Research On Variable Spot And Dynamic Scanning Method Of Selective Laser Melting Based On Thermal Imaging Detection

Selective Laser Melting(SLM)technology is a metal additive manufacturing technology with high forming accuracy and complete detail expression of parts.Compared with other metal additive manufacturing technologies,SLM technology has lower forming efficiency.The variable spot scanning method can use large spot scanning interior to improve efficiency,and small spot scanning contour to improve accuracy,which can effectively improve SLM forming efficiency and ensure accuracy,but large spot filling has a serious problem of heat accumulation.The dynamic scanning method of real-time planning of the scanning path according to the heat concentration on the forming layer helps to control the temperature spatial and temporal distribution during the forming process,optimize the uniformity of the temperature field of the large spot scanning,and improve the forming quality.Therefore,a dynamic scanning method with variable spot based on thermal imaging detection is proposed.The method is studied from four aspects: automatic calibration of infrared thermal imager,dynamic scanning strategy with variable light spot,system software and hardware design,and experimental verification.In order to solve the problem that the relative position(structure)of the optical system changes(displacement and deformation)caused by the mechanical vibration of the SLM equipment,the environmental temperature change and other factors after the installation of the infrared thermal imager,the imaging position error is uncontrollable.The dynamic implicit calibration method based on multi-point fitting uses laser beam irradiation as the calibration heat source to form a calibration grid,corrects the centroid shift of the defocused beam,and uses the error detection method to subdivide the areas with unqualified errors in the initial grid until all areas pass the error detection.Compared with the traditional calibration method,this method does not require a calibration board,does not rely on the relative position relationship between the thermal imager and the galvanometer scanning system,can detect position deviations in real time and automatically complete the calibration process,thereby providing accurate temperature field information for feedback control.Aiming at the variable spot scanning strategy,in order to solve the problem that the conventional 3D scanning cannot guarantee the size deviation of the formed part and the spot size deviation on the defocusing plane,a new variable spot scanning method is designed.Methods such as spot profile offset improve the dimensional accuracy and surface quality of variable spot forming.In order to solve the problem of efficiency loss caused by dynamic scanning,a dynamic scanning strategy for efficiency optimization is designed.The scanning sequence of the partition is dynamically optimized through the connected area to determine the heat concentration position.In the case of less scanning efficiency loss,it solves the thermal stress of variable spot scanning and improves the forming quality.On this basis,a new dynamic implicit calibration module,a variable spot dynamic path module and a real-time control module were developed to form a new SLM process and control software,and the process test of the variable spot dynamic scanning forming316 L stainless steel parts was carried out.The following conclusions are drawn:Compared with the conventional small-spot body forming efficiency,the proposed dynamic scanning method with variable spot is improved by 21%,the surface roughness of the forming surface is reduced by 22%,the roughness of the accumulation surface is increased by 18%,the ultimate tensile strength is reduced by 64.2MPa,and the elongation is increased.22% and hardness increased by 8%;compared with the large-spot scanning method without optimization,the surface roughness of the forming surface is reduced by 54%,the roughness of the accumulation surface is reduced by47%,and the temporal and spatial distribution of the temperature field is more uniform,which effectively solves the problem of heat input concentration.The residual stress amplitude is reduced by about 35%,the ultimate tensile strength is increased by20.9MPa,the elongation is increased by 4.3%,and the hardness is increased by 9.5%,verifying the effectiveness and reliability of the proposed scanning method.The above research results show that the use of a dynamic scanning method based on thermal imaging detection with variable spot can effectively improve the forming efficiency of the SLM while ensuring the forming quality.