توانمندی تولید کنندگان و نمودار آنالیز قیمت

To remain competitive in customer-oriented economics, the major parties in the supply chain should be integrated and managed effectively to respond to customer needs. Thus, the efficiency of the entire supply chain is a main concern, and is determined by the members of that supply chain. Partner selection thus becomes one of the key steps in supply chain construction. Given buyer–supplier information asymmetry, obtaining complete information from suppliers is difficult, since some supplier attributes cannot be definitely and quantitatively measured. This study establishes a suppliers capability and price analysis chart (SCPAC) focused on the case where the specification limits are symmetric about the target for evaluating supplier performance which applies the process incapability index Cpp introduced by Greenwich and Jahr-Schaffrath (International Journal of Quality & Reliability Management 12 (1995) 58) to measure supplier quality performance and the price index Ip is proposed here to display the difference between budget and component price. Practitioners can instantly and visually obtain information based on the locations of suppliers and price indices on SCPAC. SCPAC also provides clear directions for quality improvement, such as process accuracy and precision. SCPAC thus is an effective and efficient method for evaluating suppliers, which can simplify supplier evaluation, facilitate their effective visual selection, and provide insights into the process situation of suppliers who can become technological innovation partners.

To remain competitive in customer-oriented economics, the major parties in the supply chain, including suppliers, manufacturers, contract manufacturers, distributors and retailers, must synchronously participate in designing, manufacturing, distributing, marketing and even standing. All of these parties thus should be integrated and managed effectively to respond to customer needs and contribute the profit to the whole supply chain. Members of the supply chain thus are the critical determinant of supply chain behavior. Partner selection thus becomes one of the key steps in constructing the supply chain. Thomas and Janet (1996) investigated the importance of supplier selection, and noted that: ‘it commits resources while simultaneously impacting such activities as inventory management, production planning and control, cash flow requirements, and product quality.’ Moreover, Burton (1988) and Carr and Pearson (1999) found that purchased materials and services represent up to 80% of the total product costs of high-technology firms. Additionally, Weber et al. (1991) found that automotive manufacturers spend over 50% of their revenues on components and parts purchased from outside vendors. Clearly, careful supplier evaluation and selection is essential. Good suppliers allow enterprises to achieve good manufacturing performance and make the greatest benefits for practitioners. Supplier selection is complicated by the need to consider various criteria. Dickson (1966) examined the importance of supplier evaluation criteria and presented 23 supplier attributes that managers consider in such an evaluation, including quality, delivery, price, performance history and others, following a survey of industrial purchasing managers. Additionally, Choi and Hartley (1996) presented 26 supplier selection attributes from a survey of US automotive companies. Nakato and Michael (1998) presented 14 supplier selection attributes from a survey of Japan automotive and electronic companies. Moreover, Lamberson et al. (1976) and Monzcka and Trecha (1988) proposed linear weighting techniques for assessing supplier performance. These methods frequently considered many supplier performance attributes simultaneously, and weighted those attributes based on the opinions of purchasing managers or staff. The experience and knowledge of purchasing staff thus significantly compromises the reliability of supplier evaluation using the above methods. Such methods thus are not objective and may lead to arbitrary decision-making, due to human psychological bias. Additionally, simultaneously considering all supplier attributes is complex and difficult and requires spending considerable time and money to obtain relevant correct information, especially in buyer–supplier informational asymmetry, as well as some attributes cannot be quantitatively and definitely measured. This study applies the process incapability index Cpp introduced by Greenwich and Jahr–Schaffrath (1995) to develop a graphic evaluation model for measuring supplier quality performance, and moreover provides the price index Ip to indicate the difference between budget and price. Furthermore, this study combines process incapability index Cpp and price index Ip to create a suppliers capability and price analysis chart (SCPAC). This chart proposed here focuses on the quality characteristic with nominal-the-best specifications, that is, the specifications limits are symmetric about the target. Practically, this is the common situation. Practitioners can consider the two factors of quality and price simultaneously to assess suppliers, and moreover can instantly and visually obtain information through the locations of suppliers and price indices on SCPAC. Good quality is essential to corporations in maintaining competitiveness and customer loyalty. In supply chain management, improving product quality is no longer merely the responsibility of the manufacturer, but is also the responsibility of the suppliers who provide the parts and components. Supplier manufacturing capability determines finished product quality and customer satisfaction. Supplier manufacturing capabilities thus are the key consideration in supplier selection. Dickson (1966) identified price, quality and delivery performance as the three most important criteria in supplier evaluation. Moreover, Weber et al. (1991) reviewed 74 articles from 1967 to 1990 based on the 23 vendor selection criteria presented by Dickson (1966) and concluded that quality was the most important factor, followed by delivery performance and price on supplier evaluation, with quality being of “extreme importance” and delivery being of “considerable importance”. In the Just-In-Time (JIT) manufacturing system, quality and delivery are still the two most important criteria for supplier selection. Pearson and Ellram (1995) examined supplier selection and evaluation criteria in small and large electronics firms and concluded that quality was the most important criterion in supplier selection and evaluation for both small and large electronic firms. Furthermore, Thomas and Janet (1996) surveyed purchasing managers of US automotive companies and concluded that quality (conformance to specifications) and delivery (meeting delivery deadlines) remained the most important criteria across all levels, even 30 years after the study of Dickson (1966) on supplier selection. Olhager and Selldin (2004) investigated supply chain management strategies and practices in a sample of 128 Swedish manufacturing firms and concluded that many aspects are important when companies choose supply chain partners, but quality is the single most important criterion. From a survey conducted in 1998 on “Excellent suppliers”, the weights of elements involved in supplier assessment are 44% quality, 36% delivery on time, 24% overall costs, 19% services, 6% technology and less than 5% for the remainder, including innovation, problem solving, knowledgeable personnel, good communication and accurate paperwork (see Kevin, 1998). Chrysler, the car manufacturer, evaluates suppliers based on four factors: quality, cost management, delivery and technology. Moreover, Chrysler weights each of these factors, with quality being weighted as 40% and the remaining three factors as 20% each (see Lewis, 1995). Hill (2000) and Thomas and Janet (1996) indicated that quality had emerged as order qualifiers because suppliers with unacceptable quality performance are dropped during the screening phase. Total quality management (TQM) has had considerable success in terms of its implementation in companies. Forza and Filippini (1998) indicated that suppliers have a clear influence on several quality dimensions and proposed TQM should link with suppliers, which incorporates an orientation towards quality and guarantees stable inputs for the production process. Hence, quality is fundamental to corporate competitiveness. Price is another important factor that practitioners place a heavy emphasis on. Low cost is one competitive advantage that enterprises can use in a competitive market, because manufacturers would like suppliers to be able to provide components with process capability that satisfies the expected quality level and is also affordable. Restated, buyers want high-quality products at a cheap price. Consequently, price and quality are the two key considerations. In supplier selection, a high-quality and high-price supplier is undesirable because of cost considerations. Buyers prefer suppliers that offer products with adequate quality but at a lower cost. Hence, quality and price are two fundamental and necessary requirements for supplier selection. A reliable method is essential for practitioners to evaluate suppliers’ process capability and price restriction. Process capability indices have been widely adopted in the manufacturing industry, providing single number and unitless measures of process potential and performance, such as the indices Cp, Cpk, Cpm and Cpp. The process incapability index Cpp, developed by Greenwich and Jahr-Schaffrath (1995), is easy to apply, and provides more process information than other process indices. For example, this index provides information on process inaccuracy and process imprecision. This additional process information can help to clarify the process situations of suppliers and suggest clear directions for process improvement. Singhal (1991) provided a multi-process performance analysis chart (MPPAC), based on indices Cp and Cpk, for measuring the performance of a multi-process product with symmetric bilateral specifications. However, indices Cp and Cpk are not suitable because index Cp does not take process location into account and neither Cp or Cpk consider process centering (the ability to distinguish on-target and off-target processes). Consequently, index Cpp is preferred to indices Cp and Cpk. Chou (1994) proposed using the Cp, Cpu and Cpl indices to assess two suppliers’ processes. However, in reality, usually more than two suppliers are available to choose from. Accordingly, the SCPAC defined here based on index Cpp and price index Ip is used to assess suppliers more efficiently and reliably. Furthermore, the directions of quality improvement for all processes are visualized clearly on SCPAC based on supplier location, further enhancing the partnership between buyers and suppliers, because this way benefits both. The SCPAC thus is a powerful tool enabling practitioners to monitor supplier process capability and the difference between budget and price over long periods. Section 2 introduces the characteristics of incapability index Cpp and also defines the price index Ip. Subsequent sections then describe the SCPAC and discuss the application of SCPAC. Finally, a practical example is presented and conclusions are drawn.

