| Large-scale CNC gear hobbing machines are widely used in processing large gears.With the support of the national major project "High-end CNC machine tools and basic manufacturing equipment",the first six-axis four linkage large-scale CNC gear hobbing machine with a maximum workpiece diameter of 3.2 meters in China has been successfully developed.However,because the evolution mechanism of the precision of large-scale CNC hobbing machine has not been fully revealed,the machining precision and precision stability of domestic large-scale CNC hobbing machine still have a large gap compared with similar international models.It can not satisfy the machining demand of high precision large gears of major equipment and engineering.It is urgent to carry out the research on the precision evolution mechanism and control method of large-scale CNC hobbing machine.Large-scale CNC hobbing machine has complex structure,large component size,long transmission chain and heavy working load.Due to the long transmission path and complex mutual coupling mechanism,it is more difficult to trace and compensate the errors.The results of theoretical and technical researches on the machining precision of small and medium-sized gear processing machines are not completely applicable.Therefore,this paper has carried out the following research.(1)The comprehensive multi-source errors modeling method of large-scale CNC hobbing machine under the force and thermal coupling.The generation and coupling mechanism of geometric motion errors,inter-axis assembly errors,thermal deformation errors and force deformation errors of large-scale CNC hobbing machines is studied,and an unified modeling method of multi-source errors of large-scale CNC hobbing machine based on multi-body system theory is proposed.A multi-source errors model of gear hobbing machine including 76 errors is established.(2)Precision allocation method of large-scale CNC hobbing machine based on precision-cost comprehensive optimization.A precision allocation method of gear hobbing machine based on precision-cost comprehensive optimization is proposed.The fuzzy comprehensive evaluation method is used to establish the precision-cost multi-objective comprehensive optimization model.The multi-objective gray wolf optimization algorithm and TOPSIS multi-objective decision analysis method are used to solve the precision allocation model and make decision.It provides a new method of precision allocation for machine tool design,which can realize the comprehensive optimization of machine tool machining precision and manufacturing cost.(3)Method of two-stage comprehensive errors decoupling and traceability of gear hobbing machines based on the generating principle.Firstly,based on the principle of differential transformation,the hob-workpiece relative pose errors are decoupled into the positioning errors of the six moving axes of the hobbing machine,and then the secondary decoupling is carried out based on the machining principle of the generating method of the hobbing machine,and the errors are equivalently mapped into the positioning errors of driving axles A,X and C.On this basis,the comprehensive errors traceability model of the gear hobbing machine is established,and the influence of the position of the motion axes on the traceability results is analyzed by using the orthogonal experiment method,which lays a foundation for the realization of error compensation.(4)Comprehensive error compensation method of large-scale CNC hobbing machine based on two-stage decoupling and traceability.Based on the established gear hobbing machine comprehensive error model and the two-stage decoupling and traceability model,the comprehensive error compensation model of large-scale CNC gear hobbing machine is established to eliminate the inherent error of machining system and improve the precision of gear machining.The error identification and compensation experiments are carried out on a large-scale CNC hobbing machine.The results show that it can effectively reduce the machining system errors of gear hobbing machine and improve the gear machining precision using the proposed comprehensive error compensation model. |
