A large aerospace manufacturer purchased an aircraft component from two suppliers. These components frequently exhibited excessive variability on a key dimension that made it impossible to assemble...

A large aerospace manufacturer purchased an aircraft component from two suppliers. These components frequently exhibited excessive variability on a key dimension that made it impossible to assemble them into the final product. This problem always resulted in expensive rework costs and occasionally caused delays in finishing the assembly of an airplane. The materials receiving group performed 100% inspection of these parts in an effort to improve the situation. They maintained and R charts on the dimension of interest for both suppliers. They found that the fraction of nonconforming units was about the same for both suppliers, but for very different reasons. Supplier A could produce parts with mean dimension equal to the required value, but the process was out of statistical control. Supplier B could maintain good statistical control and, in general, produced a part that exhibited considerably less variability than parts from supplier A, but its process was centered so far off the nominal required dimension that many parts were out of specification. This situation convinced the procurement organization to work with both suppliers, persuading supplier A to implement SPC and to begin working at continuous improvement, and assisting supplier B to find out why his process was consistently centered incorrectly. Supplier B’s problem was ultimately tracked to some incorrect code in an NC (numerical controlled) machine, and the use of SPC at supplier A resulted in considerable reduction in variability over a six-month period. As a result of these actions, the problem with these parts was essentially eliminated.