THE ECONOMIC BENEFIT OF FINISH TURNING WITH COATED CARBIDE

Surface roughness values are an important consideration in component d esign and are increasingly specified on engineering drawings. A value of surface finish (roughness) may be specified so that expensive finis hing processes are eliminated, thereby reducing costs, or alternativel y to improve the mechanical properties of a component. The careful fin ishing of components can lead to longer life, improved efficiency and other benefits. The investigation reported in this paper was carried o ut on behalf of a medium sized engineering company who wished to learn whether a change from uncoated carbide to coated carbide could be eco nomically justified for finish turning operations. It was desired to i dentify the most cost effective combination of cutting speed, feed and tool material for a finish turning operation, useful tool life being taken when the surface roughness deteriorated beyond a predetermined l evel. It is shown that the lowest cost per component is achieved by us ing the highest cutting speed possible on the lathes available within the company, coupled with the highest cutting tool feed rate commensur ate with finish turning. Significantly however, it is shown that the l owest cost when machining with coated carbide is 30% less than when ma chining with uncoated carbide during finish turning operations.