The big idea: An additive technique builds an object one layer at a time, each layer bonded to the one below.
Every strength and every limitation of 3D printing follows from that: the layer height sets the surface, the orientation sets which way the part is weak, and the overhangs set what support has to be printed and thrown away.
CAD model → orient → slice → build → finish, then the three techniques the guide names.
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| Technique | How each layer is made | What it gives you |
|---|---|---|
| LOM — laminated object manufacture | Sheets of paper, plastic or metal foil are glued down one at a time and each is cut to its outline with a blade or laser | Cheap materials and large parts, with a wood-like block that can be sanded — but the cut-away material is waste and the part is weak between layers |
| FDM — fused deposition modelling | A filament of thermoplastic is melted and extruded through a moving nozzle, drawing each layer as a path | Cheap machines and real engineering plastics, with visible layer lines and a part noticeably weaker between layers than along them |
| SLA — stereolithography | A laser or projector cures liquid photopolymer resin one layer at a time on a platform lifting out of a vat | The finest detail and smoothest surface of the three, from a material that is brittle, degrades in sunlight, and must be washed and cured |
Same chain, different way of making a layer: All three take a CAD model, orient it, slice it and build it layer by layer.
What differs is only how each layer is created — glued and cut, extruded, or cured with light — and that difference decides the material, the finish and the cost.
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Four consequences of building in layers
Layer lines on every curve
A sloping surface is a staircase of layer edges. Thinner layers reduce it and take proportionately longer, which is a direct trade of finish against time.
Weakness between layers
The bond between layers is weaker than the material itself, so a printed part breaks along a layer. The build orientation therefore decides which direction it can be loaded in.
Support under overhangs
Nothing holds up material printed over air, so overhangs steeper than about 45° need support printed underneath and removed afterwards — material and time, both wasted.
Shapes nothing else can make
Internal channels, lattices and parts that would need a mould split into six pieces are all possible, because the machine never has to remove a tool from inside the part.
The orientation question: If a printed hook will hang a load, print it so the load runs along the layers rather than trying to peel them apart.
The same part, printed the other way up, can be several times stronger — for exactly the same material and the same machine time.
How this is tested — explaining how components are produced using additive manufacturing, including LOM, FDM and SLA. It comes up two ways:
Paper 1 — multiple choice
- Identify an additive technique from a description of the machine.
- Choose the technique that suits a stated requirement.
Paper 2 — analysing a product
- Explain how a named component is produced by an additive technique.
- Justify the choice of one additive technique over another.
The trap: Describing a machine without the consequence. Layer lines, directional weakness and support material are what a designer has to live with, and they are where the marks are.
A jeweller needs a master pattern for a ring, with fine surface detail, to be used in casting. Justify the additive technique you would choose.
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