Few industries face the range of competition as today's automakers. This has spurred DaimlerChrysler to examine its supply chain for ways to create efficiencies and reduce costs. An important element of the carmaker's supply is the stamping plants that produce metal panels and assemblies for auto production.

The company's Twinsburg, Ohio stamping facility recently automated much of its materials handling to keep up with production demands, improve plant safety, promote ergonomics, improve quality and reduce costs. Central to the changes in the 1.5 million square foot facility was the addition of automatic guided vehicles (FMC Technologies, www.fmcsgvs.com) and materials handling robots guided by a highly-accurate vision system (Cognex Corp., www.cognex.com).

Prior to the new upgrades, a fleet of 103 lift trucks was required to keep materials moving within the plant. Such a sizeable number of trucks often created traffic problems. Strict guidelines and extensive training were necessary to keep everyone safe. Lowering the dependence on lift trucks was a major priority.

'Since adding the automatic guided vehicles (AGVs), we have been able to reduce our lift truck fleet by 35 vehicles and have 40-50 less drivers,' says Conrad Hawley, production control manager. 'This has allowed us to re-deploy that labor elsewhere in the plant.'

Another safety issue involved manual handling of parts in process. Stamped parts are notoriously dangerous, with sharp edges and protruding imperfections. Many of these parts also are heavy, requiring chest-high lifting beyond desired ergonomic limits. The vision-guided robots now perform much of the heavy and dangerous lifting previously handled by workers.

Twinsburg is one of three stamping plants serving DaimlerChrysler production in the U.S. Fifteen lines produce parts and assemblies 24/7 here for Dodge and Chrysler minivans, the Dodge Neon, and the Durango and Ram truck models. A total of 1,000 racks of stamped goods must be processed during each shift.

Production begins with the arrival of raw materials. Large coils of steel are offloaded from delivery trucks and taken by crane to a blanking operation. Here the steel is unrolled and cut into squares and other shapes. The cut steel is then automatically loaded onto racks, which are picked up by lift trucks and carried two hundred feet to stamping machines.

Completed stampings are placed into shipping racks. Lift trucks pick up the racks, which with their load weigh about 1,700 pounds, and deposit them onto AGVs for transport 2,000 feet to shipping. Other AGVs take remaining parts to the assembly lines.

'We now use the AGVs to handle all of the long-distance travel within the plant,' says Brad Dailey, assembly project and tooling manager.

The assembly operations weld or fasten parts together to create truck beds, doors, and panels. Upon arrival there, lift trucks offload the racks from the AGVs and place them onto a turntable. The turntable must rotate 180 degrees for the picking robot to access products within the rack.

The robot's vision system first does an inspection of the part to make certain it is the expected part and in the proper position. Two of the lines use optical sensors, essentially security-type cameras mounted on the ceiling. The sensors each view the rack, collecting geometric data. The data is then fed to the interface software where it is compared to known dimensions of the racks and the parts that should be present. The software also examines the structural integrity of the part.

Once the system verifies that the part is present, is of good shape and in the correct position, it instructs the robot to pick the part from the rack and deposit it onto carrier fixtures resting on a conveyor line. The conveyor then feeds the assembly operation which utilizes other robots for welding and assembly tasks.

Since installation, the picking robots have proven to perform much faster than the previous human handling, which has resulted in higher throughput. Safety has also been enhanced, as workers are no longer trying to keep up with the line's demands while lifting dangerous metal stampings.

'Not only do we have manpower savings, but we have also resolved our ergonomic issues,' says Hawley. 'The robot is faster and works continuously.'

Two additional lines are also equipped with similar picking robots. Due to the location of the parts in their racks, ceiling mounted sensors were not workable. Instead, three sensor cameras are mounted onto the arms of each robot to properly guide movements.

Once assembly has been completed, automatic guided vehicles pick up the parts for transport to the shipping area. There, lift trucks gather the racks of finished parts. They load assemblies heading to plants in St. Louis, Delaware and Mexico directly onto rail cars, while parts for the Windsor, Ontario assembly plant are placed into over-the-road trailers.

The AGVs have been a welcome addition to production operations, says Hawley. 'They have performed even better than we expected.'

The Twinsburg plant hopes to reduce its reliance on lift trucks even further. The plant currently has 31 AGVs on hand. Eventually some 40-50 AGVs are expected to patrol the facility floor.

'We are also now looking into placing a fork attachment on the AGVs to eliminate the need for lift trucks to make the transfers,' adds Jim Petruna, materials handling engineer.

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