Abstract: 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.
1 Lu B H. Research progress of advanced manufacturing technology in Xi’an Jiaotong University[J].Engineering Sciences,2013,15(1):4(in Chinese). 卢秉恒.西安交通大学先进制造技术研究进展[J].中国工程科学,2013,15(1):4. 2 Marquis F D S. Development of laser-powder additive manufacturing for industry: historical perspective, current and future applications[M]∥Powder materials: Current research and industrial practices Ⅲ. New York: John Wiley & Sons, Inc.2014:211. 3 Breuninger J. Additive manufacturing: Challenges and advantages for the medical industry[J].Puerto Rico Health Sciences Journal,2000,19(1):57. 4 Zhang A, Dichen L I, Liang S, et al. Development of laser additive manufacturing of high-performance metal parts[J].Aeronautical Manufacturing Technology,2016,517(22):16. 5 黄卫东.激光立体成形[M].西安:西北工业大学出版社,2007:1. 6 Yao C H, Zhan Z L, Liu J X, et al. The research of development and application of rapid prototyping technology[J].Journal of Kunming University of Science and Technology(Natural Science Edition),2000,25(5):83(in Chinese). 姚长虹,詹肇麟,刘建雄.快速原型制造技术的发展与应用研究[J].昆明理工大学学报(自然科学版),2000,25(5):83. 7 He Q, Zhou C C, et al. Research on 3D laser rapid forming technology[J].Machine Tool & Hydraulics,2015,43(19):16(in Chinese). 贺强,周长春,等.3D激光快速成形技术研究[J].机床与液压,2015,43(19):16. 8 Buchbinder D, Meiners W, Pirch N, et al. Investigation on reducing distortion by preheating during manufacture of aluminum components using selective laser melting[J].Journal of Laser Applications,2014,26(1):012004. 9 Kempen K, Vrancken B, Humbeeck J V, et al. Selective laser mel-ting of crack-free high density M2 high speed steel parts by baseplate preheating[J].Journal of Manufacturing Science & Engineering,2014,136(6):061026. 10 Liu Q C, Elambasseril J, Sun S J, et al. The effect of manufacturing defects on the fatigue behaviour of Ti-6Al-4V specimens fabricated using selective laser melting[J].Advanced Materials Research,2014,891:1519. 11 Huang W D, Lin X. Research progress in laser solid forming of high performance metallic component[J].Materials China,2010,29(6):12(in Chinese). 黄卫东,林鑫.激光立体成形高性能金属零件研究进展[J].中国材料进展,2010,29(6):12. 12 Shamsaei N, Yadollahi A, Bian L, et al. An overview of direct laser deposition for additive manufacturing; part Ⅱ:Mechanical behavior, process parameter optimization and control[J].Additive Manufactu-ring,2015,8:12. 13 Zhang Y, Shi L, Li G. Characterization on laser melting deposition of metallic components[J].Rare Metal Materials and Engineering,2011,40(3):27. 14 Zhang F Y. The laser rapid forming technology with low cost hydrogenation dehydrogenization titanium alloy powders[D].Xi’an: Northwestern Polytechnical University,2006(in Chinese). 张凤英.低成本氢化脱氢钛合金粉末的激光快速成形[D].西安:西北工业大学,2006. 15 Bram M, Buchkremer H P, Stöver D. Reproducibility study of NiTi parts made by metal injection molding[J].Journal of Materials Engineering & Performance,2012,21(12):2701. 16 Zhang F, Chen J, Tan H, et al. Research on forming mechanism of defects in laser rapid formed titanium alloy[J].Rare Metal Materials & Engineering,2007,36(2):211. 17 Zhong C L.Investigations on high deposition-rate laser metal deposition for additive manufacturing application based on inconel 718[D].Changchun: University of Chinese Academy of Sciences,2015(in Chinese). 仲崇亮.基于Inconel718的高沉积率激光金属沉积增材制造技术研究[D].长春:中国科学院大学,2015. 18 Zhong C, Biermann T, Gasser A, et al. Experimental study of effects of main process parameters on porosity, track geometry, deposition rate, and powder efficiency for high deposition rate, laser metal deposition[J].Journal of Laser Applications,2015,27(4):042003. 19 Campanelli S L, Angelastro A, Signorile C G, et al. Investigation on direct laser powder deposition of 18 Ni (300) marage steel using mathematical model and experimental characterisation[J].International Journal of Advanced Manufacturing Technology,2016,89(1):885. 20 徐滨士,董世运.激光再制造[M].北京:国防工业出版社,2016:1. 21 Everton S, Dickens P, Tuck C, et al. The use of laser ultrasound to detect defects in laser melted parts[C]∥TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. San Diego,2017:105. 22 Song J, Chew Y, Bi G, et al. Numerical and experimental study of laser aided additive manufacturing for melt-pool profile and grain orientation analysis[J].Materials & Design,2018,137:286. 23 Majumdar J D, Pinkerton A, Liu Z, et al. Microstructure characterisation and process optimization of laser assisted rapid fabrication of 316L stainless steel[J].Applied Surface Science,2005,247(1-4):320. 24 Zhang F Y, Chen J, Tan H, et al. Research on forming mechanism of defects in laser rapid formed titanium alloy[J].Rare Metal Mate-rials and Engineering,2007,36(2):211(in Chinese). 张凤英,陈静,谭华,等.