Rapid Dynamics Prediction Of Tool Tip And Analysis Of The Chatter Stability In Robotic Milling System

As a novel method of milling,it can not only improve labor productivity and guarantee the processing quality,but also reduce the processing costs to apply industrial robots into the manufacturing of large-size parts with complex surface.With concatenated cantilever structure,industrial robots' dynamics is obvious posture-dependent,which results in great difference of milling SLD(stable lobe diagram)in different manufacturing area.Thus,it is meaningful to establish the FRF(frequency response function)prediction model and multi-axis milling stability model of robot-milling system,and analyze the specific effect of various parameters upon milling stability.The research will provide theoretical guidance for processing parameter optimization.The FRF of manipulators changes much in different postures,for which the FRF prediction model of mechanical arm based on binary tree and RCSA(receptance coupling substructure analysis)is proposed.The FRF coupling model is analyzed for manipulators with single revolute joint based on RCSA theory,and then the FRF weighting model in arbitrary posture is deduced.According to least square method the modal parameters prediction model is analyzed and the equation to standardize the modal parameters is presented as well.Based on the arrangement mode of full binary tree and method of hierarchical solving,the FRF prediction model of manipulators with multiple axis is proposed.It's usually necessary for the robotic milling system to change milling tool to satisfy different conditions and the FRF of various combination of robot-spindle-holder-tool differs much from each other.The robotic milling system is divided into robot-spindle-holder substructure and tool substructure.The material parameters of tool substructure are optimized according to Timoshenko beam finite element theory through particle swarm optimization algorithm.And after identifying the dynamics of flexible joint by the use of IRCSA method,the tool tip FRF of robotic milling system can be modeled through RCSA method.The FRF experiments of robot-spindle-holder parts and robot-spindle-holder-tool parts are respectively conducted to verify the model above.To analyze the role of cutter orientation and redundant freedom played in robotic milling system,the robotic multi-axis milling stability model is proposed.And engagement between the tool and the workpiece is determined through characteristic curve,intersection curve and projective curve.Meanwhile the dynamic chip thickness of multi-axis milling system is discussed.To obtain the multi-axis milling SLD,a novel FFDM(fast full-discretization method)based on historical data is proposed without considering the “island effects”.Through the FFDM the computational efficiency is improved by 90% compared with that of FDM.Based on the milling stability model,the specific effect of cutter orientation and redundant freedom upon robotic milling stability is analyzed.Through robotic milling experiments,the proposed robotic mulit-axis milling stability model is verified.Above all,FRF prediction model and robotic milling stability model are built in this paper for the purpose of better parameter optimization and productivity improvement in machining propeller.