OPTIMAL SELECTION OF PROCESS PARAMETERS OF ULTRASONIC MACHINING (USM) SYSTEM

Transcription

1 OPTIMAL SELECTION OF PROCESS PARAMETERS OF ULTRASONIC MACHINING (USM) SYSTEM BY H. L A L C H H U A N V E L A B.E. (Mech), MNNIT, Allahabad (Formerly M.N.R.E.C., Allahabad), 1987; M.Tech. (Mech), IT-BHU, 1999 THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ENGINEERING IN THE FACULTY OF ENGINEERING & TECHNOLOGY JADAVPUR UNIVERSITY DEPARTMENT OF PRODUCTION ENGINEERING JADAVPUR UNIVERSITY KOLKATA INDIA

2 OPTIMAL SELECTION OF PROCESS PARAMETERS OF ULTRASONIC MACHINING (USM) SYSTEM SYNOPSIS Submitted by H. L A L C H H U A N V E L A B.E. (Mech), MNNIT, Allahabad (Formerly M.N.R.E.C., Allahabad), 1987 M.Tech. (Mech), IT-BHU, 1999 THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ENGINEERING IN THE FACULTY OF ENGINEERING & TECHNOLOGY JADAVPUR UNIVERSITY DEPARTMENT OF PRODUCTION ENGINEERING JADAVPUR UNIVERSITY KOLKATA INDIA

3 NAME, DESIGNATION & INSTITUTION OF THE SUPERVISORS : Dr. B. BHATTACHARYYA Professor, Dept. of Production Engg. Jadavpur University Kolkata , INDIA Dr. B. DOLOI Head & Associate Professor, Dept. of Production Engg. Jadavpur University Kolkata , INDIA (ii)

4 SYNOPSIS Ultrasonic machining (USM) is a non-conventional mechanical material removal process in which material is removed by repetitive impact of abrasive particles carried in liquid medium on the work surface, by a shaped tool, vibrating at ultrasonic frequency. The application of ultrasonic energy for machining of engineering materials was first reported by Wood and Loomis in However, American engineer Lewis Balamuth invented the USM process in USM has been variously termed as ultrasonic drilling; ultrasonic cutting; ultrasonic dimensional machining; ultrasonic abrasive machining and slurry machining. From 1950s it has been commonly known as ultrasonic impact grinding or USM. In ultrasonic machining process, the converter transforms electrical energy into high frequency mechanical vibrations. The process parameters of USM includes the static pressure, vibration amplitude, vibration frequency, rotational speed of tool for rotary USM (RUM), diamond grit concentration, grit size, diamond and bond type, slurry concentration and coolant etc. Some of the advantages of USM are high accuracy and good surface finish, no heat generation during machining, capability of drilling circular and non-circular holes on very hard materials, no thermal effects on mechanical workpiece and ability to machine electrical conductive as well as non-conductive materials can be machined. Unlike other non-traditional processes such as laser beam machining and electro-discharge machining etc., ultrasonic machining process generates the work surface with no thermal damage and low level of residual stress, which is important for the survival of brittle materials in service. The newest and most exciting class of advanced engineering materials are alumina, zirconia, silicon carbide, silicon nitride, boron carbide and boron nitride, etc. those can be machined by USM. There is tremendous need of ultrasonic machining and it has great potential application in the field of advanced manufacturing. The in-depth parametric analysis of USM process is highly demanded for improving the machining performance during generating the noncircular hole geometry on advanced engineering materials such as ceramics. (iii)

5 Research works on the area of ultrasonic machining to make it more efficient material removal processes for advanced materials have been demanded to fulfill the need of modern manufacturing industries. Although good number of research activities have already been carried out on ultrasonic machining process, a research in optimal selection of various dominant process parameters are still needed for the successful adoptability of the ultrasonic machining process in fulfilling the material machining needs of the modern manufacturing industries. Keeping the above considerations in view, the objectives of the present research work has been modulated as follows: - (i) To analyse the machining characteristics of ultrasonic machining on ceramics based on the material removal mechanism of ultrasonic machining process and also to identify the effect of various machining parameters on the machining performance of USM process for selecting the range of different process parameters. (ii) To develop the work holding unit for performing drilling operation using USM experimental set up and also develop the tool holding arrangement for fixing circular and non-circular tools in such a manner that the system is capable for carrying out experimentations. (iii) To carry out basic experimental studies on USM process for machining various type of engineering ceramics for analyzing the effects of various dominant process parameters i.e. abrasive grit size, slurry concentration, power rating, feed rate and slurry flow rate on the important machining criteria i.e. material removal rate, surface roughness, hole taper and radial overcut. (iv) To plan and carry out experimental studies as per Taguchi method on USM process for machining high alumina ceramics for analyzing the effects of process parameters on material removal rate, surface roughness, hole taper and radial overcut. (v) To determine the optimal parametric combinations of grit size, slurry concentration, power rating and feed rate based on Taguchi (iv)

