Design Tips for SLS 3D Printing: Boost Strength, Accuracy & Efficiency

Selective Laser Sintering (SLS) 3D printing is a game-changer for functional prototypes and low-volume production—it creates complex, high-strength parts without support structures, using durable materials like PA12 and PA11. But even the best SLS printers can’t fix a poorly designed part: thin walls may warp, trapped powder can ruin functionality, and ignored shrinkage can break assemblies. The key to success? Following proven design tips for SLS 3D printing. This guide breaks down 8 actionable strategies to optimize your designs, with real-world examples, data, and solutions to common pitfalls—so you get parts that are strong, accurate, and ready to use.

Why SLS Design Matters (And What Goes Wrong Without It)

SLS’s unique process—sintering plastic powder with a laser—creates specific design challenges you won’t face with FDM or CNC machining. A bad design can lead to:

• Warping: Large flat surfaces or uneven wall thicknesses trap heat, causing parts to bend during cooling (up to 4% shrinkage for PA12).
• Powder Residue: Hollow parts or closed channels trap unsintered powder, adding weight and weakening the part.
• Brittleness: Thin walls or slender features break easily during post-processing (e.g., sandblasting) or use.
• Fit Issues: Mating parts with too little clearance fuse together; too much make assemblies loose.

Example: A startup printed a PA12 gear with 0.4mm thin walls. The gear warped during cooling and broke after 10 test rotations. By adjusting the design to 1.3mm walls (per SLS best practices), the next batch lasted 500+ rotations—no warping, no breakage.

Tip 1: Master Wall Thickness (Avoid Warping & Brittleness)

Wall thickness is the foundation of strong SLS parts. Too thin, and parts warp or crack; too thick, and heat builds up, causing internal stress. Follow these rules to get it right:

Key Guidelines for SLS Wall Thickness

Pro Tips to Avoid Mistakes:

• Keep thickness consistent: Sudden changes (e.g., 1mm wall to 3mm wall) create stress points—use gradual transitions.
• Reinforce weak areas: Add 1–2mm thick stiffeners to thin walls (e.g., the base of a bracket) to boost strength.

Case Study: A medical device company designed a PA11 surgical guide with 0.8mm walls. 30% of the guides cracked during sterilization. Increasing walls to 1.3mm and adding stiffeners reduced failure rates to 0%—saving $2,000 in reprints.

Tip 2: Design for Easy Powder Removal (No Trapped Residue)

SLS doesn’t use supports—unsintered powder fills hollow parts and channels. If you don’t design ways to remove this powder, it will:

• Add unnecessary weight (up to 15% of the part’s total weight).
• Block moving parts (e.g., hinges or gears).
• Weaken the part by creating internal gaps.

How to Optimize Powder Removal:

1. Add large, accessible powder evacuation holes:
   • Minimum diameter: 3.5mm (larger is better—5mm holes speed up cleaning).
   • Place holes on opposite sides of hollow parts (e.g., top and bottom of a container) to create airflow.
2. Keep internal channels smooth: Avoid sharp bends or narrow sections (under 3mm) that trap powder. Use gradual curves (radius ≥5mm) for easy cleaning.
3. Avoid closed cavities: If you need a hollow part, never seal it completely—even a small 3.5mm hole is better than none.

Example: A drone manufacturer printed a PA12 battery case with a single 2mm powder hole. Powder compacted inside, making the case 10g heavier than intended. Redesigning with two 5mm holes let them remove 99% of the powder—saving weight and improving battery fit.

Tip 3: Optimize Holes & Channels (Fight Shrinkage)

SLS parts shrink 3–4% during cooling—more than FDM or CNC. This shrinkage is worst for holes and channels, which can close partially or become misshapen. Use these tips to keep them accurate:

Hole & Channel Design Rules:

Data Point: Tests by Yigu show that teardrop-shaped holes have 80% less shrinkage than round holes for PA12 parts—critical for parts that need to fit with screws or pins.

Tip 4: Set Proper Clearance for Mating Parts (No Fused Assemblies)

One of SLS’s best perks: you can print fully assembled parts (e.g., a hinge with a pin) in one go. But if clearance is wrong, parts will either fuse together (too little clearance) or be loose (too much).

Clearance Guidelines for Mating Parts:

Pro Tip:

Print a test pair first! SLS clearance varies by material—PA12 needs slightly more clearance (0.6mm) than PA11 (0.5mm). A 5-minute test print saves hours of reworking full assemblies.

Case Study: A toy company printed a PA12 puzzle with 0.2mm clearance between pieces. 90% of the puzzles fused together. Increasing clearance to 0.5mm let all pieces separate easily—no more failed prints.

Tip 5: Avoid Large Overhangs & Unsupported Spans

SLS doesn’t need supports, but overhangs (features sticking out from the main part) still sag or deform due to gravity and residual heat. This is worst for large spans or steep angles.

