additive-manufacturing

name	additive-manufacturing
description	Additive manufacturing (3D printing) — process selection (FDM/SLA/SLS/DMLS/LPBF), design for AM (DfAM), topology optimization, support structures, material properties, post-processing, tolerances.
metadata	{"priority":7,"promptSignals":{"phrases":["additive manufacturing","3D printing","FDM","SLS","DMLS","LPBF","design for AM","DfAM","topology optimization","metal printing"],"minScore":3}}

Additive Manufacturing — Complete Skill

Process Comparison

Process	Material	Layer [μm]	Tolerance	Surface Ra	Strength	Cost
FDM (Fused Deposition)	Thermoplastic (PLA/ABS/PETG/Nylon/PEEK)	100-300	±0.3-1mm	10-30 μm	60-80% of bulk	Low
SLA (Stereolithography)	Photopolymer resin	25-100	±0.1-0.2mm	1-5 μm	80-90%	Medium
SLS (Selective Laser Sintering)	Nylon PA12, PA11, TPU	80-120	±0.2-0.3mm	8-15 μm	85-95%	Medium
DMLS/LPBF (Laser PBF)	Ti, Al, Inconel, SS, CoCr	20-60	±0.05-0.15mm	6-15 μm	95-110% bulk	High
EBM (Electron Beam PBF)	Ti6Al4V, CoCr	50-100	±0.1-0.3mm	20-35 μm	~bulk Ti	High
DED (Directed Energy Dep.)	Metals, alloys	200-1000	±0.5-1mm	20-50 μm	~bulk	Medium
Binder Jetting	Metals, sand, ceramics	50-200	±0.1-0.3mm	5-10 μm	90-95% (sintered)	Medium
Material Jetting (PolyJet)	Photopolymer, wax	16-30	±0.05mm	1-3 μm	Moderate	High

Design for AM (DfAM) Rules

Overhangs and Support Structures

Self-supporting angles: FDM: ≤45° from horizontal (some machines to 60° with cooling) LPBF/DMLS: ≤45° from horizontal (rule of thumb); depends on material Below threshold → requires support structures

Minimize supports (expensive to remove, leaves marks):

• Orient part to minimize overhanging surfaces
• Self-supporting features: domes (hemisphere), diamond/teardrop holes (vs. circular)
• Teardrop hole: point at top, circular at bottom → self-supporting

Minimum Feature Sizes

FDM: wall min = 0.4mm (1 nozzle width); hole min = 2mm SLS: wall min = 0.8-1.5mm; hole min = 1.5mm LPBF: wall min = 0.2-0.4mm; hole min = 0.5mm; lattice struts min = 0.3mm SLA: wall min = 0.3mm; feature min = 0.1mm

Holes and Channels

Horizontal holes (FDM): require supports below; use diamond/teardrop profile Vertical holes: accurate, no support needed Internal channels: use lattice support (LPBF) or design with self-supporting cross-section

Fit and Clearance

Clearance for moving parts: FDM: 0.3-0.5mm clearance between mating parts SLS: 0.3-0.5mm LPBF: 0.1-0.2mm (more accurate)

Pin holes: typically under-size by 0.1-0.2mm → drill/ream to final size after printing

Wall Thickness

FDM: min 0.8-1.5mm (2-4 perimeters) SLS: min 1mm; recommended 2-3mm for structural LPBF: min 0.4-1mm; thin walls risk distortion No maximum (unlike injection molding) — but thin = risky, thick = expensive

Text and Surface Features

Embossed text: min 0.5mm height (FDM), 0.3mm (SLA) Engraved: min 0.5mm wide, 0.4mm deep Mark part ID in XY plane (not Z) for best resolution

Topology Optimization

SIMP Method (Solid Isotropic Material with Penalization)

Minimize: C = {U}ᵀ[K]{U} (compliance = strain energy) Subject to: V_material ≤ V_frac × V_total (volume fraction constraint)

Density ρ_e ∈ [0,1] per element (0=void, 1=solid) Penalized stiffness: E_e = ρ_e^p × E₀ (p=3 pushes toward 0/1 distribution) Iterate: sensitivity-based update → grey elements → solid/void

Tools: ANSYS Topology Optimization, Altair OptiStruct, nTopology, Simulia TOSCA SolidWorks Topology Study (easy entry)

Design Space and Load Cases

Define: design domain, keep-out regions (holes for fasteners, interfaces) Multiple load cases: minimize compliance for all loads simultaneously Manufacturing constraints: min member size, symmetry, draw direction (avoids unmakeable geometry)

Interpretation and Smoothing

Raw TO result: jagged, impossible to manufacture → smooth and interpret Smoothing: isosurface extraction, remesh, B-spline fit Validate: re-run FEA on smoothed geometry → check stress ≤ allowable

Material Properties — AM vs. Wrought

Metal AM (LPBF)

Generally anisotropic: Z-direction (build direction) weaker Ti-6Al-4V LPBF (HIP): Sy=830 MPa, Su=900 MPa, El=12% (equivalent to wrought after HIP) Ti-6Al-4V LPBF (no HIP): Sy=960 MPa, Su=1050 MPa, El=8% (higher strength, lower ductility) Inconel 625: Sy=620 MPa, Su=890 MPa (similar to wrought) 316L SS: Sy=480 MPa, Su=680 MPa

Fatigue (LPBF): lower than wrought unless:

• Post-machined surface (eliminates surface defects)
• HIP'd (closes internal pores, gas bubbles)
• Shot peened (compressive residual stress) Without post-processing: AM fatigue ~60-80% of wrought

Polymer AM (FDM)

PLA: Sy≈65 MPa, E≈3.5 GPa (brittle, poor temperature resistance) PETG: Sy≈50 MPa, E≈2.0 GPa (tougher than PLA, chemical resistant) ABS: Sy≈40 MPa, E≈2.1 GPa (common, warps) Nylon PA12: Sy≈48 MPa, E≈1.6 GPa (flexible, wear-resistant) PEEK: Sy≈100 MPa, E≈4.0 GPa (high temperature, chemical resistance, expensive) Carbon-fiber filled: 2-4× stiffer, often printed with continuous fiber (Markforged)

Post-Processing

Metal AM

• Support removal: wire EDM, milling
• HIP (Hot Isostatic Pressing): 100-200 MPa inert gas + high temp → close pores → improve fatigue
• Stress relief / solution anneal: reduce residual stress from rapid cooling
• Machining: critical surfaces (bores, threads, sealing faces) always CNC machined
• Surface finish: bead blast, electropolish, hand polish
• NDT: CT scan (detect internal porosity), PAUT for structural parts

Polymer FDM

• Support removal
• Sanding, priming, painting
• Acetone smoothing (ABS only)
• Epoxy coating (strengthen/seal)

Design Rules Summary

✓ Orient critical surfaces in XY plane ✓ Avoid horizontal overhangs >45° without supports ✓ Integrate complexity: hollow sections, internal channels, organic topology ✓ Lattice structures: reduce weight, control stiffness ✗ Don't directly copy casting/forging/machining designs — redesign for AM ✗ Don't use AM if wrought part is cheaper and same weight (AM advantage is complexity)

Cost Drivers

Metal LPBF: material cost ($50-500/kg powder), machine time (€200-1000/hr), post-processing Break-even vs. machining: complex parts with internal features, <50 qty Break-even vs. casting: complex, low volume (<500 parts)

Output

Provide: process recommendation for application, DfAM rule checklist, orientation recommendation, support strategy, post-processing steps, expected mechanical properties (Sy, Su, El), tolerance achievable [mm].