Research On Forming Accuracy Control Of Laser Deposition Manufacturing Based On Molten Pool Monitoring

During laser deposition manufacturing process,the forming width of the single track is mainly controlled by the molten pool width.In this paper,the size of laser molten pool is taken as the research object,and the factors influencing the final forming width are analyzed by the evolution of the melt pool width.In order to improve the precision of laser deposition forming,the corresponding strategy of controlling the size of molten pool is put forward.Firstly,the main factors that influence the width of single channel forming are studied.In order to establish an empirical model exactly describes the relationship between process parameters(laser power,scanning speed and powder feeding rate)and molten pool size,laser control in the uneven speed stage and Kalman filtering are used to denoise the measured data of the molten pool width.As a result,the accurate detection of the forming process of molten pool width can be achieved and the prediction accuracy of molten pool width can be guaranteed.Based on the orthogonal experiment,a multiple regression model is established as Empirical model.And the goodness-of-fit is up to 94%,and the maximum error is less than4.5%.The results of single variable experiments conducted to validate the model show that the molten pool width has a positive correlation to the laser power and a negative correlation to the scanning speed.The experimental results are in good agreement with the regression analysis.Then,the effects of heat accumulation in single-channel multi-layer deposition process on the morphology and deposition width of the molten pool are explored.A three-dimensional(3D)multi-layer model for LDMed TA15 titanium alloy is developed to discover thermal cycle characteristics,temperature distribution of molten pool and molten pool geometry.Meanwhile,the change of nodes temperature,the morphology and temperature distribution of molten pool are compared and analyzed.Results show that there is a phenomenon of heat accumulation during deposition process,which causes the area of the molten pool to gradually become larger.Besides,a real-time monitoring test of molten pool in LDM process by using the same process parameters as simulation is carried out to verify ANSYS results.The results show that thermal accumulation is strongly correlated to melt pool width and melt pool inclination,however,melt pool temperature and width gradually become relatively stable after a certain number of layers.The experimental data and Empirical model prediction show a good agreement.Finally,control system of molten pool size during LDM process is investigated in this paper.Experiments of step laser power and step scanning speed are designed.The dynamic relationship between the process parameters and the molten pool width is identified by ARMAX model to provide the design basis for the molten pool width control system,and the model output is compared with the experimental data to verify the reliability of the model.And the closed loop control system of the molten pool width based on the classical incremental PID controller with relatively high control precision is established.