D. Petković 1, M. Madić 1, G. Radenković 1

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1 Science of Sintering, 47 (2015) doi: /SOS P UDK Selection of the Most Suitable Non-Conventional Machining Processes for Ceramics Machining by Using MCDMs D. Petković 1, M. Madić 1, G. Radenković 1 1 University of Niš, Faculty of Mechanical Engineering, Aleksandra Medvedeva 14, Niš, Serbia Abstract: Selection of the most suitable non-conventional machining process (NCMP) for a ceramics machining represents a multi-criteria decision making (MCDM) problem. This paper describes the application of relatively novel MCDM methods for selecting the most suitable NCMP for the ceramics machining. By applying WASPAS and COPRAS methods, ten NCMPs (alternatives) were ranked based on the ten criteria. Comparison of obtained ranking performances with other MCDM methods used by previous researchers was carried out in order to demonstrate WASPAS and COPRAS applicability and capability for nonconventional machining process selection. Keywords: Non-conventional machining process, Multi-criteria decision making, WASPAS, COPRAS, Ceramics machining. 1. Introduction Machining of materials can be generally divided in two techniques, i.e. conventional (traditional) and non-conventional. Conventional machining involves direct interaction of tool and workpiece. Highly hard and brittle materials such as ceramics are difficult to machine by conventional machining processes such as turning, drilling, shaping and milling [1]. However, ceramics is widely used in electronic engineering due to its excellent electrical properties, high mechanical resistance, low dielectric loss and high temperature resistance [2]. These kinds of materials have structural applications in wear industry due to their super toughness and wear resistance [3]. Ceramic materials are also applied in dentistry for dental implants due to high hardness and bending resistance, as well as materials in medicine for artificial bone due to good bio-compatibility [4, 5]. Machining of complex shapes of such materials by traditional processes is even more difficult. Non-conventional machining processes (NCMPs) are defined as a group of machining processes that remove excess material by various techniques involving mechanical, thermal, electrical or chemical energy as well as combinations of these ones. They can easily process the contemporary difficult-to-cut materials, like ceramics and ceramic-based tool materials, generating complex and intricate shapes in materials with high strength-to-weight ratio. Due to the presence of a large number of NCMPs the precise choice can be very complicated and time consuming process [6]. In the literature, researchers have proposed the use of various multi-criteria decision making (MCDM) methods for selection of the most suitable NCMP for the given application. Yurdakul and Cogun [1] proposed a NCMPs selection procedure based *) Corresponding author: dulep@masfak.ni.ac.rs

2 230 D. Petković et al. /Science of Sintering, 47 (2015) on a combination of analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) methods. Chakladar and Chakraborty [7] proposed the use of a combined method using TOPSIS and AHP methods to select the most appropriate NCMP for a specific work material and shape feature combination. Sadhu and Chakraborty [8] proposed the use of data envelopment analysis (DEA) method for solving NCMP selection problems. Chakraborty [9] explored the application of the multi-objective optimization on the basis of ratio analysis (MOORA) method to solve different MCDM problems in manufacturing environment including NCMP selection problem. Karande and Chakraborty [10] solved NCMPs selection problem using an integrated PROMETHEE (preference ranking organization method for enrichment evaluation) and GAIA (geometrical analysis for interactive aid) method. Chatterjee and Chakraborty [11] explored in details the applicability, suitability, and potentiality of evaluation of mixed data (EVAMIX) method for solving the NCMP selection problems. Recently, Prasad and Chakraborty [12] developed a decisionmaking model in Visual BASIC 6.0 to automate the NCMP selection procedure with the help of graphical user interface and visual decision aids. Roy et al. [6] presented research which emphasized on the selection of NCMPs taking into consideration the product and process characteristics and utilizing the pragmatic approach of fuzzy AHP and QFD (quality function deployment). This paper comprises a comparative study of the use of WASPAS and COPRAS MCDM methods to aid in selection of the most suitable NCMP for a given ceramics machining. 2. WASPAS method Weighted aggregated sum product assessment (WASPAS) method presents a combination of two well-known MCDM methods, i.e. weighted sum model (WSM) and weighted product model (WPM) [13]. Determination of the total relative importance of i th alternative is developed as below [14]: n (1) (2) w j Qi = λqi + ( 1 λ)qi = λ xijwj + ( 1 λ) xij j= 1 j= 1 (1) λ = 0, 010.,. 2,..., 0. 91, (1) Q i (2) Q i where and are the total relative importance based on the WSM and WPM, respectively, and x ij and w j are the normalized value of the performance of i th alternative with respect to j th criterion and weight of j th criterion, respectively. The candidate alternatives are ranked based on the Q values, so that the best alternative has the highest Q value whereas the worst alternative has the lowest one. When the value of λ is 0, the WASPAS method is transformed to the WPM, and when λ is 1, it becomes the WSM method. Till date, the WASPAS method has only few applications, such as location selection problems, civil engineering domain and manufacturing environment. n 3. COPRAS method In 1994, Zavadskas and Kaklauskas [15] created a method of complex proportional evaluation assessment (COPRAS). The selection of the best alternative is based considering both the ideal and the anti-ideal solutions. Utility values (U i ) of the candidate alternatives range from 0% to 100%, where greater value of the U i means the higher priority of the alternative [16]. This approach allows for evaluating the direct and proportional dependence of significance