Overhang Design Rules:

• Maximum overhang angle: ≤45° from the build platform. Angles steeper than 45° cause sagging (e.g., a 60° overhang will have a rough, uneven surface).
• Maximum unsupported span: ≤2mm. Longer spans (e.g., 3mm) bend during printing.
• Use self-supporting shapes: Replace flat overhangs with arches, domes, or chamfers (30° angle) to distribute weight evenly.

Example: A furniture designer printed a PA12 shelf bracket with a 50° overhang. The overhang sagged 0.8mm, making the shelf uneven. Redesigning the overhang to 40° with a chamfer fixed the issue—perfectly straight shelves every time.

Tip 6: Size Small Details Correctly (No Blurry Logos)

SLS can print fine details (e.g., embossed logos or text), but undersized features become blurry or wear off during post-processing. Use these guidelines to keep details sharp:

Small Detail Size Rules:

• Embossed text/engravings: Minimum height/depth of 1mm. Details under 1mm wear away during sandblasting.
• Text font size: Minimum 2mm tall (sans-serif fonts like Arial work best—serifs are too fine and blur).
• Add draft angles: Tilt text or logos 5–10° from vertical. This makes them more durable and easier to clean.

Case Study: A brand printed PA12 promotional keychains with 1.5mm tall text. The text was clear, but 20% of the keychains lost letters during sandblasting. Increasing text height to 2mm and adding a 5° draft angle kept the text intact—100% of keychains looked perfect.

Tip 7: Reinforce Slender Features (No Broken Pins)

Slender parts (e.g., pins, thin rods, or small tabs) are prone to breaking during printing or handling. SLS’s high temperatures weaken these features, making them brittle.

Slender Feature Rules:

• Minimum pin diameter: 0.8mm (1mm+ is recommended for durability).
• Connect to the main part: Use gussets (triangular supports) to attach slender features to the part. Gussets distribute stress and prevent bending.
• Print parallel to the build platform: Slender features printed vertically (Z-axis) break easily. Print them horizontally (X-Y axis) for strength.

Example: A electronics company printed a PA12 connector with 0.7mm pins. 40% of the pins broke during assembly. Increasing pins to 1mm and adding gussets reduced breakage to 2%—saving $1,500 in replacement parts.

Tip 8: Account for Shrinkage (Keep Tolerances Tight)

SLS’s 3–4% shrinkage is unavoidable—but you can design around it to keep parts accurate. This is critical for parts that need to fit with other components (e.g., a gear that mates with a motor).

How to Handle Shrinkage:

1. Scale your CAD model: Add 3–4% to all dimensions (e.g., a 100mm part should be designed as 103mm). Most CAD software (Fusion 360, SolidWorks) has a scaling tool for this.
2. Focus tolerances on critical areas: Only apply tight tolerances (±0.3mm) to mating surfaces (e.g., a hole that fits a screw). For non-critical areas (e.g., the back of a bracket), use looser tolerances (±0.5mm) to save time.
3. Use standard sizes: Design holes and pins to match standard drill bit sizes (e.g., 4mm, 5mm). If shrinkage makes a hole too small, you can drill it to size post-print.

Data Point: SLS parts have a typical tolerance of ±0.3mm (or ±0.3% of the part size)—good enough for most functional parts. For ultra-tight tolerances (±0.1mm), use post-processing (e.g., reaming holes with a drill).

SLS Design Specifications Cheat Sheet

Use this table to quickly reference key design limits for SLS 3D printing (based on Yigu’s technical data):

Yigu Technology’s Perspective on SLS 3D Printing Design Tips

At Yigu Technology, we guide clients to turn SLS design challenges into strengths. For PA12 parts, we prioritize 1.3mm walls and 3.5mm powder holes to avoid warping and residue. For mating parts, we test clearance with small prototypes before full batches. We also help scale CAD models for shrinkage—critical for parts that need precise fits. Our team uses SLS’s design freedom to create complex parts (like lattice structures) that FDM can’t make, while following these tips to keep them strong and accurate. For us, SLS design isn’t just about rules—it’s about making parts that work, last, and deliver value.

FAQ About Design Tips for SLS 3D Printing

1. Can I print SLS parts with walls thinner than 0.6mm?

Technically yes, but it’s not recommended. Walls under 0.6mm are brittle—they break easily during post-processing (e.g., sandblasting) or use. For functional parts, stick to 0.6mm (with support) or 1.3mm (without support) to ensure durability.

2. How do I fix powder residue in hard-to-reach channels?

If powder is trapped in narrow channels, try these fixes:

• Use compressed air (30–50 PSI) to blow out residue.
• Soak the part in warm water (40–50°C) for 10 minutes—this loosens compacted powder.
• Redesign the channel with a larger diameter (≥3mm) for future prints.

3. Do I need to scale all SLS parts for shrinkage?

Yes—SLS parts shrink 3–4% regardless of material. Even small parts (e.g., 20mm pins) need scaling: a 20mm pin should be designed as 20.6mm (20mm + 3% shrinkage) to end up at 20mm after cooling. Most SLS service providers (like Yigu) can handle scaling for you, but it’s good to account for it in your CAD model.