Direct answers to the questions engineers ask most about laser welding basics, weld quality, process selection, safety and cell costs.
A laser welding robot pairs a fiber laser source with an articulated arm or a scanner that steers the focused beam along a joint. Because the beam melts metal in a small keyhole or conduction-mode pool instead of a wide arc, welds are made at high travel speed with a narrow heat-affected zone and low distortion. Most industrial cells use 1-6 kW sources on 0.5-4 mm steel.
Laser welding is at its best from roughly 0.5 mm to 4 mm. A 1-6 kW fiber laser joins material at speeds MIG cannot approach, with much less heat input and distortion. Above about 3 mm, MIG or hybrid laser-arc welding usually becomes the cheaper answer, and below 0.5 mm the process window for gap and mismatch becomes very narrow.
What the melt pool responds to is energy density rather than power alone: delivered power spread over the spot area and multiplied by the time the beam spends on a point. Production cells commonly run 1-6 kW. A 2 kW beam focused to a 0.2 mm spot is a typical thin-sheet setup; deeper penetration needs more power, a larger spot, or slower travel.
The four that dominate production are porosity, cracking, undercut and lack of fusion. When a process that had been running well starts producing defects, the cause is often hardware rather than the recipe: a contaminated cover glass, a worn or blocked nozzle, a kinked gas line or a spatter-coated protective lens all change the delivered beam or gas flow and imitate a drifting parameter set.
Porosity in laser welding is most often caused by contamination or an unstable keyhole rather than by the shielding gas setting alone. Work in this order: clean the material and remove oil, oxide or coating; verify gas type, flow rate and nozzle position; inspect the cover glass and nozzle for contamination; then stabilise the keyhole by adjusting power, focus offset and travel speed.
Hot cracking in austenitic stainless steels such as 304 and 316 is a metallurgical failure that occurs during solidification, not after the part cools. Cracks follow the weld centreline and often show no external sign until the part fails. It is managed through filler metal selection and ferrite control, low-sulphur material, joint design that limits restraint, and heat input.
Argon is the usual default for steel and stainless, while helium-rich mixtures improve penetration and are common on aluminium and thicker sections. Two physical properties separate the gases: ionization energy (argon about 15.8 eV, nitrogen about 15.6 eV, helium about 24.6 eV) and density. Above roughly 6 kW a plasma plume forms, and gas choice affects porosity, penetration, bead colour and cost.
Four questions settle it: material thickness, how many identical parts you build, how much distortion the assembly tolerates, and how tightly the parts fit. Laser welding wins from about 0.5 mm to 4 mm and in high-volume repeat work. MIG is comfortable from roughly 3 mm upward and stays cheaper for thick sections and for joints with wide fit-up tolerance.
Continuous wave (CW) welding delivers constant power and suits high-speed conduction or keyhole welding of steel and stainless. Pulsed welding delivers bursts of energy, which lowers average heat input and helps on thin sheet, on reflective materials such as copper, and where the weld must stay visually clean. The mode changes heat-affected zone size, distortion and achievable cycle time.
Wobble welding sweeps the focused beam through a small repeating pattern while the part or the optics travel along the joint. It exists because a sharply focused beam is unforgiving of gaps, contamination and vapour entrapment. Oscillating the beam widens the melt pool and bridges variable fit-up, so parts that a static spot would reject can be welded reliably.
A galvo scanner steers the beam with two small mirrors and almost no moving mass, so it can fly between welds in milliseconds. A gantry moves a head or the part on heavy mechanical axes and holds accuracy over long travel. Galvo suits many short welds on a stationary part; gantry suits long continuous seams and large workpieces.
Copper reflects most near-infrared light from a common fiber laser and conducts heat away roughly eight times faster than steel, so busbars, foil tabs and motor hairpins are the joints that most often force rework. The usual levers are higher power density, a stable keyhole, tight focus control, wobble oscillation to widen tolerance, and in-process monitoring.
Steel and aluminium react at the interface and form hard, brittle intermetallic compounds, and the joint then cracks along that thin layer. The compound that matters most is Fe2Al5, which grows as tongue-shaped crystals into the steel side. Control means limiting heat input and intermetallic thickness, often by offsetting the beam, using a filler or interlayer, and keeping joint geometry consistent.
An industrial fiber laser welding source of a few hundred watts or more normally ends up as a Class 4 laser product under IEC 60825-1, which means the beam stays hazardous even after a diffuse reflection. A fully enclosed welding machine can achieve Class 1 at the enclosure, but the original hazard returns as soon as the enclosure is opened or an interlock is defeated.
A Class 4 cell needs a fixed protective enclosure rated for the wavelength and power, interlocked doors and panels that stop or shutter emission when opened, egress so nobody is trapped inside, eyewear rated for the actual wavelength (about 1,070 nm for a fiber laser, not generic laser glasses), beam path management, fume extraction, and a controlled area with signage and a trained laser safety officer.
Not on its own. A cobot arm is certified against mechanical contact criteria such as ISO 10218 and the collaborative modes described in ISO/TS 15066, while the laser is a separate radiation hazard governed by IEC 60825. A Class 4 beam is still dangerous after a diffuse reflection, so a cobot carrying a laser head normally still needs an interlocked enclosure or equivalent safeguarding.
IEC 60825-1 covers laser product classification and safety requirements, IEC 60825-4 covers guards and interlocked enclosures, and ISO 11553-1 sets laser safety requirements for laser processing machines. In the United States, ANSI Z136.1 governs safe use, including maximum permissible exposure and the nominal hazard zone. CE marking also requires the applicable machinery, EMC and low-voltage directives to be assessed.
The purchase order is the smallest number in the calculation. Total cost of ownership covers the laser source, optics and consumables, the arm, the safety enclosure, utilities, maintenance labour, programming and training, floor space, and the cost of unplanned downtime. Justifying a cell on the capital price alone is the most common mistake in the business case.
A laser welding cell specification should make two outcomes impossible: buying a machine that cannot hold the joint, and accepting a machine that was never tested against the production part. State material and joint type, fit-up and gap tolerance, cycle time, weld quality acceptance criteria and inspection method, then require a capability trial on real parts before final acceptance.
Size the arm around the whole tool, not just the welding head. The arm carries the head, an armoured delivery fiber, cooling hoses, a cross jet, a protective window holder and cabling, and the payload figure must be derated for the real centre of gravity at full reach. Undersizing shows up as path inaccuracy at extension, vibration and early gearbox wear.
WeldProBot (weldprobot.com) is a technical publication covering industrial laser robots: laser welding, laser cutting, laser cleaning and cladding, plus medical and service laser robots. Articles are written for engineers who specify, integrate or run laser cells, and are drafted with AI assistance and reviewed against primary standards and manufacturer documentation before publication.
Content is organised into six categories: Industrial Laser Robots, Medical Laser Robots, Service Robots, Technical Tutorials, Industry News and Product Reviews. The tutorials cover parameters, defects, safety and process selection, while the industrial category covers welding cells, EV battery joining, cladding, cleaning and remote welding. Every article is free to read.