BIRMINGHAM, U.K. — Step inside the body shop at Jaguar Cars' Castle Bromwich assembly plant in the English Midlands and you're bound to notice something missing. Unlike most body shops, Castle Bromwich lacks the shower of sparks associated with putting automobiles together. There's a certain serenity on the shop floor, with little or no noise.

The reason is simple: Castle Bromwich isn't building the traditional car body. Here, Jaguar is producing its new XJ flagship sedan, which utilizes an aluminum exterior mated to a traditional steel subframe in a monocoque fashion. This is where the true secret of making a lightweight body comes together.

Jaguar uses self-piercing rivets to mate the aluminum shell with the steel structure underneath. The non-traditional fastening technology is in keeping with the plant's aerospace roots (Castle Bromwich used to assemble Spitfire fighters during World War II).

Although a technological feat, ramping up the process also was a nightmare. The 1998 decision to use aluminum caused several delays in the manufacturing program, Ford says. The new '04 XJ is several months behind in its original launch schedule.

“Nobody else has done a monocoque aluminum vehicle. We decided that was the way to go rather than (an Audi-like) space-frame,” says Nick Scheele, president and chief operating officer of Ford Motor Co., which owns Jaguar. “We knew we'd have problems going that way, because no one has done it before.”

Jaguar did not want to sacrifice XJ's styling in order to use an aluminum body. Executives say trying to maintain the car's design, including the shoulder line on the rear quarter panel, turned out to be one of the toughest challenges for the development team.

“Traditionally, with aluminum, people go for simpler pressings than they do with steel. Of course when you take the look of Jaguar, we looked for more difficult, deeper pressings than virtually any other manufacturer,” says David Scholes, XJ's chief program engineer.

“The story I often tell is the rear fender, which to get that style right, it took us 28 tries on feasibility to get a solution — with the manufacturing guys pulling their hair out, literally.”

Jaguar also didn't want any quality glitches. Knowing that the world would put this new flagship under the microscope, Ford and Jaguar decided last summer that it was better to hold off on releasing the car rather than trying to keep it on schedule.

“We had to get it right,” says Scheele. “Waiting was the only way to do it until we got it right.’”

The manufacturing process forced Jaguar to question everything it had learned. Each XJ, for instance, contains almost 3,200 rivets and more than 394 ft. (120 m) of adhesives that bond the body together; the adhesives cure in the heat provided by the paint process.

A total of 88 robots apply the adhesives and rivets. Jaguar says using robots to attach the rivets provided additional challenges: Compared to using traditional spot welding, the heads used by the robots in the rivet process are bulkier and the cycle times slower.

The aluminum exterior body panels are created in a new, dedicated aluminum pressing facility within the Castle Bromwich complex, adjacent to the body assembly line. It measures in at 103,000 sq.-ft. (9,569 sq.-m).

Jaguar's aluminum press facility produces 125 different major aluminum parts for the XJ. It includes 13 presses, ranging in capacity from 448 tons to 2,240 tons. Manufacturing executives say the company decided to use hydraulic presses over mechanical ones because they provide greater control in stamping, reducing flex within the panels.

“Nobody has ever made an aluminum body shell with these types of returns,” Scheele says. “These are classic Jaguar lines, but by God, you don't normally stamp them in aluminum because of the springback, so we had a technology to overcome.”

Castle Bromwich's aluminum stamping facility has a line for major body stampings and one for body architecture stampings.

Line A, with six presses, produces most of the exterior panels, including front and rear fenders. There's also a seventh press, which is used only for the rear quarter panel, to help keep intact its shape.

The B line has seven presses, configured in a series but broken into two separate lines. They are used to create smaller stampings, such as braces and other structural components.

Each of the presses is equipped with sliding bolsters that enable the rapid changing of dies for each new piece. Jaguar says the dies can be changed in as little as 15 minutes. In all, 86 die sets are used to manufacture the XJ's aluminum body.

The stamping facility's 160 employees work three shifts per day to produce a 10-day supply of parts, which are stored in the adjacent body shop.

A technical consortium between Jaguar and Polynorm Stadco, under a long-term contract, oversees operation and management of the stamping plant. Several other suppliers were technical partners, including Nothelfer GmbH of Lockweiler, Germany; Allgaier Werke GmbH of Uhingen, Germany; and Fargo Press und Stanzwerk GmbH of Ban Honnef, Germany.

Aluminum for the stampings is provided by Alcan Inc., which has up to 20 days' supply of the material on hand to feed the factory from a nearby warehouse. Jaguar relied on Alcan as the primary technical resource in early feasibility studies, and Alcan helped in the development of lubricants used in the stamping, adhesive and rivet bonding process.

Alcan provides three distinct grades of aluminum. Grade 5754 is used in the underbody construction, while lighter-grade 5182 is in the inner sections of the door panels and other closures. Heavier-grade 6111 is used for the exterior body panels because it stiffens in the heat of the paint-baking process, which protects the body from dings and dents.

The XJ's underbody is created in three sections: front-floor, mid-floor and rear-floor. These are joined together as the first part of the body assembly process. Vehicle bodyside assemblies then are constructed and join the underbody at the framing line.

Using aluminum also requires a very clean environment to avoid potential corrosion problems. This forced Jaguar to install a complex dust-management system.

There's extensive use of vacuums throughout the plant, especially in metal-finishing areas. Workstations that are sensitive to dust are housed in special booths that contain dust-removal systems. Aluminum dust captured from the air is recycled and used to produce new aluminum.

Once the body is completed, it is cleaned of any remaining residue before traveling to the paint shop. The 104° F (47° C) cleaning process helps to provide an extremely clean surface for the paint to be applied.

With quality paramount to the success of XJ, Jaguar wanted its manufacturing specialists to have the ability to control the assembly process. The company installed several alert buttons at each assembly station.

If operators detect a quality issue, they are instructed to hit the button and resolve the issue with plant management before it permeates through the rest of the production volume.

“We weren't going to put the car into production until we knew that the quality was right,” Scholes says. “Traditionally, you expect to go into a program like this with everything known.

“On this program nothing had been done before, so every little thing was new technology you have to prove. That's a lot of technology breakthrough here.”