Welding process selection for repairing nodular cast iron engine block by integrated fuzzy data envelopment analysis and TOPSIS approaches Seyed Mostafa Mirhedayatian a , Seyed Ebrahim Vahdat b , Mostafa Jafarian Jelodar a , Reza Farzipoor Saen c,⇑ a Young Researchers Club, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran b Department of Engineering, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran c Department of Industrial Management, Karaj Branch, Islamic Azad University, P.O. Box 31485-313, Karaj, Iran article info Article history: Received 15 April 2012 Accepted 4 July 2012 Available online 14 July 2012 Keywords: Designer Welding process selection Fuzzy data envelopment analysis Supplier TOPSIS abstract The selection of welding process is one of the most significant decision making problems and it requires a wide range of information in accordance with the type of product. Hence, the automation of knowledge through a knowledge-based system will greatly enhance the decision-making process. A combined fuzzy data envelopment analysis (DEA) and TOPSIS is proposed to investigate the relative welding process selection factors and it can compare and evaluate different welding processes. The proposed approach compares each decision making unit (DMU) with the worst and the ideal virtual DMU and it ranks them via the relative closeness index. The proposed approach is used for ranking eleven welding processes which are commonly used for repairing nodular cast iron engine block in four cases and it is shown that the approach is sensitive to changes in dataset. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Engine block crack repairing has become one of the today’s hot topics. It may be carried out under emergency conditions. Mount- ing a new engine block needs more time and expense compared with engine block crack repairing. Cast irons are used widely by designers and welding of nodular cast iron has been investigated. There are several welding processes for repairing cracks in cast ir- ons. The problem is to select the best welding process for repairing cracks. The welding process selection has been done by a few researchers via different approaches but none of them deal with selecting welding process for crack repairing of nodular cast iron engine block. Veilleux and Petro [1] have defined welding as a materials join- ing process in which localized coalescence is occurred throughout the faying surfaces of the materials. Coalescence is done either by heating the materials up to suitable temperatures or by importing pressure. In some welding processes, filler material is added during the welding. There are more than 50 different welding processes. These processes can be classified as either fusion or solid state (nonfusion) methods. Fusion welding processes, in which the materials are melted together at their faying surfaces, is the most commonly used processes and also is discussed in this paper. Since the biggest and heaviest part of the engine is engine block, Vahdat and Tavakkoli-Moghaddam [2] studied engine block. Engine block repairing may be performed in the field only under high crisis con- ditions and where a replacement engine block is not available. Vahdat [3] and Challen and Baranescu [4] have studied engine block material that is thin-wall and higher operating temperatures cause many engine blocks to crack, and often in areas that are hard to repair. Cracks between the seats, that expand deeply into ports or run all the way across the top of the engine block are commonly met in many engines. In the other hand, good rebuild-able engine blocks for old model engines are difficult and many engine rebuild- ers are now repairing engine blocks. Grubišic ´ et al. [5] and Carley [6] have studied engine block repairing that involves a certain amount of risk and that is why most of the crack repair activity in the past was limited to high cost heavy-duty diesel engine blocks that justified the time, effort and danger. For these reasons, engine block crack repairing has become one of today’s hottest subjects. Vahdat [3] has studied cast iron that is an extremely useful material for diesel engine block material because it is hard, wear- resistant and comparatively inexpensive. Also, it is available in var- ious shapes and compositions. While we usually think of cast iron as having low ductility, this is not true of all cast irons like nodular cast iron, sometimes called ductile iron or spherical graphite cast iron (SG iron). Almost every cast iron contains well over 2.0% equiv- alent carbon (CE); some contain as much as 4.0%. In addition, cast iron usually contains 1.2–2.5% Si, 0.5–0.8% Mn, small percentages of S and P and the rest is Fe. In cast iron, most of the carbon is usu- ally present in uncombined form, as graphite. The differences be- tween the general types of cast iron most widely used happen 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.07.010 ⇑ Corresponding author. Tel.: +98 263 4418144 6; fax: +98 263 4418156. E-mail addresses: mstf.mirhedayatian@yahoo.com (S.M. Mirhedayatian), e.vah dat@iauamol.ac.ir (S.E. Vahdat), m.jafarian@iauamol.ac.ir (M.J. Jelodar), farzipour @yahoo.com (R.F. Saen). Materials and Design 43 (2013) 272–282 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes