Manufacturers seeking an alternative to expensive, inflexible inspection fixtures need look no further. Several new designs of inspection fixtures are now on the market. The Alufix, the flexible fixture developed by Marino Gages in conjunction with Stellar Engineering, is made of pre-machined modular components that include precision bars, base plates, angle plates, clamps, connectors and datum blocks that can be assembled according to an inspector's needs. This modularity makes it ideal for inspecting products as they evolve in size and shape. Once the manufacturing process is complete, the Alufix can be disassembled and rebuilt into new configurations for diverse future uses.

The inspection process for the front fenders and hood of an automobile would be an example of this technology at work. To inspect a production hood, rails can be attached to the fixture to simulate the fenders. To check the fenders, the inspector can remove the fender rails and attach rails simulating the hood. The removable rails provide automakers and their suppliers with a variety of ways to inspect panels. If more detail is necessary, inspectors can remove all of the rails and load the inspection fixture, or a portion of it, onto a coordinate measuring machine (CMM) which only takes about five minutes.

The Alufix's "erector set" style design, a box-shaped frame with a grid pattern of holes, allows its users not only to reconfigure the fixture but also to break it down entirely. Automakers can divide the Alufix and send relevant portions to other members of the design and production team, both inside and outside of the company. If the automaker has multiple suppliers making prototype panels for the car, it can detach the appropriate segments of the Alufix and distribute them to each respective prototyping shop. When each shop delivers its prototype, the segment is returned. The automaker can then reassemble the Alufix and inspect each panel.

The frame of the Alufix can also be used with detail blocks to hold pieces of clay in the styling phase. Afterward, the blocks can be updated as the design changes from clay styling to prototyping, pilot production and final production. Thus, the flexible Alufix can serve as the master gage through every stage of production, doing the job of six conventional tools. "Tools made from weldments can't be modified in a cost effective manner because they don't fit back together correctly," explains Paul Marino, president of Marino Gages. "If a detail changes, the whole tool has to be sent to the manufacturer so that a team of skilled trades could cut off the detail, machine a new one and weld it onto the frame. Then inspectors would have to check it on a CMM to make sure the heat from the welding process didn't twist the frame."

Another company, Brown and Sharpe Manufacturing Co., have developed two sets of reconfigurable fixtures for supporting contoured panels on CMMs; the System Five and the Five U-nique. Both of these utilize a cylinder-based design to achieve modularity. Reconfiguring the fixtures is only a matter of moving their cylinders to the correct location on the CMM bed, adjusting their heights accordingly and attaching the correct holding devices. The difference between the two systems is that the System Five builds itself automatically and the Five U-nique is manual. Both come with interactive software that allows inspectors to generate fixture-configuration programs automatically and give the product its theoretical geometry during the inspection cycle. The fixturing points come from the original CAD file of the part.

Though both the System Five and the Five U-nique are expensive, their flexibility saves manufacturers money. "A preconstructed hard fixture would be quicker, but could cost 2 to 10 times higher," says David Genest, director of corporate communications at Browne and Sharpe. "Whenever you change sheet metal prototypes, which occurs constantly before production, you have to cut, weld and grind new features on the hard gage. Consequently, automakers and their suppliers spend hundreds of millions of dollars per body type on body fixtures."

Another benefit of both the System Five and the Five U-nique is that the CAD file becomes the master gage throughout the company and its supply chain. Revisions become a matter of updating the file and sending the new geometry to every operation in the production process. Because of innovations like these, the System Five and Five U-nique, as well as the Alufix, can save manufacturers of metal products enormous amounts of money and lead-time.

Source: Flexible Inspection Fixtures: A Dream Come True?
James R. Koelsh
Quality Online, June 2000
http://qualitymag.com/articles/2000/jun00/0600f3.asp