Laser Welding Glossary

Comprehensive definitions of technical terms, acronyms, and concepts used in laser welding. Organized alphabetically for quick reference.

Conduction vs Keyhole Mode Comparison

Understanding the two fundamental laser welding modes

Conduction ModeKeyhole ModeLow PowerMaterial SurfaceWidth: LargeShallowPower: <10⁵ W/cm²D/W: <1.0Stable, No PlasmaHigh PowerMaterial SurfaceKeyhole(Vapor)Width: SmallDeepPower: >10⁶ W/cm²D/W: >1.5Plasma Plume PresentMolten MetalHAZKeyhole CavityWeld Profile

✓ Conduction Mode Advantages

  • • Stable process, easy control
  • • Low spatter, good appearance
  • • Suitable for thin materials (<1mm)
  • • No plasma interference

✓ Keyhole Mode Advantages

  • • Deep penetration (up to 10-15mm)
  • • High aspect ratio (D/W: 3-10)
  • • Efficient energy use
  • • Single-pass thick section welding

Transition Zone: Power density 10⁵-10⁶ W/cm² can create unstable mixed mode. Aim for clear conduction (<10⁵) or keyhole (>10⁶) operation.

A

Absorptivity
The fraction of incident laser energy absorbed by the material. Higher absorptivity means more efficient energy coupling.
Aspect Ratio
The ratio of weld depth to width (D/W). High aspect ratios indicate deep, narrow welds typical of keyhole mode.
Autogenous Welding
Welding without filler material, relying solely on fusion of base metals.

B

Beam Quality (M²)
Measure of laser beam focusability. Lower M² values (closer to 1) indicate better beam quality and tighter focus.
BPP (Beam Parameter Product)
Product of beam radius and divergence angle. Related to beam quality; lower BPP means better focusability.

C

Conduction Mode
Welding mode where heat is conducted into material from surface. Produces wide, shallow welds with D/W < 1.
Coaxial Gas
Shielding or assist gas flowing coaxially with laser beam through welding head nozzle.
Carbon Equivalent (CE)
Formula to assess steel hardenability and crack susceptibility. Higher CE indicates greater crack risk.

D

Depth of Focus (DOF)
Distance over which laser beam remains sufficiently focused for processing. Larger DOF provides more process tolerance.
Dross
Resolidified material on weld underside, common in cutting but should be minimal in welding.

E

Energy Density
Power per unit area (W/cm²). Higher energy density enables keyhole mode and deeper penetration.
EWI (Electron and Welding Institute)
Organization providing welding research, education, and certification.

F

Focal Position
Location of laser beam focus relative to workpiece surface. Negative = below surface, positive = above surface.
Fresnel Number
Dimensionless parameter describing beam focusing characteristics.

G

GB 7247
Chinese national standard for laser products - Safety classification and requirements.
Gaussian Beam
Laser beam with intensity profile following Gaussian distribution. Most fiber lasers produce near-Gaussian beams.

H

HAZ (Heat Affected Zone)
Region of base material adjacent to weld that experiences thermal cycle but does not melt. Properties differ from base material.
Heat Input
Energy delivered per unit weld length (J/mm). Calculated as Power/Speed.
Humping
Weld defect where periodic bumps form along weld bead, typically at high speeds.

I

ISO 13919
International standard for quality requirements and inspection of electron and laser beam welded joints.
ISO 11553
Safety requirements for equipment for laser beam welding and allied processes.

K

Keyhole Mode
Welding mode where vapor cavity forms in material, allowing deep penetration. Characterized by D/W > 1.5.
Kerf Width
Width of material removed during cutting. In welding, analogous to weld bead width.

L

LEV (Local Exhaust Ventilation)
Ventilation system that captures fumes and particles at the source, essential for safe welding.
LIA (Laser Institute of America)
Professional society for laser applications, safety, and standards.

M

MPE (Maximum Permissible Exposure)
Highest level of laser radiation to which eye or skin may be exposed without damage.
Melt Pool
Volume of molten metal during welding. Stability affects weld quality.

N

NOHD (Nominal Ocular Hazard Distance)
Distance beyond which laser exposure is below MPE for eye safety.
Nd:YAG
Neodymium-doped Yttrium Aluminum Garnet. Traditional solid-state laser, now largely replaced by fiber lasers.

O

OEL (Occupational Exposure Limit)
Maximum concentration of airborne contaminants to which workers can be exposed.
OD (Optical Density)
Measure of laser safety eyewear effectiveness. Higher OD blocks more laser radiation.

P

Penetration Depth
Vertical distance from top surface to deepest point of fusion in weld cross-section.
Porosity
Gas-filled cavities in weld metal. Caused by contamination, insufficient shielding, or excessive speed.
Plasma Plume
Ionized gas above melt pool during welding. Can shield or defocus laser beam if excessive.

Q

Quality Grade
Classification per ISO 13919. Grade B (stringent), C (intermediate), D (moderate) define acceptance criteria.

R

Ra (Roughness Average)
Arithmetic average of surface profile deviations. Primary surface roughness metric.
Reflectivity
Fraction of incident laser energy reflected by material. High reflectivity (copper, aluminum) requires more power.

S

Spatter
Molten metal droplets ejected during welding. Excessive spatter indicates unstable process.
Spot Size
Diameter of focused laser beam at focal point. Smaller spot = higher power density.

T

Thermal Conductivity
Material property defining heat transfer rate. High conductivity (aluminum) requires more power.
TWA (Time Weighted Average)
Average concentration of airborne contaminant over specified time period (typically 8 hours).

U

Undercut
Groove melted into base material at weld toe. Caused by excessive power or speed.
UT (Ultrasonic Testing)
Non-destructive inspection method using ultrasonic waves to detect internal defects.

W

Wavelength
Laser light wavelength. Fiber lasers typically 1064nm (near-infrared).
Weld Pool Oscillation
Periodic movement of molten metal. Can indicate unstable process if excessive.

How to Use This Glossary

This glossary provides quick definitions of terms commonly encountered in laser welding. For more detailed explanations, see our Technical Articles or use the search function to find relevant calculator pages.

Notation Conventions

  • Acronyms: Spelled out on first use, abbreviated thereafter
  • Units: SI units unless otherwise specified
  • Standards: Referenced by official designation (e.g., ISO 13919-1)