A New ‘Digital Twin' Of Laser-Directed Energy Deposition Repair Technology

Researchers develop a numerical processing analysis system that automatically determines optimum forming conditions

Conventional metal 3D-printed repair of damaged mechanical parts in machines requires bulky equipment and wastes metal powder. Although laser-directed energy deposition overcomes this challenge, the optimum forming conditions had to be hitherto determined by trial and error. To this end, a team of researchers from Tokyo University of Science have developed a numerical method that automatically generates metal powder deposition elements and predicts forming process conditions, temperature distribution, deformation state, and residual stress distribution in advance.

Mechanical parts in industrial machinery and structures that develop thinning or cracks need to be replaced with new ones. In recent years, attempts to repair them have been considered, in order to improve industrial sustainability. So, repair technology for machines has been a hot topic of research and development. Conventional metal 3D-printed fabrication uses the surface of a mechanically laid powder bed that is irradiated with a laser or electron beam to melt the metal particles and fuse them. However, this method requires bulky fabrication equipment. Also, a large amount of metal powder is disposed after the fabrication process. However, laser-directed energy deposition (LDED) is a promising technology that overcomes the challenges. In this technique, metal powders are deposited at the focus of a laser beam, then melted and stacked.

The advantages of LDED are not only related to the compactness of the equipment, but also the significant reduction of metal powder waste. Furthermore, this technology enables in-situ metal powder fabrication in a 3D shape on the surface of a substrate. This means it can be used to repair machines made of metal as well!

A group of researchers, which include Professor Masayuki Arai from the Department of Mechanical Engineering, Faculty of Engineering, Tokyo University of Science (TUS), Japan, Mr. Toshikazu Muramatsu, also from TUS, and Dr. Kiyohiro Ito from Department of Mechanical and Electrical Engineering, Suwa University of Science, Japan, has, in collaboration with the Thermal Spray Technology Development Laboratory of TOCALO Co. Ltd., Japan, developed a repair technique using LDED."Using our technique, the surface shape of a metal structure can be completely restored on-site, and the disposal of the metal powder required for repair can be significantly reduced. However, the optimum forming conditions required for the widespread application of this technology in industry had to be hitherto determined by a trial-and-error process," explains Prof. Arai, who has been actively involved in the research of damage mechanics and repair technology.

In a recent article published in Journal of Thermal Spray Technology on November 23, 2022, the researchers have devised a mathematical model of LDED that automatically generates a metal powder deposition region using a death-birth algorithm, eliminating the guesswork needed to optimize the production."The thermal radiation-thermal conduction model and the viscoplastic-thermoplastic constitutive model are applied to the stacked elements that constitute the deposited region, so that a wide range of state changes from melting to solidification of the deposited layer of metal powder can be faithfully simulated. By incorporating these models into a finite element analysis program, we have developed a new machining analysis system that has never been used before", notes Prof. Arai. The team numerically simulated the restoration process, and thus, predicted the forming process conditions, temperature distribution, deformation state, and residual stress distribution in advance and verified the findings through experiments. They found that the residual stresses in the deposited layer were much lower than those obtained via conventional repair processes.

This novel 3D machining numerical analysis system is a digital twin of the existing core machining technology based on the fusion of metal in the area to be repaired. The numerical analysis method developed here could be applied to various industrial applications in the future, such as planning the repair of cavitation thinning on the surface of a blade used in power plant's circulating pump and devising a method for reducing residual deformation after repairing the thinning of the tip of a gas turbine's rotor blade. Taken together, the features of automation and advance prediction of process conditions by the numerical machining analysis system make 3D metal layered metal fabrication by LDED repair technology more effective, with efficient resource management to improve its sustainability.

About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.

With a mission of "Creating science and technology for the harmonious development of nature, human beings, and society", TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.

About Professor Masayuki Arai from Tokyo University of Science
Dr. Masayuki Arai is a Professor of Mechanical Engineering at the Faculty of Engineering, Tokyo University of Science (TUS), Japan. His research focuses on materials/mechanics of materials (Solid Mechanics, Damage Mechanics, Interface Mechanics). He earned his Ph.D. from Tokyo Institute of Technology. He has authored over 150 refereed papers, over 300 conference presentations and has 3 patents to his credit. He has served as a guest editor, associate editor in the editorial boards of several reputed journals. He has also served in the scientific committee of Asia-Pacific Conference on Fracture and Strength (2018), the Japan Society of Mechanical Engineers (2016-2017).