Brass (Cu‑Zn alloy) absorbs 2–3× more energy than pure copper at 1070 nm (≈12–18% vs. ≈5–7% at room temperature) because zinc has lower reflectivity and higher absorptivity. Consequently, a 2 kW fiber laser can cut 2 mm brass cleanly at 4–5 m/min with 15 bar nitrogen, while the same laser struggles to cut 2 mm pure copper (requires 4 kW, 1–2 m/min, 20 bar nitrogen). For both materials, high‑purity nitrogen (Grade 4.5), negative focus, and clean nozzles are essential. However, brass cutting produces zinc oxide fumes (hazardous), requires fume extraction, and may cause edge discoloration (yellow tint) if gas purity is marginal. This article compares absorption mechanisms, parameter tables, and practical process adjustments for cutting brass (C26000, C28000) and pure copper (C11000) on fiber lasers.
Brass and pure copper are both high‑copper alloys, but their laser cutting behaviors diverge significantly due to the presence of zinc in brass. Understanding these differences allows fabricators to optimize parameters, avoid common defects, and select the right laser power for each material.
Absorption Rate Difference – The Zinc Effect
At room temperature, the reflectivity of copper and brass at 1070 nm:
| Material | Composition | Absorption (%) | Reflectivity (%) | Reason |
|---|---|---|---|---|
| Pure copper (C11000) | ≥99.9% Cu | 5–7 | 93–95 | High free electron density |
| Brass C26000 (cartridge) | 70% Cu, 30% Zn | 12–15 | 85–88 | Zn disrupts electron band structure |
| Brass C28000 (Muntz) | 60% Cu, 40% Zn | 15–18 | 82–85 | Higher Zn content increases absorption |
| Zinc (pure) | 100% Zn | 20–25 | 75–80 | Baseline for comparison |
Mechanism: Zinc has a lower reflectivity and higher absorptivity at near‑IR wavelengths. As zinc content increases, the alloy’s absorption rises nearly linearly. For a 30% Zn brass, absorption ≈ (0.07 × 0.7) + (0.23 × 0.3) = 0.049 + 0.069 = 0.118 (12%). This matches measured values.
Practical implication: Cutting brass requires 30–50% less laser power than pure copper for the same thickness. A 2 kW laser suitable for 2 mm brass would need 4 kW for 2 mm copper.
Temperature‑Dependent Absorption – Both Improve with Heat
As the material heats, absorption increases for both brass and copper, but brass reaches high absorption at a lower temperature because zinc’s absorption rises faster.
| Temperature | Pure copper absorption (%) | Brass (70/30) absorption (%) |
|---|---|---|
| 25°C | 6 | 14 |
| 200°C | 10 | 20 |
| 400°C | 18 | 28 |
| 600°C | 25 | 35 |
| Melting point (1083°C / 900°C) | 35–40 | 45–50 |
Once a keyhole forms, both materials achieve >90% effective absorption. The challenge is initiating the keyhole – brass is much easier.
Parameter Comparison Table (Fiber Laser, Nitrogen Assist)
The following table gives starting parameters for pure copper (C11000) and cartridge brass (C26000) using Grade 4.5 nitrogen (99.995%), clean centered nozzle, standoff 1 mm, focus offset = –0.5× thickness.
| Thickness (mm) | Material | Laser power (kW) | Speed (m/min) | N₂ pressure (bar) | Nozzle (mm) | Edge quality |
|---|---|---|---|---|---|---|
| 1 | Brass | 1.0 | 7–8 | 10 | 1.0 | Silver |
| 1 | Copper | 2.0 | 3–4 | 12 | 1.0 | Silver (marginal) |
| 2 | Brass | 2.0 | 4–5 | 12–15 | 1.2 | Silver |
| 2 | Copper | 4.0 | 1.5–2.5 | 15–18 | 1.2 | Silver (needs 4 kW) |
| 3 | Brass | 2.5 | 2.5–3.5 | 15 | 1.5 | Silver to light straw |
| 3 | Copper | 6.0 | 1.0–1.5 | 18–20 | 1.5 | Silver (with 6 kW) |
| 4 | Brass | 4.0 | 2.0–2.5 | 18 | 1.8 | Light straw |
| 4 | Copper | 8.0 | 0.8–1.2 | 20–22 | 1.8 | Light straw (difficult) |
| 5 | Brass | 5.0 | 1.5–2.0 | 20 | 2.0 | Straw (acceptable) |
| 5 | Copper | Not recommended | – | – | – | Very difficult |
Observation: For the same thickness, cutting brass is 2–3× faster than cutting copper and requires 2× less power. Copper cutting quickly becomes impractical above 3 mm without very high power (≥6 kW).
