DaimlerChrysler robots are now programmed to weld several different vehicle madels.

Welding a Sebring 4-door's roofline at the Sterling Heights Assembly Plant.

Auto manufacturers are streamlining their build processes from traditional assembly lines set up specifically for each vehicle, to lines that produce families of vehicles. DaimlerChrysler recently invested $278 million

to put a version of this concept into production at its Sterling Heights, Mich., assembly plant, for the production of its 2008 Dodge Avenger. The plant was shut down for less than seven weeks while its assembly line was converted.

The multi-tasked weld cells
DaimlerChrysler's Flexible Manufacturing Strategy – its version of a lean manufacturing program – takes an alternate approach to the application of automation on production lines. Rather than having multiple lines of robots welding the same locations on each model that passes them, the corporation's new strategy is to run multiple vehicle architectures from the same "family" of vehicles through a single line of robots. The robots are programmed to adapt to each vehicle that passes through.

Such a line can switch between similar models built on the same platform, such as the Sebring and the Avenger, as well as between two-door and four-door models. They also can adapt to models that may have additional stiffeners, an alternate roofline or no roof at all, as when convertible vehicles are introduced.

This production strategy works in other areas as well, such as in glass installation and chassis building areas, and eventually may be used to assemble vehicles as unrelated as an economy sub-compact and a pickup truck, all on the same line.

"The plant enhancements have made the facility more flexible and efficient," Fred Goedtel, Chrysler's vice president for Small/Premium/Family Vehicle Assembly, said. "The assembly operation now has the capability to build multiple upper bodies and multiple vehicle families or architectures, which will allow for the flexibility to add new models from other plants in order to better meet the dynamics of the market."

The key to the process lies in informing the robots grouped in a cell exactly what has arrived before them. The automated pallets bringing assemblies into the Sterling Heights body weld line carry a Versacoder, a proprietary optical encoder created by engineers at Comau Inc. (www.comau.com), the company contracted to develop the new assembly line.

The Versacoder directs the speed and direction of the transfer pallet to which it is attached, and its electronics also function as an identification chip. Once a pallet enters a welding cell, a reader identifies the code on the pallet, and relays the information to the computers that govern the cell's robots. The computer responds by switching to the appropriate weld program for that model.

There are still a few areas that require manual arc welding. David Taylor, Body-in-White Manager for DaimlerChrysler's Sterling Heights facility, said that the particular spot welds, which are in the rear quarter panel area on only one of the vehicles produced at the plant, need the special attention because of their location along the assembly process. However, he said he believes that a few alterations will bring the model to consistency with the rest of the plant.

Creating the Sterling Heights shop
The plan for the Sterling Heights plant was initiated more than two years ago, according to Neal Willetts, president and chief operating officer for Products and Technologies for Comau Inc. Comau, with decades of prior experience developing assembly lines for other vehicle manufacturers, was able to provide DaimlerChrysler a complete turn-key system for the Sterling Heights facility

Comau engineers designed and mapped every step of the new production line using RobCad (www.ugs.com). The same software permitted the engineers to program every robot in each workcell, and then run the cell through an animation simulation to check for problems such as robots colliding with one another or with any peripheral equipment. Any glitches then were corrected, and the overall operations were fine-tuned before the equipment was installed.

As an added precaution, Comau set up and ran sections of the assembly line on their own shop floor. By the time the DaimlerChrysler plant stopped production for retooling, all pieces for the new line were ready for fast installation and start-up.

When the plant shut down for re-tooling in May 2006, the body, paint and assembly shops were gutted of equipment used to build the previous Sebring model, with the exception of a pallet system that carries assemblies along the floor. Of the original array of robots, 112 were kept, and now work alongside 620 new units. There are 275 robots that carry spot welding end effectors, as well as pedestal spot welding robots and robot units that perform specific material handling duties.

The body weld line is arranged with several stations for a vehicle in process. Robots are grouped for efficiency and to avoid collision between units. With this set-up, six to 10 robots at one station can weld rear fascia and forward interior locations on a vehicle, then the vehicle is moved to the next station where eight other robots place welds around the door seams and engine compartment.

One of the benefits of the DaimlerChrysler Flexible Manufacturing Strategy is that the working life of the corporation's robots will be lengthened. Typically, a dedicated assembly line considers robots part of the tooling that needs to be replaced when the particular vehicle line is dropped from a company's line up. With adaptive assembly, DaimlerChrysler's new robots will be re-programmed for the production of a new line of vehicles, and have the potential to stay on the job for as long as 12 years.

The Sterling Heights plant was not DaimlerChrysler's first facility configured for Flexible Manufacturing Strategy.

A restructured facility in Belvidere, Ill., where the company builds its Dodge Caliber, Jeep Compass and Jeep Patriot models, became operational early in 2006. The company also has similar assembly operations in its Windsor, Ontario plant, and is exploring converting another plant in Mexico. DaimlerChrysler's retooling of its Sterling Heights and Belvidere facilities will allow the company to shift production back and forth between the two plants. The company hopes to be able to maintain production at 78 percent of the plants' capacity because of the flexible lines.

Frank Ewasyshyn, Chrysler Group's executive vice president for manufacturing, said during a 2005 management seminar speech that flexible robotics appear complex and costly, in reality they are neither. While there is a high degree of software engineering involved and the algorithms in the robots themselves are sophisticated, the technology comes as "standard equipment" with the robots.

"We're really not spending any extra money to get this new capability," Ewasyshyn said. "That's important for the Chrysler Group. We don't have the luxury of spending extra dollars for flexibility. Our mantra in manufacturing is ‘Flexibility is free.' Or, if not free, it had better be cheap!

"The real beauty of flexible robotics is in its relative simplicity. We're not depleting our capital budget to convert all of our plants, because we don't feel we need to. Instead, we're strategically implementing this initiative as we go — product by product, plant by plant.

"My greatest fear with technology is to make a huge investment on a generation or type of technology and then have to sit and watch the world go by for the next five or 10 years. You risk finding yourself in a pretty deep hole that can be difficult to climb out of. That's why we'll continue to move forward on an evolutionary track; one that we believe allows us to best leverage new technology as it becomes available."