3 D. Petković et al./science of Sintering, 47 (2015) and utility degree of the considered alternatives in a decision-making problem involving multiple criteria, their weights and performance values of the alternatives with respect to all the criteria. The COPRAS method was successfully used to solve various problems in the field of material selection, construction and property management, and economics. In this study, the COPRAS method was used because of its several advantages such as low computational time, very simple and transparent mathematical procedure, high possibility of graphical interpretation over other MCDM methods such as EVAMIX, TOPSIS, VIKOR and AHP. 4. Application of WASPAS and COPRAS methods - Case study In order to validate the proposed approaches a case study of a ceramics machining is analyzed. The main aim is to select the best-suited NCMP to achieve required quality of machining, simplicity in manufacturing and thereby increasing productivity. In this study alternatives are focused on these ten NCMPs: Ultrasonic machining (USM), Water jet machining (WJM), Abrasive jet machining (AJM), Electrochemical machining (ECM), Chemical machining (CHM), Electric discharge machining (EDM), Wire electric discharge machining (WEDM), Electron beam machining (EBM), Laser beam machining (LBM), and Plasma arc machining (PAM). The paper considers the following ten criteria that usually influence the NCMP decision selection [8]: Tolerance and surface finish (TSF), Power requirement (PR), Material removal rate (MRR), Cost (C), Efficiency (E), Tooling and fixtures (TF), Tool consumption (TC), Safety (S), Work material (M), and Shape feature (F). Among these ten criteria, the attributes of alternatives with respect to TSF (μm), PR (kw) and MRR (mm 3 /min) are expressed quantitative, having absolute numerical values; the attributes of alternatives with respect to C, E, TF, TC, S, M and F have qualitative measures for which a ranked value judgment on a scale of 1 5 (1 is the lowest, 3 is moderate and 5 is the highest) is suggested [17]. Yurdakul and Cogun [1] considered the machining of 930 cylindrical through holes drilling on non-conductive ceramics by applying NCMP. The hole diameter and slenderness ratio (L/D) were taken as 0.64 mm and 5.7, respectively. The same shape feature and work material combination is also taken for analysis in this paper. Tab. I Initial decision matrix No. NCMP TSF PR MRR C E TF TC S M F 1 USM WJM AJM ECM CHM EDM WEDM EBM LBM PAM

