A predictive model for burr formation in ultrafast laser ablation based on accumulated fluence

• Novel burr indicator with a shared threshold for dimples and lines is presented. • The burr characterisation method is based on height, area, and volume. • Burr formation first maximises the area coverage before increasing the height. • The burr indicator can be integrated into laser process parameter-prediction model. Femtosecond lasers are powerful tools for precise surface texturing. They minimise the occurrence of heat-affected zones, which helps avoid surface defects such as burrs. However, the use of suboptimal parameters can still result in burr formation. Burr formation is critical in tribological applications, but its evolution has not been systematically characterised in the literature. Existing approaches typically rely on estimating the temperature reached by the material to assess the heat accumulation. However, this method has proven insufficient across a wide range of average laser powers and ablation geometries. This study introduces and validates a novel semi-empirical model that employs accumulated fluence, defined as the total accumulated energy per unit area, as an indicator that is independent of power and geometry. This method highlights burr formation in multi-shot and line ablation. Comprehensive qualitative and quantitative analyses of burr evolution were conducted using height, area, and volume variables, which minimised the sensitivity to measurement artefacts. Based on the geometrical features of the generated burrs, three burr regimes were identified for dimples and two for lines. Despite the differences in burr evolution, a shared burr formation threshold was identified at an accumulated fluence of 92 J/cm 2 for 316L stainless steel. The proposed indicator enables the cost-effective calibration of a burr-free laser processing parameter window. The new indicator can be integrated into laser parameter prediction models to optimise the process design and facilitate the industrial applicability of femtosecond laser technology.