Maintenance: Tram wheel profiling machine

Tram wheel machine gets a performance boost

Who

Engineering firm Emotec has boosted the performance of a tram wheel profiling machine used by the Zurich public transport organisation VBZ by retrofitting it with a lathing capability and CNC system from NUM. The upgraded machine can re-profile all four wheels on a bogie within a couple of hours – a task that previously took up to a day.

Technology

Nearly all tram wheels are fitted with flanged metal tyres, which require regular re-profiling to compensate for wear. VBZ performs wheel re-profiling operations using a machine that was originally supplied by Kellenberger in 1991.

Until recently, the re-profiling machine used a form-grinding wheel to bring the tyres back into shape but this proved time-consuming. The form-grinding wheel had to be changed to accommodate different diameter tram wheels.

VBZ has recently brought several new types of tram with lower floors into service. They are equipped with fewer wheel-sets and smaller wheels than their predecessors, which means they are subjected to higher loads and greater wear.

Emotec helped VBZ determine that it would be possible to adapt the existing re-profiling machine by adding a lathing capability and a CNC system. By turning the tram wheels on a lathe prior to grinding, the re-profiling could be accelerated. Lathing the type of extremely hard metals used on tram tyres has only recently become tenable with the advent of specialised turning tools and powerful 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 closely with NUM to develop a replacement for the existing unit. The final system configuration comprises two NUM Axium CNC units and NUM’s MDLU3 drive technology, controlling 16 axes. 

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 is raised by hydraulic actuators until its rubber drive wheels are in contact with the tram wheels. The machine can re-profile two tyres simultaneously.

Application

The advantages of turning are much shorter machining times and the ability to re-profile the flange and the back of the wheel. Other advantages include the option of machining different tyre profiles without having to adapt the tools, and optimised turning processes for roughing and finishing.