In 2003, Jaguar set out on a risky mission: Develop a mass-production vehicle using an aluminum monocoque body design. That was the charge given to the team developing the flagship XJ sedan. Sure, Audi had been using an aluminum body structure in its A8 for many years, but the German luxury brand’s flagship relies on an aluminum space frame, not a full monocoque. The challenge proved daunting for Jaguar’s development engineers, so the XJ’s launch schedule was pushed back a few months to work out the kinks, but the lessons learned turned out to be quite valuable and the green light was given for aluminum to take a prominent role in the development of future Jaguar models.
Even before the XJ rolled off the line at Jaguar’s Castle Bromwich, U.K., plant, designers and engineers began penciling the next challenge, the ’07 XK Coupe/Cabriolet (code-named “X150”), which itself utilizes the same aluminum monocoque processes perfected for the XJ, while incorporating new advancements gained as the sedan worked through its own trials and tribulations. When the last of the previous generation XKs exited Castle Bromwich in May, 2005, crews went to work gutting the 131,300-ft2 body shop to install more than 30 ABB robots, 120 fixtures and two dedicated skillet lines to prepare the XK for its launch in November. The car will begin shipping to dealers in Europe and the U.S. beginning in January ‘06, with full output (60 vehicles per day) targeted to begin in late-February.
During a recent tour of the “Castle Brom” (as insiders call it), Richard McDonald, vehicle plant launch manager for XK, points to a number of empty spaces in the plant: “We still have yet to install a number of tools for the final assembly operations,” he says. As pilot assembly of body structures gets underway, the lack of noise and flying sparks in the plant are almost eerie. Since the XK’s monocoque is fastened together by self-piercing rivets, there’s essentially no need for welding, except for one crucial area on the coupe where the roof meets the rear hatch. This section requires the use of automated MIG welding, to assure the body remains structurally sound and visually appealing. (After all, who would want to see rivet marks running across the top of their $80,000+ luxury sports coupe?)
Like its XJ sedan sibling, the XK’s body is created at the stamping facility adjacent to the assembly operations, which is operated under a consortium between Jaguar and Polynorm Stadco, along with the expertise of several German suppliers: Nothelfer GmbH, Alliagr Werke GmbH, and Stanzwerk GmbH. Aluminum used in the stamping process is provided by Alcan, which stores up to a 20 days’ supply of the material in a warehouse nearby the factory. The XK’s underbody is created in three sections: rear-floor, mid-floor and front-floor, with front-floor modules featuring a barcode that designates whether the car is a coupe or cabriolet. Once body style designation has been identified, the three body pieces move to a marrying station, where a ThyssenKrupp sliding framing gate marries the various pieces together as rivet guns enter to begin the joining process (100% of the under body of both models is common; 95% of the body structures are shared between the two models). The coupe body is bonded together utilizing 2,620 Henrob self-piercing rivets, along with three different adhesives measuring more than 295 ft. in total length. The cabriolet, meanwhile, receives slightly less adhesive material and 2,430 rivets (compared to 5,000 spot welds on the previous steel convertible body), due to its topless design. The adhesives utilized in the manufacturing process include two grades, one for sheet joints and another with high bonding quality for heavy-gauge joints. Russ Varney, chief engineer for the XK program, says the use of self-piercing rivet technology and bonding provides the XK with a body shell that is 31% stiffer than the previous model, along with a 10% improvement in power-to-weight ratio, with total vehicle curb weight limited to 3,516 lbs.
Once the body is assembled and painted, the undercarriage is married to the body and the vehicle moves into its final assembly stage on a skillet system, where the XK travels through 28 different stations, each manned with three or four employees. Workers are aided by a trolley containing the necessary interior pieces which follows the vehicle down the skillet lines. Chief engineer Varney says Jaguar decided to use the trolley system compared to the previous line-side delivery process because it proved to be more efficient and required less floor space than the fixed structures used in the previous set-up. The efficiency improvements and higher penetration of automation enabled Jaguar to limit manpower on the XK line to approximately 160 hourly workers.
The XK represents another significant milestone in Jaguar’s attempt to truly differentiate the structure and composition of its vehicles from the labyrinth that is its parent: Ford Motor Co. While there had to be undeniable temptation within Ford to limit the use of high-priced aluminum on such an extensive level, credit should be given to the leadership at Ford’s Premiere Automotive Group for allowing Jaguar to remain unique. The ’07 XK hopefully will play the role of another building block in Jaguar’s plan to build unique products that stand apart from the Volvos and Lincolns in the Ford stable.