Scientists explore the use of Bessel beams to improve porosity and defect issues in 3D metal printing

Laser based 3D printing technology, with its scalability and complexity, has completely changed the production of metal parts. However, traditional laser beams used for metal printing still have drawbacks, which may lead to defects and poor mechanical performance. Exploring alternative shapes for Gaussian beams commonly used in high-power laser printing processes, researchers at Lawrence Livermore National Laboratory (LLNL) are attempting to address this issue, with one breakthrough being laser powder bed melting (LPBF).

In a recent paper published in Science Advances, researchers conducted experiments on the shape of a strange beam called Bessel beams. This type of beam has some unique characteristics, such as self-healing and non diffraction. Research has found that the application of these types of beams reduces the possibility of pore formation and keying, while the use of Gaussian beams exacerbates the pore induced phenomenon in LPBF. This work was reflected on the cover of the magazine on September 17, 2021.

LLNL researchers say that this work indicates that alternative shapes such as Bessel beams can alleviate the main problems in LBPF technology: the huge thermal gradient and complex melt instability that occur at the point where the laser meets the metal powder. These problems are mainly caused by the Gaussian beam shape that most existing high-power laser systems typically output.

The main author of this paper LLNL research scientist Thej Tumkur Umanath said, "Using Gaussian beams is much like using a flamethrower to cook your food; you can't control how heat deposits around the material very well. With Bessel beams, we redistribute some energy away from the center, which means we can design thermal curves, reduce thermal gradients, help refine microstructure grains, and ultimately lead to denser components and smoother surfaces.".

Another drawback of traditional light beams is that they are prone to diffraction (diffusion) during propagation. Bessel beams, due to their non diffraction properties, can provide greater focusing depth. Therefore, the author of the paper observed that when using Bessel beams, the tolerance of the workpiece relative to the laser focus position increased. Placement is a challenge for industrial systems, as these systems often rely on expensive and sensitive techniques to locate ongoing construction within the focal depth of the focused beam each time a layer of metal powder is deposited.

Tumkur explained, "Bessel beams are widely used in imaging, microscopy, and other optical applications due to their non diffractive and self-healing properties, but beam shape engineering methods are quite rare in laser-based manufacturing applications. Our work addresses the seemingly disconnected issue between photophysics and material engineering in the field of metal additive manufacturing, which involves designing beam shapes to achieve control over the dynamics of the melt pool.".

Prev: Scientists have discovered that using artificial intelligence can efficiently predict protein molecular structure