measurement of cutting tool temperature

MEASUREMENT OF CUTTING TOOL TEMPERATURE

The ncessity of cutting temperature is to evaluate for the

(i) assessment of machinability in terms of cutting forces,temperature and tool life

(ii) design and selection of cutting tools

(iii) evaluation of various machining parameters on cutting temperature

(iv) proper selection and application of cutting fluid

(v) analysis of temperature distribution in the chip, tool and job.

The temperatures to be measured are given below.

(i) Average shear zone temperature, θs

(ii) Average (and maximum) temperature at the chip-tool interface, θi

(iii) Temperature at the work-tool interface (tool flanks), θf

(iv) Average cutting temperature, θavg.

1. Methods of Measuring Cutting Tool Temperature

(i) Calorimetric method:

This method is very simple and low cost but it is inaccurate and it gives only the grand average value.

(ii) Decolourising agent:

Some paint or tape is pasted on the cutting tool to show the variation in temperature. According to the cutting tool temperature, the colour change is shown for the indication. 

(iii) Tool-work thermocouple:

This method is simple and inexpensive but it gives only the average or maximum value. 

In a thermocouple, two dissimilar electrically conductive metals are connected at two junctions. When one of the junctions is heated, the difference in temperature at the hot and cold junctions produce a corresponding current in milli-voltmeter. During machining such as turning, the tool and the job act as the two dissimilar metals. Similarly, the cutting zone acts as the hot junction. Then the average cutting temperature is calculated in terms of millivolt through a proper calibration. The tool-work interface can be measured using thermocouple in many ways.

(a) Moving thermocouple technique 

(b) Embedded thermocouple technique 

(c) Using compound tool

(d) Indirectly from Hardness and structural transformation

(e) Photo-cell technique

(f) Infra ray detection method.