High-Power Precision: Cutting 20mm Stainless Steel with CNC Lasers
Cutting thick metal plate, particularly stainless steel (20mm+), with a CNC fiber laser is often perceived as a simple matter of increasing the power. While a high-power laser source (6kW+) is non-negotiable, the key to achieving a clean, square, and efficient cut lies in optimizing the process parameters.
As we covered in Article #02, Heat Affected Zone (HAZ) control is critical in cladding to prevent metallurgical breakdown. In cutting, parameter optimization prevents dross, slag, and edge angularity, ensuring the structural and aesthetic integrity of the component. To maximize the performance of Intouchray’s 12kW+ fiber lasers on heavy plate, four core parameters must be precisely balanced.
- The Right Assist Gas: Nitrogen vs. Oxygen
For cutting 20mm stainless steel, the selection of assist gas is paramount for edge quality.
Nitrogen (N₂): The standard for thick stainless when edge quality is critical. Nitrogen cutting (fusion cutting) uses high gas pressure to rapidly “flush” molten metal from the kerf before it can oxidize. The result is a clean, silver, oxide-free edge ready for immediate welding or painting. The challenge is the high gas pressure requirement (often >18 bar) for effective melt removal on thick plate.
Oxygen (O₂): Used for reactive cutting of carbon steels. While it can cut thick stainless faster by utilizing the exothermic reaction, it results in a heavily oxidized, rough, and potentially discolored edge that requires post-processing. For high-end industrial applications using Intouchray machines, high-pressure Nitrogen is typically the optimal choice for precision.
- Focal Point Position: Penetration is Key
Unlike thin sheet metal, where the focal point is placed on or just below the surface, cutting 20mm stainless requires the focal point to be submerged inside the material. This ensures that the beam maintains a narrow, focused energy distribution throughout the entire thickness of the plate.
Correct focal point positioning ensures a square kerf. If the focal point is too high (at the top surface), the beam diverges towards the bottom, causing an angled cut and heavy dross. Conversely, positioning it too low inside the plate can also cause unstable cutting and dross.
- Cutting Speed vs. Gas Pressure: The Delicate Balance
For thick plate, cutting speed is not simply “as fast as possible.” It is about matching the speed with the laser’s power and the capacity of the assist gas to remove molten material.
If the cutting speed is too fast, the auxiliary gas cannot keep up with the melt rate, leading to slag and dross accumulation on the bottom surface of the plate and an angled edge. If the speed is too slow, you risk overheating the kerf, resulting in a wide, rough cut and poor surface quality.
The key is a precise calibration: as laser power increases (e.g., from 6kW to 12kW), you can increase the cutting speed while maintaining high Nitrogen gas pressure. This allows for both efficiency and a premium edge. A practical pro-tip for diagnosing parameter imbalance is to examine the dross—a ‘clean’ dross formation on the bottom often indicates a correctly balanced speed/gas relationship.
- Nozzle Selection: Diameter and Stand-off Distance
For stable, high-pressure gas flow (especially with Nitrogen), the nozzle must be appropriately sized (e.g., 2.5mm+ diameter) and maintained at a specific stand-off distance (often 1mm) from the plate surface. This ensures that the gas jet remains focused and powerful enough to clear the kerf efficiently on 20mm+ plate without turbulent interference.
