Metal Foams: A Design Guide

202 Metal Foams: A Design Guide
flux per unit area of structure. In design for the environment, the metric is a
measure of the environmental load associated with the manufacture, use and
disposal of the material. Each performance metric defines an objective: an
attribute of the structure that it is desired to maximize or minimize. Models
are developed for the performance metrics following the method of Chapter 5;
the resulting performance equations contain groups of material properties or
‘material indices’. The material that maximizes the chosen performance metric
has the highest technical merit. But for this to be a viable choice, the performance
must be balanced against the cost.
16.3 Cost modeling
The manufacture of a foam (or of a component made from one) consumes
resources (Table 16.1). The final cost is the sum of these resources. This
resource-based approach to cost analysis is helpful in selecting materials and
processes even when they differ greatly, since all, no matter how different,
consume the resources listed in the table. Thus the cost of producing one
kg of foam entails the cost Cm ($/kg) and mass, m, of the materials and
feedstocks from which it is made, and it involves the cost of dedicated tooling,
Ct ($), which must be amortized by the total production volume, n (kg). In
addition, it requires time, chargeable at an overhead rate CL P (with units of $/h
or equivalent), power P (kW) at an energy cost Ce ($/kW.h), space of area
Table 16.1 The resources consumed in making a
material
Resource Symbol Unit
Materials: inc. consumables Cm $/kg
Capital: cost of equipment Cc $/unit
cost of tooling Ct $/unit
Time: overhead rate CL P $/hr
Energy: power P kW
cost of energy Ce $/kW.h
Space: area A m2 cost of space PCS $/m2 .h
Information: R&D Ci
royalty payments