Piercing thick plates is a critical process in laser cutting. Improper parameters may result in nozzle damage, lens contamination, poor cutting quality or failure to penetrate the plate. The core idea for thick plate piercing is taking a gradual and gentle approach. Input energy moderately and allow sufficient time for molten metal slag removal.
Function: Controls laser energy intensity. Adjustment principle: Piercing power shall be lower than the formal cutting power. Excessively high power causes rapid vaporization on the plate surface and sparks, and the rebounding high-temperature spatter will damage nozzles and lenses. Medium power melts materials first and then gradually deepens the piercing depth. Reference setting: Piercing power accounts for 60%‑80% of cutting power.
Function: Duration of single-point laser irradiation. Adjustment principle: Insufficient time fails to penetrate the plate; excessive time leads to over-melting of the plate, large counterbore, heavy slag sticking at the bottom and waste of gas. Reference setting: Increase with plate thickness. For 20mm steel plate, approx. 1‑2s; for 40mm steel plate, 3‑5s or longer. Use just penetration and minimal spatter as the standard; on-machine testing is required.
Function: Blows away molten metal and cools the workpiece. Air pressure: Air pressure should not be too high during piercing. High pressure removes heat, making piercing difficult and aggravating spatter. Switch to high cutting pressure after piercing is completed. Gas selection: Oxygen for carbon steel for heat generation via combustion support; nitrogen for stainless steel and aluminum alloy. Stainless steel and aluminum require relatively higher piercing pressure with the same low-first-then-high rule.
Function: Determines where laser energy concentrates. Adjustment principle: Negative defocus is widely adopted for thick plate cutting. The focus is placed below the plate to obtain a wider kerf and improve slag removal. The piercing process can adopt the same focus as cutting, or slightly adjust defocus toward positive value to concentrate energy on the surface for easier penetration (e.g., adjust from ‑3mm to ‑1mm).
Principle: Do not complete piercing with one set of fixed parameters. Set power and air pressure in multiple stages. Typical 3-stage configuration:
Advantages: Greatly reduce spatter, protect optical components, and achieve high piercing yield and quality.
Adopt high power + high air pressure to forcibly penetrate the plate in a short time. Only for thin plates; NOT allowed for thick plates. It causes violent bursts and massive spatter on thick plates, damaging the machine.
Thick plate piercing essentially controls energy input and molten slag removal. Progressive piercing is preferred. Follow the principle of low power, long time and low air pressure. Fine-tune parameters via test plate cutting to protect equipment while guaranteeing piercing quality.