Lecture 19 TEMPERATURE DISTRIBUTION IN METAL CUTTING

Figure 18.2 shows an experimentally determined temperature distribution in the workpiece and the chip during orthogonal metal cutting [2. This is a typical temperature distribution for orthogonal chip formation. As a point X in the material, which is moving toward the cutting tool, approaches and passes through the primary deformation zone, it is heated until it leaves the zone and is carried away within the chip. Point Y, however, passes through both deformation zones, and it is heated until it has left the region of secondary deformation. It is then cooled as the heat is conducted into the body of the chip, and eventually, the chip achieves a uniform temperature throughout. Thus, the maximum temperature occurs along the tool face some distance from the cutting edge. Point Z, which remains in the workpiece, is heated by the conduction of heat from the primary deformation zone. Some heat is conducted from the secondary deformation zone into the body of the tool. Thus, 

Pm = φc + φw + φt  ………………………………………..(4) 

where 

Pm = total rate of heat generation 

φc = rate of heat transportation by the chip 

φw = rate of heat conduction into the workpiece 

φt = rate of heat conduction into the tool 

FIGURE 18.2 Temperature distribution in workpiece and chip during orthogonal cutting (obtained from an infrared photograph) for free-cutting mild steel where the cutting speed is 75 ft/min (0.38 m/s), the width of cut is 0.25 in. (6.35 mm), the working normal rake is 30 degrees, and the workpiece temperature is 611 °C. (Boothroyd, G., Proc. Inst. Mech. Eng., Vol. 177, 789, 1963.) 

Fig. 18.3 Temp. distribution on the tool