摘要
目的研究激光粉末床熔融(LPBF)中成形腔内保护气的流动规律,获得气流速度脉动和旋涡等流场非稳态特征及其变化规律。方法利用热线测速计测量腔内的瞬时速度,研究保护气的速度分布及其脉动特性;基于数值模拟方法探究腔内气流形成的旋涡情况,分析涡的分布及其旋转速度;利用烟雾示踪方法对保护气流场进行可视化处理,分析气流的运动过程。结果腔内气流经历了射流扩散、上下波动、大涡流、汇流等复杂运动过程,气流速度随时间的变化呈明显脉动特征,且气流脉动幅度受位置影响较大,进出风口的平面流速最大可达2.4m/s,最小为0.25m/s。同时,气速随平面高度的增大而逐渐减小;腔内存在以纵向大尺度旋涡为主、若干小尺度旋涡共同作用的涡流,由腔内边壁至中心,涡流切向速度呈先上升后下降的趋势,且随入口气速的增大而增大,在切向速度急剧降低的腔体角落、透镜等区域,易形成流动“死区”,导致烟尘颗粒聚集且难以排出,影响构件的高质量成形制造。结论保护气在LPBF成形腔内形成了复杂的非稳态流动,并以剧烈的速度脉动和多尺度的涡流为典型特征,而针对非恒定的层流、成形腔结构的优化设计仍需进行更深入的研究。
The work aims to obtain the unsteady flow characteristics and variation such as flow velocity pulsation and vor-tex by studying the flow pattern of shielding gas in the forming chamber of laser powder bed fusion(LPBF).The instantaneous velocity in the chamber was measured by hot-wire anemometer,and the velocity distribution and pulsation characteristics of the shielding gas were studied.Based on numerical simulation methods,the formation of vortex in the chamber flow was investi-gated,and the distribution and rotational speed of vortex were analyzed.The shielding gas flow field was visualized by smoke tracer method and the movement process of flow was analyzed.The flow underwent complex motion processes such as jet dif-fusion,up-and-down fluctuation,large vortex,and gas confluence.The flow velocity exhibited obvious pulsation characteristics,and amplitude of flow pulsation varied greatly with the position.The maximum and minimum velocities at the middle plane across the air inlet and outlet were 2.4 m/s and 0.25 m/s,respectively.Simultaneously,the flow velocity decreased gradually with the increase of the plane height.There were vortices in the chamber,including the large-scale longitudinal vortex and sev-eral small ones.The tangential velocity of vortices increased firstly and then decreased from the inner wall to the center,and in-creased with the increase of inlet flow velocity.Those vortices of which tangential velocity decreased sharply led to the"dead zones"at the corners of the chamber and below the lens.Then,the small floating particles were accumulated and difficult to discharged,affecting the high-quality manufacturing process of components.The shielding gas forms a complex unsteady flow in the LPBF forming chamber,characterized by intense velocity pulsation and multi-scale vortices.For constant laminar flow,further research on the optimization design of the forming chamber structure is needed.
作者
姚杨
孙占朋
张茹
杨光
YAO Yang;SUN Zhan-peng;ZHANG Ru;YANG Guang(School of Mechanical Engineering,Hebei University of Science&Technology,Shijiazhuang 050018,China;Hebei Additive Manufacturing Research Institute,Shijiazhuang 050018,China)
出处
《精密成形工程》
北大核心
2023年第10期196-203,共8页
Journal of Netshape Forming Engineering
基金
中央引导地方科技发展资金项目(206Z806G)
河北省自然科学基金京津冀基础研究合作专项(H2022208073)
河北省“三三三”人才工程资助项目(B20221004)。
