines — UC Riverside Mechanical Engineering Department Machine Shop