| Ti-6Al-4V is a light alloy with high strength,stiffness and other excellent properties.It has been widely used and studied in aerospace,biomedical and other fields.As a subversive manufacturing technology,metal additive manufacturing has high process flexibility,which can effectively solve the difficult problem of complex structural parts processing,but also has the advantages of rapid forming and low cost.As one of the main processes of additive manufacturing,metal fuse additive manufacturing has attracted much attention due to its high material utilization rate,low cost and low pollution.However,the parts of this process have the problems of poor surface roughness and low dimensional accuracy,which restricts its wide application.In this study,Ti-6A-4V titanium alloy was taken as the research object,a low power and high-quality metal fuse additive manufacturing process was proposed,and the forming process,microstructure and properties of the single deposition layer and multi-layer thin-walled parts were further studied.The main research contents of this paper are as follows:Aiming at the research of single pass forming process of metal fine wire,the influence law of main process parameters such as laser power,Joule current and wire feed speed on the geometrical characteristics of single pass deposition layer was analysed,and the process parameter window suitable for deposition was determined.Orthogonal test was used to analyse the influence of technological parameters on geometric characteristics,and better forming technological parameters were obtained,which laid the technological foundation for the deposition of multilayer thin-walled parts.Aiming at the research on the forming process of multi-layer thin-walled parts,the influence law of laser power,wire feed speed and moving speed on the width and height of thin-walled parts is analysed,and the forming process characteristics of thin-walled parts are revealed.The influence law of process parameters on surface roughness Ra of thin-walled parts was studied and analysed to provide guidance for improving surface quality of thin-walled parts.Based on the analysis of the defects such as wire spheroidization and forming collapse in wire feeding additive manufacturing,the forming process of titanium alloy thin-walled parts with high dimensional accuracy and low surface roughness was optimized by means of gradient control of heat input and precise control of interlayer increment.In order to study the forming quality and properties of thin-walled titanium alloy parts,XRD,OM,SEM and other means are used to analyse the phase and macro and micro structure characteristics of the deposited samples.The results show that the main phase of the deposited state is α phase,the macro structure is columnar crystal penetrating through the thin-walled parts,and the micro structure is typical Vickers structure at the bottom due to the influence of heat input mechanism.The middle part and the top part are the netted basket structure.The mean hardness of the deposition state is maintained at about 337 HV,and the mechanical properties of the deposition direction are better than that of the horizontal direction,and the mechanical properties can be comparable with forgings and castings.Finally,aiming at the forming defects of thin-walled ring parts in side-axis wire feeding deposition,the limitations and causes of defects in side-axis wire feeding additive manufacturing were analysed,and the forming process was optimized by head-tail spiral transition deposition,which solved the problem of interface defects between layers and completed the deposition of thin-walled ring parts with a certain size.This study can realize the forming of high quality additive parts under the condition of low energy consumption,which can provide process reference for the quality improvement of metal fuse additive manufacturing,and also has important reference significance for aerospace and orbital metal fuse additive manufacturing. |
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