| Carbon fiber reinforced composite materials(CFRP)are widely used in the aerospace field due to a series of excellent material properties(such as high specific strength,high specific stiffness and corrosion resistance,etc.).For large-size parts,it is usually used a robot to edge trimming along its contour to meet the high-precision assembly requirements after processing.However,the edge trimming quality inevitably is reduced for the processing chatter and milling force fluctuations caused by the robotic poor stiffness characteristics.To this end,robotic rotary ultrasonic milling technology was used in this paper to achieve high-efficiency and high-quality processing,and a calculation method was proposed based on milling force fluctuations and the stability region of robotic edge trimming in a poor stiffness environment.Through systematic investigation on the system stability,milling force and edge trimming quality of robotic edge trimming under different workpiece stiffness and ultrasonic amplitudes,the feasibility of applying robotic rotary ultrasonic milling technology to the field of poor rigid composite material milling was explored.The main investigation contents of this article are as follows:(1)Modal simulation analysis of robotic rotary ultrasonic edge trimming systemFirstly,the equivalent mass-spring-damping system was established to determine the robotic rotary ultrasonic edge trimming system in the feed direction(X),perpendicular to the feed direction(Y)and along the spindle direction(Z)dynamic characteristics based on the posture of the mobile robotic system when edge trimming.Secondly,the natural frequencies and damping ratios along the X,Y,and Z directions of the robot in a fixed posture were obtained from the hammering experiment.Then the carbon fiber reinforced composite material poorly rigid workpiece was used as the research object.the finite element simulation analysis software was used to obtain the stiffness and modal parameters of different working conditions.Finally,the modal parameters of the robotic rotary ultrasonic edge trimming system under different working conditions were obtained through the coupling frequency response function of the robotic rotary ultrasonic edge trimming system.(2)Investigation on stability of robotic rotary ultrasonic edge trimming composite workpiece with poor rigidityFirstly,considering of the influence of high-frequency tool vibration on the modal coupling between the poorly rigid of the robotic milling system and the workpiece system,instantaneous dynamic cutting thickness model in a single vibration cycle was established.Secondly,the milling force coefficient was obtained through the edge trimming experiment.Then the vector expression of the dynamic milling force in the frequency domain during the edge trimming process was established.the external excitation force model of the stability region analysis of the robotic rotary ultrasonic edge trimming was constructed.Finally,the influence of ultrasonic energy,different workpiece thicknesses and different workpiece overhangs on the stability of robotic edge trimming were analyzed separately.As a result,the stability region of was increased by the introduction of rotary ultrasonic vibration.In addition,the smaller the component overhang,the better the stability of edge trimming would be.The bigger the thickness of the workpiece,the better the stability of edge trimming would be.(3)Investigation on milling force of robotic rotary ultrasonic edge trimming composite workpiece with poor rigidityFirstly,for the problem of the sharp fluctuation of the milling force caused by the poor rigidity of the robot,the appropriate experimental parameters were selected from the stability lobe diagram,and milling force experiment of the ultrasonic and normal edge trimming of CFRP was carried out based on robot to analyze the effect of ultrasonic vibration on the fluctuation and mean of milling force.The results show that the ultrasonic effect was the best when the overhang condition was 120 mm,and the milling force fluctuation can be reduced by62.71%.Secondly,based on the analysis on milling force and milling force fluctuation under different workpiece overhangs of robotic rotary ultrasonic edge trimming,the influence of workpiece rigidity on the milling force and milling force fluctuations was explored.The results show that for the milling force in all directions,the average value and fluctuation of the milling force decreases first and then increases with the increase of the overhang of the workpiece.(4)Investigation on surface quality of robotic rotary ultrasonic edge trimming composite workpiece with poor rigidityFirstly,the impact of edge trimming quality under different robot stiffness was analyzed.robotic edge trimming experiments in different poses were carried out,and the effect of ultrasonic vibration on the improvement of edge trimming quality quality under different robot stiffness was determined.The results show that the effect of ultrasonic vibration can achieve the edge trimming requirements under different robotic stiffness,the quality of ultrasonic edge trimming was improved by 32.17% through comparison.Secondly,the effect of ultrasonic vibration on the quality of robotic edge trimming was analyzed.The robotic rotary ultrasonic and normal edge trimming experiment under different processing efficiency was carried out,the three-dimensional surface roughness and two-dimensional surface roughness of CFRP were measured and analyzed,the mechanism of ultrasonic energy’s suppression of edge trimming damage was explained.The results show that the edge trimming damage was effectively suppressed by ultrasonic vibration,and the surface roughness of edge trimming was reduced by 33.75%.Finally,the influence of workpiece rigidity on the edge trimming quality of the robot was analyzed.based on the analysis of robot ultrasonic edge trimming quality under different workpiece overhangs,the influence law of workpiece rigidity on edge trimming quality was explored,and the best working condition of robotic edge trimming was determined.The results show that when the overhang condition was 100mm-120 mm,the milling force fluctuates less and the machining stability was better,so that the edge trimming quality was the best. |
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