Cost Estimation and the Viability of Metal Foams** By Elicia Maine and Michael F. Ashby* 1. Introduction Are metal foams viable? By viable we mean that the bal- ance between performance and cost is favorable. The answer has three ingredients: a technical model of the performance of the material in a given application, a cost model giving an es- timate of material and process costs, and a value model which balances performance against cost. Viability is assessed by constructing a value function which includes measures of both performance and cost. It allows ranking of materials by both economic and technical criteria. At present all metal foams are produced in small quanti- ties using time and labor-intensive methods, and all, relative to the solid metals from which they derive, are expensive. But it is not the present-day cost which is relevant; it is the cost which would be obtained were the process to be scaled and automated to meet the increased demand of one or a portfolio of new applications. The role of a cost model is to assess this, to identify cost drivers, to examine the ultimate limits to cost reduction, and to guide process development. Here we describe progress in constructing and using cost models for two of the processes by which metal foams are made, and describe our method for assessing the viability of a new material. 2. Technical Cost Modelling Arriving at a point cost estimate for a component pro- duced by a novel process or material is important but can be accomplished by a simple model or calculation. Greater pre- dictive power can be obtained by introducing elements of technical cost modeling (Field and de Neufville, 1988; Clark et al. 1997) which exploit the understanding of the way in which the control-variables of the process influence produc- tion-rate and product properties. In addition it uses informa- tion on the way the capital cost of equipment and tooling scale with output volume. These and other dependencies can be captured in theoretical and empirical formulae or look-up tables which are built into the cost model, giving greater res- olution. In addition, informed sensitivity-analysis and scenar- io-building are enabled through the capturing of the linkages between the technical limitations of the process, intermediate variables such as cycle time, and cost line items. A schematic of the structure of a technical cost model (TCM) is shown in Figure 1. Each of the empty boxes in this figure represent the calculation of intermediate variables that capture the technical limitations of the process under varying RESEARCH NEWS ADVANCED ENGINEERING MATERIALS 2000, 2, No. 4 205 ± [*] Prof. M. F. Ashby, E. Maine Engineering Department Trumpington Street, Cambridge, CB2 1PZ (UK) E-mail: mfa2@eng.cam.ac.uk [**] We wish to acknowledge the support of the Körber Foundation, the Cambridge Canadian Trust and of the UK EPSRC through the Engineering Design Centre at Cambridge, and of Granta Design, Cambridge, who developed the software illustrated in this article. At present all metal foams are produced in small quantities using time and labor-intensive methods, and all, relative to the solid metals from which they derive, are expensive. Thus, one may ask if metal foams are viable. By viable a favorable balance between performance and cost is meant. Viability is assessed by constructing a value function which in- cludes measures of both performance and cost. It allows ranking of ma- terials by both economic and technical criteria. The authors describe progress in constructing and using cost models for two of the processes by which metal foams are made, and describe their method for assessing the viability of a new material. 1438-1656/00/0404-0205 $ 17.50+.50/0