Additive Manufacturing
Additive manufacturing builds parts layer by layer from digital models. Learn the seven ISO/ASTM process families, metal powder-bed fusion, DED and binder jetting, energy density, supports, post-processing and design for AM.
Instead of removing material, additive manufacturing (AM) adds it only where needed. It builds complex internal channels, lattices and organic shapes impossible to machine or cast — rocket engine injectors, lightweight brackets, custom implants, conformal-cooled moulds.
Industrial AM is a serious production technology, but it has its own physics, defects and design rules.
An analogy
Building a loaf of bread slice by slice from the bottom up — each slice exactly the right shape, so any internal cavity is possible.
The seven process families (ISO/ASTM 52900)
Each builds layers differently.
- Material extrusion (FDM/FFF): melted filament through a nozzle.
- Vat photopolymerisation (SLA/DLP): UV light cures liquid resin.
- Powder bed fusion (SLS, SLM/LPBF, EBM): laser/electron beam melts powder.
- Material jetting: droplets of photopolymer (multi-colour, multi-material).
- Binder jetting: glue binds powder; metal parts are then sintered.
- Directed energy deposition (DED, WAAM): wire/powder melted as it's deposited — large parts and repair.
- Sheet lamination: bonded or ultrasonically welded sheets.
Metal powder-bed fusion
A laser scans each layer of 20–60 µm powder in inert gas. Parameters (power, speed, hatch, layer) set energy density: too low leaves lack-of-fusion pores, too high causes keyhole pores and spatter. Parts are stress-relieved, removed from the plate, supports cut off, often HIPed and machined.
Design for AM
Exploit topology optimisation and lattices, consolidate assemblies into one part, add conformal channels. Respect limits: overhangs below ~45° need supports, minimum wall and hole sizes, powder removal paths, and anisotropy (weaker in build direction for many processes).
Qualification and economics
Residual stresses, distortion, porosity and surface roughness must be controlled; aerospace and medical parts need material and process qualification, in-situ monitoring (melt-pool cameras) and CT inspection. AM wins for low volumes, complexity and performance; conventional processes still win for simple, high-volume parts.
Formulas
- Energy density (PBF):
E_v = P / (v · h · t) - Layer count:
n = part height / layer thickness - Build rate (PBF):
Ṽ ≈ v · h · t (per laser)
Worked example: Energy density
Given: P = 200 W, v = 1000 mm/s; h = 0.1 mm, t = 0.03 mm
Find: E_v.
- E_v = 200/(1000 × 0.1 × 0.03) = 66.7 J/mm³
Answer: 66.7 J/mm³ (typical for 316L/AlSi10Mg windows)
Worked example: Build height
Given: Part 90 mm tall; Layer 30 µm, recoat 8 s, scan 25 s per layer average
Find: Layers and build time.
- n = 90/0.03 = 3000 layers
- t = 3000 × 33 s = 99 000 s ≈ 27.5 h
Answer: 3000 layers, ≈ 27.5 h
Common mistakes
- Wrong: Printing a design meant for machining unchanged. — Right: Redesign for AM: consolidate parts, optimise topology, orient for minimal supports.
- Wrong: Assuming as-built parts are finished. — Right: Plan stress relief, support removal, HIP, machining of interfaces and inspection.
Applications
- Aerospace & space: GE fuel nozzles, rocket combustion chambers, lightweight brackets.
- Medical: Patient-specific titanium implants with porous bone-ingrowth lattices.
- Tooling: Injection moulds with conformal cooling cutting cycle times 20–40 %.
Key takeaways
- Seven ISO/ASTM families; choose by material, size, detail and volume.
- LPBF quality depends on E_v = P/(v·h·t).
- Design for AM: consolidate, optimise, orient, minimise supports.
- Post-processing and qualification are part of the process.
Going further
- HIP: Hot isostatic pressing closes internal porosity, greatly improving fatigue life of AM metal parts.
- In-situ monitoring: Melt-pool pyrometry and layer imaging with ML detect defects during the build.
- Multi-laser & large-format: Machines with 4–12 lasers and metre-scale build volumes are pushing AM into series production.