4 232 D. Petković et al. /Science of Sintering, 47 (2015) Results and discussion Total relative importance values of alternatives obtained by using Eq. 1 are shown in Tab. II. Beside Tab. II, the effect of varying values of λ on the performance scores and rankings (in brackets) of the considered NCMP selection is graphically presented in Fig. 1. It is clearly visible that the rankings of the best and the worst NCMP alternatives remain relatively unaffected for different λ values. It is also obvious that total relative importance (performance scores) depends significantly on λ. Higher performance scores are achieved for the higher value of λ, i.e. when the WASPAS method behaves like the WSM method. Tab. II Effect of λ on ranking performance of WASPAS method. No. λ USM (2) (1) (1) (1) (1) (1) (1) (1) (1) (1) (2) 2 WJM (9) (10) (10) (10) (8) (8) (7) (7) (7) (7) (7) 3 AJM (8) (7) (6) (4) (4) (4) (3) (3) (3) (3) (3) 4 ECM (7) (8) (9) (9) (10) (9) (9) (9) (9) (9) (9) 5 CHM (5) (5) (5) (5) (6) (6) (6) (6) (6) (6) (6) 6 EDM (3) (3) (4) (6) (7) (7) (8) (8) (8) (8) (8) 7 WEDM (4) (6) (7) (8) (9) (10) (10) (10) (10) (10) (10) 8 EBM (6) (4) (3) (3) (3) (2) (2) (2) (2) (2) (1) 9 LBM (10) (9) (8) (7) (5) (5) (5) (4) (4) (4) (4) 10 PAM (1) (2) (2) (2) (2) (3) (4) (5) (5) (5) (5) Based on the results, without any doubt, it can be concluded that USM process is the best choice. Similarly, it can be claimed that the worst choice is WEDM. However, taking into account the fact that ranks of EBM and PAM alternatives are pretty colorful, the both ones are the competitors for the second ranked position. The authors proposed the ranking order accomplished when parameter of λ is equal 0.5. Thus, ranking list of the alternatives based on the WASPAS assessment is USM-EBM-PAM-AJM-LBM-CHM-EDM-WJM-ECM- WEDM. Relative significances of the alternatives and quantitative utility for each alternative were calculated according to the COPRAS method, respectively (Tab. III). Based on the results, the ranking of the alternative NCMPs is obtained as PAM-USM-AJM-LBM-EBM- CHM-WJM-EDM-WEDM-ECM. Hence the best choice is PAM, while USM is the second ranked choice. The third ranked alternative is AJM, but the last ranked one is ECM. Quantitative utility of PAM-USM-AJM-LBM-EBM are above the mean quantitative utility value (51.2 %). The other five alternatives are significantly below the mean indicating their unsuitability for this application.

5 D. Petković et al./science of Sintering, 47 (2015) Fig. 1. Variations of the total relative importance of NCMP selection depended on λ. Comparative rankings of WASPAS and COPRAS methods as well as previous researched approaches are listed in Tab. IV. Selection the most suitable NCMP, based on obtained ranking results by applying WASPAS and COPRAS methods, is pretty ambiguous. Namely, using the WASPAS method USM is observed as the best choice but the COPRAS method recommends PAM as the most suitable choice. Additionally, only the sixth ranked alternative is the same (CHM). Tab. III Relative significance and utility values of the alternatives. No NCMP USM WJM AJM ECM CHM EDM WEDM EBM LBM PAM Relative significance of alternative (Q i ) Quantitative utility (U i ) For the same shape feature and work material combination, with the help of graphical user interface and visual decision aids integrated with QFD technique, Prasad and Chakraborty [12] ranked NCMPs as USM AJM EBM LBM-WJM-CHM. Karande and Chakraborty [18] observed the ranking of the feasible NCMPs as USM-AJM-WJM-LBM- EBM-CHM while employing a reference point-based approach. The ranking of the NCMPs by using DEA method is obtained as USM LBM AJM EBM PAM EDM WEDM ECM [8]. Chakladar and Chakraborty [7] ranked the alternative NCMPs as USM EDM EBM WEDM LBM, whereas incorporating a combined TOPSIS AHP method-based approach. On the other hand, Yurdakul and Cogun [1] ranked the NCMPs as USM LBM EBM CHM AJM for the same machining application while using a multi-attribute based selection methodology.

