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SEVERAL YEARS AGO, Douglas Commercial Aircraft Co. in Long Beach, Calif., ran some simulations of their design and manufacturing operations to determine what drives the costs of airliner construction. The company discovered that the costs of assembly, fabrication, quality assurance, and ten overhead--inventory levels, tracking, and purchasing--all depend on the parts count.
Ron Suiter, general manager for aircraft systems and interior design at Douglas, and several colleagues were given the task of finding out what could be done to cut the parts count of some of the company's products. They lined up candidates for product redesign and assembled multidisciplinary design teams that included design engineers, manufacturing engineers, shop floor mechanics, and supplier representatives, as well as specialists in production support,
Team members were taught Design For Manufacturing and Assembly (DFMA) techniques--an exacting design-review method that identifies the optimal part design, materials choice, and assembly and fabrication operations to produce an efficient and cost-effective product. "Walking through the existing design in a very specific procedure prompted throughout by the DFMA methodology, everybody started looking at the designs in a new way," Suiter said. "Analyzing every part and operation in a basic assembly makes the team rigorously confront the complexity of a design and work to simplify it."
The results of the Douglas DFMA project were impressive, Suiter said. One success story was the redesign of the ram air door assembly on the MD-11, the company's 300-seat airliner. The original ram air door assembly, a passage through which outside air enters the cabin's air conditioning system, was a long-serving design borrowed from the Douglas DC-10 airliner. With 2172 parts, the complex door unit was considered difficult to install and adjust.
Simplifying the ram air door assembly design using DFMA techniques took about two weeks. The effort led to a 3 percent reduction in the number of parts (to 1383), a 34 percent decrease in the number of assembly operations (from 4038 to 2649)) and the elimination of 107 pounds, a significant mass reduction in an airplane. Moreover, the newly reconstituted door unit design was significantly more reliable and easier to maintain. "There are fewer parts to wear out," Suiter said. "Even the unit's function has improved."
TYPICAL RESULTS
The success of Douglas Commercial Aircraft in applying DFMA...