Industrial laser welding has had a dramatic impact in the Machine Tool Industry over the years and has become the answer to many problems brought about by traditional welding methods. Many metalworking companies have turned to laser spot and laser seam welding due to these advantages. Automation, high welding speeds and contact-free processing help laser welding users achieve economic advantages very quickly.
Since laser welding produces pure, concentrated energy, it creates deeper welds while leaving high production output. This is one of the many reasons laser spot and seam welding systems are used in manufacturing in this industry. Items we use every day in our gadgets, electronics and parts have gone through laser welding technology in the course of their production.
Laser Spot Welding & Laser Seam Welding
Laser spot welding, laser seam welding, and direct welding are highly useful and slightly differing applications of laser welding technology. Laser spot and seam welding refer to welding functions applied to a single point or along a line. By setting a laser welding system to a high speed and extremely narrow weld geometry, the laser welder can produce extremely fine spot welding. Also, you can adjust the system to weld on continuous wave mode, welding with several kilowatts of power. The ideal laser speed for laser spot or seam welding projects varies according to the particular laser model, the laser power setting, and the material being laser welded.
Laser welding requires that the laser raise the temperature of the material to be welded. The fiber laser light must be absorbed by the material to induce a temperature rise. In effect, the fiber laser light beam is focused onto the material similar to the way the sun can be focused by a magnifying glass. The difference is that the laser’s power density is many orders of magnitude higher.
Laser light photons, packets of light energy that make up the laser, impinge onto the material and are partly or wholly absorbed. The energy of the photon is absorbed in the metal material and causes a heat waves within the metal. Repeated absorption of photons eventually leads to metal surface breakup and melting.
Even for metals that absorb well, such as steel, the laser is initially reflected. A small percentage of the laser is absorbed, heating the metal surface. The increased surface temperature increases the absorption of the fiber laser light photons. This creates a snowball effect, in which the material is rapidly heated by the laser, leading to melting and formation of the weld.
Fiber laser welding, like other laser-machining methods, is a non-contact technology that has a limited, heat-affected zone (HAZ), which is why the technology is a preferred method for welding delicate products at high speeds. Laser welding is also a more repeatable and consistent process than other welding methods, and is capable of producing high-strength bonds without the need for filler material, flux, prepping, or secondary cleaning and finishing processes. Fiber Laser Welding has enabled many applications, such as energy storage with lithium ion batteries and implantable medical devices, to be manufactured in extreme scales, at much lower costs, with greater consistency, at greater speeds, and with much less waste and quality-control issues. Moreover, a laser welding manufacturing process is much more reliable than other welding technologies, as the latest laser-welding machines require little to no maintenance, and virtually no downtime.
All lasers with a wavelength between 532 nm and 1070 nm deliver the laser to the welding area using a flexible fiber optic cable. The convenience of fiber delivery greatly facilitates the integration of the laser into turnkey laser welding systems. Typically the length of the delivery fiber is between 5-10 meters (m), though it can be up to 50 m, depending upon the type of laser being used. This enables flexible positioning of the laser, which can be particularly useful for certain production lines.
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 follows and characterized by different laser oscillation modes :
Pulsed laser beam welding (ideal for spot welding)
Continuous laser beam welding (ideal for seam welding)
Even 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.
Fiber laser welding is a high power density process that provides a unique welding capability to maximize penetration with minimal heat input. The weld is formed as the intense laser light rapidly heats the material – typically in fractions of milliseconds. There are three types of welds, based on the power density contained within the focus spot size: conduction mode, transition keyhole mode, and penetration/keyhole mode.
Conduction mode welding is performed at low energy density, typically around 0.5 MW/cm², forming a weld nugget that is shallow and wide. The heat to create the weld into the material occurs by conduction from the surface. Typically this can be used for applications that require an aesthetic weld or when particulates are a concern, such as certain battery sealing applications.
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.
Transition mode laser welding occurs at medium power density, around 1 MW/cm2, and results in more penetration than conduction mode due to the creation of what is known as the “keyhole.” The keyhole is a column of vaporized metal that extends into the material; its diameter is much smaller than the weld width and is sustained against the forces of the surrounding molten material by vapor pressure. The depth of the keyhole into the material is controlled by power density and time. Because the optical density of the keyhole is low it acts as a conduit to deliver the laser power into the material.
Keyhole or penetration mode welding – Increasing the peak power density beyond 1.5MW/cm2 shifts the weld to keyhole mode, which is characterized by deep narrow welds with an aspect ratio greater than 1.5. The penetration depth rapidly increases when the peak power density is beyond 1 MW/cm2, transitioning the weld mode from conduction to keyhole/penetration welding.
Penetration or keyhole mode welding is characterized by narrow welds. This direct delivery of laser power into the material maximizes weld depth and minimizes the heat into the material, reducing the heat affected zone and part distortion. In this keyhole mode, the weld can be either completed at very high speeds – in excess of 500mm per second with small penetration typically under 0.5 mm – or at lower speed, with deep penetration up to 12 mm.
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 to the heat 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).
A pulsed laser produces a series of pulses, discrete packets of energy, at a certain pulse width and frequency until stopped. The “pulsed” descriptor refers to a laser that can produce a peak power that is greater than its average power.
A continuous wave (CW) laser produces extended output – the laser remains on continuously until stopped.
For example, a 25 W pulsed Nd:YAG laser can produce peak powers of up to 5 kW for a few milliseconds. This means it can produce a spot weld that would require a CW laser sized at 5 kW! With pulsed lasers a seam weld is created by a series of overlapping spot welds. For a continuous weld the laser remains on for the duration of the seam. A CW laser can also produce discrete pulses of laser light – known as gated or modulated output. In this case the CW laser peak power does not exceed the laser’s rated average power.
An Nd-YAG laser operates only in pulsed mode
Diode lasers operate in continuous wave
Fiber lasers can operate in both modes.
Choosing when to use pulsed, continuous wave, or modulated output is determined by the specific application. Spot welding typically uses pulsed operation. For seam welding, the selection is made based on heat input and cycle time. For instance, when seam welding an implantable device, a pulsed laser is used to minimize heat input and maintain a uniform weld around a complex geometry with varying welding speeds. In contrast, for airbag initiators, welding at high speed using CW operation is
Above all, the use of laser welding for metal parts improves productivity by reducing the time spent on welding and straightening the welded parts, and allows greater freedom in the designing of parts (simpler assemblies). Laser welding also helps make savings by reducing production costs and the materials consumed by the welding process. This welding method also affects the quality of the assembly by offering mechanical strength that is at least equal to that of the base material, and by reducing the part deformation rate. Laser welding is also an excellent solution for joining subassemblies of dissimilar parts or treated parts (carbonitrided, case hardened, etc)
- Welding productivity can increase by up to 800 %
- Reproducible process
- Reduction or even elimination of the time for straightening welded pieces
- Overall reduction of production costs
- Mechanical resistance at least equivalent to that of the base metal
- Reduction of welding consumables
- Great freedom in the designing of parts
- Welding of dissimilar materials (steel to cast iron, stainless steel to Inconel, etc)
- Welding of precious materials
- Welding close to delicate components
- Welding time is reduced to a tenth
- Reduced deformation of parts
- Welding of parts with limited accessibility
- Process that can be automated
- Assembly with no filler metal
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