| 彭谦,董世运,闫世兴,门平,王斌.激光熔化沉积成形缺陷及其控制方法综述[J].材料导报,2018,32(15):2666-2671, 2683 |
| 激光熔化沉积成形缺陷及其控制方法综述 |
| An Overview of Defects in Laser Melting Deposition Forming Products and the Corresponding Controlling Methods |
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| DOI：10.11896/j.issn.1005-023X.2018.15.019 |
| 中文关键词: 增材制造 激光熔化沉积 气孔 熔合不良 裂纹 缺陷控制 |
| 英文关键词: additive manufacturing, laser melting deposition, pore, poor fusion, crack, defect control |
| 基金项目:国家重点研发计划项目(2016YFB1100205) |
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| 摘要点击次数: 3928 |
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| 中文摘要: |
| 激光增材制造技术作为一种新型的快速成形技术,在快速精准成形的同时,还能够满足个性需求,这种成形方式完全颠覆了传统减材制造的成形理念,因而很快成为最能代表当今信息化时代的一种制造技术。常见的激光增材制造技术主要有以送粉为特征的激光熔化沉积技术(Laser melting deposition,LMD)和以粉末铺床为特征的选区激光熔化技术(Selective laser melting,SLM)。激光熔化沉积技术是采用同步送粉的方式通过大功率激光将同种或不同种的粉末熔化,然后逐行逐层地进行扫描堆积成形。利用这种方法所制备的零件不仅形状复杂,而且各项力学性能均优于铸件。相对于选区激光熔化技术,激光熔化沉积技术具有三大优势:(1)成形尺寸不受限制,可进行大尺寸的零件制造；(2)可以实现不同成分和比例的梯度材料成形；(3)可以进行零件修复与再制造。 激光熔化沉积成形过程是一个涉及温度场、应力场等多物理场的耦合过程,由于材料急热、急冷的特点使得利用激光熔化沉积法制备的零件组织为非平衡态组织,过程复杂,不稳定性因素多,因此制件容易出现翘曲变形、熔合不良、尺寸精度不高、开裂等宏观缺陷,内部也容易产生气孔、夹杂、裂纹等微观缺陷,其中激光熔化沉积制备的零件中较大残余应力的存在使得裂纹对其性能的影响更为显著。 当前,研究者们主要通过工艺实验及数值模拟研究了产生缺陷的原因,在一定程度上找出了产生气孔、熔合不良、裂纹等缺陷的主要影响因素,并针对这些因素进行逐步分析,在控制粉末特性,调节激光功率、扫描速度、送粉速度、搭接率等工艺参数,引入基板预热,热处理等缺陷控制方法方面取得了一定的进展。同时还利用外界先进检测、传感技术对缺陷进行了实时监测及闭环控制,为激光熔化沉积成形缺陷的控制提供了良好的辅助手段,大大提高了激光熔化沉积成形零件的性能。 本文总结了近年来国内外有关激光熔化沉积成形缺陷及其控制方法的研究进展,按照缺陷的种类进行了分类归纳,分析了缺陷形成原因及影响因素,汇总了目前研究的缺陷控制方法,并探讨了当前存在的问题和未来发展前景。 |
| 英文摘要: |
| As a new type of rapid prototyping technology, laser additive manufacturing can flexibly attain the requirements of different individuals while rapidly forming accurately. This forming strategy completely subverts the forming concept of traditional subtractive materials manufacturing, and has quickly become the most representative manufacturing technology in the information age. The common laser additive manufacturing techniques include laser melting deposition (LMD) identified by powder feeding, and selective laser melting (SLM) characterized by powder coating. In laser melting deposition process, the homogeneous or heteroge-neous powders were firstly melted by high-power laser in a synchronous feeding mode, and then the layer-by-layer scanning deposition was conducted. Through LMD we can manufacture workpieces with both exquisite shape and higher mechanical properties compared with casted ones. LMD technic has three superiorities to SLM:Ⅰ. unlimited forming size which enables the manufacturing of large-size parts; Ⅱ. the ability of forming materials with composition gradient; Ⅲ. adaptability to parts’ repair and remanufacturing. The LMD process is a complicated multi-physical-field (temperature and stress) coupling process that involves several uncertainties, and the material’s acute heat and rapid cooling make the resultant microstructure a non-equilibrium state. So the LMD product is prone to display the macro-defects of warping deformation, poor fusion, size imprecision and cracking, also tends to have micro-defects such as internal pores, inclusions and micro-cracks. Furthermore, residual stress in the laser melting deposited products exaggerates the influence of micro-cracks. In the past few years, researchers were dedicated to discover and analyze the causes of defects, e.g. pores, poor fusion and cracks, through technological experiments and numerical simulation. Some achievements have been made in controlling the powder characteristics, adjusting the processing parameters, such as laser power, scanning speed, feeding speed, lap rate, etc., and adopting preliminary substrate heating and posterior thermal treatment. Moreover, the use of advanced detection and sensing technics for real-time monitoring and closed-loop control of the defects provides assistant methods for defect control, and facilitate to greatly improve the performance of LMD parts. This review delineates the worldwide research progress in recent years upon laser melting deposition forming defects and the corresponding control methods. According to the types of defects, we summarize the causes and influencing factors of defect formation, and introduce the current defect controlling methods. The paper ends with a brief discussion of the unresolved problems and the future prospect. |
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