| With the advantages of high specific strength,high specific modulus,repeated melting and solidification,and friendly to the environment,carbon fiber reinforced thermoplastic composites(CFRTP)have become the preferred material for weight reduction and efficiency of high-end equipment.To meet the service requirements of equipment in extreme environments,CFRTP components often need to be assembled with metal components.The fusion joining technology,which makes use of the multiple melting and solidification characteristics of CFRTP substrates,enables non-destructive joining with metals and is receiving a lot of attention from related manufacturing companies.Laser joining technology using laser as the heating source has the advantages of non-contact,high energy density and easy automation,which can realize efficient and highly reliable CFRTP/metal joining and has become a research hotspot in recent years.In the process of CFRTP/metal laser joining,the high temperature of the matrix resin tends to decompose and produce pore defects inside the joint,which seriously affects the performance of the joint,while the clamping pressure will affect the resin flow and bonding state of the joint.In this thesis,a temperature and pressure regulated laser joining process for CFRTP/Al aluminum alloy is proposed,and the pore defects are suppressed by controlling the amount of resin extrusion from the joint.The main research contents are as follows:(1)In order to predict the process variable of resin extrusion,a simulation model of the temperature field of CFRTP/A6061 laser joint was firstly established,and a model of molten resin extrusion flow was established based on viscous fluid mechanics,and a coupled simulation model of temperature field-solid mechanics was established by combining the two.Finally,based on the ANOVA,a numerical model was derived to predict the extrusion volume of CFRTP/A6061 laser joining resin,and the influence of temperature and pressure process parameters on the resin extrusion volume was clarified.(2)To investigate the relationship between resin extrusion and joint performance,CFRTP/A6061 laser joining experiments with different clamping pressure,laser power and resin layer thickness were carried out.The effect of resin extrusion on the joint performance was obtained,and the suppression effect of controlled resin extrusion on the joint porosity defects was analyzed by combining the joint section morphology and cross-sectional characteristics.Finally,the temperature-compression process parameters were optimized based on the response surface method with the joint performance as the constraint,and the maximum failure load of the joint could reach 4222 N.(3)Based on the temperature and pressure regulated laser joining process,the ultrasonic-assisted laser joining process was initially explored to further suppress the porosity defects of the joint.A non-contact ultrasound-assisted laser joining experimental device was designed to effectively suppress the porosity defects by applying ultrasound during joining,which can improve the joint performance by nearly doubling the maximum shear force of about3104 N without adding resin,and the mode of action of ultrasound on the joint was investigated with simulation analysis.(4)Based on the CFRTP/A6061 temperature and pressure regulated laser joining process parameter optimization method,the design index of the laser joining robot was developed.Then,the robot structure and end-effector structure were designed,including the follow clamping module and the laser auto-focus module,and the theoretical verification and selection calculation were carried out,and finally the laser joining robot was built with the functions of follow clamping,laser auto-focus and surface joining and meets the design index. |
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