Original Date: 08/07/1995
Revision Date: 01/18/2007
Best Practice : F-22 Variability Reduction
Lockheed Martin Tactical Aircraft Systems (LMTAS) has established a Variability Reduction (VR) program to meet a contractual requirement of the F-22 program. Under the contract, the VR program and related activities are designated as award fee criteria. There are several defined objectives under the contract which includes: to reduce variation of key characteristics; estimate the impact of process variations on key characteristics; verify that key characteristics requirements are compatible with the manufacturing process; identify producibility studies for improving quality, increasing integrity and/or reducing production cost; characterize key manufacturing processes using statistical data; reduce scrap, rework and repair; and, reduce reliance on end item inspection.
A seven-step approach has been developed to meet these objectives. This approach begins by identifying key characteristics. A key characteristic is a feature of a material, part, or assembly critical to the fit, performance, or integrity of the product. The VR team used Design of Experiments and Quality Function Deployment tools in a structured approach to systematically break down top-level requirements into lower level components. These lower level requirements are examined to decide key characteristics that are then associated with related individual control characteristics. The second step in the program is to correlate the identified key characteristics to processes. This is followed by prioritizing and selecting firm key characteristics. Step 4 involves developing VR Instructions for each of the selected key characteristics. These instructions include product definition, key characteristic description, manufacturing approach, data collection, tooling approach, process assessment, process analysis, and product feedback. Once developed, the VR Instructions are incorporated into the Product Development and Definition build- to package. Step 6 involves actual process control of the key characteristics, and the final step provides feedback reporting for monitoring and continuous improvement activities.
The VR team on the F-22 has identified 2561 product key characteristics. These are part-number driven and equate to the 678 processes/part families that led to the development of 126 VR Instructions. Lessons learned during this process include the need to incorporate VR into normal engineering requirements to help early identification of key characteristics. This would ease earlier usage of Design of Experiment and Quality Function Deployment tools. Cross functional VR teams greatly simplified the implementation of VR, the use of quality tools was widely accepted by the Integrated Product Team (IPT), and active coordination among the three primes ensured a common approach.
No award fee on the F-22 has been lost since the implementation of the VR program. An example of other benefits can be shown by looking at improvement in the NC trim operation of composite doors, skins, webs and floors. Since this system has been in place, the Cpk for this operation has improved to its current level of 1.2 or about 99.9%.
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