Processes and Workflow
The additive processes compared, and the path from a CAD model through the slicer to a finished part.
What additive manufacturing is
Additive manufacturing (AM) builds a part by joining material layer by layer from a 3D model, in contrast to subtractive manufacturing (machining, which cuts material away) and formative manufacturing (molding and casting, which shape material in a mold). Because each layer is made independently, internal channels, lattices and one-piece assemblies are as easy as solid blocks, there is no tooling to make, and a change to the model costs only another print. The price is slow build rates, a rougher surface, and material properties that depend on the direction of the layers. ISO/ASTM 52900 groups the processes into seven families; four of them matter in a workshop.
The processes compared
| Process | How it works | Typical layer | Strengths | Limits |
|---|---|---|---|---|
| FDM / FFF (material extrusion) | A heated nozzle extrudes melted plastic filament in lines | 0.1 to 0.3 mm | Cheap machines and materials; strong engineering plastics; large parts; easy to use | Visible layer lines; lower detail; strength depends on direction |
| MSLA / SLA / DLP (vat photopolymerization) | UV light cures liquid resin layer by layer, usually at 405 nm | 0.025 to 0.1 mm | Fine detail and smooth surfaces; good for small parts and molds | Washing and curing; resin is a skin irritant; brittle parts; small build volume |
| SLS and MJF (powder bed fusion) | A laser, or heat and a fusing agent, bonds nylon powder | 0.08 to 0.12 mm | No supports; strong, near-isotropic nylon parts; parts nest in the bed | Costly machines; powder handling; usually bought as a service |
| Metal powder bed (DMLS / SLM) and binder jet | A laser melts metal powder, or a binder is sintered | 0.02 to 0.06 mm | Complex metal parts, internal channels | Expensive; stress relief, supports and machining are needed; service bureaus |
| Material jetting, DED, sheet lamination | Droplets, deposited wire or laminated sheets | varies | Full color, multi-material, large metal structures | Specialist and industrial; rarely in a small shop |
The rest of this guide concentrates on FDM, the process most workshops own, and gives resin and powder printing their own page (Resin and Powder Processes).
From idea to part: the workflow
- 1. Design the model in CAD (solid modeling in millimeters), or download one. Design for the process: see Designing for 3D Printing.
- 2. Export as STL or 3MF (or open the CAD file directly in a slicer that reads STEP).
- 3. Slice: choose the orientation, layer height, walls, infill, supports and temperatures (Slicer Settings and Print Quality).
- 4. Print from the G-code: a first-layer check in the first minutes saves most failures (Calibration and Maintenance).
- 5. Finish and inspect: remove supports, clean, sand or cure, then measure the part against the drawing (Post-processing and Finishing, Strength, Accuracy and Fits).
- 6. Iterate. A fit that does not assemble, or a surface that is too rough, goes back to step 1 or 3.
Model files: STL, 3MF and STEP
| Format | What it holds | Notes |
|---|---|---|
| STL | A surface made of triangles (no units, no color) | The universal exchange format. It is an approximation: curved surfaces become flat facets, and the file has no units, so check the scale (millimeters by convention) |
| 3MF | Triangles plus units, colors, materials and print settings in one compressed file | Modern replacement for STL; slicers can save a whole project in it |
| OBJ / AMF | Triangles with color or material information | Used for multicolor and textured models |
| STEP | The exact solid geometry (curves and surfaces), not triangles | Best for exchanging CAD between programs; some slicers import it and tessellate at slicing time |
| G-code | The instructions for one printer | Not a model: it is the result of slicing and is specific to a printer and filament |
Worked example: how fine should the STL be?
- A 10 mm radius hole is exported as a regular polygon of n sides. The largest error is the sagitta s = r (1 − cos(π ÷ n)).
- A coarse export with 48 sides (n = 48 around the full circle, so the half-angle is π ÷ 48): s = 10 × (1 − cos(π ÷ 48)) = 0.021 mm. With 24 sides s = 0.086 mm (the facets would show as a visible polygon).
- To keep the error at 0.01 mm (smaller than the printer can resolve) we need cos(π ÷ n) ≥ 1 − 0.01 ÷ 10 = 0.999, so n ≥ π ÷ arccos(0.999) = 70.2, say 71 sides: the error is then 0.010 mm.
- More triangles give a smoother file but a bigger one and slower slicing, and below the nozzle’s resolution (about 0.1 mm) there is no benefit: set the export tolerance to 0.01 to 0.05 mm.
