Direct metal laser sintering builds a part by spreading a thin layer of metal powder and fusing it with a laser, one layer at a time, inside an inert atmosphere. Despite the name the powder is fully melted rather than merely sintered, so parts come out close to fully dense. What comes out of the machine is not a finished part, and understanding that is most of understanding the cost.
What the machine actually produces
A part welded to a steel build plate, carried on support structures, full of residual stress from thousands of rapid melt and freeze cycles, with a rough as built surface and internal cavities possibly still holding loose powder. Every one of those is a task: depowdering, stress relief while still on the plate, plate removal, support removal, then finishing.
Alloys and where they are used
Stainless and tool steels, aluminium alloys, titanium alloys, nickel superalloys and cobalt chrome are the common list. Aerospace and medical drove the early adoption because their parts are complex, low volume and expensive to machine, which is exactly the profile that suits the process. The available alloy list per machine is much shorter than the list overall.
Design rules that decide whether it works
Overhangs below a threshold angle need supports, and supports in an internal channel may be impossible to remove. Unsupported horizontal holes deform, so orient them or make them teardrop shaped. Thin walls and large flat downward faces are trouble. And design in machining stock on every surface that has to be accurate, because the as built tolerance will not hold a bearing fit.
Cost and when it is justified
Build time is driven by height and by how much of each layer is solid, so nesting several parts into one build is how the machine hour is amortised. The case is strong when the geometry cannot be machined at all, when an assembly collapses into one part, or when internal channels do work, as in conformal cooling for tooling. It is weak for simple shapes in quantity.
Questions people ask about dmls
Does DMLS actually sinter?
Not in the usual sense. The laser fully melts the powder, producing a near fully dense part. The name is historical and the process is a form of laser powder bed fusion.
How accurate is a DMLS part?
Good enough for general geometry and not good enough for fits, threads or sealing faces. Those features are printed oversize and machined afterwards as standard practice.
Do parts need heat treatment?
Stress relief is normal before the part leaves the build plate. Where fatigue properties matter, hot isostatic pressing and a full heat treatment cycle are often specified as well.
Can supports always be removed?
No, and that is a design constraint rather than a detail. Supports inside a closed channel may be unreachable, so orientation and self supporting geometry have to be planned from the start.