Views: 118 Author: DR.LIU XIANG Publish Time: 2026-04-29 Origin: Site
Bottom dross — the resolidified metal burr adhering to the lower edge of a laser‑cut part — is the most frequent quality defect in laser cutting of carbon steel, stainless steel, and aluminum. It accounts for more than 60% of rework requests in many job shops. Dross is not a random defect; it is a direct symptom of incorrect energy balance, gas dynamics, or material interaction. Every dross type points to a specific parameter error. Fixing dross requires identifying which of the five primary causes is active: cutting speed too high or too low, assist gas pressure incorrect, focus position offset, gas purity insufficient, or nozzle condition degraded.
This article provides a diagnostic decision tree based on dross appearance (drop‑like, continuous strip, hard adherent, or one‑sided spiking). For each cause, it gives quantitative parameter adjustments and references to the Yihai laser cutting manual’s defect‑solution tables. A step‑by‑step troubleshooting protocol is included, along with a preventive maintenance checklist to keep dross from returning.
Before changing any parameter, examine the dross with a 10× magnifier and note its shape, location, and adhesion. The Yihai manual (Section 5.1.6) distinguishes several dross types for carbon steel cut with oxygen:
Dross appearance | Yihai manual description | Primary cause | Likely parameter error |
|---|---|---|---|
Drop‑like, small, easily removed | “The burrs on the bottom surface are similar to slag, in drops, and easy to remove.” | Speed too high, low pressure, focus too high | Speed > optimal, gas pressure < recommended, focus above surface |
Continuous metal burr, removable as a whole | “A series of metal burrs can be removed as a whole.” | Focus too high | Focus position positive (above surface) |
Hard, adherent burr, difficult to remove | “The metal burrs on the bottom are difficult to remove.” | Speed too high + low pressure + gas impurities + focus too high | Multiple combined errors |
Spikes on one side only | “There are only spikes on one side.” | Nozzle not centered or damaged | Coaxiality error |
Very fine, hair‑like dross | Not explicitly named | Focus too high (slightly) or nozzle standoff too large | Focus just above the surface |
Large globules, almost welding spatter | “The material is discharged from the top.” | Power too low, speed too high (severe) | Insufficient energy; the melt was not ejected |
For stainless steel cut with nitrogen, dross tends to be finer and more adherent, often accompanied by blue or gray discoloration. For aluminum, dross is often a stringy, silvery residue caused by the high viscosity of molten aluminum.
Speed errors account for approximately 40% of dross problems.
Speed too high: The laser does not have enough time to penetrate fully, or the gas jet outruns the melt. Dross appears as small, easily removable drops. The striations on the cut edge will show a pronounced backward drag (curved lines). Remedy: reduce speed by 10–15%. Use the spark method: if sparks trail backward (away from the cutting direction), reduce speed.
Speed too low: The material overheats, the kerf widens, and the molten pool becomes too large for the gas to eject. Dross appears as heavy, globular beads that are difficult to remove. The cut edge may have a melted, washed appearance. Remedy: increase speed by 10–20%.
The optimal speed window narrows with increasing thickness. For 10 mm carbon steel, the window is ±8%. For 20 mm, it is ±5%. A speed ramp test (cutting lines at 0.1 m/min increments) will identify the exact maximum speed with zero dross.
Gas pressure directly affects the ejection force. Too low and the melt stays in the kerf; too high and turbulence entrains air, causing irregular oxidation and dross.
Low pressure (most common): Dross appears as drop‑like or hard adherent burrs. The cut may have a rough, oxidized appearance. Remedy: increase pressure by 2–4 bar. For oxygen cutting of carbon steel, the typical pressure is 6–12 bar, depending on thickness. For nitrogen cutting of stainless steel, 12–20 bar.
High pressure: Dross may be absent, but the cut edge can be rough, striated, or have a “washboard” pattern. Remedy: Reduce pressure by 2–3 bar until the cut smooths out.
The Yihai manual notes that for carbon steel, “when the air flow is too large, the cutting surface is relatively coarse, and the seam is wide.” This is often mistaken for a speed error – check the pressure first.
Focus position determines the energy density at the bottom of the kerf. For oxygen cutting of carbon steel, the focus is typically 0.5–1.5 mm below the surface (negative focus). For nitrogen cutting of stainless steel, the focus is also slightly negative.
