Less Interference Tool-Path Planning Method For Internal Cylindrical Thread Helical Milling

Thread parts,as common fixed connection and motion conversion parts,have been widely used in aerospace,petroleum,electricity,and many other fields.Its manufacturing accuracy directly affects the performance and service life of mechanical products.Thread machining usually includes turning,tapping,milling,grinding and other machining methods.With the rapid development of thread CNC milling technology,thread milling method is more and more used in thread machining because of its inherent advantages.However,due to the incomplete coincidence between the envelope surface of the thread milling cutter and the profile of the standard thread profile,there are serious interference errors in the whole process of internal thread helical milling,which restricts the improvement of thread machining accuracy.Therefore,in order to realize thread precision milling,how to rationally planning the thread milling tool-path to reduce interference is the key problem to be solved urgently.Aiming at the helical milling process of the cylindrical internal thread,interference errors of thread milling is analyzed,and the tool-path parametric equation is established by means of space curve parameterization theory,UG NX11.0 software,machining simulation software VERICUT,DMU50 five-axis CNC machining,automatic image measurement platform,and other methods.The method of tool-path correction in helical milling of internal cylindrical threads is explored in order to reduce machining interference errors.The specific research work is as follows:1)The principle of internal straight thread helical milling is analyzed.According to different thread rotation and milling methods,the motion trajectory of the thread milling cutter is analyzed.The common penetration and retraction methods and main processing steps of internal straight thread helical milling are analyzed,which provides a theoretical basis for tool path planning of thread milling.2)Less interference tool-path planning method for the thread milling portion and the penetration-retraction portions in internal straight thread helical milling.Based on the theory of space curve parameterization,the tool-path parameterization equations are established for the thread milling portion and the penetration-retraction portions in thread milling respectively.The interference errors of thread milling portion and penetration-retraction portions are analyzed.On this basis,a less interference tool-path planning method for thread milling portion based on machining interference errors to correct the helical radius of tool-path and the cutter tooth profile height is proposed.Aiming at the half revolution penetration-retraction and the quarter revolution penetration-retraction modes,a method of less interference tool-path planning for revolution penetration and retraction portions is proposed,which simultaneously adjusting the position of the start point of the thread milling cutter in the penetration trajectory and the end point of the thread milling cutter in the retraction trajectory in the X-axis and Z-axis directions.3)The simulation and milling experiment of internal straight thread helical milling.Based on UG NX11.0 software,the example analysis and validation of the less interference tool-path planning method for thread milling portion are carried out.The validity of the less interference tool-path planning method for revolution penetration and retraction portions is verified by using machining simulation software VERICUT and thread milling experiments.The effect of offsetting coefficient on interference errors are analyzed for revolution penetration and retraction processes,and the less interference tool-path planning of penetration and retraction portions can be realized by adjusting the offsetting coefficient.According to machining simulation and milling experiment results,the effect of size of thread and cutter on interference errors for the thread milling portion and the penetration-retraction portions are analyzed.In summary,the research in this paper will lay the theoretical foundation for the development of the thread precision milling process,and will further expand its machining application range.