Research On Weld Forming Process And Quality Evaluation Method For Laser Welding Of Dissimilar Materials

To meet the requirements for the comprehensive performance of product,the laser welding of dissimilar materials is more and more widely applied in the field of manufacturing industries.Compared with the laser welding of same material,the differences in properties between dissimilar materials make the laser welding process of dissimilar materials prone to welding defects such as solute segregation and cracks,which seriously affects the quality of welded joint.In this work,the research on the weld forming process of laser welding of Q235-316 L dissimilar materials is mainly carried out.A quantitative evaluation model for the weld morphology quality of laser welding is proposed.A threedimensional multi-phase flow numerical model considering molten pool and keyhole coupling for laser welding is developed,which reveals the weld forming mechanism of laser welding of dissimilar materials.This work has important theoretical value and guiding significance for actual welding process.The main contents are as follows:(1)The experimental platform for laser welding is built by using laser,welding head,robot and other experimental equipments.The laser welding experiments of Q235-316 L dissimilar materials under the welding process conditions of different laser powers P,welding speeds S,focus positions FP are carried out by orthogonal experiment method.The formed welds under different process conditions are obtained.(2)The characteristics of typical weld morphologies for laser welding of Q235-316 L dissimilar materials under different welding process conditions are analyzed.The weld geometrical indexs including weld integrity I,weld width W,symmetry of upper and lower widths UD and symmetry of left and right widths LR are extracted.The relationship model between weld geometrical indexs and morphology quality and the relationship model between welding process parameters and weld geometrical indexs are established,respectively.Based on the above two relationship models,the quantitative evaluation model of weld morphology quality with welding process parameters as input is proposed.The effectiveness of the evaluation model is verified.(3)The Fresnel absorption,inverse bremsstrahlung absorption,and the influence of property difference between dissimilar materials on the boundary conditions such as force and heat transfer in the laser welding process are comprehensively considered.A multi-phase flow numerical model considering molten pool and keyhole coupling for laser welding of same material and dissimilar materials is developed.The effectiveness of the multi-phase flow model is verified.(4)Based on the multi-phase flow model considering molten pool and keyhole coupling for laser welding,the influences of the evolution processes of the molten pool and keyhole on the weld forming processes for laser welding of 316L-316 L same material and Q235-316 L dissimilar materials are studied,respectively.The asymmetric characteristics of laser welding process of dissimilar materials are analyzed.The influence of keyhole forming on weld forming process of the welding of dissimilar materials is discussed.The influencing law of process paramaters including laser power and welding speed on the evolution of keyhole and the temperature field,flow field and alloy composition distribution in the mixed molten pool in the laser welding of dissimilar materials are obtained,and the weld forming mechanism of laser welding of dissimilar materials is revealed.