How does fiber laser welding work?

Many factories fight with weak joints, warped parts, and slow cycle times. I have seen those headaches break tight delivery dates.

Fiber laser welding fuses metal with a tiny, high‑energy light spot. It is faster, cleaner, and stronger than arc welding because it adds only the heat you need.

Some owners still cling to sticks and torches. Let me walk you through each core idea so you can decide with clear facts.

What is the principle of fiber laser welding?

Thin sheets bend. Shiny metals bounce heat away. Old methods leave pores and cracks.

The principle is simple: a focused laser beam melts two edges, the liquid pools blend, and the joint cools into one solid line.

Energy Focus and Keyhole Physics

A fiber laser sends more than one megawatt per square centimeter into a spot as small as a grain of sand. That power makes a “keyhole¹,” a narrow cavity where metal vapor pushes molten walls outward. Surface tension then closes this keyhole as the beam moves on. The result is a deep, slim weld with tiny heat‑affected zones.

Process Parameters and Control

I dial in three levers every day:

Lever	Typical Range	What It Changes	Common Pitfall if Wrong
Power (kW)2	0.5 – 3	Penetration depth	Lack of fusion or blow‑through
Speed (mm/s)	5 – 60	Width of bead	Excess spatter at low speed
Pulse Width (ms)	0.5 – 10	Heat input per pulse	Craters if pulse is too short

Balancing these levers keeps the keyhole stable. At Kirin Laser I train new buyers to save three starting recipes for thin stainless, thick carbon steel, and reflective copper. They tweak from a known good base instead of guessing.

Material Behavior and Shield Gas

Aluminum needs helium or a helium‑argon mix because that gas clears the plasma faster. Stainless likes pure argon. I once had a client who saved 20 % gas cost by switching, yet saw no drop in quality. Simple adjustments pay big dividends.

How does the laser welding work?

Shop staff often ask, “Is it just light or is there more going on?” The answer mixes optics, motion, and feedback.

Laser welding converts electrical power into a stable beam, guides it through fiber, focuses it on the part, and steers it with hand or robot.

From Wall Plug to Weld Pool

1. Power Supply
   AC power feeds diode banks with >45 % electrical‑to‑light efficiency.

2. Fiber Amplification
   The ytterbium‑doped core traps pump light, amplifies the signal, and delivers a single‑mode beam with M² ≈ 1.2.

3. Beam Delivery
   A 15‑meter armored fiber cable stays flexible. I often route it through cable chains on robots.

4. Focusing Optics
   A collimator straightens the beam, then a lens shrinks it to 0.15 mm. Shorter focal lengths give sharper spots but less stand‑off room.

5. Motion System
   Handheld heads weigh about 800 g. Robotic heads mount on six‑axis arms for repeat jobs.

Closed‑Loop Monitoring

At Kirin Laser I add real‑time power meters³ and high‑speed photodiodes. They watch back‑reflected light⁴. When that spike crosses a limit, the controller lifts power for a millisecond to keep the keyhole alive. This loop turns tough copper seams from red‑hot guesswork into steady flow.

Sensor Type	What It Reads	Response Time	Benefit
Photodiode	Back reflection	<10 µs	Stops blow‑outs
Pyrometer	Pool temperature	1 ms	Cuts heat stains
CCD Camera	Melt pool width	5 ms	Guides seam tracking

My Field Story

A Midwest appliance maker fought soot marks on brushed stainless doors. By adding pyrometer feedback⁵, we dropped their re‑polish steps to zero. The payback for the sensor kit came in six weeks.

How does the fiber laser work?

Big CO₂ lasers take floor space and water chillers. Fiber units sit on a small cart and sip power.

A fiber laser uses a rare‑earth‑doped glass fiber as both gain medium and waveguide, so light builds strength while staying perfectly aligned.

Anatomy of a Fiber Laser

Section	Main Parts	Task
Diode Module	Pump diodes, heat sink, driver	Create pump light at 915 nm
Gain Fiber	Ytterbium‑doped core, cladding	Amplify seed at 1064 nm
FBG Pair	Two fiber Bragg gratings	Form resonator mirrors
Combiner	Fiber bundle splice	Merge many pump fibers
Output Fiber	QBH or QD connector	Carry final beam to work head

The glass cladding traps pump light by total internal reflection. That pumping energizes ytterbium ions, which then release photons in phase with the seed. Because the fiber is long and narrow, cooling is natural; air fans often suffice up to 3 kW.

Reliability in Numbers

Metric	CO₂ Laser	Solid‑State YAG	Fiber Laser
Wall Plug Efficiency6	8 %	20 %	35–45 %
Mean Time Between Failures7	8 000 h	12 000 h	>100 000 h
Warm‑up Time	5 min	3 min	<30 s
Mirror Alignment	Monthly	Weekly	None

I stress the last row to every buyer. Less alignment means less downtime. In my own demo lab, our oldest 1 kW source has run a decade with only one fan replacement.

Beam Quality and Modulation

Fiber delivers single‑mode beams, giving high focusability. For thin foils I modulate power in kilohertz bursts. That lets metal cool between pulses, stopping burn‑through even on 0.05 mm foils. Try that with an arc torch—impossible.

Can a fiber laser weld?

People doubt the reach of one tool for many alloys. They fear reflectivity or thermal cracks.

Yes. A fiber laser welds steels, aluminum, copper, brass, titanium, and even dissimilar pairs if you tune the settings.

Material‑Specific Notes

Material	Key Setting to Watch	Shield Gas	Typical Speed (mm/s)	Trick I Use
Stainless Steel8	Power	Argon	20–40	Add wire at gaps >0.2 mm
Carbon Steel	Speed	Argon	25–35	Pre‑clean rust with laser cleaner
Aluminum	Pulse Width	Helium mix	15–25	Use oscillation to break oxide film
Copper	Peak Power	Argon	8–15	Apply black marker to start seam
Dissimilar (Cu‑Al)	Focus	Argon	8–12	Incline head 5 ° to mix pools

Joint Types and Fixturing

I weld butt, lap, and flange joints. Butt joints need gaps under 0.15 mm. Lap joints can hide minor burrs, but I remind users that stack‑ups trap gas. A small vent hole saves blowouts.

For odd shapes, a handheld system shines. My client who built reflector housings moved from TIG to our 1500 W gun. Their scrap on polished brass fell from 12 % to 1 %. They recovered the machine cost in four months.

Codes and Testing

We meet AWS D17.1⁹ for aerospace work. Fiber welds pass dye‑penetrant¹⁰ and X‑ray tests with fewer pores than MIG. Our in‑house pull tests show joints equal to or stronger than parent metal in 95 % of trials.

Conclusion

Fiber laser welding¹¹ rests on a clear principle: focus light, melt only the joint, and leave the rest of the part untouched. By understanding beam physics, sensor feedback, and material quirks, you can weld almost any industrial metal with speed and confidence. At Kirin Laser I drive this knowledge into every machine we ship and every training we run, so partners like you can cut scrap, boost uptime, and deliver products that speak for themselves.