Cutting Brass – Specific Considerations
1 Fume Hazard – Zinc Oxide
When brass is laser cut, zinc vaporizes (boiling point 907°C) and oxidizes in air to form zinc oxide (ZnO) fume. ZnO is hazardous to inhale (metal fume fever). Mandatory:
- Local exhaust ventilation (LEV) with HEPA filter.
- Enclose the cutting area.
- Regular air monitoring if cutting brass >10 hours/week.
2 Edge Discoloration – Yellow Tint
Brass cuts often exhibit a faint yellow tint on the edge, especially if gas purity is <99.995%. This is due to zinc oxide (yellow) and is not a defect if it does not affect function. However, for cosmetic parts, use Grade 5.0 nitrogen (99.999%) and increase the pressure by 2 bar to reduce oxidation.
3 Nozzle Contamination – Zinc Spatter
Zinc has a low boiling point and tends to vaporize and recondense on the nozzle, causing rapid spatter buildup. Clean the nozzle every 1–2 hours when cutting brass. Use a ceramic‑coated nozzle to reduce adhesion.
4 Back‑Reflection – Lower Risk than Copper
Brass’s higher absorption means less reflected power. A standard fiber laser with basic back‑reflection protection (not necessarily a heavy‑duty isolator) is usually sufficient. However, for very thick brass (>5 mm), monitoring is still advisable.
Cutting Pure Copper – Special Challenges
1 Power and Speed – The Limits
Copper requires very high power density. For 2 mm copper, a 4 kW laser is the practical minimum. For 3 mm, 6 kW. For 4 mm, 8 kW, the quality is marginal.
Why not use even higher power? – 12 kW could cut 4–6 mm copper, but the capital cost is very high. Many fabricators use alternative processes (plasma, waterjet) for thick copper.
2 Piercing – Step Piercing Required
Copper’s high reflectivity makes piercing difficult. Use a step‑piercing sequence (as described in the previous article: laser cutting pure copper) to avoid blow‑back and lens contamination.
3 Nozzle Life – Very Short
Copper spatter erodes nozzles quickly. Replace the nozzle every 2–4 hours of cutting. Use a cross‑jet to protect the lens.
4 Back‑Reflection – High Risk
Pure copper cutting requires a laser with a heavy‑duty Faraday isolator and real‑time back‑reflection monitoring. Without it, the laser source can be destroyed instantly.
Absorption Rate Table – Detailed Values
| Material | Zn % | Absorption at 25°C (%) | Absorption at 600°C (%) | Required power for 2 mm (kW) | Speed (m/min) |
|---|---|---|---|---|---|
| Pure copper | 0 | 5–7 | 25 | 4 | 1.5–2.5 |
| Red brass (C23000) | 15 | 10–12 | 30 | 2.5 | 3–4 |
| Cartridge brass (C26000) | 30 | 13–15 | 35 | 2.0 | 4–5 |
| Muntz metal (C28000) | 40 | 15–18 | 40 | 1.5–2.0 | 4.5–6 |
| Zinc | 100 | 20–25 | 50 | 1.0 | 6–8 |
These values are for fiber lasers (1070 nm). Green or blue lasers would have much higher absorption (40–70%) for copper.
