How to Get the Best Finish from SLS and MJF 3D Printing?

How Do SLS and MJF Work?

Both are powder bed fusion processes. They build parts layer by layer inside a bed of plastic powder.

What Is the SLS Process?

A high-power laser (like a CO2 laser) scans the shape of each layer. It sinters (fuses) the powder particles together. The surrounding loose powder acts as natural support. This allows amazing design freedom.

What Is the MJF Process?

An inkjet array first sprays a fusing agent onto the powder where the part will be. Then an infrared heat source passes over the entire bed. The areas with the fusing agent absorb more energy and melt. This makes MJF generally faster than SLS.

Why Is the Surface Grainy?

The powder particles themselves cause the texture. Even the finest powders leave a micro-rough surface. This “as-printed” finish feels like fine sandpaper. It’s the starting point for all post-processing.

What Materials Can You Use?

The material choice defines the part’s core strength and feel.

Nylon PA12: The Workhorse

This is the most common material for both SLS and MJF.

• Traits: Excellent balance of strength, flexibility, and chemical resistance. Good for many functional parts.
• Natural Finish: Uniform, fine grit.
• Best For: Housings, brackets, connectors, functional prototypes.

Nylon PA11: The Flexible Choice

Made from renewable castor oil, it has different traits.

• Traits: Higher impact resistance and elongation (it can stretch more). More flexible than PA12. Also has better UV resistance.
• Natural Finish: Slightly less gritty than PA12, often a bit smoother.
• Best For: Snap-fits, living hinges, outdoor parts, sports equipment.

Glass-Filled Nylon (PA12-GF): The Stiff One

Nylon is mixed with fine glass beads.

• Traits: Higher stiffness, strength, and heat resistance. Less prone to warping. The surface is harder.
• Natural Finish: Gritty, with a slightly more abrasive feel from the glass.
• Best For: Structural parts, tools, fixtures, high-heat applications.

TPU: The Flexible Elastomer

A flexible, rubber-like material.

• Traits: High elasticity, tear strength, and shock absorption.
• Natural Finish: On MJF, it can be quite smooth and rubbery. On SLS, it’s more matte.
• Best For: Gaskets, seals, grips, dampers, wearable items.

What Are the Surface Treatment Options?

This is where you control the final look and feel. Treatments range from basic cleaning to high-gloss finishes.

Option 1: Basic Cleaning & Bead Blasting

This is the minimum step after printing.

• Process: Parts are removed from the powder bed. Loose powder is blown off with air. Then, they are often bead blasted with tiny plastic or glass beads.
• Result: Removes all loose powder. Leaves the natural, slightly smoothed matte finish. The grain is still visible but clean.
• Best For: Internal or non-cosmetic functional parts. It’s fast and cheap.

Option 2: Vibratory Tumbling (Media Polishing)

The most common upgrade for a better feel.

• Process: Parts are placed in a vibrating tub with abrasive media (often plastic or ceramic triangles). They rub together for hours.
• Result: A uniform, satin-smooth matte finish. It rounds sharp edges and eliminates the sandy grit. The layer lines become faint. This is the standard “industrial finish.”
• Best For: Any part that will be handled. Great for consumer products, enclosures, and prototypes.

Option 3: Dyeing

Adds color and can be combined with tumbling.

• Process: Cleaned parts are immersed in hot dye. The porous nylon absorbs the color.
• Result: Deep, even color throughout the part (not just a surface coat). Available in many colors. Works best with natural white PA12.
• Best For: Branding, product color coding, aesthetic parts.

Option 4: Painting & Coating

For specific colors or textures not possible with dye.

• Process: Primer and paint are sprayed on. Or a protective coating (like epoxy or urethane) is applied.
• Result: A smooth, painted surface. Can be matte, glossy, or textured. Seals the part’s surface.
• Watch Out: Paint can chip if the part flexes or gets hit. Adds cost and time.

Option 5: Vapor Smoothing

A chemical process for a very smooth finish.

• Process: Parts are exposed to a solvent vapor (like acetone for certain plastics). The vapor slightly melts the surface layer.
• Result: A glossy, sealed surface. Can almost eliminate the grain look. Improves water-tightness.
• Watch Out: Can slightly change dimensions. Not all nylons are suitable. Requires special equipment.

Treatment Comparison Guide

How Do You Choose the Right Combo?

Follow this logic to decide.

Step 1: Define the Part’s Job

• High-Stress Functional Part? Choose PA12 or PA12-GF. Finish with bead blasting or tumbling. Skip paint that can hide cracks.
• Flexible or Outdoor Part? Choose PA11 or TPU. Tumbling works well for PA11. TPU often needs no treatment.
• Consumer Product with Good Feel? Choose PA12. Finish with tumbling and dyeing.

Step 2: Define Your Surface Needs

• “It just needs to work.” Use the as-printed or bead blasted finish.
• “It needs to feel good in hand.” You need vibratory tumbling.
• “It needs to be a specific Pantone blue.” You need dyeing or painting.
• “It needs to be shiny and waterproof.” Look into vapor smoothing.

Step 3: Consider Cost and Lead Time

More steps = more cost and time.

