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DMLS gives engineers access to geometry that machining cannot produce — but that freedom has hard limits defined by laser spot size, powder layer physics, and thermal gradients. Violating these rules produces parts that warp, crack, or fail inspection. Following them produces parts that outperform castings.

Wall Thickness

Minimum wall thickness: 0.4 mm for vertical walls; 0.6 mm recommended for structural walls.

Walls thinner than 0.4 mm absorb so much laser energy per unit area that the surrounding powder zone melts, causing thermal distortion and potential keyhole porosity. For 17-4 PH and Inconel, which have higher thermal conductivity, minimum is effectively 0.5 mm.

For titanium (lower conductivity), 0.3 mm is achievable but requires careful laser parameter management and is not standard in production.

Overhangs and Support Angles

Self-supporting threshold: 45° from horizontal (in most alloys).

Geometry angled below 45° (measured from the build plate) requires support structures. Supports serve two functions: mechanical (preventing warping from residual stress) and thermal (conducting heat away from overhanging geometry). Unsupported overhangs below 30° virtually always fail.

Design strategies to reduce supports:

  • Orient the part so overhangs are above 45°
  • Use chamfers instead of horizontal ledges
  • Use diamond/teardrop cross-sections instead of round for downward-facing channels
  • Add internal chamfers on holes parallel to build direction

Internal Channels

Minimum diameter for self-supporting channels: 8 mm (horizontal). Below this, channels form a “smile” cross-section — the bottom deforms due to lack of support.

For channels < 8 mm horizontal: use diamond or teardrop cross-section, or orient channel parallel to build direction.

Powder removal: All internal channels must have entry/exit paths for loose powder removal. Minimum 2 access ports per channel. Curved channels must have sufficient diameter for powder to flow out by gravity and compressed air.

Tolerances in Practice

FeatureStandard ToleranceTight (machined finish)
Linear dimension±0.003" + ±0.001"/in±0.001"
Hole diameter±0.005"±0.001" (after bore)
Surface flatness±0.005"±0.001" (after mill)
Cylindricity±0.005"±0.001" (after turn)

As-printed tolerances are adequate for non-mating surfaces. Functional surfaces (bearing bores, sealing faces, precision fits) require post-print machining.

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