How Does 3D Printing Work? — Simple Guide to FDM, SLA & SLS

Introduction

3D printing — also called additive manufacturing — turns a digital design into a physical object by building it layer by layer. From hobbyist printers that extrude plastic filament on your desk to industrial machines that fuse metal powder for aircraft parts, 3D printing lets designers make shapes that would be difficult or impossible with traditional manufacturing. This guide explains the full workflow (model → slice → print → post-process), the main printer technologies (FDM, SLA, SLS and others), typical materials, why slicing and G-code matter, common applications, limitations, and practical tips so beginners and decision-makers alike understand what happens inside a 3D printer.

1. The basic idea: additive vs. subtractive

Traditional manufacturing is often subtractive — you cut or machine away material from a bigger block. 3D printing is additive: the object is created by successively adding tiny layers of material until the full geometry is complete. That layer-by-layer approach is what makes complex internal geometries, porous lattices, and one-piece assemblies feasible. Additive manufacturing is now widely used in prototyping, tooling, and increasingly for end-use parts across industries.

2. The 4 main steps of a 3D print job

1. Create or obtain a 3D model (CAD / scan). You design in CAD (Fusion 360, SolidWorks, TinkerCAD) or download an STL/OBJ from a library.
   
2. Prepare the model (repair & orient). Check for holes, non-manifold geometry, and choose an orientation to minimize supports and improve strength.
   
3. Slice the model into layers and generate G-code. A slicer (Cura, PrusaSlicer, Simplify3D) converts the model into horizontal layers and generates G-code — the printer instructions for movement, extrusion, temperature and more. This step defines layer height, infill, shells, and support structures.
   
4. Print and post-process. The printer follows the G-code to build the object. After printing you remove supports, cure or sinter parts (if needed), sand, paint, or heat-treat depending on the technology and material.
   

3. Slicing & G-code: the invisible bridge

Slicing turns a 3D shape into a stack of 2D slices and produces G-code: readable lines like “move X to 40.0, extrude filament at speed Y.” Slicer settings (layer height, wall thickness, infill percentage, print speed, retraction) determine surface finish, strength, material usage, and print time. Good slicing choices often improve success more than buying a pricier printer. 

4. Common 3D printing technologies (how each one physically works)

Below are the technologies you’ll encounter most often.

FDM / FFF (Fused Deposition Modeling / Fused Filament Fabrication)

How it works: a thermoplastic filament (PLA, PETG, ABS, TPU) is fed into a heated extruder, melted, and deposited through a nozzle in layers. The nozzle moves in X–Y while the build platform steps in Z. FDM is affordable, easy to use, and great for functional prototypes and hobby parts. Limitations: visible layer lines, lower dimensional accuracy, and weaker interlayer bonding than some other methods.

SLA / DLP (Vat Photopolymerization — Stereolithography)

How it works: a vat of liquid photopolymer resin is selectively cured (hardened) by a UV laser (SLA) or projector (DLP) one layer at a time. Because curing is precise, SLA parts have much smoother surfaces and higher resolution — ideal for jewelry, dental models, and high-detail prototypes. Post-curing is usually required.

SLS (Selective Laser Sintering)

How it works: powdered material (nylon thermoplastic or metal powders in specialized machines) is spread into a thin layer and a laser fuses selected areas. Since the powder bed supports the part, SLS can produce complex geometries without support structures. SLS parts are strong and used in industrial prototyping and small-batch production.

Metal AM (DMLS/SLM, Binder Jetting, DED)

How it works: metal powders are fused using lasers (Direct Metal Laser Sintering / Selective Laser Melting) or bound and sintered (binder jetting), or deposited with an energy source (Directed Energy Deposition). Metal additive manufacturing enables consolidated components (fewer assembled parts), topology optimization, and lightweight high-strength parts used in aerospace, medical implants, and tooling.

5. Materials: what you can print

• Plastics: PLA, ABS, PETG, Nylon, TPU (flexible), composite filaments (carbon fiber, wood-filled).
  
• Resins: standard, tough, flexible, dental, castable resins.
  
• Powders: nylon (SLS), metal powders (steel, titanium, aluminum) for industrial machines.
  
• Specialty: ceramics, concrete (construction printers), edible materials (experimental food printers). Material choice affects strength, heat resistance, finish, and cost.

6. Post-processing: from raw print to finished part

After printing you often need to:

• Remove supports (mechanical or chemical).
  
