Tool wear

Some general effects of tool wear include: • increased cutting forces • increased cutting temperatures • poor surface finish • decreased accuracy of finished part • May lead to tool breakage • Causes change in tool geometry Reduction in tool wear can be accomplished by using lubricants and coolants while machining. These reduce friction and temperature, thus reducing the tool wear. A more general form of the equation is : V_c T^n \times D^x S^y=C where • V_c=cutting speed • T=tool life • D=depth of cut • S=feed rate • x and y are determined experimentally • n and C are constants found by experimentation or published data; they are properties of tool material, workpiece and feed rate. ==Temperature considerations==

At high temperature zones crater wear occurs. The highest temperature of the tool can exceed 700 °C and occurs at the rake face whereas the lowest temperature can be 500 °C or lower depending on the tool. ==Energy considerations==

Energy comes in the form of heat from tool friction. It is a reasonable assumption that 80% of energy from cutting is carried away in the chip. If not for this the workpiece and the tool would be much hotter than what is experienced. The tool and the workpiece each carry approximately 10% of the energy. The percent of energy carried away in the chip increases as the speed of the cutting operation increases. This somewhat offsets the tool wear from increased cutting speeds. In fact, if not for the energy taken away in the chip increasing as cutting speed is increased; the tool would wear more quickly than is found. ==Multi-criteria of machining operation==

Malakooti and Deviprasad (1989) introduced the multi-criteria metal cutting problem where the criteria could be cost per part, production time per part, and quality of surface. Also, Malakooti et al. (1990) proposed a method to rank the materials in terms of machinability. Malakooti (2013) presents a comprehensive discussion about tool life and its multi-criteria problem. As an example objectives can be minimizing of Total cost (which can be measured by the total cost of replacing all tools during a production period), maximizing of Productivity (which can be measured by the total number of parts produced per period), and maximizing of quality of cutting. ==See also==