Study on the Kinetic Characteristics of Droplet Formation in Pneumatic Microdroplet Injection

doi:10.3901/JME.2020.23.203

Abstract

Abstract: As a new and cutting-edge technology in the field of additive manufacturing, droplet injection additive manufacturing technology has a broad application prospect. Droplet generation characteristics have a great influence on substrate spreading, bonding, solidification and other processes of droplet in additive manufacturing. The study on droplet generation characteristics is of great significance for improving the size, frequency and stability of droplet generation. The micro-droplet injection behavior under the action of aerodynamic on-demand injection was studied through experiments, to explore the influence of nozzle size, viscosity, supply pressure and other factors on the jet fracture process and droplet formation stability, and to further study the influence of the change of formation angle on the fracture sequence of the liquid bridge and the generation of satellite droplets. The results show that with the decrease of nozzle diameter, weber number (We) decreases significantly. When the nozzle diameter decreases to 100 μm, We becomes 0.33, and the ratio of droplet size to nozzle diameter increases sharply. With the increase of viscosity, the liquid bridge and droplet size in the necking section of the jet increased significantly. Under the condition of ensuring the generation of a single droplet, when the supply pressure is low, the two ends of the liquid bridge break successively to form satellite droplet, and finally merge with the lunate surface; With the increase of pressure, the bridge only breaks once, and the remaining jet retract to the nozzle. Since upstream formation Angle is always greater than downstream formation angle, the liquid bridge always breaks first near the droplet end in the pneumatic injection mode. The results of this study are helpful to improve the droplet generation quality of the pneumatic microdroplet injection device.

Key words: pneumatic drive, drop-on-demand, liquid bridge, droplet diameter, satellite droplet

CLC Number:

TG156

LIU Zhaomiao, ZHONG Xixiang, YANG Gang, PANG Yan, REN Yanlin, XU Yuandi, GAO Shanshan. Study on the Kinetic Characteristics of Droplet Formation in Pneumatic Microdroplet Injection[J]. Journal of Mechanical Engineering, 2020, 56(23): 203-211.

