It travels at 299.792.458 meters per sec. Its visible spectrum ranges from 400 to 700 nanometers. Its smallest unit is a packet of energy, a photon. It is light, and its use is growing in tube and pipe production and fabrication facilities throughout the world.
In most of its natural and artificial forms, light has little power. However, a groundbreaking invention in the latter half of the 1950s increased its power and concentrated it in a small area. Thus was born a modern and revolutionary concept: Light Amplification by Stimulated Emission of Radiation, or laser.
A fiber laser is generated within a flexible doped glass fiber that is typically 10 to 30 feet long and between 10 and 50 microns diameter. Ytterbium is usually used as the doping element. You do not have to align the medium to cavity mirrors, nor maintain optics and alignment. In fact, it’s such an efficient lasing process that this laser can be small, air-cooled, and provide high wall plug efficiencies. Fiber lasers offer great “focusability” and a range of beam qualities, which can be tuned for each welding application.
A fiber laser is a special type of laser in which the beam delivery as well as the laser cavity is integrated into a single system inside an optical fiber with the beam generated within the fiber, unlike conventional lasers where the beam is generated outside and sent into the system. Considered as a special category of solid state laser, fiber lasers provide many benefits compared with other laser technologies, such as:
Ease of use
High integration capability
Fiber lasers are "the" recognized powerhouse in the manufacturing sector of numerous industries because of the throughput, reliability, and low cost of operation they make possible for machines that cut, weld, mark, and micromachine materials. Specific design elements distinguish fiber lasers among other industrial laser sources, and their unique attributes are enabling breakthrough manufacturing process capabilities. Specifically, high-power single-mode lasers for remote welding and widely flexible pulsed fiber lasers for cutting can address different process challenges by the full electronic control of all operating parameters.
The fiber laser is exceptional efficient at converting relatively low-brightness pump light from laser diodes into high-brightness output, where the output beam quality is often the only spatial mode allowed by the physics of the fiber design. Even though fiber lasers were capable of very high (100 W) output as early as the 1990s, it took the crash of the fiber communications market in 2001 to enable the commercial development of reliable fiber lasers. During the 1990s, companies spent billions of dollars solving the basic problems of coupling diodes to fibers with high reliability, splicing fibers with high power density, qualifying component technologies to meet the 25-year reliability required by undersea communications, and reducing the cost of these high-performance, high-reliability components.
Then, in the early 2000's, with the communications market all but gone, the technology investment was quickly redirected and tuned for use in the design of industrial fiber lasers.
Fiber lasers are unique among all other industrial laser types because of two attributes: a sealed optical cavity and a single-mode, guided-wave medium. Modern fiber lasers, by design, have a fully sealed optical path that is immune to environmental contamination and remains optically aligned without need for adjustment. All internal components are either in-fiber or hermetically fiber-coupled, and the only free-space interfaces occur at the beam delivery optic, which includes a fused beam spreader to reduce the intensity at the first free-space interface. The active optical path is typically within a fiber waveguide that allows only one spatial mode of propagation (currently up to about 20 kW of optical power). Higher-power fiber lasers combine single-mode modules into high-brightness delivery fiber in fused fiber combiners.
The combination of the single-mode waveguiding and the fully sealed optical cavity provides a robust laser design that is fixed and measured at the time of manufacture and has minimal variation over time and temperature. Sealed pump diodes and nondarkening fiber technology result in lasers that can be used continuously in production for years without adjustment or degradation.
Continuous wave (CW)
With a CW laser, the laser output remains on until being turned off. For spot welding either a single weld or a seam, the laser output can be modulated – this means the laser is turned on and off rapidly. The CW laser’s peak power is the same as its maximum average power, so focused spot sizes are generally under 100 microns. CW fiber lasers are usually a good choice for general seam welding up to 1.5 mm depth for a 500W laser, high speed seam welding of same and dissimilar materials, and producing spot welds below 100 microns in diameter.
Quasi-continuous wave (QCW)
The QCW fiber laser’s peak power and pulse width characteristics are similar to those of the Nd:YAG laser. The QCW lasers offer single mode to multi-mode options with spot sizes from 0.02 to 1.0 mm. These lasers also shine in small spot size applications and penetration applications, although they really can handle many micro welding applications.
