Study On The Forming Mechanism Of Laser Fillet Welding Of Plate Of Moderate Thickness

In today’s environment where industrial automation is rapidly developing and product quality requirements are gradually increasing,products need to be produced with high quality and efficiency to meet the needs of modern society,and laser welding,which can provide high quality welds and high stability,is naturally favored by the welding industry.304 stainless steel,which is very common in our life,is often used as the material for hydraulic tank because of its strong corrosion resistance.Plate connection is a kind of manual arc welding with greater thermal influence and difficulty in ensuring the consistency of quality,which greatly restricts the development of enterprises.And the 304 stainless steel and laser welding are relatively good.After laser welding,the heat affected zone of the 304 stainless steel weld is smaller and the quality is better,which can greatly improve the production efficiency of the enterprise and promote social development.Excellent weld joints are closely related to the morphology and microstructure of the weld.In order to achieve the purpose,it is necessary to conduct single-factor experiment to study the influence law of laser fillet welding process parameters on the morphology,microstructure and mechanical properties of the weld,so as to obtain the appropriate process parameters,which is of great significance to the production of enterprise box.In this paper,the fillet welding of 304 stainless steel plate was taken as the research object.Firstly,the influence of welding process parameters(including laser power,welding speed and defocusing distance)on the weld morphology was studied through single-factor experiment,and the influence law was obtained by quantifying the weld width,the collapse of the upper surface and the hump at the bottom.Then,the microstructure of the weld was observed in the polished and corroded metallographic sample,and it was found that the microstructure of the weld was completely different from that of the base material.Since the heat-affected zone of 304 stainless steel was not obvious,the microstructure was mainly focused on the change of the grain size of the equiaxed crystals at the center of the weld and the width of the columnar crystals at theedge of the weld.Then the distribution of microhardness in the weld was measured,and the influence of weld microstructure on microhardness and the influence law of process parameters on the average microhardness was studied.The average microhardness was as high as 227.6HV.After the tensile test,it was found that the fractures were in the weld and the maximum tensile strength was 576.4 MPa.The tensile strength was analyzed by combining the weld structure and the fracture structure obtained after the tensile test,and the influence law of welding process parameters and tensile strength was obtained.In addition,based on the actual welding situation,the Simufact Welding software is used to select and establish a suitable laser fillet welding heat source model.The heat source model is checked in accordance with the criterion of the pool boundary to obtain a weld with the same "nail head" shape as the experiment.The numerical simulation of the temperature field of laser fillet welding was carried out,and the temperature field distribution of laser fillet welding and the thermal cycle curves of different regions were obtained,especially the heating condition of the wing plate.The thermal cycle curve is used to quickly obtain the temperature gradient change of the weld,and the origin and distribution of different microstructures in the fillet weld are explored.