Stereolithography (SLA) vs. Selective Laser Sintering (SLS): Choose the Best 3D Printing Method for Your Needs

The Problem: Confused About Which 3D Printing Technology to Use?

Are you stuck trying to figure out if SLA or SLS is right for your project? Many of our customers at Istar Machining face this same problem. You need parts made fast. You need them to be strong. You need them to look good. But which 3D printing technology will give you the best results? The wrong choice can mean:

• Parts that break too easily
• Rough surfaces when you need smooth ones
• Paying too much money
• Getting parts that can’t handle heat or stress

The Situation Gets Worse

The more you look into it, the more confusing it gets. One website says use SLA. Another says SLS is better. If you pick the wrong technology, you might:

• Waste money on parts that fail
• Miss deadlines when parts need to be remade
• Lose customers who aren’t happy with the results
• Ruin your project before it even gets started At Istar Machining, we see customers make these mistakes all the time. But we can help you pick the right path.

The Solution: Know Exactly How SLA and SLS Compare

We have put together this complete guide to help you understand the differences between SLA and SLS 3D printing. By the end, you’ll know exactly which technology is right for your needs.

How SLA and SLS Work: The Basics

SLA (Stereolithography)

SLA uses a liquid resin that turns hard when hit with a laser. The process works like this:

1. A platform dips into a vat of liquid resin
2. A laser draws the first layer, hardening the resin
3. The platform moves up slightly
4. The next layer is drawn
5. After printing, parts need cleaning and extra curing

SLS (Selective Laser Sintering)

SLS uses powdered materials that get fused together by a laser. Here’s how it works:

1. A layer of powder is spread across the build area
2. A laser melts (sinters) the powder where the part should be
3. The platform moves down slightly
4. A new layer of powder is added
5. After printing, parts need to cool and have powder removed

Material Options: What Can You Make?

Let’s look at what materials each technology can use:

Key Point: SLS can use metals, but SLA cannot.

How Strong Are the Parts?

When it comes to strength, SLS parts are usually stronger:

• SLA parts:
  • Good for models and prototypes
  • Can be brittle
  • Not good for parts that snap together
  • Strength: 50-70 MPa
• SLS parts:
  • Good for working parts
  • Can take more stress
  • Better for parts that need to bend without breaking
  • Strength: 45-70 MPa

At Istar Machining, we help customers pick the right process based on how strong parts need to be.

How Do the Parts Look?

The surface finish is very different between these technologies:

SLA Surface Quality

• Very smooth surfaces
• Fine details (25-100 µm layers)
• Can be clear/transparent
• Looks almost like injection molded parts

SLS Surface Quality

• Gritty texture like sandpaper
• Less detailed (80-150 µm layers)
• Always opaque
• Porous surface

Which Technology Costs More?

Cost is often a deciding factor. Here’s how they compare:

Applications: When to Use Each Technology

Best Uses for SLA

• Detailed visual models
• Dental models and guides
• Clear parts (like lenses or fluid channels)
• Master patterns for molds
• Jewelry prototypes

Best Uses for SLS

• Functional prototypes that need to work
• Complex parts with moving features
• End-use parts that need to be strong
• Heat-resistant components
• Metal parts (through DMLS)

Size Limitations

Each technology has limits on how big parts can be:

SLA Build Volumes

• Desktop: 145 × 145 × 175 mm
• Industrial: Up to 1500 × 750 × 550 mm

SLS Build Volumes

• Desktop: 150 × 200 × 150 mm
• Industrial: Up to 700 × 380 × 560 mm

Design Considerations

When designing parts, remember these key differences:

SLA Design Tips

• Needs support structures that must be removed
• Can have thin walls (0.5-1mm)
• Best for organic shapes
• Good for text and logos

SLS Design Tips

• No support structures needed (powder supports the part)
• Good for complex internal shapes
• Can make interlocking parts in one print
• Needs escape holes for trapped powder

Safety and Environmental Factors

Both technologies have safety concerns:

SLA Safety

• Toxic resins before curing
• Need gloves and eye protection
• Need good ventilation
• Creates liquid waste

SLS Safety

• Powder inhalation risks
• Fire risks with some materials
• Needs special disposal for waste powder
• Needs good dust control

Real-World Applications

Let’s look at how these technologies are used in real industries:

Dental Uses

• SLA: Biocompatible resins make precise surgical guides and models
• SLS: Rarely used due to limited biocompatible powders

Aerospace Uses

• SLA: Used for non-structural parts like housings
• SLS: Used for functional ducts and brackets that can handle heat

Consumer Products

• SLA: Used for smooth, detailed prototypes
• SLS: Used for snap-fit parts and functional prototypes

The Accuracy Test: How Precise Are They?

Precision matters for many projects:

Post-Processing: Getting the Final Look

After printing, both technologies need more work:

SLA Post-Processing Steps

1. Remove from build platform
2. Wash in solvent to remove uncured resin
3. Post-cure in UV chamber
4. Remove supports
5. Sand support marks
6. Paint or finish as needed

SLS Post-Processing Steps

1. Cool down in the machine
2. Remove from powder
3. Clean with air or bead blasting
4. Smooth surfaces if needed
5. Dye or color as needed

When to Use CNC Machining Instead

Sometimes 3D printing isn’t the best choice. At Istar Machining, we recommend CNC machining when you need:

• Higher strength parts
• Tighter tolerances
• Metal parts with specific properties
• Production quantities
• Materials not available in 3D printing

Decision Guide: Which Technology Should You Choose?

Choose SLA When You Need:

• High detail and smooth surfaces
• Clear or translucent parts
• Biocompatible materials
• Dental or medical applications
• Visual prototypes that look great

Choose SLS When You Need:

• Functional parts that can take stress
• Complex geometries without supports
• Flexible materials
• Heat resistance
• Metal parts through DMLS

Case Studies: Real Examples

Case Study 1: Medical Device Prototype

A medical device company needed a prototype with fine details and biocompatible materials. They chose SLA because:

• It could produce the small features
• It had FDA-approved resins
• The smooth surface was easier to sterilize

Case Study 2: Automotive Component

A car parts manufacturer needed a functional prototype that could handle heat and stress. They chose SLS because:

• The nylon material could handle the heat
• The part needed to snap into place
• The complex internal structure would be hard to make with supports

Comparing Speed: Which is Faster?

When time matters, here’s how they compare:

How to Prepare Your Files

For the best results with either technology:

1. Export as STL file
2. Check for watertight meshes
3. Add supports for SLA models
4. Orient parts to reduce supports
5. Consider build orientation for strength

Combining Technologies for Best Results

Smart companies often use both technologies:

• SLA for detailed master patterns
• SLS for functional testing
• CNC machining for final production

At Istar Machining, we can help you with both 3D printing and CNC machining for the perfect workflow.

Technical Specs Comparison Table

Final Thoughts

The choice between SLA and SLS comes down to what matters most for your project:

• Choose SLA for beautiful, detailed visual models
• Choose SLS for functional, strong working parts

Still not sure? Talk to our experts at Istar Machining. We can help you pick the right technology or even suggest when CNC machining might be a better choice than 3D printing. Ready to get started? Contact us today for a quote on your next project.