Combining laser polishing with a steady magnetic field creates smoother, harder surfaces

When a continuous-wave laser melts material to polish a surface, an overflow region can form along the direction of the beam, which creates a peak at the end of the pool of melted material, leading to new secondary roughness. Xiao et al. demonstrated a method of increasing surface smoothness by suppressing this secondary roughness.

The authors showed by applying a magnetic field to this process, the induced Lorentz force acts as a drag on the melt flow, suppressing the overflow and reducing the unwanted peak responsible for the secondary roughness. This method can decrease the initial surface roughness by 91%, an improvement of up to 45% as compared to the case without applying the magnetic field. Additionally, this technique increases the microhardness of the surface more than twofold.

By varying the intensity of the applied steady magnetic field, the researchers observed the field’s effects on properties of the polished surfaces, confirming the molten pool overflows are the cause of the secondary roughness. However, to avoid overcompensating for the overflow and creating a new roughness in the opposite direction, the magnetic field must be tuned to balance the Lorentz force with the surface tension and fluid viscosity forces.

“The demand for polishing the surface of product parts is everywhere,” said author Yongquan Zhou. For example, many components of consumer electronics, automobiles and medical devices require a polishing treatment.

Using their technique combining a continuous-wave laser with a steady magnetic field, the authors believe commercial polishing methods can be improved with no added drawbacks compared to traditional methods.

Source: “Laser polishing of tool steel using a continuous-wave laser assisted by a steady magnetic field,” by Haibing Xiao, Yongquan Zhou, Mingjun Liu, and Xiaomei Xu, AIP Advances (2020). The article can be accessed at https://doi.org/10.1063/1.5116686 .