Influence of keyhole and conduction mode melting for top-hat shaped beam profiles in laser powder bed fusion

The application of non-Gaussian beam sources, such as diode lasers, could reduce the costs of Laser Powder Bed Fusion (LPBF) machines. The effect of the lower beam quality and intensity on the process is not well understood. In this work, the potential process efficiency of diode laser systems in LPBF was investigated. The multistage relationship between the intensity distribution and process parameters, the induced melting mechanism and the melt pool shape and the attainable process efficiency were studied for top-hat shaped beams with a spot diameter between 100 mu m and 200 mu m. 288 single melt tracks and 389 cubic specimens were produced and analyzed to cover an extensive parameter range. The melt pool shape and the predominant melting mechanism could be predicted as a function of the line energy and the intensity. The transition between keyhole mode melting and conduction mode melting was smooth. Dense (mu > 99.95 %) specimens were produced for both process regimes with energy densities E-v < 57 J/mm(3), demonstrating the potential of utilizing either regime efficiently. Below the intensity threshold I approximate to 8...10.10(5) W/cm(2), the attainable process efficiency was found to decrease. This indicates that LPBF processes can be efficient as long as the intensity threshold is exceeded.