Standard DMLS tolerances are ±0.003 inch + ±0.001 inch per inch accumulated. Micro-scale parameter sets achieve ±0.001 inch on small features by using tighter process parameters, smaller laser spot, and reduced layer thickness.
What Changes in Micro-Scale Parameters
| Parameter | Standard | Micro-Scale |
|---|---|---|
| Layer thickness | 40-50 µm | 20-30 µm |
| Laser spot diameter | 80-100 µm | 60-80 µm |
| Scan speed | 800-1200 mm/s | 400-600 mm/s |
| Build rate | 5-15 cm³/h | 2-5 cm³/h |
Smaller spot size improves feature resolution. Slower scan speed with thinner layers gives finer melt pool control. The tradeoff: build rate drops 50-75%.
Where Tolerance Limits Come From
Melt pool dynamics: Even at optimized parameters, the melt pool width exceeds the laser spot by 1.5-2x. This sets a practical floor on minimum feature size near 0.15 mm.
Thermal shrinkage: Metal contracts 0.2-0.5% on solidification. Parts are scaled up in the build file to compensate, but residual error after stress relief contributes to dimensional variation.
Surface finish: As-printed Ra 2-4 µm on micro-scale. After bead blast: Ra 1.6 µm. After electropolish: Ra 0.4 µm. Final machining: Ra 0.8 µm or better.
Practical Guidance
Design critical dimensions for post-machining, not as-printed. Allow machining stock of 0.2-0.5 mm on functional surfaces. Specify as-printed tolerance (±0.003 inch) for non-critical surfaces and post-machined tolerance for mating faces.