engineering-skills/additive-manufacturing/references/support-structures.md

Supports in AM — Technical Guide by Process

General Principle

Supports serve to:

1. Anchor the part to the build plate (prevent thermal distortions — critical in metal AM)
2. Support overhangs beyond the critical angle of the process
3. Dissipate heat during printing (especially LPBF)

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FDM/FFF — Polymer Supports

When they are needed

• Overhang angles > 45° from vertical
• Bridges (bridging) > 50–60mm (depends on material and cooling)
• Horizontal holes > ø5mm

FDM support types

Type	Material	Removal	Finish	Use
Normal (same material)	= part	Mechanical	High Ra at interface	Default, low cost
Soluble PVA support	PVA	Dissolution in water	Excellent	Complex geometries, internal features
Soluble HIPS support	HIPS	Dissolution in limonene	Excellent	Mainly for ABS
Soluble Breakaway support	Special (Ultimaker, Bambu)	Snap-off	Good	Moderate geometries

FDM support patterns

• Lines/Grid: Standard, easy to remove, adequate for most cases
• Tree supports (organic): Minimise contact with the part, excellent finish → recommended for aesthetic parts
• Custom supports (manual): For critical parts where the interface is not accessible

Critical FDM support parameters

Parameter	Typical value	Effect
Support Z distance	0.15–0.25mm	Higher → easier removal but worse finish
Support XY distance	0.5–1.0mm	Lateral distance from the part
Interface layers	3–5 layers	Layers between support and part — use different pattern (e.g. lines)
Support density	10–20%	Do not increase beyond this: unnecessary and makes removal harder
Support roof/floor layers	2–4	More layers → smoother surface under part

Orientation to minimise FDM supports

• Rotate the part to bring critical surfaces (aesthetics, tolerances) to the top (top surface = best quality)
• Exploit bridging: FDM can bridge linearly up to 50–80mm with good cooling — position horizontal holes on bridges

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SLA / DLP / MSLA — Resin Supports

Particularity: inverted printing

The part hangs from the build plate — peeling forces at each layer generate stresses. Supports must:

• Anchor the part to the build plate (or raft)
• Resist peeling forces (critical for flat geometries)

SLA support types

Type	Tip diameter	Use
Light	0.3–0.4mm	Aesthetic surfaces, fine detail
Medium	0.5–0.6mm	Standard
Heavy	0.8–1.0mm	Heavy parts, large surfaces

SLA rules

• Raft: Almost always necessary for medium/large parts (distributes peeling forces)
• Tilt angle: Tilting the part 15–30° drastically reduces supports and improves exposure uniformity
• Islands: Any surface disconnected from the main part requires support
• Touchpoint: Reduce touchpoint density on visible surfaces — prefer supports on hidden surfaces

Post-removal SLA

• Remove supports BEFORE post-curing if possible (uncured resin is more brittle → support breaks more easily)
• Exceptions: flexible resins → remove AFTER curing

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SLS / MJF — No Structural Supports

Why SLS/MJF do not require supports

The surrounding unsintered powder supports the part during the build. This is the main advantage of SLS/MJF over FDM/LPBF.

What still needs to be managed

• Powder escape holes: MANDATORY for closed cavities (≥ ø5mm, ideally 2 opposite holes to avoid pockets)
• Powder trapped in narrow channels: Internal channels < ø4mm can retain powder — design with exit ports or use ø≥5mm
• Packing density: The packing density in the build chamber affects distortions — consult the service provider

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LPBF / DMLS / SLM — Metal Supports

Specific functions for metal AM

1. Thermal anchoring: The part heats and cools cyclically — without adequate support it distorts or detaches from the build plate
2. Heat sink: Supports conduct heat towards the build plate (critical for alloys with high thermal conductivity such as AlSi10Mg)
3. Mechanical support: Overhangs > 45°

LPBF support types

Type	Structure	Removal	Use
Block support	Solid	Difficult, milling required	Very heavy parts, high heat
Contour support	Hollow shell	Medium difficulty	Standard
Tree/Branch support	Branched tree	Easier	Accessible aesthetic surfaces
Lattice support	Lattice	Easy (break-off)	Modern standard — recommended
Cone support	Conical	Easy	Single points, complex geometries

Critical LPBF support parameters

Parameter	Typical value	Importance
Top Z offset	-0.1 to +0.05mm	Critical: too much gap → detachment; too much overlap → irremovable support
Bottom Z offset	0.0–0.1mm	Interface with build plate
Tooth height (perforated)	0.5–1.0mm	Facilitates removal while maintaining anchoring
Perforated support	Yes for critical surfaces	Reduces marking on the surface
Lattice density	30–50%	Trade-off between heat dissipation and ease of removal
XY support offset	0.05–0.2mm	Gap between support and part — critical for removal

Orientation to minimise LPBF supports

• Main rule: Orient the build axis to minimise horizontal downward-facing surfaces
• Critical angles: < 30° from horizontal → always support; 30–45° → evaluate case by case
• Trade-off: Anti-support orientation may increase distortions or worsen metallurgy on critical surfaces

Strategy for critical surfaces (tolerances, Ra)

• Surfaces with tight tolerances (±0.05mm) → orient in the XY plane (not Z) AND plan for post-machining
• Sealing/mating surfaces → do not place supports on them — if unavoidable, use perforated supports + machining

Material-specific notes for LPBF supports

Alloy	Support criticality	Specific notes
AlSi10Mg	High (high conductivity, low melting point)	Dense supports mandatory; stress relief before removal
Ti-6Al-4V	Medium	Supports in same material; HT before removal
316L	Low-Medium	Relatively easier to manage
Inconel 718/625	High (high T, thermal gradients)	Very dense supports; significant distortions
17-4PH	Medium	Stress relief critical before removal

MANDATORY sequence for metal AM with supports

1. Print
2. Thermal stress relief (before removing from build plate and before supports)
3. Removal from build plate (EDM wire or saw)
4. Support removal (manual + tools + milling where necessary)
5. Heat treatment (if required — e.g. 17-4PH H900, IN718 aging)
6. HIP (if required)
7. Post-machining of critical surfaces
8. Inspection

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EBM — Lightweight Supports

• EBM operates in vacuum with powder pre-heating → thermal gradients much lower than LPBF
• Supports needed but less critical: Often only lightweight anchoring structures (mesh)
• Critical angle ~35° (better than LPBF due to lower thermal gradient)
• Support removal: mechanical, easier than LPBF

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Binder Jetting — No Supports (green state)

• The powder acts as support during the printing phase (like SLS)
• Watch out for sintering phase: The part may collapse if overhang geometries are excessive → plan ceramic setters or custom sintering supports
• Internal channels: verify they can be cleared after sintering

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Support Checklist — Pre-Build

• Are all overhangs beyond the critical angle of the process supported?
• Do critical surfaces (tolerances, Ra) avoid contact with supports, or is machining planned?
• For LPBF: is stress relief planned BEFORE support removal?
• For SLS/MJF: are powder escape holes present on all closed cavities?
• Is support removal accessible (physical access with tools)?
• Do supports not interfere with functional features (holes, sealing surfaces)?
• For complex parts: has a removability test been run in simulation (e.g. Magics)?