Industries

LAP sensors minimise scrap when forging railway wheels

Growing axle loads and increasing speeds of the railway vehicles call for ever more efficient wheel set systems. The Bochumer Verein has therefore equipped its existing contour measuring system downline of the hot forming section with an optical laser contour measuring system from LAP Laser. The laser sensors measure wheels immediately after forging and supply the exact profiles in real time. Using the measurement data it was possible to achieve a lasting improvement in the production process and to increase efficiency.

The wheel sets of a railway vehicle bear the vehicle weight, provide the guidance of the vehicle on the track and transmit the tractive and braking forces to the rail. The demands on the wheels are correspondingly diverse. Increasing axle loads and speeds demand ever more performant materials, optimised production processes and continuous documentation for the consistently high quality of the wheels. 

One of the first production steps is the hot forming of the wheels. Precise and complete monitoring of the production at this early stage is of crucial importance for the final quality, but also for the cost-effectiveness of the whole production process. 

The Bochumer Verein Verkehrstechnik GmbH (BVV) therefore decided to measure each individual wheel immediately after hot forming. Should deviations from the tolerances be discovered here, the machine operator can intervene immediately. In order to achieve this, the Bochumer Verein had to bring the measuring equipment on the wheel line to the state-of-the-art. 

Three sensors for the exact wheel profile
 A concept developed together with LAP provided for the installation of modern Antaris Scan triangulation sensors, complete reprogramming of the evaluation software and the replacement of the PC and electronic hardware. With these measures and an intelligent cooling concept for the sensors, LAP achieved the precise and complete measurement of the wheels and a significant increase in availability.

At the start of hot forming at the Bochum works, sawn steel ingots are heated to forging temperature and delivered to the forging press which forms wheel blanks with a force of up to 6,000 tonnes. When the wheel rolling machine has rolled out the wheel blanks to the rough dimensions, the 2,000 tonne closed-die forging press gives the wheels their final rough form.

The smallest diameter that is produced on the closed-die forging press at the Bochumer Verein is 385 millimetres, the largest wheels have a diameter of up to 1,470 millimetres. The diameters of the hubs range from 75 to 230 millimetres, the hub height of the roughly 1100°C hot wheels lies between 80 and 350 millimetres.

A manipulator takes the red-hot wheels out of the closed-die forging press and places them onto the turntable of the measuring equipment. The LAP system scans the wheel contour during a 360 degree rotation and measures the exact profile. 

The Antaris Scan sensors employed operate at a scanning rate of up to 40 profiles per second and require roughly 18 seconds for the measurement of the wheel. The LAP software calculates the exact profile and the deviations from the nominal contour from the measurement data of the three sensors in real time. The main dimensions are recorded in a measurement protocol and checked against the specified tolerances.

Quick overview for the operator
 The system displays the result of the measured values extremely clearly as a graphic representation, each with the nominal values and the actual contour. A colour code shows the user at a glance where the wheel is within the set tolerance, or at which points the values are outside the tolerance band. 

The operators can thus gain a quick overview of the geometry of the wheels. If it is recognisable that the given tolerances are not being observed, they can immediately take the necessary measures. Furthermore, the operating crew uses the data to optimise the press settings for the next wheel. 

The manipulator then takes the wheel and places it into the wheel store. Wheels whose dimensions are outside the specification are later discarded. The whole cycle from the removal from the press up to the depositing of the wheel in the wheel store is completed within 60 seconds. The cycle time of the forging press is thus significantly longer than the time required for the measurement. The measurement therefore causes no delay in the production process. 

Every thirtieth wheel is additionally inspected by the operator who checks the wheels visually and assesses them on the basis of criteria such as wheel flange width or diameter. 

 High-precision measurements in harsh environments
 The LAP Antaris Series operates using the triangulation method: A laser point moves along a straight line over the surface of the forged wheels, automatically “following” the contour of the wheel as it rotates on the turntable. High-resolution line scan cameras capture via a lens the position of the laser point which changes with the shape of the measured object. 

