Nearly everyone who’s driven the new F25 X3 has remarked upon its solidity and high-quality feel. Indeed, the new X3 might be the best-built BMW ever thanks to an unprecedented degree of automation in the body assembly process. By using robots to perform tasks previously done by humans, BMW is achieving greater precision while also reducing the injury rate among assembly line workers.
“We’ve gone from about 30% automation to about 98%,” says Bobby Hitt, spokesperson for BMW Manufacturing in Spartanburg, South Carolina. “What we really see the machine as doing is helping us with increased volume and quality. Humans can’t do what those machines do.”
What the machines do, of course, is to build new X3s to an exacting standard, something for which the original X3 wasn’t really known. To improve the vehicle once built under contract by Magna-Steyr of Austria, BMW brought production of the new F25 in-house to Spartanburg, to the line that built first-generation Z4 roadsters. (Production of the second-generation Z4 now takes place in Germany.)
Normally, the introduction of a new model would mean a complete line replacement using all-new equipment. For the F25 X3, however, the associates (as BMW terms its employees) managed to engineer a state-of-the-art body assembly line using much of the existing equipment from the old Z4 line: conveyors, platforms, lights, air lines and even 120 assembly robots.
“With each life cycle, we’re keeping our assets, spending more wisely on capital investment and integrating more components into the existing line,” says Chad Johnson, project manager for the X3 body shop. “It makes it more difficult for engineering, but the capital savings should get us into a better position.”
Instead of donating them to a technical school as might otherwise have been done, BMW was able to refurbish and reprogram 120 assembly robots from Z4 production to build X3s, extending the life cycle of each robot from seven years to 15 and saving millions of dollars in the process. Built by ABB of Norway, the six-axis robots could actually be used far longer were it not for advances in control technology.
“After two life cycles, there are so many technology changes with the IT, not the hardware, that you have to ask whether it’s obsolete or not,” Johnson says.
Even though they’re no longer new, the robots are performing cutting-edge functions designed to increase the accuracy of X3 body assembly while improving ergonomics for the line workers.
“Traditionally, a lot of the robotics were driven by the way we used to build cars,” Johnson said, explaining that body shop workers had previously been required to lift heavy weld guns and large parts like hoods and tailgates, which often led to injury.
Humans were eliminated from much of the welding process some years ago, and these days, they MIG-weld only a few spots the robots can’t reach. The X3 line takes that a step further by having the robots do the heavy lifting, as well. Where assembly line workers were previously required to handle heavy objects like the 45-pound doors whose weight is compounded by an awkward size and shape, today that work is done exclusively by robots, leaving humans to lift nothing heavier than a screw gun or the front fender that weighs just seven pounds.
In addition to their ergonomic advantages, robots perform their task exactly the same way every time, improving the quality of construction by eliminating a variable.
“From a quality point of view, to make a process repeatable by a human being is very difficult,” says Don Dickerson, who led the design and engineering of the X3 production line. “The fitting process is very difficult, and it has to be performed precisely to eliminate variations. With a human, you add a massive variable.”
Part I: Body
You also add to the likelihood that delicate body parts will be damaged in assembly. “The significant change between an automated and a non-automated process is the person who’s handling the door,” Dickerson says. “They bump it and bang it and do surface damage, but the robots do it exactly the same and they don’t touch the surface or damage the part. That’s a major quality improvement."
Another major quality improvement, also unique to the X3 line, comes from the use of lasers to guide parts into place and confirm correct fitment.
While each X3 body is built to exacting standards and minimal tolerances, variations exist that are invisible to the human eye but detectable by lasers trained to see crucial points relative to the attachment of “hang-ons” like doors and hoods.
“The lasers know exactly where the part is and where the car is, and they self-correct for quality,” says Johnson.
As we watch a robot pick a door from the stack alongside the assembly line and hold it in place, a human associate attaches it to the X3 body using a screw gun pre-set to 66 Newton-meters (49 lb-ft) of torque. He hasn’t had to lift the door or twist his body to get it into position, nor to enlist another worker to hold it while he bolts it on. That means fewer workers—just five instead of 16—are needed to build X3 bodies than were needed for the Z4.
Nonetheless, Johnson says that the workers themselves were fully on-board with the increased automation, even working to facilitate its adoption in the final finish stage of production. No one, he says, has been laid off in favor of robots—most moved over to final assembly, which is less automated than the body shop and which employs more people thanks to the higher production volumes enabled by automation elsewhere. “None of those 11 associates left this facility,” he says, “but it did avoid some hiring. For the people who were here, there was no disadvantage to helping with that efficiency program, and it eliminated potential ergonomic and safety issues.”
