The Research On Thin-wall Overlap Deposition Of Metal Laser Additive Manufacturing

Laser metal additive manufacturing is a new manufacturing technology that has been developed in recent years.A solid part can be directly formed from a model.This technology can reduce the intermediate process and deposit functionally entities and homogeneous entities.It has a wide range of applications in many fields,such as automotive,electronics,medical,aerospace and so on.With the advantage of the technology,metal laser additive manufacturing will be applied in many fields.The thinwall forming technology in metal laser additive manufacturing has been researched by many scholars and the application of thin-wall structures in aerospace area is quiet common.However,the researches of thin-wall deposition have always been a tough problem.The existing researches are concentrated on the study of simple models such as single-track multi-layer model or multi-layer multi-layer model,etc.And few research on aero-engine turbine blades,especially model with thin-wall structures.Therefore,this paper proposes a study on the thin-wall structure depositon.The main contents are as follows:1.Considering the characteristics of laser thin-wall structure deposition,a monitoring system for detecting melt pool temperature and melt pool profile was built.So the state of the melt pool can be observed in real time.At the same time,the preprocess of the melt pool temperature data and profile data is proposed to improve the signal-to-noise ratio.So the accuracy of the analysis of the data can be improved.2.For the overlapped area of thin-wall structure,theoretical analysis of the effect of powder concentration distribution and laser power density distribution are proposed.The theoretical analysis shows that the deposited cross-section profile of the cladding layer will affect the distribution of powder concentration.Since the thin-wall structure is more sensitive to the changes of the process parameteras,the cumulative error of the powder concentration changes directly affects the thin-wall structure deposition.The effect of larger width-to-height ratio on the powder concentration distribution is less than the effect of smaller width-to-height ratio.At the same time,the laser power intensity suddenly attenuates at the overlapping position and the larger width-to-height ratio of the cladding layer weakens this phenomenon;3.A finite element analysis model was established to simulate the thin-wall overlap model.Using the finite element analysis software ANSYS and its life-and-death element method,the addition of metal materials and the movement of the laser heat source were realized.The variation of temperature along the laser scanning direction in the overlapping position was analyzed.The temperature variation from the non-overlapped position to the overlapping position were analyzed.The simulation results show that when the laser scan the overlapping area,the melt pool will suddenly become smaller and the cooling rate of the melt pool will suddenly increase at the overlapping area.By adjusting the process parameters,it is found that increasing the width to height ratio of the cladding layer can reduce this situation.4.Corresponding experiments were carried out to validatae theoretical analysis and numerical simulation.The state of the melt pool was monitored during the entire experiment process.The experimental results show that the cumulative error caused by the effect of a larger width-to-height ratio on the powder concentration was smaller than the smaller width-to-height ratio.With the large width-to-height ratio,there are no defects such as voids in the overlapped area.The monitoring of the melt pool temperature and profile reveals that when the laser scan the overlapping position,the melt pool suddenly becomes smaller and the temperature of the melt pool suddenly decreases.The effect of this fluctuation will lead to convex near the overlapped position.This defect can be reduced by increasing the width-to-height ratio of the cladding layer.