Views: 106 Author: DR.LIU XIANG Publish Time: 2026-04-27 Origin: Site
A high‑quality laser cut on carbon steel exhibits no dross (bottom edge clean), fine perpendicular striations that are evenly spaced, no discoloration beyond a thin heat‑affected zone, and a straight cut face with taper ≤1°. The evaluation is performed visually with a 10× magnifier and by touch with a gloved finger. Acceptable cuts have striations that are uniform and vertical; unacceptable cuts show curved “drag lines,” heavy adherent dross, or a rounded top edge. The Yihai manual provides a detailed defect‑cause‑solution table for carbon steel cut with oxygen: bottom drag lines offset indicate speed too high; drop‑like dross easy to remove indicates speed too high or pressure low; continuous metal burr removable as a whole indicates focus too high; hard‑to‑remove burr indicates multiple causes including impure gas or speed too high. Quantitative acceptance criteria per ISO 9013: for cutting quality class 1 (highest), permissible striation depth ≤20 µm, dross height ≤5 % of material thickness.
You receive a shipment of laser‑cut carbon steel parts. Some have smooth, bright edges; others have rough, blackened bottoms with adherent slag. Your customer rejects the batch. You look at the cut edge but cannot decide which cuts are acceptable and which are not. You have no written standard.
The cut cross‑section speaks to every parameter error. A trained operator can read the striations, dross, and discoloration to diagnose exactly what went wrong – speed, focus, gas pressure, or purity. This article provides a systematic evaluation method based on the Yihai laser cutting manual (Section 5.1.6), ISO 9013, and industry practice. It includes a grading scale, defect photographs (described), and a decision tree for quality improvement.
A laser‑cut carbon steel edge (viewed from the side, through a magnifier) reveals five features:
Feature | What it tells | Optimal |
|---|---|---|
Striations (drag lines) | Energy balance, speed, focus | Fine, perpendicular, evenly spaced |
Bottom edge dross | Melt ejection, gas pressure | None, or easily wiped off |
Kerf shape (taper) | Focus position | Slightly wider at top (≤1°) |
Top edge rounding | Focus height, power | Minimal, sharp corner |
Color/discoloration | Oxidation, heat input | Bright silver or light straw |
A good cut has all five features within acceptable limits. A bad cut has one or more defects.
Striations are the fine lines perpendicular to the cut direction. They are caused by the cyclic melting and ejection of material.
Striation pattern | Diagnosis | Parameter adjustment |
|---|---|---|
Fine, straight, perpendicular, evenly spaced | Optimal speed | None |
Wide, deep, curved backward (drag lines) | Speed too high | Reduce speed by 10–15% |
Very fine but bottom edge has a “shelf” | Slightly too fast | Reduce speed by 5% |
Irregular, chaotic, some areas smooth | Focus too high | Lower focus (more negative) |
Swirling, circular patterns | Gas pressure too low | Increase pressure by 2–4 bar |
No striations – melted, glazed surface | Speed too low (overheating) | Increase speed by 15–20% |
The Yihai manual states: “No bristles, same pull cord – power appropriate, feed rate appropriate.” That describes optimal striations. “The traction line at the bottom is much more offset, and the cut at the bottom is wider – feed rate too high, laser power too low, low pressure, focus too high.”
Quantitative striation measurement: For ISO 9013 quality class 1, the maximum striation depth (distance from the peak to the valley on the cut surface) shall be ≤20 µm. Class 2: ≤50 µm. Class 3: ≤100 µm. Most structural applications accept class 3.
Dross is resolidified molten metal adhering to the bottom edge. The Yihai manual distinguishes several types:
Dross type | Appearance | Diagnosis (Yihai manual) | Correction |
|---|---|---|---|
No dross | Clean bottom | Optimal | None |
Drop‑like, easy to remove | Small globules can be flicked off | Feed rate too high, low pressure, focus too high | Reduce feed rate, increase pressure, lower focus |
Continuous metal burr, removable as a whole | A single strip across the bottom | Focus too high | Lower focus |
Hard‑to‑remove, large burr | Adherent, requires grinding | Feed rate too high, low pressure, gas impurities, focus too high | Reduce feed rate, increase pressure, use purer gas, lower focus |
Spikes on one side only | Asymmetric projection | Nozzle not aligned or defective | Center nozzle; replace nozzle |
Acceptance criteria per ISO 9013: Dross height shall not exceed 5% of material thickness for class 1, 10% for class 2, and 20% for class 3. For 6 mm steel, class 1 allows dross up to 0.3 mm – barely perceptible to touch.
The kerf is the width of the cut. Taper is the difference between the top and bottom kerf widths.
