Automation in car body construction at the Mühlacker site

_{^{10.07.2020 I Hannah Pospisil}}

Whether as a systems partner for components in the auto industry or for automation solutions for electric storage and drive systems - thyssenkrupp has a wealth of know-how and experience in plant construction. In car body manufacturing, our colleagues in Mühlacker, Baden-Württemberg, used up to 220 robots in a fully automated production line.

In March 2017 the divisional turning point was reached for the construction of the thyssenkrupp Mühlacker site. Since June 2018, a 60,000 m² site has been under construction body platforms for electric vehicles of the Porsche brand.  175 employees currently supervise the fully automated production with around 220 industrial robots. In cooperation with the automated helpers, the entire process chain of body production is mapped out – from the design of the tools, through the construction and commissioning of the fully automated systems, to the production of prototypes and series bodies.

Initially the production volume was 160 bodies per day. In the meantime, automation has increased the number of pieces many times over. A success story: We asked our colleagues from System Engineering what they had done to equip their production halls for the automotive industry of tomorrow.

Success with a variety of technologies

“Apart from laser technology, we offer the entire spectrum of joining technologies for car body construction,” explains Gregor Borner, sub-project manager for automation in the Car Body Technologies Division.

“Here at the site, for example, steel pressed parts, tubular elements, extruded profiles, aluminium sheets and injection moulded parts are combined. When planning the plant, we therefore had to consider above all how all these forms could be combined economically with each other”.

The number of technologies required is correspondingly high: from spot, friction and MigMag welding, clinching and riveting to flow punch screws or gluing, everything is represented. “A total of around 4,500 joints flow into a car body,” explains Marcel Dietz, Head of Maintenance. “That alone is 68 meters of adhesive seam per vehicle.” Because of the many aluminum parts, about twice as much is bonded as in classic steel body construction, the only way to ensure the necessary stability. “Particularly with regard to lightweight construction, the large-area adhesive application makes a car body particularly stiff, and very safe in the event of a crash,” says Dietz.

Currently, a trend towards such adhesive joints can be observed in car body construction. “But alone, this technology is not yet fully trusted,” adds Borner. This is why the Mühlacker site cannot yet do without the diversity of the other joining technologies.

More than just body construction: The plant of tomorrow

“The outsourcing of processes is increasing among automobile manufacturers, while at the same time the classic body-in-white is declining,” says Borner, describing the current trend. As a result, suppliers such as thyssenkrupp System Engineering are being used as an extended workbench, while for auto manufacturers part of the risk is being transferred to the suppliers.

The responsibility of the experts at thyssenkrupp System Engineering in Mühlacker therefore goes well beyond pure body-in-white production. “In response to the requirements of the auto manufacturers, we must constantly adapt our portfolio and find the right balance to incorporate new topics and further develop our know-how and processes,” says the maintenance manager. “For us, having our own production facility in Mühlacker offers a good opportunity to accompany production engineering and automation over a longer period of time – and to transfer the experience gained to the lines we supply to automobile manufacturers and co.”.

Proven automation technology: When robots are at work

“One important point: There are enough programmers for our control technology,” adds Dietz. The degree of automation at the Mühlacker plant is therefore very high. All systems are designed to run for as long as possible without the intervention of employees – usually between 30 and 60 minutes. Almost 40 modern S7 control systems are interlinked at the plant. With the help of these control systems, the plants independently monitor and record the quality of the incoming parts, the respective process steps and the manufactured products – entirely in the spirit of a Smart Factory.

“With PLC technology (programmable logic control) it is possible to trace in which vehicle a certain part is installed,” says Dietz, explaining the advantage for quality assurance. “Even every single weld spot is recorded.” Thus, the employee receives feedback immediately after a production step as to which spot needs to be checked or reworked, if necessary. In addition, the semi-finished tools are also randomly tested during production.

Once they have been fully assembled, a complete measurement report is generated for each body platform. A robot-guided measuring system checks around 160 to 180 measuring points for this purpose. “The tolerances are less than a tenth of a millimeter,” says Borner. “That’s pretty little when you consider that we have assembled more than 200 individual parts by then.

Strong robots for heavy loads

For the robots, the experts in Mühlacker have consistently opted for models from Kuka. The exception is nine heavy-duty ABB robots, which take the car body platforms from one station to the next and lift them over the safety fences into the respective plant areas. They transport loads of up to 550 kg on specially manufactured linear axes from the manufacturer FEE.

“Because the quantities in our production have increased, the transport capacity of our heavy-duty robots is now quite exhausted,” explains Dietz. “In order to take the reduced cycle times into account, we are therefore now sometimes using two robots per linear axis. “Almost every centimeter of production space is used, and yet our robots are surprisingly mobile,” says Dietz.

The future of the systems depends in part on the acceptance of the electric vehicles produced. “We have very future-proof systems here at the plant and are therefore well positioned for follow-up projects,” assures Dietz.

_{Source (German): “Kernkompetenz fügen in allen Formen”}