Process Optimization by Material
| Parameter | Brass | Copper |
|---|---|---|
| Focus offset | –0.5× thickness | –1.0× thickness (more negative) |
| Gas purity | Grade 4.5 (≥99.995%) | Grade 4.5 (≥99.995%) |
| Gas pressure | 12–18 bar | 15–22 bar |
| Nozzle cleaning interval | Every 1–2 hours | Every 30–60 minutes |
| Piercing | 2‑step (30 ms total) | 4‑step (150 ms total) |
| Back‑reflection risk | Low | High |
Troubleshooting – Differences in Defects
| Defect | Brass | Copper | Correction (common) |
|---|---|---|---|
| Heavy dross | Pressure too low | Pressure too low | Increase pressure by 2–4 bar |
| Rough, irregular edge | Speed too high | Focus too high | Reduce speed; lower focus (more negative) |
| Yellow discoloration | Zinc oxide (normal faint) | Oxygen contamination | For brass, acceptable unless severe; for copper, increase purity |
| Blue edge | Turbulence or off‑center nozzle | Same | Center nozzle; reduce pressure by 2 bar |
| No penetration | Insufficient power | Very common | Increase power or reduce speed; for copper, you may need a higher-power laser |
| Increase power or reduce speed; for copper, you may need higher power laser | Zinc recondensation | Copper blow‑back | Clean frequently; use cross‑jet |
Cost and Productivity – Brass vs. Copper
For a 2 mm sheet, cutting brass is much more economical:
| Metric | Brass (2 mm) | Copper (2 mm) |
|---|---|---|
| Required laser power | 2 kW | 4 kW |
| Cutting speed (m/min) | 4.5 | 2.0 |
| Gas consumption (L/min, 15 bar) | ≈120 | ≈150 |
| Approximate cost per meter | $0.12 | $0.45 |
Copper cutting cost is 3–4× higher due to slower speed, higher power consumption, and more frequent nozzle changes.
Conclusion
Brass and pure copper require significantly different laser cutting parameters because of the zinc content in brass, which increases absorption from 5–7% (copper) to 12–18% (brass). Consequently, brass cuts at 2–3× the speed of copper with the same laser power, and brass can be cut with lower‑power lasers (2 kW up to 3 mm, 4 kW up to 5 mm). Copper cutting demands high power (≥4 kW for 2 mm, ≥8 kW for 4 mm), strict back‑reflection protection, and slower speeds.
Operators should treat brass and copper as distinct materials, not interchangeable. Use the parameter tables in this article as a starting point, then fine‑tune speed and pressure based on edge color and dross. For brass, manage zinc oxide fumes with proper extraction. For copper, monitor back‑reflection and replace nozzles frequently.
Read More: Absorption Rate Variations of Brass and Pure Copper in Fiber Laser Cutting
Frequently Asked Questions
Q: Can I cut brass with a laser that does not have back‑reflection protection?
A: Yes, brass’s higher absorption results in lower reflected power. Most standard fiber lasers with basic protection can cut brass safely. However, thick brass (>5 mm) may still generate significant reflection – check your laser’s specifications.
Q: Why does my brass cut have a white powdery residue?
A: That is zinc oxide (ZnO). It is normal for brass cutting. Wipe off with a dry cloth. If excessive, increase nitrogen pressure or use higher purity gas.
Q: Can I use oxygen to cut brass for faster speed?
A: Oxygen increases cutting speed but produces a dark, oxidized edge and may create hazardous zinc oxide fume. Not recommended for cosmetic or electrical parts.
Q: What is the maximum thickness of brass that a 2 kW laser can cut?
A: Approximately 4 mm with nitrogen, at 0.8–1.2 m/min, with a light straw edge. For a silver edge, limit to 3 mm. For 6 mm, 4 kW is recommended.
Q: How do I know if my copper cut edge will be conductive enough for electrical busbars?
A: Silver edge indicates minimal oxide – conductivity remains >90% IACS. If the edge is blue or black, oxide acts as an insulator; grind off the edge. Always verify with a conductivity meter.
References
- Yihai Laser Cutting Machine Operation Manual. Section 5.1.4: Cutting auxiliary gas – purity and pressure. (Company internal document)
- IPG Photonics. (2021). Fiber Laser Cutting of Copper and Brass Alloys. IPG Application Note AN‑CU‑2021.
- Laser Institute of America. (2020). Absorption Coefficients of Metals at 1 µm Wavelength. LIA Technical Guide TG‑ABS‑2020.
- ASTM B36/B36M. Standard Specification for Brass Plate, Sheet, Strip, and Rolled Bar.
- Adams, S. M. (2005). Sheet Metal Bend Allowance. KETIV Virtual Academy.
- ISO 14175:2008. Welding consumables – Gases and gas mixtures for fusion welding and allied processes.
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