FAQs About Fiber Laser Welding

Key Takeaways

Power density matters more than rated power in copper welding.
BPP can be more informative than M² when evaluating real-world focusing performance.
Fiber lasers can replace TIG welding in many thin-sheet applications.
Contaminated or damaged fiber connectors are among the most common causes of laser failures.

1. How Much Laser Power Do You Need for Copper Welding?

Answer:

Less than you might think—provided you have the right beam quality.

Copper reflects approximately 95% of 1070 nm light at room temperature. Overcoming this high reflectivity and establishing a stable keyhole requires a sufficiently high power density, typically on the order of ~100 MW/cm² under the conditions described below.

In practical terms:

14 μm single-mode @ 1,500 W → ~100 MW/cm² ✅ Around the threshold
100 μm multi-mode @ 6,000 W → ~50 MW/cm² ❌ Below the threshold

For thin copper (0.2–2 mm), a 1.5–3 kW single-mode laser can outperform a 6–10 kW multi-mode system when high power density and precise focusing are required.

Power density is the key—not rated power alone.

2. Single-Mode or Multi-Mode—How Do You Choose?

Ask yourself one question:

Precision or penetration?

Single-mode (M² < 1.3):

Thin copper or aluminum (<3 mm)
Tight weld geometry required
EV batteries, hairpin/flat-wire motors, medical components
Typical power range: 1–4 kW

Multi-mode:

Thick plates (>5 mm)
High-throughput applications requiring deep penetration
Weld appearance is less critical
Typically 6 kW+

Define the application requirements first, then select the appropriate beam quality.

3. Why Am I Getting So Much Spatter When Welding Copper?

There are three major causes, roughly in order of likelihood:

① Power density below the keyhole threshold

Insufficient power density prevents a stable keyhole from forming.

Solution: Increase power density with a smaller spot size, higher laser power, or both.

② Unstable keyhole geometry

A single beam can generate an asymmetric vapor plume, causing the keyhole opening to become unstable.

Solution: Consider ring-mode / FRM beam shaping. In copper busbar welding, FRM beam shaping has been reported to reduce spatter by 60–80% compared with single-mode beam profiles, depending on process conditions.

③ Surface contamination

Even slight oxidation or contamination can change local absorptivity and destabilize the welding process.

4. What Causes Porosity in Aluminum Laser Welding?

There are three fundamental causes:

① Hydrogen porosity

Dissolved hydrogen becomes trapped as the weld pool solidifies.

Solution: Thorough surface preparation, dry filler wire, and high-purity argon (99.999%).

② Keyhole porosity

The keyhole collapses before trapped gas can escape.

Solution: Optimize power modulation or apply slight defocusing to improve keyhole stability.

③ Insufficient power density

If the process operates below the stable keyhole regime, penetration and keyhole stability can suffer.

For aluminum, the stable keyhole threshold can be above ~3.5 MW/cm², depending on material and process conditions.

5. What Is BPP, and Why Can It Be More Important Than M²?

M² describes how closely a beam approaches an ideal Gaussian beam and is useful for comparing lasers under consistent measurement conditions.

BPP (Beam Parameter Product) provides a practical measure of beam quality and focusing performance:

BPP = Beam Waist Radius (mm) × Half-Angle Divergence (mrad)

Examples:

14 μm / 0.065 NA → BPP ≈ 0.45 mm·mrad
50 μm / 0.12 NA → BPP ≈ 3.0 mm·mrad

Generally:

Lower BPP → tighter focusing → higher achievable power density

For demanding copper welding applications at 3 kW, a BPP of approximately ≤0.5 mm·mrad can be advantageous.

6. Can Fiber Lasers Replace TIG Welding?

For many thin-sheet applications, yes.

Speed: Fiber laser welding can be 5–20× faster than TIG for comparable applications and process conditions.

Heat input: Laser welding delivers a narrower and more localized heat-affected zone, resulting in less distortion and a smaller HAZ.

Automation: TIG relies heavily on skilled operators, while fiber laser welding can be highly automated and integrated with robotic systems.

For components with wall thicknesses below 4 mm, the economic payback of switching from TIG to laser welding can often be achieved within 12–18 months, depending on production volume and equipment configuration.

7. Which Shielding Gas Should Be Used for Laser Welding?

Argon (Ar)

A versatile choice for:

Copper
Aluminum
Stainless steel
Titanium

Advantage: Cost-effective and widely available.

Helium (He)

Suitable for:

High-power applications >4 kW
Deep penetration
Applications requiring stronger plasma suppression

Disadvantage: Higher cost.

Ar/He Mixtures

Can be considered for:

6 kW+ applications
Stainless steel
Titanium

Nitrogen (N₂)

Can be used for non-critical carbon steel applications and offers low cost.

Avoid nitrogen for stainless steel or highly reactive metals when metallurgical properties are critical.

8. How Do You Choose the Right Delivery Fiber Diameter?

The delivery fiber diameter affects the minimum achievable focused spot size and the maximum achievable power density.

14–20 μm

Copper welding
Precision applications
1–4 kW

50 μm

General welding
Thin-sheet processing
3–10 kW

100 μm

Thick-plate welding
Structural components
6–20 kW

Important:

Smaller fiber cores generally require smaller minimum bend radii.

This is especially important when integrating the laser into robotic or collaborative-robot welding heads.

9. Conduction Welding vs. Keyhole Welding—What’s the Difference?

Conduction Welding

<1 MW/cm²

Laser energy is absorbed at the surface and transferred through thermal conduction.

Typical characteristics:

Wide, shallow weld pool
Lower penetration
Low spatter

Keyhole Welding

Typically >1–5 MW/cm², depending on the material and process conditions.

The laser vaporizes material and creates a vapor-filled cavity, significantly increasing energy coupling.