6 methodology for maximum material removal rate, minimum surface roughness, hole taper and radial overcut during ultrasonic machining circular hole on ceramics. (vi) To perform analysis of variance (ANOVA) to find out percentage contribution of USM process parameters on material removal rate, surface roughness, hole taper and radial overcut. (vii) To determine the optimum parametric combination of grit size, slurry concentration, power rating and feed rate based on single-objective optimization and multi-objective optimization using Taguchi methods with Principal Component Analysis for maximum material removal rate, minimum surface roughness, hole taper and radial overcut during ultrasonic machining of alumina, Al 2 O 3. (viii) To study the influence of predominant USM process variables on the performance characteristics during ultrasonic drilling of alumina ceramics based on the observations of micrographs of the machined job samples. (ix) To plan and carry out experimental studies on USM process based on Response Surface Methodology for analyzing the influence of process parameters on material removal rate and surface roughness during machining of high alumina ceramics. (x) Development of mathematical models to establish relationship between USM process parameters for analyzing the influence of parametric combinations on material removal rate and surface roughness. (xi) To determine the optimal parametric combinations of abrasive grit size, slurry concentration, power rating, tool feed rate and slurry flow rate based on RSM for maximum material removal rate and minimum surface roughness during ultrasonic machining of high alumina. (xii) To carry out verification experiments and ANOVA for testing adequacy of the additive models for selecting parametric combinations of USM to achieve desired MRR and surface finish at various designed considerations. (xiii) To perform the experimental studies on ultrasonic machining characteristics and analyze the influences of different parametric (v)

7 combinations e.g. grit size, slurry concentration, power rating, tool feed rate and slurry flow rate on machined hexagonal hole profile accuracy. (xiv) To study the effects of parametric combinations on profile accuracy based on micrographs of machined hexagonal hole generated by USM. (xv) To develop mathematical models based on RSM to establish relationship between different machining parameters and various factors of hole profile accuracy such as angular deviation at corners, dimensional deviation across corners and dimensional deviation across flats as well as analyse the profile accuracy of hexagonal hole based on developed models with predominant process parameters of USM. (xvi) To carry out single objective optimization as well as multi-objective optimization based on developed models and analyze improvement of geometrical profile accuracy of drilled hexagonal holes on ceramics by USM. The complete work is presented in the thesis form from chapter 1 to chapter 7 in a well designed manner. Brief description of the contents of each chapter has been given as following: Chapter 1 contains introduction to ultrasonic machining methods, their comparative features, applications and relative merits and demerits. Various aspects of ultrasonic machining (USM) have been detailed; need of USM, applications of ultrasonic energy and fundamentals of USM. Extensive review on literatures has been presented on the development of ultrasonic machining and recent reports from researches in the areas of conventional ultrasonic machining processes. Fundamentals of ultrasonic machining processes, mechanism of material removal rate with literature and model and also basic influences of some parameters during USM process are presented in Chapter 2. Chapter 3 details the description of various components of USM, workpieces and abrasive grits, about the fabrication of tool holding plates and whole experimental setup for conducting the experiments as per planning. Results of experimental investigation for optimal parametric combination of process parameters such as abrasive grit size, slurry concentration, power rating and tool feed rate during ultrasonic machining on alumina ceramics with tubular tools using Taguchi method of robust design and also results of multi-objective optimization of USM process parameters applying (vi)

