Metal 3D printing design check
Laser powder bed fusion (LPBF, also called SLM) builds a metal part layer by layer from powder. Most failures are decided by geometry before the first layer is printed. These are the limits a check looks at, with the values Dokimion uses.
The limits that matter
| What | Typical limit used here | Why it matters |
|---|---|---|
| Overhang | surfaces steeper than 45° from vertical need support (50° for Ti6Al4V) | unsupported overhangs sag and warp; support is cut and ground off afterwards |
| Thin wall | 0.4 mm by default, 0.3 mm AlSi10Mg, 0.25 mm Ti6Al4V; design for about 1.5 mm | below the limit the wall may not form; the 1.5 mm value is our working assumption for reliable parts |
| Channel and pin | 0.5 mm (Ti6Al4V 0.43 mm and 0.32 mm) | smaller features fill with sintered powder or break |
| Horizontal hole | over 8 mm needs support or a teardrop shape (12 mm for Ti6Al4V) | the top of a wide round hole is an overhang |
| Bridge | up to 2 mm unsupported (Ti6Al4V 1.2 mm) | longer spans sag |
| Down-facing surface | rough below 30° from horizontal (45° for AlSi10Mg) | support marks and dross; plan for machining |
| Powder escape hole | at least 3 mm in an enclosed cavity | trapped powder cannot be removed and adds mass |
| Cross-section jump | more than 3 times between layers is flagged | sudden change of heat flow distorts the part (working assumption) |
How to fix the common problems
- Rotate the part. Support volume often changes several times between positions. In one of our case studies the same part needed from 4.3 to 32.6 cm³ of support depending on position.
- Replace round horizontal holes over the limit with a teardrop or diamond shape that points up.
- Add powder escape holes of at least 3 mm to every closed cavity, or open the cavity.
- Thicken thin walls to the working value and keep fillets at section changes.
- Leave machining stock on surfaces that must be smooth, especially down-facing ones.
What Dokimion checks for metal
The check reads the part mesh and reports the overhang area and support volume per region, hanging points and edges, thin walls, small channels, horizontal holes, trapped powder, cross-section jumps and compactness, for AlSi10Mg, Ti6Al4V, 316L, 17-4PH, IN718, IN625, CuCrZr and CoCr. It ends with a score from A to E (see the Kolesar Score), three suggested positions and a cost estimate per part.
The limits above are typical values. They depend on the machine, parameters and powder, so confirm them with whoever builds the part. Every threshold in the report shows its source, and assumptions are marked as assumptions.
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