6.1. Setting the Scene

Components Inc. is a manufacturer of aluminum components for high-end audio equipment. Components are anodized to protect against corrosion and wear, and the anodized parts are dyed to produce a smooth, rich, black surface that helps to make the final product visually pleasing. Components Inc. has one major customer, and, given the premium price of the equipment it assembles and sells, buyers are very sensitive to its workmanship and aesthetics, not just its audio performance.

In the spring of 2008, Components Inc. begins to experience what becomes a significant problem with chronic discoloration of the components it is making. Lot yields, determined by an outgoing visual inspection, range from 0 to 40 percent, so there is substantial rework and scrap. The low yields mean that on-time delivery of components in sufficient quantity is very poor. In addition, the quality of even the shipped components is often considered marginal when assessed by Components Inc.'s customers, so some lots that are shipped are returned. Unless Components Inc. can successfully improve yield and optimize the quality of its components, it stands to lose millions of dollars, as well as the business of its major customer.

Anodizing is an electrolytic process, used to increase the thickness and density of the natural oxide layer on the surface of metal parts. The anodized surfaces are porous, and the pores may be filled with a dye or a corrosion sealer to improve corrosion resistance. In the case of Components Inc., the pores are filled with a dye to obtain the required black color. The anodizing process used by Components Inc. is referred to as a Type II anodize, where the anodizing is done in a sulfuric acid bath. The parts are suspended in the acid bath and a direct current is applied in such a way that the parts become the anodes of an electrolytic cell (hence the term anodize). Oxygen is generated on the surfaces of the aluminum parts, causing a buildup of aluminum oxide. The parameters used in the anodizing process not only have a significant impact on the coated thickness, but also affect the shape and size of the pores that form in the coating. This, in turn, affects the ability of the anodized surface to retain dye or other coatings.

For Components Inc., a defect occurs and yield is reduced when the surface of an anodized part has either a purple or a smutty black appearance. The purple color varies from a very light to a deep purple, while the smutty black appearance gives the impression that the finish is smudged and not blemish-free. An acceptable surface has a rich, black, clear, and blemish-free appearance.