| Electrochemical additive manufacturing(ECAM)based on cathodic electrodeposition has great development potential in the field of metal additive micro-manufacturing due to the advantages of its good quality,no thermal defects,low internal stress,flexible operation and low operating temperature.Up to now,it has been developed in several electrochemical micro additive manufacturing processes with different methods and capabilities.Among them,Liquid Beam Electrodeposition Additive Manufacturing(LB-ECD AM)has more potential engineering application prospects because of its high yield and high forming flexibility.However,few studies have been reported on LB ECD Meso AM with the feature size ranging from 0.1mm to1 mm.In this paper,a Localized Liquid Beam Electrodeposition Additive Manufacturing(LLB-ECD AM)is proposed to fabricate Meso scale three-dimensional(3D)complex metal components.LLB-ECD AM is an electrochemical additive manufacturing technology in which the steady electrolyte beam with a low Reynolds number,length of several millimeters and diameter of hundreds of microns formed between the electrode nozzle with an internal inert anode and the cathode is used as a tool,and localized deposition is stacking layer by layer in the 3D spatial scanning movement of the tool relative to the cathode.Aiming at fabricating intricate 3D solid and hollow Meso scale columnar components,and guided by the research of generating high-quality Meso scale electrolyte beam for high quality electrodeposition,fundamental research of LLB-ECD AM including the columnar shape forming mechanism,the flow characteristic of Meso scale steady electrolyte beam and the evolution of three-dimensional solid/hollow components were carried out in experimental and simulation analysis.The main research contents and conclusions are as follows.(1)The formation conditions and working characteristics of Meso scale steady electrolyte beam were investigated and analyzed.The evolution of flow field,electric field distribution with increasing deposition height under the action of steady electrolyte beam were elaborated by numerical simulations.The columnar shape forming mechanism of LLB-ECD in the constant voltage and constant current mode were compared.The results show that,the inlet pressure is the key factor in the flow stability of the electrolyte beam in the given nozzle size and the inlet pressure above 8k Pa is conducive to obtaining the columnar electrolyte beam with a uniform size of the nozzle in the flow range.During the process of increase of electrodeposition height,the flow field of the electrolyte beam to cathodic surface has gradually developed from the classic flow characteristics of the central stagnation surrounding by the flat electrolyte film to the steady growing flow characteristics of the stagnation localized on the dome shape with the electrolyte film flow downward along the cylinder wall.Correspondingly,the electric field on the cathode surface gradually shrinks from the low current density scattering within the initial thin electrolyte film to a concentrated high current density focused on the dome shape growth,while the dispersed current on the substrate and the columnar cathodic surface is ignored.The whole process of Meso scale columnar growth has experienced the initial transitional growth period with increasing deposition localization and the subsequent homogeneous growth period with the dome shape growth and steady deposition rate.Compared with constant current and constant voltage electrodeposition,the current density distribution on the dome shape in the constant current mode is only related to the applied current,while the current density and growth rate in constant voltage mode continue to increase with the decrease of electrode spacing.(2)The formation conditions of Meso scale steady electrolyte beam and the evolution mechanism of solid components by LLB-ECD AM were experimentally studied.The influence of constant voltage/current on the electrodeposited formation and process parameters were discussed.The feasibility of Meso scale 3D intricate components by LLB-ECD AM was experimentally explored and evaluated.The results show that,Meso scale electrolyte beam with the nozzle size diameter and centimeter scale length was formed under appropriate inlet pressure,while the nozzle height,nozzle offset angle and cathode surface shape have little effect on the electrolyte beam.The growth process of constant current electrodeposition experiment was consistent with the simulation results.The electrodeposited solid columnar component of LLB-ECD has a dome shape composed of effective electrodeposition area and non-effective electrodeposition area,and the electrodeposited layer continues to grow overlapping in the columnar structure.Under the given constant current electrodeposition conditions,the growth rate of electrodeposited column is ranged from20 μm/min to 64 μm/min,while the dimensional deviation of columnar diameter is less than 3%.By utilizing different scanning path planning and control strategies,such as small nozzle displacement,little amplitude follow-up deflection of electrolyte beam,alternative beam size and initial interlacing electrodeposition,3D intricate nickel components such as curved columnar structures,U-shaped,spiral,Z-shaped and interlacing structures were successfully manufactured via the proposed technique.The diameter of the 3D nickel components is 190 μm to 750 μm with a deviation less than5% and the surface roughness of Ra 0.1～0.25.(3)The steady electrolyte beams with inbuilt single or double insulation filaments were introduced and the evolution of flow field and electric field matching the deposition growth under the action of the electrolyte beam were numerically simulated and analyzed.The feasibility of preparing Meso scale single / double channel hollow components was experimentally implemented.The results show that the Meso scale electrolyte beams with single or double insulation filaments inbuilt were formed at suitable pressure with the columnar size of nozzle outlet along the flow trail.Similar to the evolution mechanism of solid components growth without filament,the hollow component manufactured based on LLB-ECD has experienced the transitional growth period and stable growth period.Due to the existence of the inbuilt filament,the stagnant ring around the filament is emerged surrounding the growth top end of the hollow component in the simulation,and the stability of the flow field is not easy to maintain.Correspondingly,the current density at the growth top is further concentrated,and double filaments will aggravate the uneven distribution of the flow and electric field,resulting in the deterioration of the local mass transfer conditions.Compared with the solid component deposition,the hollow component of LLB-ECD AM should apply a smaller current density.Combined with the methods of small angle follow-up deflection of cathode substrate and spatial displacement transformation,3D intricate nickel hollow components including bent shape,hook shape,U and D-shape were successfully manufactured with an outer diameter ranging from 320μm to 440 μm and inner diameter from 50μm to 100μm.The channels inside the hollow components were verified high quality without obvious pores and crack defects and the surface roughness was about Ra0.1 to 0.3,which has shown the feasibility of Meso scale hollow components with LLB-ECD AM. |
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