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为了研究送粉量对表面粉末粘附的影响规律,试件在激光功率为700W、扫描速率为700mm/min、离焦量为+22mm、送粉气流量为10L/min下进行制备。由图 5可知,随着送粉速率的增加,粘附在薄壁件侧表面的粉末逐渐增加,粘粉的程度愈加严重,薄壁件表面愈粗糙。送粉速率越大,单位时间内送出的粉末越多,粉末在进入熔池前受激光辐照,吸收大量能量,由于激光功率没有发生变化,激光射入熔池的能量减少,每颗不锈钢粉末吸收的能量减少,会形成更多未完全熔化的不锈钢金属粉末颗粒粘附在熔池边缘,而熔池的吸收的能量无法将粘附在熔池边缘的不锈钢金属粉末通过热传导的方式熔化。
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图 6所示是激光功率为700W、扫描速率为700mm/min、离焦量为+22mm、送粉速率为13.54g/min时,不同送粉气流量所对应零件侧表面的图片。
Figure 6. The influence law of feeding air flow on the degree of adhesive powder of single-layer thin-walled parts
由图 6可知,随着送粉气流量的增加,粘附在薄壁件侧表面的粉末逐渐减少,粘粉的程度有所改善,但单道多层的沉积高度有所下降。送粉气流量越大,从喷粉头喷射出的不锈钢金属粉末速度越快,由于送粉速率没有变,粉末在进入熔池前受激光辐照,吸收能量减少,激光射入熔池的能量增加,每颗不锈钢粉末吸收的能量减少,大部分未进入熔池中心的粉末不会形成似熔未熔状态,粘附在熔池附近的不锈钢金属粉末由于熔池热传导,将粘附的不锈钢金属粉末熔化。
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在直接金属沉积过程中,单道多层的堆积与激光能量的输入大小是紧密相连的,在直接金属沉积技术中采用激光输入能量是用激光能量密度去衡量的,其计算公式为:
$ \mathit{E}{\rm{ = }}\mathit{P}{\rm{ /(}}\mathit{Dv}{\rm{)}} $
(1) 式中, E为激光能量密度, P为激光功率, D为激光光斑直径, v为扫描速率。E为单位面积上的熔覆层所受到的激光辐射能量, 在激光光斑直径一定时, 常用P/v值来反映激光能量密度,激光能量密度主要取决于激光功率与扫描速率的大小。
表 1及图 7分别是离焦量为+22mm、送粉气流量为10L/min、送粉速率为13.54g/min时加工薄壁件的工艺参量及不同激光功率、扫描速率所对应零件侧表面图片。通过表 1及图 7可知,随着扫描速率从500mm/min增加到1166mm/min,P/v值从1.4W·min-1·mm-1下降到0.6W·min-1·mm-1,粘附在薄壁件侧表面的粉末无明显变化,在本实验参量下粘粉的程度对扫描速率的变化不敏感;随着激光功率从980W下降到420W,P/v值从1.4W·min-1·mm-1下降到0.6W·min-1·mm-1,粘附在薄壁件侧表面的粉末无明显变化,仅在激光功率为560W时出现较多粘粉,在本实验参量下粘粉的程度对激光功率的变化不敏感;综合扫描速率、激光功率对薄壁件侧表面粉末粘附程度的影响,可以看出在一定工艺参量条件下薄壁件侧表面粉末粘附程度对线能量密度P/v值的变化不敏感。
Table 1. Direct metal deposition process parameters under different linear energy densities
激光直接金属沉积316L不锈钢表面粘粉工艺研究
Study on surface powder adhesion process of 316L stainless steel by laser direct metal deposition
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摘要: 为了探究激光直接金属沉积316L不锈钢的表面粉末粘附工艺规律, 利用高速摄像机分析粉末粘附类型, 采用单因素试验的方法, 定量研究了单道多层沉积中的送粉速率、送粉气流量和线能量密度对粉末粘附的影响规律。结果表明, 粉末粘附主要包括熔池熔液逸出和未熔粉末粘附两种类型; 随着送粉速率的增加和送粉气流量的减小, 薄壁件侧表面粉末粘附程度增加, 而粉末粘附程度则对激光线能量密度的变化不敏感; 激光功率700W、扫描速率700mm/min、送粉量13.54g/min、送粉气流量14L/min、离焦量+22mm时, 激光直接金属沉积薄壁件表面粉末粘附较少。研究结果能够成为改善316L不锈钢增材制件表面质量的重要依据。Abstract: In order to investigate the surface powder adhesion process of 316L stainless steel by laser direct metal deposition, the type of powder adhesion was analyzed by high-speed camera. The influence of powder feeding rate, gas flow rate and linear energy density on powder adhesion in single-channel multilayer deposition was studied quantitatively by single factor test method. The results show that, adhesion powder mainly includes two types: molten solution escaping from molten pool and unmelted powder adhesion. With the increase of powder feeding rate and the decrease of powder feeding gas flow rate, the adhesion degree of powder on the side surface of thin-walled parts increases. However, the degree of powder adhesion is insensitive to the change of laser linear energy density. With laser power of 700W, scanning speed of 700mm/min, powder feeding rate of 13.54g/min, powder feeding gas flow rate of 14L/min and defocusing rate of +22mm, powder adhesion on the surface of thin-walled parts by laser direct metal deposition is less. The results can be used as an important basis for improving the surface quality of 316L stainless steel products.