• Clean (wash uncured resin for SLA).
  
• Cure (SLA resins need UV post-cure).
  
• Sinter or heat-treat (metal AM).
  
• Surface finish (sanding, vapor smoothing ABS, dyeing, painting). Post-processing affects mechanical properties and appearance; plan it into schedule and cost calculations.

7. Why orientation, supports & infill matter

Orientation determines surface quality and strength direction (FDM parts are strongest along the layers’ plane). Supports are extra structures printed where overhangs would collapse; they add material and time, and require cleanup. Infill percentage and pattern control internal strength vs. weight. Thoughtful orientation and slicer settings reduce material use, printing time, and finishing work.

8. Accuracy, speed & cost tradeoffs

• Finer layers → better surface finish, but slower print times.
  
• High resolution SLA → smoother parts but more expensive resin and post-processing.
  
• SLS / Metal AM → strong, functional parts but high capital and per-part cost; best for performance or consolidation of many parts into one. Evaluate part function, volume, and budget before choosing a technology.

9. Typical applications (where 3D printing adds the most value)

• Rapid prototyping — iterate designs quickly.
  
• Custom medical devices — hearing aids, dental guides, patient-specific implants.
  
• Tooling & jigs — faster, cheaper custom factory fixtures.
  
• Aerospace & automotive — lightweight topology-optimized parts and consolidated assemblies.
  
• Low-volume manufacturing — custom products, spare parts, on-demand production. 3D printing shines when complexity, customization, or low volumes make conventional tooling expensive.

10. Limitations and common failure modes

• Speed: printing many parts is slower than injection molding for large volumes.
  
• Surface finish & tolerances: not all printers match injection molding without post-processing.
  
• Material limits: not every engineering material is printable or affordable at scale.
  
• Warping, layer adhesion, stringing, clogging: typical issues for FDM; proper temperature, bed leveling, and filament quality help. Understanding these failure modes reduces wasted prints.
  

11. Practical tips for beginners

• Start with PLA and a simple FDM printer to learn basics.
  
• Level the bed and calibrate extrusion (flow) — many print failures stem from poor calibration.
  
• Slice with conservative settings first: moderate speed, thicker layers, supports enabled.
  
• Join communities (forums, subreddits) and study printer-specific guides.
  
• Backup designs and document successful slicer profiles for repeatability.

LSI keywords used in this article

(additive manufacturing, fused deposition modeling, stereolithography, selective laser sintering, filament, resin, metal powder, CAD, slicing, G-code, layer height, infill, post-processing, topology optimization)

Conclusion

3D printing — or additive manufacturing — is a flexible way to move from digital design to physical object by building parts one layer at a time. The workflow is straightforward: design or scan in CAD, repair and orient the model, slice to generate G-code, print using a chosen technology (FDM, SLA, SLS, or metal AM), and then post-process to achieve the final properties and finish. Each technology trades cost, resolution, and material range against speed and complexity: FDM is inexpensive and accessible, SLA offers high detail, and SLS/metal AM provide industrial strength and geometric freedom. For anyone starting, learning slicing settings, bed leveling, and simple post-processing delivers the largest improvements. For businesses, 3D printing’s strengths are rapid iteration, customization, and reduced part consolidation — but for high volumes, traditional manufacturing may still be cheaper per part. With the rapid pace of material and machine innovation, 3D printing remains an essential tool for design, prototyping, and specialized production.

5 FAQs

1. How long does 3D printing take?
   Print time depends on part size, layer height, infill, and technology; a small FDM part might take 20–60 minutes, while complex or high-resolution parts take many hours. 
2. What types of 3D printers are there?
   Common types include FDM (filament extrusion), SLA/DLP (resin curing), SLS (powder sintering), and various metal AM processes (DMLS/SLM, binder jetting, DED).
3. Can 3D printers print metal parts?
   Yes — industrial metal printers use lasers or binding/sintering to produce metal components; these machines are costly but enable parts used in aerospace, medical, and tooling.
   
4. What materials can I print with at home?
   Home users commonly print PLA, PETG, ABS, and TPU on FDM printers; desktop resin printers use photopolymer resins for higher detail. Metal and industrial polymers typically require specialized equipment. 
5. Is 3D printing expensive?
   Entry-level 3D printing (basic FDM printer + filament) is affordable. However, industrial printers, specialized materials, post-processing, and large-scale production raise costs; evaluate total cost per part and production volume when planning.