[1] [1] M Zhong, W Liu. Laser surface cladding: the state of the art and challenges[J]. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2010, 224(5): 1041-1060.

[2] [2] Wang Xuyue, Wang Yanfei, Jiang Hao, et al.. Laser cladding forming of round thin-walled parts with slope angle[J]. Chinese J Lasers, 2014, 41(1): 0103006.

[3] [3] Zhu Gangxian, Zhang Anfeng, Li Dichen. Effect of process parameters on surface smoothness in laser cladding[J]. Chinese J Lasers, 2010, 37(1): 296-301.

[4] [4] C P Paul, S K Mishra, A Kumar, et al.. Laser rapid manufacturing on vertical surfaces: Analytical and experimental studies[J]. Surface & Coatings Technology, 2013, 224: 18-28.

[5] [5] R Dwivedi, R Zekovic, R Kovacevic. A novel approach to fabricate uni-directional and branching slender structures using laserbased direct metal deposition[J]. International Journal of Machine Tools & Manufacture, 2007, 47(7): 1246-1256.

[6] [6] Zhong Minglin, Liu Wenjin, Li Fengsheng. Vertical laser cladding powder feeding nozzle[P]. Chinese Patent: 021236453[P]. 2002-07-05.

[7] [7] Yang Xichen, Li Huishan, Wang Yunshan, et al.. Laser refabricating technology for repairing expensive and important equiments[J]. Laser& Optoelectronics Progress, 2003, 40(10): 53-57.

[8] [8] Yang Xichen. Laser processing robot and its industrial applications[J]. Chinese J Lasers, 2009, 36(11): 2780-2798.

[9] [9] Huang Weidong, Lin Xin, Chen Jing, et al.. Laser Solid Forming-Fast Free Forming of High Performance Dense Metal Parts[M]. Xi′an: Northwestern Polytechnical University Press, 2007: 11.

[10] [10] Yang Shi, Shi Shihong, Fu Geyan, et al.. The impact of hollow ring laser defocused amount on melting channel bump defect self healing effect[J]. Chinese J Lasers, 2015, 42(5): 0503002.

[11] [11] Wang Lifang, Zhu Gangxian, Shi Shihong, et al.. Influence of shielding gas pressure on flow field of the inside-laser powder feeding nozzle[J]. Chinese J Lasers, 2013, 40(s1): s103007.

[12] [12] Zhu Gangxian, Shi Shihong, Fu Geyan, et al.. Research on variable reference plane cladding based on laser processing robot with the inside-laser powder feeding[J]. Chinese J Lasers, 2015, 42(3): 0303010.

[13] [13] Shi Shihong, Fu Geyan, Wang Anjun, et al.. Laser Forming Manufacturing Process and Nozzle of Inside-Laser Powder Feeding[P]. Chinese Patent: 200610116413, 2006-09-22.

[14] [14] Shi Shihong, Shi Tuo, Fu Geyan, et al.. A Method and Apparatus for Space Laser Processing and Three-Dimensional Forming[P]. Chinese Patent: CN201410391418.5, 2014.

[15] [15] Shi Shihong, Fu Geyan, Li Long, et al.. Realization and research of laser cladding with method of internal wire feeding through a hollow laser beam[J]. Chinese J Lasers, 2010, 37(1): 266-270.

[16] [16] Xiao Junyan. The Characteristics of Molten Pool and Cladding Layer inside the Ring Laser Beam[D]. Suzhou: Soochow University, 2009: 3-8.

[17] [17] Li Chunsheng. Modeling for Transmission and Conversion of Hollow Circular Laser and Analysis on Coupling between Laser and Materials in Three-Dimensional Laser Manufacturing [D]. Suzhou: Soochow University, 2010: 44-58.