During the tightening process itself several parameters are recorded by the electromechanical nutrunners (for example the torque with which the screw is tightened) and compared with the respective setptions from the screws database. If all the joint of an assembly station have been made correctly, the nutrunning station automatically returns to the home position and is ready for the next drive unit. If one of the joints is faulty, the worker can correct it afterwards providing his work cycle gives him enough time to do so, or he has to acknowledge the end of the work cycle manually. The data of every single joint are transferred to the screws data server and saved additionally in the PC of the nutrunning station. These data are also transmitted wirelessly by the radio link of radio modem and leak wave conductor.
The PC of the nutrunning station receives the ID number of the respective powertrain from the plant PLC for every new work cycle. This tells it among other things which engine-gear combination currently has to be processed and the appropriate user guidance menu is displayed.
Eliminating faults and errors
The Siemens specialists have come up with a special solution for the workstations at which different sized screws are used. One example of this are the joints of the on the gear shaft. The necessary sockets of different sizes are located in a selector box with a LED indicator. The worker is promoted to change the socket at just the right time in the work procedure and a flashing LED ensures that he chooses exactly the right socket.
If he takes out the wrong socket, the assembly process is blocked and an error message appears. The further process is also blocked and an error message displayed, if the socket is not put back in the right place in the selector box after screwing. Time-wasting operation errors are therefore largely ruled out and clocking of the assembly line is guaranteed.
The final stage in the drive unit assembly is a workstation, which serves to check all the previous work steps and repair any defective joints. The user guidance on the LCD shows all the work steps and highlights those for which a not yet corrected defective screw connection has been registered. Since the majority of screw connections are okay as a rule, the worker at this station has enough time to deal with the unsolved problems. When he taps a workstep marked defective on the touchscreen, the appropriate user guidance menu opens and the worker can see at a glance which joint needs rework.
Fully automatic
The fully assembled powertrain units finally run on a roller conveyor into the adjacent assembly hall, where they are added to the married chassis and body. First they are placed on a new workpiece carrier, on which the whole chassis including rear axle and exhaust are then assembled. In the next step, the chassis components positioned exactly on the workpiece carrier are fit precisely into the body lowered from above and then connected to the chassis in several nutrunning stations. Where numerous manual processes were necessary for connecting the chassis and body in the previous Passat production, which sometimes entailed undergonomic overhead work, this process now runs fully automatically and without manual intervention.
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