In metal additive manufacturing, residual stress is an invisible but powerful force that can distort parts, crack surfaces, or even cause complete build failures. One of the most effective ways to control it lies in the scan strategy, the pattern by which the laser melts each layer of powder. While it might seem like a simple programming choice, the laser’s movement actually dictates how heat accumulates and dissipates across a build. Get it right, and the part remains dimensionally stable. Get it wrong, and stress becomes a costly problem.
Common scan strategies include rastering in alternating directions, rotating patterns between layers, or segmenting parts into islands. Each of these techniques changes the thermal gradient distribution during the build. By alternating laser directions, for example, engineers can avoid repetitive heat buildup in one area, which reduces internal stress and helps the part cool more uniformly. Segmenting strategies can localize thermal shrinkage, minimizing global deformation.
Additionally, the scan strategy can be tailored to suit specific part geometries or material behaviors. For instance, highly reflective alloys like aluminum may require lower energy densities and tighter scan spacing to prevent hotspots. Complex overhangs might benefit from slower scan speeds or reduced overlap to preserve dimensional accuracy. Modern slicing software even allows dynamic scan strategies that shift mid-build based on height or structure, giving unprecedented control over stress management.
As metal AM continues to mature, understanding and refining scan strategies will remain central to quality control. These seemingly invisible laser paths carry the weight of structural performance, dictating not only how parts look, but how they behave under real-world stress.