Pre-Flight Checklist (Safety + Stability First)
Safety & compliance
- Gas system: leaks, regulator ratings, oil-free & dry lines (dew point ≤ −40 °C recommended).
- Extraction/filtration sized for your materials; metal dust collection with fire mitigation.
- High-reflectivity materials (Cu/brass): pristine cover glass, anti-back-reflection practices.
Machine condition
- Clean cover/focus lenses; verify nozzle concentricity (ring-cut test or centering gauge).
- Chiller 18–22 °C, water quality/electrical conductivity within spec.
- Match nozzle diameter to thickness and speed target (smaller for thin/high-precision; larger for thick/high-flow).
Material readiness
- Grade and surface state (mill scale, coatings, film, brushed finish). Flatness matters—clean oxide/scale if needed.
- Label sample coupons consistently (orientation/lot) for traceability.
Baseline recipe
- Start from your most stable historical recipe (not necessarily the fastest).
Parameter System: From "Tinkering" to "Modeling"
Keep the variable set finite and define priority + direction for each symptom.
Core controllable variables (highest leverage)
1.Power / duty / frequency (controls heat input; note pulse peak power vs. average).
2.Speed (v): with power defines line energy E_line≈P/vE\_\text{line} ≈ P / vE_line≈P/v. First lever when it’s "burning" or "dragging".
3.Focus (f): thin ~0 to −0.4 mm; thick −0.5 to −1.5 mm.
4.Gas type & pressure: O₂ for reactive carbon-steel cutting; N₂ for oxide-free edges; clean dry air as a cost-effective middle ground (quality/cleanliness critical).
5.Nozzle diameter & stand-off: governs jet shear and entrainment.
Strategy variables
- Piercing mode (segmented/spiral/low-power preheat + dwell).
- Lead-in/out & micro-tabs (prevent part tip-up and edge burns at start/stop).
- Corner/small-hole plasma suppression (power reduction, speed reduction, pressure bump, dedicated hole macros).
Symptom → Variable map (to choose what to tweak first)
- Heavy bottom dross/burr: raise gas pressure → then adjust focus → then speed; especially important for N₂ on stainless.
- Top-edge melt/heat tint: excessive power or O₂ reaction → lower power / raise speed / reduce O₂ pressure or switch to N₂.
- Striations/waviness: speed-power mismatch, wrong focus, worn/off-center nozzle → refocus / replace nozzle / stabilize pressure.
- Small holes blowing out: no small-hole strategy → enable dedicated hole macro (lower power & speed, higher pressure, longer cool dwell).
- Pierce failure: inadequate pierce energy/time or surface scale → segmented pierce; clean surface.
First-Article DOE: Converge in 30–60 Minutes
Goal: Find a stable, fast-enough window with minimal coupons.
Step 1 — Define conditions & quality target
Material/grade/surface; target edge (weld-ready / polished / deburred OK); limits for burr height/taper.
Step 2 — Build a 2×3 or 3×3 matrix
- Main axes: Speed × Focus (e.g., v₁/v₂/v₃ and f = 0 / −0.6 / −1.2 mm).
- Power at “as high as possible without overheating,” gas at mid/high (e.g., N₂ 1.4 / 2.0 MPa).
- Create a separate small-hole set for holes with diameter < 1.2×thickness.
Step 3 — Standardize coupons & scoring
Consistent lead-ins, micro-tabs, nesting. Score 1–5 for: burr/dross, striations, kerf & taper, color/oxide, hole roundness. Note phenomena.
Step 4 — Lock the stability window
Pick the most stable combo first; then push speed or reduce gas to find the efficiency optimum. Apply corner/small-feature macros on top.
Step 5 — Document & regress
Publish a Parameter Card (material × thickness × nozzle × focus × speed × power × pressure × compensations). Run monthly spot checks to confirm no drift.
Quick Start Windows by Material & Gas
(Starting points only; expect tuning for your laser power, spot size, nozzle brand, and gas infrastructure.)
Carbon Steel (CS) — O₂ reactive by default
- 1–3 mm: nozzle Ø0.8–1.0 mm; O₂ 0.2–0.5 MPa; focus 0 to −0.4 mm; maximize speed while avoiding discoloration.
- 6–10 mm: nozzle Ø1.2–1.5 mm; O₂ 0.3–0.7 MPa; focus −0.6 to −1.2 mm; segmented/low-power pierce + dwell.
- Weld-ready edges? Consider N₂ inert cutting (costlier) or post-process to remove oxide.
Stainless Steel (SS) — N₂ high-pressure inert
- 1–3 mm: nozzle Ø1.0–1.2 mm; N₂ 1.4–2.0 MPa; focus −0.2 to −0.8 mm; bright edge achievable.
- 6–10 mm: nozzle Ø1.5–2.0 mm; N₂ 1.6–2.5 MPa; focus −0.8 to −1.4 mm; slightly lower speed to ensure evacuation.
