Research On Deposition Process And Dimensional Accuracy Control Of Multi-layer Single-track LMD Forming

Laser Melting Deposition(LMD)technology is one of the key technologies in the field of additive manufacturing.It can quickly manufacture high-quality complex structural components by using laser as a heat source to melt metal powder.Multi-layer single-track process forming is the basis of thin-walled parts.In the LMD forming process,the deposition process and dimensional accuracy of the parts are unstable,which seriously restricts the final forming quality of thin-walled parts.It provides guidance for the quality of the final deposition in-depth study of the dimensional accuracy of the multilayer deposition process of accumulation.The paper focuses on 30 Cr Ni2Mo VA alloy powder,and a study is carried out on the deposition process and dimensional accuracy of the material in the multilayer deposition.The deposition size forming characteristics in the multilayer deposition process and the influence of process parameters on the deposition size are analyzed.According to the forming characteristics of the process,relevant control strategies are formulated to improve the dimensional accuracy of the formed parts.The main content of the paper is as follows:In single-layer deposition,the study is carried out about the influence of process parameters on deposition size and deposition quality.A multi-factor orthogonal experiment is designed to analyze the influence of process parameters on the deposition size from the perspective of range analysis.The results show that the spot diameter and laser power have a greater impact on the deposition width,and the scanning speed and powder feeding rate have a great influence on the deposition height.In view of the problem of single-track deposition quality,the research on the deposition quality of key process parameters is carried out.The results indicate that the deposition quality on the single track can be divided into four different deposition quality areas according to the parameter range of laser power and scanning speed: discontinuous molten state,incomplete molten state,normal molten state and excessive molten state.The process parameters in the normal melting state are suitable for multi-layer accumulation,while the other three areas can improve the deposition quality through the optimization of process parameters.The study is carried out on the influence of different factors on the deposition size for the laser melting multilayer single-track deposition process.By analyzing the deposition size data under different line energy densities during the multi-layer single-track process,it shows that the size data of the same deposition layer tends to be stable.Due to the heat accumulation effect in the multi-layer stacking process,the overall size of the deposition layer near the substrate fluctuates greatly,being extremely unstable state.After a certain number of layers are stacked,the deposition size data fluctuates less and is in a relatively stable state.A quadratic regression model between laser power,scanning speed and deposition size is established.The model has high prediction accuracy and can be used to predict deposition size under different process parameters.The analysis of the deposition size of different deposition layers shows that the deposition layer size in the multi-layer process is positively correlated with the laser power and negatively correlated with the scanning speed.In the deposition size data of the accumulation method,the size of the beginning and the end is different from the middle stable area.Based on the forming characteristics and laws of the deposition size,the control strategy of the deposition size is studied.By analyzing the forming process of the LMD process,the neural network model optimized based on particle swarm algorithm is used to predict the deposition size of the LMD process.Three control strategies of fuzzy adaptive proportional control,multivariable fuzzy control and PID decoupling control are used to increase the deposition width accuracy.Through the simulation comparison of different control strategies,the results show that the fuzzy adaptive proportional control strategy has the best control effect.It only takes0.3s to reach the set value of the deposition width,and there is no overshoot during the control process.The anti-interference performance of this strategy is proved in the negative step interference test,and the set value of negative interference can be reached at about 0.24 s.The effective control of the deposition width in the multi-layer single track is realized.