Basic knowledge

How does laser welding work? Costs, advantages & disadvantages

| Author / Editor: Frauke Finus / Theresa Knell

In laser welding, two components are joined together. For this purpose, both sides of the abutting material are melted. The melt coalesces and forms the joint.
In laser welding, two components are joined together. For this purpose, both sides of the abutting material are melted. The melt coalesces and forms the joint. (Source: ©wi6995 - stock.adobe.com)

Laser welding is a joining process for metals. Like all welding and joining processes, laser welding exerts heat at specific points.

In laser welding, two components are joined together. For this purpose, both sides of the abutting material are melted. The melt coalesces and forms the joint. Laser beam welding has been in use for about 30 years. Until now, it has been used selectively and has always been in fierce competition with traditional welding methods. Due to modern, additive production methods such as 3D printing of metallic objects, laser welding is currently rapidly gaining in importance.

History of laser welding

The spiritual father of the laser is none other than Albert Einstein. About 100 years ago he published his first thoughts on the subject of light bundling. It took until 1928 for the first experiment to prove Einstein's theories. From there, however, it took another 32 years until the first laser beam could actually be generated with a ruby in 1960. The expensive ruby was replaced a short time later by gas, which made the production of laser devices much cheaper.

Laser welding of steel to aluminum.
Laser welding of steel to aluminum. (Source: LZH)

The utilization of this new, fascinating light form was not long in coming. Initially, lasers brought enormous progress to measurement technology. For the first time, it was possible to carry out precise measurements over huge distances. For instance, NASA astronauts installed a mirror on the moon. With this mirror and a laser stationed on Earth, the distance between the two celestial bodies could be determined to the centimeter. The first attempts at laser beam welding were also made in the 1960s. Initially, however, it was the laser cutting processes that was appreciated most.

The DVS - German Association for Welding and Allied Processes is a technical-scientific professional association which is active in all areas of joining technology.

The lasercut is the most precise way to cut a material. Due to its enormous energy density, the lasercut process is very fast. Not only is the cutting gap itself extremely narrow. The lateral heat-affected zones in this separation process are also so minimal that they can usually be neglected. This distinguishes laser cutting from flame cutting, for example. The plates separated by cutting torches usually have to be deburred and then milled off in order to be usable. Despite the enormous advantages in precision, speed and material protection, laser cutting, and laser welding only occupied a niche for a long time. A notable spread of systems for laser cutting and laser beam welding did not take place until the mid-1980s. Before that, these systems were only used in research institutes and specialist companies.

Above all, it was the aircraft manufacturers who were able to achieve great progress with this innovative separation and joining process. However, the material used as standard in avionics also plays a decisive role in this: The aluminum-based Dural, with a melting temperature of just 600 °C, is much easier to process than the steel used in conventional mechanical engineering. With a melting temperature of 1400 °C, this requires more than twice the amount of energy to melt. But: In order to be able to use laser welding systems efficiently in steel construction as well, the detour via aluminum welding proved to be ideal.

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Today, laser welding is still not a standard welding process. However, it has long since left its experimental status behind. Contract service providers and sheet metal processors are increasingly relying on this high-tech process, which continues to impress with its efficiency, quality and precision.

The process of additive manufacturing, which has started to spread almost 10 years ago, is currently reaching its peak with laser welding. For a long time, 3D printing was only available for ceramics and plastics. In order to manufacture metallic objects by means of 3D printing technology, the only option left until a few years ago was to use these materials for the production of casting cores. However, metal-powder laser welding now makes it possible to manufacture products of any shape by means of 3D printing. This discovery is currently providing laser welding with another boost.

The Profile Welding System (PWS) is a complete and state-of-the-art laser welding system for tubes and profiles, equipped with an integrated process sensor for weld gap detection and tracking. The PWS can be combined with various laser beam sources such as diffusion-cooled CO2 slab lasers of the DC series or the fiber lasers of the High-Light-FL series.
The Profile Welding System (PWS) is a complete and state-of-the-art laser welding system for tubes and profiles, equipped with an integrated process sensor for weld gap detection and tracking. The PWS can be combined with various laser beam sources such as diffusion-cooled CO2 slab lasers of the DC series or the fiber lasers of the High-Light-FL series. (Source: Coherent-Rofin)

Welding will be in the focus of the trade fairs Schweißtec in Stuttgart and the Welding and Cutting in Essen.

