Residual stress and stress relief (DMLS)

Theory

Each laser scan melts a small zone that solidifies in milliseconds. The surrounding solid metal constrains thermal contraction, locking in tensile stress at the surface and compressive stress beneath. Successive layers accumulate stress; without relief the part can crack, warp, or delaminate from the build plate. Stress relief (typically 2–4 h at 450–650 °C in inert atmosphere, depending on alloy) allows atomic relaxation without changing the microstructure significantly.

Application

Always perform stress relief while the part is still attached to the build plate: the plate acts as a fixture preventing gross distortion. After annealing, remove supports and machine to tolerance. Part orientation affects stress accumulation: tall, thin walls parallel to scan direction accumulate more stress: orient to minimise this.

Common mistakes

Skipping stress relief is the single most common cause of DMLS scrap. Parts that survive removal may still fail in service due to residual stress interacting with applied loads. Rapid furnace cool after stress relief can re-introduce stress: use controlled cooling rates.

Related terms: Support strategy (SLS vs DMLS), Build orientation decision, Anisotropy / Layer adhesion (XY vs Z)