One such task is checking the finish-welded body. To improve tolerances, vehicle manufacturers are moving towards 100% inspection of the body-in-white car. The most common inspection technique uses non-contact laser sensing. Laser sensors--some 150 are required for a single model--mount on a tunnel-like structure through which the body-in-white passes. If the model changes, the equipment must be adapted or altered.
French systems integrator BBR is replacing the tunnel-like structure with a team of robots at the Peugeot factory in Rennes, France. Eric Bienfait, BBR managing director, describes the setup: Four Fanuc robots manipulate Perceptron laser sensors; a Dynalog calibration system compensates for temperature variations in the factory environment. Communication interfaces are based on the Siemens Profibus.
Once in operation, each robot will measure 10 to 15 points on each welded body, in a cycle time of 24 seconds, with a precision of 0.2 mm. The calibration cycle is designed to be spread out over the passage of three or four cars in order not to disrupt production output. It involves each robot performing a self-check routine. If this highlights the presence of a positioning error, the supervisory PLC on the line initiates a complete calibration for all the robots.
Peugeot is installing two robotic cells of this type to inspect a mix of seven models of car being produced on the same line. One cell will be used to measure the under-body of the vehicles and the other for the main part of the body.
Greater production flexibility. With vehicle manufacturers seeking more flexibility from their production units, the robotic solution is much in demand. "Given that the body shop is a relatively investment-intensive area," says Bob Fanone, global stamping and structures manager at Ford Motor Co. (Dearborn, Michigan), "the company's basic strategy is to employ technologies that give us more flexibility and minimize changeover times between models. That generally implies more robotics."
Fanone notes two technological improvements are helping robots penetrate new areas. First, he explains, robot size and load capacity are increasing, allowing transfer of large components. Second, the development of smaller robots is helping increase robotic automation in spaces that are relatively confined.
One application for a smaller robot is rocker area welding, which is mostly done with fixed, dedicated automation. Ford, Fanone says, is investigating the use of robots for this task as a means of shortening changeover times between models.
In another development, electric servo-controlled spot-welding guns are starting to replace the pneumatic guns that are most commonly used, despite their cost. One of the pioneers is Peugeot.
"We started to use electric guns, supplied by the French company MFG, almost two years ago because they are significantly faster than pneumatic guns," says Terry Edmonds at Peugeot's Ryton plant in the UK. He estimates that welding cycles are 20% faster as a result. Added advantages are an improved weld quality and 20% longer tip life due to lower temperature operation.
Today, the Ryton facility uses electric weld guns to their full potential with one third of all guns being electric. "Not all applications are equally suitable for electric weld guns. Best use is made of the technology where a large number of spots, say 50, have to be placed along the same axis, and movement between the spots is limited," says Edmonds.
In the future, laser welding will become more common in automotive body shops, providing yet more tasks for robots. Lasers, according to Ford's Fanone, are already frequently used for cutting operations in the body-in-white area. Now, he says, they are starting to be used for welding, as a means of replacing spot welding.
The main advantage of laser welding is that it requires access from only one side. Welding the roof of a vehicle to the side panel is one application that is already being carried out with laser technology. But others are likely to arrive soon.
Small robots for small spaces
Three major robot builders showed new compact robot welding solutions for body shops at recent exhibitions in Detroit and Hanover. Japanese companies Nachi, Kawasaki, and France's Fanuc all claim to be able to halve the length of existing body welding lines with their new robot models. All are floor-mounted and work at a low level on the car body while the spot welds on the upper parts of the car are performed simultaneously by conventional models.
Fanuc's is the most innovative approach to a compact design. The F200i is a robot of parallel structure which, broken down to its basic components, comprises a base and tooling faceplate, connected by six servo actuated legs. Extending and retracting the legs alters the position of the faceplate producing six degrees of freedom. "This robot fits into a very tight space so it meets the needs of the auto body shops to minimize floor space," comments Rick Schneider, president and CEO, Fanuc Robotics North America.
Kawasaki's compact robot is set up on a floor-level mobile platform, whose movements are fully programmable in four axes. According to Mark Bailey, sales manager at Kawasaki Robotics (USA), it has been used to transform a line from 21 welding stations to seven stations, without impacting throughput.
Nachi's robot is similar to conventional articulated robots but with shorter body and arms. "Using this design, we can put 16 robots at one welding station, whereas a typical body shop has only four robots per station," says Yoshihisa Azuma, president of Nachi Robotic Systems Europe.