What is SLM metal 3D printing, and how does it work?

SLM metal 3D printing, short for selective laser melting, builds a solid metal part straight from your 3D file. A laser melts fine metal powder, one thin layer at a time, inside a chamber of inert gas, and each layer fuses to the one below. In Singapore we use it for metal 3D printed parts in stainless steel, aluminium and titanium that must take heat, load or wear, in shapes that are hard to machine.

SLM metal 3D printing at a glance

Lead time is a rough guide in working days for a part about 10 to 15 cm across. Bigger parts and extra finishing take longer, so check with us.

Know what you need? Send us your metal part

How SLM works: a laser melts metal powder, layer by layer

SLM belongs to the family the standards call powder bed fusion: heat fuses chosen areas of a bed of powder. In SLM the heat is a laser and the powder is metal.

1. Slicing. Software cuts your 3D model into layers 0.03 to 0.04 mm thick.
2. Spreading. A blade spreads one layer of fine metal powder over a steel build plate.
3. Melting. The laser traces that layer’s shape and melts the powder, fusing it to the layer below.
4. Repeat. The plate drops by one layer, fresh powder goes on, and the laser melts the next slice.

The chamber is filled with an inert gas, one that does not react with the hot metal. The metal melts fully, so the finished part is solid metal, not glued or pressed powder. You may also see it called DMLS (direct metal laser sintering) or laser powder bed fusion: the idea is the same.

See how SLM fits among the other 3D printing processes

Supports: metal needs them, nylon does not

In nylon powder printing (SLS or MJF), the loose powder holds the part up. Metal is different. Each layer is melted, then cools fast and shrinks, and that shrinking pulls the part out of shape. So a metal part is built on supports: thin metal scaffolding that anchors it to the build plate and carries the heat away.

• Overhangs: faces within 45° of vertical build themselves (within 35° for 316L stainless steel). Anything flatter needs supports.
• The cost of supports: the faces they touch come out rougher than the rest. Tell us which faces must stay clean and the supports go on the others.

Tell us which faces must stay clean

After printing: cut free and supplied as printed

When the build finishes, the part is still fused to the steel build plate. We cut it free, remove the supports and clean up the faces they touched. Loose powder is emptied from any hollow space, which is why a cavity needs powder holes (see the design rules below).

We supply metal parts as printed, with no heat treatment of any kind, not even stress relief. That suits most brackets, housings and mounts. If your part must be heat-treated, for example to bring 17-4PH stainless steel to full hardness, tell us before you order.

See how each metal compares without heat treatment

Surface as printed: grainy, like fine sandpaper

Every SLM part leaves the machine with a grainy, matte surface: the edges of the melted powder grains show. Faces that touched supports are rougher still. As printed, a part holds about ±0.2 mm up to 50 mm, then ±0.4% of the length, which suits brackets and housings but not a bearing seat.

Not sure the as-printed surface is enough? Ask us

Finishes: as printed, blasted, machined or polished

You choose how far to take the surface:

• As printed: grainy and matte. Fine for hidden brackets and internal parts.
• Bead or sand blasted: an even, matte surface with the loose grains blasted off.
• Machined faces: leave 0.5 mm of extra metal on any face that must fit, and we machine it to size on our CNC machines after printing. Mark which faces matter; the rest stays as printed.
• Polished: a smooth, bright surface.

Tell us the finish and the faces that must fit

Size and lead time: up to 420 x 420 x 450 mm, about 10 to 12 working days

A single metal part can be up to 420 x 420 x 450 mm. For anything bigger, send the file and we look at printing it in pieces or using another process. A normal-size part, about 10 to 15 cm across, takes about 10 to 12 working days; bigger parts and extra finishing take longer, so check with us when you have a deadline. Our lead time guide explains why.

We print 316L and 17-4PH stainless steel, AlSi10Mg aluminium and Ti6Al4V titanium, and other alloys on request. How they compare on weight, strength, rust and heat is in which metal to 3D print in.

Bigger than 420 mm? Tell us the size and we plan it

Design rules for SLM: the figures that matter most

Design to these and the part prints as drawn:

• Walls: 1.0 mm at least, 1.2 mm for a wall standing on its own, 2.0 mm for anything handled or knocked.
• Holes: 1.0 mm upright and 1.5 mm sideways at the smallest. Keep round sideways holes up to 6 mm; above that, draw a teardrop (a point at the top) so the roof builds itself.
• Hollow parts: two or more powder holes of 5 mm, at opposite ends, so the loose powder can be emptied.
• Fine detail: raised or recessed detail down to 0.5 mm; lettering with 0.6 mm strokes and letters at least 3 mm tall.
• Threads: tapped after printing, not printed. Draw the hole at the thread’s core size and tell us the thread.
• Moving parts printed together: 0.3 mm gap on each side.

Each rule, with its fix, is in metal 3D printing defects you can fix in the design, and every process side by side is in the design rules table.

Ask us to check your file against these rules

When another route suits better: CNC, sheet metal or plating

SLM earns its place when a part needs metal and a shape that is hard to cut. Otherwise, another route is often better:

• Simple solid parts, or the tightest fit: CNC machining cuts the part from a solid block, holds ±0.05 mm and leaves a cleaner surface. Our metal printing or CNC guide shows how to tell.
• Thin shells and enclosures: cut and bent sheet metal suits a plain box or cylinder better than a print, as with this stainless steel housing.
• Many identical parts: for a large batch, ask us. Casting or machining can work out cheaper per part than printing each one.
• It only has to look like metal: a painted or plated plastic print gets the look for far less.

Whichever route, a plastic test print is the cheapest way to check the fit first, as we did with this gear:

Upload your file and price a plastic test print