钛合金激光快速成形过程中缺陷形成机理研究[J].稀有金属材料与工程,2007,36(2):211. 25 Brückner F, Finaske T, Willner R, et al. Laser additive manufactu-ring with crack-sensitive materials[J].Laser Technik Journal,2015,12(2):28. 26 Gasser-Ing A, Dipl.-Ing G B, Kelbassa-Ing I, et al. Laser Additive Manufacturing[J].Laser Technik Journal,2010,7(2):58. 27 Shao Y C, Chen C J, Zhang M, et al. Research on crack issue of deloro 40Ni alloys prototype fabricated by laser additive manufacturing[J].Applied Laser,2016,36(4):397(in Chinese). 邵玉呈,陈长军,张敏,等.关于Deloro 40镍基合金粉末激光增材制造成型件裂纹问题研究[J].应用激光,2016,36(4):397. 28 Li Q G, Lin X, Wang X H, et al. Research progress on cracking mechanism and control of laser additive repaired nickel-based supe-ralloys with high content of Al+Ti[J].Applied Laser,2016,36(4):471(in Chinese). 李秋歌,林鑫,王杏华,等.高Al+Ti镍基高温合金激光增材修复液化裂纹形成机理及控制研究进展[J].应用激光,2016,36(4):471. 29 Song J L, Deng Q L, Ge Z J, et al. The cracking control technology of laser rapid forming nickel-based alloys[J].Journal of Shanghai Jiaotong University,2006,40(3):548(in Chinese). 宋建丽,邓琦林,葛志军,等.镍基合金激光快速成形裂纹控制技术[J].上海交通大学学报,2006,40(3):548. 30 Li M, Zhang S, Li H, et al. Effect of nano-CeO2, on cobalt-based alloy laser coatings[J].Journal of Materials Processing Technology,2008,202(1):107. 31 Lai Y B, Liu W J, Kong Y, et al. Influencing factors of residual stress of Ti-6.5Al-1Mo-1V-2Zr alloy by laser rapid forming process[J].Rare Metal Materials and Engineering,2013,42(7):1526(in Chinese). 来佑彬,刘伟军,孔源,等.激光快速成形TA15残余应力影响因素的研究[J].稀有金属材料与工程,2013,42(7):1526. 32 Wang J, Li L, Tao W. Crack initiation and propagation behavior of WC particles reinforced Fe-based metal matrix composite produced by laser melting deposition[J].Optics & Laser Technology,2016,82:170. 33 Chen Y, Lu F, Zhang K, et al. Investigation of dendritic growth and liquation cracking in laser melting deposited Inconel 718 at different laser input angles[J].Materials & Design,2016,105:133. 34 Shim D S, Baek G Y, Lee E M. Effect of substrate preheating by induction heater on direct energy deposition of AISI M4 powder[J].Materials Science & Engineering A,2016,682:550. 35 Zhang K, Wang S, Liu W, et al. Effects of substrate preheating on the thin-wall part built by laser metal deposition shaping[J].Applied Surface Science,2014,317:839. 36 Cabeza M, Castro G, Merino P, et al. Laser surface melting: A sui-table technique to repair damaged surfaces made in 14 Ni (200 grade) maraging steel[J].Surface & Coatings Technology,2012,212(11):159. 37 Xie R D, Lu Z L, Yi Y M, et al. Overview of defect detection and control technology in laser metal forming[J].Foundry,2017,66(1):33(in Chinese). 解瑞东,鲁中良,弋英民,等.激光金属成形缺陷在线检测与控制技术综述[J].铸造,2017,66(1):33. 38 Yang L S, Liu J S, Liu J C, et al.Study on CCD·based detection system for online monitoring of melt Pool Width in laser cladding[J].Laser Technology,2011,35(3):315(in Chinese). 杨柳杉,刘金水,刘继常,等.基于CCD的激光熔覆熔池宽度的在线检测研究[J].激光技术,2011,35(3):315. 39 Yuan C, Jafari M A. Vision-based online process control in manufacturing applications[J].IEEE Transactions on Automation Science & Engineering,2008,5(1):140. 40 Xiang S.Width control of molten pool in laser powder deposition process based on camera[D].Shanghai: Shanghai Jiaotong University,2015(in Chinese). 向森.基于相机的激光粉末沉积工艺熔池宽度控制[D].上海:上海交通大学,2015. 41 Tang L, Landers R G. Layer-to-layer height control for laser metal deposition process[J].Journal of Manufacturing Science & Enginee-ring,2011,133(2):021009. 42 Roberts I A, Wang C J, Esterlein R, et al. A three-dimensional finite element analysis of the temperature field during laser melting of metal powders in additive layer manufacturing[J].International Journal of Machine Tools & Manufacture,2009,49(12):916. 43 Gan Y, Wang W, Cui Z, et al. Numerical and experimental study of the temperature field evolution of Mg alloy during high power diode laser surface melting[J].Optik-International Journal for Light and Electron Optics,2015,126(7-8):739. 44 Qin L Y, Wang W, Yang G, et al. Experimental study on ultraso-nic-assisted laser metal deposition of titanium alloy[J].Chinese Journal of Lasers,2013,40(1):76(in Chinese). 钦兰云,王维,杨光,等.超声辅助钛合金激光沉积成形试验研究[J].中国激光,2013,40(1):76. 45 Zhou J, Xu J, Huang S, et al. Effect of laser surface melting with alternating magnetic field on wear and corrosion resistance of magne-sium alloy[J].Surface & Coatings Technology,2016,309:212. 46 Tan C, Zhu H, Kuang T, et al. Laser cladding Al-based amorphous-nanocrystalline composite coatings on AZ80 magnesium alloy under water cooling condition[J].Journal of Alloys & Compounds,2017,690:108. 47 Zhang Y K. Defects inspection of steel ball based on optical fiber sensing technique[D].Jinan:Ji Nan University,2011(in Chinese). 张永奎.基于光纤传感技术的钢球表面缺陷检测研究[D].济南:济南大学,2011.