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Original Date: 08/07/1995
Revision Date: 01/18/2007
Information : Shop Floor Statistical Process Control
Lockheed Martin Tactical Aircraft Systems (LMTAS) has implemented Statistical Process Control (SPC) on the shop floor in several applications, and the particular methodology in developing SPC on the shop floor is tailored to best fit the process being monitored.
One variability reduction (VR) activity identified fastener hole defects as a major problem category. Production of a single F-16 aircraft required the production of over 400,000 holes. Many of these holes are drilled, reamed, and countersunk to close tolerance. The large number of hole defects experienced led to a VR effort in the production area on the shop floor. An initial study determined the need to implement SPC processes to keep the processes under control. It was determined that use of electronic gages and automated SPC would solve the problem; however, the proposed system was too costly. Consequently, a step gage approach was developed which has proven to be a cost- effective method of controlling the drilling and reaming processes. Step gages are calibrated to allow the nominal size limit to pass through the hole up to a step that is sized to the upper limit. If the step also passes through the hole, then an additional hole is drilled and inspected to check for potential operator error. If the second hole fails, the process requires correction, normally by replacing a drill bit or reamer. Operator instructions include hole check frequency and charting requirements. The charting is accomplished on a simple form that the operator fills in after each hole check.
In the countersink area, electronic gages (Gagetalker III system) are used to check and automatically record data. This is a compact, portable, handheld unit that records data and produces real time SPC displays for the operator. Recorded data can then be transferred from the system cartridge to a mainframe for continual monitoring.
A complete set of step gages for the various hole sizes at each workstation was purchased for approximately $50K, as opposed to the projected cost of $750K for the required number of electronic gages. Since the implementation of the system in 1991, hole defects have been virtually eliminated. Savings accredited to this system from a single work breakdown structure (WBS) was calculated to be in excess of $73K annually.
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