References

[1] ORME M. A novel technique of rapid solidification net-form materials synthesis[J]. Journal of Materials Engineering& Performance,1993,2(3):399-405.
[2] 齐乐华,钟宋义,罗俊.基于均匀金属微滴喷射的3D打印技术[J].中国科学:信息科学,2015,45(2):212-223. QI Lehua,ZHONG Songyi,LUO Jun. 3D printing technology based on uniform metal droplet ejection[J]. Scientia Sinica Informationis,2015,45(2):212-223.
[3] GOGHARI A A,CHANDRA S. Producing droplets smaller than the nozzle diameter by using a pneumatic drop-on-demand droplet generator[J]. Experiments in Fluids,2008,44(1):105-114.
[4] YOKOYAMA Y,ENDO K,IWASAKI T,et al. Variable-size solder droplets by a molten-solder ejection method[J]. Journal of Microelectromechanical Systems,2009,18(2):316-321.
[5] ŠTURM R,GRUM J,BOŽIÈ S. Influence of the alloying elements in Al-Si alloys on the laser remelting process[J]. Lasers in Engineering,2011,22(1):47-61.
[6] ZHONG Songyi,QI Lehua,XIONG Wei,et al. Research on mechanism of generating aluminum droplets smaller than the nozzle diameter by pneumatic drop-on-demand technology[J]. International Journal of Advanced Manufacturing Technology,2017,93(5-8):1771-1780.
[7] PARK B K,KIM D,JEONG S,et al. Direct writing of copper conductive patterns by ink-jet printing[J]. Thin Solid Films,2007,515(19):7706-7711.
[8] LI L,SAEDAN M,FENG W,et al. Development of a multi-nozzle drop-on-demand system for multi-material dispensing[J]. Journal of Materials Processing Tech,2009,209(9):4444-4448.
[9] BERKLAND C,KIM K,PACK D W. Fabrication of PLG microspheres with precisely controlled and monodisperse size distributions[J]. Journal of Controlled Release Official Journal of the Controlled Release Society,2001,73(1):59-74.
[10] 蔡基利,吴和保,刘富初,等.微滴喷射快速成形Al₂O₃陶瓷微球的性能[J].材料工程,2018,46(11):88-93. CAI Jili,WU Hebao,LIU Fuchu,et al. Properties of Al₂O₃ ceramic microspheres by droplet injection rapid prototyping[J]. Materials Engineering,2018,46(11):88-93.
[11] XU J,ATTINGER D. Drop on demand in a microfluidic chip[J]. Journal of Micromechanics and Microengin-eering,2008,18(6):065020.
[12] EDD J F,DI CARLO D,HUMPHRY K J,et al. Controlled encapsulation of single-cells into monodies-perse picolitre drops[J]. Lab on a Chip,2008,8(8):1262.
[13] SCHENA M,HELLER R A,THERIAULT T P,et al. Microarrays:Biotechnology\"s discovery platform for functional genomics[J]. Trends in Biotechnology,1998,16(7):301-306.
[14] VAEZI M,CHUA C K. Effects of layer thickness and binder saturation level parameters on 3D printing process[J]. International Journal of Advanced Manufacturing Tech-nology,2011,53(1-4):275-284.
[15] 张楠,林健,王同举,等.用于打印柔性导线的液态金属微滴制备过程研究[J].电子元件与材料,2018,37(7):5-11. ZHANG Nan,LIN Jian,WANG Tongju,et al. Study on the preparation process of liquid metal microdroplets for printing flexible wires[J]. Electronic Components and Materials,2018,37(7):5-11.
[16] 肖渊,吴姗,刘金玲,等.织物表面微滴喷射反应成形导电线路基础研究[J].机械工程学报,2018,54(7):216-222. XIAO Yuan,WU Shan,LIU Jinling,et al. Basic research on microdroplet spray forming conductive circuit on fabric surface[J]. Journal of Mechanical Engineering,2018,54(7):216-222.
[17] CHAO Y P,QI L H,XIAO Y,et al. Manufacturing of micro thin-walled metal parts by micro-droplet deposition[J]. Journal of Materials Processing Technology,2012,212(2):484-491.
[18] YI H,QI L,LUO J,et al. Hole-defects in soluble core assisted aluminum droplet printing:Metallurgical mechanisms and elimination methods[J]. Applied Thermal Engineering,2019,148:1183-1193.
[19] YI H,QI L,LUO J,et al. Direct fabrication of metal tubes with high-quality inner surfaces via droplet deposition over soluble cores[J]. Journal of Materials Processing Technology,2019,264:145-154.
[20] CHEN A U,BASARAN O A. A new method for significantly reducing drop radius without reducing nozzle radius in drop-on-demand drop production[J]. Physics of Fluids,2002,14(1):L1.
[21] CHENG S,CHANDRA S. A pneumatic droplet-on-demand generator[J]. Experiments in Fluids,2003,34(6):755-762.
[22] CHENG S X,LI T,CHANDRA S. Producing molten metal droplets with a pneumatic droplet-on-demand generator[J]. Journal of Materials Processing Tech-nology,2005,159(3):295-302.
[23] ZUO H S,LI H J,QI L H,et al. Effect of wetting behavior on generation of uniform aluminum droplets obtained by pneumatic drop-on-demand technique[J]. Journal of Materials Processing Technology,2014,214(11):2566-2575.
[24] WANG T J,LIN J,et al. Droplets generator:Formation and control of main and satellite droplets[J]. Colloids and Surfaces A,2018,558:303-312.
[25] GERDES B,ZENGERLE R,KOLTAY P,et al. Direct printing of miniscule aluminum alloy droplets and 3D structures by StarJet technology[J]. Journal of Micro-mechanics and Microengineering,2018,28(7):074003.
[26] AMIRZADEH A,CHANDRA S. Small droplet formation in a pneumatic drop-on-demand generator:Experiments and analysis[J]. Experimental Thermal and Fluid Science,2010,34(8):1488-1497.
[27] AMIRZADEH A,RAESSI M,CHANDRA S. Producing molten metal droplets smaller than the nozzle diameter using a pneumatic drop-on-demand generator[J]. Experimental Thermal and Fluid Science,2013,47:26-33.
[28] BANITABAEI S A,AMIRFAZLI A. Pneumatic drop generator:Liquid pinch-off and velocity of single droplets[J]. Colloids and Surfaces A:Physicochemical and Engin-eering Aspects,2016,505:204-213.
[29] ZHAO X,JIA Z,LI W,et al. Numerical simulation of micro droplet formation combined with pneumatic and piezoelectric drive[J]. Microsystem Technologies,2018.
[30] ZHANG D,QI L,LUO J,et al. Direct fabrication of unsupported inclined aluminum pillars based on uniform micro droplets deposition[J]. International Journal of Machine Tools and Manufacture,2017,116.
[31] LUO J,QI L H,ZHOU J M,et al. Modeling and characterization of metal droplets generation by using a pneumatic drop-on-demand generator[J]. Journal of Materials Processing Technology,2012,212(3):718-726.
[32] TURKOZ E,PERAZZO A,KIM H,et al. Impulsively induced jets from viscoelastic films for high-resolution printing[J]. Physical Review Letters,2018,120(7):074501.
[33] SCHULKES R M S M. The contraction of liquid filaments[J]. Journal of Fluid Mechanics,1996,309(309):277-300.
[34] HOSSAIN A,FARHAN N M,HOOMAN V T. Effects of fiber wettability and size on droplet detachment residue[J]. Experiments in Fluids,2018,59(7):122-129.