Body manufacturing for the Audi A3
The ultra-lightweight bodies of the Audi A3 and A3 Sportback are produced with innovative technologies on highly advanced manufacturing systems. The new N 60 production hall in Ingolstadt, in which 800 employees manufacture up to 855 car bodies per work day in three shifts, sets the benchmark for the automotive industry – including in its energy efficiency.
Hubert Hartmann, Head of the A3/TT Body Shop, calls the N 60 hall at the northeast of the Ingolstadt production site the “most advanced body manufacturing facility in the world.” It houses an impressive array of systems and equipment. 429 welding robots, 335 handling robots and 86 gluing robots work together here; many robots that join the individual parts, such as the wheel housing, are combined into groups. In many areas, bonding and welding are performed in one work step – which is referred to as spot welding/bonding; this saves time, cost and weight. All stations at which adhesives are processed are enclosed by closed cells from which solvent vapors are exhausted.
Two of the systems are special highlights, as Hartmann explains: “What is known as the Group Framer is used to join the large side wall frames to the body-in-white, after it has precisely positioned the parts for assembly. A laser brazing system joins the roof to them. The practically invisible zero gap join that this produces demands precision with a maximum tolerance of three tenths of a millimeter.”
Optical laser measurement systems, which consist of several stations, monitor all of the car bodies during their production. The first stations check the individual weld sub-groups, while the latter check the finished assembly; over 4,000 key points are checked altogether. The finished bodies with add-on parts are inspected 100 percent for seam flushness. A tactile measuring system, which samples over 100 points, takes representative measurements of entire body assemblies or individual components.
Hall N 60, in which Audi has invested around 340 million euros, is a massive structure – the concrete used to construct it would be enough to build over 3,000 single-family homes. At a length of 219 meters (718.50 ft) and width of 134 meters (439.63 ft), it offers around 60,000 m2 (645,834.63 sq ft) of useful floor area, as much as eight soccer fields. A full 30 meters (98.43 ft) tall, the hall contains two production levels, each eight meters (26.25 ft) in height plus seven meters (22.97 ft) for the conveyor equipment. At the very top are the supply pathways with lines for ventilation, media, gases and electricity. The logistics building in the north area, which offers 4,300 m2 (46,285 sq ft) floor area, acts as a transfer and distribution area. Housed in two ancillary buildings are offices, break rooms and various technical areas.
The hall is very bright – its north facade integrates windows with over 2,000 m2 (21,528 sq ft) surface area. The lighting concept is completed by 3,000 fluorescent lamps, and motion detectors automatically switch them on and off. At night, the hall is thoroughly ventilated, but during the day the windows remain closed for energy reasons. The ventilation system, which consists of 16 individual modules, exchanges 1.6 million cubic meters (56.50 million cu ft) of air per hour without workers feeling any drafts or cold air. That would be enough air to fill 320 hot air balloons. Heat wheels that exchange cold and warm air reduce energy consumption.
Installed on the roof of the new production hall is a photovoltaic system; it converts sunlight into electrical energy over its 7,500 m2 (80,729 sq ft) of surface area. It generates around 460,000 kWh of electricity annually, the majority of which is used in the hall. This amount, which would cover the electrical energy needs of a moderately sized neighborhood of single-family homes, avoids 250 metric tons (275.58 US tons) of CO2 emissions. Seven percent of the electricity used for body manufacturing in hall N 60 goes to lighting, 27 percent to ventilation, and 28 percent to heating. The lion’s share of 38 percent supplies the manufacturing systems.
The equipment is all state-of-the-art. The robots are more compact and lighter than the previous robots; the roof framer with its large moving masses consists largely of carbon-fiber-reinforced polymer (CFRP), which makes it 70 percent lighter. The drives for the welding electrodes use electric motors – they are faster, more precise and more rugged than the previous pneumatic drives; their quiet operation also makes a significant contribution towards lowering noise levels in the hall. They are cooled by process water; a heat exchanger improves efficiency in this circulation loop.
The lasers that Audi uses are also the latest generation and particularly energy-efficient. Instead of the usual solid-state lasers, compact and powerful disk or diode lasers are installed, and their efficiency is significantly higher. An especially complex process is the remote laser welding of vehicle doors, which is performed in an enclosed cell. A robot guides the laser beam with swiveling optics, and jumps extremely quickly from one weld to the next – in just 26 seconds it completes 50 narrow, lightweight and precise welds, each 25 mm (0.98 in) in length.
Each manufacturing cell in A3 body manufacturing has a display that visualizes its momentary electrical or compressed air consumption. This lets employees detect potential losses quickly, so that they can then correct them. The vertical conveyors that transport the bodies recover energy during braking; this saves 86,000 kWh of electricity – equivalent to the annual consumption of 25 single-family homes. When the body manufacturing facility switches to standby mode over the weekend, an intelligent shut-down strategy just keeps the most important computers and switchgear energized. This reduces weekend electrical consumption by 80 percent.
When it comes to cleanliness, Audi is also embarking on new paths: The sweeping machines - equipped with coconut brushes and vacuums - clean the systems and the hall floor without any chemicals. Altogether they keep around four kilometers (2.49 miles) of driving lanes and corridors clean. At the station where the roof zero gap join is ground, custom-built suction devices with brushes and vacuum cleaners remove several kilograms of dust from the system every week. Hubert Hartmann: “Our body manufacturing facility is not only the most advanced in the world, it is also a very clean operation.”