New Schemes for Final Edge Machining of Worm Threads

Abstract

Machining of helical surfaces of threads and worms is commonly spread in mechanical engineering. Profile generation is determined by requirements to localization of initial adjacency of conjugated surfaces (usually at the central part of the thread height); and it implies application of means for controlling the profile geometry at thread cutting. While the layouts of traditional thread grinding and worm grinding machine-tools are provided with the mechanisms for precise adjustment of angles and shape of the generated thread profile, the profile of threads at edge machining is traditionally rigidly related to the tool profile, thus complicating the geometry correction. The paper considers the possibilities of such a correction at edge cutting by tools provided with hard alloy disposable plates. This ensures both the required geometry of threads and high production efficiency of machining. In particular, certain schemes are considered for machining at commonly spread CNC lathes by circular (rounded) and rectilinear cutting edges of the assembled cutter, and also by the assembled cutting head implying a comparatively simple implementation at the majority of mechanical engineering enterprises. The means for controlling the parameters are proposed to be linear displacements of a tool across and along the center line of the machine-tool (for schemes of machining by a straight cutting edge and face cutting head) and parameters of the trajectory of the tool feed (for the scheme with a circular (or rounded) plate). Numerical examples are presented to show the possibilities and efficiency of controlling the profile geometry and results of cutting the worm test samples. Main requirements to mounting of hard alloy plate are determined; they are related to providing the positioning accuracy, strength and rigidity of plate fastening. Application of the proposed methods will allow in some cases to eliminate the costly grinding of threads by applying the advanced features of CNC lathes and providing the high accuracy and high production efficiency of machining parts with helical surfaces. Future prospects of the methods are related to optimization of controlling parameters and their application for machining the heat strengthened parts with helical surfaces.