- Staircase effect: a wall leaning 30° from vertical, printed in 0.20 mm layers, steps over by 0.115 mm each layer; the cusp depth measured square to the surface is about 0.100 mm. On a 60° slope it is 0.173 mm: shallow surfaces show the layers most, and the layer height, not the STL, limits the finish.
What the slicer does
The slicer cuts the model into horizontal layers and plans the nozzle path for each: the outer walls (perimeters), the infill inside, the solid top and bottom skins, supports for overhangs and a skirt, brim or raft for adhesion. For each move it computes how much plastic to extrude. The slicer also chooses speeds, fan, retraction and temperatures. Popular slicers (PrusaSlicer, OrcaSlicer, Cura, Bambu Studio and Simplify3D) share most settings; the next pages explain them.
Worked example: how many layers?
- A part 60 mm tall at 0.20 mm layers has 60 ÷ 0.20 = 300 layers. At 0.1 mm it has 600 layers and takes roughly twice as long; at 0.3 mm, 200 layers and roughly two thirds of the time.
- The slicer’s Z moves must land on whole layers, so choose a layer height that divides the part height: a 60 mm part prints exactly at 0.2 mm (300 layers), while 0.25 mm gives 240 layers; 61 mm at 0.2 mm is cut at 61 ÷ 0.2 = 305 layers (the first layer may be thicker, which changes the count).
G-code: what the printer reads
G-code is a plain text list of commands. A few lines look like this: G1 X50.0 Y20.0 E1.52 F3600 means “move in a line to X = 50, Y = 20 while extruding 1.52 mm of filament, at a feed of 3 600 mm/min (60 mm/s)”. M104 S210 sets the nozzle temperature to 210 °C, M140 S60 the bed to 60 °C, M106 S255 turns the fan to full, and G28 homes the axes. A slicer’s start and end G-code (set per printer) heats the machine, homes, purges a line and finishes; errors in it are a common cause of a bad first layer.
The extrusion value follows from geometry: for a line of width w and layer height h, the extruded filament length per millimeter of travel is w × h ÷ (π d² ÷ 4), with d = 1.75 mm: for 0.45 × 0.2 mm that is 0.037 mm of filament per mm of travel, so a 22 mm move uses 0.82 mm of filament.
When to print, and when not to
| Print it when… | Use something else when… |
|---|---|
| You need one to a few parts, or a fast iteration of a design | You need hundreds or thousands of identical parts (molding or machining is cheaper per part) |
| The shape is complex: internal channels, lattices, organic forms, integrated hinges | The part is a simple block, plate or round bar (machining or laser cutting is faster and stronger) |
| A jig, fixture, enclosure or mock-up does not need to be strong or hot | The part carries a safety-critical load, runs hot or sees chemicals, unless you have tested it |
| Tight tolerances are not essential, or you can finish critical features by machining | Tolerances are tighter than about ±0.1 to ±0.2 mm without post-machining |
| A custom, one-off or obsolete part is needed | A standard catalog part already exists at a lower cost |
A mixed approach is common: print the awkward housing, and machine or buy the bearings seats, shafts and fasteners. See Prototyping Techniques and CNC Machining.
Related
- 3D Printing and Additive Manufacturing: the overview of this guide.
- FDM Printer Hardware: the machine itself.
- Slicer Settings and Print Quality: the settings the slicer chooses.
- Resin and Powder Processes: resin and powder processes in more depth.
- Prototyping Techniques: choosing the process.
FAQ
Should I use STL or 3MF?
Use 3MF when your slicer and CAD program support it: it carries units and settings. STL is universal and still fine, as long as the export tolerance is fine enough and the scale is in millimeters.
Can I print directly from a CAD file?
Some slicers open STEP or the native CAD file and triangulate it at slicing time, which avoids a separate export step. The result is the same as exporting a fine STL.
Why does my printed hole come out too small?
Printed lines are rounded and pressed inwards, and small holes especially print 0.1 to 0.3 mm undersize. Make holes larger in the model, or drill them to size: see Strength, Accuracy and Fits.
Is metal printing possible at home?
Not practically. Metal powder machines are industrial, though some hobbyists print metal-filled filament and sinter it, or order parts from a service. Most makers print a pattern and cast or machine the metal.
References
- ISO/ASTM 52900, Additive manufacturing: general principles and terminology (seven process families).
- Gibson, I., Rosen, D. and Stucker, B., Additive Manufacturing Technologies, Springer.
- 3MF Consortium, 3D Manufacturing Format specification; slicer documentation (PrusaSlicer, Cura, OrcaSlicer).
Last reviewed: October 2026. Layer heights and build rates are typical: they vary with the machine and the material.