Laser Additive Manufacturing at Machine Tools Lab, IIT Bombay.
Image Credit : Aaditya Puranik

The following article was originally written by Mr. Ankush Banerjee and published here.

Here’s how IIT Bombay’s Laser Remelting technique is fixing weak spots without slowing down production

What do baking a cake and 3D printing have in common? You can rush both processes, but you’re almost guaranteed to end up with a hunching, sloppy mess by the end of it. While 3D metal printing has proven itself to be a godsend for the manufacture of highly intricate components, there is much to be desired in the time and energy it takes to print something. You can certainly speed up the process, but only if you’re prepared for a horde of structural defects, voids, weak spots, and unwanted phases in the material.

This challenge of speed is exactly what Rajendra Hodgir, a PhD student, Prof. Ramesh Singh and Prof. Soham Mujumdar from the Department of Mechanical Engineering, Indian Institute of Technology Bombay (IIT Bombay) tackled in their latest work. Their research, with Rajendra as the lead author, introduces an extra step, called in-situ laser remelting, in the 3D printing process, where a laser remelts each printed layer before the next one is added. The result is a structure that is stronger and denser compared to before—all while printing 2.5 times faster!

3D printing, also termed “additive manufacturing,” works by the precise layer-by-layer deposition of material fused with the help of external heat or lasers. One of the more common methods of 3D printing metals is Laser-Directed Energy Deposition (L-DED), where fine metal powder is fed through a nozzle and melted by a high-powered laser to fuse layers of metal, one atop the other. Such printing methods are often chosen to create complex parts that are impractical or prohibitively expensive to produce using existing fabrication methods. Features such as intricate lattice structures, multi-material parts with continuous property gradients, and hollow internal channels with complex curvatures are some examples of designs that are uniquely suited to additive manufacturing.

Demand for high-end, precision-manufactured parts is growing, especially in fields like aerospace and biomedical engineering, prompting India to import not just these components but also advanced 3D printing technologies. However, trying to accelerate the metal 3D printing process brings challenges. “High deposition rates—printing a lot of material too quickly—often lead to defects such as porosities, cracks, and residual stresses,” Prof. Mujumdar explains. “In some cases, large grains can weaken the overall structure. Smaller grains are usually preferred since their boundaries act as barriers to crack propagation, making the material stronger and tougher.”

Grains are small crystalline regions within the metal where atoms are arranged in a consistent pattern. In addition to the size of grains, the porosity of the structure is another concern that needs addressing. As the molten metal solidifies, gas gets trapped to form tiny pockets, creating voids that compromise the strength of the 3D-printed structure. To fix these issues, engineers usually rely on time- and energy-intensive post-processing techniques, like heat treatment or hot isostatic pressing (applying large amounts of heat and pressure to metals). Instead of waiting until the end to fix these flaws, researchers at IIT Bombay thought of tackling them during the printing process itself—by remelting each layer just after it’s deposited, before the next one is added.

The researchers found that briefly reheating the material helped eliminate voids and refined the grain structure. The researchers carried out this work at the Machine Tools Lab, Mechanical Engineering Department, IIT Bombay, utilizing the experimental laser DED setup developed in-house by Prof. Singh’s group. They found that compared to the regular L-DED process, laser remelting could reduce the porosity of the 3D printed structure by 83%, improve surface smoothness by 59%, and increase the metal’s microhardness by 34%. The best part is the fact that the technique requires zero new machinery. “It’s happening on the same machine. You just turn off the powder and run the laser,” Mujumdar noted.

The next challenge was to find that sweet spot between speed and quality. Using a high laser power certainly helped with the porosity problem by deepening the remelting, but it also takes a large amount of energy to fuel this process. On the other hand, lower power helped refine grain structure and strengthen the material, but it wasn’t nearly as successful at eliminating the defects in the structure. The researchers experimented with different power levels and scan speeds until
they found an optimal combination, allowing them to maintain high build rates while improving material integrity.

They discovered that using 2000 W power and a 400 mm/min scan speed created the densest final structure in stainless steel (SS316L), the material used in this study. SS316L stainless steel is used everywhere—from aerospace components to biomedical implants, from industrial machinery to kitchen appliances. Not only will a faster, more reliable 3D printing method transform manufacturing in these industries, it can be a great push towards India’s focus on self-reliance in advanced manufacturing.

“The manufacturing sector is booming right now because of the government’s initiative to make everything in India,” Mujumdar explained. Innovations like in-situ laser remelting could help the country move closer to that goal, strengthening its industrial and technological capabilities. However, since different metals have varying thermal and mechanical properties, these specific parameters may not apply universally. Further research would be needed to determine the optimal conditions for other materials.

The researchers are now refining the process to make it even more energy and time-efficient. Instead of remelting after every layer, they are testing whether doing it every second or third layer can achieve the same benefits at a lower cost. They are also developing computational models to predict how different remelting parameters influence material properties, allowing for smarter and more optimized manufacturing.

Funding Information: This research was funded by a grant from the Science and Engineering Research Board (SERB), (now, Anusandhan National Research Foundation), Government of India.

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The original academic article titled Simultaneous Enhancement of Build Rate and Microstructure in SS316L Additive Manufacturing Through In-Situ Laser Remelting was written by IIT Bombay’s researchers and published in the Journal of Manufacturing Processes, Volume 133.

The original paper can be found here.