| Wire and Arc Additive Manufacturing is a 3D printing forming technology in which arc is used as heat source and melted metal wire is piled up layer by layer.In recent years,wire and arc additive manufacturing technology has attracted more and more attention in industrial manufacturing and other related industries because of its advantages such as high deposition rate,low equipment cost,wide range of materials,high material utilization rate,forming integration,high density of forming parts,good mechanical properties and unrestricted size of forming parts.At present,there are more researches on the simple structural parts of wire and arc additive manufacturing technology,but less on the wire and arc additive manufacturing of complex structural parts.The research on wire and arc additive manufacturing of complex structural parts is helpful to realize the production of complex structural parts that are difficult to be produced by traditional manufacturing technology,and can promote the rapid development of wire and arc additive manufacturing technology and the application of actual production.In this thesis,three kinds of complex structure with arc section,split partition and propeller blade are designed,and 316 L stainless steel welding wire is used to prepare the forming parts.In the preparation process,according to the characteristics of the cross-section structure,the deposition direction,current mode and interlayer residence time were changed for the arc cross-section structure,the current mode,pulse duty ratio and heat input were changed for the partition partition structure,and the deposition path was changed for the propeller blade structure.The forming quality analysis,metallographic structure analysis,hardness test,tensile property test,fracture morphology analysis,performance test after heat treatment of the forming parts were carried out to compare and analyze the influence of each variable on the forming quality and performance of the forming parts.The experimental results show that,under the influence of gravity and heat accumulation,the volume of molten pool increases with the increase of the number of deposited layers,and the outer wall of the forming part has a slight flow,and the inner wall is well formed.The forming quality of the curved section structure was compared and analyzed.The reciprocating deposition,pulse current mode and interlayer residence time of120 s were adopted.The deposition height of the formed parts was uniform without defects,the deposition process was stable and the forming quality of the formed parts was good.The forming quality of the inner,outer and partition walls prepared by pulsed current is better than that of the constant current mode.With the increase of pulse duty ratio,the peak pulse current increases,the volume of the relative molten pool also increases,the wall thickness of the obtained forming parts increases,and the corresponding height decreases.With the increase of heat input,the height and wall thickness of the forming parts increase,but the surface quality decreases.For the propeller blade structure prepared by continuous deposition path,the forming appearance of the formed parts is good without defects,because arc and arc are avoided in the deposition process,and the forming quality of the blade and shaft parts is better than that of piecewise deposition.The height of the formed parts obtained by continuous deposition is reduced,and the wall thickness is increased.The microstructure of the forming parts is mainly austenite with a small amount of ferrite,dendritic crystals are above the interlayer fusion line,and columnar crystals are below.The effects of current mode,deposition path and interlayer residence time on the microstructure and properties are not obvious.With the increase of heat input,the grain size increases and the properties change.The change of pulse duty ratio under the same heat input is similar to that of heat input.The larger the duty ratio is,the larger the grain size is,and the mechanical properties are different.The fracture morphology of the tensile specimen was observed by scanning electron microscope.Dimple was the main fracture,which belonged to typical ductile fracture.The samples were heat treated on the curved section and the separator forming parts.The microstructure and mechanical properties were observed after heat treatment.The results show that the boundary color between layers becomes lighter and the microstructure becomes more uniform and fine after heat treatment.After heat treatment,the hardness decreased,the strength increased and the toughness increased. |