Overall, few body shop associates do manual labor any more. “We still have plenty of people, but they’re minding the machines,” Hitt says. That means tending to the robots’ mechanical, pneumatic and hydraulic components as well as taking care of the computers that control them.
“The associates have to be more computer-minded,” Johnson says. “They have to know mechanics, too, of course, but also a lot more programming.”
Johnson himself started as a welder after studying industrial engineering in college. After a stint at Bosch making fuel pumps, he joined BMW when the plant opened in 1992.
“I took an hourly job and worked my way up,” he says.
That sort of background is crucial, Hitt says, because understanding the manual process facilitates efficient assembly processes and effective use of automation.
“They understand what the machines are doing,” Hitt explains. “It’s not some engineer sitting somewhere else around the world designing the layout that they implement. They are inside the minds of the machines, because they have done it the old fashioned way. Any time you look at advanced technology, you need to have people who have a ‘then and now’ mentality. If you don’t, you might go to far into what’s not feasible, because you don’t understand the limits of the machine or what the machine is really doing.”
Part II: Paint
Precision in the paint shop
Johnson’s progression from hands-on welder to body shop project manager is mirrored by the similar journey undertaken by Michael Davis, who started painting
car bodies by hand 15 years ago and now runs the Integrated Paint Process at BMW Manufacturing.
“I can still paint if I want to,” Davis says, “But I like working with the robots and working from that side. The work has gone from being more hands-on and physical to being more mental.”
The fully automated Integrated Paint Process, or IPP, is a marvel of efficiency, not to mention safety and environmental friendliness. Having first been used to paint MINIs in England, it’s now being applied to all BMWs built at Spartanburg: X3s, X5s and X6s.
Once SAV bodies are completely assembled and finished but before their ancillary components like engines, transmissions and suspension components are installed, they’re put through a bath of green “e-coat” that combines rustproofing, sealer and primer into a single layer of material that is then baked on.
The e-coat eliminates the old two-stage process, which required both a separate application and subsequent baking for the rustproofing and primer layers. Combining these two processes saves time and energy as well as chemical waste, savings that are echoed in the IPP. Although the water-based color and clear coats are still applied separately, the paint process itself is more efficient than ever thanks to a brand-new cartridge system from ABB.
Davis says that BMW Manufacturing is the first in the industry to use the cartridge system, although Toyota is using a similar bladder-type system in its factories. The cartridge system allows a car to be painted any color as it comes down the line, regardless of which color was applied to the car before it, and it uses less paint than ever as well as fewer cleaning solvents.
“The old process had a 20-foot tube of paint that had to be cleaned between color changes,” Davis says, “but the cartridge-based IPP system loses just 1-2cc of paint per vehicle and needs just a 3cc wash. We don’t purge any more. And the system learns. As it’s painting a vehicle, it’ll actually gauge how much paint is left, and it’ll reduce how much is in each cartridge.”
As they do in the body shop, robots are able to perform their tasks better than even the most highly skilled human, as verified by laser measurement of paint thickness.
“The accuracy is unbelievable,” Davis says. “With the older paint style, you have little peaks and valleys in which you see shifts of 3-6 microns. With the new style, it’s almost flat, with variations of only one or two microns. It’s practically nonexistent, and it surpassed both what ABB told us and our own expectations.”
Perhaps even more important, the use of robots in the paint shop eliminates human exposure to some of the most hazardous conditions in any auto plant.
“All of those hazards are gone—VOC exposure, carbon monoxide—and the amount of time the associates are involved with solvents for cleaning has been reduced, as well,” Davis says. “Humans are now pure operators. Even the manual zone isn’t really a manual zone. It’s more of a manual inspection in which we walk around, look and make sure the car’s paint is formed like it should be. There’s no touch-up any more. I was skeptical, but the electrostatic application is just so much better. It gets all the nooks and crannies, and there’s so much less waste.”
That’s what automation is really all about: using robots to perform tasks that they do with greater accuracy than humans, eliminating inefficiency while improving quality. It also makes an auto plant a safer place than ever for its human operators by reducing their exposure to chemicals and other physical hazards, making increased automation a win-win for those who drive the cars and those who build them.
Part III: Assembly