Process control and safety during laser welding

Laser beam welding is a largely automated process. It cannot be compared with the traditional manually guided welding methods. Therefore, this joining process is a very safe production step. During laser beam welding, the workpiece is firmly clamped in a fixture. The operator usually keeps a distance. The only danger to people present during this procedure is to accidentally look into the laser beam. For this purpose, special protective goggles were developed that absorb, attenuate and disperse the incoming laser light. Provided all people present pay attention to their personal protective equipment, laser beam welding is a particularly safe process.

Quality assurance in laser beam welding

Laser beam welding is a non-contact joining process. It is always carried out automatically. Modern laser beam welding systems are equipped with an integrated measuring system, which independently checks the dimensions of the manufactured component. This makes these systems particularly precise, which is the basis for guaranteeing constant quality.

Costs for a laser beam welding system

The costs are still the biggest disadvantage of these innovative processes. It depends strongly on what and which material is to be processed with the laser welding system. Even simple micro systems used, for example, for engraving wedding rings can cost several thousand euros. Brand-new high-performance plants rarely cost less than 100,000 euros, rather more. These expenses are offset by excellent manufacturing quality and high productivity. In fact, laser welding is usually carried out at a much higher speed than conventional electric or inert gas welding processes.

How does laser welding work?

Welding by laser beam is basically very simple: Two precisely cut sheets are held together. The laser melts the edges of the sheet metal. The melt flows into each other - and the joint is complete.

The VdLB Verband deutscher Laseranwender – Blechbearbeitung e.V. (Association of German Laser Users - Sheet Metal Working) represents the interests of owners, managing directors and company executives in the wide materials processing market - in this case, of sheet metal. Their aim is to encourage cooperation for the benefit of all parties involved. Cooperation, exchange of experience through intensive dialog, technical information and further training are in the focus.

Aluminum sheets are continuously welded. In the case of steel sheets, especially thicker cross-sections, seam welding is preceded by tack welding. The staples stabilize the sheet metal parts and guarantee constant precision during joining.

Components of laser welding systems

The powerful turning positioner that handles large parts in the Trulaser Weld 5000. Its rotary axis aligns the components so that the integrated welding robot can optimally reach the seam positions.
The powerful turning positioner that handles large parts in the Trulaser Weld 5000. Its rotary axis aligns the components so that the integrated welding robot can optimally reach the seam positions. (Source: Trumpf)

A laser welding system consists of the laser optics, a motorized guide and, if necessary, a worktable. In any case, the semi-finished products to be welded must be firmly clamped to enable precise joining. A distinction is therefore made between mobile and stationary laser welding systems. In the case of mobile laser beam welding systems, the device is brought close to a product. Stationary laser welding machines have a worktable with a clamping device. The insertion and clamping of the stationary laser welding systems is either motorized or automatic. However, the size of the worktable limits the dimensions of the products to be processed. In addition to the welding optics and the precisely working servos of the robot arm, the control system is the most important component of a laser beam welding system. It guides the arm to the intended points and regulates the duration and intensity of the laser beam.

The ideal complement to a laser welding system is a laser cutting system. The precise lasercut shapes provide the exact geometry that a laser beam welding machine can use to produce the best possible results.

The Lasys trade fair in Stuttgart and the Laser World of Photonics trade fair in Munich are dedicated to lasers as tools.

What speed is possible with laser welding?

In addition to precision and low heat input, the working speed is one of the outstanding properties of laser welding. Under ideal conditions, a long, straight endless seam can be welded at a speed of up to 60 m/minute. Since the intensity of the laser beam can be varied, the impact of the material used is less decisive for the working speed of a laser welding system. Even thick sheets can be precisely joined in a matter of seconds.

What temperatures are generated during laser welding?

Select Fiber is a universal manual welding laser for precise CNC welding with manual or semi-automatic assembly. It is equipped with a servo-controlled axis system, CNC and now also with a fiber laser.
Select Fiber is a universal manual welding laser for precise CNC welding with manual or semi-automatic assembly. It is equipped with a servo-controlled axis system, CNC and now also with a fiber laser. (Source: Rofin)

To be able to weld a material, a temperature just above its melting point must be reached. In conventional welding processes, the melting temperature of the material is therefore a limiting factor: Not every material can be processed with every welding process. Only electric welding has a certain scope as to the intensity of spot heat it can emit at its electrodes. Laser beam welding is different: Of all welding processes, it offers the greatest flexibility in terms of welding temperature. This overview of commonly used materials and their melting points illustrates the range of materials that can be processed by laser beam welding:

  • Plastics: 150 to 350 °C
  • Aluminum: 600°C
  • Glass: 600 to 800°C
  • Copper: 1085 °C
  • Steel: 1400 °C

In practice, much higher temperatures are achieved during laser beam welding. Nevertheless, this spectrum clearly shows how variable this joining process is.

