Fused deposition modelling, also called fused filament fabrication, melts a thermoplastic filament and lays it down line by line, layer by layer. It is the process most people picture when they hear 3D printing, it is by far the cheapest, and its one structural weakness explains almost everything about where it should and should not be used.
How it works and what that implies
A heated nozzle extrudes a bead of molten polymer along a path, and each bead fuses to its neighbours and to the layer beneath. Because that fusion is a weld between partly cooled beads rather than a continuous solid, the bond between layers is weaker than the material itself. Parts are therefore strongly anisotropic and fail along layer boundaries.
What that means in practice
Orientation is a strength decision, not a convenience. A bracket printed lying down and the same bracket printed standing up have genuinely different load capacities. If a printed part fails, the first question is which way the layers ran, and the first fix is usually to reorient rather than to thicken.
Where it is the right answer
Shape, fit and envelope checks, where the material barely matters and cost does. Jigs and fixtures on a shop floor, especially in filled filaments. Large parts, since the process scales cheaply. Anything needed today, because the machines are ubiquitous. And anything that will be iterated several times this week, which is the case for most early design work.
Where to use something else
Load bearing parts where the load crosses layers. Fine detail, where resin printing is far better. Snap fits and living hinges, where sintered nylon behaves and filament does not. Watertight parts, since layer boundaries leak. And anything where surface appearance matters without post processing, because layer lines are always visible.
Questions people ask about fdm printing service
What does FDM stand for?
Fused deposition modelling, also called fused filament fabrication: melting a thermoplastic filament and depositing it line by line to build the part.
Why are FDM parts weak in one direction?
Because the bond between layers is a weld between partly cooled beads rather than continuous material. Parts fail along layer boundaries, which makes orientation a strength decision.
Is FDM good enough for functional parts?
For fixtures, housings and non critical parts, often yes, especially in filled filaments. For load bearing parts where load crosses layers, choose sintered nylon or machining.
Why is FDM so cheap?
Machines and materials are commodity items, there is no powder handling and no controlled atmosphere, and the process needs little post processing beyond support removal.