• Fastest/CHEAPEST: As-printed parts.
• Best Value: Tumbled parts. Vastly better feel for moderate cost.
• Most Expensive: Painted or vapor-smoothed parts.

Real Case Study: A medical device company needed a handheld case. It had to be durable, chemical-resistant, and easy to clean. They chose MJF PA12 for strength. The as-printed finish was too rough and could harbor germs. Vibratory tumbling made it smooth and easy to wipe down. They dyed it blue for a clean, professional look. The combo was perfect.

SLS vs. MJF: Which Should You Pick?

The choice affects quality and cost.

Surface Finish Comparison

• MJF often has a slightly finer and more consistent surface grain right out of the machine. The layer lines can be less visible.
• SLS can have a very uniform matte grain, but may show more laser scan patterns.
• After tumbling or dyeing, this difference often disappears. Both can achieve excellent satin finishes.

Material Property Comparison

• MJF PA12 is known for having more isotropic properties. This means it is equally strong in all print directions. SLS parts can be slightly weaker in the direction perpendicular to the laser scan.
• MJF offers a wider range of durometer (hardness) in TPU materials.

Cost & Speed Comparison

• For small batches (1-10 parts): Costs are similar. SLS might be cheaper for very complex, dense parts.
• For larger batches (50+ parts): MJF is often faster and cheaper per part due to its faster print process.

How to write a spec that gets priced correctly

A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.

• File format and units, with the model exported in millimetres
• Process and material grade, not a trade name
• Critical features and the tolerance each one needs
• Surface finish and the faces it applies to
• Quantity for the pilot build and for the year

The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.

What actually drives the price

Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:

• build volume and orientation
• layer height and support structure
• material grade and colour
• post-processing and hand finishing
• quantity per build plate

Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.

Problems you will meet, and the fix

Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.

• Warping on long flat faces where the part lifts off the plate
• Layer lines showing through a cosmetic surface
• Support scars on a mating face nobody flagged
• Dimensional drift on thin walls after cooling

Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.

What to check on the first article

The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.

• Every dimension on the drawing, with the measured value written beside it.
• The material certificate, matched to the heat or lot number on the parts.
• The finish against the sample you approved, under the same light.
• Fit against the mating part, assembled rather than measured.
• Packaging, because parts that arrive damaged were never in tolerance.

Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.

How to compare two quotes fairly

Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.

Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.

Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.

Scaling from one part to a batch

The first part teaches you the process. The hundredth teaches you the process cost.

Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.

Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.

How to read a supplier's quote

A quote is a short document with a long shadow. Four things in it decide whether the job runs smoothly, and only one of them is the price.

• The scope line. It should name the process, the material and the finish, not just the part.
• The tolerance basis. General tolerance or the drawing, and which standard it follows.
• The exclusions. Tooling, freight, certificates and inspection are the usual omissions.
• The validity date. Material prices move, and an open-ended quote is a promise nobody can keep.

Read the exclusions before you read the total. A quote that leaves out tooling is not cheaper. It is a quote for a different job.

What to send with the first order

The first order sets the pattern for every order after it. Send a complete package once and the shop files it, and the second order takes a fraction of the time.

• A STEP or native model plus a PDF drawing carrying the same revision letter.
• The material callout by standard number, not by trade name.
• The finish and the exact faces it applies to.
• Any test the part must pass: fit, seal, drop, salt spray, dielectric.
• A contact who can answer a question inside one working day.

Then write down what was agreed. An email that confirms the material, the finish and the date is worth more than a longer purchase order that leaves them open.

When this is the wrong choice

A good supplier tells you when the process does not fit. These are the cases where we say so.

• The volume is so low that setup costs more than the parts are worth.
• The tolerance is tighter than the process can hold without a second operation.
• The geometry cannot be made without a tool feature that will not pay back.
• The material you need is not available in the form the process requires.
• The schedule is shorter than the tooling or setup time, and nobody has said so yet.

None of these are refusals. They are reasons to look at a different route, and the earlier that conversation happens the cheaper it is. The most expensive mistake in manufacturing is a process chosen before the question was understood.

What Are Common Mistakes to Avoid?

1. Not Planning for Shrink/Warp: All powder processes have slight shrinkage. Design with tolerances in mind.
2. Ignoring Powder Traps: Complex internal channels must have powder escape holes. Design holes (min. 3mm) to let powder out.
3. Choosing Paint When Dye is Better: For nylon, dye is more durable than paint. Paint can peel, especially on flexible parts.
4. Not Communicating Needs: Tell your manufacturing partner the part’s end use. They can suggest the best material and finish combo.

Getting a quality part from SLS or MJF is a three-part recipe: choose the right material for strength, select the right process (SLS or MJF) for quality and cost, and apply the right surface treatment for finish and feel. Nylon PA12 is your reliable core material. Vibratory tumbling is the most transformative treatment for the cost. For the best balance of speed, strength, and surface in production, MJF often has the edge. Always start with the end use in mind. A well-finished SLS or MJF part is not just a prototype; it’s a ready-to-use product.

How we can help

YiguProto runs 3D printing in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.

Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.

Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our 3D printing. You can also talk to an engineer before you commit to a drawing.

Frequently asked questions

The short version

Good parts reward the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.

Tighten only what mates. Test a sample before the run. Then let the process do the rest.