Laser welding uses a focused beam of light to melt and fuse metal, producing narrow, deep welds with minimal heat distortion. The process is roughly four times faster than TIG welding and puts far less heat into the surrounding material, which means less warping and smaller heat-affected zones. Whether you’re running an industrial fiber laser or picking up one of the increasingly popular handheld units, the core principles are the same: get the beam focused, the joint fitted tightly, the shielding gas flowing, and the parameters dialed in for your material.
How Laser Welding Actually Works
A laser beam is focused down to a tiny spot on the workpiece, concentrating enough energy to melt metal almost instantly. What happens next depends on how much power density hits the surface, and this splits laser welding into two distinct modes.
In conduction mode, the laser heats the surface and the metal melts outward through heat conduction alone. The material barely evaporates, so you get a wide, shallow weld pool. This mode works well for thin sheet metal and cosmetic welds where you want a smooth surface finish without deep penetration.
In keyhole mode, the power density is high enough to vaporize the metal, creating a narrow vapor channel (the “keyhole”) that the laser beam dives into. The beam bounces off the walls of this channel two or three times before the energy leaks out, which drives heat deep into the joint. Keyhole welding produces the narrow, high-penetration welds that laser welding is known for. The tradeoff is that it requires more precise control. If power or speed drifts, the keyhole can collapse, trapping gas and creating porosity.
Choosing the Right Laser Type
The two most common laser sources for welding are fiber lasers and CO2 lasers. They differ in wavelength, beam quality, and what thicknesses they handle best.
Fiber lasers emit light at 1,064 nm, a wavelength that metals absorb efficiently. They produce stable, narrow beams that focus precisely, making them the go-to choice for sheet materials up to about 5 mm thick. They remain effective up to around 20 mm, though their advantage narrows as thickness increases. Fiber lasers are also compact, energy-efficient, and require less maintenance since the beam travels through a fiber optic cable rather than through mirrors.
CO2 lasers operate at a much longer wavelength of 10.6 micrometers. They come into their own on thicker materials, particularly in the 10 to 20 mm range and above. Steel plates up to 100 mm thick typically require oxygen-assisted CO2 lasers. High-powered CO2 units can produce poorer beam quality unless the resonator is quite long, so they’re generally found in larger industrial setups rather than compact workstations.
For most newcomers and small-shop applications, a fiber laser is the more versatile and practical starting point.
Joint Design and Fit-Up Tolerances
Laser welding is far less forgiving of gaps than MIG or TIG. The focused beam is so small that any air gap between parts can cause the laser to blow through rather than bridge the joint. For butt joints, gaps need to stay below 10% of the material thickness to avoid defects. On 2 mm steel, that means a maximum gap of 0.2 mm.
Common joint configurations include butt joints, T-joints, lap seams, lap fillets, and lap edge joints. Lap joints are often the most practical for beginners because they’re easier to fixture tightly and the overlapping material gives you more margin for error. Butt joints demand the tightest fit-up but produce the cleanest results when done well.
Good fixturing is not optional. Clamps, jigs, or tack welds should hold parts firmly with consistent contact along the entire seam. Any springback or slight misalignment that you might get away with in traditional welding will show up as a defect in a laser weld.
Shielding Gas Selection
Like other welding processes, laser welding needs shielding gas to protect the molten metal from oxygen and nitrogen in the air. The gas you choose affects penetration, weld appearance, and defect rates.
- Argon is the most widely used. It produces clean, bright welds and provides stable shielding. It works well for most applications, though it can trap gas pores in thicker materials if flow isn’t well controlled.
- Helium improves energy transfer into the workpiece, giving deeper penetration and reducing porosity and spatter. It’s the preferred choice for reflective materials like copper and aluminum. The downside is cost: helium is significantly more expensive and consumed at higher flow rates.
- Nitrogen promotes smooth, reflective weld surfaces and can increase welding speed. It works well on stainless steel, but on some alloys it can form brittle nitride compounds in the weld zone, so it’s not universally appropriate.
If you’re seeing discoloration or excessive gas pores, the flow rate is likely too low or unevenly distributed across the weld zone. Start with the manufacturer’s recommended flow rate and adjust upward in small increments until the bead runs clean.