8 Taguchi method with Principal Component Analysis are highlighted in chapter 4. Chapter 5 highlights the observations based on experimental investigation in to the influence of ultrasonic machining process parameters such as abrasive grit size, slurry concentration, power rating, tool feed rate and slurry flow rate on material removal rate and surface roughness on workpieces using Response Surface Methodology (RSM). Chapter 6 contains detail analysis of experimental results in the context of profile accuracy of the generated hexagonal hole by USM. It also contains results and analysis based on developed mathematical relationships utilizing Response Surface Methodology (RSM) for determining the influence of various process USM parameters such as grit size, slurry concentration, power rating and feed rate on different factors of profile accuracy such as angular deviation at corners, dimensional deviation across corners and flats of the hexagonal holes. Chapter 7 is all about the conclusions of this research work. This chapter also highlights the limitations of the study and scope for future work in this area. This chapter is followed by References. The present research work reveals that USM process has great potential for machining various geometrical shapes on engineering ceramics. From the fundamental study of the USM process regarding material removal mechanism; it is evident that material removal from the workpiece takes place due to the direct impact of abrasive grains on workpiece caused by longitudinal vibration of the tool. It has been observed that the performance characteristics of USM on material removal rate, surface roughness, hole taper and radial overcut to different machined holes depend on process parametric combinations during ultrasonic machining operations. Attempts have been made to search out influences of various process parameters on ultrasonic machining characteristics and selection of optimal process parametric combinations. Hence considering these views, investigation on the performance characteristics of USM parametric combinations for the ultrasonic machining on engineering ceramics has been carried out accordingly. Within limitations of the present experimental work and optimal analysis based on the detailed experimental observations during ultrasonic machining for generating circular and non-circular holes on engineering ceramics, following conclusions can be drawn: (vii)

9 (i) (ii) (iii) (iv) (v) (vi) From the present study, it is clear that ultrasonic machining process can be utilized for machining of hard and brittle materials like ceramics and glasses etc. by using different shape of circular or non-circular tools. The details study of previous researches in the areas of ultrasonic machining will provide essential information regarding various process parameters and it is clear that those major ultrasonic machining criteria i.e. MRR, Ra, Ht, ROC, etc. depend on various process parameters during ultrasonic machining of work samples. The role of predominant process parameters such as abrasive grit size, slurry concentration and power rating, etc. have been considered during the development of USM system setup and planning for experimentation. The USM experimental setup with all its subsystems such as electrical power supply unit, slurry recirculation system, tool feed device, work holding device and fabricated tools for the present set of research work is a unique one in the area of developing existing USM system capable of machining in optimal operating conditions. The USM experimental setup has the provision of modifying work holding device as well as geometrical shape of tools. During preliminary study on USM process for machining of ceramics, it was observed that machining time is more comparably long for fine abrasive grit numbers such as 400, 500 and 600 under power supply rating of 40%, slurry flow rate of 8 lit/min and slurry concentration of 40%. Considering various machining performances based on different variables of process parameters, the most suitable levels of ranges for each of the process parameters have been selected. USM process with fabricated tools has been successfully employed for machining different type of shapes on engineering ceramics, Al 2 O 3. It was observed that higher grit numbers are better for surface finishing but not preferable for machining thicker work samples. Investigation has been carried out successfully using Taguchi method based robust design to study the relative significance and effect of process parameters i.e. abrasive grit number, slurry concentration, power supply rating and tool feed rate. From the analysis based on Taguchi (viii)

10 (vii) (viii) (ix) (x) methodology, the optimal parametric combinations for maximum MRR in the ultrasonic machining of alumina has been found as A 1 B 3 C 2 D 1 ; i.e. grit size of 63 µm, slurry concentration of 50%, power rating of 500 W and feed rate of 0.84 mm/min. Based on ANOVA, it was found that abrasive grit size has the largest contribution i.e % followed by power supply rating i.e. 8.18% on material removal rate during generation of circular hole. It was also found that abrasive grit size has the largest contribution i.e % followed by power supply rating i.e % on surface roughness during generation of circular hole. In case of hole taper, abrasive grit size has the largest contribution i.e % followed by feed rate and power supply rating with minimal values during generation of circular hole on work samples of Al 2 O 3. The optimum parametric combination observed in single-objective optimization based on Taguchi methodology for minimum surface roughness was found as A 3 B 2 C 2 D 1, i.e. abrasive grit size of 14 µm, slurry concentration of 40 %, power rating of 50 % (500 W) and tool feed rate of 0.84 mm/min. Similarly, optimum parametric combination observed in single-objective optimization based on Taguchi methodology for minimum hole taper was found as A 3 B 3 C 1 D 2 i.e. abrasive grit size of 14 µm, slurry concentration of 50 %, power rating of 40 % (400 W) and tool feed rate of 1.02 mm/min. Abrasive grit size has the significant contribution on hole taper. The optimum parametric combination observed in single-objective optimization based on Taguchi methodology for minimum radial overcut (ROC) is A 3 B 1 C 1 D 3 i.e. abrasive grit size of 14 µm, slurry concentration of 30 %, power rating of 40 % (400 W) and tool feed rate of 1.2 mm/min. Power supply rating has the largest influence in radial overcut. The optimum combination of parameters according to multi-objective optimization using Taguchi method with Principal Component Analysis has been observed as A 3 B 2 C 1 D 3 i.e. abrasive grit size of 14 µm (grit number 600), slurry concentration of 40 %, power rating of 40% (400W), and tool feed rate of 1.20 mm/min. Utilizing the results of multi-objective (ix)

