Experimental Study And Numerical Simulation On CFRTP/Stainless Steel Laser Direct Joining

Carbon fiber reinforced thermal polymer(CFRTP)has the characteristics of high strength,corrosion resistance,fatigue resistance and good heat resistance.It is an important material for lightweight manufacturing and has wide application prospect in aerospace and new energy vehicles.Achieving high quality joints between CFRTP and metal materials is a key technology for its applications.Laser direct joining technology has the characteristics of high speed,high strength,small vibration stress and flexible process.It has lots of advantages compared with the glue connection and the mechanical connection in CFRTP and metal materials connecting.In order to clarify the joining mechanism between CFRTP and metal materials,to explore the process parameters and to obtain high quality joints.In this thesis,CFRTP and stainless steel were selected as experimental materials.A fiber laser was employed to join the CFRTP and stainless steel by using laser direct joining.The thermal mathematical model of laser joining was established,and the temperature field in laser joining process was predicted and analyzed by using the finite element method.Firstly,the fiber laser was used to join the CFRTP and stainless steel by using laser direct joining.The effect of process parameters(laser power,scanning speed and clamping pressure)on the joint quality(joint strength,joint melting width and stainless steel melting width)were studied by single factor experiment.The results showed that the process parameters determines the joint quality directly.The interface of the joint was observed and detected by the laser scanning confocal microscopy(LSCM),the scanning electron microscopy(SEM)and the energy dispersive spectrometer(EDS).The analysis results showed that there are mechanical bonding(anchoring effect),physical bonding(van der Waals force)and chemical bonding in the joint interface.Secondly,the response surface methodology(RSM)was employed to design experimental process based on the results of single factor experiment.The mathematical models between the process parameters and joint quality were built.The effects of the process parameters and their interactions on the joint quality were analyzed,and the process parameters were optimized based on three different optimization criteria.The optimal combination of process parameters was as follows: the laser power was 280 W,the scanning speed was 3.9mm/s,the clamping pressure was 0.15 MPa,and the joint strength was up to 11.79 MPa with this process parameter.Finally,a mathematical model of thermal effect of laser joining was established based on the interface thermal conductivity of CFRTP/stainless steel.The finite element method was used to simulate the thermal effect.It was found that the model can accurately characterize the effect of clamping pressure on joint quality.The thermal contact model could be used to characterize the influence of clamping pressure on the laser joining quality accurately,and the relative error of the joint melting width was reduced to 6.7% from 17.8% compared with the traditional model.Based on the thermal contact finite element model,the temperature field of the laser joining process was simulated.The temperature field at the joint interface was analyzed,and the effect of process parameters on the temperature field was analyzed.The comparison between the numerical results and the experimental results showed that the thermal contact finite element model was reliable.The model can be used to optimize the process parameters and guide the process experiments.