In short: Fused Deposition Modelling (FDM) melts plastic filament and builds components layer by layer – economically, robustly and on a large scale. Stereolithography (SLA) cures liquid resin with light and delivers the finest details. Selective Laser Sintering (SLS) fuses plastic powder with a laser and produces durable series parts entirely without support structures. The choice of which of the three 3D printing processes is suitable depends on component size, surface finish, load and number of units.
The short answer
FDM melts plastic filament and builds robustly, economically and in large format. SLA cures liquid resin with light and delivers the finest details and smoothest surfaces. SLS fuses powder via laser and is suitable for durable functional parts and small batches without support structures. The appropriate process follows from function, surface finish and volume.
What is Fused Deposition Modeling (FDM)?
Fused Deposition Modelling is the world's most widely used 3D printing method. A thermoplastic filament is melted in a heated nozzle and deposited layer by layer onto a build platform. Each layer fuses with the one beneath it until the component is fully built. The method is also known by the synonyms Fused Filament Fabrication (FFF) or melt deposition.
The term Fused Deposition Modelling originates from the 1980s and was long protected by trademark. Today, FDM is an umbrella term for all extrusion processes that deposit molten plastic layer by layer.
How does FDM 3D printing work?
The FDM process runs in five steps:
- Prepare CAD file: The 3D model is exported as STEP, 3MF, or STL.
- Taglio A software programme breaks the model down into horizontal layers and calculates the print paths as well as necessary support structures.
- Melt The filament is heated in the nozzle to between 200 and 500 °C, depending on the material.
- Layer structure: The print head deposits track by track, the layer height is typically between 0.1 and 0.4 mm.
- Post-processing: Support structures are removed, surfaces are sanded, smoothed, or painted as required.
Crucial for quality are nozzle temperature, build chamber temperature, and printing speed. Industrial systems such as the large-format 3D printer SAM from Mach-3D work with a closed, heated build chamber – this prevents warping in technical plastics and makes fibre-reinforced materials processable in the first place.
Welche Materialien eignen sich für FDM?
The material selection for Fused Deposition Modelling is greater than for any other 3D printing process: PLA and PETG for prototypes and visual models, ABS and ASA for weather- and temperature-resistant parts, TPU for flexible components, PA (Nylon) for wear-resistant functional parts, as well as fibre-reinforced materials such as PA-CF, PA-GF, PP-GF and high-performance plastics such as PPS-CF.
Advantages and limitations of FDM
Strengths Lowest cost per component, largest material selection, largest available build volumes, robust functional parts, no post-curing required.
Limits visible layer lines, details under approx. 0.3 mm difficult, anisotropic strength (lower in Z-direction), support structures required for overhangs.
What is Stereolithography (SLA)?
Stereolithography is the oldest 3D printing process there is and works with liquid photopolymer resin. A laser or a UV projector cures the resin point by point or layer by layer. The component grows out of a resin bath.
How does SLA 3D printing work?
The build platform dips into the resin vat, exposing only a thin film of resin. A UV light source cures the exact contour of the current layer, the resin polymerises and solidifies. The platform then lifts by one layer height – typically 0.025 to 0.1 mm – and the process repeats. After printing, cleaning in isopropyl alcohol and post-curing under UV light are mandatory.
Because the layers are so thin and the laser is finely focused, SLA achieves accuracies of up to ±0.05 mm with wall thicknesses from 0.4 mm – no other plastic process delivers smoother surfaces straight from the machine.
Advantages and limitations of SLA
Strengths Highest detail level, smooth surfaces without post-processing, high dimensional accuracy, ideal for visible parts, precision mechanics, dental technology, and master models for mould making.
Limits smaller build volumes, resins are less impact-resistant than engineering thermoplastics, UV sensitivity over time, complex post-processing.
Was ist selektives Lasersintern (SLS)?
In selective laser sintering, fine plastic powder – usually PA12 – is applied layer by layer and fused by a laser precisely where material is intended to form. The unfused powder remains in the build chamber and supports the component throughout the entire print.
How does SLS 3D printing work?