11 optimization based on Principal Component Analysis as compared to single-objective optimization, the quality of machined hole is improved. The results of simultaneous optimization of multi responses are closer to the predicted values of single objective optimization. The differences between predicted values based on single objective optimization and experimental results obtained based on multi-objective optimization have been found as: 2.73 % for MRR, 4.47% for Ra, 8.82% for Ht and 5.55% for ROC. (xi) It was clearly observed from micrographs and photographic view of the machined job samples that the quality of drilled hole depends upon type of abrasive grits used for machining. Moreover, parametric combinations of process parameters play significant role for achieving higher profile accuracy during machining of ceramic materials. (xii) The developed Response Surface Methodology (RSM) based mathematical modeling has the potential to evaluate MRR and Ra under various process parameter settings and also to analyze the influence of machining process parameters on MRR and Ra during ultrasonic machining on high alumina ceramics, Al 2 O 3. (xiii) From the analysis of response surface graphs, it has been observed that higher level of slurry concentration, slurry flow rate, tool feed rate, larger size of abrasive grain and higher power rating give higher material removal rate during generating hexagonal hole on alumina ceramics, Al 2 O 3. (xiv) From the analysis of response surface graphs, it has also been observed that surface roughness decreases with decrease in abrasive grit size and power rating. Abrasive slurry concentration, tool feed rate and slurry flow rate have less effects on surface roughness of hexagonal hole surface generated on alumina, Al 2 O 3. (xv) From ANOVA results, it has been revealed that the developed mathematical models for MRR and Ra have been found to be adequate at 90 and 95% of confidence limits respectively during ultrasonic machining operation. It has also been observed that all the lack-of-fit is insignificant for MRR and Ra. (x)

12 (xvi) The optimum parametric combination of process variables for maximum material removal rate and minimum value of surface roughness have been obtained based on RSM as: abrasive grit size of 55 µm in diameter, slurry concentration of 50%, power rating of 40%, feed rate of 1.01 mm/min, and slurry flow rate of 10 lit/min during ultrasonic drilling of alumina ceramic. The errors in the predicted values of material removal rate and surface roughness at optimal parametric combination are 3.57% and 2.22% respectively. (xvii) Based on experimental results, it was observed that job profile accuracy is greatly influenced by the size of abrasives used during ultrasonic machining operation utilizing hexagonal tools. From test results, job s profile related to angular deviation and both dimensional deviation across flats and corners as considered for the investigation decrease with increase in grit number. It can be concluded that better hole accuracy can be obtained at largest abrasive grit number i.e (xviii) Increase in abrasive slurry concentration decreases hole profile accuracy. More abrasive particles at the slurry causes more stagnation of grains on the walls of the machined hole resulting poor surface quality and more taper of the drilled hole on the workpiece. Higher profile accuracy of the hexagonal hole can be obtained with lower slurry concentration i.e % at normal flow rate i.e. 8 lit/min. (xix) The influence of power rating on hole profile accuracy is small in comparison with the effects of abrasive grit size, slurry concentration and tool feed rate. From the experimental results, it can be concluded that 50% of power rating is sufficient for achieving higher profile accuracy of the machined hole with satisfactory machining rate. (xx) From analysis of profile accuracy based on micrographs on the effects of abrasive grit number 220 and 400 during ultrasonic machining of work samples while other process parameters have been kept constant as: slurry concentration of 40%, power rating of 40%, feed rate of 1.08 mm/min and slurry flow rate of 8 lit/min. It can be observed that the effect of smaller grit size i.e. abrasive grit number 400 on cut profile is far better than that of abrasive grit number 220. The generated corner (xi)

