Metal Foams: A Design Guide

$/Unit
Melting
Schematic of the liquid-state foaming process.
PM Batch process
Holding Foaming Delivery
PM continuous
Liquid state
1 100 200 300 400 500
Production volume (Thousands of units/Year)
Figure 16.3 Schematic of the liquid-state foaming process
Cost estimation and viability 205
ž Melting of the pre-mixed alloy
ž Holding, providing a reservoir
ž Foaming, using compressed gas and a bank of rotating blades
ž Delivery, via a moving belt
The output of one step forms the input to the next, so the steps must match,
dictating the size of the equipment or the number of parallel lines in each
step. The capital and tooling costs, power, space and labor requirements for
each step of the process are cataloged. Data are available characterizing the
dependence of material density and of production rate on the gas flow rate
and the stirring rate in the foaming step. These empirical relationships and
relationships between equipment and production rate allow the influence of
scale-up to be built into the model.
The outputs of the model (Figure 16.4) show the way in which the cost of
the material depends of production volume and identifies cost drivers. Significantly,
the model indicates the production volume which would be necessary
to reach the plateau level of cost in which, in the best case shown here, the
cost of the foam falls to roughly 2.5 times that of the constituent materials.
Models of this sort (Maine and Ashby, 1999), applied to metal foam production,
suggest that, with large-volume production, the cost of aluminum foams
made by the melt foaming method (Section 2.2) could cost as little $3/lb;
those made by the powder route, about $6/lb.