THE EFFECTS OF TEMPERATURE VARIATION ON THE CUTTING EDGES HARDNESS OF SELECTED SINGLE POINT CUTTING TOOLS

Abstract

Cutting tool life depends to a large extent on the degree of resistance it gives to wear and abrasion of its cutting edges. Since wear of tools cutting edge seems practically inevitable, it is therefore imperative that a suitable and cost effective means of determining this rate of wear be provided particularly in a developing nation like ours in order to determine the life of tools. Rockwell class ‘A’ (HRA) hardness test was employed in testing the hardness of four different samples of tool steels at varying temperature in the course of this study. The tools samples are two High Speed tool steels (M4 and M1) and two High Carbon tool steels (Q275 and A36) according to Society of American Engineers (SAE) steel grades. The temperature variation was achieved by heating the samples in a digital electric furnace at varying temperature from 150 oC to 750 oC as specified by the SAE standard, in step of 50oC. The hardness number was read directly by using a digital display unit of the Rockwell hardness tester known as identec to determine the corresponding hardness of the cutting edge (tip) of the tool. The results obtained, after comparison with the standards, were analyzed using statistically regression model. A software package named Tool Tip Hardness Predictor (TTHP-2014) was developed, using Visual Basic Version 6.0, to quicken the computation process. From the experimental results obtained, the high speed tool steels showed better hardness of 75 HRA for M4 HSS tool and 64 HRA for the M1 HSS tool at higher temperatures of 600oC than high carbon tool steels which showed hardness of 42 HRA for Q275 HCS tool and 34 HRA for the A36 HCS tool at the same temperature. These specified temperatures and corresponding hardness values obtained from the experiment are good representation of those quoted in the SAE standards. This indicated that this experimental method is a good alternative to existing complex dynamic methods of determining tool hardness loss.