Conventional machining processes utilise the ability of the cutting tool to stress the material beyond the yield point to start the material removal process. This requires that the cutting tool material is harder than the workpiece material. New materials which are having high strength to weight ratio. heat resistance and hardness, such as nimonic alloys, alloys with alloying elements such as tungsten, molybdenum, columbium are difficult to machine by the traditional methods. Machining of these materials by the conventional methods is very difficult as well as time consuming, since the material removal rate reduces with an increase in the work material hardness. Hence, there in the need for development of non-traditional machining processes which utilise other methods such as electro-chemical processes for the material removal. As a result, these processes are termed as unconventional or non-traditional machining methods. The complex shapes in these materials are either difficult to machine or time consurning by the traditional method. In such cases, the application of the non-traditional machining processes finds extensive use. Further, in some applications a very high accuracy is desired besides the complexity of the surface to be machined. These processes are not meant for replacing the conventional process but are, in fact, supplement them. The main for using the non-traditional machining processes are:
High strenght alloys:
When the hardness of the work material is often higher than the cutting tool material or when it becomes necessary to use the machining process on hardened material in such cases, the Electro-chemical Processes (ECM) described would be required.
When very complex surfaces in three dimensions need to be produced,such as those in moulds and dies, where the workpiece surface being the hardened tool steel would be difficult to be processed by the conventional means, the non-traditional processes would be required.
Higher accuracies and surface finish:
The accuracy and surface finish desired in hard workpiece materials require the conventional machining to be done very slowly as well as adding a number of finishing processes, making the process very slow and uneconomical Difficult geometries: In addition to the complex geometries, sometimes it is required to produce difficult geometries such as long holes with length-to-diameter ratio approaching that of 100, very small size holes such as those with less than 0.1 mm in diameter which are almost impossible to be produced by the conventional methods.