Laser Welding is a welding technology used to join several metal components. A laser produces a beam of high-intensity that is concentrated into one spot. This concentrated heat source enables fine, deep welding and high welding speeds.
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 and the traditional pulsed Nd:YAG welding lasers are limited by the maximum welding speed, the minimal spot size that can be achieved and the electrical to optical energy conversion efficiency that is very bad.
With fiber laser welding, the output power and the oscillation form of the laser beam is possible to change. Fiber Laser Welding is also very suitable for welding materials with a high melting point or with high thermal conductivity due to a very low thermal effect during welding. The energy conversion rate is very high and all this makes fiber laser highly adaptable to various applications for use in various welding assembly processes.
The fiber laser beam used for welding can be adapted as folows and characterized by different laser oscillation modes :
Pulsed laser beam welding (ideal for spot welding)
Continuous laser beam welding (ideal for seam welding)
Ever more applications are demanding a higher precision control, lower heat input and lower electrical energy consumption.
Fiber Laser Welding is a technology that offers ALL those features.
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 (pulse mode). 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 3~4mm depth for a 1000W fiber laser, high speed seam welding of same and dissimilar materials, and producing spot welds below 100 microns in diameter when not applying the wobbling function.
Pulse Width (Laser Welding)
When a laser is in pulse mode, the duration of the pulse is known as the pulse width. In many process applications pulse width is used to tune the process, as opposed to peak power which is the gross process adjustment.
For welding, milliseconds are typically used; in cutting, microseconds and in marking and micromachining nanoseconds.
Heat conduction welding is a laser welding method that features a low power output laser beam. This makes for a penetration depth of no more than 1 to 2 mm. With the ability to handle a relatively wide power range, heat conduction welding can be adjusted to the ideal power level, and the shallow penetration makes it possible to weld materials that are susceptible to heat effects under optimal conditions.
This welding type is used for butt joints, lap joints, and other welding applications for thin plates, and can also be used for welding hermetic seals and other seals. Heat conduction welding is also suitable for volatile alloys such as magnesium and zinc, for which keyhole (deep penetration) welding is not suitable.
Keyhole welding (deep penetration welding) uses a high power output laser beam for high-speed welding. The narrow, deep penetration allows for uniform welding of internal structures. Because the heat-affected zone is very small, distortion of the base material due heath from the welding will be minimized.
This method is suitable for applications requiring deep penetration or when welding multiple base materials stacked together (including for butts, corners, Ts, laps, and flange joints).
Materials are joined without the addition of extra materials which requires the highest level of fixturing and joint preparation.
Since no material is added, it is necessary for the materials to be welded to remain in intimate contact during the welding process. Any significant separation of the materials can result in an unacceptable weld profile or complete failure of the welded joint.
Fixturing to ensure consistent fit-up of the weld joint is a key to successful fiber laser welding. An important benefit of fiber laser is welded joints with exceptional cosmetic appearance. In some cases, these welds are almost perfectly blended with the surrounding material. Depending on the fixturing and joint fit-up, some welds may have small amounts of concavity (which may not be acceptable for product designs that require fatigue properties similar to those of the base material) or convexity.
Additive Welding or Deposit Welding:
Material is added to the weld joint usually in the form of metallic wire or powder.
This method is also referred to as laser cladding or direct metal deposition. Welding involves the use of a filler material, with the surfaces of the filler material and the base material melting to form a metallurgical bond. Common filler materials are wire or metal powder. This method can be either automatic or manual depending on the application. Laser deposit welding can be used not only for joining but also for repairing weld surface defects, for manufacturing mesh-shaped components by forming weld beads, and for processing metal surfaces.
Three reasons for adding material to the weld are:
- Joint fit-up: By adding extra material, the joint becomes more tolerant to joint mismatch. Acceptable welds may be produced from joints with less than perfect fit-up.
- Weld geometry: Addition of filler metal is used to control the shape and size of the weld. Maintaining a crown (convex surface of the weld) creates a reinforcement which is important for joints requiring mechanical strength and fatigue life in the overall product’s design performance.
- Dissimilar metals: Filler metal is added to facilitate welding of dissimilar metals and alloys which are otherwise metallurgically incompatible.
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Fiber lasers in the power range of 1000 W to 5000 W can weld heavier metals connections at high speeds. Applications can be as diverse as stainless steel sheets for kitchen tops, galvanized steel backplates for flat screen LCD TV’s, sheet steel for stators in electric motors, structural parts such as turbocharger waste gates, stainless steel bellows, copper wires, tabs for batteries, etc. Thicknesses of up to 5 mm can be welded and speeds of up to 50 cm/second can be achieved.
Fiber lasers in this power range are increasingly replacing other welding processes such as Resistance Welding (spot welding), TIG welding, MIG welding, Electron beam welding, etc. With lasers at these power levels, the weld speed is typically only limited to the speed of moving the system or the parts and feeding the parts to and from the system. In the coming years, the power of these lasers is expected to increase by 20% - 30% year on year and even more traditional welding processes will be replaced by laser welding.
Affordable handheld fiber lasers for a normal workshop are between 500 and 2000 Watt light power. This makes the welding of steel of 5 mm thickness easilyposssible and very fast. Everybody can weld now with a handheld fiber laser welder.
Fiber lasers with 500 W to 1200 W and a fiber core diameter of between 100 and 300 microns, typically replace the older Pulsed YAG and les precise disk lasers for precision metal welding. In this range, the fiber laser will provide greater welding speed for the same investment level. The welding speed may be up to ten times higher. As an indication, a 500 W fiber laser will give a weld of 1 mm deep and 1 mm wide at about 1 cm/second in mild steel. This fiber laser is difficult to beat in terms of value for money if the application is suited to this type of welding.
A special type of welding is achieved with lasers in the power range of up to 500 W that have a very small diameter fiber of 20 microns or below. Due to this small diameter, a very high energy concentration will be obtained. This produces keyhole welding.
This type of welding is normally coupled with a scanner head which allows the laser beam to progress at very high speeds. The laser beam can be moved in a linear manner or in a circular or wobble pattern to achieve a wider weld beam.
It is possible to weld even the smallest parts with low power Fiber lasers, typically in the 100 W to 200 W average power range. These fiber laser levels are well suited for this type of welding because of their features: Fiber Laser Welding penetration depth
Very small fiber laser beam core diameters.
The low power level and high beam quality allow power of up to 500 W to be fired into 10 or 20 micron cores. This results in very small weld spot sizes.
Excellent power stability.
A fiber laser will be stable down to about 10% of its power level. For example, a 200 W laser will be stable to 20 W power. When combined with a 1 ms pulse length, it is possible to achieve weld pulse energies of 20 mJ. This is sufficient for the finest welds that can be found in precision metal welding.
Typical applications are stents, small medical meshes and thin membranes for pressure sensors. Typical materials are 50 micron Nitinol wires, 10 to 50 micron platinum coil wires, 10 micron stainless steel foils, etc.