Study On Process Of Thin Wall Formation Of TC4 Powder In Selective Laser Melting

Selective laser melting(SLM)is a rapid prototyping technology that utilizes a laser heat source to selectively melt powder and form three-dimensional solid parts layer by layer,under the control of a computer system,and thus possessing ability to fabricate relatively complex three-dimensional structures.At the same time,for grids and honeycombs composed of thin-walled parts with higher mechanical performance requirements,titanium alloys have been widely used for lightweighted structure in fields such as aerospace industry,due to their advantages of high specific strength,heat resistance and corrosion resistance.Therefore,aiming at titanium alloy(TC4),this paper utilized SLM technology with characteristics of additive manufacturing to study the sintering forming process of thin-walled structures,in order to provide technical and application basis for formation of titanium alloy thin-walled structures.1.The study analyzed the SLM forming process of thin walls.Based on the preliminary analysis of the line-by-line and layer-by-layer stacking mechanism of SLM forming,the process of metal powder(TC4)forming tracks after laser radiation as long as its parameters’ main influence are analyzed.Based on remelting of single and multiple track stacking,processing methods of SLM manufacturing of thin-walled structures was analyzed,which provided a basis for the subsequent research on track sintering and thin-walled formation.2.Basic TC4 sintering through simulation and experimental methods was studied.The process parameters of the sintering process were optimized,from which the research obtained optimized range of process parameters that could realize track sintering and obtaining corresponding width and height of tracks.At the same time,combined with the simulation results,experiments were carried out on TC4 powder with powder thickness h1=25 μm,h2=40 μm and h3=55μm.The relationship between different linear energy densities e,their corresponding track width Be and track height He was obtained.The study further optimized line energy density range intended for effective sintering of tracks,which was ei=0.060～0.115 J/mm,e2=0.110～0.82 J/mm and e3=0.220-0.252 J/mm for 3 different values of powder thickness.3.TC4 thin-walled SLM forming experiment was carried out based on forming results of the single-layer experiment,and thin-walls were accumulated in characteristic geometric shapes.Simple square-shaped thin-wall sintering experiments were carried out by layer-by-layer sintering with single and double tracks respectively.For the single track experiment,12 groups of different parameters with powder layer thicknesses of 25 μm and 40 μm were selected,among which continuous thin walls with thickness δt of 176.0 μm,200.6 μm and 271.6 μm,and corresponding height-thickness ratio of 34.8,32.9 and 25.5 were obtained,with powder thickness of 40 μm,and linear energy density e of 0.217 J/mm、0.273 J/mm and 0.333 J/mm respectively.While in the double-track thin wall forming,experiments were carried out using two nominal wall thicknesses calculated from remelting ratio of 25%and 35%between tracks for each set of parameters.When the thickness of the powder layer was 25 μm and 40 μm respectively,multiple sets of parameters under different energy density have succeeded in forming continuous thin walls.Thin walls with relatively minimal wall thickness of 169.0 μm and height-thickness ratio of 24.7 was obtained using parameters of h1=25 μm,e=0.078 J/mm,and remelting ratio R=35%.In addition,experimental sintering of circular thin walls was also carried out,and the results were consistent with square ones.4.Based on the experiments of simple geometric thin-walled structures,gridshaped and honeycomb-shaped TC4 thin-walled structures,whose grid pitch was 5 mm and 2 mm,was sintered layer-by-layer using single tracks formed with higher energy and double tracks formed with lower energy,and their minimal wall thickness was 176.0 μm and 169.0 μm accordingly.Through the work above,the study preliminarily realized SLM formation of thinwalled structures,and concluded optimized parameters for effectively forming them,providing a technological basis for improving the quality and lowering minimal thickness of thin walls in the future.