What are the precautions for fiber laser cutting of rusty plates？Cutting rusty metal plates with a fiber laser presents significant technical and safety challenges. Rust (iron oxide) has a different absorption rate and thermal conductivity than clean steel, which often leads to poor cut quality and damage to the machine’s optics.
1. Protect the Optics (The Primary Risk)
The biggest risk of cutting rusty plates is “slag splashing” or “blowouts.” During the piercing process, the uneven rust layer can cause mini-explosions that shoot molten metal and dust straight up into the cutting head.
- Protection: Always check your protective lens frequently (sometimes every hour) for pits or dust accumulation.
- The “Oil Trick”: Lightly misting the rusty plate with a thin layer of cutting oil or WD-40 before piercing can help stabilize the thermal reaction and prevent rust dust from adhering to the nozzle. Warning: Do not soak the plate, as excess oil creates heavy smoke that can fog the lens.
2. Implement a “Vaporization Pass”
For thick or heavily rusted plates, do not attempt to cut through the rust directly. Instead, use a two-step process:
- Step 1: Run a high-speed, low-power pass (defocused) along the cut path to vaporize the rust layer. This creates a clean “silver road” for the actual cut.
- Step 2: Perform the actual cut on this cleaned path. This significantly reduces dross and prevents lens damage.
3. Adjust Piercing Parameters
Rust interferes with the laser’s ability to create a clean initial hole.
- Pulse Piercing: Use Pulse Mode instead of Continuous Wave (CW) for the initial pierce. This reduces heat buildup and minimizes the chance of a “blowout.”
- Increase Piercing Time: Allow more time for the laser to penetrate the uneven oxide layer before the head begins to move.
4. Optimize Gas and Nozzle Settings
- Gas Purity: Ensure your assist gas (Oxygen or Nitrogen) is pure. Impurities can worsen the uneven combustion caused by rust.
- Nozzle Inspection: Rusty plates often cause the nozzle to become clogged or deformed by spatters. If you notice a “wavering” beam or irregular sparks, stop immediately and clean or replace the nozzle.
- Gas Pressure: Slightly increase the assist gas pressure to blow away the more viscous molten rust more effectively.
5. Height Sensor Sensitivity
The rust layer can interfere with the Capacitive Height Sensor (the “follow” system).
- Issue: Rust is non-conductive or poorly conductive, which can cause the cutting head to crash into the plate or maintain an inconsistent distance.
- Solution: Calibrate the height sensor on a clean spot of the metal first. If the rust is very thick, you may need to increase the “Follow Height” slightly to prevent collisions.
6. Health and Safety
Cutting rust releases a higher concentration of fine iron oxide particulates than clean metal.
- Ventilation: Ensure your dust extraction system is at maximum power.
- Personal Protection: Wear a high-quality respirator mask (P100 or N95) even if the machine is enclosed, as fine dust escapes during plate loading and unloading.
Comparison: Rusty vs. Clean Plate Cutting
| Feature | Clean Mild Steel | Rusty Mild Steel |
| Piercing Speed | Fast / Stable | Slow / Prone to “Blowout” |
| Edge Finish | Smooth | Rough / “Dross” at the bottom |
| Lens Lifespan | Long | Significantly Shortened |
| Height Sensing | Highly Accurate | Unstable / Crash Risk |