International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 Cookware material selection by multi-criteria decision making (MCDM) methods Javier Martínez-Gómez#1, Gonzalo Guerrón*2, Ricardo A. Narvaez C*3. 1 Instituto Nacional de Eficiencia Energética y Energías Renovables (INER), Adress: 6 de Diciembre N33-32, Quito, Ecuador. Tel +593 (0) 2 3931390 ext: 2079, Abstract - Material selection has great importance in design and development of the products. The success and competitiveness of the producers also depends on the selected material. This paper reports of the application of different preference rankingbased MCDM method for the base of an induction cookware for the National Efficient Cooking Program of Ecuador which tries to replace liquefied petroleum gas cookers for induction cookers. Selection of an appropriate material is necessary for improve the efficiency in the system cookwareinduction cooker. This efficiency is measured with the energy efficiency, cost saving, high heating rate, and workability. The MCMD method implemented is operational competitiveness rating analysis (OCRA). The criteria weighting was performed by compromised weighting method composed of analytic hierarchy process (AHP) and Entropy methods. Using these methods, a list of all the possible choices from the best to the worst suitable materials is obtained taking into account different material selection criteria. According to the results, Ni would be the best material for the base of an induction pot. Keywords- Multi-criteria decision making methods, MCDM, induction heating, induction cookware, National Efficient Cooking Program, Ecuador. I. INTRODUCTION Material selection is one of the most challenging issues in the design and development of products, and it is also critical for the success and competitiveness of the manufacturing organizations [1, 2] Material selection for engineering design needs a clear understanding of the functional requirement for each individual component/product and various important criteria also need to be considered [3, 4] The improper selection of one material could negatively affect productivity, profitability and reputation of an organization because of the growing demands for extended producer responsibility. The objectives and criteria in the material selection process are observed to be often in conflicts and it involves trade-offs amongst decisive factors, such as desired properties, operating environment, production process, cost, market value, availability of supplying sources and product performance [1, 2] ISSN: 2231-5381 The objectives and criteria in the material selection process are observed to be often in conflicts and it involves trade-offs amongst decisive factors, such as desired properties, operating environment, production process, cost, market value, availability of supplying sources and product performance [5-7]. Thus, the material selection process can be regarded as a multi-criteria decisionmaking (MCDM) problem. Hence, a systematic and efficient approach to material selection is necessary in order to select the best alternative for a given engineering application [8, 9]. Thus, efforts need to be extended to identify those criteria that influence material selection for a given engineering application to eliminate unsuitable alternatives and select the most appropriate alternative using simple and logical methods [10, 11]. Currently Ecuador is running a world pioneer campaign called “National Efficient Cooking Program” (NECP), which aims the migration of 3 million of liquefied petroleum gas (LPG) based cookers to electric induction cookers, in order to enhance the security of energy supply and reduce emissions of greenhouse gases and other pollutants [12, 13] A cookware manufacturing project for induction cookers is necessary to accomplish these policies, it is expected to fabricate and use 3 million of induction cookware sets between 2014 and 2016 [12, 13]. To make the selection of materials for an induction cookware is necessary to keep the interplay between the requirements of design, materials and processing. This research focuses on selecting an alternative material which best fits the technological requirements to make high efficiency induction cookware and has a good price for the consumer than the conventional stainless steel 430 to improve the overall efficiency of the induction cooker. This paper solves the problem of selecting the material for the base using recent mathematical tools and techniques for accurate ranking of the alternative materials for the base of an induction cookware using OCRA method. The criteria weighting was performed by compromised weighting method composed of AHP and Entropy methods. For these methods, a list of all the possible choices from the best to the worst suitable materials is obtained, taking into account different material selection criteria. The rankings of the candidate materials derived using these four methods prove the universal http://www.ijettjournal.org Page 394 International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 applicability of these methods as