Volkswagen AG, Emden (Deutschland)

Published in: Move Up 1 / 2005

Intelligent nutrunning stations at VW

Travelling nutrunners

The introduction of a new model is often the instigator for updating the existing production technology and investing in new solutions. VW took the generation change in the Passat series as an opportunity to install an almost completely new assembly line at their Emden factory which sets new standards from the production technology to the automation. An interesting aspect here is the assembly line for the powertrain units of the new Passat in which Siemens has implemented a new kind of nutrunner technology with built-in intelligence and visual user interface.

The VW factory in Emden is one of the largest employers in the region with a staff of near 10,000. The legendary "Beetle" of which 2.4 million were built once rolled off this line to be shipped directly to the USA from the nearby port. The T2 and T4 series of the VW transporter were also produced at the VW site in Emden with its ideal situation for worldwide export. Just like the small transporters Kurier and Taro and the US versions of the Audi 80 and Santana limousines.

Since 1977 Emden has above all been the production site for the Passat of which the sixth generation is since being built. The factory works in close cooperation with other VW sites especially in Germany and Poland and procures parts from about 660 suppliers of which nine deliver just-in-time and are located partly in the immediately vicinity of the factory.

New model, new production technology

VW took the preparations for the new Passat generation (B6) in Fall 2004 as an opportunity to update large sections of the two Passat assembly lines at the Emden factory and bring them up to the latest state of the art. A job for which Siemens was chosen as general supplier.

In the course of a project lasting several months all the plants in the area of the powertrain pre-assembly, the conveyor technology and above all the fully automatic chassis assembly were designed and planned in detail first. Siemens cooperated with the central VW planning department in Wolfsburg and was in close contact with the on-site production planning department ultimately responsible for a trouble-free Passat production in Emden throughout the project. Despite the project's extraordinary complexity, the prescribed deadlines were extremely demanding.

In addition to the project management, the complete automation and control technology for numerous newly designed production steps were central issues of the project in which Siemens was able to exploit its wide range of products. As a general supplier Siemens also used external providers specifically. The Siemens Projects Automation Industry based in Nuremberg together with the Frankfurt branch were responsible for management of this project. This Siemens division had already handled several large international projects in the automotive industry in the past and therefore has wide experience for a project of this size.

Nutrunners which are always on hand

A particularly fascinating solution was chosen in the section of production in which the powertrain of the new Passat is assembled. Here the engine block and gear have to be fitted with the drive shafts and springs and all peripheral engine components so that a functional drivetrain is finally produced which is ready for installation in the body.

Until now the individual components of the powertrain unit had to be mounted using various nutrunning systems - from handheld EC nutrunners to pneumatic nutrunners - which hung down from overhead rails and had to be pulled to the respective working position by the workers. An assembly technique which not only demanded constant physical effort but also caused a lot of noise. Besides there was no way of ensuring and documenting the correct execution of the screw tightening process.

The former nutrunning systems have now been replaced by totally new, mobile EC nutrunning stations. They not only relieve the worker physically. They also produce a lot less noise and introduce a previously unknown intelligence which ensures a consistent quality level with a high repetitive accuracy.

Every nutrunning station is designed as a suspended unit which runs in an aluminum section rail and is driven within the assembly station by a motor. The feed is synchronized exactly with the movement of the push-pallet so that the workstation automatically follows the position of the workpiece carrier on which the drive unit is positioned. At the end of the line of an assembly station the nutrunning station automatically returns to its home position and is positioned exactly parallel to the next workpiece.

The exact position of the nutrunning station is defined by perforated rails running parallel to the carrier section which supply an absolute path-actual value. The S7-200 of the individual nutrunning stations communicates with the plant PLC over a radio line consisting of a leak wave conductor and radio modems. The path-actual value of the skid conveyor is synchronized with the nutrunning station among other things and the drive is controlled accordingly. The communication between the Siemens frequency converter Sinamics and the scanning head on the perforated rail of the screwer station takes place via RS485 interfaces. A manual forward and reverse of the nutrunner unit which the worker can control with buttons is also possible within the respective workstation in addition to the fully automatic operating mode.

The nutrunning station runs on four rollers. It is driven by a Vulkolan wheel which is pressed against the carrier rail by a spring. If a resistance of more than 150 Newton occurs - for example due to overloading or collision - the preliminary drive of the assembly is stopped automatically. The frictional connection between the motor and the drive wheel is made by an electromagnetic clutch which automatically breaks the connection in the event of a power failure or at the press of a button to stop the screwer station from moving.

Visual user guidance

Every nutrunning station incorporates a PC on which the program for guiding the worker and controlling the screw tightening process. A color LCD with touchscreen forms the user interface. At the beginning of the work process the drive unit to be processed appears on the display (different motor-gear combinations are mounted in mixed mode). The joints assigned to the respective assembly station are shown in blue.

As soon as a joint has been made correctly, the color of the screw concerned changes to green. If, on the other hand, the system has registered a NOK status, the joint is marked red and an appropriate warning is displayed.

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 setpoints from the screw database. If all the joints 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 screw 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.

Faults and errors ruled out

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 prompted 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 operating 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.

VW was soon convinced by the new nutrunning stations and has already decided to use this innovative technology in other assembly areas for the Passat B6.

Fully automatic marriage

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 unergonomic overhead work, this process now runs fully automatically and without manual intervention.

For Siegfried Rossdeutscher, Head of Production Planning Assembly 2 at the VW factory in Emden, the production technology for the new Passat is a decisive step towards more ergonomic workplaces and a further increase in precision. In addition, the new nutrunning stations for the powertrain assembly also integrate a continuous quality assurance directly in the manual work process for the first time."

He expressed great satisfaction with the smooth cooperation with Siemens and praised the committed team who has set up their own base camp directly on site for the duration of the project.

VW site Emden

The factory was founded in 1964 as a CKD assembly works for the VW Beetle. The initial production capacity of 600 units a day was later expanded to 1200 units in a two-tier operation.

In addition to 2.36 million Beetles, about 266,000 transporters (Type 2 and 4), 358,000 Golfs and 289,000 Audi 80s have been produced here. Since 1977 the Passat has been rolling off the assembly line above all as a station wagon and a limousine, with 4.4 million units to date.

The VW factory in Emden covers an area of 4.1 million square meters, 1.5 million square meters buildings, and employs almost 10,000 people. The production steps range from pressing works through bodywork and painting to body assembly and final assembly.

Essential chassis parts are delivery from Wolfsburg and Brunswick. The engines come from Salzgitter, Ingolstadt and Györ. Other sheet metal parts, coolers and gears are provided by the Hanover and Kassel works. Plus 660 suppliers of which nine work just-in-time and are partly based directly on the works premises.

The port of Emden has developed into one of the biggest automobile loading ports in Europe. 450,000 VW vehicles are shipped from here all over the work every year. 33 percent to the USA alone. Total vehicle production is 800,000 cars per year.