Taper condition | Focus position | Correction |
|---|---|---|
Top kerf = bottom kerf (parallel walls) | Optimal focus | None |
Top kerf is much wider than the bottom (V‑shaped) | Focus too high (above the surface) | Lower focus (more negative) |
Top kerf narrower than bottom (inverted V) | Focus too low (too far below the surface) | Raise focus |
Uneven taper along cut length | Beam mode or lens contamination | Check beam quality, clean optics |
For carbon steel cut with oxygen, the optimal focus is slightly negative: the kerf is slightly wider at the top (by 0.05–0.1 mm per side). Taper should be ≤1° for most thicknesses.
The Yihai manual’s focus section (5.1.1) shows that for thick carbon steel, positive focus (on surface) gives a clean top but poor bottom; negative focus gives wider kerf but better bottom quality.
The top edge of a laser cut is usually sharp. Excessive rounding indicates:
Rounding degree | Cause | Correction |
|---|---|---|
Slight (<0.1 mm) | Normal for thick cuts | Acceptable |
Moderate (0.1–0.3 mm) | Focus too high, or power too high | Lower focus, reduce power |
Severe (>0.3 mm) | Beam defocused, or too much heat input | Check focus calibration; reduce power or increase speed |
For oxygen cutting of carbon steel, the cut edge should be bright silver to light straw. Dark gray or black indicates:
Low oxygen purity (<99.5%) – the Yihai manual: “Blue plasma, workpiece not cut through – processing gas error (N2), feed rate too high, power too low. Use oxygen as a processing gas.”
Excessive heat (speed too low) – “The cut surface is not precise” (high pressure, broken nozzle, poor material)
For stainless steel (though this article focuses on carbon steel), nitrogen cutting requires silver color. But for carbon steel, a dark edge is usually due to insufficient oxygen or excessive heat.
The Yihai manual provides a comprehensive table for carbon steel cut with oxygen. The following is a condensed, actionable version:
Defect | Possible causes (Yihai) | Solution |
|---|---|---|
No dross, consistent drag lines | Power appropriate, feed rate appropriate | Optimal – maintain |
Bottom drag line is much offset, cut wider at the bottom | Feed rate too high, laser power too low, low pressure, focus too high | Reduce feed rate; increase power; increase pressure; lower focus |
Bottom surface dross, drop‑like, easy to remove | Feed rate too high, low pressure, focus too high | Reduce feed rate; increase pressure; lower focus |
Continuous metal burr, removable as a whole | Focus too high | Lower focus |
Bottom metal burr hard to remove | Feed rate too high, low pressure, gas impurities, focus too high | Reduce feed rate; increase pressure; use purer gas; lower focus |
Spikes on one side only | Nozzle not properly aligned, nozzle defect | Center nozzle; replace nozzle |
Material ejected from top | Power too low, feed rate too high | Pause immediately; increase power; reduce feed rate |
Tilted cut face, two sides good two sides bad | Full mirror unsuitable, installed incorrectly or defective | Check full mirror, deflection mirror |
Blue plasma, workpiece not cut through | Processing gas error (using N₂ instead of O₂), feed rate too high, power too low | Use oxygen; reduce feed rate; increase power |
Cut surface not precise (rough, wavy) | High pressure, nozzle broken, nozzle diameter too large, poor material quality | Lower pressure; replace nozzle; use correct nozzle; improve material |
No dross, drag line tilted, cut narrows at bottom | Feed rate too high | Reduce feed rate |
Crater formation | High pressure, feed rate too low, focus too high, rusty plate surface, workpiece overheated, impure material | Lower pressure; increase feed rate; lower focus; use better quality material |
Very rough cut surface | Focus too high, high pressure, feed rate too low, material too hot | Lower focus; lower pressure; increase feed rate; cool material |
This table is a practical diagnostic tool. Keep a laminated copy near the machine.
Use this 5‑point scale to score cut quality for production acceptance and parameter optimization:
Grade | Striations | Dross | Taper | Color | Acceptance |
|---|---|---|---|---|---|
5 | Fine, perpendicular, uniform | None | ≤0.5° | Bright silver | Excellent |
4 | Fine, slight curve at the bottom | Easily wiped (≤0.1 mm) | ≤1° | Light straw | Good – general use |
3 | Moderate drag lines (<5° from vertical) | Removable with light scraping | ≤1.5° | Straw/dark straw | Marginal – rework may be needed |
2 | Heavy drag lines (>10°) | Adherent burr, hard to remove | >1.5° | Dark gray | Poor – reject |
1 | No striations, melted surface | Large globules cannot be removed | >2° | Black | Unacceptable |
For production, aim for grade 4 or 5. For prototype or internal non‑critical parts, grade 3 may be tolerated.
