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Authors: Vishwakarma, Umesh Kumar
Keywords: During Last Few Decades
High Hardness
Toweight Ratio
High Speed Steel
Issue Date: Apr-2014
Publisher: Dept. of Mechanical and Industrial Engineering iit Roorkee
Abstract: During the last few decades, there is an increased demand of materials with high strength-toweight ratio, high hardness, high wear resistance etc. These materials have wide area of applications. Difficult-to-machine materials such as Inconel 718, high speed steel, Al-SiC MMC etc. find their applicability in the field of aerospace, automobile, medical and nuclear industries. The above stated properties of these materials makes their processing a cumbersome task. Some conventional machining methods are available to process these materials. However, high tooling cost makes conventional machining a inappropriate option. This limitation of conventional machining encourages the usage of non-conventional machining methods. A number of non-conventional machining methods are available to process difficult-to-machine materials. Each of these non-conventional machining methods have their advantages and limitations. Amongst non-conventional machining methods, EDM is one of the possible solution to machine these materials. EDM has the unique ability to machine any electrically conductive material irrespective of its hardness. It is evident from previous literatures that conventional EDM have some limitations in terms of low MRR, high tool wear and deteriorated surface quality. To overcome these limitations, many researchers have tried different variants of EDM like addition of powder in dielectric fluid, providing rotation to the tool electrode, providing ultrasonic vibrations to the workpiece etc. The main focus in development of these variants is to improve the effective removal of debris particles from inter electrode gap. These abrasive particles if entrapped cause problems like arcing and short circuiting between the tool and workpiece electrodes which leads to deterioration of machined surface. Thus, present investigation involves study of EDM process variants to machine difficult-to-machine materials. Each EDM process variants have their own area of applications. However, no comparative study among different EDM process variants was reported. Hence, a v scope to study the effect of different input process parameters of EDM on the response characteristics of Al6063-SiC was deciphered. In addition to above point, literature also revealed that EDM has drawn focus only in the area of process performance improvement. Lesser effort were made to improve the geometrical flexibility of EDM process. The advanced stage of present work involved improvement in the geometrical flexibility of EDM process. Thus, a setup was developed to provide motion to the workpiece. The novelty of developed setup was also proved by fabricating threads and some complex geometries. The entire work spectrum was presented in two broad categories viz. the EDM process variants development and machining of difficult-to-machine materials. The first phase involved development of PMEDM and REDM setup and analyzing the machining behavior of Al6063- SiC MMC. Then, workpiece movement provision was developed and used to machine HSS T1 grade and Inconel 718. In last phase, the setup was utilized to fabricate threads and different complex geometries on difficult-to-machine materials. Further, multi-criteria optimization of Phase II was carried out. In addition to above stated work, finite element models were also developed for EDM, PMEDM and REDM process to analyze the process behavior. The objectives of the present work are as under: 1. To develop experimental setup for EDM process variant − PMEDM and rotary tool EDM. The experimental setups were intended to enable variation of various PMEDM and REDM process parameters. 2. To produce Al-SiC MMCs and characterizing these to ensure uniform distribution of abrasives with minimum porosity. 3. To explore the scientific basis of EDM process and hence to attempt modelling of EDM process. vi 4. Experimental investigation of PMEDM and REDM on Al-SiC MMC for the effect of various process parameters on the response characteristics based on some preliminary experimentation. 5. To develop a 2.5D microprocessor controlled manipulator for enhancing the flexibility of EDM process. 6. To carry out extensive experimentation on difficult-to-machine materials using 2.5D microprocessor controlled manipulator. 7. To perform the experimentation using design of experiment techniques such as response surface methodology (RSM) with an aim to develop mathematical models. These models can be used for understanding and predicting the maching characteristics of difficult-to-machine materials. 8. To develop and validate predictive models using regression analysis for response characteristic of EDM. 9. To explore the scientific basis of the EDM process variants in respect of mechanism of material removal. 10. To explore the feasibility of external threads fabrication and other elaborated shapes such as spiral channels on difficult-to-machine materials. The results of this study have thrown new light on important aspect of machining difficult-tomachine materials by EDM process variants. The present work embodies the sequential procedure from modelling, process development, experimentation and analysis to optimization. The future improvements may further enhance the geometrical flexibility of EDM process. The attempted methodology can be further extended and applied to other non-conventional processes.
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