Fluorescence-Based Measurement of Workpiece Geometry and Temperature in Laser Chemical Machining.

Abstract

Laser chemical machining (LCM) is a gentle metal removal technique with micrometer resolution. LCM involves laser-driven surface heating of the workpiece, which is subjected to a flowing acid bath, locally inducing a chemical dissolution reaction. To ensure a high machining quality, the laser power is intentionally limited to avoid disturbances in material removal presumably caused by the shielding effect of boiling bubbles. To achieve both an increased removal rate and a high removal quality, the current understanding of surface removal mechanisms must be fundamentally expanded. Therefore, to create the basis of near-process quality control in the future, a near-process measurement approach is needed for the machined workpiece geometry inside the machine and the temperature in the process fluid as an important process quantity. This study introduces a fluorescence-based measurement approach capable of assessing both quantities in-situ. An experimental feasibility study demonstrated the robustness of the approach in measuring the three-dimensional geometry of a structure produced by LCM, even in the presence of streaming air bubbles in the optical path, thereby validating its near-process capability. However, systematic measurement errors, such as edge artifacts, were observed in the geometry measurements, indicating the need for a revision of the signal model. In addition, precise temperature measurements of the electrolyte solution within the LCM environment were achieved, with a random error of $1_{}^{\circ }\text{C}$ and a systematic error of $1.4_{}^{\circ }\text{C}$ .