3D printing technologies guide: FDM, SLA, SLS and more

Introduction: the additive manufacturing ecosystem

Industrial 3D printing has evolved from rapid prototyping into a competitive manufacturing technology for short runs, tooling and end-use parts. According to the Wohlers Report 2025, the global additive manufacturing market surpassed USD 20 billion, with a 19% compound annual growth rate in the industrial segment.

But "3D printing" is not a single technology: it is an ecosystem of processes with radically different physical principles. Choosing the right technology �and the right material within it� has a direct impact on the mechanical properties of the part, unit cost, lead times and project feasibility. This guide covers the five most relevant technologies in engineering: FDM, SLA/DLP, SLS, MJF and DMLS/SLM.

FDM: the workhorse of prototyping

Fused Deposition Modeling extrudes a thermoplastic filament through a heated nozzle, depositing 0.1-0.3 mm layers onto a platform. It is the most accessible technology and the entry point for most engineers.

Key engineering materials:

• PLA: Polylactic acid, biodegradable, stiff but brittle. Heat deflection temperature (HDT): approximately 55degC. Visual prototypes only.
• PETG: Good balance between strength and ductility. Tensile strength approximately 50 MPa, elongation at break approximately 15%. Resistant to moisture and mild chemicals.
• ABS: Impact and temperature resistance (HDT approximately 95degC). Requires heated bed and enclosed chamber due to warping tendency. Matte surface finish.
• ASA: Similar to ABS but with UV resistance. Ideal for exterior automotive components.
• Nylon (PA6/PA12): High mechanical strength (approximately 65 MPa tensile) and excellent wear resistance. Hygroscopic: requires pre-drying and sealed storage.
• PEEK/PEI (Ultem): High-performance thermoplastics. HDT > 170degC, tensile strength > 100 MPa. Require extrusion temperatures > 350degC. Aerospace and medical applications.
• Fiber-filled composites: Filaments loaded with short carbon or glass fiber. Increase stiffness (modulus 2-3x) but reduce ductility and are abrasive to standard nozzles.

Limitations: Significant anisotropy in the Z axis (interlayer adhesion typically reaches only 50-70% of in-plane XY strength). Surface finish with visible layer steps. Limited resolution for fine details (< 0.5 mm). Interlayer bonds act as stress concentrators.

SLA and DLP: precision with photopolymers

Stereolithography (SLA) cures liquid photosensitive resins layer by layer using a UV laser. Digital Light Processing (DLP) accelerates the process by curing an entire layer at once through a projector. Both technologies share the same physical principle and material ecosystem.

The major advantage of SLA/DLP is surface quality: 25-100 micron layers that are virtually invisible, smooth walls and fine details down to 0.1 mm. Surface finish is comparable to CNC machining in terms of roughness (Ra 1-5 micrometers).

Resin families:

• Standard resins: Good definition but brittle. Elongation at break < 5%. Only for visual models and silicone molds.
• ABS-like / Tough resins: Formulated to mimic ABS thermoplastic behavior. Elongation 20-50%, improved impact resistance. Suitable for functional prototypes with snap-fits and clips.
• High-temperature resins: HDT up to 300degC. Applications in low-volume injection molds and composite curing tooling.
• Ceramic / filled resins: Incorporate alumina, silica or glass particles. After sintering, produce dense ceramic parts with refractory properties.
• Biocompatible resins (ISO 10993): For surgical guides, dental splints and tissue-contact medical devices.

Limitations: Brittleness compared to thermoplastics (even "tough" resins have lower toughness than nylon or PC). Degradation with prolonged UV exposure (require protective coating). Mandatory post-curing in UV chamber. Limited build volume (typically < 300 x 300 x 300 mm for high-end desktop equipment).

SLS: laser sintering for production

Selective Laser Sintering selectively fuses polyamide powder (PA11, PA12) or TPU layer by layer using a CO2 laser. Unlike FDM, it requires no supports: the unsintered powder acts as a natural support, enabling geometries impossible for other technologies �internal channels, mechanisms assembled in a single print, integrated hinges and nested parts.

