If you need to see a part cross-section with µm resolution, industrial CT is unbeatable. If you need to inspect 1,000 parts per hour, CT fails on physics and economics. Acoustics fills that role – generous compromises on resolution, but orders of magnitude faster and cheaper.
The methods in brief
Industrial CT/X-ray: X-ray tube projects the part from many angles, 3D volume reconstruction. Resolution down to ~5 µm. Acquisition: 1–30 min per part.
Acoustic resonance: excitation, natural frequencies, comparison. 0.2–2 s per part. Holistic assessment.
Comparison matrix
| Criterion | CT/X-ray | Acoustic resonance |
|---|---|---|
| Speed | 1–30 min | 0.2–2 s |
| Detail resolution | ★★★★★ (≥ 5 µm) | ★★☆☆☆ (integral) |
| 3D localisation | mm precision | not possible |
| 100 % capable | low volumes only | standard |
| Investment | 500 k€ – 3 M€ | 30–250 k€ |
| Radiation safety | full shielding mandatory | none required |
| Cost per test | 5–80 € | 0.02–0.15 € |
| Inline-capable | special cases only | standard |
When CT pays off
- First-article inspection of new parts.
- Complaint / failure analysis of individual parts.
- Safety-critical low-volume parts (aerospace).
- When defect position matters for repair or forensics.
When acoustics pays off
- Inline 100 % in series.
- "Does it work?" matters more than "where is the flaw?".
- Radiation safety / permits / staffing too costly.
- Real-time inspection feeding back into process control.
Example: brake discs
1.2 M discs/year, 100 % crack inspection required.
- CT only: 90 s/part × 5 €/test = 6 M€/year and 30 CT systems.
- Acoustic only: 0.8 s/part × 0.06 €/test = 72 k€/year, 1 inline system.
- Hybrid: 100 % acoustic + 1 % CT verification = 132 k€/year, high safety + documented sample.
