Thin- and Thick-Sheet Laser Cutting: Differences and Parameter Adjustments
How to Choose Between Fiber-Laser and CO2-Laser Cutting
These topics are closely related. Sheet thickness affects not only cutting parameters but often also determines which laser equipment should be used. This article combines both topics to support a complete understanding and systematic decision-making.
Part 1: Differences Between Thin- and Thick-Sheet Laser Cutting
There is no absolute boundary between thin and thick sheet. In sheet metal fabrication, 6 mm is commonly used as an approximate dividing line: 6 mm and below is thin sheet, while above 6 mm is thick sheet. The significance of this boundary is that the cutting physics, parameter strategy, and equipment requirements change significantly beyond this thickness.
1. Characteristics and Challenges of Thin-Sheet Cutting
1.1 Advantages
Thin-sheet laser cutting is fast and efficient and is the most common sheet metal cutting condition. For example, when cutting 3 mm carbon steel with oxygen on a 10 kW-class fiber-laser machine, cutting speed can reach 4-6 m/min, providing excellent efficiency.
1.2 Common Challenges
Thin sheet may be easy to cut, but it has its own pitfalls.
(1) Over-burning and collapse
Thin sheet is highly sensitive to heat input. Slightly excessive power or slightly low speed can overheat the kerf and cause:
- The upper kerf edge to melt and collapse, with an unusually wide kerf.
- Burn marks, rough black edges, and dross on the cut face.
- Overall thermal deformation of the workpiece.
Minshuo Smart Manufacturing reminder: When cutting 1-2 mm sheet, excessive power is more likely to cause problems than insufficient power. Start with a lower power for trial cutting and increase gradually until the best cut-face quality—the “sweet spot”—is found.
(2) Material deformation
Thin sheet has low rigidity and can warp when heated during cutting, especially when cutting large flat sheets. A deformed workpiece may be positioned inaccurately in subsequent bending.
Solutions:
- Increase speed and reduce power appropriately to reduce heat input per unit length.
- Optimize the path and avoid long continuous cuts that accumulate heat, using jump cutting or segmented cutting where appropriate.
- Flatten the part after cutting.
(3) Burrs
Although thin sheet cuts quickly, burrs still require attention. A focus deviation of only 0.1 mm can significantly reduce cut quality.
1.3 Thin-Sheet Parameter Points
| Point | Practice for thin sheet (1-3 mm) |
|---|---|
| Focus position | At the sheet surface or 0.5-1 mm above it |
| Power | Moderate to relatively low; lower is safer than higher |
| Speed | Relatively high, preventing excessive heat input |
| Gas pressure | Moderate; avoid excessive pressure and turbulence |
| Piercing | Pulse piercing or low-power piercing |
2. Characteristics and Challenges of Thick-Sheet Cutting
2.1 Core Difficulties
Thick-sheet cutting is challenging mainly in terms of energy and dross evacuation.
(1) High energy demand
As thickness increases, the material volume that must be melted grows nonlinearly. Cutting 8 mm carbon steel may require 2-3 times the power needed for 3 mm carbon steel.
(2) Difficult dross evacuation
The deeper the kerf, the longer the path for molten metal to exit and the more the gas force decays. If gas pressure or velocity is insufficient, dross accumulates at the bottom.
(3) Taper
During thick-sheet cutting, the beam diverges in the kerf, making the top and bottom widths different and creating taper. Excessive taper affects dimensional and mating accuracy.
2.2 Strategies for Thick-Sheet Cutting
Strategy 1: Layered-cutting concept
Although laser cutting forms the part in one operation, parameter design can borrow a layered approach:
- Use higher power and lower speed first to ensure penetration.
- Near breakthrough, reduce power appropriately to prevent bottom over-burning.
- Some high-end equipment supports dynamic power adjustment and can change power automatically during cutting.
Strategy 2: Lower the focus
For thick sheet, focus should be positioned below the sheet surface. This distributes beam energy through the thickness instead of concentrating it on the top surface, giving the bottom sufficient energy density for stable penetration and helping dross exit smoothly. Determine the exact offset by trial cutting according to beam quality.
| Sheet thickness | Recommended focus position |
|---|---|
| 3-6 mm | 1-2 mm below the sheet surface |
| 8-12 mm | 2-4 mm below the sheet surface |
| 15-20 mm | 4-6 mm below the sheet surface |
Strategy 3: Optimize the cutting path
Cutting sequence strongly affects thermal deformation and cut-face quality:
- Cut large-area parts from the center outward.
