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Smooth Ride for Zurich’s New Trams

 Zurich, Switzerland – Engineering company Emotec has enhanced the performance of a tram wheel profiling machine used by the Zurich public transport organization, VBZ, by retrofitting it with a lathing capability and a CNC system from NUM.

 

The upgraded machine reportedly can re-profile all four wheels on a bogie within hours – a task which previously took up to a day. NUM has been providing CNC solutions to a wide variety of industries, including the Woodworking industry, for more than 20 years. 

 

Re-Profiling

 

Nearly all tram wheels are fitted with flanged metal tires, which require regular re-profiling to compensate for wear – failure to do this would lead to impaired performance and a less comfortable ride. VBZ performs wheel re-profiling operations at its maintenance hangar adjacent to the Zurich-Oerlikon station, using a machine that was originally supplied by the Kellenberger company back in 1991.

 

Until recently, the re-profiling machine used a form grinding wheel to bring the tires back into shape. However, this process proved time-consuming – especially in compensating for heavier degrees of wear, when it was sometimes necessary to remove several millimeters of tire in order to bring the wheels back to a uniform diameter.

 

Furthermore, the form grinding wheel had to be changed whenever it was necessary to accommodate a different diameter tram wheel, which again contributed to delays and lack of throughput. In addition to this, the machine’s control unit, which was nearly 20 years old, was becoming increasingly unreliable and expensive to maintain.

 

Surface Finishing 

 

When VBZ decided to bring several new types of tram into service in Zurich, it sought the advice of Emotec AG, a company which specializes in surface finishing technology and the application of CNC. The new trams feature lower floor heights – to make it easier for passengers to board and disembark – and are equipped with less wheel-sets and smaller wheels than their predecessors, which means that they are subjected to higher loads and thus greater wear.

 

After investigating the process, Emotec determined that it would be possible to adapt the existing re-profiling machine by adding a lathing capability and a modern CNC system, instead of requiring that VBZ purchase an entirely new machine. By turning the tram wheels on a lathe prior to grinding them, the tire re-profiling operation could be accelerated. Lathing the type of extremely hard metals used on tram tires has recently become tenable, with the advent of specialized turning tools and CNC systems.

 

The demands placed on the control unit of a machine capable of handling both form grinding and lathing are considerable, so Emotec worked with NUM to develop a high performance replacement for the existing unit. The final system configuration comprises two NUM Axium CNC units and NUM’s MDLU3 drive technology, controlling a total of 16 axes. NUM also developed the control and visualization software.

 

Very Clear Guidance 

 

A further key requirement was that since the two machining processes are completely different, the machine operator would need very clear guidance about the various procedures involved. To achieve this, the machine is equipped with two NUM FSi-151 control panels, which provide an exceptionally intuitive and easy-to-use HMI (human-machine interface).

 

The retrofitted wheel re-profiling machine occupies the same physical space as its predecessor. The tram is driven into position in VBZ’s maintenance hangar and the machine – which is effectively located on a lower level in the building – is then raised by hydraulic actuators until its rubber drive wheels are in contact with the tram wheels. The machine can now re-profile the tires of two tram wheels simultaneously, doubling its throughput, and because, depending on wear, the tires are now either lathe-turned prior to grinding, or are only lathe-turned, the entire process is much faster. www.num.com

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