Laser Waveguiding And Energy Coupling In V Groove During Laser Pressure Welding Of Aluminum Alloy

In order to build lighten vehicles,aluminum-alloy and Laser Pressure Welding（LPW）are playing a more and more important role in the vehicle manufacture industry.However,Laser welding of aluminum-alloy still suffers from numerous problems,such as welding gas pore,cracks,joint softening,and stress deformation.LPW is one of the most effective welding methods,using high reflection of metallic material for vertical polarized laser beam.Between two pieces of materials,laser energy can be absorbed after multiple reflections in the V-groove.After the absorption on the surface of the work-piece,a thin layer is heated and melted rapidly;the materials are jointed together under the pressure.LPW demonstrates a variety of advantages in aluminum-alloy laser welding.For instance,it has high welding efficiency,little heat input,and high welding strength.Combining all the promising advantages together,LPW will bring a possibility of better quality and higher efficiency.Nowadays,the professional has little research and shallow understanding of the laser pressure welding.To show physical mechanisms for LPW and to guide the optimization of LPW technics,we studied on the features of transmission and absorption of laser beam in V-groove,and compared how technological parameters’effects the patterns.Based on Geometrical Optics and Fresnel formula,this study applied ray-tracing methods to build a theoretical model of laser transmission and energy coupling and tried to summarize a pattern between laser energy attenuation and power-density distribution in a V-groove.The result can be concluded as following:in the V-groove,along with the laser transmission,the maximum power density increased first and then suddenly decreased.Because of the influence of incidence angle,the smaller groove angle is,the appropriate defocusing distance,and the larger focal length of laser can cause more laser energy transmissions to the groove.Since different metal materials could influence the laser absorption rate,the absorption in waveguide process could be different.The higher absorption rate material,parallel polarized laser,shorter wavelength laser,and surface roughness would all make material absorb more energy when laser beam propagated in the incident groove during the waveguide process,and count against the convergence effect of laser energy.We used both 1.07μm wavelength fiber laser and 10.6μm CO₂ laser to carry out a laser scan welding experiment on a prefabricated A1060 aluminum-alloy V-groove model.The purpose was to testify how materials melt in the groove while are affected by several factors,such as un-polarized laser wavelength,power,defocusing distance,lens focal length,groove angle,materials,welding speed,incidence angle,and protective gas.The experimental results basically matched the previous calculation.For high reflectivity materials such as aluminum-alloy,when a laser beam passes the incidence of V-groove,LPW will increase the power density and enhance the melting result.The melting behavior of a material is similar to traditional laser welding in terms of laser power,welding speed,and protective gas.Nonetheless,faster welding speed can be accomplished.LPW has proper positive defocusing and appropriate focal length;it also reduces the groove angle so that the melting effects can be improved.Aluminum-alloy has low non-polarized laser absorption rate near the Brewster angle.As a result,even the incidence angle is as same as the Brewster Angle,the aggregation effect can still be enhanced.The material absorbs laser energy every time when laser beam reflects on the groove.Therefore,the number of reflection should not be too much for the non-polarized laser.Finally,researchers adopted both non-polarized fiber laser and CO₂ laser and conducted laser pressure welding successfully on the A1060 Aluminum-alloy model.