ABSTRACT
More steel is produced than any other metal, with aluminum second in volume and in use in fabricating products. The weight of aluminum is approximately one third the weight of steel. Steel is approximately 0.3 lb/in. 3 , aluminum is 0.1 lb/in. 3 , and magnesium is 0.06 lb/in. 3 . Figure 3.1 is a nomogram for calculating weights of steel and aluminum stock. In this chapter we concentrate our discussions on parts fabricated from these two materials. Steel is made by heating iron ore and casting into pigs or ingots, or continuous casting into slabs. Aluminum is made from bauxite and converted into molten aluminum pigs or ingots using a complex chemical and electrolytic process. At this point, both metals are in their least expensive form, but suitable only for making rather poor castings. Gray cast iron is superior to raw aluminum for casting at this time. From this point on, the processes for steel and aluminum are quite similar. Gray cast iron is the lowest-cost ferrous material, since little work has been done to refi ne either its form or its material content and properties. As you continue through the process of removing impurities, adding alloying ingredients, hot rolling and cold rolling, it appears that carefully controlled sheet metal has the greatest labor content, and therefore may have the highest cost per pound. The material form is one factor that enters into the cost of a fi nished metal part, but it can seldom offset the fabrication expense of the total part cost.
