From Prototype to a New Generation of Machines for Helical Gears

The prototype used for the evaluation was based on a conventional axial forming press equipped with a servo-electric rotary drive, providing the kinematic capability required for helical gear forming. The experimental trials showed that helical gears could indeed be produced, although the resulting component quality did not yet meet the required specifications. The observed profile slope deviation and total helix deviation led to the early conclusion that the torsional stiffness of the machine frame was insufficient to withstand the complex loading conditions of helical gear forming. This made a detailed structural analysis necessary to quantify the cause-and-effect relationships between machine stiffness and the resulting gear geometry. Based on these findings, structural FEM simulations were conducted to systematically investigate the torsional behavior of the system. The simulated loads were intentionally increased conservatively compared to the actual process parameters in order to account for both safety margins and potential scaling possibilities. All FEM simulations were conducted using identical boundary conditions, including an applied torque of 9,000 Nm. The resulting torsion angle was evaluated at two critical positions: the forming axis and the clamping device. The relative deformation between these points is crucial for process accuracy, as this is where the direct tool-workpiece interaction occurs. Even minor elastic torsional deflections can lead to measurable deviations in the resulting gear geometry.

The results of these analyses enabled a targeted evaluation of alternative guidance concepts. The original dual-arm configuration of the prototype shown in Figure 4a exhibited significant torsional deformation of the tool holder. The version with additional guide arms, shown in Figure 4b, was substantially stiffer. Simulation and experimental results both showed that it reduced the torsional deflection by about 41 percent. This was directly reflected in improved gear tolerances and confirmed the effectiveness of the modified guidance concept. For the development of a new generation of machines specifically designed for helical gears, the objective was to reduce torsional deflection by at least 50 percent compared to the first prototype system, in order to significantly expand the process limits. This target was not only achieved but clearly exceeded. The new concept incorporates four highly rigid guide columns with internal tie rods, enabling a nearly closed and flexurally rigid load path between the press plates. The comparison of torsional deformations for the evaluated guidance and machine concepts, as shown in Table 1, indicates that the new machine generation reduces torsional deflection by 78.6 percent compared to the prototype configuration, which corresponds to nearly five times the torsional stiffness. This improvement provides the necessary precision and process reliability for helical gear forming for the first time. The helical gear machine (Figure 5) is designed to substantially expand the process window of the previous axial forming machine. Its press plates, tie rods and column guides form a highly rigid assembly that keeps tool movement virtually free of tilt, and a tandem cylinder, with its larger piston area, provides higher axial forces. The mandrel axis inside the tandem cylinder supports the inner diameter of tubular workpieces or parts with internal bores and keeps thin-walled components from buckling.

The central functional element of the new machine is the cylinder-driven ram, which is designed to withstand axial forces of up to 1,000 kN and incorporates a bearing system that ensures play-free rotation of the tool holder under load. Torque of up to 10 kNm is supplied by a play-free system consisting of a servo motor and gear assembly, enabling highly dynamic and precise rotational movement of the tool. A switchable clutch also allows the system to operate in a freely rotating mode, permitting the tool to be withdrawn from the interlocking mechanism with virtually no load once the forming process is complete. This protects both the tool and the component.

“For automotive suppliers, technological capability and cost efficiency are no longer the only priorities; process robustness and investment security are increasingly moving into focus.”