Optimized brake line assembly

Axles, axles, axles. BMW produces more than 330,000 units annually at its Regensburg plant for various models in the 1 Series (3- and 5-door), the 3 Series Sedan and the M3 Sedan, the BMW X1 and X2, the 4 Series Convertible as well as the M4 Convertible and the BMW 2 Series GranTourer. Highly qualified assembly staff work in three shifts to ensure that the brake lines are correctly tightened on every one of the hundreds of thousands of axles. They receive important support from mechatronic torque wrenches of the MWR series (MWR stands for Mechatronic WRench) and Focus-61 controls, which Atlas Copco Tools has developed for industrial series production.

Werker informs - Assembly in flow
How BMW uses this intelligently networked technology can be clearly seen on an axle module for a 3 Series that has just entered the assembly station. The conveyor section represents an assembly cell in which nimble hands immediately begin placing hydraulic hoses for the brakes at the designated points. After threading their threaded connections, the assemblers tighten them precisely to final tightness using MWR's document-ready buckling wrenches. "The immediate feedback on the tool and via information screens in the cell gives the operators reassurance about the assembly result and they can move on to the next component," says Christian Böhm, Quality Assurance Specialist at Atlas Copco Tools.

Continuous documentation-safe data transfer
"The battery-powered MWRs transmit the torque and angle of rotation of each individual bolted joint to the Focus 61 control system installed in the station via radio data transmission in sync with the bolting processes," Böhm explains. The control system communicates with BMW's own production management and control system and knows exactly to which car the next incoming axle belongs. According to Böhm, BMW's production managers particularly appreciate the fact that the Atlas Copco system records all the tightening data in a fraction of a second and marries it to the data records of the respective vehicle without any intervention on the part of the workers. "The colleagues thus relieved can now concentrate entirely on the actual bolting process, and BMW still maintains an overview across the board." In addition, the values are still clearly traceable after many years, which is very valuable against the background of possible product liability issues.

Ergonomic production and testing tool in one
Because the coloured information displays in the employees' field of vision provide immediate feedback on each individual tightening result in the manner of traffic lights and also with the measured values, the assembly employees can immediately take countermeasures or make improvements if the strict BMW tolerances are exceeded. Because the handy MWR production wrenches weigh less than their predecessors despite their integrated radio modules, work has once again become easier thanks to better ergonomics.

However: "Ordinary torque wrenches confirm that a minimum torque has been reached, but overtightened bolted connections remain undetected," warns the quality expert. This poses a certain risk, especially in the case of safety-critical bolted joints, such as this one on the brake system. Structural changes in the material due to overloading during tightening could, in the worst case, lead to a lack of braking effect. This basic problem would not have been solved even by the semi-intelligent buckling wrenches of the next generation. Although the latter already monitored the torque, they were not yet able to detect, let alone document, the tightening angle.

Smart Connected Assembly
The fact that the combination of Focus-61 control and the MWR wrenches has a high optimization value for BMW was already recognized after the first joint tests with Atlas Copco Tools: Thanks to its trend-setting compatibility, the communication-capable screwdriving and testing technology could be integrated into the existing system with minimal effort, and all relevant data was transferred to BMW's data world without errors right away. Now there is no longer any mistake as to whether a screw connection is OK or not, confirm the production managers.