Calculating the Workpiece Quality Using a Hobbing Simulation

Abstract

Gear hobbing is one of the most productive manufacturing processes for cylindrical gears. The quality of the gears is a result of the tool quality, the precision of the workpiece, tool clamping and kinematics of the machine. The dry gear hobbing process allows machining of gears with a quality according to the DIN standard of up to IT 5. To evaluate which gear quality is possible to machine with a given clamping and hob it is useful to simulate the process in advance. This is also an opportunity to order the required quality of the hob according to its application.The objective presented in this paper is to simulate non-ideal gear hobbing processes and to calculate the geometry and topography of the workpiece. To achieve this goal, a simulation for continuous gear hobbing was developed. By calculating planar intersections of transverse sections of both gear and tool, the resulting gear geometry is determined. Beside it is possible to calculate different characteristic values for the hobbing process such as chip thickness and cutting volume. By an evaluation of tool and clamping tolerances these deviations can be used to modify the simulation model. Afterwards a non-ideal hobbing simulation can be performed and the resulting gear geometry can be analyzed using a virtual measurement machine. An advantage of this non-ideal simulation is also the possibility of calculating the tool load taking these deviations into account and to use the results for further process designs to reduce the risk of tool failure.The virtual measurement machine analyses the geometry according to VDI/VDE 2612/2607 and DIN 3961. The resulting measurements of the flank and lead lines can be used for a classification of the gear quality. By using this simulation program it is possible to reduce the costs and time effort of setting up a new hobbing process.