Cutting Temperatures: Lesson 54 of Industrial Engineering ONLINE Course
Lesson 11 of Process Industrial Engineering ONLINE Course (Module)
Tool–Work Thermocouple Method and Related Techniques
Infrared Methods
Lesson 11 of Process Industrial Engineering ONLINE Course (Module)
Introduction - Effect of Cutting Temperatures on Productivity of Machining
When metal is cut, energy is expended in deforming the chip and in overcoming friction between the tool and the workpiece. Almost all of this energy is converted to heat and high temperatures are produced in the deformation zones and surrounding regions of the chip, tool, and workpiece. Cutting temperatures affect machining performance. Temperatures in the primary deformation zone, where the bulk of the deformation involved in chip formation occurs, influence the mechanical properties of the work material. Complete analyses of the mechanics of cutting use temperature-dependent constitutive models.
Temperature Measurement Techniques
Tool–Work Thermocouple Method and Related Techniques
The tool–work thermocouple method was first developed in the 1920s. It uses the tool and workpiece as the elements of a thermocouple. The hot junction is the interface between the tool and the workpiece, and the cold junction is formed by the remote sections of the tool and work piece, which must be connected electrically and held at a constant reference temperature. Required insulation has to be there.
Infrared Methods
Cutting temperatures can also be estimated by measuring the infrared radiation emitted from the cutting zone. Since reliable point sensors have been available for some time, they have been applied by a number of researchers to measure rake and relief face temperatures in both cutting and grinding
2004
https://www.tandfonline.com/doi/abs/10.1081/MST-200038984
2004
https://www.tandfonline.com/doi/abs/10.1081/MST-200038984
Factors Affecting Cutting Temperatures
The process parameter with the greatest influence on cutting temperatures is the cutting speed. Increasing the cutting speed increases the rate at which energy is dissipated through plastic deformation and friction, and thus the rate of heat generation in the cutting zone. Increasing the feed rate also increases heat generation and cutting temperatures. For moderate ranges of these variables, the cutting speed has a greater influence. The tool–chip interface temperature increases with the square root of the cutting speed but the third root of the feed.
Industrial engineers are interested in increasing cutting speed, feed and depth of cut to increase productivity of machining. They have to follow the research in the area of metal cutting temperatures to identify the opportune time to increase productivity of machining. Industrial engineers also have to engage in research in each and every metal cutting variable that has an effect on metal removal rate. Number of such variables are discussed in this series of article highlighting industrial engineering and productivity aspects of metal cutting.
Thermal expansion can produce dimensional and form errors in precision machining processes. Errors can be caused by the hot chips falling and remaining on flat surfaces of the machine tool. Methods for controlling these errors, include design modifications to eliminate flat surfaces, the use of coolants to ensure chip removal, and the use of constant-temperature fluid baths to control temperatures throughout the system. Errors result from the conduction of cutting heat into the tool or workpiece. The available work research indicates that the expansion of the tool generally produces more significant errors than the expansion of the workpiece. The tool temperatures are usually higher than workpiece temperatures. The thermal expansion of the tool can be reduced by using brazed or clamped, rather than bonded, cutting tools. Using toolholders cooled by cold fluids pumped through internal cooling passages is also researched and presently tool suppliers are supplying such tool holers.
The expansion of the workpiece produces significant errors in precise hole-making processes. Thermal errors in boring can be reduced by increasing the cutting speed, because the higher cutting speed reduces the proportion of heat entering the workpiece. Carbide boring cutters are being replaced by ceramic or PCBN cutters designed for use at high cutting speeds in most automotive engine boring operations to reduce thermal induced errors. In dry drilling applications, the workpiece often heats up and expands. When the drill is retracted, the workpiece contracts, reducing the drilled hole diameter. In high precision operations, for work piece cooling cold air is used. Provision for Internal cooling of the drill is also made by some suppliers.
The thermal problems are more serious issue in grinding.
In dry cutting operations, which are now becoming popular, thermal problems are an important issue. Hard turning is often carried out with ceramic tools in dry cutting. The cutting speed is relatively low and the specific cutting energy is high and a significant heat flux goes into the workpiece with potential thermal distortions. Thermal expansion of the workpiece is also a issue in Minimum Quantity Lubrication (MQL) techniques.
Problem of Thermal Expansion of Workpiece and Tool
Thermal expansion can produce dimensional and form errors in precision machining processes. Errors can be caused by the hot chips falling and remaining on flat surfaces of the machine tool. Methods for controlling these errors, include design modifications to eliminate flat surfaces, the use of coolants to ensure chip removal, and the use of constant-temperature fluid baths to control temperatures throughout the system. Errors result from the conduction of cutting heat into the tool or workpiece. The available work research indicates that the expansion of the tool generally produces more significant errors than the expansion of the workpiece. The tool temperatures are usually higher than workpiece temperatures. The thermal expansion of the tool can be reduced by using brazed or clamped, rather than bonded, cutting tools. Using toolholders cooled by cold fluids pumped through internal cooling passages is also researched and presently tool suppliers are supplying such tool holers.
The expansion of the workpiece produces significant errors in precise hole-making processes. Thermal errors in boring can be reduced by increasing the cutting speed, because the higher cutting speed reduces the proportion of heat entering the workpiece. Carbide boring cutters are being replaced by ceramic or PCBN cutters designed for use at high cutting speeds in most automotive engine boring operations to reduce thermal induced errors. In dry drilling applications, the workpiece often heats up and expands. When the drill is retracted, the workpiece contracts, reducing the drilled hole diameter. In high precision operations, for work piece cooling cold air is used. Provision for Internal cooling of the drill is also made by some suppliers.
The thermal problems are more serious issue in grinding.
In dry cutting operations, which are now becoming popular, thermal problems are an important issue. Hard turning is often carried out with ceramic tools in dry cutting. The cutting speed is relatively low and the specific cutting energy is high and a significant heat flux goes into the workpiece with potential thermal distortions. Thermal expansion of the workpiece is also a issue in Minimum Quantity Lubrication (MQL) techniques.
Updated on 14 January 2021
First published on 10 July 2020
Read on 23 July 2022.
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