Cold extrusion of gears with selective reduction of friction surface - Guided Material Flow (GMF) process

• Applicant: Professor Dr.-Ing. Mathias Liewald
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Engineering Design, Machine Elements, Product Development
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450218053

Toothed components are manufactured by machining or forming processes according to the required toothing accuracy of today. Although the machining of the gearing results in a high degree of gearing accuracy, this technology causes a considerable time and material consumption as well as a reduced component strength prior heat treatment. Gears produced by cold forming, on the other hand, disclose an increased operational strength, with likewise high gearing accuracies. Completely toothed components in industry today are manufactured by cold extrusion using the Samanta process. This process requires a quite high pressing force, which results in critical stress values and considerable elastic deformation of the die. An approach to reduce the pressing force and thus to increase the toothing accuracy in the Samanta process consists in the geometric modification of the die contact surface and the associated promotion of the material flow. Based on the Samanta process, the so-called Guided Material Flow (GMF) process was designed within the framework of the preliminary work at IFU, in which the gear forming takes place by means of a totally newly designed die contact surface.This transformation consists of an axial extension as well as tangential and radial transformation of the forming zone in pressing direction and the incorporation of an undercut in the gear cavity. The modified die contact surface leads to a tremendous drop of pressing force along an extended forming stroke with simultaneous functional compensation of the resulting increase in friction surface.The feasibility of this new method was shown numerically and experimentally for only one gear geometry, whereby the geometric shape of the die working surface was created based solely on experience. To elaborate design methodology, the GMF process is to be investigated with regard to the interaction between die geometry and material flow and the resulting press force and die filling. This investigation will be performed numerically using the FE simulation software DEFORM by varying the gear geometry to be formed and the geometric parameters of the die contact surface. In addition, the process sensitivity with respect to changes in the tribological boundary conditions and the workpiece strength also is intended to be analyzed. Based on the numerical results, metamodels will be generated, which serve for the geometric optimization of the die contact surface of the GMF process in the last stage of proposal. The aim of the project is thus to develop design guidelines for the extrusion of gears with controlled friction surface reduction (GMF process) for the production of different gear geometries with the best possible accuracy in contour and dimension as well as minimum use of force.

• DFG Programme: Research Grants