- Avoid concentrating cuts in one area for a long time.
- Reduce speed at corners to limit heat accumulation.
Minshuo Smart Manufacturing experience: In thick-sheet cutting, we pay special attention to corners and sharp corners. The laser naturally slows while changing direction, so heat accumulates easily. These are high-risk areas for dross and over-burning. We normally add corner speed compensation to keep kerf quality uniform.
2.3 Thick-Sheet Parameter Points
| Point | Practice for thick sheet (6-20 mm) |
|---|---|
| Focus position | Below the surface and lower as thickness increases; verify by trial cut |
| Power | As high as possible within equipment limits |
| Speed | Relatively low to ensure melting and dross evacuation |
| Gas pressure | Depends on gas: low-pressure oxygen for carbon steel to avoid excessive oxidation; high-pressure nitrogen for stainless steel to evacuate dross |
| Nozzle | Larger orifice to ensure gas flow |
| Piercing | Progressive piercing or pulse/blast piercing |
3. Thin vs. Thick Sheet: Summary Comparison
| Item | Thin sheet (<=6 mm) | Thick sheet (>6 mm) |
|---|---|---|
| Core challenge | Over-burning and deformation | Penetration, dross, and taper |
| Focus | Surface or above surface | Below surface |
| Power strategy | Moderate to relatively low | As high as possible |
| Speed strategy | Fast | Slow |
| Gas strategy | Moderate | Low-pressure oxygen / high-pressure nitrogen |
| Main defects | Collapse and burrs | Dross, taper, and incomplete cuts |
Part 2: Choosing Fiber-Laser or CO2-Laser Cutting
1. Basic Principles
1.1 Fiber Laser
A fiber laser operates at 1064-1070 nm in the near-infrared band. The laser is generated and amplified in a rare-earth-doped fiber. It offers good beam quality, high electro-optical conversion efficiency (>30%), and low maintenance cost.
1.2 CO2 Laser
A CO2 laser operates at 10600 nm (10.6 μm) in the far-infrared band. The laser is generated in a CO2 gas mixture. Its long wavelength gives it very high absorption on non-metal materials, but relatively low absorption on metals, especially aluminum and copper.
2. Core Comparison
| Comparison item | Fiber laser | CO2 laser |
|---|---|---|
| Wavelength | 1064 nm | 10600 nm |
| Metal-cutting efficiency | ★★★★★ | ★★★☆☆ |
| Non-metal cutting | ★★☆☆☆ | ★★★★★ |
| Electro-optical efficiency | >30% | 8%-12% |
| Maintenance cost | Low | Relatively high |
| Equipment size | Compact | Larger |
| Aluminum/copper cutting | Relatively good | Relatively poor |
| Price trend | Continues to decrease | Relatively stable |
3. How to Choose
Choose a fiber laser when:
- The main work is cutting metal sheet such as carbon steel, stainless steel, and aluminum.
- High cutting speed and processing efficiency are required.
- Equipment maintenance cost and energy consumption matter.
- Reflective metals such as aluminum and copper must be cut.
Choose a CO2 laser when:
- Non-metal materials such as acrylic, wood, fabric, and leather must be cut.
- A special cut-edge requirement exists, because CO2 can produce a smoother edge on some materials.
- A CO2 machine is already available and replacement is not planned in the short term.
Minshuo Smart Manufacturing recommendation: For companies focused on sheet metal fabrication, fiber lasers are the mainstream choice. Fiber lasers have largely replaced CO2 lasers for sheet metal applications. Unless non-metal cutting is required, a new equipment purchase should generally prioritize a fiber laser.
4. Summary
The difference between thin- and thick-sheet cutting and the choice between fiber and CO2 lasers both concern how energy can act on material efficiently and accurately. Whether the sheet is thin or thick, there is no “universal parameter,” only the parameter best suited to the material and thickness. Accumulate experience and record data to find the best process window for every material and thickness.
As laser technology develops, the boundary of cutting capability continues to expand. Minshuo Smart Manufacturing follows leading technologies, regularly upgrades equipment and process standards, and aims to provide higher-precision, higher-quality, and more efficient sheet metal fabrication services.
This article is based on practical production experience and is provided for reference only. Parameters are for reference.
