Requirements for Helical Gearing on the Machine and Tool

The production of splines and helical gears using axial forming requires forming presses that meet the highest standards of precision and rigidity. Only in this way can dynamic loads be reliably absorbed and the required manufacturing accuracy of the gears be achieved with process stability. This applies in particular to the precise alignment of all components involved in the load path, especially tools, mandrels, clamping devices and workpieces, which must exhibit only minimal deviations in coaxiality relative to one another. To ensure that this accuracy is maintained across the entire gear length, the axis guides must provide excellent overall runout as well as high repeatability and positioning accuracy. This prevents geometric errors such as runout or wobble and protects the tools from unacceptable transverse loads caused by tilting or off-center loading. These basic requirements apply equally to presses used for manufacturing helical gears. However, the additional rotational kinematics raise further technical requirements. Since helical gears are produced by the superposition of axial and rotational tool movements, which are provided by separate drives, highly precise control of these movements is essential. The electric rotary axis and the hydraulic stroke axis must operate in precise synchronization both during stationary operation and during acceleration phases, as well as during the cyclic reversal of the modulation. Furthermore, the rotational axis must be designed to be free of play and torsionally rigid so that the required pivoting angles can be achieved with high precision even under heavy loads. Only in this way can the helix angle and the resulting gear tolerances, such as total helix deviation, be maintained. Beyond the design of the drives and guides, the entire press frame must also provide the necessary rigidity to safely absorb the torques introduced by the rotary drive without significant elastic torsion or elongation. If these conditions are met, the workpiece itself becomes the most compliant element in the overall system consisting of the press frame, tools and clamping device. In conventional axial forming of splines, this compliance has only a minor effect, as the resulting component deviations occur primarily in the axial direction and can be directly compensated by tolerances or by a simple correction of the final position. In helical gear forming, however, the situation is significantly more complex, since elastic strain and torsion components do not remain constant throughout the process and can influence the helix angle. These factors must therefore be considered and compensated for already during the forming operation. As the tool moves toward the clamping device, the length of the component, over which the torque from the helical gear forming acts, decreases. Consequently, the effective angular error resulting from the torsional elasticity of the workpiece is reduced over the course of the process and must be accounted for in the machine control system. In addition to the elastic effects, the risk of undesired plastic deformation of the workpiece must also be considered. While conventional axial forming transmits only compressive forces through the workpiece into the clamping device, the additional rotational movement in helical forming generates torsional stresses that must be safely absorbed and withstood by the component. As the outer diameter increases, the polar moment of inertia of the workpiece and thus its torsional stiffness also increases, thereby reducing the risk of unwanted stress-induced deformation. The tools, as well as the tool assembly consisting of the die and the reinforcement, are subject to more stringent requirements necessary for the axial forming of helical gears. The reinforcement assembly performs several mechanically critical functions in this process. The preload generated in the die ensures that the high internal pressures occurring during the forming process are absorbed. At the same time, the radial stiffening of the system reduces elastic die deformation, thereby improving the dimensional accuracy of the resulting gear. Beyond these functions, the press fit also serves to mechanically fix the die. Although the axial forming forces are transmitted through a positive fit, the die is retracted during the backward stroke and prevented from slipping or rotating during helical gear forming by the frictional fit in the reinforcement. This requires a specifically engineered press?fit design. The frictional stresses must be high enough to reliably transmit the required torque, while the permissible radial press?fit limits must not be exceeded, as excessive reinforcement would lead to unacceptable stress conditions and material damage. The helix angle in helical gears generates additional lateral loads on the tooth profile of the die. These loads are the primary cause of failure in the form of tooth breakage. The shear stress occurring in the tooth root must therefore remain within permissible limits. Likewise, inaccuracies in tool movement must be avoided, as even minor deviations lead to increased transverse and bending moments on the teeth and significantly exacerbate the stress situation. Due to these constraints, the design of the gear profile requires careful selection of the manufacturing process. Each available manufacturing technology produces specific geometric characteristics, such as edge radii, surface roughness or manufacturing deviations, that directly influence tool loading and the achievable component quality. Experimental investigations and numerical forming simulations were used to determine the optimal combination of manufacturing process and tool loading.