DSpace JSPUI

Surface modification processes are in general dedicated for surface treatment only and applied at the end of the manufacturing processes in a different setup. An attempt is made to explore the feasibility of using some manufacturing process itself for the desired surface alteration to take place. Electrodischarge machining (EDM) is thought to be one such process, where apart from machining; it is possible to alter the work surface by changing the operating conditions. EDM is one of the most extensively used non-conventional material removal processes and is a well accepted practice in die and mould making industries for quite a few decades. Whereas surface modification by electrodischarge is relatively a new concept and is yet be commercially exploited. Under certain conditions, the electrode materials get transferred to the machined surface and accreted there in the same form or get alloyed with the workpiece material. Thus the surface integrity of the workpiece changes significantly. This phenomenon inspires the researchers to tailor the workpiece surface by conventional EDM using P/M compacts as electrodes. The P/M compact electrodes enhance the transfer of electrode materials to the workpiece and can be fabricated easily by mixing powders of any compositions. In the present study surface modification with powder metallurgy (P/M) green and sintered compact electrodes using EDM is attempted, during a die sinking operation in hydrocarbon dielectric fluid. Studies are carried out with W-Cu sintered compacts, WC-Cu green compacts and also with W-Co and W-Co-Cu sintered compact electrodes. The workpiece material selected through out the studies is C-40 grade plain carbon steel. EDM process have been carried out for different tool parameters like composition, compaction pressure, sintering temperature and EDM operating parameters like peak current setting, pulse duration and polarity, at a fixed duty factor. Different studies have been made like evaluation of material transfer rate (MTR), tool wear rate (TWR), surface roughness, microhardness, optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and X-ray diffraction (XRD) analysis etc. Taguchi approach of design of experiment is applied initially to observe the effect and significance of each controlling parameter over a wide working range. An optimal condition is achieved among the selected parameters using overall evaluation criteria (OEC) to get a uniform layer over the work surface. The confirmation experiment is conducted as per the predicted optimum condition and verified. After going through the Taguchi analysis a detailed experimentation is performed to observe the effect of each controlling parameter on various output measures in detail. The electrode material is successfully transferred to the workpiece in the form of a deposited layer. For W-Cu electrode material, a wide range of MTR from 1mg/min to 191mg/min and a range of deposited layer thickness from 3µm to 785µm are achieved. The deposited layer is found to be harder than the base material. It is of the order of 9GPa to 15GPa. A gradual increase in hardness is observed from the base material to the deposited layer. Artificial Neural Network (ANN) is applied for mapping the controlling parameters with output measures in surface modification phenomena with W-Cu sintered electrodes. The attempt of using ANN is quite successful to correlate the input parameters like compaction pressure, sintering temperature, peak current, pulse on/off time with output measures like material transfer rate (MTR) and average layer thickness (LT). Introduction is presented in Chapter 1 and literature review in Chapter 2. Objective and scope of investigation are given in Chapter 3. Experimentation techniques, setups and equipments are discussed in Chapter 4. Chapter 5 and Chapter 6 deal with the studies with W- Cu electrodes in two phases. Chapter 7 deals with the studies with WC-Cu green compact electrodes. A brief study with W-Co and W-Co-Cu electrodes is given in Chapter 8. The application of ANN is presented in Chapter 9. Finally the discussions and conclusions are given in Chapter 10 which is followed by References and Appendices.