Abstract
Heat accumulation due to successive laser pulse (HAP) incident on the same spot and heat accumulation due to successive scans (HAS) of the laser beam over the same spot significantly influences the process result, especially when the resulting temperature of the workpiece exceeds the melting temperature. In particular, heat accumulation is one of the dominating effects during short-pulse laser functionalization of surfaces and strongly affects the resulting surface structures. Within this study, a novel heat accumulation model is introduced to calculate the temperature increase in the workpiece for the whole process including the effects of HAP and HAS in which the latter is differentiated between heat accumulation due to multiple passes (HAS-I) and heat accumulation due to multiple layers (HAS-II). With the new model, the surface structure was successfully predicted when using an ultra-short pulsed (USP) laser with an average power of 420 W for laser surface structuring of polished AISI 316L.
Highlights
Heat accumulation occurs when the time between successive heat inputs on the same spot is too short for the processed material to cool down to the initial temperature [1]
When processing with a pulsed laser beam, the heat accumulation from pulse to pulse (HAP) is determined by the number Npps = ds ⋅ f/vfeed of pulses that are incident at one spot, where ds is the diameter of the laser beam on the surface of the workpiece, f is the pulse repetition rate of the laser, and vfeed is the feed rate
For 1D heat flow, the temporal evolution of the resulting temperature increase caused by HAP on the processed surface of the workpiece just before the incidence of the subsequent pulse can be approximated by [10]
Summary
Heat accumulation occurs when the time between successive heat inputs on the same spot is too short for the processed material to cool down to the initial temperature [1]. The thermal diffusion length is ldiff = (4·κ/f)0.5 = 7.11 μm [9], where κ = 3.75 × 10−6 m2/s is the thermal diffusivity of the processed material Since this is small compared to the diameter ds = 500 μm of the beam on the workpiece used in this study, 1D heat flow can be assumed for the time between two consecutive pulses [9]. When the ablation of a larger area is considered as sketched, the relevant thermal diffusion length (assuming immediate reposition between the scan lines) is ldiff = (4·κ·(M·dl/vfeed))0.5, where M = 160 is the number of processing lines considered in this study This diffusion length is found to be smaller than the width b = 10 mm of the processed square as long as the feed rate exceeds 0.24 m/s. When ablating several consecutive layers, one should take into account that every processed layer may lead to a change of the surface topography, which can lead to a change of the absorptance of the surface for one layer to the [10,11,12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