A scraper draws a thin powder layer across the build platform. The build chamber is preheated just below the melting point so that the laser only needs to introduce a small amount of energy. The laser traces the cross-sectional contour, sintering the powder particles together. The platform then lowers by one layer height, new powder is applied, and the process repeats. After printing, the entire powder cake slowly cools down – only then are the parts unpacked and excess powder removed.
The decisive advantage: Because the powder bed supports, No support structures needed. This allows for undercuts, nested assemblies and even moving mechanisms that come directly out of the machine, assembled.
Advantages and limitations of SLS
Strengths Maximum design freedom without supports, mechanically loadable and series-production-compatible parts, uniform strength in all directions, good suitability for small series due to dense build space utilisation.
Limits Slightly rough, sandblasted surface, narrower material palette than FDM, higher plant and material costs, longer cooling times.
FDM, SLA and SLS compared directly
- Accuracy SLA (±0.05 mm) before SLS (±0.1 mm) before FDM (±0.1 to 0.2 mm)
- Surface SLA smooth, SLS fine-grained, FDM with visible layer lines
- Mechanical strength: SLS and technical FDM significantly ahead of SLA
- Maximum component size: FDM ready for the front – up to 900 × 900 × 1000 mm in one piece on the SAM
- Cost per component: FDM is cheapest, SLS is competitive for complex geometries in larger quantities.
- Support structures: only SLS manages completely without
- Material selection: FDM is the broadest, SLS is focused on polyamides, SLA on resins
Which 3D printing process for which use case?
Conceptual model for form testing: FDM – fast and inexpensive, often available within 24 hours.
Visible component, precision mechanics or dental application: SLA – because of surface finish and level of detail.
Resilient functional part or small batch with complex geometry: SLS – or technical FDM with fibre-reinforced material.
Large component, panelling, housing or device: Large-scale FDM – no other plastics processing method is economical here.
Spare part without existing tools: FDM or SLS, depending on load and quantity.
3D printing processes in practice: how to proceed
In practice, the process alone is rarely the deciding factor; rather, it is the combination of requirements, schedule and budget. The following sequence is sensible: define requirements (function, temperature, load, appearance) – select material – derive the process from this – adapt the design to the process (Design for Additive Manufacturing).
Mach-3D in Altenholz near Kiel offers all three processes under one roof and provides neutral advice – from Prototyping about the 3D printing contract manufacturing until large-scale 3D printing for XXL components. Anyone who wants to master the processes themselves will find in the Mach-3D Academy hands-on advanced training courses on FDM, SLA and SLS using real machines.
Frequently asked questions about 3D printing processes
FDM steht für Fused Deposition Modeling, ein 3D-Druckverfahren.
FDM stands for Fused Deposition Modeling, in German Schmelzschichtung (fused layer modelling). A plastic filament is melted and deposited layer by layer. The term FFF (Fused Filament Fabrication) is also used synonymously.
What is the biggest difference between FDM, SLA and SLS?
The starting material and how it is solidified: FDM melts filament, SLA cures liquid resin with light, and SLS sinters powder with a laser. This results in all further differences in surface finish, strength, geometric freedom, and cost.
Which 3D printing method is the cheapest?
For most components, FDM is the most cost-effective because material and machine costs are the lowest. For complex geometries in volume, SLS can work out cheaper per part, as support structures and their removal are completely eliminated.
How accurate is 3D printing?
SLA achieved to ±0.05 mm, SLS about ±0.1 mm, FDM depending on the machine and material ±0.1 to ±0.2 mm. The actual accuracy additionally depends on component size, geometry and material shrinkage.
Which process is suitable for large components?
FDM. Large-scale 3D printers like the SAM from Mach-3D produce components up to 900 × 900 × 1000 mm in one piece, without the need for parts to be glued or bolted together.
Can I have components manufactured using all three processes at Mach-3D?
Yes. Mach-3D manufactures FDM, SLA and SLS in Kiel and provides preliminary advice on which process is best suited to your component both technically and economically.
Directly from Kiel & Altenholz
FDM, SLA or SLS – upload your file and compare the price of your component instantly.
Conclusion
FDM, SLA and SLS solve different tasks: FDM for resilient, large and inexpensive components, SLA for precision and surface finish, SLS for complex functional parts in series production. The choice starts with the intended use, not the technology. Anyone who is unsure can upload the file into the 3D printing calculator and compares the processes directly on their own component.