Process capability indices provide single-number assessments of process potential and performance and have been widely applied in diverse manufacturing industries. This study applies the Cpp index to evaluate supplier process performance, and proposes using the price index Ip to measure the difference between the budget and the component price offered by the supplier. Moreover, the suppliers capability and price analysis chart (SCPAC) is established, based on the Cpp index and price index Ip, to provide practitioners with a powerful tool for evaluating suppliers. First, SCPAC allows practitioners simultaneously to consider the two key influences—quality and price. Second, SCPAC facilitates visual distinguishing of the process quality performance of each supplier, as well as adequate price level, and thus simplifies supplier evaluation. Finally, SCPAC also provides guidance for achieving quality improvement for all processes, and strengthening the partnership between buyers and suppliers because good quality performance benefits both sides. SCPAC thus is efficient, reliable and easy to use, and its use for supplier evaluation should be encouraged. Furthermore, the delivery performance is another important criterion for selecting suppliers especially for a company with the JIT manufacturing system. The possible application can be recommended for practitioners that the delivery performance can be incorporated into SCPAC. Suppose the delivery performance of suppliers can be defined and scored, then grade the scores, transform the scores into recognized symbols, and finally attach the symbols on SCPAC. Hence, SCPAC displays three key supplier evaluation criteria, process capability, price and delivery, clearly. This possible expansion of SCPAC could be recommended and applied in the feature.