Process Simulation And Technology Analysis Of Overhanging Structure Fabricated By Selective Laser Melting

It is very easy to produce poor surface quality,edge warp and other serious defects when forming a structure with overhanging area by selective laser melting.This article carries on the simulation analysis and technology research about overhanging structure characteristics formed by selective laser melting.The influence of process parameters such as laser power and scanning speed is explored on the forming characteristics of the overhanging structure through theoretical analysis,numerical simulation by finite element method and experimental verification.The relation between the key processing parameters and weld pool temperature is obtained by fitting the temperature distribution function which expresses a laser movement process on a semiinfinite plane's surface.The following conclusions are obtained: When the scanning speed is in the vicinity of 2.1a?6),the temperature of the molten pool center is moderate to the susceptibility of the scanning speed and laser power with a better energy utilization ratio.At the same time,the line energy input density can well reflect the change law of the temperature of the molten pool.When the scanning speed have larger difference with 2.1a?6),there is a great difference about the change law between the line energy input density and the temperature of the molten pool which cause the difference about the change law between the line energy input density and quality of test parts;The laser power required for forming pieces of different materials is proportional to the melting point and thermal conductivity and inversely proportional to material energy absorption rate.The distribution and change regulation of temperature field and stress field are obtained by the finite element numerical simulation for fabricating overhanging structure by selective laser melting.The analysis results show that in the process of selective laser forming overhanging structure,the temperature of molten pool located at overhanging position is obviously higher than that located at the center position when laser scanning these position.The maximum residual stress occur at coincident crossover points of layer scan region and substrate.The vertical direction tensile stress was detected at the bottom edge of printing piece,while the vertical direction compressive stress was detected at the bottom center of printing piece.The vertical direction stress distribution at the top of printing piece was not obvious.Obvious deformation occurs at the position of the overhanging structure.When the ratio of laser power to sweep velocity is constant,the greater the laser power,the more deformation of the overhanging structure.Through the experimental research on forming overhanging structure by elective laser melting,we can draw the following conclusions: There is obvious upward warping at the position of overhanging structure formed by select laser melting which has a accumulation trend layer by layer.The surface quality is poor with serious surface adhesion powder phenomenon.The grain size of the printed piece is below 1 ?m which is fine at interior of the melt channel is fine compared with the grain at the edge position of the melt channel.Many pores is found at the edge position of the melt channel which size are about 10?m.The number of pores at the overhanging position is more than that at inside of printing piece.The change regulation of deformation is similar to the central temperature of the molten pool.When the laser power increases or the scanning speed decreases,the deformation tends to increase.When the energy input density is fixed,the more the laser power is,the more serious the warping is.The arrangement also have important influence on the quality of molding parts.The mechanical property of the drawing parts at the horizontal direction is more stable than those at the vertical direction.And the extend direction of overhanging should be same as the moving direction of scraper for better forming quality.