Multi-physics modeling of plasma discharge and material removal in micro electro-discharge machining process

by Soham Sanjeev Mujumdar

Institution: University of Illinois – Urbana-Champaign
Year: 2016
Keywords: Micro-EDM; EDM plasma; Material Removal
Posted: 02/05/2017
Record ID: 2134006
Full text PDF: http://hdl.handle.net/2142/90491


Micro electro-discharge machining (micro-EDM) is a machining process capable of removing material in sub-grain size range and machining a range of materials irrespective of their hardness. Due to the unique capabilities offered by micro-EDM process in manufacturing high accuracy micro-scale parts with complex geometries, it has potential to meet wide spectrum of current and future needs in the electronics, automotive, optics and bio-medical industries. Despite these advantages, one of the major disadvantages of the micro-EDM process has been its low productivity in terms of material removal rate (MRR). To improve the MRR, the micro-EDM process has been subjected to numerous parametric optimization studies. However, machining characteristics of the micro-EDM process are influenced by a large number of controllable process parameters. This makes it very cumbersome to conduct full-scale parametric studies and find optimum machining parameters without understanding of material removal mechanism. Therefore, there is a strong need for development of a physics-based model to gain fundamental knowledge of the micro-EDM process. In this research work, a multi-physics model of the micro-EDM process has been developed to understand formation and expansion of micro-EDM plasma, and the process of formation of melt-pool and material removal at the workpiece. Initially, a model of micro-EDM plasma has been developed using a ’Global Model’ approach in which the plasma is assumed to be spatially uniform, and equations of mass and energy conservation are solved simultaneously along with the dynamics of the plasma bubble growth. One of the unique features of this model is the plasma chemistry module that enables understanding of chemical as well as energy interactions of various species in the plasma. Using the micro-EDM plasma model, complete temporal description of the micro-EDM plasma is obtained in terms of the composition of the plasma, temperature of electrons and other species, radius of the plasma bubble, the plasma pressure and heat flux to the electrodes. The model is also used to study the effect of electric field in the inter-electrode gap and the gap distance on the plasma characteristics. The model predicts that the application of higher field at a fixed gap increases the electron density, plasma temperature, plasma radius, plasma pressure and the heat flux to the workpiece, while increasing gap distance for a fixed electric field results in decreased overall plasma density and increased heat flux. The micro-EDM plasma model is further enhanced to predict time-transient electrical characteristics of a micro-EDM discharge such as plasma resistance, voltage, current and discharge energy. In micro-EDM, due to smaller value of the plasma resistance, it is often difficult to separate the voltage drop across stray impedances in the circuit from exact voltage drop across micro-EDM plasma alone using direct measurements. A model-based approach can be useful in this case to obtain accurate information about the time transient… Advisors/Committee Members: Kapoor, Shiv G. (advisor), Kapoor, Shiv G. (Committee Chair), Ferreira, Placid (committee member), Ruzic, David (committee member), Curreli, Davide (committee member).