What is Machinability of Metals?
Machinability of metals is an ability of a metal to be machined. It refers to an ease with which a metal can be machined.
Basically, the two main parameters (i.e surface finish and tool life) are the main measures of machinability.
If the surface finish is good, cutting forces are less, heat generation is less, and tool wear is less, then it can be said that the machinability of that material is good.
Machinability of metals can be measured in terms of following conditions;
- Tool life: If tool life is higher, then it indicates that the machinability of metal is higher.
- Surface finish: Better surface finish obtained on the workpiece indicates better machinability.
- Power consumption: lower power consumption during the machining process indicates better machinability.
- Cutting force: If cutting force required for machining is less, then it shows that the machinability of the metal is good.
Which factors affect machinability of metals?
Various factors that affect the machinability of the metals are discussed below.
#1) Factors related to workpiece properties
Hardness of metals: If the metal is very hard, then it will require more power consumption and it will generate high temperatures. Hence the tool wear may occur which leads to poor machinability.
Chemical composition: The cutting force and tool wear are very high while machining a pure metal. But if a small amount of carbon, manganese, lead, sulfur and phosphorus are added to the steels, it results in improved machinability.
Also the production rate and the surface finish gets improved.
Low carbon steels which contain 0.01% to 0.15% carbon shows poor machinability because of its high ductility and toughness.
If the carbon content is more (i.e from 0.25% to 0.3%), then it shows good machinability.
Adding 1% of manganese as well as 0.15% of phosphorus improves machinability of metals.
If sulfur and phosphorus are present in the metals, then the machining chips break easily due to brittleness.
However, some metals like silicon, nickel, chromium, vanadium and molybdenum added to steels shows an unfavorable effect on machinability.
Microstructure: If the metal contains abrasive inclusions and non uniform structure with large and distorted grains, then the metals will show less machinability.
Treatment given to metal: Cold worked steels show better machinability as it increases tool life as well as its machining can be done at high cutting speed.
Machinability of high carbon steels can be increased by their hot working.
Various heat treatments like normalising, annealing, tempering, etc helps in machinability.
#2) Factors related to cutting tool
Various factors related to cutting tools that affect machinability of metals are listed below.
- Tool material
- Tool geometry
- Nature of cutting
- Tool rigidity
#3) Factors related to cutting conditions
Various factors related to cutting conditions that affect machinability of metals are listed below.
- Cutting speed
- Feed and depth of cut
- Cutting temperature
- Cutting fluids
#4) Factors related to machine
The machine tool used for machining operations should be rigid and strong to get better machinability of the workpiece.