Manufacture by the minute

The EQC rolled off the production line in Assembly Hall 9 at the Mercedes-Benz Bremen plant in May 2019. The new, all-electric vehicle was integrated into regular series production. A look behind the scenes of the flexible production.

"Watch out for the forklifts," warns deputy supervisor Marc-Oliver Ellger on the way to the battery joining center. You can't really miss the orange forklifts which criss-cross the aisles here like busy ants. Unless you get distracted by the spectacle taking place above your head: shining car bodies glide through the air on rails - on what is essentially a second level of the spacious hall. "Like a string of pearls. It never ceases to amaze me," states Marc-Oliver Ellger, the deputy supervisor who leads a 39-strong team on today's shift. The pearls move on to the next station by the minute until, at the end of their journey, they roll into the final inspection area, complete with all their seals and shock absorbers, windshields and wing mirrors, suspension, wheels, and activated electronics. The product diversity at the Bremen production plant is something to behold,especially in Hall 9: models rolling off the production line here include the C-Class Sedan and Wagon, the GLC and the GLC Coupé, and the EQC, which joined in May 2019.

This means that a vast range of drive types is now represented here: gasoline models, diesel cars, plug-in hybrids, and HV battery vehicles are assembled on the same line. The plant, which received the "Automotive Lean Production Award" among other honors in 2017, is a prime example of flexible production. What does that actually mean?

Electric goes in series

"At the beginning there's always the question of how to integrate a new vehicle into regular series production. We do technical planning for this," explains Markus Völkel, who as the plant's Project Lead is responsible for new model projects. "Here at the site, we also ensure that the workforce has the necessary qualifications and that the plant processes are adapted appropriately. This isn't that easy, since to do this we have to forecast a model mix based on how many vehicles of which type we think we'll sell in the next year."

Markus Völkel is responsible for the new model projects at the Bremen plant.

The assembly sequences get realigned as well. A jigsaw puzzle: particularly since the sequence of operations for an electric car is not the same as that for a vehicle with a combustion engine. Not least when it comes to the battery installation process. "To continue working by the minute, we have to define the activities that need to be performed for everyparticular vehicle model at each station, right down to the finest detail."

One of these stations is 'mechanization', also known as the 'marriage' in auto-construction circles: this is where the car body is joined with the suspension, transmission and engine.This joining process is fully automated in Bremen. Enclosed by blue cages, meter-high industrial robots heave the heavy vehicle parts upward and bolt them to the suspended car body. This is where the EQC gets its two electric powertrains instead of the transmission. A machine operator from Marc-Oliver Ellger's team tracks the process on the monitor, checking that all the joins are correct.

Ready for the '2nd marriage'

The car bodies, with their freshly installed suspension components, then glide on toward the battery joining station, the newest station at the plant. Here a sensor detects the EQC as an electric model before the vehicle gets positioned. A poster proclaiming "So fährt sich die Zukunft" ("The future of driving") hangs next to a monitor showing the next three models which will soon pass through the station. The operator feeds the bolts into the machine and returns to the control screen. An AGV – automated guided vehicle – approaches the joining center and deposits the heart of the EQC: the 650-kilogram lithium-ion battery.

The by-the-minute process continues: the body comes in and is deposited on a frame. Support arms lift the battery onto the vehicle floor from below. Once the two frames are lined up exactly, the bolting begins – this is the 'second marriage'. "The machine operators prepare for the new machine by attending special training courses," explains Marc-Oliver Ellger.

Further tasks at the station include: monitoring the installation process of the batteries delivered from the Kamenz production plant and logging everything. "All employees who come in contact with the battery at any stage of the process receive appropriate training on dealing with electricity," states Marc-Oliver Ellger.

The team tags along

No doubt: assembly in Hall 9 gets more and more complex with each new model. “Try to search for two equal cars in this hall. You won’t find them,” explains Markus Völkel. This is due to the large variety of models and drives, but also the special equipment.”

Most of the employees rotate several times during the course of their shift, meaning that they regularly switch to another station. Ergonomics is a key word here. Then there are the different control concepts, which are typical for flexible production. "Everything we do here has the goal of meeting current market demands and customer requests as precisely as possible. This applies to all vehicles from combustion-engine models and plug-in hybrids to our EQC and the AMG variants, our high-performance vehicles," explains Michael Feldhaus, responsible for the assembly process in his role as floor manager.

Michael Feldhaus in the assembly hall.

In order to react flexibly to customer demands, the machine operator from the battery joining center is also qualified to work at another station parallel. Somewhere else so-called "tag-along" teams of various sizes are deployed, so that they can accompany a certain vehicle model through several stations.

All of this makes working in assembly more diversified, but also more challenging. "There are more and more tasks to deal with, new developments in vehicle architecture are being made all the time, and networking increases," says Michael Feldhaus. "That's why we constantly invest in the further qualification of our employees at this plant."

Digital bakes better

Advancing digitalization also helps to manage complexity. Instead of large assembly posters filled with information, the paperless factory has monitors from which the team can read off the main operations at each station. "It's a bit like baking bread. If you only bake one type, it's easy to remember each step of the process. But if you add pies and cakes into the mix, things get more complicated", says Michael Feldhaus. "A digital kitchen aid which tells us what to do step by step ensures that the desired end product comes out of the oven." The auto industry is using more and more digital tools, which specify the work steps, control processes themselves using sensors, and then log everything.

What does it mean for employees when machines take an increasing amount of their original work away from them? "It largely depends on which unit they work in", explains Feldhaus. "Engineers and foremen need to master data analysis above all - so that they can ensure process continuity by implementing the right measures in the event of disruptions. The priority for production employees on the other hand is to get used to working with digital media and machines. This enables us to react quickly and flexibly." Marc-Oliver Ellger confirms this: "There is an increasing number of areas in assembly where a team member now monitors the process rather than intervening manually. This requires a much better technical understanding."

“Currently we are using robots mainly for lifting heavy parts or work steps overhead,” explains Markus Völkel. “However, those robots are only able to move in a defined area. They are blind and deaf.” The next generation is sensor-equipped. It can perceive its surroundings, and thus also people, better.

The direction of the journey becomes clear on Line 41 in Hall 9, where Zübeyde Genc is instructing the station robot to pick up the suitcase-size battery for the car body of a plug-in hybrid, which will arrive at the station soon. She uses a control panel to position the robot's gripper arm, which transports the battery through the vehicle's narrow trunk in one fluid movement before depositing it in exactly the right position, so that Zübeyde Genc can insert the bolts. It's ultra-precision work, which a robot can reproduce far more quickly and accurately than a human. And it's an amazing and flexible division of labor between human and machine. Because flexibility is more indispensable than ever in multi-line production at the Bremen plant.

In the future, robots will be able to operate more precisely. The latest installations are already screwing in screws with a slightly jerky movement, as a human being would do. Nevertheless, they have difficulties with parts that do not have a clearly defined behaviour. "Laying a cable or untangling a knot", for Markus Völkel this is no question: "People are simply unbeatable in this respect!

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