What is machinability? Definition and examples
Machinability is a characteristic of a material, such as a metal, that makes it easy to drill, shape, cut, grind, etc. The term refers to the ease with which we can machine, for example, a metal. In this context, ‘to machine’ means ‘to cut, drill, shape, etc.’
Materials with good machinability can be cut with relatively little power and low cost. It is possible to cut them quickly so that we can obtain a good finish easily. Additionally, they do not wear the tooling much.
Most factors that improve a material’s performance are bad for its machinability. Engineers, therefore, are challenged to find materials with relatively good machinability that do not undermine performance.
Collins Dictionary has the following definition of the term:
“The machinability of a material is how easily it can be machined using a cutting tool.”
Predicting machinability is a challenge
Machining has many variables, which can make it extremely difficult to predict how easily materials can be machined. Engineers focus on two sets of factors:
- The work materials’ condition. This includes grain size, microstructure, chemical composition, hardness, yield strength, tensile strength, and heat treatment.
- The work materials’ physical properties. This includes the modulus of elasticity, thermal expansion, thermal conductivity, and work hardening.
According to Wikipedia:
“Other important factors are operating conditions, cutting tool material and geometry, and the machining process parameters.”
Percentage of a normalized value
We express machinability as a percentage of a normalized value. The AISI has determined AISI No. 1112 carbon steel a machinability rating of 100%. AISI stands for the American Iron and Steel Institute.
Engineering Toolbox has a list of some common materials and their machinabilities in relation to AISI No. 1112.
No two materials are the same
No two materials that are subject to machining can behave identically when cutting them with the same tool, identical feed rates, the same cutting speed, and using the same machine.
Some materials, such as mild steel, may produce long curly chips. Cast iron, on the other hand, produces short chips.
One material may end with a rough surface while another gets a smooth finish. Others produce lots of heat and rapidly blunt the tool.