A novel method to fabricate metal tubes with smooth cavity via soluble core assisted aluminum droplet printing


3D metal printing involves building a metallic object layer by layer through the deposition of molten metal. This technique is advantageous in that it results in limited material wastage. Moreover, metal 3D printing techniques have shown more benefits when it comes to the direct fabrication of complex 3D structures, particularly, the micro thin-walled systems which possess a relatively complex cavity. Specifically, droplet-based 3D printing- a novel direct-writing technique that has numerous applications, such as printing of flexible circuits, advanced electronic components and metal parts- has become the center of research owing to the fact that it does not require expensive equipment, has low energy consumption and is environmentally friendly. Nonetheless, the surface of the formed parts produced using this technique have a tendency to have scalloped shape of metal droplets, hence a challenge in printing parts with high-quality inner surfaces.

To this effect, researchers at Northwestern Polytechnical University led by Professor Lehua Qi in collaboration with Dr. Ni Li at California State University developed a novel hybrid manufacturing method to fabricate tubes with ultra-high inner surface quality. They achieved this by combining the merits of soluble cores and droplet-based 3D printing, based on inspiration from conventional casting processes. Their work is currently published in Journal of Materials Processing Tech.

In brief, the research method employed commenced with the development of an experimental system with a rotating and translating receiver stage, so as to satisfy the forming principle of uniform droplet rotation deposition manufacture. Next, the researchers advanced a selection strategy of rotating angles, followed by multiple deposition experiments purposed to assess the effects of two processing parameters on the quality of formed parts. After the processing parameters were well tuned, a hexagonal metal part was fabricated directly. Lastly, the quality of the fabricated parts was characterized by the standard Archimedes method, industrial CT, and laser scanning confocal microscope, respectively.

The standard Archimedes test showed that the density of the formed part was up to 98%. The industrial CT scanning results also proved a porosity-free inner structure. In addition, the inner surface roughness was measured to be ~Ra 4.38 μm by using a laser confocal microscope scanning, and the roughness was only ~0.37% of the droplet diameter. These measurement results indicate that the authors have achieved a new milestone in the development history of metal droplet printing.

In summary, Dr. Hao Yi and colleagues presented a new and novel technique for manufacturing metal tubes with high-quality inner surfaces via deposition of aluminum droplets over soluble cores. To achieve this, they developed an experimental system with a four-axis receiver stage for use in fabricating the metal tubes. Altogether, their work has presented a future potential method to directly fabricate complex metal tube structures with high inner surface quality.

A novel method to fabricate metal tubes with smooth cavity via soluble core assisted aluminum 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 and material engineering, fluid mechanics and heat/mass transfer during droplet impacting. Dr. Hao Yi has done seminal research work in metal 3D printing and additive manufacturing, and he has published a series of research papers on some scientific journals, such as: Applied Physics Letters; International Journal of Machine Tools and Manufacture; Applied Thermal Engineering; Journal of Materials Processing Technology; Materials Letters, etc. Moreover, he has authorized and applied 6 invention patents of China.

Dr. Hao Yi is serving as a member of the editorial board of 14 international journals and a peer reviewer for approximately 20 SCI indexed journals, such as: International Journal of Machine Tools and Manufacture; Applied Thermal Engineering (Outstanding Reviewer-2018); Robotics and Computer-Integrated Manufacturing; Materials Science & Engineering A; Journal of Physics D-Applied Physics; International Journal of Precision Engineering and Manufacturing-Green Technology; JOM; Journal of Manufacturing Processes; International Journal of Advanced Manufacturing Technology; Vacuum; Materials Science and Technology; International Journal of Precision Engineering and Manufacturing; Atomization and Sprays; Powder Metallurgy; Micro & Nano Letters; 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.

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).


Hao Yi, Lehua Qi, Jun Luo, Daicong Zhang, Ni Li. Direct fabrication of metal tubes with high-quality inner surfaces via droplet deposition over soluble cores. Journal of Materials Processing Tech, volume 264 (2019) page 145–154.

Go To Journal of Materials Processing Tech

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