Focus too high (positive): The beam diverges before reaching the bottom, so the bottom kerf is narrow, and the melt is not fully fluid. Dross appears as a continuous metal strip that can be peeled off as one piece. Remedy: lower focus (more negative) by 0.5–1.0 mm.
Focus too low (excessively negative): The spot at the top is large, reducing power density. The top edge may be rounded, and dross may appear as heavy drops. May the cut have a “V” shape with the bottom narrower than the top? Actually, focusing too low gives a wider kerf at the top and sometimes a rough, drossy bottom because the beam is not concentrated. Remedy: Raise focus (less negative) by 0.5 mm.
The Yihai manual’s “continuous metal burr removable as a whole” is a classic focus‑too‑high symptom. Run a focus ramp test (cut lines at focus offsets from –2 to 0 mm in 0.5 mm steps) and examine the bottom edge.
Impure oxygen or nitrogen degrades cutting efficiency and almost always produces dross. For carbon steel, oxygen purity below 99.5% causes heavy, hard‑to‑remove dross and a dark, scaly edge. For stainless steel, nitrogen purity below 99.995% (Grade 4.5) allows oxidation, and the dross is often accompanied by blue or yellow discoloration.
The Yihai manual states: “A 2% decrease in oxygen purity will reduce the cutting speed by nearly 50%, and lead to significantly worse cut quality.” If dross persists after adjusting speed, pressure, and focus, check your gas certificate. A simple test: cut a known clean part with a fresh, high‑purity cylinder. If dross disappears, your gas supply is contaminated.
A nozzle that is worn, spattered, or off‑center produces asymmetric gas flow. This results in dross on one side of the cut only, or a cut that has a rough edge on one side and a smooth edge on the other.
The Yihai manual’s tape test (Section 5.1.2) is the standard diagnostic: apply tape to the nozzle exit, fire a low‑power pulse, and check that the burn mark is centered. If not, center the nozzle. Replace the nozzle if the orifice is out of round or if spatter has built up on the inner bore. A worn nozzle can cause dross even when all other parameters are correct.
Follow this sequence. Do not change multiple parameters at once.a
Step 1 – Visual inspection:
Is dross on one side only? → Clean and center nozzle; replace if damaged.
Is dross a continuous strip that peels off? → lower focus by 0.5 mm.
Is dross drop‑like, small, and widespread? → increase gas pressure by 2 bar; if still present, reduce speed by 10%.
Step 2 – Check gas purity (if dross persists after Step 1):
For carbon steel, verify oxygen cylinder certificate (≥99.5%). If not available, test with a known good cylinder.
For stainless steel, ensure the nitrogen grade is at least 4.5.
Step 3 – Perform focus ramp test:
Cut 10 lines at focus offsets from 2 to +2 mm in 0.5 mm increments.
Examine the bottom edge. The focus with the cleanest, dross‑free edge is optimal. Record it.
Step 4 – Run speed ramp test:
At the optimal focus, cut lines at speeds from 70% to 120% of your current speed, in 5% increments.
The highest speed with zero dross is your new optimal speed.
Step 5 – Adjust gas pressure (fine-tuning):
Once speed and focus are set, vary pressure in ±1 bar steps. Lower pressure slightly if dross appears as fine drops; increase pressure if dross is heavy and adherent.
Step 6 – Document parameters for that material and thickness.
Material | Assist gas | Dross type | Most likely cause | Typical fix |
|---|---|---|---|---|
Carbon steel (<6 mm) | O₂ | Small drops, easy to remove | Speed too high | Reduce speed 10–15% |
Carbon steel (>10 mm) | O₂ | Heavy, hard burr | Focus too high or low purity | Lower focus; check O₂ purity |
Stainless steel (all) | N₂ | Fine, stringy, often discolored | Low gas purity or speed too slow | Use Grade 4.5 N₂; increase speed |
Aluminum (thin) | N₂ | Silvery, stringy, sticking to the edge | Focus too high; viscosity high | Lower focus; increase pressure |
Galvanized steel | N₂ or O₂ | Very fine, powdery | Zinc vapor condensing | Increase pressure; use a larger nozzle |
For aluminum, dross is more difficult to eliminate because of high melt viscosity. Some level of fine, powdery residue may be acceptable for non‑critical parts.