13 angle is also improved to º from120.45º. Similarly, higher quality of machined surface and profile accuracy can be obtained with finer abrasive grit sizes i.e. grit numbers 500 and 600 under normal machining operations. (xxi) Mathematical models for profile accuracy correlate to angular deviation at corners (D A ), dimensional deviation across corners (D C ) and dimensional deviation across flats (D F ) of hexagonal generated machined hole on work samples with predominant process parameters have been obtained separately and tested. Results of ANOVA test justify the adequacy of the developed models for prediction of hexagonal type of profile generation during ultrasonic machining of ceramics. (xxii) From response surface graphs based on different process parameters, it has been observed that higher slurry concentration is desirable for increasing material removal rate whereas considering profile accuracy, lower level of slurry concentration usually gives better surface profile on machined holes. (xxiii) From response surface graphs, it has also been observed that mean deviation of all the factors considered for profile accuracy of the hexagonal hole decrease with increase of abrasive grit number., i.e. decrease in abrasive grit diameter. Lower to medium level of power supply rating to some extent be more suitable for achieving better profile accuracy. Feed rate with smaller grit size of abrasive and lower slurry concentration can be used effectively for controlling the machining characteristics to achieve higher hole profile accuracy. (xxiv) The confirmation test results at optimal parametric conditions considering different deviations for profile accuracy have been performed and are verified with predicted results. The predicted value of percentage errors of deviations for angular deviation at corners (D A ), dimensional deviation across corners (D C ) and dimensional deviation across flats (D F ) have been found as 6.07%, 7.79% and 6.51% respectively. It is concluded that the additive models for predicting optimal results can be considered as adequate at these optimal conditions. (xii)

14 From the various experimental analysis and test results, genuine attempts have been made to justify the uniqueness of the research work in exploring out the most dominant parametric combinations on USM process variables for achieving desired controlled process combination criteria yield during ultrasonic machining of engineering ceramics. It is expected that the research work on multi-objective optimization of control factors in ultrasonic machining process on ceramics will be useful for enabling and understanding ultrasonic machining of engineering ceramics in modern manufacturing industries. The observed values can also be used as information for the technical guidelines to carry out further research activities in the areas of ultrasonic machining of ceramics for fabricating ceramic die and other ceramic components. Research activities on optimization of USM based on RSM will open up many challenging possibilities such as selection of controlling parameters for production of non-circular holes and cavities on ceramics with geometrical and dimensional accuracy. Some of the important findings related to profile accuracy of machined jobs during USM of ceramics might be effectively utilized during USM operation for better design of tools. (xiii)

15 LIST OF PUBLICATIONS: International / National Journals : 1. State of the art on ultrasonic machining of engineering ceramics, Journal of Manufacturing Technology Today (MTT) Vol.7, Issue 7, (2008), pp Parametric analysis on ultrasonic drilling of alumina based on Taguchi Method, Journal of Institution of Engineers (India), PRODUCTION ENGG. Volume 92 SEP. (2011), pp Enabling and Understanding Ultrasonic Machining of Engineering Ceramics using Parametric Analysis, Journal of Materials and Manufacturing Processes, (Taylor & Francis Group), Vol.27, 4 (2012), pp Analysis on profile accuracy for ultrasonic machining of alumina ceramics, International Journal of Advanced Manufacturing Technology (Springer) (under Second Review) LIST OF PATENTS : NIL (xiv)

16 LIST OF PRESENTATIONS IN NATIONAL / INTERNATIONAL: National Conferences 1. Application of ultrasonic energy in the areas of manufacturing, Proceedings of the National Conference on Emerging Trends in Mechanical Engineering (ETME-2007), June 4-5, 2007 at S.V. National Institute of Technology, Surat, (2007), pp Study on ultrasonic machining of advanced ceramics, Proceedings of the National Conference on Advanced Materials and Manufacturing Technology (AMMT-2007), September 21-22, 2007 at Punjab Engineering College, Chandigarh, (2007), pp Parametric analysis on ultrasonic drilling of alumina based on Taguchi method, National Conference on Recent Trends in Manufacturing Technology (RTMT2009) at Anna University, Chennai (March 5-6), (2009), pp.1-6. International Conference 1. Experimental investigation based analysis on ultrasonic drilling of alumina, Proceedings of the 2 nd International & 23 rd All India Manufacturing Technology, Design and Research (AIMTDR) Conference at IIT Madras, 15 th 17 th December, 2008, IIT Madras, (2008), pp (xv)