Setting Your Parameters
The three core variables are laser power, travel speed, and focal point position. These interact with each other, so changing one usually means adjusting the others.
Power controls how much energy reaches the workpiece. Too little and you won’t get full penetration. Too much and you risk blowing through thin material, excessive spatter, or creating conditions for cracking. Travel speed determines how long the beam interacts with any given point. Slower speeds increase heat input per unit length, which deepens penetration but also widens the heat-affected zone and raises the risk of defects. Faster speeds reduce heat input but may produce incomplete fusion.
Focal point position matters more than many beginners realize. Placing the focus at the surface maximizes power density on top. Dropping the focus slightly below the surface can improve penetration in keyhole mode. Raising it above the surface spreads the beam and shifts toward conduction mode, which can be useful for sealing passes or cosmetic work.
The best approach is to run test welds on scrap material of the same type and thickness, starting with parameters from your machine’s reference charts and making one adjustment at a time. Cut your test welds in cross-section if you can. What looks good on the surface doesn’t always have full penetration or a sound internal structure.
Welding Different Metals
Laser welding handles most common metals well, including carbon steel, stainless steel, and titanium. Aluminum and copper are more challenging because they reflect laser light and conduct heat rapidly, pulling energy away from the weld zone. Higher power or helium shielding gas (or both) helps compensate.
Joining dissimilar metals is where things get genuinely difficult. Aluminum welded to steel forms brittle compounds at the interface that reduce ductility and fatigue life. The key mitigation is controlling heat input carefully: higher welding speeds reduce the time iron and aluminum spend reacting, producing thinner brittle layers and stronger joints. Using a copper backing block to accelerate cooling can also suppress the formation of these damaging compounds.
Copper welded to steel, common in electric vehicle battery manufacturing, presents its own problems. The large difference in melting temperatures and thermal conductivity makes achieving a complete bond challenging. Molten copper can penetrate steel grain boundaries and cause cracking. The most reliable technique is offsetting the laser beam toward the steel side, keeping the copper mostly solid and minimizing how much the two metals intermix. Successful joints have been produced with very low copper dilution in the weld, under 1 atomic percent.
Troubleshooting Common Defects
Porosity (small gas pores trapped in the weld) is the most frequent defect in laser welding. It usually comes from contamination on the surface, inadequate shielding gas coverage, or an unstable keyhole that collapses and traps vapor. Cleaning the joint thoroughly before welding, ensuring consistent gas flow, and stabilizing your travel speed address most porosity issues.
Hot cracking happens when the weld solidifies under tension and the partially solidified metal splits along grain boundaries. It’s most common in aluminum alloys and high-alloy steels. High heat input and high power density together make cracking more likely. Reducing heat input to around 30 J/mm or lower significantly reduces the risk in aluminum. Faster travel speeds help by producing finer grain structures with more grain boundaries, which distributes stress rather than concentrating it. If cracking persists, the root cause may be elemental segregation: alloying elements like silicon, chromium, and iron can concentrate between grains during solidification, weakening those boundaries.
Undercut (a groove along the edge of the weld) and burn-through (blowing a hole through the material) both indicate excessive heat input. Reduce power, increase speed, or both.
Safety Requirements
Laser welding involves Class 4 lasers, the highest hazard classification. Direct or reflected beams can cause instant, permanent eye damage and skin burns. Proper laser safety eyewear rated for your specific wavelength is mandatory any time the beam path isn’t fully enclosed. Industrial systems typically operate inside interlocked enclosures that shut the laser off if a door or panel opens. Handheld laser welders rely on the operator wearing appropriate protective eyewear and skin coverage instead.
Fume extraction is equally important. Laser welding vaporizes metal, producing fine particulate that’s easily inhaled. A local exhaust ventilation system positioned near the weld zone is necessary regardless of the material being welded. Applicable safety standards include the ANSI Z136 series for laser safety, IEC 60825-4 for laser guards, and ISO 11553-1 for laser processing machine safety. OSHA references these standards for workplace compliance in the United States.