Monitoring and analysis of melt-assisted deformation behavior of 304L stainless steel during multipass laser forming process using IR pyrometer and laser-based displacement sensor

In the present study, online monitoring of melt-based laser forming using a 2 kW Yb-fibre laser to understand the effect of partial sheet melting on bending behavior and mechanism to achieve precise deformation is investigated. A 1 mm thick 304L stainless steel sheet was used as substrate. The melt and non-melt-based sheet deformation and temperature signals were monitored using a laser-based non-contact type displacement sensor and an IR pyrometer, respectively for five consecutive scans on the same path having laser power, scan speed and spot diameter as input parameters. Variation in melt depth with process parameters and its effect on counter bending angle, net bending angle and significance of melt percentage with respect to sheet thickness on dictating the bending behavior was investigated. The bending mechanism reported in case of melt-based laser forming was found to vary from established solid metal sheet forming mechanisms and was termed as “melt-based TGM” mechanism. A maximum bending angle of 9.2° was obtained after five scans with 82 μm of melt depth. Microstructural and Phase variations of the melt and non-melt zone were studied for understanding their effects on material properties for melt–based laser forming. Finally, the mechanical behavior like modulus, Nano hardness and micro hardness of the melt and non- melt formed samples were studied to understand the applicability of melt-based laser formed sheets.