Last month, the rail engineer visited Graz, the historic capital of Styria and Austria’s second city, for the launch of the new SF7000 bogie which Siemens intends to use on the new Desiro City trains that it will shortly be building for the Thameslink programme.
During that visit, Siemens’ engineers were keen to show how modern bogies are manufactured in a factory which can turn out 4,000 a year.
Dating from the 1850’s, when it commenced making railway wagons and then, more recently, carriages, Siemens converted its earlier 26% holding in the factory to 100% in 2001.
Since then, the Graz plant has concentrated purely on bogie design and manufacture and is now Siemens’ Centre of Excellence for bogies, where they make bogies for everything from trams to high speed trains.
Design is carried out in the same way as for any other mechanical assembly these days. A team of experienced engineers, working on CAD screens and using finite element and other techniques, come up with new ideas and modifications to earlier designs.
These designs are then tested, in computer simulations so that changes can be made before an actual prototype is even manufactured.
Diemo Wojik, Head of Bogie Projects, explained how the design process has progressed in the last ten years. When Siemens established the Graz centre in 2001, they were already using computer simulation techniques as part of the design process.
Completed designs were subjected to a multitude of simulated running conditions to see how they would react in operation – under load, under braking and on good and bad track. It was important to make sure that bogies were stable, and didn’t pass unwelcome movement onto the passenger carriage to which they were mounted.
In 2002, strength analysis was added to the computer models, and in 2005 a routine was introduced to help optimise the acoustic characteristics of the bogie. Most of the noise emitted by a running train comes from the wheels and bogies, and increasing public sensitivity to this made the ability to design a quiet bogie essential.
By 2007, Siemens was developing routines to design with maintenance in mind. What were the operating life expectancies of the various components, and could this be increased? Whole life costs were becoming important benchmarks for customers, and a few extra Euros spent on a design or a component that reduced maintenance in the long term were now a good investment for operators.
A programme to design for weight commenced in 2007. Weight had always been an important element as heavy bogies give high axle loads and thereby damage track more easily.
However, now lightness was increasingly important as it also has a bearing on fuel economy. So light bogies, underneath aluminium-bodied trains, were becoming the norm in metro applications. The new programme examined the weight of everything, from frames to axles and even brackets, in a drive to get as much weight reliably out of the product as possible.
2012’s programme takes the concept of designing for maintenance a step further.
“Bogie Monitoring” fits the bogie with a number of sensors measuring movements, resistance to movement, and other variables to establish the condition of the bogie and its components.
This means the bogie can self-diagnose any faults, and report back through the train’s control system, so maintenance engineers are notified when essential work is needed, or can postpone routine maintenance when it is not, so saving cost.
All this design and development work is undertaken by the 210 engineers at Graz before a new bogie is even released for manufacture. Then a pilot run is made, tested in the laboratories at Graz, and then shipped off to Siemens’ own test track at Wildenrath on the German / Dutch border. There, fitted under a test train, the performance of the new design can be evaluated in actual working conditions.
After all the static and dynamic testing is complete, and any design modifications have been made, then the new bogie is passed over to the factory for tooling up and series production.
The bogie itself starts life as a collection of shaped steel plates. These are procured from a range of approved suppliers, and arrive at the factory cut and bent to shape, with holes drilled as required, and with big chamfered weld-preparations already on the edges. When butted up against the next component, these chamfers form a deep v-channel which will be filled up in the welding process ensuring that the weld is the full depth of the plates.
The component parts are then assembled onto large jigs. These are unique to each design of bogie and represent a major part of the cost of tooling up each new design.
The various plates and other parts are clamped into the jigs until the whole sub-assembly is complete, and they are then tacked together manually by an experienced welder so that the structure becomes rigid.
To allow access to all the joints, the whole jig moves in three dimensions, rotating and swivelling so the welder can ensure that everything has been correctly attached. And with a bogie frame measuring three metres across and weighing a couple of tonnes, this assistance is very necessary.
Once the assembly is complete and stable, it comes out of the jig and goes off to the main welding robots. It is attached to another jig, which also moves in three dimensions, but this one is mounted directly under a big robot welding arm. Behind protective screens, the bogie frame and the welding head move and swivel while a multi-pass weld is built up in all those v-shaped channels.
To maintain capacity, there are four of these units and they weld all the volume bogie frames and large sub-assemblies. Smaller components are welded by hand.
After welding, the frame is placed on an automated line that checks all the critical dimensions have been achieved. Welds are checked for integrity, and then the whole thing is cleaned up, shot blasted, and sent for painting. Dangling from chains on a moving track, the frames are first sprayed with primer (an interesting salmon-pink colour) and then finished in a colour to the customer’s specification. This usually seems to be a form of battleship grey. After drying in an oven, the next stage is assembly.
One major item that is fastened into every bogie is, of course, the wheel set (or more strictly – two wheel sets). This is the axle complete with wheels and, possibly, brake discs. Until recently, Siemens also bought these from outside suppliers. However, a new workshop now allows them to be assembled in house, although some are still procured.
The wheelsets, springs, shock absorbers, brakes, brakelines, gearboxes, electric motors, sensors, cables and other items that will together become a complete bogie are hand-assembled on large tables in cells rather than on a production line. One or two fitters complete each bogie, and at full capacity the factory is turning out about five each shift. Currently working 10 shifts a week, the production line can be geared up to 19 shifts a week if necessary.
To make sure that each bogie has been assembled properly, it is placed on a large test machine which hydraulically applies a load to the mountings for the carriage. The weight on each wheel is measured, and adjustments made until everything is square and all four wheel loads are in specification.
The only thing left to do is to ship the complete bogies off to the various Siemens factories. At one end of the range, Graz makes small, lightweight bogies for trams that go off to Vienna, and at the other extreme large, high-speed bogies for the 1,520 mm gauge Velaro RUS EVS (Sapsan) that is built at Krefeld and Erlangen in Germany.
So next time you catch a train, peer over the platform edge at the bogies hidden underneath, and remember all the technology and engineering that goes into those oft-forgotten essential components.