Siemens rail builds high-tech chassis for rail cars. These vehicles could have 20 to 30 points that need to be measured. Siemens had been working with standard gauges, attached with magnets to measure these points. But that was a challenge to the goal of producing 4,000 vehicles a year. The Radian along with the Intelliprobe 360 helped Siemens technicians make the measurements far more quickly.
Laser-based 3D Measurement Technology at Siemens Rail Systems in Graz
Siemens’s Bogie factory in Graz, where the company’s high-tech chassis is developed and manufactured, is an important partner in the global rail vehicle industry. Whether it is manufacturing bogies, or rail wagons, for trams, locomotives, passenger or high-speed trains, the Siemens Global Center of Excellence offers a complete range of products for rail traffic. The high productivity of the center reflects a level of automation that is unique worldwide. In particular, Siemens’s use of technology in mechanical production sets new standards. When setting up and clamping, the chassis frames are measured using laser trackers and wireless 3D sensors.
It all starts with the set-up
One of the core functions s of the Graz plant is the production of bogie frames and components. This starts with the alignment of the components on modular clamping fixtures. In order to meet the plant’s efficiency standards, Siemens technicians must make sure the metrology keeps up with the production capacity. This ultimately required new measurement systems. Siemens needed to easily measure the chassis frames and clamping units, and then clamp them to their jigs without any distortion or stress for the rest of the manufacturing process.
In the past, Siemens worked with standard gauges that were attached to the jigs with magnets. From the very start, it was necessary to measure points that were often difficult to access, as many as 30 points on some models, which required lengthy set up and clamping procedures. Up to 20 gauges per bogie were used simultaneously for the measurements. Over the course of time, it became clear that this measurement strategy could not keep up with Siemens’s production.
Modern measurement systems – and decisive disadvantages
Measuring points that are difficult to access are always a special challenge. Even new and portable measurement systems, such as measurement arms, could not meet the challenge of the measurement points imposed by the bogie design, which often in-laid the components 200 to 300 mm (7 to 11 inches) deep. The use of laser trackers was being investigated in parallel in Graz, and promised higher accuracies due to their laser-based measurement principle. Like measuring arms, trackers today are increasingly replacing conventional measurement systems such as measuring machines.
But Siemens found that the contactless measurement technique of the laser tracker, which is usually a great advantage over measuring arms and can still measure very much larger parts , still caused a problem for them. As Siemens techncians were testing the laser tracker, they discovered that the target for the laser beam, called the SMR (Spherical Mounted Reflector) could not reach into the recesses of the chassis frame that needed to be measured, and therefore could not carry out the measurements.
Better is the enemy of good
In principle, Siemens managers saw the superior precision and accuracy of laser-based systems, but none of the laser tracker provider could convince them to acquire a system. The disadvantages of the various systems, which were all similar technically, were too large. But that outlook changed when the Graz metrology specialists saw a new generation of hand-held sensors that had a significant advantage over standard SMR. In the meantime, two laser tracker manufacturers have offered sensors that enabled hand-held tactile measurements to be made with a probe tip (a measuring pin with a ruby tip). These wireless sensors can replace the existing SMRs within the tracker workspace. Depending on the length of the tip (with extensions up to 30 cm), the data points lying in the recesses of the chassis frame could now be reached and measured.
The new handheld wireless probes finally solved Siemens’s problem with the deep chassis recesses. In order to keep pace with the increase in production capacity, however, further steps were required with respect to the measurement strategy.
The new measurement strategy
After completing comprehensive tests, Siemens decided to purchase the Radian laser tracker from API, the the smallest, and therefore most portable laser tracker. The installation location for the measuring system had to be optimized. The machinery set up made it impossible to take measurements from a tripod-mounted tracker on the ground. It also could not be mounted on the wall because vibrations from an overhead crane would affect the measurements. Instead, the tracker was mounted on a specially built column between the clamping stations, about 6 meters (18 feet) off the ground.
To analyze the Radian data, Siemens uses Spatial Analyzer software from New River Kinematics. The data is displayed on two large LCD screens mounted high on the wall of the hall allowing the readings of the two workstations to be checked. The tracker itself does not need to be operated, and remains permanently switched on.
Automated Measurement Procedures
But there were still things to be done. The high degree of automation in the Lead Factory in Graz, whose maximum annual capacity is about 4,000 chassis, required additional measures in the implementation of the tracker setup and clamping that had to follow the machining in the different layer models.
“What we needed was process reliability in shift operation,” said Josef Kaufmann, Head of Mechanical Production at Siemens in Graz. “The measurement system should guide the staff. We needed a meaningful documentation of the measurements and the visualization of the processes.”
Due to the machining being carried out in shift operation, a skilled worker has to be able to carry out all the measurements on his own without the assistance of a measurement technician. These tasks require a high degree of automation of the measurement processes, in which the specialists at Siemens, in cooperation with the measurement system manufacturer, not only define all the bogie types to be produced, but also save the processing steps in the sequence in which they should be executed. This approach simplified the measurement process considerably. According to Josef Kaufmann, however, it was not only measuring time that was saved.
Siemens also needed flexibility and process reliability, up to and including the final measurements of the bogie frames. Because a laser tracker measures dynamically, the distortion, among other things, can be controlled in real time when clamping the frame. Overall, the measurement strategy thereby follows the cyclic assembly at Siemens aligned to the Lean Principles, which guarantees high quality bogies “just-in-time.”
Siemens Graz is currently one of the world’s largest developers and manufacturers of bogies for metros, trams, trainsets, high-speed trains and locomotives. The plant is capable of producing up to 4,000 bogies per year. This is possible, in part, thanks to the extremely high level of automation in production.
Dr. Stefan erlach, Siemens Ag Österreich | email@example.com | +43 (0) 5 1707 – 60651