Christoph Schttler Maschinenfabrik GmbH (Schma) specializes in developing and manufacturing diesel-engine locomotives. The company produces a wide range of models, but about 90% of the locomotives it produces each year are destined for use in building railroad tunnels.
Each construction project brings specific requirements, and each country through which the locomotives travel has different environmental and safety legislation. Schma uses a modular system to meet a diverse range of customer requirements and the resulting need for a variety of equipment and product versions. One of the tasks facing the company is working out how to equip the locomotives for transportation by rail on differing track widths. Another requirement is locomotives with driving wheels featuring diameters between 600 and 900 mm, depending on local track usage.
Faced with even more demanding requirements in terms of production capacity and flexibility, Schma managing director Christoph Schttler decided to add a cycle-controlled Seiger Record LC 1400 lathe to his inventory of machines. “We opted for a head-turning machine, as we do not need a tailstock to produce driving wheels, axle bearing housings, and gear wheels. It is working just as we envisioned, so we obviously made the right decision,” says Schttler.
Schma constructs about 120 locomotives each year, which equates to 480 wheels. In addition, there are repair orders that increase the workload to between 560 and 600 driving wheels per year. These wheels are produced in two mountings from forged blanks on the cycle turning machine. The first mounting is used to machine the wheel flange on the reverse side and the wheel hub. The shaft-locating bore is pre-turned. In the second mounting, the first task is to pre-turn the driving wheel profile, then the rolling circle level and the wheel shaft locating bore are finished.
The cycle turning machine is controlled by a Siemens Sinumerik 840D sl CNC, equipped with the ShopTurn software package with manual machine feature. If required, ShopTurn PERFECT CONTROL A hardware and software solution combines the flexibility and benefits of conventional machining with the productivity and efficiency of a CNC programming can be performed on a separate PC as part of an operator’s work planning, without interrupting the work sequences on the machine. The programs are routed to the machine via the network, where they are called up as required, depending on the workpieces to be produced. The Sinumerik CNC is used for numerical machine control and for manual operation with the ShopTurn’s Manual Machine functions. In manual mode with electronic handwheels, the machine behaves just like a conventional lathe with an actual value display.
During face and longitudinal turning, the process operates with the entered feed and spindle speed. The real highlight of the system is that every cycle can be used straightaway, without having to create a custom program. At Schma, the option for manual intervention is used to set the zero point or for simple contours. Diameters are determined manually, if driving wheels have been newly profiled or if driving wheel profiles require resurfacing. The wheel profiles abrade as a result of the high loads experienced in heavy-duty operation or on poor-quality tracks, or as a result of the driven wheels skidding.
“With a machine that uses only CNC, it is difficult to rework the driving wheels, as it is not possible to determine how much material needs to be removed. With this optional manual mode, however, users can adopt a careful approach. ” explained Walter Horstmann, head of mechanical production and wheel set construction at Schma.