laser-cutting

name	laser-cutting
description	Laser cutting process design — CO₂ vs. fiber laser, kerf width, cutting speed, assist gas, power density, material-specific parameters (steel/aluminum/stainless/CFRP), heat-affected zone, edge quality, dimensional tolerance, nesting optimization, ISO 9013 cut quality.
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Laser Cutting — Complete Skill

Laser Types and Selection

CO₂ Laser (10.6 μm wavelength)

Power range: 1–15 kW (industrial production) Best materials: organic (wood, acrylic, PETG, leather, CFRP), non-metallic; also cuts metals well Absorptivity in metals: Steel (mild): 5–10% (at 10.6 μm); requires high power Stainless: 8–12% Aluminum: 2–5% (highly reflective at CO₂; needs more power than fiber) Copper/brass: 2–4% (very reflective; difficult)

Beam delivery: mirrors + lenses (ZnSe focusing lens); no fiber transmission possible Focal spot size: D_spot = 4 × f_lens × λ / (π × D_beam) [f_lens = focal length; D_beam = input beam diameter] Typical D_spot = 0.15–0.5 mm for metal cutting

Fiber Laser (1.06 μm wavelength — 10× shorter than CO₂)

Power range: 500 W–20 kW (and growing) Key advantages over CO₂:

• Absorptivity in metals 3–5× higher at 1.06 μm → same power cuts faster
• Fiber delivery: flexible fiber optic cable → machine flexibility, less maintenance
• Electrical efficiency: 30–40% wall-plug (vs. 10–15% CO₂)
• Better for reflective metals (Cu, Al, brass): safe cutoff reflection, shorter λ absorbed better

Absorptivity at 1.06 μm: Mild steel: 35–40%; Stainless: 30–35%; Aluminum: 15–20%; Copper: 5–10% (highly reflective still; use ring-mode beam) Beam quality (M²): 1.1–1.5 for fiber vs. 1.1–2.0 for CO₂; better → tighter focusable spot at long focal length

Disk laser: Yb:YAG disk (1.03 μm); high power (> 4 kW); excellent beam quality; high brightness; for stainless > 15 mm

Beam Characteristics

Power density (irradiance) at focus: I = P / (π/4 × D_spot²) [W/m²] Cutting threshold: I > 10⁷ W/cm² for metal cutting Example: P = 4 kW, D_spot = 0.2 mm → I = 4,000 / (π/4 × 0.04²) = 4,000 / 1.26×10⁻³ = 3.2×10⁶ W/cm² (at edge for cutting)

Rayleigh length (depth of focus): z_R = π × w₀² / λ [w₀ = 1/e² spot radius; λ = wavelength] CO₂ (λ=10.6 μm, w₀=0.2 mm): z_R = π × 0.04 / (10.6×10⁻³) = 11.8 mm (long; robust to focus variation) Fiber (λ=1.06 μm, w₀=0.05 mm): z_R = π × 0.0025 / (1.06×10⁻³) = 7.4 mm → focus-critical for thick material

Cutting Parameters

Cutting Speed

Empirical relationship (approximate): v_cut ≈ P / (ρ × c_p × ΔT_melt × t × k_f) [mm/s; P = power [W]; ρ = density; c_p = specific heat; ΔT_melt = temperature rise to melt; t = material thickness; k_f = process efficiency factor ≈ 0.2–0.5]

Rule of thumb for fiber laser: Mild steel: v_cut [m/min] ≈ P[kW] / t[mm] × 3–5 (empirical factor; O₂ assist gas) Stainless (N₂ assist): v_cut ≈ P[kW] / t[mm] × 1.5–2.5 Aluminum (N₂ assist): v_cut ≈ P[kW] / t[mm] × 2–4

Standard cutting speeds (4 kW fiber, O₂ for steel):

Thickness [mm]	Speed [m/min]
1	25–40
3	8–15
6	3–6
10	1.5–3
20	0.5–1.0
30	0.2–0.5

Assist Gas

O₂ (oxygen assist — mild steel): Chemical reaction: Fe + O₂ → FeO + heat [exothermic; adds 30–60% energy → faster cutting] Result: darker oxide edge; not suitable for stainless (chrome oxidation) or precision cuts Pressure: 0.5–2 bar; increase with thickness

N₂ (nitrogen assist — stainless/aluminum/precision): Inert; no oxidation; bright, clean edge (no oxide layer); suitable for medical, food equipment No energy addition → slower than O₂ for mild steel Pressure: 5–20 bar; higher pressure for thicker material; minimum 15 bar for stainless > 8 mm

Air assist: Cheaper than N₂; slight oxidation; good for aluminum ≤ 3 mm; limited stainless applications Pressure: 3–8 bar

Compressed air (cutting non-metals): Wood, plastics: air removes debris, cools, prevents reignition No reactive chemistry needed

Focal Position

Focal position (Z_focus relative to top surface): Steel (thin, O₂): focus on top surface or 0.5 mm below top Steel (thick, O₂): focus at 1/3 depth below surface (wider melt channel) Stainless/Al (N₂): focus at surface or 0.5 mm below

Effect of defocus: larger effective spot → lower power density → slower speed; compensates for Rayleigh limit in thick material Adaptive focus heads: continuously adjust focus position for consistent cut quality on tapered/warped material

