What is cutting temperature in machining?
During the metal cutting process, the metal gets plastically deformed and the friction energy gets converted into heat, which raises the temperature of the chip, workpiece as well as cutting tool. This temperature is called cutting temperature.
Cutting temperature rises very high while machining ferrous metals as well as other high strength metals.
During the metal cutting operation, the heat generation depends on the rate of metal cutting, cutting speed, specific heat, thermal conductivity of the cutting tool as well as thermal conductivity of the workpiece.
Amongst all the above mentioned factors, the cutting speed generates most of the heat during metal cutting.
And the majority of heat generation takes place in the machining chips that are produced during metal cutting.
Factors affecting cutting temperature
Various factors affecting cutting temperature are mentioned below.
#1) Material of workpiece and tool
If the material is very hard and has a higher tensile strength, then it requires more cutting force. And hence more heat is generated and cutting temperature will be more.
If the thermal conductivity and specific heat of the tool and workpiece material is more, then it will promote the heat conduction and hence the cutting temperature can be lowered.
#2) Tool geometry
The rake angle has a major role in increasing the cutting temperature.
If the rake angle increases in a positive direction, then the cutting force as well as heat generation will decrease.
But one thing you should keep in mind is that a higher rake angle weakens the cutting edge and also reduces the heat conduction capacity.
The negative rake angle leads to greater deformation and heat generation is also more.
Larger nose radius increases the conductivity of heat and hence it helps in reducing the cutting temperature.
If the cutting tool has a shank with a larger cross section, then it promotes more heat conduction.
#3) Cutting parameters
Cutting speed is a major factor which generates heat during machining.
As the cutting speed increases, the friction between the tool and workpiece increases. This leads to an increase in cutting temperature at the tool-workpiece interface.
The rise in cutting temperature also occurs due to increase in feed and depth of cut.
When the feed increases, more metal is removed which creates more friction with the tool and hence it increases the cutting temperature.
This same phenomenon occurs when the depth of cut is increased.
#4) Cutting fluids
Cutting fluid helps in reducing the heat generated during the machining process.
It also helps in reducing the friction between the tool and workpiece.
Cutting fluids having higher thermal conductivity and specific heats provides a better cooling effect during the machining process.
How does cutting temperature affect the tool and workpiece?
- Cutting temperature effect on cutting tool: Due to high cutting temperature, rapid tool wear occurs which reduces the tool life.
If the tool material is not hot hard, then it may show plastic deformation due to heat and pressure.
Built-up edge formation as well as fracturing of cutting edges takes place due to high cutting temperatures.
- Cutting temperature effect on workpiece: Thermal distortion as well as expansion and contraction of workpiece takes place due to high cutting temperatures, which leads to dimensional inaccuracy.
Oxidation of the workpiece, burning, stress induction as well as micro cracks occurs on the workpiece surface due to high temperature.
How a chip-tool interface temperature is measured?
Chip-tool interface temperature can be measured by following methods;
- Tool work thermocouple
- Embedded thermocouples
- Radiation pyrometer
- Indirect calorimetry technique
- Temperature sensitive paints
Out of the above mentioned techniques, the tool work thermocouple technique is widely used to measure the chip-tool interface temperature.