Multi Axis CnC Manufacturing of Straight and Spiral Bevel Gears

Abstract

Multi Axis CnC gear manufacturing offers gear-makers the sort of versatility in tooth shape and tooling that no dedicated gear-cutting machine can offer, but that versatility usually comes at the expense of production volume. However, any gear-cutting machine, whether dedicated or CnC, is affected by build and wear errors that are transmitted to the workpiece. The same applies to the tools. Manufacturing errors on the tooth flank topography resulting from machining and tooling can be quite significant, and must therefore be controlled by Closed Loop. Commercially-available Computer Aided Manufacturing programs rely on a point cloud, such as IGES or STEP files, to describe the tooth flank topography. Despite being a very general approach, this method requires an external Tooth Flank Generator to create the point cloud, and therefore Closed Loop cannot be applied effectively. This document presents an integrated approach to Tooth Flank Generation, Closed Loop, and multi-axis CnC manufacturing of straight-bevel and spiral-bevel gears, in which a Unified Model is applied to different gear types. The Unified Model is used to calculate tooth flank topography, generate CMM target coordinates and use CMM output to minimize manufacturing errors. The machine settings describing tool and workpiece positions and movements in a gear-cutting machine, either before or after Closed Loop, are used to define equivalent positions and movements in a multi-axis CnC machine. Actual examples of gears cut and corrected on 5 Axis CnC machines show that the presented method is general, fast, and accurate.