Imagine a laser beam slicing through solid metal like a hot knife through butter. No, this isn’t a scene from a sci-fi classic, but a standard processing technique commonly used in the manufacturing sector. Laser processing is often used to 3D print diverse structures made from a variety of materials, from metals to plastics and ceramics.
Laser processing is a technique well-suited for creating intricate forms as the intense light beam melts the material on impact, quickly sculpting it to create the final product. However, these high-energy lasers can cause collateral damage, said Guglielmo Vastola, a senior scientist at A*STAR’s Institute of High Performance Computing (IHPC).
When lasers come into contact with a material, they can create indentations in the material called keyholes which are surrounded by molten material known as melt pools. “If the keyhole is too deep, it destabilises and can spill bubbles of metallic vapor over to the surrounding material, creating pores,” Vastola explained, adding that these pores can compromise the overall quality of the final product.
According to Vastola, understanding how and why keyholes and melt pools form is critical to optimising laser processing techniques. To fill this knowledge gap, Vastola and his team developed a series of complex physics-based simulations to model the mechanisms underlying these defects.
Simulation images depict the evolution of a keyhole and melt pool in a Ti-6Al-4V alloy under a stationary laser beam.
In doing so, however, the team was faced with tough technical challenges. Because laser energy is very concentrated, its interaction with the metal is very complex, and therefore requires very accurate physical modelling to be fully understood. To achieve this goal, the team developed multiple computational techniques to map laser energy transfer, while melt pool fluid dynamics and heat transfer had to be integrated to accurately model the physical changes occurring around keyholes.
Armed with this array of technologies, Vastola’s group succeeded in generating high-fidelity computational simulations of keyholes and melt pools that lined up with the results captured by high-speed X-ray camera, verifying the precision and reliability of their model. Importantly, the simulation tool was able to capture the spilling of bubbles from the keyhole and their entrapment into the solidified metal as a pore.
The researchers used their new model to determine how best to modulate laser processing settings to prevent spill-over events. They see this innovation being a huge boon to manufacturers that use laser processing to improve the quality of their printed products. Furthermore, because the model was designed with flexibility in mind, it can easily be customized to simulate different materials as well as a range of laser-processing techniques.
The team is planning to expand the scope of the computational model beyond the stationary laser beam. “The next step is to tackle the case of a moving laser, which more closely matches the situation during manufacturing,” he said.
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing (IHPC).
