Original Date: 10/20/1997
Revision Date: 01/18/2007
Best Practice : Process Variability Reduction
Northrop Grumman implemented a Process Variability Reduction (PVR) system to improve the manufacturing processes on its F/A-18 C/D and E/F programs. The PVR system consists of a Statistical Process Control (SPC) system, a Manufacturing Process Performance System (MPPS), and a Manufacturing Process Data Base (MPDB). All of these components are computer-based, open-system architecture tools used by management, the engineering design staff, and the shop floor. In 1992, market competition encouraged Northrop Grumman to begin SPC pilot projects. Since that time, the company’s full SPC system has gained control of process variabilities and significantly reduced or eliminated the associated costs of nonconformance and rework.
The SPC component of the PVR system tightly tracks process variability, which allows Northrop Grumman to understand where problems arise and to address them immediately within that shift. Accessible in real time to all employees, the on-line SPC system is considered a certifiable skill for shop floor mechanics and is a requirement for completing any work. A lapsed certification in SPC or any other skills will prevent a mechanic from performing any work until certification is reinstated. All mechanics, engineers, mechanical engineers, quality assurance personnel, supervisors, and upper management must complete SPC training.
SPC usage has also reduced rework and administrative costs substantially. On the F/A-18 C/D program, the average number of defects per production unit decreased 79% between 1995 and 1996. Cycle time, hours per unit for rework, and administrative actions associated with those defects decreased 70% between 1995 and 1996, despite a 20% increase in production rate. Even further benefits are now being seen with the new E/F program. The use of an entirely CAD-based design for all parts and tooling has improved tolerances. However, Northrop Grumman does not monitor all of its processes by SPC. The decision-making process to identify which process should be applied to the PVR system includes pareto charts.
MPPS encompasses the SPC data collection on the shop floor as well as the data analysis and reporting used daily in IPT meetings. This data enabled Northrop Grumman to switch from 100% inspection to a sampling method, reducing inspection times by 70% per unit. Sampling rates are based on the higher figure from either process performance data or the American National Standards Institute (ANSI) recommended values.
MPDB, the on-line deliverer of process capability data, includes a catalog of all Process Codes, Process Specifications, APWIs, and Process Performance Data. Northrop Grumman tracks processes not parts. Process Codes are cross-referenced to Process Specifications which, in turn, correlate to specific Cost Centers on the shop floor.
APWIs are electronically available on the shop floor. These work instruction documents support individual Assembly Line Operation Orders (ALOOs). ALOOs tie together all requirements (e.g., reference drawings, manufacturing notes, work instructions, inspection items) to complete a process that typically requires six to eight hours per shift. Tool and Equipment Kits are also kitted to specific ALOOs. These kits include all power and hand tools and parts for a process.
Northrop Grumman continues to track process data through its PVR system. The company has gained improved manufacturing processes and cost savings for the F/A-18 C/D and E/F programs. In addition, the PVR system has enabled Northrop Grumman to earn the McDonnell Douglas Preferred Supplier Silver Rating.
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