Automatic Laser Control System for Selective Laser Sintering

The quality of SLS products is dramatically degraded by excessive temperature gradients in the thermal profile of the powder bed. Thermal gradients in the presintering temperature, which is defined as powder temperature before laser scans, are inevitable in commercial SLS machines due to various reasons. Such a gradient will propagate to the postsintering temperature, which is defined as the material temperature right after laser scans, if constant laser power is used for sintering. To eliminate thermal gradients in the postsintering temperature, this paper proposes an automatic laser control system to adjust laser power according to the presintering temperature. Infrared cameras are used for presintering temperature measurements, which are used to compute optimal laser power profiles. Two control granularities are implemented: 1) vector-level control eliminates thermal gradients in the postsintering temperature of a single scan line and 2) layer-level control minimizes the difference of postsintering temperature of several areas, each of which consists of a number of scan lines, on the build surface. Experimental results show that variations in the postsintering temperature have been reduced by both implementations (to 60% and 20% respectively) compared to the presintering temperature.