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Multi-Cycle Process Signature of Laser-Induced Thermochemical Polishing

Laser-induced thermochemical polishing (LCP) is a non-conventional processing technique that uses laser radiation to smooth the surface of self-passivated metallic parts by initiating a localized anodic material dissolution. This technology can be used to selectively micro-polish without the need for masking or thermal and mechanical stress. However, there is still a lack in understanding the surface quality depending on the applied laser machining parameters. This paper takes up the concept of Process Signatures and interprets the surface smoothing as result of multiple, recurring internal material loads of a constant energy amount. The laser-induced thermal impact is identified as the relevant internal material load and is correlated with the surface roughness. This derives an empirical-based functional relation as multi-cycle Process Signature. The experiment results show an exponential decay in surface roughness with increasing cycle loads for titanium, Ti6Al4V, Nitinol, Stellite 21, and metallic glass. The Process Signature of LCP is a solution to a differential equation with respect to the cycle loads. The paper demonstrates how the multi-cycle Process Signature helps determine suitable machining parameters to predict the surface roughness, as well as to scale the polishing rate.