Tickel, Craig M.; Constable, Gordon K.; Cleary, Michael J. (1988, ASQC) Productivity-Quality Systems, Inc., Dayton, OH; Wright State University, Dayton, OH
The loss of market share and quality position by US firms due to increased world competition has generated a high level of interest in quality management and statistical process control in American companies. Led by the automotive industry, extensive efforts have and are being made to implement the quality management philosophy and statistical process control techniques into manufacturing operations. A number of large companies, such as Ford Motor Company, IBM, and Procter and Gamble have hastened the implementation efforts by mandating that their suppliers become involved.
The implementation of the quality management philosophy involves more than the use of mathematical techniques and the use of charts. It is more of a change in the way things are done - a change in management style. The definition of a quality product must become one of producing a uniform product to a "target" rather than the production of units "within" a specification range. Under this philosophy, product quality becomes the process of continuing improvement. A study conducted by Ford in 1984 of its suppliers found that only 50% of the processes were in control and capable of meeting product specifications.
One of the management principles inherent to the successful implementation of quality management, is that of increased communication between a manufacturer and a supplier regarding the ongoing performance of the process. Capability indices provide a method of communicating this information in a consistent, unitless format so that comparisons can be made among various processes. Capability values can be used to set priorities for areas of improvement and to provide a snapshot of current performance. The most common capability indices in use today are: C-, C-k, and Cr. Articles by Sullivan1 and Kane2 have done much to help clarify the differences between these indices.
This paper will first review the calculation of the capability indices, and discuss the interrelation among these indices. Secondly, we will consider how we might use any of the indices to monitor the progress towards continuing improvement and finally, we will investigate the use of spec-less indices to accomplish the same task.
Customer supplier relationships