NIST Industrial ImpactPrecision Asembly Process Improves Vehicle Quality and Reduces CostsWhat a difference a few millimeters make. A precision assembly process that improves the "fit and finish" of American cars and light trucks is expected to extend billions of dollars in economic benefits to consumers, the more than 580,000 U.S. firms in vehicle-related businesses, and other industrial sectors that do business with the auto industry or its suppliers. Developed with the support of NIST's Advanced Technology Program (ATP), the "2 millimeter" assembly process is credited with improving both vehicle quality and customer satisfaction. The innovative approach, named for the world-class dimensional variation target of the early 1990s, is readily adaptable to the tighter tolerances expected in the future. And, because vehicle-related businesses employ 7 percent of U.S. workers and every dollar invested in auto manufacturing adds $2.50 to the U.S. economy, the ATP project is expected to benefit virtually every U.S. household. For example:
"It has turned out to be amazingly successful for the whole American plant scene," says Ernie Vahala, president of the Auto Body Consortium, Inc. (ABC), the group of automotive suppliers that sponsored the ATP joint venture and received the grant. GM and Chrysler, which received no ATP funds, covered most of the industry cost-share requirement and, along with two universities, assisted with the research. The research team solved a problem that long has plagued U.S. car makers, which until now have tolerated dimensional variations of up to 5 or 6 mm. Poor fit can cause all sorts of problems in a vehicle, which consists of 300 stamped parts. The underbody, side frames, roof, shelves, and backpanel are assembled first; the doors, hood, and other panels then are fitted into the openings. When the parts do not fit properly, custom manual reworking may be needed. Sometimes a partially assembled vehicle has to be discarded. The problem was not solved easily because it had many causes. The solution was to address many aspects of metrology, the science of measurement, using a systems approach. The contributing factors were studied concurrently by tooling suppliers, engineering service companies, automotive engineers and assembly line operators, and academic researchers. Among their innovations are an automated process for positioning and calibrating optical sensors that measure dimensional variations, a laser line-scanning system that certifies die surfaces for forming panels and sheet metal parts, and hardware and software for optimizing the fitting process. An automated monitoring and diagnosis system was designed that synthesizes sensor data in real time to characterize assembly line performance very accurately. (Data on 60 to 80 critical dimensions can be gathered in 15 to 20 seconds.) If variation is detected, then the operator consults a knowledge base of potential causes based on data on assembly-line failure modes and frequencies. A case study method also was developed for use as a diagnostic tool. Assembly plants using the process have reduced the variation in vehicle body dimensions to 2 mm or less, the benchmark for world-class status. The vehicles have a superior "fit and finish," resulting in minimal water leakage, a quiet ride, well-fitting trim, and reduced corrosion and wear--characteristics that convey the "feel" of a quality car. Although individual defects can be minute, like a grain of sand in the paint, reduced total defect counts translate into higher product quality. Consumers have noticed, according to Vahala. After the new assembly was implemented at several GM truck assembly plants, customers consistently reported fewer problems in independent market surveys, he says. The economic benefits include a net savings in production costs estimated at $10 to $25 per car, or up to $160 million annually for GM and Chrysler combined once all their plants adopt the technology, according to an economic analysis performed by CONSAD Research Corp. of Pittsburgh and funded by NIST. The average savings in maintenance costs is estimated at $50 to $100 over the useful lifetime of each vehicle, or up to a combined $650 million annually. Much of this savings will go to car makers during warranty periods; vehicle owners will get the rest. "The benefit comes to the consumer, the benefit comes to the manufacturer, and the benefit comes to the federal government through the fact that tax receipts increase when productivity in America is improved," says Dwight Carlson, chairman of the ABC board, who has become a strong supporter of ATP's role in catalyzing high-risk research to develop enabling technologies that can generate such substantial payoffs. Implemented initially at five plants, the 2 mm technology now is being transferred to other GM and Chrysler plants as well as to Ford Motor Co. In addition, project results are being incorporated into the production of assembly line tooling and other technologies supplied to car makers. For example, a new type of clamp has been designed that may have commercial potential. The 2 mm technology also is finding its way into other industrial sectors that share suppliers with the auto industry, Carlson says. Further technology transfer is possible in the future; project participants have held discussions with representatives of the aerospace, appliance, and metal furniture industries. The success of the 2 mm project is expected to increase GM and Chrysler's combined market share by as much as 2 percent, stimulating a substantial increase in U.S. industrial output and potentially thousands of new jobs, according to CONSAD. Meanwhile, the project has inspired two more ATP-funded projects aimed at developing precompetitive technologies to improve sheet-metal stamping and welding. Companies:Auto Body Consortium, Inc. Other Participants:Chrysler Corp. Business:Motor vehicle manufacturing
April 1998 |