Knowledge Base

SLS and SLM Are Both Powder Bed — So Why Does Cost Differ Tenfold?

2026-08-21

Short answer: first ask whether a polymer part can meet the mechanical and thermal requirements. If it can, SLS typically costs an order of magnitude less per part — no supports, parts nest densely in Z, no inert gas, no mandatory heat treatment. Go to SLM only when you genuinely need metal properties: strength, temperature capability, thermal or electrical conductivity, weldability.

SLS and SLM get discussed together because they are routinely conflated — "both are lasers fusing powder". From a production standpoint, though, they are very different undertakings, and nearly all of the difference cascades from one fact: whether the powder is a polymer or a metal.

Cascade One: Supports or No Supports

In SLS the un-sintered powder is the support. Parts can be oriented freely and stacked in Z, so packing density in a build can be very high. For small-batch functional parts this single fact largely determines cost per part: the same build time amortised over 10 parts or 200 parts differs by a factor of twenty.

SLM cannot do this. Thermal stress in the melt pool has to be conducted away through support structures that also anchor the part to the build plate, so parts essentially stand on the plate and cannot be stacked; packing density is inherently far lower. Supports then have to be cut off and the witness marks dressed — pure labour cost.

Cascade Two: How Long the Process Chain Is

An SLS part usually needs de-powdering and bead blasting, optionally dyeing or infiltration, and it is ready. An SLM part is only beginning: cut from the plate, remove supports, stress-relief heat treatment (skip it and residual stress will distort the part during later machining), optional hot isostatic pressing for density, then CNC finishing of mating surfaces. The conformal-cooling mould inserts mentioned elsewhere almost always go onto a 5-axis mill after printing.

Dimension	SLS (nylon / polymer powder)	SLM (metal powder)
Supports needed	No — un-sintered powder supports the part	Yes — for heat conduction and anchoring
Stacking in Z	Yes, high packing density	Essentially no; parts stand on the plate
Inert atmosphere	Generally not required	Required (nitrogen / argon)
Mandatory post steps	De-powder, bead blast	Cut from plate, remove supports, stress relief
Usually also	Optional dyeing, infiltration	CNC finishing of mating faces, HIP if needed
Powder reuse	Reusable blended with virgin powder; control refresh ratio	Reusable after sieving; control oxygen pickup
Safety requirements	Dust protection	Explosive-dust control + inert gas + powder recovery
Common materials	PA12, PA12-CF, TPU	Ti TC4, 316L, AlSi10Mg, CoCr, In718, 18Ni300
Cost per part	Low	High — often several to more than ten times SLS
Typical work	Grippers, ducting, clips, batch functional parts	Conformal-cooling inserts, lattice lightweighting, aero parts, dental implants

The cost multiple is an order-of-magnitude guide; the real figure depends on part volume, packing density and how much finishing is required. Quote per part for anything real.

The Order to Decide In

First: are polymer strength, stiffness, temperature and wear resistance sufficient? If yes → SLS, stop here
Second: is metal needed for mechanical reasons, or only because it "should look metal"? If the latter, consider a metallised SLS part
Third: metal genuinely required → few parts with complex geometry (internal channels, lattices) → SLM; simple geometry in quantity → price CNC or casting first
Fourth: going SLM — what tolerance do the mating faces need? Quote precision faces as "print + 5-axis finishing", not print alone
Do not overlook the facility: SLM powder explosion control, inert gas and recovery systems require a safety review in many plants

The most common waste in practice is sending grippers, fixtures and ducting to SLM when SLS nylon would have done. Metal looks more "industrial", but if PA12-CF meets the actual load case, the order-of-magnitude premium buys nothing. The reverse also happens: a load-bearing part done in plastic to save money, failing in the field. Which is why question one deserves an honest answer.

Frequently Asked Questions

Can SLS parts survive continuous industrial use?

PA12 and carbon-fibre-reinforced nylon offer solid fatigue strength and wear resistance, and are widely used in continuously running grippers, ducting and clip fittings. Watch moisture absorption and the long-term temperature ceiling — validate with a sample part for hot or humid duty.

Do SLM parts reach forged-material properties?

With proper heat treatment (and hot isostatic pressing where needed), many alloys reach static strength close to or at wrought levels, but fatigue performance is more sensitive to internal defects and surface condition. For fatigue-critical parts, surface finishing and non-destructive inspection are usually not optional. Request the material test report for specific figures.

How many times can powder be reused?

Both allow reuse but for different reasons. SLS requires controlling the virgin-powder refresh ratio, because repeated thermal exposure changes flowability and crystallisation behaviour. SLM is mainly about sieving and oxygen pickup, since repeated exposure raises oxygen content in some alloys. Keep reuse batch records in both cases — essential for parts with certification requirements.

Is buying an SLM machine worth it for only a few metal parts?

Usually not. SLM's hidden costs go well beyond the machine: inert gas, powder management, heat-treatment equipment or subcontracting, a compliant facility, and an operator who understands the process. With irregular volume, outsourcing almost always wins. We offer both, so you can validate the process as a service first and revisit equipment once volume stabilises.