- Ensure N₂ purity ≥ 99.95% and dry, oil-free lines.
Aluminum Alloys
- Priority is minimizing burr/entrained dross and small-hole blowout. Use N₂ high pressure or clean dry air where acceptable.
- Focus −0.6 to −1.2 mm typical; enable small-hole macro; moderate speeds.
Copper/Brass (High-Reflective)
- Favor higher peak power density, dry inert gas, frequent cover-glass checks; anti-reflection strategies as available.
- Focus −0.6 to −1.0 mm to start; conservative speed for stability.
Nesting & Path Strategy (Throughput + Thermal Control)
- Inside-out: cut holes/slots first, outer profiles last to avoid early part release.
- Skip/thermal-balancing: alternate regions to prevent heat buildup and warpage.
- Common-line cutting: saves time/material but concentrates heat—use micro-tabs, reduce local line energy.
- Corners & tiny features: enable plasma suppression (power/speed/pressure tweaks), corner rounding, and curve segmentation to smooth motion.
Quality Metrics & Metrology (Turn “looks good” into numbers)
- Reference ISO 9013 (thermally cut edge classes) or define internal grades.
- Measure: burr height, dross residue (visual + weight if critical), kerf width/taper, surface roughness (Ra/Rz), roundness & dimensional error, HAZ width, and weldability checks (bend/tensile/visual).
- Acceptance: define A/B/C thresholds; first-article and sampling frequency (e.g., 1/50) on the traveler.
Troubleshooting Cheat-Sheet(h2)
| Symptom | Likely causes (priority order) | Actions |
|---|---|---|
| Heavy dross/burr | Gas pressure too low → focus too low → speed too low / wrong power split → worn/off-center nozzle | Raise pressure (N₂/air); move focus toward −0.4 to −0.8 mm; increase speed; check nozzle concentricity/diameter |
| Top-edge melt / heat tint | Power too high; O₂ pressure too high; speed too slow | Lower power / increase speed / reduce O₂ pressure or switch to N₂ inert |
| Striations/wave marks | Speed-power mismatch; wrong focus; unsteady jet | Re-focus; replace/true nozzle; stabilize gas pressure |
| Small-hole blowout | No small-hole macro; pierce energy/time wrong | Enable hole macro (−20–40% power, −30–60% speed, +0.2–0.5 MPa pressure), increase cool dwell |
| Piercing failure | Scale/coating; pierce routine mismatch | Clean surface; segmented/spiral pierce with preheat + dwell |
| Discoloration / oxide | O₂ participation or low N₂ purity | Raise N₂ purity/pressure; switch to inert process where needed |
Maintenance & Calibration Rhythm(h2)
Daily: clean cover glass/nozzle; verify nozzle concentricity and stand-off; check chiller temp/level; observe filters.
Weekly: calibrate height following; verify nozzle orifice; clean rails/ducts; check gas dew point/oil content.
Monthly: re-check focus calibration coupons; parameter-card regression (3 common materials); inspect grounding and cable wear.
Any change (lens/nozzle/gas source/controller update): force a DOE regression and update the parameter card.
FAQ
Q1: I’m getting dross on stainless with N₂—what should I check first?
A:Start with pressure and nozzle concentricity. In the 6–10 mm range you may need 1.6–2.5 MPa at the nozzle. If dross remains, reduce negative focus magnitude and increase speed.
Q2: For carbon steel, do I have to avoid O₂ to get weld-ready edges?
A: Not strictly—but O₂ leaves an oxide layer that typically needs grinding or blasting. If post-processing isn’t allowed, use N₂ inert cutting (higher cost) or plan a de-oxidizing step.
Q3: When is air cutting appropriate?
A: For non-structural parts where slight discoloration is acceptable and cost sensitivity is high. Air quality (dry, oil-free) is crucial; poor air leads to instability and deposits.
Q4: Small holes deform or show blowout—how to fix?
A: For hole dia < 1.2×thickness, enable a small-hole macro: reduce power 20–40%, reduce speed 30–60%, increase pressure, and add longer cool dwell after piercing.
Summary
Stabilize before you optimize: lock gas purity/pressure, nozzle concentricity, clean optics, and coolant at 18–22 °C.
Run a fast 3×3 DOE (speed × focal offset) for each material × thickness to map the stable window.
Freeze a Parameter Card (power / speed / focus / pressure / nozzle Ø / defocus / pierce routine) and schedule monthly regression checks.
Troubleshoot in order: gas pressure → focus → speed → power → nozzle/alignment.
Process picks: O₂ for faster carbon-steel cuts, N₂ for oxide-free stainless/aluminum, dry air when quality allows to reduce cost. For small features use micro-tabs, corner macros, and inside-out toolpaths to keep edges consistent.
