Conventional machining usually involves changing the shape of a workpiece using an implement made of a harder material. Using conventional methods to machine hard metals and alloys means increased demand of time and energy and therefore increases in costs; in some cases conventional machining may not be feasible. Conventional machining also costs in terms of tool wear and in loss of quality in the product owing to induced residual stresses during manufacture. With ever increasing demand for manufactured goods of hard alloys and metals, such as Inconel 718 or titanium, more interest has gravitated to non-conventional machining methods. Conventional machining can be defined as a process using mechanical (motion) energy. Non-conventional machining utilises other forms of energy. The three main forms of energy used in non-conventional machining processes are as follows : • • •
Thermal energy Chemical energy Electrical energy
One example of machining using thermal energy is laser. Thermal methods have many advantages over conventional machining, but there are a few of disadvantages. •
Inconel 718, titanium and other hard metals and alloys have a very high melting point. Using thermal methods will require high energy input for these materials. Concentrating heat onto any material greatly affects its microstructure and will normally cause cracking, which may not be desirable. Safety requirements for thermal methods, especially laser, are demanding in terms of time and cost. Machining large areas or many surfaces at the same time using thermal methods is not normally possible.
The methods using electrical energy are electrodischarge machining (EDM) and anodic machining (AM), which are similar in practice. EDM, often refered to as spark erosion, uses pulsed voltage to remove material from a workpiece and a non-conductive medium
to clear the debris. Because the medium is electrically...