Enter beam power, spot size, and travel speed to see where a laser or electron-beam weld sits relative to the material's keyhole threshold. The map also estimates power density, specific energy, and the weld's depth-to-width ratio.
Use the spot diameter at the work surface (1/e² or D86 for lasers, FWHM-equivalent for EB). Defocusing to a larger spot is the usual way to drop from keyhole into conduction mode.
Normalized enthalpy as a multiple of the keyhole threshold. Red marks the unstable transition band.
A keyhole forms when the surface gets hot enough to boil and the recoil pressure of the vapor pushes the melt aside. Whether that happens depends on how fast energy arrives compared with how fast the metal conducts it away.
Defocusing the same 3 kW to a 2 mm spot drops it to conduction mode, with a wide, shallow bead.
Hann, Iammi and Folkes (2011) showed that melt depth for many metals and lasers collapses onto one curve when plotted against the normalized enthalpy ΔH/hs. King et al. (2014) set the theoretical keyhole onset at ΔH/hs ≈ πTb/Tm, roughly 6 for steels.
Hann's expression grows without limit as speed approaches zero. This tool replaces it with the surface temperature of a uniform disc source, which stays finite when stationary and matches Hann's form exactly at welding speeds. The ±25% band around the threshold reflects real scatter: in that zone the keyhole opens and collapses intermittently.
In keyhole mode the beam acts like a line source through the thickness. Holding a cylinder the size of the spot at the boiling point takes a power per unit depth of
q′ = 2πk(Tb − T0) / [I0(Pe)·K0(Pe)], Pe = vr / 2κ
so depth ≈ Akh·P / q′. Width is taken at the widest point of the melting isotherm of the same line source, and is never less than the spot diameter. This gives the waist of the weld, not the wider nail-head at the top surface. In conduction mode the pool is at most hemispherical (D/W ≤ 0.5).
| Material | 1 µm onset | Green | Keyhole |
|---|---|---|---|
| Titanium | 0.40 | 0.55 | 0.80 |
| Steels | 0.35 | 0.50 | 0.80 |
| Aluminum | 0.20 | 0.30 | 0.70 |
| Copper | 0.15 | 0.40 | 0.60 |
Onset values are for a hot or molten surface. Cold, polished aluminum and copper reflect far more at 1 µm, which is why their keyhole onset is abrupt and less repeatable. Electron beams couple at 0.75-0.95, depending on backscatter.
Jeffrium runs process-window studies, thermal simulation, and parameter development for laser and electron-beam welding of titanium, nickel alloys, aluminum, and copper, from first trials to a qualified schedule.