【摘要】 在"中国制造2025"、美国《国家先进制造战略计划》、欧洲航天局《惊奇计划》、日本《增材制造科研计划》、新加坡《工业增材制造项目》以及欧盟《3D打印标准化路线图》等全球新型制造技术迅猛发展的机遇下,金属激光3D打印融合了计算机辅助设计、材料加工与成形技术,以数字化模型文件为基础,通过软件与数控系统将特制材料逐层堆积固化,制造出实体产品,该技术日益成为国内外专家学者的研究热点。它与传统的对原材料进行切削、组装的加工模式不同,是通过材料累加的原理,从无到有地制造产品的新型技术工艺。也正是由于增材制造的这种技术特点,使得它受到全球的广泛关注,将可能会给传统的制造业带来一系列深刻的变革。其中同轴送粉式金属激光3D打印技术因具有成形尺寸大、可利用材料范围广、成形件的材料性能优异等特点,在航空航天、交通、医疗与能源等领域有着广阔的应用前景,成为金属增材制造主流的工艺技术。3D打印熔池中存在着传热、对流、传质、气-液界面冶金反应以及固-液界面扩散等复杂的动态物理冶金过程。熔池的流体力学行为直接影响材料组织的均匀性以及致密性,因此,如何通过流体力学方法对熔池的流体动态过程进行模拟,建立熔池温度和流场的三维非稳态模型,并定量分析浮力、表面张力、粉末冲击力以及综合作用对3D打印过程温度场、速度场和熔池形态的影响是需要解决的关键问题。数值仿真模拟是研究同轴送粉式金属激光3D打印熔池动力学过程的重要手段之一。目前,在关于同轴送粉式金属激光3D打印数值模拟和激光焊的数值模拟研究中,已包含较为全面的多尺度数值模型,例如光-粉耦合作用数值模型、熔池气-液界面和固-液混合区界面追踪模型、熔池瞬时变化的热场和流场分析模型、熔池中合金元素的分布过程介观模型以及基于相场法的熔池形貌和显微组织凝固元胞自动机模型等。本文主要阐述国内外研究学者对同轴送粉式金属激光3D打印仿真模拟的研究进展,主要集中在3D打印过程中熔池瞬时变化的热场和流场分析、合金元素的分布过程以及熔池形貌和显微组织凝固等方面。由于数值模拟方法具有一定的通用性,为了更全面地介绍与同轴送粉式金属激光3D打印技术相关的数值模拟方法,本文也涉及了少量送粉式激光熔覆以及激光电弧填粉焊接等过程的数值模拟工作。更多还原

【Abstract】 In the exceptional historical opportunity of"Made in China 2025",the"National Advanced Manufacturing Strategic Plan"of the United States,the"Amazing Plan"of European Space Agency,the Japanese"Additive Manufacturing Research Program",the"Industrial Additive Manufacturing Project"in Singapore and the EU "3 DPrinting Standardization Roadmap",the metal laser 3 Dprinting has become the focus of research among scholars at home and abroad.Metal laser 3 Dprinting is a technique that integrate computer-aided design,material processing and forming technology,and manufacture products by stacking and solidifying special materials through software and numerical control system based on the digital model files.Different from traditional machining mode of cutting and assembling raw materials,it is a innovative technique that manufacture products from scratch based on the materials accumulation principle.Just because of the technological characteristics of addictive manufacturing,it has attracted worldwide attention,and will evoke a series of profound changes to the traditional manufacturing industry.The coaxial powder feeding type metal laser 3 Dprinting technique possesses broad application prospects in the field of aviation,aerospace,transportation,medical treatment and energy,because of its large forming size,wide range of available materials and excellent material properties of shaped parts,which has become the main stream technology of additive manufacturing.There are complex dynamic physical metallurgical processesincluding heat transfer,convection,mass transfer,gas-liquid interface metallurgy and solid-liquid interface diffusion in the 3 Dprinting pool.The fluid dynamic behavior of the weld pool directly affects the homogeneity and compactness of the material structure.Therefore,there still exist several key problems to be figured out in metal laser 3 Dprinting,which are the simulation of the fluid dynamic process of the weld pool by fluid mechanics,establishment of three-dimensional unsteady model of the temperature and flow field of the weld pool,the influence of buoyancy,surface tension,powder impact force on the temperature field,velocity field and molten pool shape of 3 Dprinting.Numerical simulation is one of the important methods to study the dynamic processin the welding pool of co-axial powder feeding metal laser 3 Dprinting.At present,research on the numerical simulations of coaxial powder laser metal 3 Dprinting and laser welding have included more comprehensive multiscale numerical models,such as light-powder coupling numerical model of molten pool,the interface tracing model of gas-liquid interface and solid-liquid mixed zone in molten pool,the temperature field and fluid flow analysis model of instantaneous variation of molten pool,the mesoscopic model for the distribution of alloying elements in the molten pool and the model for the morphology of the molten pool and the cellular automata for microstructure solidification based on the phase field method.This article mainly elaborates the domestic and international researches on simulation of the coaxial powder metal laser 3 Dprinting,which mainly focus on the analysis of thermal field and flow field with instantaneous variations in the molten pool,the distribution process of the alloying elements,the morphology of the molten pool and solidification of the microstructure during the 3 Dprinting process.Owing to the universal applicability of numerical simulation method and in order to introduce the numerical simulation methods related to coaxial powder feeding metal laser 3 Dprinting technique in a more comprehensive manner,this article also involves a small amount of numerical simulation about coaxial powder laser cladding and laser arc welding.更多还原