Development of a process for the two-stage production of gears

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Cold forging has been applied since numerous years in industrial gear production. To produce straight and helical spur gears, lateral extrusion is a commonly used cold forging manufacturing process. Usually lateral extrusion processes require high process forces to fill a toothed die contour. These results in a high elastic deformation of the active die surface and a huge elastic springback in the workpiece after the ejection from the die. Therefore, lateral extrusion with without corrected die profile does not achieve the required accuracy of gears. An improvement of mould filling and gearing precision as well as a reduction of process forces can be achieved by multi-stage forming or the utilization of incremental forming processes. Another method to improve mould filling while simultaneously reducing process forces and tool loading can be achieved by the established principle of the divided flow method. The newly discovered effect of lateral cavity filling is based on the same principle as the divided flow method, and has been demonstrated experimentally and numerically as part of the preliminary studies for the proposed research project. Simulations have been performed to illustrate the positive effect of lateral cavity filling with the example of a two-staged lateral extrusion process to manufacture an external gearing. By applying this innovative method, a considerable reduction of punch forces of over 40 % was achieved as a result of the targeted material flow along the freestanding workpiece surfaces in the tooth flanks.In the applied research project an innovative technological approach for manufacturing gears using lateral extrusion by means of numerical and experimental investigations will be examined. The forming process of the teeth occurs in the second forming stage using the above-mentioned effect of lateral cavity filling in order to achieve a reduced forming force and correspondingly tool load. By systematic material pre-distribution in the first forming stage and a specific asymmetrical positioning of the preform in the second forming stage, the tooth profile is formed with a minimised die surface contact. This innovative forming process results in a significantly reduced pressing force and tool load during mould filling and, consequently, improves tooth accuracy compared with conventional, single-stage toothing presses using lateral extrusion.