Residual stress builds in every layer, and it decides whether the build survives
Rapid solidification under constraint locks stress into the part. Enough of it and the part curls off the plate mid-build.
Every layer in a powder bed fusion build is heated to melting and cooled within milliseconds, while attached to the cold material beneath. That material resists the contraction, and the result is tensile stress in the newly solidified layer and compressive stress below.
Accumulated over hundreds or thousands of layers, that stress reaches magnitudes that deform parts and can exceed the strength of the connection to the build plate.
What it causes
Distortion after removal. A part that is dimensionally correct while attached deforms when cut free, as the constraint is released. This surprises people who measure on the plate.
Curling during the build. Stress can lift an edge, particularly on down-facing surfaces with inadequate support. A lifted edge collides with the recoater, which ends the build.
Cracking. In crack-sensitive alloys, stress plus a susceptible microstructure produces cracks during or shortly after building.
Support failure. Supports carry the stress; if they fail, the part detaches.
What reduces it
Scan strategy. Short scan vectors produce less stress than long ones, because contraction is over a shorter length. Island or chessboard strategies divide each layer into small regions scanned in a randomised order, which is standard practice and effective.
Rotating scan direction between layers prevents stress aligning in one direction.
Plate heating. Raising the build plate temperature reduces the thermal gradient and therefore the stress, at the cost of longer heat-up and cool-down, and potential powder degradation.
Part orientation. Large flat areas parallel to the plate accumulate more stress than the same area oriented at an angle.
Support design. Supports must carry stress as well as conduct heat, and support failure is frequently a stress problem rather than a geometry one.
Stress relief
Heat treatment before removing the part from the plate is standard for critical work. Relieving stress while the part is still constrained prevents the distortion that would otherwise occur on cutting free.
That sequence matters: stress relieve on the plate, then remove. Doing it the other way produces a distorted part and then relieves the stress in the distorted shape.
Shops that learned this the expensive way generally learned it once.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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