DMLS (Direct Metal Laser Sintering) and SLM (Selective Laser Melting) are both laser powder bed fusion processes. In practice they describe the same physical mechanism: a laser scanning a bed of metal powder and fusing it into fully dense metal, layer by layer.
Where the difference in name comes from
The names originate from different machine manufacturers rather than from different physics. "Sintering" is historically misleading — in both cases the metal is fully melted, not partially sintered as it would be in a true solid-state sintering process. The neutral, standards-aligned term for both is Laser Powder Bed Fusion (L-PBF), or PBF-LB.
What actually differs between suppliers
- Laser count and power, which affects build rate.
- Build envelope, which sets the maximum part size and nesting capacity.
- Layer thickness and parameter sets, which affect accuracy and surface finish.
- Powder handling, inert gas control and qualification, which affect consistency.
- Available and validated alloys.
What this means when you specify a part
Specifying "DMLS" or "SLM" on a drawing rarely adds useful information. Specify the alloy, the condition (as-built, stress relieved, heat treated), the features that must be machined, the tolerances and surface finish required, and the inspection evidence you need. The process route can then be selected to meet that specification.