SPC: Use in Low-Volume Manufacturing Environment


Koons, George F.; Luner, Jeffery L.   (1988, ASQC)   McDonnell Aircraft Company, St. Louis, MO

Annual Quality Congress, Dallas TX    Vol. 42    No. 0
QICID: 3475    May 1988    pp. 541-547
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Article Abstract

During 1986, the McDonnell Aircraft Company (MCAIR) adopted "a 90% improvement in quality and a 40% reduction in the cost of its product by 1991" as its Significant Business Issue. These very ambitious goals were selected because they will only be achieved when the company changes the way it conducts its business. One cultural change which is necessary is a greatly increased usage of statistical methodology in all phases of the business. This paper discusses an application of Statistical Process Control (SPC) in the MCAIR Machine Shop.

One concern about the use of SPC in MCAIR was that the company is a low-volume manufacturer, shipping about 15 aircraft per month to our customers. Concerns about the myriad number of parts, the uncountable number of part characteristics, and the short production runs of any particular part immediately raised questions about the practicality of applying SPC techniques within MCAIR. These concerns were evaluated using a pilot site in the Machine Shop.

The solution was to study the process, not the product. Rather than characterizing specific dimensions on specific parts, the processes that produced those dimensions were identified. The machines in the pilot area perform six different processes. Every part characteristic is created by performing a particular combination of these processes. Dimensions that were produced by each process were monitored over a two month period. During this process capability phase, two "special-causes" of variation were discovered. More importantly, it appeared tht all dimensions that were monitored on a wide variety of parts could be considered as having been produced from the same process. After modifications are made in the operation to prevent the recurrence of special-causes, the process will be highly capable of achieving specified engineering tolerances. The pilot project demonstrated one approach to applying SPC in a low-volume operation. It also reinforced the concepts of studying the process and not the product, that is, applying SPC rather than SQC; emphasized that the objective must be to reduce variability about the target dimension; and showed that substantial improvements can be made with very small expenditures.


Aerospace industry,Department of Defense (DOD),Short runs,Statistical process control (SPC)

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