efficient tools for material selection decision-making. II. MATERIALS AND METHODS Definition of the decision making problem. The induction heating is based on the static magnetic field principle. Induction cooking heats a cooking vessel by magnetic induction, instead of by thermal conduction from a flame, or an electrical heating element. In an induction cooker, a coil of copper wire is placed under the cooking pot and an alternating electric current is passed through it (Figure 1). The resulting oscillating magnetic field induces a magnetic flux which repeatedly magnetizes the pot, treating it like a loss magnetic core of a transformer. This produces large eddy currents in the cookware, which because of the resistance of the pot, heats it by the Joule effect. They should have some specific properties in order to maintain their function during heating. A cooking vessel must be made of, or contain, a ferromagnetic metal such as cast iron or some stainless steels. However, copper, non-magnetic stainless steels, and aluminum vessels can be placed on a ferromagnetic interface disk which improve the thermal diffusivity of a conventional hotplate. In order to meet all these requirements, the most important material property is considered to be cost ($/Kg), the low values of which are desired in order to provide a competitive advantage among manufacturers. The second property required is high values of relative permeability (µ) due to magnetize the base of the pot. A high Thermal diffusivity (α), which indicates how fast heat is transferred through and out of the material, is important. Yield strength (Y) for the workability cookware is desired in order to decrease the energy required to build the cookware and be a good cookware. Electric conductivity (σ) is important for the eddy current generated in the base of the pot. Density (ρ) is important to reduce the weight of the base of the pot. Thermal conductivity (λ) to transfer heat from one part of the pan to another very quickly and efficiently. Finally Specific Heat (Cp) is important to the thermal energy transfer. Among these eight criteria, the cost, yield strength, electric conductivity and density are a non-beneficial properties. Eight alternatives for the base of an induction cookware were taken into consideration: Permalloy 80, No oriented Electrical Steel ASTM A677, Mumetal, AISI 430 stainless steel, AISI 410 stainless steel, cast iron, Co and Ni. The properties required for the base of an induction cookware alternatives with their quantitative data are given in Table I and their average values were used. Figure 1. Working principle of induction effect over magnetic pot bases Table 1. Material properties for the base of an induction cookware [9-15] (1) Permalloy 80 (80 % Ni, 4% Mo, 16% Fe) 37.50 (2) ASTM A677 Steel M-47 No oriented Electrical Steel (3) Mumetal (77% Ni. 4% Mo. 14% Fe. 5% Cu) 0.975 11550 18.20 300 2.70 7.75 65.00 0.46 38.00 127500 7.65 715 1.695 8.74 33.50 0.495 (4) AISI 430 1.50 850 6.95 513.5 1.60 7.80 24.90 0.46 (5) AISI 410 2.00 850 6.90 1180 1.70 7.80 24.70 0.46 (6) Cast Iron 0.125 425 7.40 385 9.00 7.18 26.60 0.505 (7) Co 30.00 155 21.85 225 1.60 8.80 84.60 0.44 (8) Ni 18.00 670 19.85 52 1.125 8.89 79.00 0.455 Thermal diffusivity [·106 m2 s-1] (α) 7.90 Yield strength [MPa] (Y) 321 Electric conductivity [·107 S m-1] (σ) 1.71 Specific Heat [kJ kg-1 K] ( ) 0.50 Relative permeability ( ) 190000 Material cost ($ Kg-1) Material Density [g cm-3] (ρ) 8.24 Thermal conductivity [W mK-1] (λ) 32.50 III. MULTI-CRITERIA DECISION MAKING METHODS ISSN: 2231-5381 http://www.ijettjournal.org Page 395 International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 IV. I. CRITERIA WEIGHTING. The criteria weights are calculated using a compromised weighting method where the AHP and Entropy methods were combined in order to take into account the subjective and objective weights of the criteria and to obtain more reasonable weight coefficients. The synthesis weight for the jth criteria is: (1) The consistency of the results is resumed by the pairwise comparison of alternatives. Matrix can be ranked as 1 and = n. 3) Consistency assessment In order to analyze the consistency of the results it is necessary to distinguish the importance of alternatives among them. In equations (4) and (5) is shown the consistency indexes required to validate the results. (4) where αj is the weight of jth criteria obtained via AHP method and βj is the weight of jth criteria obtained through Entropy method. III. I. I. ANALYTIC HIERARCHY PROCESS (AHP) This method set weights of an alternative over others. The mathematical model was developed by [16]. The AHP approach depends on [16]: 1) Hierarchy rank, 2) Comparison among selection criteria, 3) Assessing consistency in results. 1) Hierarchy rank. Every alternative is assigned a value in order to identify its importance in an application. The ranking is composed by three levels: a). general objective. b). criteria for every alternative. c). alternatives to regard [16]. 