Colloquia

Summary

Dimensional accuracy and precision of small metal parts are among the biggest challenges in manufacturing, and USP laser ablation could be used as a post-processing step. The main driving factor in a mass production environment is the cost per part, so the ablation rate needs to be maximized while maintaining a proper surface finish and without overheating the part.

A research gap is found for the optimum wavelength for AISI 420 steel and how the heat input changes with different settings. Studies on the heat input of USP laser ablation are limited, and only single laser settings are tested. The residual energy coefficient (REC), the fraction of the laser energy that is converted to heat, is around 34% in the literature for stainless steels. Studies directed at optimizing the ablation efficiency (mm3/(W⋅min)) show: an optimum fluence needs to be used to increase the efficiency; a pulse duration of approximately 1 ps shows an optimum; a wavelength around 517 nm is optimal; the repetition rate shows particle shielding and heat accumulation; an increase in spot size lowers the efficiency; and burst mode also lowers the efficiency. A novel technique called ablation cooling shows promising results, but the technique is not yet well understood. Studies show high ablation rates of up to 42.42 mm3/min with an average power of 312 W.

Experiments are performed for the determination of the most efficient wavelength for AISI 420 stainless steel and the REC values for different fluences. Also, experiments are conducted to measure the surface quality at different laser powers, the relative absorbance of AISI 420 stainless steel, and a forced air-cooling system for a small metal part. A sample and sample holder are designed for ablation efficiency and REC measurement, considering minimized heat losses during the process. A Z focus scan and a knife-edge measurement are used for the laser setup. Different laser fluences at 1028 nm, 514 nm, and 343 nm wavelengths are used in an ablation process using a constant average power of 0.1 W.