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Key words:
- laser technique /
- adhering powder /
- single factor test /
- direct metal deposition
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Table 1. Direct metal deposition process parameters under different linear energy densities
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[1] KOCH J, MAZUMDER J. Rapid prototyping by laser cladding[J]. Proceedings of the SPIE, 1994, 2306: 556. [2] MURPHY M L, STEEN W M, LEE C A. Novel prototyping technique for the manufacture of metallic components[C]// Proceeding of ICALEO'1994. Orlanda, USA: Laser Institute of America, 1994: 31-40. [3] XIONG Y H, SMUGERESRY J E, AJDELSZTAJN L, et al. Fabrication of WC-Co cermets by 1aser engineered net shaping[J]. Materials Science and Engineering, 2008, A493(1/2):261-266. [4] QIU C L, RAVI G A, DANCE C, et al. Fabrication of large Ti-6AI-4V structures by direct laser deposition[J]. Journal of Alloys and Compounds, 2015, 629:35l-361. [5] ZHONG M L, NING G Q, LIN W J. Research and development on laser direct manufacturing metallic components[J]. Laser Technology, 2002, 26(5):388-391(in Chinese). [6] HUANG S H, LIU P, MOKASDAR A, et al. Additive manufacturing and its societal impact: A literature review[J]. International Journal of Advanced Manufacturing Technology, 2013, 67(5/8):1191-1203. [7] FRAZIER W E. Metal additive manufacturing: A review[J]. Journal of Materials Engineering & Performance, 2014, 23(6):1917-1928. [8] GUO N, LEU M C. Additive manufacturing: Technology, applications and research needs[J]. Frontiers of Mechanical Engineering, 2013, 8(3):215-243. [9] TABERNERO I, LAMIKIZ A, UKAR E, et al. Numerical simulation and experimental validation of powder flux distribution in coaxial laser cladding[J]. Journal of Materials Processing Technology, 2010, 210(15):2125-2134. doi: 10.1016/j.jmatprotec.2010.07.036 [10] KUMAR A, PAUL C P, PADIYAR A S, et al. Numerical simulation of laser rapid manufacturing of multi-layer thin wall using an improved mass addition approach[J]. Numerical Heat Transfer, 2014, A65(9):885-910. [11] GU D, MEINERS W, WISSENBACH K, et al. Laser additive manufacturing of metallic components: Materials[J]. Processes and Mechanisms, 2012, 57(3):133-164. [12] CONG W, NING F. A fundamental investigation on ultrasonic vibration-assisted laser engineered net shaping of stainless steel[J]. International Journal of Machine Tools & Manufacture, 2017, 121:61-69. [13] NARKHADE S S, RATHI M G. Additive manufacturing of metals: A review [J].Journal of Advances in Science and Technology, 2017, 13(1): 253-258. [14] DEBROY T, WEI H L, ZUBACK J S, et al. Additive manufacturing of metallic components—process, structure and properties [J]. Progress in Materials Science, 2018, 92:112-224. doi: 10.1016/j.pmatsci.2017.10.001 [15] HERZOG D, SEYDA V, WYCISK E, et al. Additive manufacturing of metals [J].Acta Materialia, 2016, 117:371-392. doi: 10.1016/j.actamat.2016.07.019 [16] LIU R Ch, YANG Y Q, WANG D. Research of upper surface roughness of metal parts fabricated by selective laser melting [J]. Laser Technology, 2013, 37(4):425-430(in Chinese). [17] TAN H, HU G, ZHANG F Y, et al. Formation mechanism of adhering powder and improvement of the surface quality during laser solid forming [J]. International Journal of Advanced Manufacturing, 2016, 86(5/8):1329-1338 [18] GHARBI M, PEYRE P, GORNY C, et al. Influence of various process conditions on surface finishes induced by the direct metal deposition laser technique on a Ti-6Al-4V alloy[J]. Journal of Materials Processing Technology, 2013, 213(5):791-800. doi: 10.1016/j.jmatprotec.2012.11.015 [19] GHARBI M, PEYRE P, GORNY C, et al. Influence of process conditions on surface finishes obtained with the direct metal deposition laser technique[J].Journal of Materials Processing Technology, 2013, 213(5):791-800. doi: 10.1016/j.jmatprotec.2012.11.015 [20] YUAN F B, WEI H Y, HUANG C, et al. The Taguchi experimental investigation on process energy efficiency of laser direct metal deposition [J]. Laser Technology, 2018, 42(1):24-29 (in Chinese).