Based on the Yihai manual and field data:
Observed dross | Speed adjustment | Pressure adjustment | Focus adjustment | Nozzle action |
|---|---|---|---|---|
Drop‑like, easy to remove | –10% | +2 bar | –0.5 mm (if any) | Clean if asymmetric |
Continuous strip, peels off | 0% | 0% | –1.0 mm | – |
Hard, adherent, difficult | –15% | +4 bar | –0.5 mm | Check purity |
One‑side spikes | 0% | 0% | 0% | Center or replace |
Large globules, top ejection | –20% | +5 bar | +0.5 mm | Increase power if possible |
Very fine, hair‑like | –5% | –1 bar | +0.2 mm | – |
All adjustments are relative; fine‑tune by trial after each change.
Nozzle standoff (distance from nozzle tip to workpiece) affects gas jet coherence. For most fiber laser cutting heads, the optimal standoff is 0.5–1.5 mm. A standoff that is too large (>2 mm) causes the gas jet to diverge, reducing ejection force and promoting dross. A standoff that is too small (<0.5 mm) risks collision with spatter and may cause back‑pressure that also creates dross.
If dross appears after a lens change or head service, check the standoff. Many cutting heads have a mechanical stop or auto‑focus that maintains a fixed standoff; if the nozzle is not screwed in fully, the standoff increases.
Daily: Check nozzle for spatter; clean with brass brush. Perform a tape test weekly.
Weekly: Clean protective lens. Inspect focus calibration with the ramp test.
Monthly: Check gas filters (coalescing and particulate). Record cutting speed for a reference part; if speed drops >10% without parameter change, measure gas purity or laser power.
Per batch: When changing material supplier or thickness, run a speed ramp test. Document the optimal speed.
Bottom dross is not a mystery. It is the language the cut uses to tell you what is wrong. Drop‑like dross means speed too high or pressure too low; a continuous peel‑off burr means focus too high; one-sided spiking means nozzle misalignment; hard, adherent dross means multiple issues, often including impure gas. The Yihai manual provides a comprehensive defect matrix – use it as a diagnostic tool.
Fix dross by following a systematic sequence: check the nozzle and alignment first, then optimize focus with a ramp test, then adjust speed, then fine‑tune pressure. Always verify gas purity when dross persists. With proper parameter settings and regular maintenance, dross‑free cuts are achievable for carbon steel up to 20 mm and stainless steel up to 12 mm.
Q: Can I remove dross by post‑processing instead of fixing the cutting parameters?
A: Yes, but it adds cost and time. Mechanical methods (grinding, tumbling) or chemical pickling can remove dross, but they risk dimensional changes or surface damage. It is always cheaper to fix the cutting process.
Q: Why does dross appear only at the start or end of a cut?
A: Start dross is often due to piercing parameters (power too low or dwell too short). End dross can be from deceleration of the cutting head; program a lead‑out or reduce speed near the corner.
Q: Does the type of cutting gas affect dross formation differently for carbon steel?
A: Only oxygen is used for carbon steel. Using nitrogen on carbon steel produces a very rough, dross‑covered edge because the exothermic reaction is missing. Do not use nitrogen for carbon steel.
Q: What is the acceptable dross height for a weldable part?
A: For welding, any dross must be removed completely; otherwise, it can cause porosity. Specify “dross‑free” on the drawing. For structural applications, dross up to 0.2 mm may be tolerated if it does not interfere with fit‑up.
Q: How often should I run a focus ramp test?
A: After any lens replacement, after cleaning the cutting head optics, when changing to a different material thickness, or when dross appears unexpectedly. In a stable production environment, once per month is sufficient.
Yihai Laser Cutting Machine Operation Manual. Section 5.1.6: Cutting section evaluation – carbon steel with O₂ (defect‑cause‑solution table).
XC3000S Series Laser Cutting System User Manual. Raytools AG. Section on process parameters and nozzle centering.
HypCut Laser Cutting Control Software User Manual, Version 1.4. Section 5.7: Focus auto‑test.
Laser Institute of America. (2021). Dross Formation in Laser Cutting: Causes and Remedies. LIA Technical Guide TG‑DROSS‑2021.
IPG Photonics. (2020). Troubleshooting Carbon Steel Cutting Quality. IPG Application Note AN‑CS‑2020.
Adams, S. M. (2005). Sheet Metal Bend Allowance. KETIV Virtual Academy.