2) Comparison among alternatives. The weight of criteria respect to other is set in this section. To quantify its coefficient it is required the experience and knowledge of the assessing team or technician. [16], classified the importance parameters show in Table II. The values 2, 4, 6 and 8 are applied to differentiate slightly differing judgements. The comparison among n criteria is resume in matrix A ( ), the global arrange is expressed in equation (2). (5) Where: : Number of selection criteria. : Random index. : Consistency index. : Consistency relationship. Largest eigenvalue. If should be greater than 0.1, otherwise, the importance coefficient (1-9) has to be set again and recalculated (8). III. I. II. ENTROPY METHOD. Entropy measures the uncertainty in the information formulated using probability theory. The description of the method is explained by [17]. Equation (6) shows the decision matrix A of multicriteria problem with alternatives and criteria: ; ; (6) Where =1 (2) Afterwards, from matrix it is determined the relative priority among properties. The eigenvector is the weight importance and it corresponds with the largest eigenvector ( ): (3) ISSN: 2231-5381 is the performance value of the alternative to the criteria. The normalized decision matrix is calculated (7), in order to determine the weights by the Entropy method. (7) The Entropy value obtained as: http://www.ijettjournal.org of criteria can be Page 396 International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 (12) (8) Where is a constant that guarantees and m is the number of alternatives. The degree of divergence ( ) of the average information contained by each criterion can be obtained from Eq. (9): (9) Thus, the weight of Entropy of defined as: (13) III. II. OCRA METHOD. OCRA uses an intuitive method for incorporating the decision maker’s preferences about the relative importance of the criteria [18]. In OCRA method, in the first step, the preference ratings with respect to non- beneficial or input criteria are determined; in the second step, the preference ratings of the output criteria are determined and in the last step, the overall preference ratings of the available alternatives are evaluated where both the cardinal and ordinal data are used. The general OCRA procedure is described as below [18]: Step 1: Compute the preference ratings with respect to the non- beneficial criteria. The aggregate performance of alternative with respect to all the input criteria is calculated using the following equation: j=1.2.….n) Where indicates the number of beneficial attributes or output criteria and is calibration constant or weight importance of output criteria. The higher an alternative’s score for an output criterion, the higher is the preference for that alternative. It can be mentioned that Step 4: Calculate the linear preference rating for the output criteria using the following equation: (14) Step 5: Compute the overall preference ratings. The overall preference rating for each alternative is calculated by scaling the so that the least preferable alternative receives a rating of zero. The overall preference rating ( ) is calculated as follows: (i=1.2.….m. (15) (11) The alternatives are ranked according to the values of the overall preference rating. The alternative with the highest overall performance rating receives the first rank. Where is the measure of the relative performance of alternative and is the performance score of ith alternative with respect to input criterion. If alternative is preferred to alternative with respect to criterion, then indicates the difference in performance scores for criterion , between alternative and the alternative whose score for criterion is the highest among all the alternatives considered. Step 2: Calculate the linear preference rating for the input criteria. ISSN: 2231-5381 to the least preferable alternative. represents the aggregate preference rating for alternative with respect to the input criteria. Step 3: Compute the preference ratings with respect to the beneficial criteria. The aggregate performance for alternative on all the beneficial or output criteria is measured using the following expression: criteria can be (10) . Then term This linear scaling is done to assign a zero rating V. RESULTS AND DISCUSSION The results for weights of each criteria were computed by the AHP method and Entropy method. V. I. CRITERIA WEIGHTING The weight of each alternative was assigned according to the AHP method. The comparison among properties of every alternative are in Table 1 (4), (5). The properties identification appears under the name of each property as ($ kg-1). (µ). (α). (Y). (σ). (ρ). (λ). and ( ). In Table 2 is can be showed the scale of relative importance used in the AHP http://www.ijettjournal.org Page 397 International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 method. In Table 3, the decision matrix generated is shown which take into account the importance of each criteria. The most important criteria to generate the matrix was considered ( ); slightly more important was taken (µ); strongly more important was considered (α) and (Y); demonstrably more important were taken (σ) and (ρ); extreme more important were considered (λ), and ( ). The coefficients were assigned based on the heating principle on induction cookers. The results are consistent due to the value of the consistency index (CI = 0.0489) and the consistency ratio (CR = 0.0347) which are lower than the limit 0.1. At the final step, the compromised weights of the criteria ( ) were calculated using the Eq. (1). In Table 4, the weight coefficient of every criterion was determined based in results of AHP and Entropy methods. On one hand, the most representative values are relative permeability 46.10% and cost 28.40%. On the other hand, less than 30% of the overall weight is distributed in (α), (Y), (σ), (ρ), (λ), ( ). Table 2. Scale of relative importance Definition Equal importance Moderate importance Strong importance Very strong importance Extreme importance Intermediate importance Intensity of importance 1 3 5 7 9 2, 4, 6, 8 Table 3. Comparison among criteria for balanced scales AHP method ($/Kg) ( ) (α) (Y) (σ) (ρ) (λ) ( ) 1.00 3.00 5.00 5.00 7.00 7.00 9.00 9.00 0.33 1.00 3.00 3.00 5.00 5.00 7.00 7.00 0.20 0.33 1.00 1.00 3.00 3.00 5.00 5.00 0.20 0.33 1.00 1.00 3.00 3.00 5.00 5.00 0.14 0.20 0.33 0.33 1.00 1.00 3.00 3.00 0.14 0.20 0.33 0.33 1.00 1.00 3.00 3.00 0.11 0.14 0.20 0.20 0.33 0.33 1.00 1.00 0.11 0.14 0.20 0.20 0.33 0.33 1.00 1.00 Table 4. Criteria weighting by the AHP ( ), balanced scales ($/Kg) (µ) (α) (Y) (σ) (ρ) 0.401 0.22 0.11 0.11 0.05 0.05 0.02 0.02 0.096 0.28 0.10 0.05 0.02 0.17 0.10 0.17 0.285 0.46 0.09 0.04 0.01 0.07 0.01 0.03 ISSN: 2231-5381 (λ) entropy ( ) and compromised weighting ( ) methods V. II. OCRA METHOD. The aggregate performance of the alternatives with respect to all the input criteria is calculated with equation (11) from data from Table I. Applying equation (13), the aggregate achievement of the alternatives on all the beneficial or output criteria are then determined and subsequently, the linear preference ratings for the output criteria are calculated. Finally, the overall preference rating for each alternative material is determined using equation (15). The detailed computations of this method are illustrated in Table 5. In this method, the ranking of material alternatives is obtained as 8-4-72-3-1-6-5, which suggests that Ni attains the top rank. AISI 430 is the second best choice and AISI 410 has the last rank and Cast iron is the second last rank. Table 5. Computation details for OCRA method Material 1 2 3 4 5 6 7 8 2.054 615.645 186.508 646.296 644.660 650.724 583.586 609.479 0.000 613.591 184.454 644.242 642.606 648.669 581.532 607.425 0.956 0.056 0.712 0.016 0.026 0.010 0.155 0.094 0.947 0.047 0.702 0.006 0.016 0.000 0.145 0.085 0.000 612.691 184.209 643.301 641.676 647.722 580.730 606.562 VI. DISCUSSION In this research it has been observed that the MCDM are an important tool to recognize and identify the best alternative in a bunch of several of them. These methods can adapt to different sort of environments and conditions that would affect the final result and that is why these approaches are applied in different areas of science, engineering and management [19, 20] In this case, we take advantage of MCDM methods in order know the best alternative for the materials of the base in an induction cookware. Ni attains the top rank. AISI 430 is the second best choice and AISI 410 has the last rank and Cast iron is the second last rank. This results are in agreement with the results exposed by [21] which developed a Magnetic material selection using multiple attribute decision making approach. Where, it has been applied magnetics properties for the material selection as the magnetic permeability. (Cp) VII. CONCLUSIONS In this paper the material selection problem for the base of an induction cookware has been solved utilizing a decision model. The weighting of the http://www.ijettjournal.org Page 398 Rank 8 4 7 2 3 1 6 5 International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 8- April 2016 material properties was performed using the compromised weighting method composes of the AHP and Entropy methods. Ranking scores which were used to rank the alternative materials were obtained as results of the methods. In this case, we take advantage of MCDM in order to contribute to the Ecuadorian government in the new model of energetic management (matrix). According to the results. Ni would be the best material for the base of an induction pot. This material is adequate for its high permeability in order to induce Eddy currents and generate heat. The trend in the results has changed only in OCRA method due to the wide range of variability in the magnitude of every criterion. It was validated that the MCDM approach is a viable tool in solving the complex material selection decision problems. The model which was developed for material selection of the base of the cookware can be applied on other mechanical components for material selection problems. ACKNOWLEDGEMENTS The authors of this research acknowledge to the Secretaría Nacional de Planificación y Desarrollo (SENPLADES) for financing the execution of the present research. 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