An interesting discovery of the influence of wrinkles on the overlapping fusion in metal droplet printing


3D printing is one of the latest exciting and revolutionary technologies in the manufacturing industries. It enables the fabrication of complex three-dimensional parts from their computer-aided design drawings. Owing to its flexibility and efficiency, its use has been extended to several other applications for printing structures such as advanced electronic components. The fusion at the droplet/droplet interface is very significant for the printing of 3D metal structures. Therefore, extensive research is being done to improve on the existing 3D printers for the manufacturing of high-quality products for a wide range of materials such as aluminum.

Generally, molten aluminum alloys exhibit large surface tension and high-temperature gradient that hinder printing of high-quality structures from the molten aluminum droplets. This results in defects such as cold lap pores due to poor remelting conditions between the droplets. Recently, determination of the critical remelting conditions has attracted significant attention of many researchers. Despite a number of proposed theoretical and experimental models, cold cap pores remain a serious defect thus lowering their performance. This has led to consideration of other potential factors during the remelting process.

Recently, Northwestern Polytechnical University researchers Dr. Hao Yi, Professor Lehua Qi, Professor Jun Luo, Dr. Daicong Zhang and Professor Hejun Li in collaboration with Professor Xianghui Hou at the University of Nottingham observed that the surface morphologies of solidified droplets are potential and significant influencers of the remelting between droplets during 3D printing for the first time. They investigated the effects of surface morphologies in the remelting process between neighboring droplets by considering the ripples and the solidification angles. Their work is published in International Journal of Machine Tools and Manufacture, and this investigation successfully updates the understanding of metal droplet-based 3D printing.

The authors divided the remelting process between the neighboring droplets into two stages. In the first stage, they observed that the internal defects like cold laps can occur even though the remelting conditions are theoretically satisfied. This is because the surface of the previously deposited droplet contains ripples that tend to block the contact with another droplet. Consequently, in the second stage, solidification angles greater than 900 results in the incomplete filling of the liquid phase that produces cold laps on the bottom surface.

The study is the first to experimentally investigate the effects of the solidification angles and the blocking effects of the ripples on the fusion between the droplets. Furthermore, an effective method for promoting the remelting process of the droplets by decreasing solidification angles and eliminating the ripples by using a lower thermal conductivity substrate is also verified. The research forms the basis for minimizing internal defects and thus improving the metallurgical bonding during droplet-based 3D printing. Therefore, it will advance the use of 3D printers in the various field for manufacturing of complex parts especially metal structures.

influence of wrinkles on   overlapping fusion in metal droplet printing - Advances in Engineering

About the author

Dr. Hao Yi is an early-stage researcher in metal 3D printing and additive manufacturing. He received his Bachelor of Mechanical Engineering from Northwest A&F University (NWAFU), China. He then enrolled in the master and doctoral programs of Mechanical Engineering under the supervision of professor Lehua Qi at Northwestern Polytechnical University (NPU), China. He is now working at the Centre for Advanced Coating Technology (CACT) at University of Toronto (UoT) under the supervision of distinguished professor Javad Mostaghimi.

His current research focus on droplet printing and additive manufacturing, manufacturing processes for metals, fluid mechanics and heat/mass transfer during droplet impacting. Dr. Hao Yi has done seminal research work in metal 3D printing, and he has published a series of research papers on some high-level journals, such as: Applied Physics Letters, International Journal of Machine Tools and Manufacture, Applied Thermal Engineering, Journal of Materials Processing Technology, Materials Letters, etc.

Dr. Hao Yi is serving as a member of the editorial board of 10 international journals and a peer reviewer for over 10 SCI journals, such as: Applied Thermal Engineering, Journal of Physics D: Applied Physics, International Journal of Advanced Manufacturing Technology, Journal of Micromechanics and Microengineering, Vacuum, International Journal of Precision Engineering and Manufacturing, Atomization and Sprays, Journal of the Brazilian Society of Mechanical Sciences and Engineering, etc. Moreover, he is a member of the following professional societies: ASME, ACM, CMES, CSAA.

More information about Dr. Hao Yi can be found at Researchgate.
Email addresses: [email protected] (H. Yi);
[email protected] (H. Yi).

About the author

Prof. Lehua Qi is a lifetime professor of mechanical engineering at Northwestern Polytechnical University (NPU). She received her B.S. degree in Plasticity Forming from Luoyang Institute of Technology (LIT), M.S. degree in Plasticity Forming from Harbin Institute of Technology (HIT), and Ph.D. degree in Systematical Engineering from NPU. She is serving as the chair professor of the major of Machinery Manufacturing and Automation at NPU. She is also a member of the academic committee of NPU and key lab of contemporary design and integrated manufacturing technology, Ministry of Education. She has published over 300 research papers in referred journals and international conference proceedings, and she has authorized over 60 invention patents of China.

Prof. Lehua Qi is known internationally for her research on the droplet-based 3D printing and metal matrix composites.

Her research spans the areas of accumulated material forming with spraying micro-droplet, liquid metal extrusion technology for fabricating tube and bar products of Al alloy and metal matrix composites, semi-solid extrusion technology for metal matrix composites, computer simulation and control on the CVI process and microstructure of carbon-carbon composites. Specially, in terms of droplet-based 3D printing, she has built a micro-manufacturing lab for both the fundamental and application research of uniform metal droplet formation, microstructure and properties, process control, numerical simulation and optimization, etc.

In 2012, Prof. Lehua Qi was awarded the National Technology Invention Second Prize by the Ministry of Science and Technology of China. In 2014, she was awarded the National Model Teacher by the Ministry of education of China. In 2007, she was awarded the 100 excellent Ph.D. dissertations of China by the Ministry of education of China.

Email addresses: [email protected] (L. Qi).

About the author

Prof. Jun Luo is currently an associate professor at School of Mechanical Engineering in NPU. He obtained his Ph.D. in 2010 in Northwestern Polytechnical University, under the supervision of Professor Lehua Qi. He did his postdoctoral research in NPU from 2010 to 2012. In 2015, he visited the Physics of Fluids (POF) group as a visiting scholar at the University of Twente in the Netherlands.

For many years, he concentrates in developing metal droplet-based printing technologies. In NPU, he and his colleague keep developing molten metal droplet printers. Now the accomplished printers can work at the temperature beyond 1000 oC . Solder, aluminum and copper droplet printing have been successfully tested. He also has a keen interest in the fundamental research about molten metal droplet ejection, impact, and deposition behaviors. In POF group, he coordinated with Class-Willem Visser, under the supervision of Chao Sun and Detlef Lohse, to explore the first multi-material nanosecond laser-induced forwards transfer (ns-LIFT) system for printing micron-scaled functional metal structure. Based on this collaboration, several interesting topics on the metal droplet impact are still undergoing.

He has published papers in journals such as Small, Int. J. Mach. Tool and Manuf., J. Mater. Process. Technol. Applied Thermal Engineering, Materials Letters etc. His a peer reviewer for over 10 journals, such as: Int .J. Mach. Tool. and Manuf., Science reports, Int. J. Multiphase Flow, Journal of material processing technology, powder technology, Chinese Chemical Letters etc.

More information about associate professor Luo Jun can be found at  Researchgate.

Email addresses: [email protected] (J. Luo); [email protected] (J. Luo).


Yi, H., Qi, L., Luo, J., Zhang, D., Li, H., & Hou, X. (2018). Effect of the surface morphology of solidified droplet on remelting between neighboring aluminum droplets. International Journal of Machine Tools and Manufacture, 130-131, 1-11.

Go To International Journal of Machine Tools and Manufacture

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