[1] A manufacturer of industrial pump housings currently machines each housing from a solid block of aluminum, cutting away and discarding roughly half the metal as shavings in the process. [2] An engineer has proposed replacing this method with a casting process, in which molten aluminum is poured into a reusable mold and allowed to solidify into the approximate shape of the finished housing. [3] Because casting wastes almost no metal, and because the price of the aluminum stock is the largest single component of each housing's production cost, the engineer expects the change to lower material expenditures considerably. [4] On this basis the engineer concludes that adopting the casting process would substantially reduce the total cost of producing each housing.
Which of the following, if true, most seriously weakens the engineer's argument?
