A new method for calculating laser intensity distribution on workpiece surface in laser-directed energy deposition process by considering powder stream distribution and laser attenuation

Laser-directed energy deposition is a fast-growing method for manufacturing complex geometries and materials that are hard to shape with conventional manufacturing methods. However, there are some aspects of this process that need more researches and experiments to be completely understood. Two of these are laser attenuation and laser intensity distribution on the workpiece surface. In this paper, a new method is proposed for calculating laser attenuation without simplification applied in previous works. Despite other studies that consider a predefined powder distribution, the result of a developed 3D CFD model of the powder stream is utilized for defining the position of particles in the powder stream. The divergence and spatial distribution of the laser beam are considered by dividing the laser beam in a radial direction. A GUI has been developed in MATLAB to take CFD model output as input for calculating laser attenuation with Beer-Lambert law and plotting the laser intensity on the workpiece surface after being attenuated. The influence of powder mass flow rate, powder size, and workpiece position on laser attenuation and its intensity distribution is investigated. It is shown that increase in powder flow rate would increase laser attenuation almost linearly. It has also indicated that smaller particles would attenuate more energy than larger ones while the powder mass flow rate is kept constant. More specifically, decreasing powder size from 100 to 20 µ increases attenuation from 18% up to 55%. The size of powder particles affects powder stream distribution, and consequently, this affects the laser intensity profile on the workpiece surface. The result of investigating the workpiece position shows that the position of the workpiece influences the laser attenuation, powder catchment, and maximum intensity of laser energy.