SURFACE QUALITY OF THE EDM PROCESSED MATERIALS
The article presents the importance of the EDM technology in the industry of machine building. It is mostly used in the machining of stamps and special processes in which the conventional technologies are inefficiently. It's known that only condition of machining with this method is that the material should be electro conductive. The main parameters that are followed during the process are the precision and the roughness of the surface. The collective tried to emphasise the importance variation of the roughness concerning some machining parameters. Some of the measurements were conducted at ETH Zurich using an electronic microscope.
Case studies on productivity improvement and supplier selection
Two case studies have been reported (i) improvement of productivity in Electrical Discharge Machining (EDM) and (ii) Multi-Criteria Decision Making (MCDM) approach for supplier selection.Case study (i) highlights EDM of stainless steel in which best process environment (optimal) has been determined to satisfy productivity and quality requirements simultaneously. Material Removal Rate (MRR) during the process has been considered as productivity estimate with the aim to maximize it. Where as surface roughness i.e. (Ra value) of the machined surface has been chosen as surface quality estimate with the requirement to minimize it. These two contradicting requirements have been simultaneously satisfied by selecting an optimal process environment (optimal parameter setting). Desirability Function (DF) approach coupled with Taguchi method has been used to solve the problem.In case study (ii), usefulness of grey based MCDM approach method has been highlighted to solve multi-criteria decision making problem of supplier selection. The method has been found efficient to aggregate multiple attribute values into an equivalent single quality index (overall grey relation grade) which facilitates ranking/benchmarking as well as selection of the appropriate alternative supplier
Electrostatic and Hydrodynamic Effects in the Electrical Breakdown of Liquid Dielectrics
Optical studies of pre-breakdown events in insulating liquids enable one to distinguish three stages in the breakdown of negative point-plane gaps: (1) The creation of a rapidly expanding vapor cavity adjacent to the point electrode. (2) The instability of the surface of the cavity, characterized by the growth of wave-like disturbances, and (3) The runaway growth of the instability leading to vapor streamers that bridge the gap and cause the actual breakdown. This paper contains an analysis of the electrostatic and hydrodynamic forces acting on the cavity and on the resulting streamers. It is assumed that the vapor in the cavity is ionized due to the high Field, so that the potential at the bubble surface is close to that of the point electrode. This assunption enables one to calculate the electrostatic force expanding the cavity. The electrostatic force on the cavity wall also leads to an instability of the interface, and the runaway growth of the instability leads to the generation and propagation of streamers; by combining simple electrostatic and hydrodynamic concepts, we derive an equation for streamer velocity that is in approximate agreement with measured values.