Process to perfection
Efficiency levels at Volkswagen’s transmissions plant have soared following the installment of a state-of-the-art RFID system
With around 13,000 employees, the Volkswagen Kassel plant in Baunatal is the second-largest German manufacturing site and also the leading transmissions plant of Volkswagen AG. In addition to centralized original parts supply, this industrial hub concentrates on the production of exhaust systems and chassis parts for vehicles rolling off the Passat, Golf and Polo platforms, as well as around three million manual and automatic transmissions a year.
The ancillary light-alloy foundry is the largest in Europe and supplies the necessary aluminum and magnesium housing parts. As a result of continuous investment, the Kassel plant represents state-of-the-art production technologies, outstanding quality and optimal production logistics. In fact, Volkswagen broke new ground with the construction of a new assembly line in Baunatal on which the rear axle transmissions for Audi and the VW badged cars, such as the Phaeton, are produced.
“We have been backing RFID technology from Siemens in transmission manufacturing since 1987,” says Alexander Hermann, production planning for transmission assembly at Volkswagen in Kassel. “Our first system here was Moby M. We are now working successfully with the third generation.” Code-named the Simatic RF300 system, this third-generation technology from Siemens has been in use throughout the production of rear axle transmissions at the VW plant for more than a year.
The promised benefits of the RFID technology meant that its implementation in the transmissions plant was soon realized in the form of a pilot application. The assembly line was comprehensively automated by Lubach Engineering. With 10 employees, this company specializes in industrial systems in the automobile and paper industry.
The decision to make use of the RF300 system was made easier due to the fact that the mobile tags corresponded to those of the predecessor system, Moby I. “It was important for us to be able to accommodate the relevant data volumes on the tags without having to make any additional investment in this area, or even having to completely rethink the solution,” adds Hermann.
However, the decisive factor for the changeover turned out to be the higher performance capability of the RF340R read/write devices, simply because they are three times faster at reading and writing than the Moby I predecessor system. A total of 37 read/write stations have been installed in the new rear axle transmission production system, and this means that the benefit multiplies to a productively quantifiable time gain.
Shorter throughput times
“Three seconds of the processing times of the machining stations are reserved for reading and writing the data,” states Hermann. “With the high-speed RF300, we still manage to read out the data on 80% of the stations in the bay. Along with other optimization measures, this has made a significant contribution towards substantially reducing the throughput times on the new line compared to the other systems.”
At the entry to the line, the identification number for the ordered transmission and the required recipe are written to the tag and combined with a processing pallet number. The Simatic RF350T mobile tag offers 32KB of RAM for this purpose. When the pallet reaches a machining station, it is stopped and the tag is read. To save time, the read/write device reads only the data record that is relevant to the processing steps. After the relevant instructions have been followed, the components are tested and acknowledgement-specific production and quality data (such as tightening torque and angle of rotation for screws and slot widths) are written to the tag of the processing pallet.
Such a process allows for gap-free documentation and so the most important production and quality data is created in the production sequence. At the end of the line, this is transferred to the higher-level MODEAS system for archiving and quality tracking at Volkswagen. “By using the RF300 system, we were able to reduce the processing time of the individual stations by up to 20 seconds,” says Gerson Lubach, CEO of Lubach Engineering. “No sooner have the pallets entered the machining station than the machine powers up. With the old system, you could stand and count the seconds until all the necessary data became available.”
The RFID system from Siemens’ sensor range was a fundamental and consistent choice for the automation provider. Apart from the fact that Siemens is a specified vendor at Volkswagen, the Simatic RF300 system – as the official successor to Moby I technology – not only offers cost benefits, but is also characterized by its level of integration with other automation and drives. For example, on the Simatic MP277 Touch Multi Panel that is used for operating the individual stations, an off-the-shelf diagnostics screen can be used for the RF300 system. This is based on Transline HMI Lite CE, software from the Siemens Transline range for engine and transmission manufacturing plants. The vendor’s sensor specialists adopted the HMI Lite pilot project for RF300 diagnostics under the Simatic WinCC flexible configuring and visualization system. Lubach Engineering simply had to adapt the screen form to the specific application at Volkswagen.
The diagnostics screen shows the status of all RF components on Profibus so that the operator can see at a glance whether a read/write device has failed, or a tag is simply faulty. “The development of an integrated automation system was also decisive for us because we had to integrate machines from different manufacturers here as smoothly as possible,” adds Lubach. For this reason, a Profinet-enabled Simatic S7-300 with CPU 319 PN/DP, the fastest of this series, is used for all controllers. Simatic ET200 pro distributed I/O devices represent a further highlight, and these can be installed direct at the machines, saving on control cabinets and cabling. Drives of the Sinamics S120 and S160 types complete the Totally Integrated Automation (TIA) aspect of this application.
For the RFID system itself, the automation vendor points to the RF310M mobile read/write device that significantly eases work on the line. In normal mode, only the relevant data on the tags is read and provided for display by the individually permanently installed read/write devices. Should it be necessary to check an upstream machining stage without the RF310M, the operator would first have to reject the pallet and then read the tag manually. In addition to this, the mobile terminal enables replacement of any faulty tag at any time with only the pallet number requiring to be re-entered. This also allows extended quality control on the production line. Such a setup allows for dimension fluctuations on the pallets that can be tracked conveniently and systematically with the RF310M using the pallet number.
The transmission production planning department at Volkswagen Kassel is completely happy with the new RFID system: “The system has been running for six months completely problem-free,” states Hermann. “And it is reassuring to know that not only have we been able to implement shorter processing times, but we also have a solution that is as powerful as it is flexible and that is available for other production models such as just-in-sequence production down to a batch size of one.
“We are currently also producing larger batch sizes, for transport cost reasons alone. The line produces 20 to 30 types of transmissions per shift in parallel and with different parts. The logistics control for the internal material flow works on the pull principle. Nevertheless, one-off production runs are nothing unusual at the Kassel plant – after all, the transmissions for Walter Röhrl’s Audi Quattro originated in this factory. Moreover, after the positive experience in Kassel, the Simatic RF300 RFID system has been generally specified, so it can be used in all Volkswagen plants worldwide.”
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