A Computer-Based Economic Analysis for Manufacturing Process Selection

An important part of financial planning in product development is considering whether the capital expenditures meet volume and cost goals. A good business plan should provide investors with the implications of process selection on the company's bottom line. It is estimated that there are least 1000 manufacturing processes and sub-processes. Considering the number of process choices and quantity of cost data, an economic analysis for process selection may pose a challenge for decision makers. This paper provides an insight to Ashby’s cost modeling method for generating an estimate of unit product cost. The cost model provides a broad indicator for competing processes for shaping a product at the early stage of product development. This model takes into account the cost of resources associated with manufacturing a component. Using the Cambridge Engineering Selector software the impact of various cost factors on process selection is investigated. Introduction With advancement of technology in recent decades and increasing level of sophistication and variety in manufacturing processes, facility planners and engineers may face a nontrivial task of process selection. The implication of manufacturing process selection on a company’s management is it may indirectly influence widely varying aspects such as company policy, availability of facilities and trained personnel [1]. The selection of a process for shaping a component is not an isolated task. It requires considering several factors among which the type of material, shape and cost of component are the most significant ones. Figure 1 depicts the interaction among major factors involved in material and process selection. It is estimated that there are between 40,000 and 80,000 materials available today and at least 1000 different ways to process them [2]. Considering such variety of materials and processes, the economic analysis for selecting a process may require handling a large amount of data and performing calculations. The use of conventional data sources, e.g., handbooks, datasheets, is not sufficient to manage the growing volume of data for materials and manufacturing process selection purpose. While numerious experimental academic papers have been published in recent years [3][4], only a few commericial online and CD-ROM based material and process selectors have emerged. One of the most widely publicized CD­ ROM systems known as Cambridge Engineering Selector (CES), developed by Ashby [5] Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 Product D esign R equirem ents: Shape & Function -configuration -connections -com ponents P roduct P rocess C hoice of S ingle Process M ateria l C hoice of S ingle M ateria l B usiness/M anagem ent Im plications Cost: m ateria l/process, e tc. Environm eta l im pact Facility im pact M arket dem and Figure 1. Integrated process, material and product design and commercialized by Granta Design Limited. Originally conceived as an educational tool, CES's evolution into a user-friendly software system, combined with the quantity of technical data it offers, allows its application to any industrial situation [6]. It also provides graphical selection and ranking methods as well as an in-depth analysis tool for research and education. CES offers several capabilities including a) material property data for metals, polymers, ceramic and composites, b) material selection using multiple attributes, and c) a process selector module. The process selection module of CES is perhaps the only available commercial software for such purpose. The module offers a cost modeling function for economic analysis of various material shaping processes which is the focus of this paper. Manufacturing Process Selection In general, a manufacturing process selection identifies feasible processes by screening and eliminating those which do not satisfy certain constraints. Often such process selection is prerequisite to equipment selection which traditionally has been accomplished using the general knowledge and expertise of engineering staff. However, with growing number of processes and sub-processes, an elaborated and systematic selection method is needed to take into account the various factors such as material, product design and environmental constraints, while meeting capital and operating cost limits. Figure 2 shows a sequence of typical steps involved in a manufacturing process selection. The sequence incorporates the following attributes for search and screening of processes: Material Class: Includes the type of material to be used from metal, polymers, ceramics or composites categories. Physical constraint: Includes the mass of a product. Proceedings of The 2008 IAJC-IJME International Conference ISBN 978-1-60643-379-9 No Shape Constraints: Include a component's section thickness and its overall geometry, e.g. circular, non-circular, hollow, or solid. Process Characteristics: A decision must be made whether the process should be a primary process such as casting or forging or a secondary process such as machining. It is also necessary to determine whether the process should be a discrete or continuous one. Environmental Constraints: Environmental concerns regarding a manufacturing process may include gases, fumes, heat and noises generated by the process. The amount of energy required for processing a material may also be considered in the selection process. Economic Constraints: Include capital equipment cost, tooling cost, economic batch size and so forth. The economic constraints will be discussed in more detail in the next section. All Processes Material Classs? Physical Constraints? Shape Constraints? Final Selection (s) Process Characteristics? Environ. Constraints? Economic Constraints? 1