Every laser-cut contour begins with piercing. During piercing, the molten pool can boil and eject material violently. If energy is not properly controlled, defects such as craters, solidified spatter, and oversized holes may form at the cut start. These defects affect appearance and can cause dross during subsequent cutting. Two-stage piercing, combining segmented and progressive piercing methods, is an effective approach for reducing start-point defects on low- and medium-power laser cutting machines.
Single-stage piercing concentrates high laser power at one point to penetrate the material in a single operation. Its limitations are particularly noticeable when processing thick plates and highly reflective materials.
1.1. Molten-metal spatter: Excessive instantaneous energy causes molten metal to eject upward, potentially contaminating the nozzle and protective lens and leaving spatter around the piercing point.
1.2. Hole-edge erosion: Heat accumulates around the piercing hole, producing an opening significantly larger than the cutting kerf and leaving a crater at the starting point.
Two-stage piercing divides penetration into two controlled steps:
Stage 1 — Preliminary piercing: Use a lower duty cycle and a deeper focus setting. Segmented or progressive piercing produces a small, relatively shallow pilot hole, removes some molten material, and reduces the initial energy impact.
Stage 2 — Through-piercing: Switch to a second set of focus and duty-cycle parameters to complete penetration through the pilot hole. Because the molten pool has already been established, the required instantaneous energy may be reduced, helping limit spatter and heat accumulation.
Examples from the supplied process settings include progressive + segmented piercing for thick carbon steel (Stage 1 focus: −6 mm; progressive delay: 1,000 ms; Stage 2 focus: −2 mm, with laser-off gas blowing); segmented + progressive two-stage piercing for 2–3 mm brass (Stage 2 focus: −6 to −8 mm); and segmented piercing for 2–3 mm stainless steel, with focus and delay adjusted according to thickness.
Parameter | Setting guideline |
Piercing stages | Use two-stage piercing for materials thicker than 2 mm; the source recommends it for thick plates and highly reflective materials. |
Stage 1 focal position | Set the focus deeper than the cutting focus to concentrate energy within the material and reduce surface erosion. |
Duty cycle | 55%–88%; use a longer, controlled energy delivery period to limit molten-pool spatter. |
Piercing delay | Increase with material thickness. Thick carbon steel may require 1,000 ms or more; confirm penetration using the piercing-complete signal or observed sparks. |
Laser-off gas blowing | Enable between stages to clear molten material from the hole and cool the hole edge. |
Nozzle height | Raise the nozzle appropriately during piercing (e.g., 3–8 mm) to reduce spatter adhesion to the nozzle. |
Two-stage piercing typically increases piercing time by approximately 30%–50% according to the source, so its benefits should be balanced against cycle time.
4.1. Recommended applications: Oxygen cutting of carbon steel over 3 mm; stainless steel and aluminum over 2 mm; highly reflective brass at any thickness; closely spaced part contours; and parts with visually critical cut-start locations.
4.2. When it may be unnecessary: For 1–2 mm sheet metal, where single-stage piercing already provides reliable penetration, adding a second stage may reduce production efficiency.
4.3. Common misconception: Two-stage piercing does not mean piercing twice at different locations. Both stages act at the same point with progressively adjusted settings. If Stage 1 creates an oversized hole, reduce its duty cycle or delay rather than adding more energy.
Start-point defects are often caused by excessive instantaneous energy during piercing. Two-stage piercing distributes that energy over two controlled steps—first establishing a pilot hole, then completing penetration. It can provide cleaner cut starts when processing thick or highly reflective materials with low- and medium-power equipment. By matching multistage piercing parameters to material type and thickness, manufacturers can improve start-point consistency while maintaining cutting quality in production.
Technical note: Numerical values and categorical recommendations above are translated from the supplied article and have not been validated against a specific laser source, cutting head, controller, or material-grade parameter table. Confirm settings by controlled test cuts before production.