The selection of process parameters is critical to the success of the additive manufacturing process, because it determines how the material will melt and solidify to form the parts we need. Since each alloy powder absorbs laser energy, transfers heat, flows and solidifies in different ways, the process parameters must be selected according to the specific characteristics of the alloy to be melted. The primary consideration for determining the selection parameters of the “operating window” is to make fully dense parts with uniform quality. Part density is a key indicator of melting quality-if there are pores, the required strength, ductility, and fatigue/creep resistance cannot be achieved.
But how to choose the right combination among countless parameters? Turn the complexity into simplicity, and get twice the result with half the effort. For each given workpiece, the chemical properties and particle size distribution of the powder are determined. The layer thickness can also be determined according to the fineness of the part and the surface finish requirements. After the laser spot size is determined (many equipment does not allow to change the spot size during processing), you only need to select the laser power, scanning speed and scanning line distance.
Figure 1: The relationship between laser power and scanning speed-how the process results change with the selection of parameters. If the scanning speed is too fast and the laser power is too small, some areas of the part may not be completely melted, resulting in “insufficient melting” And produce pores. Conversely, if too much power is applied at the selected speed, it may overheat the molten pool and penetrate too deeply into the energy, leading to a “deep hole” effect. Between these two extremes is an “operating window”, within which a good part density can be obtained. In this window, the laser energy is sufficient to completely melt the powder and the metal layer below it, without penetrating too deeply. It can be seen from Figure 1 that increasing the laser power and scanning speed at the same time can improve the processing efficiency, which is feasible to a certain extent. However, there is a limit to power and speed. Once this limit is exceeded, the molten pool will become unstable and a “spheroidization” effect will occur. When the laser power increases, spatter may also increase.
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