How does 3D printing work? In short, it builds a part by adding material layer by layer instead of removing it — the opposite of how most manufacturing works, and that’s why it seems almost counterintuitive the first time you encounter it. Most manufacturing processes work by removing material — cutting, grinding, milling away from a solid block until the shape you want is what’s left. 3D printing does the opposite: it builds up a part layer by layer from nothing, adding material only where it’s needed. That fundamental difference is why it’s called additive manufacturing. If you have ever wondered how a printer can produce a hollow sphere or an interlocking mechanism in one piece with no assembly required, that subtractive-versus-additive difference is the whole answer.
The core process is straightforward. A digital 3D model is sliced into thin horizontal layers by software. The printer then deposits, fuses, or cures material one layer at a time, stacking each one on the last until the full three-dimensional form is complete. The result is a physical object that matches the digital file.
What Is 3D Printing, Exactly? (And How Does 3D Printing Work?)
3D printing, also called additive manufacturing, is the process of building a physical part directly from a digital 3D model by adding material layer by layer until the part is complete. That’s the short answer. The longer answer is that ‘additive manufacturing’ is really an umbrella term covering several distinct technologies — FDM, SLA, and SLS chief among them — that all share the same layer-by-layer logic but differ in how each layer actually gets formed.
What makes 3D printing genuinely useful in manufacturing isn’t novelty, it’s flexibility. A single printer can produce a one-off prototype today and a complex geometry tomorrow without retooling, which is something CNC routing and molding can’t do as easily. That flexibility is also its limit: printed parts trade some material strength and finish quality for that freedom, which is exactly why most fabrication shops use 3D printing alongside other processes rather than as a replacement for all of them.
What Happens Before Printing: From Model to Machine
Everything starts with a 3D model — typically a CAD file in STL, OBJ, or STEP format. That file is imported into slicing software, which converts it into a series of horizontal cross-sections and generates the toolpath instructions the printer will follow. Slicer settings — layer height, print speed, infill density, support structures — have a significant effect on print quality, strength, and time.
Support structures are worth understanding upfront. Most 3D printing processes can’t print in mid-air. Overhanging geometry that lacks support below it will collapse or deform during printing. The slicer automatically generates temporary support material where needed; this is removed after printing, either by hand, with solvents, or through a secondary process depending on the technology.
What Are the Main 3D Printing Technologies — FDM, SLA, and SLS?
Not all 3D printers work the same way. The technology determines what materials can be used, what level of detail is achievable, and what the parts are suitable for.
- FDM (Fused Deposition Modeling) — The most widely used technology. A spool of thermoplastic filament is fed into a heated nozzle, which melts it and deposits it in precise paths layer by layer. Fast, affordable, and available in a wide range of materials. Best for functional prototypes, structural parts, and general-purpose use where surface finish is not the primary concern.
- SLA (Stereolithography) — Uses a UV laser to cure liquid photopolymer resin layer by layer. Produces very high surface quality and fine detail. Ideal for presentation models, intricate geometry, and applications requiring smooth surfaces. Parts are more brittle than FDM by default, though engineering resins have closed that gap considerably.
- SLS (Selective Laser Sintering) — A laser fuses powdered material — typically nylon — layer by layer. No support structures needed, since unsintered powder supports the part during printing. Produces strong, functional parts with good mechanical properties. The go-to technology for complex geometries, functional end-use parts, and small production runs.
Choosing the right technology depends on what the part needs to do, not just which one sounds the most advanced. FDM is usually the right default for functional prototypes and structural parts where cost and turnaround matter more than surface finish. SLA earns its place when a part needs to look finished straight off the printer — presentation models, jewelry patterns, anything with fine detail. SLS is the move for complex geometries that need real mechanical strength, since the powder bed eliminates the need for support structures that would otherwise be impossible to remove from an enclosed shape.
n
We cover this in more depth in our guide to choosing the right 3D printing technology.
Layer by Layer: What’s Actually Happening During a Print
During printing, the machine is executing the slicer’s toolpath instructions with high precision. Each layer is deposited, cured, or fused in sequence. The build platform typically lowers (or the print head rises) by one layer height — commonly 0.1–0.3mm for FDM, finer for SLA — after each layer is complete, and the next layer begins immediately on top of it.
The bond between layers is the structural weak point of most 3D printed parts. Because material is added in layers, parts tend to be strongest in the X and Y directions (within a layer) and somewhat weaker in the Z direction (between layers). For structural or load-bearing applications, print orientation matters — parts should be oriented so that critical stresses run with the layers rather than across them.
Post-Processing: What Happens After the Print
Most 3D printed parts require some work after the printer finishes:
- Support removal — Manually breaking away supports (FDM), washing in solvent (dissolvable supports), or rinsing in isopropyl alcohol (SLA resin parts).
- Curing — SLA parts need UV post-curing to reach full material properties. This is typically done in a dedicated UV curing station.
- Surface finishing — Sanding, priming, painting, vapor smoothing, or media blasting depending on the application and required appearance.
- Functional post-processing — Heat-set inserts, threading, drilling, or light machining for features that require tighter tolerances than printing alone achieves.
How long all of this takes depends heavily on part size, technology, and how much post-processing it needs. A small FDM prototype can be printed and ready same-day. A large SLA part needing post-cure, support removal, and finishing might take several days start to finish. SLS parts generally need the least post-processing since there are no supports to remove, but powder cleanup and any secondary finishing still add time. None of this is a reason to avoid 3D printing — it’s just worth planning around if a part is on a deadline.
Where 3D Printing Fits in a Fabrication Workflow
3D printing is most powerful when it’s one tool in a broader fabrication strategy rather than a standalone solution. At Kemperle Industries, our 3D printing services regularly work alongside CNC routing and machining and molding and casting — 3D printing handles complex geometry and rapid iteration; other processes handle surface finish, material properties, or volume requirements that printing can’t match alone.
If you’re not sure which process actually fits your part, call us at 718-557-9578 and we’ll talk through the geometry, material, and quantity before you commit to one approach over another.
If you’re trying to figure out whether 3D printing is the right process for a specific part or project, get in touch — it’s a question worth thinking through carefully before committing to a manufacturing approach and a production timeline.
