Study On Fiber Laser Welding Technology Of Ultra-thin Metal Sheets

As the development of modern manufacturing industry,the application of ultra-thin metal sheets welding became wide in the precision welding area.Small craft window,defects of rosin joint and burning through with improper process parameters and deformation in the welding process all were welding difficulties of ultra-thin.Laser welding had the advantages of high speed,high precision,small deformation and high automaticity,so it is the best way for ultra-thin welding.But the study of laser welding for ultra-thin sheets was very little in abroad.The study of laser welding for ultra-thin sheets focused on procedure in nationwide,and most of which used pulse laser of low efficiency.Dissimilar metal welding of ultra-thin sheets was not been researched at all.Laser welding system consisting of fiber laser device,welding robot,laser head of reflective focusing and control software were used in this paper.Same metal and dissimilar metal laser welding of SUS304 and T2 copper which were representative metal in material property and industrial application were held in these experiments.The purpose of this paper were conducting a further discussion of ultra-thin sheets welding procedure,and having some certain research for the defects and mechanism in welding.The results of experiments showed that the weldable range of laser power and welding speed were wide in single factor experiment for 0.2mm thick SUS304 lap laser welding,and the microstructure in the welding joints of ultra-thin sheets was similar with thicker sheets.The width of welding seam was greater than the thickness of sheet,so tensile fracture following tearing instead of shear fracture were happened in tensile tests.The load was about 1.9kN,88%of the base metal.The affordable load of welding joints could decrease as the increase of heat input when complete penetration,and the fracture place moved from fusion line to HAZ or base metal.Lower laser power with lower welding speed could get stronger welding joints than high laser power with high welding speed,which showed that laser power had more effect than welding speed.The results of experiment of lap laser welding for 0.2mm T2 copper sheets showed that sound welding seam could be obtained in high laser power with high welding speed while could not in low welding speed.As the high laser reflectivity of copper,laser power density had great influence to welding seam formation.Laser power density affected welding mode,and the critical laser power density was different in different welding speed.When welding speed was 0.5m/min,the critical power density was 2.4×10~6W/cm~2,and the microstructure in the welding seam center was columnar crystal growing along the welding direction while it was equiaxed crystal in high laser power with high welding speed,of which the craitical laser power density was 4.0×10~6W/cm~2.The grain size in HAZ grew in both welding joints of two different processing parameter,but the grain size obtained in low laser power with low welding speed grew more seriously,which made it had lower microhardness.The tensile tests showed that HAZ was the place where fracture happened,and the properties of welding joints in high laser power with high welding speed were greater.The tensile strength was about 200MPa.The results of dissimilar metal lap laser welding with above two metal sheets showed that because of the inconsistent deformation,gap was formed between two lap sheets during welding with general clamping condition,and joint could not form.When the fixture was improved,joint could be obtained even gap was still exist,and tensile fracture place was in HAZ.To prevent the gap,sandwich lap welding of steel-copper-steel was used and achieved nice results.The weldable range of laser power and welding speed were wide in single factor experiment.Layered stripes were observed in the joints microstructure.The EDS results showed that each element distributed all the welding seam,but the lower seam have copper cluster,and the copper content was high in the stripes.The microhardness tests showed that the most soft area was HAZ in copper layer,and the unilateral HAZ width was larger than copper-copper lap welding joints.The tensile tests showed that the fracture was happened in HAZ of copper layer,and the tensile strength was also about 200MPa.