Laser Welding Technical Terms and Definitions

Plain technical definitions for laser welding terms, safety acronyms, inspection words, and standards references used in setup records, quality plans, and calculator output.

Quick answer for laser welding technical terms

Laser welding technical terms usually fall into five groups: beam and optics terms such as spot size and focus position, weld-mode terms such as keyhole mode and conduction mode, inspection terms such as porosity and undercut, safety acronyms such as NOHD and MPE, and standards references such as ISO 13919 and GB/T 7247.1-2024.

Most searched definitions

HAZ, NOHD, MPE, OD, keyhole mode, penetration depth, porosity, undercut, spatter, and heat input.

Use this glossary when

A drawing, procedure, calculator result, or standards note uses a term that needs a short engineering definition before the next weld trial.

Search by term family

Safety terms

NOHD, MPE, OD, LEV, OEL, GB/T 7247.1-2024, IEC 60825-1, ISO 11553-1, and ANSI Z136.1.

Open the GB 7247 laser safety map

Process terms

Keyhole mode, conduction mode, focus position, spot size, shielding gas, heat input, and absorptivity.

Check heat input and energy planning

Inspection terms

Penetration depth, porosity, undercut, spatter, HAZ, roughness, quality grade, and ISO 13919 context.

Check surface quality indicators

Glossary routes for the next check

NOHD, MPE, OD, or laser classMove from the definition to protection-distance and eyewear planning.ISO 13919, quality grade, porosity, or undercutMove from the definition to inspection and acceptance-context lookup.

Conduction vs Keyhole Mode Comparison

Understanding the two fundamental laser welding modes

✓ Conduction Mode Advantages

• Often easier to stabilize during early trials
• Often useful where shallow fusion is the target
• Lower vapor-cavity sensitivity than keyhole mode
• Still needs section and surface inspection

✓ Keyhole Mode Advantages

• Can support deeper penetration
• Can produce a higher aspect-ratio weld profile
• Needs tighter stability monitoring
• Acceptance depends on the qualified window

Transition Zone: Mixed conduction and keyhole behavior can occur when the setup sits between modes. Confirm the operating mode with bead profile, cross-section, and stability evidence.

A

Absorptivity: The fraction of incident laser energy absorbed by the material. It varies with wavelength, surface condition, temperature, oxide state, and angle of incidence, so process checks should use the actual setup.
Aspect Ratio: The ratio of weld depth to width (D/W). A higher aspect ratio can indicate a deeper, narrower weld profile, but the weld mode should be confirmed by cross-section and stability checks.
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 the surface. It commonly produces a wider, shallower weld profile than keyhole welding under comparable setup conditions.
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: Beam power distributed over an effective area. It influences weld-mode tendency together with travel speed, material response, focus position, and shielding conditions.
EWI (Electron and Welding Institute): Organization providing welding research, education, and qualification resources.

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 a vapor cavity forms in the molten material. It can support deeper penetration, but stability and acceptance still depend on the validated process window.
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, important for exposure-control planning.
LIA (Laser Institute of America): Professional society for laser applications, safety, and standards.

M

MPE (Maximum Permissible Exposure): Laser safety exposure limit used in hazard assessment. The applicable value depends on wavelength, exposure duration, viewing condition, and the controlling safety standard.
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 or voids in weld metal. Investigation normally checks surface condition, shielding, moisture, oxide state, and keyhole stability before changing multiple parameters.
Plasma Plume: Ionized gas above melt pool during welding. Can shield or defocus laser beam if excessive.

Q

Quality Grade: ISO 13919 quality-level reference. Grade B (stringent), C (intermediate), and D (moderate) support planning, while acceptance criteria still come from the applicable specification.

R

Ra (Roughness Average): Arithmetic average of surface profile deviations. Primary surface roughness metric.
Reflectivity: Fraction of incident laser energy reflected by material. Reflective materials require verification of wavelength, surface condition, focus, and process coupling on the actual setup.

S

Spatter: Molten metal droplets ejected during welding. Excessive spatter normally triggers checks of surface condition, focus, shielding, fit-up, travel behavior, and process stability.
Spot Size: Diameter of the focused laser beam at or near the focal plane. It affects power density and weld width together with delivered power, beam quality, focus position, and motion strategy.

T

Thermal Conductivity: Material property defining heat transfer rate. High-conductivity materials need documented heat-sinking, fixture, and section-check assumptions during process development.
TWA (Time Weighted Average): Average concentration of airborne contaminant over specified time period (typically 8 hours).

U

Undercut: Groove or depression at the weld toe. Investigation normally checks edge fit-up, beam alignment, focus, travel behavior, and power density.
UT (Ultrasonic Testing): Non-destructive inspection method using ultrasonic waves to detect internal defects.

W

Wavelength: Laser light wavelength. Safety limits, eyewear selection, and material absorptivity checks should use the actual source wavelength listed by the laser manufacturer.
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 planning calculations, connect the term to the related heat-input, safety, surface-quality, material, or troubleshooting page before changing a weld procedure.

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)