Figure CS-43 is a water pump impeller used by a major automotive parts manufacturer. The outer diameter of the component is 2.75 inches and the height is specified at 0.75 ± 0.005 inches. The I.D. of the center hole is 0.625 inches. The dimensions and positioning of the six blades is important from the viewpoint of vibration and balance. Smooth finish is desirable for good fluid flow. The operating temperature range has been estimated as -60°F to +300°F, and the mechanical property requirements have been given as 30,000 psi minimum tensile strength and a minimum eleongation of only 0.5%. Since there is no metal-to-metal contact, high wear resistance is not necessary. The contact fluid should be a water/antifreeze mixture with corrosion-resistant additives. Production volume should be high, so a low total cost (material plus manufacturing) is a prime objective.
1. Based on the size and shape of the product, describe at least three reasonable ways in which the component could be produced. For each method, briefly discuss its relative pros and cons.
2. What types of engineering materials might be able to meet the desired requirements? What would be the pros and cons of each general family?
3. For each of the shape generation methods in part 1, select an appropriate material from the alternatives discussed in part 2. (Note: Casting alloys should be matched with casting processes, high machinability alloys would be favored for cutting applications, etc.)
4. Which of the above alternatives do you feel would be the "best" solution to the problem? Did you consider making the part in a manufacturing cell? For this system, outline the specific steps that would be necessary to produce the part from reasonable starting material.
5. For your proposed solution in part 4, would any additional heat treatment or surface treatment be required? If so, what would you recommend?
6. Could this be a possible application for molded nylon, other polymer, or composite material? If so, what would be the candidate material? What would be the major differences in properties, performance, and manufacturing process?

FIGURE CS-43