Effects of channel contour laser strategies on fatigue properties and residual stresses of laser powder bed printed maraging steel

Abstract

Laser-Powder Bed Fusion is widely used for tooling applications, such as mold insert: conformal cooling channels are designed to decrease cycling time and homogenize the cooling rate. The Achilles' heel of AM mold is the cooling channels close to the surface which generate high stress concentration and are not machined; as a result, they create weaknesses in the part and are likely to reduce the lifespan of the mold. It is necessary to study the impact of such channels on properties (fatigue, residual stresses, microstructure) and determine optimized laser strategies to reduce porosity that may occur near a contour. Residual stresses were first estimated above an internal channel after different heat treatments and fatigue specimens were printed with a 3 mm diameter channel on an EOS M270 printer using different strategies such as several contours with a concentric offset. The impact of these strategies on fatigue properties were analysed through microstructural observations. Here, it was found that a double contour with an offset improved the fatigue life of the part by more than 10 times compared to the standard single contour strategy.