A Statistical Quality-Control Program

In the fall of 1955, initial steps were taken at the old Biltmore plant (Draper Corporation) toward a statistical quality-control program. Approximately 9 month’s data have been accumulated on the techniques of specification, production, and inspection. After a careful evaluation of the manufacturing process, it became evident that existing shuttle-block specifications were inadequate for use in a quality-control program. An attempt was made to remove the ambiguity and spell out in more definite terms the exact requirements of the product being manufactured. Further revision of the specifications was made by managements of the Hopedale and Swannanoa plants. With the specifications clarified, the next step was in the direction of the production process itself. The problem was simply one of reducing the number of rejected shuttle blocks per inspection period. The standard practice after 100 percent green inspection in the warehouse had been to return an invoice to the various production units with the number and percent of rejects, contained in the inspection lot. The next step in the quality-control program was to clarify the rejects. This was done for each sawyer in the sawmill, with added emphasis placed on the category or categories that needed correction. Three essential things had to be determined: 1) Was a change in percentage of rejects merely due to the unstable system of chance causes? 2) Was the process getting better? 3) Was the process getting worse? A control chart would provide these answers and information concerning the status of the production process.

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