The Antaris laser sensors are arranged in a measuring frame and measure the wheel contour from the top, bottom and from the side. Via the identification number of the wheel, the LAP measuring system retrieves the nominal values of the main dimensions and the nominal contour values from the Bochumer Verein database via network link. 

Protective housings shield the sensors from the harsh environmental conditions. They are cooled with filtered ambient air and are therefore independent of the media supply of the works. The system requires neither cooling water nor compressed air – a great advantage, as a water cooling system is maintenance-intensive and always a potential source of danger in combination with electronics. 

The filtered ambient air creates a slight overpressure in the protective housing and escapes at apertures in front of the sensors. The constant air flow prevents steam and dust getting into the housing. 

 "The Antaris Scan sensors can be used on practically any surface and thanks to the large measuring distance are very well suited for measuring hot or glowing materials," says Dr. Axel Schulz, Sales Manager Metal Industries at LAP, explaining the field of application of the sensors. Apart from measuring profiles, the laser sensors can also be used to measure distances and diameter, straightness or flatness as well as position and orientation." 

Evaluation and visualisation computers supply nominal and actual profile in real time

The new measuring system in the Bochum works consists of an evaluation computer, the front-end PC, for measurement data acquisition and processing, and a visualisation computer for representation, protocolling and archiving of the data. The measured values from the sensors come together in the front-end PC; all signals from the measuring systems are monitored and controlled from here. 

The visualisation computer receives the data, stores them in the database and compares them. The system receives the nominal values for the contour of the forged wheels from the existing database of the Bochumer Verein, compares them with the actual profile data and outputs them in graphic form. New nominal contours are entered at another PC located in the tool design department. 

The system synchronises the sensors independently and balances them so that the individual measurements supply the complete wheel profile in real time. The software compensates and eccentricity in the event that the wheel is deposited off-centre on the turntable. The measuring system is checked routinely once a day by means of a calibration on a calibration wheel.

Lasting improvement in the production process
 Thanks to the vast experience of LAP, the new contour measuring system was delivered, installed and commissioned within just three months of placement of the order, despite the complex specifications and the great number of nominal contours to be provided for. The accuracy of the dimension measurements achieved is better than ± 1 millimetre, the repetition accuracy of the profile coordinates is better than ± 0.5 millimetres. 

"With the precise measurement it is now possible to make a well-founded decision on the further processing of wheels intended for processing in the Bochum works,“ concludes Dr. Schulz. "Furthermore, the new measurement and analysis values now available permit complete tracing back of each individual wheel for quality control purposes. In the event of a complaint, the archived geometric data can be immediately called up from the database." 

Moreover, the archiving and single-item logging functions provide valuable data for continuous optimisation of the production process. Even the tool engineering department uses these data for the design of new wheel systems. 

The new optical contour gauge in operation on the wheel line of Bochumer Verein Verkehrstechnik GmbH now provides the operators of the sizing press with a clear picture of the geometry of the hot-formed wheel in virtually no time. 

They can now intervene much faster whenever there are indications that the preset tolerances are not being met. That gives first-class control over the forging process. 

Production planning can adapt the mechanical further processing of out-of-spec wheels and thus significantly reduce scrap. Ultimately the new LAP measuring system has made production far safer and prevents scrap from the outset.

About Bochumer Verein Verkehrstechnik GmbH
 Bochumer Verein Verkehrstechnik GmbH is a medium-sized company with some 600 employees. The world's leading manufacturer of rolling stock for railways has been producing in Bochum since 1842 and supplies wheel set systems and related services to its customers on all five continents. 

One of its outstanding strengths is customised manufacturing – covering all stages from the selection of the material via hot forming and heat treatment through to machining of the product. Its customers include Alstom Transport, Bombardier Transportation, Siemens Transportation Systems and Stadler Rail.

Your Press Contact

    Thomas Armbruster

    Tel.: +49 (0)4131 951195
    Fax: +49 (0)4131 951196
    t.armbruster(at)lap-laser.com

    LAP GmbH
    Laser Applikationen
    Zeppelinstr. 23
    21337 Lüneburg
    Germany

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