06-04-2017, 09:42 AM
The motivation for micro polished laser polishing is to reduce the roughness of the surface of the parts whose surface texture can approach the size of the feature. Being able to predict the magnitude of the polishing and the frequency (wavelength) of the surface content will help in the design of optimal processing parameters with minimal experiments. Laser pulses are used to create surface fusion pools with a controlled size (eg, depth) and duration to allow surface tension forces to "drag" roughnesses with a small radius of curvature. No ablation occurs in the process being modeled. The depth and duration of the melt is predicted with a transient two-dimensional axisymmetric heat transfer model with temperature dependent material properties. The surface of the fusion pool is analytically modeled as stationary capillary wave oscillations with damping resulting from the forces of surface tension and viscosity. Above a critical spatial frequency, a significant reduction in the amplitude of the Fourier spatial components is expected.
The work described in this paper extends the concept of critical frequency to a prediction methodology based on physics to predict spatial frequency content and surface roughness after polishing, given the characteristics of the original surface, the properties of the material and the Parameters of the laser. The proposed prediction methodology was validated using line polishing data for the results of 316L stainless steel polishing and surface polishing for pure nickel, Ti6Al4V and Al-6061-T6. The expected average surface roughness was within 12% of the values measured on the polished surfaces.
