How Fiber Laser Welding Works

Fiber laser welding is one of the most efficient ways to join metal in modern factories. Compared with TIG/MIG and resistance welding, a fiber laser can deliver very high energy density into a small, controllable spot. The result is deep penetration, small heat-affected zones, and smooth weld seams that require little grinding or rework.

This article explains how fiber laser welding actually works — from the laser source and beam delivery to keyhole formation, wobble motion, shielding gas and process parameters.

What Is a Fiber Laser Welding System?

A fiber laser welding system converts electrical energy into a focused beam of light and delivers it to the workpiece through optical fiber and a welding head. At a high level it consists of:

• Fiber laser source (typically 1070–1080 nm wavelength)
• Beam delivery fiber (flexible optical fiber cable)
• Collimating and focusing optics inside the welding head
• Wobble or scanning module to control beam movement
• Shielding gas system to protect the melt pool
• Motion system — handheld, gantry, or robot

The combination of high beam quality, flexible delivery and advanced control makes fiber laser welding suitable for both manual operation and fully automated production lines.

Inside the Fiber Laser Source

Wavelength and Gain Medium

Industrial fiber lasers used for welding typically operate around 1070–1080 nm in the near-infrared range. The gain medium is rare-earth-doped optical fiber (for example, ytterbium-doped fiber). When pumped by diode lasers, this fiber amplifies light and produces a high-power laser beam with excellent beam quality.

Beam Quality and Mode

Beam quality, often described by BPP (beam parameter product), determines how tightly the beam can be focused. A good beam quality allows the system to create a smaller spot size and higher energy density on the workpiece. This is one of the key reasons why fiber lasers can weld deep seams with relatively modest power (800–2000 W) compared with traditional arc processes.

Continuous vs Modulated Output

Most industrial fiber welding systems operate in continuous wave (CW) mode with the ability to modulate power using high-frequency PWM (e.g. 1 kHz). Modulation is used to:

• Control heat input on thin materials
• Reduce spatter on carbon steel
• Stabilize the keyhole on aluminum

Some systems can also provide pulsed operation for spot welds, but continuous or quasi-continuous modes cover the majority of sheet-metal applications.

From Laser Source to Welding Spot: Beam Delivery & Focusing

Delivery Fiber

The laser beam leaves the source and enters a flexible delivery fiber. This fiber can be several meters long, allowing the welding head to move freely along parts, fixtures and robotic arms. Because the beam stays fully contained inside the fiber, alignment is stable and maintenance requirements are low compared with mirror-based systems.

Collimation

At the entrance of the welding head, collimating optics transform the divergent beam exiting the fiber into a nearly parallel beam. This prepares the beam for focusing by the final lens.

Focusing Optics and Spot Size

The focusing lens concentrates the collimated beam into a small spot on the workpiece. Typical focal lengths are between 100 and 200 mm for handheld welding. Spot diameter is often in the range of 0.6–1.5 mm, depending on optics and beam quality.

Energy density on the surface is approximately:

Energy Density ≈ Laser Power / Spot Area

With 1200 W power and a 0.8 mm spot, the power density can easily exceed 10⁶ W/cm². This is sufficient to form a keyhole and achieve deep penetration.

Keyhole Formation and Melt Pool Behavior

Conduction Welding vs Keyhole Welding

At lower power densities or larger spot sizes, laser welding operates in conduction mode. Heat flows from the surface into the material and forms a shallow weld pool. This mode is suitable for cosmetic welds or very thin sheets.

When the power density is high enough, vapor pressure opens a narrow cavity in the molten metal — the keyhole. The laser beam couples into this cavity and penetrates deeper into the material, creating a slender but deep molten zone. This is keyhole welding, ideal for structural joints in 1–4 mm stainless or carbon steel.

Melt Pool Dynamics

Inside the keyhole, vapor pressure, surface tension and gravity interact to shape the weld pool. Proper control of power, speed, wobble width and gas flow is essential to:

• Maintain a stable keyhole
• Prevent collapse or excessive spatter
• Achieve smooth, uniform seams

For example, on 2 mm stainless steel, a 1200 W system might run at 40–55% power with a moderate welding speed and 1.5–3.0 mm wobble width to balance penetration and surface finish.

Heat Input and Heat-Affected Zone (HAZ)

Laser welding delivers heat in a confined area and for a short time. Compared to TIG/MIG, the same penetration depth is achieved with far lower total heat input. This results in:

• Smaller HAZ
• Less distortion and warping
• Reduced need for straightening or rework

Wobble Welding: Why Motion Matters

What Is Wobble Welding?