The nanosecond fiber laser is a relatively new addition to the family. Often used for laser marking applications, nanosecond fiber lasers actually make a very cost effective welding solution. The nanosecond laser provides multi-kilowatt peak power, but with pulse widths around 60-250 nanoseconds that can be delivered between 20-500 kHz. This high peak power enables welding of almost any metal, including steels, copper, and aluminum. The nanosecond fiber laser’s very short pulse widths means you can get very fine control for welding small parts. This one is also a good choice if you need to weld dissimilar materials.
Of course, there are Limitations that must be addressed, and high-wattage fiber lasers are proving to offer their own manufacturing balancing acts. Some might consider these "good" issues, but they do require additional planning. A 6kW fiber laser is significantly faster than the 4 and 2kW fiber laser machines, as well as any CO2 laser alternative. Add plasma and water jet in the mix, and the productivity of this one machine will double or even triple throughput from the same or less floor space compared to previous operations. Some manufacturers have even reported that their machine is so fast that the Green Light On is actually lower than their slower predecessors, mainly because of the fact that these lasers are piling up downstream processes. This ability to overload production has forced manufacturers to rethink downstream processes like material handling and bending operations. A balanced shop flow can be easily altered by just one high-powered machine and can often mean that the next capital investment may need to be focused on the bending process, such as auto-tool-change press brakes and robotic technology. And what about material handling? These are serious considerations that may not have been considered before—but make no mistake, high-power fiber lasers will improve overall throughput.
In summary, high-power fiber lasers have evolved and quickly found their place in the fabricating industry for many reasons. They are as easy to operate as their lower-powered counterparts. Any additional capital investment can be offset by significantly higher production and lower operating costs than CO2 laser machines in that power range. The ability of fiber lasers to process thick plate has also opened the door to alternative processes, such as plasma and water jet. The industry has lifted the veil of obscurity and shown fiber lasers to be a viable solution for today's blanking needs, such that it suddenly has become the blanking solution to address that ever-shrinking wiggle room between low-volume orders and profitable production output. High power, more production, less cost, more flexibility, and more profit—today's fiber laser offers all of this to manufacturers.
In metal working applications, medium power Fiber Lasers in the range 50W to 2000W offer new degrees of operational freedom and process control. The ability to operate with pulse lengths continuously tunable from a few microseconds to full CW operation and with pulse repetition rates up to tens of kilohertz offers the applications engineer the ability to optimise the process conditions over a wide range of applications.
Due to their monolithic single mode fiber construction Fiber Lasers do not suffer from changes in focus position due to thermal lensing as the average power is changed, and don’t require periodic adjustment or tuning of the Laser cavity or component maintenance to ensure output stability.
Traditional laser welding technologies, such as continuous-wave CO2 welding lasers are limited in terms of accuracy and undesired, high heat input into the weld. On the other hand, the limitations of traditional pulsed Nd:YAG or the newly developped pulsed QCW are the maximum welding speed, the minimal spot size that can be achieved and the electrical to optical energy conversion efficiency that can be obtained. Ever more applications are demanding a higher precision control, lower heat input and lower electrical energy consumption. Continuous Wave Fiber Laser Welding is a technology that offers those features.
In a fiber laser, the laser light is generated in an active fiber and guided to the work piece by means of a flexible delivery fiber, which acts as a “light guide”. The flexibility of the delivery of this laser beam is an important feature for many forms of material processing such as laser cutting, laser welding, laser marking and laser engraving.
Continuous Wave versus Pulsed Wave for metal welding
Fiber lasers are available with both type of energy delivery: Continuous and Pulsed.
As the name states, the Continuous Wave (CW) lasers deliver a continuous, uninterrupted output. This output can have an upslope (soft-start) when switched on, an energy modulation while active, and a downslope when switched off (crater filler). Of course, this type of laser can also be switched on and off to create pulses. However, the maximum power level can never exceed the average power.
In contrast, the Pulsed Fiber lasers deliver a pulse of energy which is typically ten to twenty times higher than their average power. For example, a laser can have 300 W average power and 4000 W peak power. These lasers are often referred to as Quasi Continuous Wave (QCW) Fiber Lasers.