Magnification | What to examine | Action |
|---|---|---|
5–10× | Striation direction, spacing, drag line angle | Compare to the reference image |
10–20× | Bottom edge droll, micro‑cracks | Check for dross adhesion |
20× | Kerf wall roughness, micro‑porosity | Not usually needed for carbon steel |
Reference images: If available, keep samples of grade 5, 3, and 1 cuts labeled with parameters. Use them for operator training.
Step 1 – If dross is present:
Drop‑like, easy to remove → increase gas pressure by 10% or reduce speed by 10%.
Hard, adherent → check gas purity first; if pure, increase pressure and reduce speed significantly.
Spikes on one side → center nozzle.
Step 2 – If striations are curved (drag lines):
Reduce speed by 10–15%. If still curved, check focus.
Step 3 – If top edge rounded:
Lower focus (more negative) by 0.5 mm increments.
Step 4 – If kerf taper excessive (V‑shape):
Lower focus.
Step 5 – If cut surface is rough, wavy:
Check nozzle condition; replace if worn.
Reduce gas pressure (if too high).
Check material quality.
Step 6 – If blue plasma occurs:
Verify gas is oxygen, not nitrogen.
Reduce speed; increase power.
Step 7 – If material ejected from top:
Immediately stop – risk of lens damage.
Increase power, reduce speed.
Observation (6 mm carbon steel, 3 kW laser):
Bottom edge: hard, adherent dross over entire length.
Striations: wide, curved backward (≈15° from vertical).
Top edge: slightly rounded.
Color: dark gray.
Diagnosis:
Hard dross + curved striations → speed too high.
Top edge rounded → focus too high.
Dark color → possible low oxygen purity or secondary effect of speed.
Correction:
Reduce speed from 2.2 m/min to 1.8 m/min.
Lower focus from –1.0 mm to –1.5 mm.
Check oxygen purity (should be ≥99.5%).
Result after correction:
Bottom dross gone.
Striations perpendicular, fine.
Top edge sharp.
Color: light straw. Grade 4.
Evaluating carbon steel laser cut cross‑sections is a skill that every operator and quality technician must master. The cut edge reveals everything: speed errors show as curved striations; focus errors show as taper or top rounding; gas problems show as dross type and color; nozzle problems show as asymmetric spikes.
The Yihai manual provides a detailed defect matrix. Use it to diagnose and correct. Quantify quality with the 5‑point grading scale. Keep reference samples. Train operators to read the cut.
A few minutes of edge inspection after every parameter change prevents hours of rework and scrap. The cut cross‑section does not lie. Learn to read it, and you will master laser cutting.
Q: What magnification do I need to evaluate striations?
A: 10× is sufficient for carbon steel up to 12 mm. A simple illuminated loupe or a USB microscope (20–50×) is ideal.
Q: How do I distinguish between dross caused by low purity oxygen vs. dross caused by incorrect speed?
A: Low purity oxygen produces dark, heavy dross that is hard to remove, and the cut may have a brownish tint. Speed‑caused dross is usually lighter in color and may be accompanied by curved striations. Try increasing speed slightly; if dross worsens, it is likely gas purity.
Q: What is the acceptable dross height for a structural steel part that will be welded?
A: For welding, dross must be removed completely because it can cause porosity. So the acceptable dross height is zero. Specify “dross‑free” on the drawing.
Q: Can I use the same evaluation criteria for stainless steel?
A: No. Stainless steel nitrogen cutting has different striation patterns and color criteria (silver is good; blue is bad). Refer to a separate standard.
Q: How often should I cut test coupons to verify cut quality?
A: At the start of each shift, after changing material batch, after any maintenance (lens, nozzle, focus), and after changing gas cylinder. Also, if you see any change in cut quality, stop and run a test coupon.
Yihai Laser Cutting Machine Operation Manual. Section 5.1.6: Cutting section evaluation – carbon steel with O₂ (defect‑cause‑solution table).
ISO 9013:2017. Thermal cutting – Classification of thermal cuts – Geometrical product specification and quality tolerances.
XC3000S Series Laser Cutting System User Manual. Raytools AG. Section on process parameters.
HypCut Laser Cutting Control Software User Manual, Version 1.4. Section 5.1: Graphics editing.
Laser Institute of America. (2020). Quality Assessment of Laser‑Cut Edges. LIA Technical Guide TG‑QC‑2020.
Adams, S. M. (2005). Sheet Metal Bend Allowance. KETIV Virtual Academy. (Measurement principles)