The result is isotropic parts with mechanical properties comparable to injection molding (approximately 95% of theoretical density). Sintered PA12 tensile strength reaches 48 MPa with elongation of 15-20%. The elastic modulus (approximately 1.7 GPa) is practically identical in all directions.

Key advantages over FDM:

• Real isotropy: no weak planes between layers
• Support-free: total geometric freedom
• Batch production: parts can be nested in 3D within the build volume
• Uniform surface finish (slightly grainy, Ra 5-15 micrometers)
• Layer resolution: 0.1 mm typical (100 microns)

Materials available for SLS:

• PA12 (Nylon 12): Most common. Good stiffness-ductility balance, low moisture absorption. Ideal for functional parts, housings, brackets and mechanical assemblies.
• PA11: Higher ductility and impact resistance than PA12. Better fatigue performance. Bio-based (castor oil).
• PA6: Higher stiffness and thermal resistance (HDT approximately 175degC with reinforcement), but more hygroscopic.
• TPU: Elastomeric. Shore hardness 65A-95A. For gaskets, bellows, dampers and flexible guards.
• PP (Polypropylene): Similar to injection-molded PP. Chemical resistance, low density, ductility. Ideal for tanks and fluid-contact components.
• Reinforced PA: PA12 with glass fiber (increases stiffness 80%) or carbon fiber (stiffness +150%, but brittle). Aluminum-filled for thermal conductivity and metallic appearance.

Limitations: High equipment cost (from EUR 50,000). Post-processing required (powder cleaning with sandblasting or compressed air). Surface porosity requiring sealing for fluid contact. Powder waste: only 30-50% of the powder in each cycle is sintered; the rest can be reused but requires mixing with virgin powder to maintain properties.

MJF: HP fusion technology

Multi Jet Fusion is HP's play to compete with SLS. Instead of a laser, it selectively deposits a fusing agent onto a PA12 or PA11 powder bed, then applies an infrared lamp that heats only the agent-treated areas. A second agent (detailing) is applied at the edges to improve surface definition.

The main difference from SLS is productivity: by not relying on a laser that must scan each layer, MJF can print complete layers in a single pass, resulting in build times up to 10x faster for the same part volume.

Mechanical properties of MJF PA12: Tensile strength approximately 50 MPa, modulus approximately 1.8 GPa, elongation approximately 20%. Values very similar to SLS, but with slightly better surface finish and less internal porosity. MJF parts show 5-10% less moisture absorption than SLS equivalents due to lower residual porosity.

Distinctive advantages of MJF:

• Speed: up to 10x faster than SLS for series production
• Surface finish: Ra 5-10 micrometers, with less "orange peel" effect than SLS
• Consistency: more uniform properties batch to batch thanks to closed-loop thermal control
• Color: ability to dye parts black with colorants integrated into the process
• Lower operating cost than SLS in high-utilization regimes

Limitations: Material ecosystem limited to PA11, PA12, TPU and PP (versus the wider variety of powders for SLS, which includes PEEK, PEKK and other high-performance polymers). Not suitable for high temperatures (max HDT approximately 175degC with PA12). Resolution of fine details slightly lower than SLS. Post-processing still requires powder cleaning.

DMLS/SLM: metal powder bed laser fusion

Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) fully melt metal powder layer by layer with a high-power fiber laser (200-1000W), producing parts with > 99.5% of theoretical density. The difference between DMLS and SLM is subtle: DMLS sinters at particle level (partial melting of alloys with different melting points), SLM fully melts (single alloys). In practice, the industry treats them as synonyms.

This technology represents the biggest qualitative leap in additive manufacturing: functional metal parts with mechanical properties equivalent to �and occasionally superior to� forging or casting, with geometric freedom impossible in subtractive or molding processes.

