SUPPLIER SELECTION CRITERIA IN SUSTAINABILITY PROCESS

The process of selecting the right supplier is very complicated because profitability and customer satisfaction directly affect the process. The supplier selection process has become a difficult task for the business since controversial criteria will be used while selecting the right supplier. According to Umarusman (2019), all the criteria for sustainable economic selection directly or indirectly follow the criteria defined by Dickson as a very crucial average value. This means conventional supplier selection usually applies to economic criteria. Technological advancements, diminishing natural resources with a growing population, environmental pollution harm to the ecosystem, and socio-cultural changes have taken the criteria that relate to the definition of sustainability in the selection and evaluation of suppliers to a more substantial level in the last 20 years. The first study on conventional Supplier Selection Criteria (SSC) was carried out by Dickson (1966). Afterward, from different perspectives, Dempsey (1978), Roa and Kiser (1980), Bache etal. (1987), Weber cl al. (1991), Cheraghi etal. (2004), andThiruchelvam and Tookey (2011) expanded SSC. Oz^elikand Avci Oztiirk (2014), Groveretal. (2016), Ghoushchi etal. (2018), and Li etal. (2019) classified within the frame of Triple Bottom Line (TBL) for sustainable SSC. Humphreys et al. (2003) proposed a frame for environmental criteria to be included in the selection process and defined the criteria and sub-criteria. Increased environmental awareness led to the emergence of the Green SC paradigm, and thus green criteria were included in SSP (Genovese etal., 2010). According to Umarusman and Haciveliogullari (2020), Green SSC are compatible with TBL criteria when SC processes are examined, so S-SCM includes Green SCM. There are scientific studies on Green SSC that take part in literature. For instance, Chiou etal. (2008) listed the global criteria and sub-criteria weights for green supplier selection. Govindan et al. (2015) classified the Green SSC used within the framework of Multiple Criteria Decision Making (MCDM) as a result of its literature research. Chen et al. (2016) provides the criteria that is most widely used in the literature for evaluating environmental and economic performance of green supplier selection. Haeri and Rezaei (2019) determined criteria, within the frame of TBL, frequently used in literature.

It is expected to use different criteria on a sectoral basis while evaluating and selecting suppliers in SC processes. On the other hand, the favorableness level will increase with supplier evaluation and managing accurately the process of determining the most appropriate method in supplier selection.

Literature Survey

Many different methods are used in solving Conventional/Sustainable/Green SSP. Such problems were classified by Ghodsypour and O’Brien (1998), De Boer et al. (2001), Humphreys et al. (2003), Ding et al. (2005), Genovese et al. (2010), Ware et al. (2012), Chai et al. (2013), Govindan et al. (2015), Ayhan and Kilic (2015), Trisna et al. (2016), Mukherjee (2017), Ozyoruk (2018), Banasik (2018), Umarusman (2019) and Chai and Ngai (2019) from different viewpoints. In this study, a literature review that includes multiple objective decision making (MODM) and Fuzzy MODM methods was done considering scientific studies conducted between 2010 and 2020. In the literature review, besides methods used in related studies. Table 7.1 shows that objective/goal functions are created in which criteria.

According to the literature review, when an evaluation was made in terms of supplier selection type, it was determined that in the studies conducted between 2010

The Classifications in Supply Chain Processes

TABLE 7.1

TABLE 7.1 (Continued)

The Classifications in Supply Chain Processes

TABLE 7.1 (Continued)

The Classifications in Supply Chain Processes

and 2020, Conventional SSP was used as 70%, Sustainable SSP was used as 18%, and Green SSP was used as 12%. These rates are shown in Figure 7.1.

New classifications can be made regarding the criteria and methods used in supplier selection processes using the information provided in Table 7.1. A new' assessment has not been made because of the studies above, in which both methods and criteria are reviewed in the literature. However, the results can be drawm as follows

FIGURE 7.1 Type of supplier selection problems.

regarding the criteria and methods: Cost, Quality, Delivery Time criteria are much preferred in the establishment of Objective/Goal functions when Table 7.1 is analyzed.

Formulation of Multiple Objective Supplier Selection Problem

Although the mathematical formulation of SSPs accepted as a special extension of Multiple Objective Linear Programming (MOLP) was realized by Gaballa (1974), Moore and Fearon (1973) discussed linear programming could be used in supplier selection for the first time. In literature, Weber and Ellram (1993), Ghodsypour and O'Brien (1998). Amid el al. (2011), and Umarusman (2019) organized the mathematical model of multiple objective SSP according to different objective functions. The arrangement made for three objective functions in the maximization type of multi objective supplier selection problem is given below in this study. The total budget has been used in restricting the amount to be purchased in this model.

Subject to (1)

Zi, Z₂. Z₂: Maximization-typed objective function for the criteria,

В: Total budget,

}]: Unit cost of the product to be purchased from i'th supplier,

X;: The amount to be purchased from i-th supplier,

D: Demand over period,

C,: Capacity of ith supplier, n: Number of the suppliers.

Equation (1) is accepted as MOLP problem, when investigating the solution, defining non-dominate solutions set is the first step. Moreover, the number of solutions in terms of non-dominate solutions set in (1) is quite a few. The basic process to evaluate non-dominate solution points is how the proximity to ideal solutions will be determined (Cohon, 1978, p. 69). Therefore, ideal solutions are designated at first. In (1), for each objective function, Positive Ideal Solution (PIS) set is Г = {Zj,Z2,...Z*;W,^sW₂*,...,W„*], and Negative Ideal Solution (NIS) is

Г ={zr,Z2,...Z_n;W, ,W₂",...,W_n"} (Zeleny, 1973). Afterward, using the methods in MODM classification, the solution of (1) is made. In the literature research given above, methods that can be used in the solution of (1), and integrated methods have been given. According to this literature research, it has been detected that the solution of Conventional/Sustainable/Green SSP is not made using the Fuzzy Global Criterion Method (Fuzzy GCM).