In fiber laser welding, wobble means that the laser spot follows a small oscillating path (e.g. circular, figure-eight, or linear patterns) while moving along the weld seam. Modern welding heads can adjust wobble amplitude (e.g. 0.5–5 mm) and frequency (e.g. 10–300 Hz) in real time.

Benefits of Wobble Motion

• Wider seam without increasing heat input
• Better gap bridging for joints with 0.3–0.6 mm gaps
• Improved weld appearance and smoother edges
• Higher stability when welding aluminum or galvanized steel

For example, when welding 1.5–2.0 mm aluminum plates, a wobble width of 2–3 mm with moderate frequency can reduce porosity, stabilize the pool and improve overall seam quality.

Wobble Patterns

Common wobble patterns in industrial laser welding include:

• Linear oscillation (left–right)
• Circular or elliptical paths
• Infinity (∞) shaped trajectories

Each pattern changes how energy is distributed across the joint and can be tuned for specific materials and thicknesses. The ability to adjust these patterns on the fly is one of the main advantages of modern handheld and robotic fiber welding systems.

Process Parameters That Control Fiber Laser Welding

A successful welding process is the result of matching several parameters to the material and joint type. Key variables include:

Laser Power and Peak Power

Power determines how much energy enters the material per unit time. Many systems express settings as a percentage of rated power (for example, 30–80% on an 800 W or 1200 W source). Thicker materials and higher speeds typically require higher peak power.

Travel Speed

If speed is too slow, the weld becomes wide and may overheat or burn through thin material. If speed is too fast, penetration decreases and the seam may be incomplete. For 0.8–2.0 mm stainless steel, typical handheld welding speeds are in the range of 300–900 mm/min depending on power and joint design.

Focus Position

Focus can be set at the surface, slightly inside the material, or above the surface (positive focus). Small changes in focus can significantly affect penetration and surface appearance:

• Negative focus (below surface) — deeper penetration, narrower seam.
• Zero focus (on surface) — balanced penetration and surface quality.
• Positive focus (above surface) — shallower penetration, wider top bead, often used for aluminum.

Wobble Amplitude and Frequency

Amplitude controls seam width and gap tolerance; frequency influences how uniformly energy is distributed along the joint. Higher frequencies generally make the seam smoother but require adequate power to maintain penetration.

Shielding Gas Type and Flow

Shielding gas protects the molten pool from oxidation and affects cooling rate, color and porosity:

• Nitrogen (N₂) — widely used for stainless steel; cost-effective.
• Argon (Ar) — excellent protection, often used for aluminum and titanium.
• Mixed gases — customized solutions for specific alloys.

Typical flow rates for handheld welding are between 15 and 25 L/min, with nozzle design and standoff distance influencing actual coverage.

Wire Feeding (Optional)

Some fiber laser welding applications use filler wire to:

• Bridge larger gaps
• Match alloy composition
• Build up fillet welds

Wire diameter (0.8–1.6 mm) and feed speed must be matched to laser power and travel speed to avoid lack of fusion or excessive reinforcement.

Role of Shielding Gas and Surface Preparation

Gas Protection and Weld Appearance

Good shielding creates bright and uniform welds. Poor shielding leads to discoloration, oxidation, porosity and inconsistent mechanical properties. Proper nozzle design, angle, and distance from the workpiece are just as important as flow rate.

Cleaning and Joint Preparation

Fiber laser welding is tolerant to small imperfections but still benefits from clean surfaces:

• Remove oil, grease and paint from the weld area
• For aluminum, remove oxide layer shortly before welding
• Ensure consistent fit-up and clamping to avoid joint movement

Well-prepared joints reduce the risk of porosity, undercut and incomplete fusion, especially at high welding speeds.

Why Fiber Laser Welding Is So Attractive for Factories

From a business perspective, fiber laser welding is attractive because it converts process control into repeatable parameters and software settings instead of relying solely on operator skill. The main benefits include:

• Higher throughput — 2–5× faster than TIG/MIG for many sheet-metal jobs.
• Less rework — cleaner seams and minimal distortion mean less grinding, straightening and polishing.
• Stable quality — once parameters are set, results are highly repeatable across shifts.
• Easier automation — fiber lasers integrate easily with robots, gantries and vision systems.

For factories dealing with stainless enclosures, carbon-steel frames or aluminum structures in the 0.5–4 mm thickness range, fiber laser welding can significantly reduce manufacturing cost per part while improving aesthetic quality.