Main alloys:

• AlSi10Mg: Aluminum with silicon and magnesium. Density 2.67 g/cm3. Tensile strength approximately 350 MPa (after T6 treatment). Excellent thermal conductivity. Weldable. The most used alloy in DMLS for lightweight components, heat exchangers and automotive parts.
• Ti6Al4V (Grade 5): Alpha-beta titanium. Tensile strength > 1000 MPa, density 4.43 g/cm3, biocompatible. Extensive use in medical implants, aerospace components and customized prostheses. Post-build heat treatment for stress relief.
• Inconel 718: Nickel-chromium superalloy. Tensile strength > 1400 MPa, maintains properties up to 700degC. For turbine components, exhaust systems and cryogenic applications. Difficult to machine by traditional methods �DMLS avoids this problem.
• Stainless Steel 316L: Corrosion resistant, weldable, biocompatible. Tensile strength approximately 580 MPa, elongation > 40%. Parts for food, marine and medical industries. Excellent ductility among printed metals.
• Maraging Steel MS1: High-strength martensitic steel. After aging: > 1900 MPa tensile strength. For injection tooling with conformal cooling channels.
• Copper (CuCrZr): Thermal and electrical conductivity > 350 W/mK. For heat exchangers, inductors and particle accelerator components. One of the most challenging materials to process due to high reflectivity and thermal conductivity.
• CoCr (Cobalt-Chrome): High hardness (40-50 HRC), biocompatible, wear resistant. Dental crowns and bridges, orthopedic implants.

Limitations: Very high cost: equipment from EUR 250,000, metal powder at EUR 50-400/kg. Slow build speed (approximately 5-20 cm3/h). Supports required for heat dissipation and part anchoring �adding material cost and post-machining for removal� which increases post-processing costs. Residual stresses from thermal gradients, requiring post-build stress relief heat treatment. Elevated surface roughness on inclined surfaces (Ra 10-30 micrometers) requiring post-machining on functional areas.

Technology comparison table

The following table summarizes the key characteristics of each technology to facilitate decision-making during the selection phase:

Parameter	FDM	SLA/DLP	SLS	MJF	DMLS/SLM
Accuracy	+/- 0.5% (min 0.2 mm)	+/- 0.15% (min 0.1 mm)	+/- 0.3% (min 0.15 mm)	+/- 0.3% (min 0.2 mm)	+/- 0.1% (min 0.05 mm)
Surface roughness (Ra)	10-25 um	1-5 um	5-15 um	5-10 um	10-30 um
Isotropy	Low (Z weak)	Moderate	High	High	Very high
Equipment cost	EUR 0.2K-50K	EUR 0.5K-100K	EUR 50K-500K	EUR 80K-400K	EUR 250K-2M
Material cost	EUR 15-300/kg	EUR 50-400/L	EUR 50-120/kg	EUR 40-100/kg	EUR 50-400/kg
Supports	Required	Required	Not required	Not required	Required
Post-processing	Support removal	Wash + UV cure	Powder cleaning	Powder cleaning	HT + support removal
Typical build volume	200-600 mm3	150-300 mm3	300-700 mm3	380 x 280 x 380 mm	250 x 250 x 300 mm

Selection criteria: which technology to choose

The technology decision is not binary but depends on a combination of technical and economic requirements. The following decision flow covers the most common engineering cases:

Case 1 -- Visual or conceptual prototype: FDM with PLA or PETG. Minimal cost, fast iteration. Accuracy and strength are not critical; iteration speed and cost are.

Case 2 -- Functional prototype with fine detail: SLA with ABS-like resin. Professional surface finish, functional snap-fits, transparency if needed. Ideal for client presentations and fit validation.

Case 3 -- Short run of functional plastic parts (10-1000 units): SLS if material variety or specific properties are required. MJF if speed and per-part cost are the priority. Both enable tooling-free production with day-level lead times.

Case 4 -- Metal part with complex geometry: DMLS/SLM. When CNC machining is not viable due to internal geometry (conformal channels, lattice structures) and casting requires tooling that is not justified for short runs. Example: heat exchangers with internal helical channels.

Case 5 -- Production tooling: FDM with high-performance materials for light tooling (drill guides, assembly fixtures). DMLS with Maraging Steel for injection molds with conformal cooling channels that reduce cycle time by 20-40% versus straight machined channels.

Case 6 -- Elastomeric parts: SLS with TPU for gaskets, bellows, flexible guards. Shore hardness 65A-95A, no molds needed. Runs of 10-500 units economically viable versus silicone or rubber molding.

Post-processing: from printer to final part

Post-processing is not optional: all technologies require subsequent operations that impact total cost (often 30-50% of the finished part cost). Ignoring post-processing during the selection phase leads to unrealistic cost estimates.

Common operations by technology:

• FDM: Manual support removal (pliers and cutters), sanding to smooth layers (progressive 120-400 grit), chemical polishing with acetone (ABS only) or ethyl acetate (PLA) for surface gloss. Chemical polishing reduces surface roughness by 70-90% but can affect dimensional tolerances.
• SLA/DLP: Washing in isopropyl alcohol (IPA) or detergent solution (10-20 min) to remove uncured resin. Post-curing in UV chamber (15-60 min at 40-60degC) to reach nominal mechanical properties. Mechanical support removal with cutters and sanding of marks. Optional: painting or ceramic coating to improve UV resistance.
• SLS/MJF: Cleaning of unsintered powder with sandblasting, compressed air or vibration. Glass microbead blasting to uniform surface finish. Optional: chemical dyeing (MJF already includes coloring; white SLS parts can be hot-dyed), solvent vapor sealing for fluid-contact applications.
• DMLS/SLM: Stress relief heat treatment (controlled ramp furnace cycle, typically 1-4 hours at 600-1000degC depending on alloy). Base plate cutting by wire EDM. Mechanical support removal with hand tools or CNC. Bead blasting or sandblasting for uniform surface finish. CNC machining of functional surfaces to achieve H7 tolerances or Ra < 1 um roughness.

Trends and near future

Industrial additive manufacturing is at an inflection point. Several trends are converging to accelerate adoption in production:

• Hybrid manufacturing: Machines combining DED (Directed Energy Deposition) with 5-axis CNC machining in the same setup. Ideal for repairing high-value components (turbine blades, worn molds) and large parts with areas requiring high surface precision. The combination reduces total manufacturing time by 40-60% versus printing and then machining separately.
• In-situ monitoring with machine learning: Fusion of optical, thermal and acoustic sensors with ML models to detect defects in real time. Systems such as EOSTATE Exposure OT from EOS monitor every layer of the DMLS process and automatically adjust fusion parameters to correct deviations before they generate porosity or lack of fusion.
• Functional materials: Conductive polymers (loaded with carbon nanotubes or graphene for electrostatic dissipation and EMI shielding), piezoresistive materials (parts that detect deformation without bonded strain gauges), and metal powders with integrated sensing capabilities.
• Generative software + 3D printing: Topology optimization and generative design produce organic geometries that can only be manufactured additively. The integration of tools like nTopology with DMLS workflows is creating a new category of components �structurally optimized, with lattice structures that grade density according to the stress field, impossible to manufacture any other way.
• Sustainability: Powder reuse (SLS, MJF, DMLS: most unsintered powder can be reused mixed with virgin), FDM filament recycling (grinding and re-extrusion of defective parts and supports), and bio-based resins for SLA. Life cycle assessment (LCA) as a technology selection criterion, especially in regulated sectors.
• Large format 3D printing: Systems like BAAM (Big Area Additive Manufacturing) from Cincinnati Inc that deposit up to 45 kg/h of fiber-reinforced polymer. For aircraft wing tooling, composite molds for wind turbine blades and urban furniture. Combination with subsequent CNC milling enables traditional machining tolerances on multi-meter parts.

The convergence of these trends is transforming additive manufacturing from a prototyping tool into an industrial production technology with a central role in the supply chain. The question is no longer whether 3D printing can make a part, but which technology and material are optimal for the specific requirements of each application.