Research On Machining Stability And Surface Quality Of Industrial Robot Using Acoustic Emission Technique

Carbon fiber reinforced plastics(CFRP)are more and more widely used in large passenger aircraft and aerospace vehicles due to their high specific strength,high specific modulus and strong design.After the composite material is formed,it needs to be machined to meet the requirements of connection and assembly accuracy.Industrial robots can process large composite components due to their strong accessibility to processing space and good flexibility.However,due to the low stiffness of the serial industrial robot,vibration is easily generated during the machining process,which affects the quality of the cutting surface.In order to study the cutting stability and surface quality of industrial robots,this paper talked industrial robot cutting and machining composite materials as the research object,the characteristic signals were analyzed in time domain,frequency domain and time-frequency domain based on fast Fourier transform,short-time Fourier transform and wavelet packet decomposition,and then the identification and characterization of vibration and surface defects in the process of machining composite materials by industrial robots were studied using acoustic emission technology.The main research contents of the paper are as follows:(1)The generation mechanism of robot cutting vibration was clarified,the coupled dynamics model of the serial industrial robot machining system with the milling force of CFRP composites as the external load was established,and according to the zeroorder approximation method,a stability map with the spindle speed as the X axis and the axial depth of cut as the Y axis was drawn to predict the stability of the machining system,and an identification method of forced vibration and self-excited vibration based on acoustic emission characteristic signals was proposed.The accuracy of the vibration detection method and the validity of the stability prediction method were verified by designing a robotic milling CFRP experiment.(2)Based on the processing of acoustic emission signals,the identification methods of hole-making surface defects under different spindle speeds and feeds were studied.The type and generation mechanism of hole surface defects during the machining process were analyzed,and the influence of machining process parameters on the hole quality was explored.Through the characteristic analysis of the acoustic emission signal in time domain,frequency domain and time-frequency domain,the surface defects,vibration characteristics and the damage type of the machined surface during the machining process of the composite material were characterized.(3)The identification of surface defects of CFRP/Al laminated components under different process parameters was carried out,and the influence of process parameters on processing temperature was analyzed.The surface morphological characteristics of the pores of the CFRP layer and the Al alloy layer under different process parameters were compared and analyzed.The results showed that significant burr defects appeared at the exit of the Al alloy layer holes.A method for identifying burr defects on the surface of hole-making exit of CFRP/Al laminated components based on acoustic emission characteristic signals was proposed,which provided theoretical support for the study of efficient and precise hole-making technology for composite industrial robots.