Kerf and Edge Quality

Kerf Width

Kerf width: k_w ≈ D_spot + 2 × δ_melt [D_spot = spot size; δ_melt = lateral melt penetration; δ_melt ≈ 0.02–0.1 mm] Typical kerf: 0.1–0.3 mm (thin material); 0.3–0.8 mm (thick material)

Part dimension compensation: Programmed path offset by k_w/2 (half-kerf) → actual part edge at programmed location CNC offset: G41/G42 (left/right compensation) automatically applies in CAM software

ISO 9013 Cut Quality Classes

ISO 9013: thermal cutting of metals — geometric tolerances and quality classes

Squareness tolerance (u): deviation of cut face from perpendicular u = angle of cut face from ideal 90° → measured as linear offset over face height Classes 1–5: u ≤ 0.05 mm (class 1, finest) to u ≤ 1.2 mm (class 5, roughest)

Roughness (Rz5): 5-point mean roughness of cut face Class 1: Rz ≤ 10 μm; Class 3: Rz ≤ 40 μm; Class 5: Rz ≤ 160 μm

Drag lines: periodic striations on cut face caused by oscillating melt front Frequency ≈ cut speed / capillary wavelength; visible as parallel lines on cut face Reduce: slower speed, higher power, better gas pressure, optimize focal position

Dross: solidified melt attached to bottom edge Causes: insufficient gas pressure, slow speed, too low power density → incomplete melt ejection Prevention: increase gas pressure + speed; use correct assist gas

Heat-Affected Zone (HAZ)

HAZ width (steel): HAZ = (λ_thermal × τ_interaction)^0.5 [approximate; λ_thermal = thermal diffusivity; τ = interaction time = spot_size / cut_speed] For steel: λ_thermal = 12 mm²/s; v = 5 m/min; D_spot = 0.2 mm → τ = 0.2/83.3×10⁻³ s = 2.4 ms → HAZ = √(12×10⁻⁶ × 2.4×10⁻³) = 0.17 mm

HAZ effects: Carbon steel: martensite formation → hard, brittle HAZ (especially > 0.3% C) HAZ hardness: can exceed 700 HV (62 HRC) for high-carbon steel Stainless: sensitization (Cr₂₃C₆ precipitation at grain boundaries → corrosion) Aluminum: grain coarsening; precipitation dissolution (6xxx, 7xxx series); strength loss 20–40% in HAZ CFRP (carbon fiber): resin decomposition; fiber oxidation; delamination at HAZ → problematic → water jet preferred

Material-Specific Parameters

Mild Steel (1020, S235)

O₂ assist; fiber 4 kW: 3 mm: 15 m/min; 10 mm: 3 m/min; 20 mm: 0.8 m/min Edge quality: ISO 9013 Class 2–3 (slight oxide, small dross possible)

Stainless Steel (304, 316)

N₂ assist; fiber 4 kW: 3 mm: 6–8 m/min; 10 mm: 1–1.5 m/min Bright edge; no oxide; welding ready HAZ: small; sensitization only in very thick cuts at slow speed

Aluminum (6061, 5083)

N₂ or air assist: 3 mm: 8–12 m/min; 10 mm: 1.5–2.5 m/min Reflectivity challenge: back-reflection monitoring; use ring-mode beam (annular) for Cu/Al at high power Edge quality: slight roughness Rz 20–50 μm; possible waviness; good for most structural uses

CFRP and Composites

CO₂ preferred (better absorptivity in polymer matrix): 1 mm CFRP: 3–6 m/min; 3 mm: 0.5–1 m/min HAZ: 0.2–0.5 mm resin decomposition band; fiber damage Alternative: water jet (no HAZ) or ultrashort pulse laser (< 1 ps → cold ablation, minimal HAZ)

Nesting Optimization

Common edge cutting: parts share cut edges → saves material and time Nesting algorithm: minimize sheet waste (rectangular and true-shape nesting) True-shape nesting software: Lantek, Metamation, SigmaNEST → compute optimal layout Material utilization: target > 75% (good); > 85% (excellent); depends on part shape

Piercing: laser starts each contour with a pierce hole Pierce time: 0.1–2 s per pierce (longer for thick material; add to cycle time) Pierce location: in waste material or at lead-in start; avoid pierce scar on part

CNC Programming

G-code essentials: G00 X Y Z: rapid positioning (no cutting) G01 X Y F: linear cut at feed rate F [mm/min] G02/G03 X Y I J F: circular arc (CW/CCW) M62/M63: laser ON/OFF (machine-specific)

Lead-in/lead-out: Lead-in: straight or arc entry into profile to stabilize cut before critical geometry Length: ≥ 3× kerf width; placed in waste material for internal contours Radius lead-in: smooth transition → reduces burn at entry point

Standards

Standard	Scope
ISO 9013	Thermal cutting — geometric tolerances and quality classes
EN 1090-2	Execution of steel structures — cutting requirements
AWS C7.2	Recommended practices for laser beam welding (overlaps with cutting)
ASTM F2792	Additive manufacturing (referencing laser for context)
ISO 15614-14	Qualification of laser welding/cutting procedures

Output

Provide: laser type (CO₂/fiber/disk), wavelength [μm] and power [kW], material type and thickness [mm], assist gas (O₂/N₂/air) and pressure [bar], focal position (mm from surface), cutting speed [m/min], kerf width [mm], HAZ width [mm], edge quality ISO 9013 class, dross/squareness achieved, maximum thickness for clean cut at given power, nesting efficiency [%] and pierce count, cycle time estimate [s] for given part area, and applicable standard (ISO 9013, EN 1090-2).