The effect of applying coolant on tool wear in metal machining

Abstract

In all machining operations, tool wear is a natural phenomenon and it eventually leads to tool failure. Tool failure is considered to have occurred when there is a poor surface finish on the workpiece. The application of coolant during any machining operation is believed to reduce tool wear since the cutting fluid produces a lubricating as well as a cooling effect. A study is therefore carried out to substantiate or refute the belief that when coolant is applied, tool wear is actually reduced, thereby enhancing the tool life. This is especially important in industry in which cost of tool material may have a significant contribution to the total production cost.Experiments were conducted in which two different types of medium carbon steel were machined by turning using two different types of uncoated tungsten carbide tools. The coolant used was a water-based one. All these experiments were performed on an old-model Colchester lathe under machining conditions commonly used in workshops in Singapore and many other parts of the world.The experimental results in this paper show that, contrary to common belief, the application of coolant is not necessarily beneficial to tool life. In fact, it was discovered that one effect of the coolant is to slightly increase the crater wear and, more importantly, to shift the position of the crater wear nearer the tool tip. The worn crater also becomes deeper and narrower as a result of the coolant. This causes the tool cutting point to become much weaker.The flank wear is even more significantly affected by the application of coolant, especially at high cutting speeds. This large (30 percent) increase in flank wear due to the application of coolant can drastically decrease tool life.