| name | am-quality-control |
| description | AM quality control — in-process monitoring (melt pool, layer), CT scanning, porosity analysis, NDT for AM, dimensional accuracy, ASTM F3049/F3122/F3184, qualification strategy. |
| metadata | {"priority":7,"promptSignals":{"phrases":["AM quality control","additive manufacturing quality","CT scan AM","AM inspection","LPBF monitoring","metal AM defects","AM qualification"],"minScore":3}} |
AM Quality Control — Complete Skill
Common AM Defects
| Defect | Cause | Effect | Detection |
|---|
| Lack-of-fusion (LOF) | Low energy density; poor overlap | Fatigue crack initiation | CT, UT |
| Keyhole porosity | Excessive energy; deep melt pool | Fatigue crack initiation | CT |
| Gas porosity | Entrapped Ar/powder gas | Minor mechanical degradation | CT |
| Balling | Low laser power; oxidation | Rough surface; fusion failure | Visual, CT |
| Cracking (hot/cold) | Residual stress; low ductility | Structural failure | UT, dye penetrant |
| Delamination | Layer adhesion failure | Local weakness | UT, CT |
| Warping/distortion | Thermal gradients, residual stress | Dimensional error | CMM, 3D scan |
| Satellite particles | Spattering; un-melted powder | Poor surface; inclusions | SEM, CT |
In-Process Monitoring
Melt Pool Monitoring (LPBF)
Photodiode monitoring:
High-speed photodiode (1–10 kHz); measures melt pool emission intensity
Anomaly detection: sudden intensity drop → LOF; excess → keyhole
High-speed camera (coaxial):
Camera coaxial with laser; images melt pool shape and size
Normal: oval pool (1.0 × 1.5× scan direction); deviation → defect signature
Pyrometry:
Two-wavelength pyrometer; melt pool temperature
T_normal ≈ T_liquidus to 1.3 × T_liquidus (material-dependent)
Layer-wise imaging:
High-resolution camera after each layer; compares to CAD; detects recoater failures, cracks, surface anomalies
Resolution: 10–50 μm per pixel; image correlation detects ≥ 100 μm anomalies
OES (Optical Emission Spectroscopy)
Monitors plasma plume during DED; detects contamination and alloy composition variation
SLM Solutions EOS monitoring (proprietary)
Real-time layer review software; flags anomalous regions for post-build CT inspection
Post-Build Inspection
X-Ray Computed Tomography (CT)
Resolution: voxel size 5–100 μm depending on part size and detector
Detection limit: pore diameter ≥ 2× voxel size; typically ≥ 50–100 μm
CT workflow:
- Scan parameters: kV = 100–450 kV; tube current 0.1–3 mA; rotation 360°; 1000–3000 projections
- Reconstruction: filtered backprojection or iterative
- Porosity analysis: threshold gray level; identify void voxels
- Output: pore volume fraction [%], pore size distribution, location relative to surface, maximum pore size [μm]
Porosity measurement (ASTM F3001):
Report: total volume porosity [%], maximum defect size [mm], spatial distribution map
Accept/reject: e.g., < 0.1% total porosity; no single defect > 0.25 mm for aerospace
Limitations:
CT of dense metals (steel, Inconel): beam hardening artifact for t > 50 mm
Wall limitation: X-ray penetration limits part thickness
Ultrasonic Testing (UT) for AM
Phased array UT (PAUT):
Effective for planar defects (LOF, delamination); difficult for rough AM surfaces
Surface preparation: machine or polish surface to Ra < 2 μm for coupling
Detection: LOF > 1–2 mm planar; calibrate with reference standard with known holes
Focused beam UT:
5–15 MHz; scanning; detects pores ≥ 0.5 mm
Limitation: AS-BUILT rough surface prevents adequate coupling; machine surface first
Metallographic Analysis
Cross-section preparation:
- Section at representative location; mount in epoxy
- Grind and polish to 1 μm; etch (Kroll's reagent for Ti; 10% Nital for steel)
- Microscopy: optical (10–500×); SEM (1000–10,000×)
- Image analysis (ImageJ/Clemex): measure porosity area%, grain size, microstructure phases
Archimedes method (bulk porosity):
ρ_actual = m_air / (m_air - m_water) × ρ_water
% porosity = (1 - ρ_actual/ρ_theoretical) × 100
Fast, low cost; measures average; cannot locate defects
Dimensional Verification
CMM (Coordinate Measuring Machine):
Tactile probing; accuracy ±2–5 μm; limited for complex internal features
Industrial 3D scanning (structured light/laser):
Resolution 0.02–0.1 mm; full surface comparison to CAD; GD&T verification
Generate color map: + deviation (overbuilt) and – deviation (underbuilt)
As-built dimensional accuracy (LPBF):
Typical: ±0.1–0.2 mm for well-calibrated machine
Critical features: design with +0.1 mm to +0.2 mm compensation per axis
ASTM Standards for AM Quality
| Standard | Scope |
|---|
| ASTM F3049 | Characterizing metal feedstock; chemical composition, morphology |
| ASTM F3122 | Evaluating mechanical properties of metal AM parts |
| ASTM F3184 | Qualification/certification framework for AM parts |
| ASTM F3001 | CT scanning for AM |
| ASTM E3166 | AM defect characterization by X-ray CT |
| ISO/ASTM 52900 | AM terminology |
| ASTM F2971 | Reporting AM part properties |
Qualification Framework
Parts qualification tiers (general approach):
Tier 1 (non-critical): process qualification only; tensile coupons per build
Tier 2 (moderate): process + part-level tensile/NDT; first article test
Tier 3 (critical/flight): full process qualification + 100% CT + destructive test articles + lot acceptance testing
Process qualification:
Fix all parameters: machine, material lot, parameters, post-processing
Build 30+ tensile specimens; demonstrate σ_UTS, σ_YS, A% meet design allowables (B-basis)
Certify machine to same parameters → part released
FAA AC 33.15-2: AM qualification path for aircraft engine parts (LPBF Inconel 718)
Requires: process control plan, NDT plan, periodic verification, audit trail
SPC (Statistical Process Control) for AM
Monitor per build:
- Part mass vs. nominal (±1%)
- Density by Archimedes vs. accept limit
- Melt pool signature average per layer
Control charts (X-bar, R charts):
Monitor: mass, hardness, tensile strength per production run
UCL/LCL = μ ± 3σ from baseline characterization
Out-of-control → pause production → root cause + corrective action
Output
Provide: defect detection method (CT/UT/metallography), CT scan parameters (kV, resolution/voxel size), accept/reject porosity criteria (% and max defect size [mm]), dimensional inspection method (CMM/3D scan), GD&T tolerance comparison to CAD, qualification tier (1/2/3), process qualification test matrix (specimen count, properties), in-process monitoring strategy (melt pool/layer imaging), applicable standard (ASTM F3049/F3122/F3184), and SPC monitoring parameters.
