Laser powder bed fusion (LPBF) has broad application prospects in the manufacturing of high-performance and complex metal components. However, the traditional Gaussian laser beams have nonuniform energy distributions that lead to challenges such as poor molten-pool stability and high cooling rates during processing. These issues can result in defects such as spattering and porosity, which hinder the technology’s advancement. Beam shaping techniques can help redistribute laser energy and effectively address these distribution challenges. Research shows that flat-top laser beams possess unique advantages in controlling defect formation and microstructure development. However, the mechanisms through which these beam profiles affect stress development are not well understood. This study aims to investigate the effects of Gaussian and flat-top laser beams on temperature and stress fields during the LPBF process under the conditions of maintaining the same spot diameter and total energy input. The goal is to provide a theoretical foundation for optimizing process parameters and regulating stress distribution in LPBF.

This study employs the numerical simulation method to systematically examine the effects of Gaussian and flat-top laser beams on the LPBF forming process. A finite element model of multi-pass scanning was developed based on thermo-mechanical coupling theory, and the reliability of the model was verified through single-pass scanning experiments. In the simulation process, a comparative study of Gaussian and flat-top laser beams was conducted by controlling variables such as spot diameter and total energy input. Under the condition of scanning speed of 700 mm/s, we performed a comprehensive analysis of key thermal field parameters, including temperature peaks, temperature gradients, and cooling rates at both the center and edge regions of the laser spot for each laser type. The evolution of residual stress was also evaluated. In addition, the study analyzed the trends in temperature peaks and residual stress across various process parameter combinations, providing a theoretical basis for process optimization.

The distribution of laser energy significantly affects the spatial temperature distribution, thereby affecting temperature peaks, gradients, and cooling rates. At a scanning speed of 700 mm/s, the maximum temperature at the center of the flat-top laser beam is approximately 541.28 ℃ lower than that of the Gaussian laser beam, whereas the maximum temperature at the edge of the spot is approximately 127.95 ℃ higher. Variations in energy distribution also result in differences in temperature gradients and cooling rates. The Gaussian laser beam demonstrates higher temperature gradients and cooling rates at the center of the spot, whereas the flat-top laser beam exhibits higher values at the edge. Specifically, the maximum temperature gradients at the edges of the Gaussian and flat-top laser spot are 5.38×10⁷ ℃/m and 5.74×10⁷ ℃/m, respectively. By contrast, the maximum cooling rates at the center of the above spots are 8.66×10⁶ ℃/s and 5.82×10⁶ ℃/s (Figs. 7?8). Despite these variations, the trends in residual stress evolution show similar patterns (Fig. 10) and no significant differences in the final residual stress distribution are observed (Fig. 11). Further analysis indicates that the variations in temperature peaks are more pronounced for the Gaussian laser beam at the center of the spot, whereas the flat-top laser beam's temperature peaks are more sensitive to changes at the edge of the spot (Fig. 9). In addition, changes in laser power and scanning speed do not significantly affect the differences in residual stress between the two laser beam types (Fig. 12).

This study developed a finite element model for multi-pass scanning and performed a detailed analysis of temperature peaks, temperature gradients, cooling rates, and residual stress distributions at both the center and edge of the laser spot for Gaussian and flat-top laser beams under a scanning speed of 700 mm/s and identical total energy input. The study also explored how variations in laser power and scanning speed affect temperature peaks and residual stress. The findings reveal that the flat-top laser beam provides a more consistent temperature distribution within the spot. Specifically, the temperature peak at the center of the flat-top spot is approximately 541.28 ℃ lower than that of the Gaussian beam, whereas the temperature peak at the edge of the spot is approximately 127.95 ℃ higher. In addition, the Gaussian laser beam demonstrates greater temperature gradients and cooling rates in the center, whereas the flat-top beam shows higher values at the edge of the spot. The maximum temperature gradients are observed at the edge of the spots, measuring 5.38×10⁷ ℃/m and 5.74×10⁷ ℃/m for the Gaussian and flat-top beams, respectively. The maximum cooling rates occur at the center of the spots, recorded at 8.66×10⁶ ℃/s and 5.82×10⁶ ℃/s for the Gaussian and flat-top beams, respectively. The effects of variations in laser power and scanning speed on temperature peaks differ between the two laser beam types. At the center of the spot, the Gaussian laser beam is more significantly affected, whereas at the edge of the spot, the flat-top laser beam shows greater sensitivity to these changes. However, these variations do not significantly influence the differences in residual stress distributions between the two types of laser beams.