SLS (Selective Laser Sintering) and SLM (Selective Laser Melting) are two leading powder-based 3D printing technologies, but they differ drastically in how they process materials and deliver part performance. Understanding these differences is critical for choosing the right method—whether you’re making prototypes, industrial components, or medical implants. This article breaks down the core differences between SLS and SLM technology across 7 key areas, plus guidance on when to use each.
1. Core Difference 1: Forming Principle (Sintering vs. Melting)
The fundamental divide between SLS and SLM lies in how they interact with powder materials—a contrast that defines every other aspect of their performance.
| Technology | Forming Principle | How It Works | Simple Analogy |
| SLS | Selective Sintering | Uses an infrared laser to heat powder particles to a temperature just below their melting point. This creates bonds between particles but leaves the powder not fully melted. Layers are stacked and sintered sequentially to form the final part. | Baking cookies: Dough particles stick together when heated (but don’t turn into a liquid) to form a solid cookie. |
| SLM | Selective Melting | Uses a high-power laser to fully melt metal powder particles into a liquid state. The liquid metal then cools and solidifies completely. Layers are melted and stacked to build the part with a dense, fully fused structure. | Melting metal in a foundry: Metal is heated until it’s liquid, poured into a mold, and cools to form a solid, dense component. |
2. Side-by-Side Comparison: SLS vs. SLM Across 6 Key Areas
To quickly assess which technology fits your needs, use this comprehensive table comparing their laser types, materials, part performance, and more.
| Comparison Category | SLS (Selective Laser Sintering) | SLM (Selective Laser Melting) | Key Takeaway |
| Laser Type | – CO₂ lasers (wavelength: 9.2–10.8 microns)- Lower power density (focused on bonding, not melting). | – Short-wavelength lasers: Nd-YAG (1.064 microns) or fiber lasers (1.09 microns)- Higher power density (needed to fully melt metal). | SLM uses lasers optimized for metal absorption; SLS uses lasers for broader powder compatibility. |
| Materials Used | – Wide range: Polymers (nylon, polystyrene), metals (iron, titanium alloys), ceramics, coated sand.- Metal printing requires binder powders (low-melting-point metals or organic resins) mixed with main metal powder. | – Limited to pure metal powders: Aluminum alloys, titanium alloys, stainless steel, cobalt-chromium alloys.- No binders needed—pure metal is melted directly. | SLS offers more material versatility; SLM is specialized for high-performance pure metals. |
| Part Performance | – Porosity: Contains small gaps (porous structure).- Mechanical properties: Lower strength, poor corrosion/wear resistance.- Precision: Moderate (surface roughness: Ra 10–20 μm).- Requires post-processing (e.g., hot isostatic pressing) to improve density. | – Porosity: No gaps (fully dense structure, >99% density).- Mechanical properties: High strength, excellent corrosion/wear resistance (matches forged metals).- Precision: High (surface roughness: Ra 5–10 μm).- Minimal post-processing needed for functional use. | SLM produces industrial-grade, high-performance parts; SLS parts need upgrades for demanding applications. |
| Support Structures | – No additional supports needed. Unsintered powder acts as a “natural support” for cavities and cantilevers. | – Requires support structures for complex designs (e.g., overhangs >45°). Supports prevent deformation/collapse during melting. | SLS simplifies design (no support constraints); SLM needs extra design steps for supports. |
| Surface Quality | – Grainy texture with visible layer lines.- Requires post-processing (polishing, sandblasting, coating) to improve appearance. | – Smoother than SLS, but still has minor layer lines.- May need light polishing for high-aesthetic requirements (e.g., medical implants). | SLM has better out-of-the-box surface quality; both may need finishing for cosmetic use. |
| Application Fields | – Prototyping (fast, low-cost models), mold manufacturing, consumer goods (e.g., custom cases), medical devices (e.g., exoskeletons).- Metal use: Non-critical parts (e.g., aerospace interior components, automotive brackets). | – High-performance parts: Aerospace (engine components, turbine blades), medical (orthopedic implants, dental crowns), automotive (lightweight structural parts), mold manufacturing (complex runners). | SLS excels at prototypes and low-stress parts; SLM dominates high-performance, safety-critical applications. |
3. When to Choose SLS vs. SLM? (Step-by-Step Decision Guide)
Use this linear, question-driven process to match the technology to your project’s goals:
Step 1: Ask About Material Needs
- Need polymers, ceramics, or mixed materials? Choose SLS—it’s the only option for non-metal powder printing. For example, SLS is ideal for nylon prototypes or ceramic molds.
- Need pure, high-strength metals? Choose SLM—it processes aluminum, titanium, and stainless steel into dense, durable parts. For example, SLM is used for titanium medical implants.
Step 2: Ask About Part Performance Requirements
- Low-stress applications (e.g., display prototypes, non-critical brackets)? Choose SLS—its porous parts are cost-effective and sufficient for light use.
- High-stress or safety-critical applications (e.g., aerospace engine parts, medical implants)? Choose SLM—its fully dense structure ensures strength and reliability.
Step 3: Ask About Cost & Design Complexity
- Tight budget or complex designs with overhangs? Choose SLS—no supports reduce design time, and material costs are lower (e.g., nylon powder is cheaper than titanium powder).
- Willing to invest in quality for functional parts? Choose SLM—while more expensive, it eliminates the need for costly post-processing (e.g., hot isostatic pressing for SLS metals).
4. Yigu Technology’s Perspective on SLS vs. SLM
At Yigu Technology, we see SLS and SLM as complementary tools for different stages of product development. Many clients overspecify SLM for prototypes—for example, using SLM to make a metal display model when SLS (with metal-polymer powder) would be 40–50% cheaper. We recommend SLS for initial prototyping (fast, flexible, cost-effective) and SLM for final production of high-performance parts. For clients transitioning from prototypes to production, we also help optimize designs: For SLS, we simplify overhangs to avoid post-processing; for SLM, we minimize supports to reduce material waste. The key is to align the technology with your performance needs and budget—not to choose a “better” option.
FAQ: Common Questions About SLS and SLM Technology
- Q: Can SLS produce metal parts that match SLM’s performance with post-processing?
A: No. Even with hot isostatic pressing, SLS metal parts only reach ~95% density (vs. >99% for SLM), leading to lower strength and corrosion resistance. SLM is still required for safety-critical metal parts.
- Q: Is SLM more expensive than SLS?
A: Yes. SLM machines cost 2–3x more than SLS machines, and pure metal powders (e.g., titanium) are 5–10x pricier than SLS materials (e.g., nylon). However, SLM eliminates post-processing costs for metal parts, balancing expenses for high-volume projects.
- Q: Can SLS or SLM print large parts?
A: Both have size limits, but SLS typically handles larger parts (up to 1m³) because unsintered powder supports bigger structures. SLM is limited to smaller parts (usually <50cm³) due to the need for precise heat control during melting—larger SLM parts risk warping.