Fitting sunroofs to cars may be a long-established area of manufacturing capability, but for the Jaguar XJ sedan’s Webasto opening panoramic roof it is almost a balletic performance.
"We take the XJ body out of the existing Jaguar overhead assembly system, bring it down to floor level, fit the roof, and feed it back into the system in one totally unmanned operation. It really is quite a feat of engineering,” said Gary Sweeney, Managing Director of Materials Handling and Automation Specialist, Exmac Automation.
It is the first full glass roof ever fitted to a production Jaguar, and it represents a significant styling aspect that Jaguar Design Director Ian Callum particularly wanted to achieve.
Positioning, inserting, and bonding the roof to the car’s aluminum bodyshell demanded a complex automated conveying and handling system developed in a joint program by Exmac and Jaguar production engineers, together with Expert Tooling.
A key aspect was to ensure that the roof could be fitted without any disruption to the assembly sequence, and that the roof insertion cell could be introduced into an existing overhead conveyor system that brings bodies to the trim and final assembly line. It also had to be achieved without changing the functionality and efficiency of the transportation systems and assembly processes.
The structure and operation of a newly installed elevator in the body delivery conveyor was modified to allow the body to be removed and lowered to ground level and into a robot-controlled panoramic roof insertion cell designed by Expert Tooling.
Panoramic roofs are introduced to the new cell on specially designed platens via an Exmac two-chain conveyor and lifter system. They are positioned and inserted using proven mechanical centralizing methods and robot techniques, rather than camera vision systems, to achieve required levels of process accuracy and repeatability. A vision system would require more body design angularity than the XJ possesses.
Terry Davidson, an Expert Tooling manufacturing systems specialist, explained: “A vision system would measure the roof aperture, adjust the programming of the robot, then try to fit the roof based on those measurements. However, the absence of sharp body features on the flowing lines of the XJ makes it difficult for a vision system to operate effectively.”
The system that is used centralizes the roof panel using an ABB robot and a special gripper featuring a floating joint. Using this, the glass roof is suspended above the bodyshell in a known position on the gripper; the roof aperture is also in a known position below. The gripper joint is programmed to unlock and move into position on the car instead of trying to move the whole robot to the car. The roof panel is heated before insertion to achieve the required temperature for the polyurethane adhesive used in the bonding process.
Next, the robot positions the roof beneath an SCA Schucker applicator and the adhesive is applied. The completed roof unit, held within a specially designed fixture, is then lowered to meet the roof aperture of the XJ body.
The special joint on the gripper then disengages, allowing it to “float”; the floating gripper ensures that the roof is in the correct position to locate accurately with the aperture in the vehicle body.
Weights are applied for just four seconds to complete the bonding process and ensure precise application. The body is then fed back into the delivery system via the Exmac conveyor to continue its assembly.