6 234 D. Petković et al. /Science of Sintering, 47 (2015) Tab. IV NCMPs rankings obtained by the WASPAS, COPRAS and other methods. No. NCMP WASPAS COPRAS DEA[8] Combined TOPSIS AHP [7] Visual Reference decision pointbased aids integrated approach with QFD [18] [12] Multiattribute based selection approach [1] 1 USM WJM AJM ECM CHM EDM WEDM EBM LBM PAM Finally, it can be concluded that the results are pretty different to each other. However, the first ranked NCMP for six approaches is USM, and only the COPRAS method deviates in terms that PAM has the best ranking. Reason for that may be normalized value of MRR obtained. Namely, PAM gains the enormous higher value of MRR as a beneficial criterion in comparison to other NCMPs, which enhances directly relative significances of PAM as the alternative. The calculation results obtained by using the COPRAS method depend on the number of non-beneficial criteria and attribute values of alternatives with respect to them. However, these problems require further investigation. On the other hand, although at first glance the results of WASPAS and COPRAS methods seem to be very different, Spearman s correlation coefficient, as a statistical measure of the strength of a monotonic relationship between paired data, reveals contrary. The value of 0.88 of Spearman s correlation coefficient points out on very strong (rs > 0.8) positive correlation between the two methods. Taking everything aforementioned into account the authors dare to select USM as the best NCMP for ceramics machining. Furthermore, they propose WASPAS method for successfully solving of MCDM problems in the field of NCMP selection for a given material and shape requirements. They are also sure that any further investigation and improvement of MCDM methods are welcomed. 6. Conclusion It is quite clear that selection of a proper NCMP for a given manufacturing application is a complex task for the engineers due to limited knowledge, as well as complexity of NCMPs which involve a large number of considerations. The use of the WASPAS method is observed to be quite capable and computationally easy to yields acceptable results and making accurate decisions while selecting the most suitable NCMP from among a large number of alternative processes for generation of a desired shape feature on a ceramics. Thus, this relatively novel MCDM method can be successfully employed for solving any type of decision-making problems having any number of criteria and alternatives in the manufacturing domain. Obtained results reveal that the WASPAS method is able to facilitate NCMP selection problem. It has also been observed that the WASPAS method is very strong

7 D. Petković et al./science of Sintering, 47 (2015) correlated with the COPRAS method (Spearman s correlation coefficient of 0.88). As a future scope, a fuzzy WASPAS based methodology may be developed to aid the decision makers to take decisions in presence of imprecise and incomplete data. Acknowledgement This paper is a result of the projects ON and TR35034 supported by the Ministry of Science and Technological Development of the Republic of Serbia. 7. References 1. M. Yurdakul, C. Coğun, P. I. Mech. Eng. B-J Eng., 217 (2003) A. Terzić, Lj. Andrić, J. Stojanović, N. Obradović, M. Kostović, Sci. Sint., 46:2 (2014) Y. Tian, Y. Qiu, Y. Chai, P. Bai, C. Gong, Sci. Sint., 45:2 (2013) S. Islak, D. Kır, S. Buytoz, Sci. Sint., 46:1 (2014) B. Čolović, V. Jokanović, N. Jović, Sci. Sint., 45:3 (2013) M. K. Roy, A. Ray, B. B. Pradhan, Production & Manufacturing Research, 2:1 (2014) N. D. Chakladar, S. Chakraborty. P. I. Mech. Eng. B-J Eng., 222(12) (2008) A. Sadhu, S. Chakraborty, Expert. Syst. Appl., 38 (2011) S. Chakraborty, Int. J. Adv. Manuf. Technol., 54 (2011) P. Karande, S. Chakraborty, Management Science Letters, 2 (2012) P. Chatterjee, S. Chakraborty, International Journal of Advanced Manufacturing Technology, 68(5-8) (2013) K. Prasad, S. Chakraborty, Decision Science Letters, 3 (2014) S Chakraborty, E. K. Zavadskas, Informatica 25(1) (2014) E. K. Zavadskas, Z.Turskis, J. Antucheviciene, A. Zakarevicius, Elektronika ir Elektrotechnika Electronics and Electrical Engineering, 122(6) (2012) E.K. Zavadskas, A. Kaklauskas, V. Sarka, Technological and Economic Development of Economy 1(3) (1994) A. Kaklauskas, E.K. Zavadskas, S. Raslanas, Energ. Buildings, 37 (2005) P. C. Pandey, H. S. Shan, Modern machining processes. Tata McGraw-Hill Publishing Company Limited, New Delhi, P. Karande, S. Chakraborty in: Proceedings of the 4th International and 25th AIMTDR Conference, India, 2012, p Садржај: Избор најпогоднијег неконвенционалног поступка обраде керамике представља проблем вишекритеријумског одлучивањa. У раду је приказана применa нових метода вишекритеријумског одлучивања за избор најпогоднијег неконвенционалног поступка обраде керамике. Применом WASPAS и COPRAS метода, десет неконвенционалних (алтернативних) поступака обраде су рангирани на основу десет критеријума. Поред тога, упоређени су добијени резултати са резултатима претходних истраживања како би се показала применљивост и ефикасност разматраних метода вишекритеријумског одлучивања у области избора неконвенционалних поступака обраде. Кључне речи: Неконвенционални поступак обраде, вишекритеријумско одлучивање, WASPAS, COPRAS, обрада керамике