SLS vs SLM Metal 3D Printing: What I Learned Evaluating Both for Our Shop

Why I Even Care About SLS vs SLM

I'm not an engineer. I'm the person who manages vendor relationships and purchase orders for a 180-person manufacturing operation. So when our engineering team asked me to help evaluate metal 3D printing vendors last year, I had to get up to speed fast.

The two acronyms that kept coming up were SLS and SLM. Every vendor I talked to had a preference—usually whichever one they sold. And honestly? Most of the comparison articles I found online were written for engineers, not for someone who has to justify the spend to finance.

So here's my procurement-focused comparison. I'm looking at this through the lens of total cost, lead time, part quality, and vendor reliability—the stuff that actually affects whether your order ships on time and whether your CFO approves the next one.

Dimension 1: Surface Finish and Precision

This is where SLM clearly wins, and it's not even close.

SLM (Selective Laser Melting) fully melts the metal powder, creating a dense, near-100% solid part. The surface finish on test builds we received was around 5-10 microns Ra—smooth enough that some parts needed minimal post-processing.

SLS (Selective Laser Sintering) doesn't fully melt the powder. It heats it until the particles fuse together. The result is a porous, slightly rough surface that typically runs 15-30 microns Ra. Not terrible, but you'll notice the difference if you're holding both parts.

"What most people don't realize is that surface finish specs on metal 3D printing quotes are often measured on the best surface—the one facing away from the build plate. The underside or support-facing surfaces can be 2-3x rougher."

For our aerospace-adjacent work, the SLM finish was a requirement. For internal brackets or non-cosmetic parts, SLS would've been fine.

The procurement takeaway: If your engineers are specifying tight tolerances or cosmetic surfaces, SLM is the safer bet. If it's a functional prototype that won't be seen by customers, SLS saves you money without sacrificing much.

Dimension 2: Cost Structure—Where It Gets Counterintuitive

Here's where my assumptions got flipped.

I assumed SLS would be cheaper across the board. And on a per-part basis, it often is—the powder is less expensive, and the machines cost less to operate. But the total cost picture is messier than that.

We got quotes for a specific bracket, roughly the size of a deck of cards:

• SLS quote: $85 per part, 5-day lead time
• SLM quote: $140 per part, 7-day lead time

On paper, SLS looks like the obvious choice. But then I factored in post-processing. The SLS part needed manual support removal and surface smoothing. That added $30-40 per part and two extra days. The SLM part came off the machine with supports that broke away cleanly—maybe $10-15 in labor.

Suddenly the gap narrowed from $55 to $15-20. And the SLM part had better mechanical properties.

Now, for larger parts or higher quantities, SLS pulls ahead again—the material savings compound. But for small-batch, one-off parts, the post-processing math can erase the sticker-price advantage.

The procurement takeaway: Never compare SLS and SLM on the quoted price alone. Ask what's included in post-processing and factor that in.

Dimension 3: Material Options and Availability

SLS supports a wider range of materials—nylons, TPUs, and some composites. If you need a flexible or impact-resistant part, SLS is your only option between the two.

But for metals? SLM handles aluminum, stainless steel, titanium, and even some copper alloys. SLS is limited to a narrower metal range and the parts are less dense.

Here's something vendors won't tell you: material lead times vary wildly between the two processes. We waited three weeks for a specialty titanium powder to come in for an SLM build. The SLS vendor had nylon powder in stock and could start immediately.

So if your timeline is tight and you're flexible on material, SLS might actually be faster—not because the process is quicker, but because the supply chain is simpler.

Dimension 4: How This Connects to Our Salvagnini Work

I should mention that we're not replacing our sheet metal operations. We run a Salvagnini press brake and a fiber laser cutting machine for the bulk of our production. The 3D printing is for prototypes, low-volume replacement parts, and geometries that can't be formed from flat stock.

For anything that can be bent, cut, or punched, the Salvagnini equipment is still 10-20x faster and cheaper per part. We looked at a Salvagnini laser cutting machine price comparison last year, and even with the capital cost, the per-part economics crush 3D printing for production runs.

Where 3D printing wins is when you need a complex internal channel, a lattice structure, or a one-off part that would require custom tooling. That's where SLS or SLM earns its keep.

I also learned that some shops use extreme CNC turning for brass parts as a middle ground—faster than 3D printing, more flexible than stamping. But that's a different comparison for a different day.

Which One Should You Choose?

After six months of evaluations and maybe 30 test parts (give or take—I'd have to check the log), here's my honest take:

• Choose SLM if: You need metal parts with tight tolerances, good surface finish, and you're okay with higher material costs. Best for functional prototypes, aerospace, and medical applications.
• Choose SLS if: You need polymer parts, faster turnaround, or lower material costs for larger builds. Best for concept models, jigs and fixtures, and non-cosmetic internal parts.

And if you're not sure? Order the same part from both processes. The $200-300 you spend on test builds will tell you more than any spec sheet.

This worked for us, but our situation was a mid-size shop with a mix of prototype and production work. Your mileage may vary if you're a pure prototyping shop or a high-volume production facility.