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By J. Stanton McGroarty, CMfgE, CMRP, senior technical editor
Watch videos of a dozen industry experts explaining how AGVs are impacting manufacturing and assembly.
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Through most of the 20th century it was said that everyone, anywhere in Detroit could hear the main chain. All activity, whether in stores or bars, in the media or schools, or even at home, was conducted with an ear to the slow parade of vehicles being pulled through assembly plants across the nation. Like an orchestra conductor or some giant’s heartbeat, the main chain at once enabled and constrained the activity of the whole manufacturing organism. It provided pace and efficiency for manufacturing flows, but it also limited operational flexibility.
For example, a standard way to produce a convertible car was to build a two-door hardtop, pull the unit off the assembly line, and then have a contractor cut the roof off and hand-build the unit as a convertible. This was a costly contortion of the vehicle assembly line, but car companies were trapped. Most convertible volume was too small to justify a dedicated assembly chain, or even a set of dedicated stations that would be lightly used. Clearly there had to be a better way to produce the specials, but the main chain made auto manufacturers slaves to volume.
Beginning in the early 1970s U.S. and European auto manufacturers began to experiment with automatic guided vehicles (AGVs) as a more flexible way to produce cars. In 1973, Volvo built a line of AGVs for their own use as platforms for auto assembly. Later they sold them to other auto manufacturers, as well. Soon several other manufacturers also offered wire-guided assembly vehicles, so-called because they were guided by wires buried, at great expense, in factory floors.
In the 1970s, the combination of cumbersome AGVs, equally cumbersome manufacturing cost accounting systems, and limited guidance and data processing technology made the great AGV experiment an interesting, but questionable economic exercise. The huge investment that U.S. auto manufacturers had in conventional, chain-driven assembly plants also slowed fundamental technological change.
Now, 40 years after the first large-scale AGV assembly projects, it may be time to take a fresh look at the technical and economic picture for AGVs and vehicle assembly. Important progress has been made in the vehicle assembly plants. Successful AGV applications are in place at Chrysler and John Deere. And exciting trends in guided vehicles suggest the pace of AGV deployment is about to accelerate into several new areas of manufacturing and distribution.
“We include AGVs in many aspects of material delivery, transportation of sub-assemblies between production lines, and in some cases also use AGVs to carry the sub-assemblies during their assembly,” says Didier Papin, head of Chrysler manufacturing engineering and general assembly. “We have not used AGVs to carry complete bodies on assembly lines. For our main line assembly, we have existing conveyor solutions already in place and have not considered AGVs as a replacement.”
Figure 1. AGVs play many roles at Chrysler, including delivery of material from the receiving dock to the assembly line delivery from sequence/kitting areas to the assembly line. Nearly 150 employees hand-build 12 SRT Viper muscle cars each day at Chrysler’s Conner Avenue Assembly Plant in Detroit.
AGVs play a key role in delivering material from the receiving dock to the assembly line at Chrysler. “They also deliver sequenced and kitted material from sequence/kitting areas to the assembly line,” says Papin. “ The use of AGVs in this manner allows us to deliver material efficiently.”