Study On Laser Additive Manufacturing Technology And Deformation Of 321 Stainless Steel

Laser additive manufacturing is a technology that uses high-energy laser beam to melt specific powder and deposit it layer by layer on the surface of the substrate.With the advantages of high forming accuracy and high degree of automation,it is widely used in the fields of material surface modification and manufacturing of the parts.However,due to the uneven temperature change in the process of additive manufacturing,it is easy to cause the deformation of the parts,affecting the quality of the formed parts.The 321 stainless steel is a kind of common austenitic stainless steel,which has the advantages of good processability and weldability.In this paper,the forming process of 321 stainless steel and the deformation in laser additive manufacturing were investigated based on the laser additive manufacturing technology.The influence of laser power,scanning speed and powder feeding rate on the macro morphology of 321 stainless steel was studied by controlling single variable method.The microstructure and microhardness of cladding layer were analyzed.For single pass cladding,the results show that the height and width of the cladding layer increases with the increase of laser power;decreases with the increase of scanning speed;increases with the increase of powder feeding rate,but the trend is getting smaller.Under the following process conditions: the laser power of 2200 W,the scanning speed of 7mm/s,the powder feeding rate of 13.2g/min,the lap ratio of 30%,the surface of single-layer cladding layer is flat without macro defects.The microstructure of the cladding layer is mainly composed of cellular crystal and dendrite;the width of the remelting zone between channels is about 280?m and the width of the remelting zone between layers is about 320?m without interlayer residence time;the microhardness of the cladding layer is about 410HV;the microstructure of the overlapping zone is coarsened and accompanied with the decrease of the microhardness.The temperature field and deformation of 321 stainless steel in the process of laser additive manufacturing were analyzed by the finite element software and experiments.The results show that in the process of sequential laser additive manufacturing of 321 stainless steel,the temperature is constantly accumulating and the temperature peak is increasing due to the preheating of the previous cladding area for the latter and the insufficient heat dissipation during the continuous cladding;The substrate presents the form of raising around,and the deformation is more than 4mm.Based on the numerical model,the deformation of the substrate was controlled by setting different scanning paths,inter-track starting temperatures,and applying mechanical constraints.The results show that when using the scanning path from the middle to both sides for cladding,the temperature field is evenly distributed,the deformation of the substrate obtained by the experiment is 3.12 mm,and the deformation is reduced by 23.5%.Reducinging the starting temperature between channels can improve the heat accumulation phenomenon,when the initial temperature is 200?,the deformation is reduced by 34.8%,and the change of deformation is not obvious with the temperature reduced further.The deformation of the substrate can be reduced by applying constraints.With the decrease of the clamping distance,the deformation of the substrate decreases gradually;with the increase of the constraint width,the deformation of the substrate decreases gradually.When the clamping distance is 25 mm and the constraint width is 30 mm,the deformation obtained by the experiment is 1.16 mm,which is reduced by 71.6%.