Quality6 min read
As-built metal additive components are accurate, but they are not machined components. Accuracy is affected by thermal contraction, residual stress, build orientation, support strategy, part size and the geometry itself. Two features of the same nominal size in different orientations will not behave identically.
Why as-built accuracy varies
- Thermal gradients during the build induce residual stress and distortion.
- Down-facing surfaces are rougher and less accurate than up-facing or vertical walls.
- Small holes tend to build undersize; unsupported spans can sag.
- Support removal leaves witness marks and local material variation.
- Stress relief and heat treatment cause dimensional movement.
How tight tolerances are actually achieved
By machining. The additive process produces the complex form and the near-net shape; critical features are then produced conventionally on that part. Bearing bores, sealing faces, threads, mating flanges and datum surfaces are machined to drawing after printing and heat treatment.
Plan tolerance at the design stage
- Identify critical features early and add machining allowance to them.
- Define a datum structure that can be established on a printed part.
- Avoid applying blanket tight tolerances to every feature — cost rises sharply with no functional gain.
- Agree the inspection method before manufacture so the measurement matches the tolerance.