Advantages of laser welding

  • High precision
  • Torsion freedom
  • High joining speed
  • No burr formation
  • Consistent quality
  • Wide material tolerance

The consistently high precision of laser welding is its outstanding feature. In addition to the particularly fine seam, the low temperature input is the most important plus. In contrast to gas-shielded welding, where work is slow and a lot of heat is applied, laser welding is extremely fast and minimally invasive. This avoids a complete heating of the base material. Selective thermal expansion therefore does not take place, which also avoids distortion of the workpiece after cooling. Finishing the welded construction on a straightening bench is therefore not necessary after laser beam welding.

The uniform, pulsed beam of laser welding also ensures a particularly clean seam. Welding beads or burrs, which are often unavoidable in gas-shielded or electric welding, do not occur in this joining process. Finally, any weldable material can be processed on a laser welding machine. Of all joining processes, laser welding offers the widest range of materials that can be processed. Glass or plastic, for example, cannot be joined at all by any other process.

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Disadvantages of laser welding

A major disadvantage of laser beam welding is the high cost of the equipment. This investment must be very well thought through. The ROI should already be reasonably secured before the purchase, otherwise a laser welding system can quickly become a loss-making business. Should a contract service provider therefore consider including a laser welding system in their machine park, a correspondingly high investment in a suitable marketing campaign is recommended. Laser welding is being supported by the fact that customer demands for tolerances in production are constantly increasing. It is to be expected hat conventional welding processes will no longer be suitable for many applications. An investment in laser welding is therefore still a risk, albeit a more and more manageable one.

A limiting factor to laser welding is the type of application: The operation of a laser welding system is comparable to that of a CNC milling machine. It is true that incorrect operation cannot cause such tremendous damage as an incorrectly programmed cutting machine. Nevertheless, a well-founded education, a mathematical-technical basic knowledge and a thorough familiarization are required in order to be able to handle a laser welding machine efficiently.

With the LDM 500-60 blue Laserline offers a high-power diode laser with 450 nm wavelength - i.e. radiating in the blue spectrum. This makes the system ideal for reliable welding of non-ferrous metals, especially when thin sheets are handled.
With the LDM 500-60 blue Laserline offers a high-power diode laser with 450 nm wavelength - i.e. radiating in the blue spectrum. This makes the system ideal for reliable welding of non-ferrous metals, especially when thin sheets are handled. (Source: Laserline)

On the other hand, the health risks associated with laser beam welding are minor. It goes without saying that laser welding of aluminum requires a powerful extraction system. It should also be minded keeping distance to motor-driven kinematics. Operators must stay away from the work area of an active robot arm. This is basic fact in dealing with modern, automated manufacturing processes. After all, laser welding basically requires the wearing of laser safety goggles. This prevents accidents caused by looking into the laser light. If these safety rules are observed, laser welding poses no particular danger.

What has to be considered when laser welding specific materials?

Laser welding of metal sheets

Welding describes the joining of materials by heat. Thin sheets are generally better suited for full-surface seam welding than thick sheets. Nowadays, laser welding can process astonishing material thicknesses. Due to its variable welding temperature, it is relatively insensitive to the individual types of metal. Regardless of whether stainless steel, structural steel, copper or other types of sheet metal are to be welded, laser beam welding masters this task with consistent precision. The only prerequisites are a sufficiently narrow welding gap and precisely set welding temperature and frequency. If the joining gap is too large, a satisfactory result can still be achieved by deposition or fill welding - even with the laser welding process.

Laser welding of aluminum

When laser welding aluminum, only an aluminum-manganese alloy can be welded without filler material. All other alloys can only be laser welded with the help of additives. This applies in particular for aluminum-silicon compounds. Aluminum alloys with manganese can only be processed to a limited extent by laser welding.

Areas of application for laser welding

Laser welding is becoming more and more widely used. Typical areas are:

  • Tool construction
  • Automobile industry
  • Steel construction
  • Shipbuilding

Laser welding is popular in tool making because of its precision. It is therefore in direct competition with the eroding process. The manufacture of precise punching, pressing and casting tools by additive or subtractive laser welding is the answer to the challenges of industry 4.0.

In the automotive industry, laser welding is used because of its tool-free mode of operation. In contrast to electric welding, laser welding does not require any constant cleaning or replacement of the heads. Steel construction is experiencing completely new dimensions in terms of precision and productivity through laser welding. Fast processing of thick sheets within high tolerances is no longer a fiction due to laser beam welding. This also applies to shipbuilding: There, it is above all precision-manufactured parts such as rudders, control and drive screws that achieve their desired tolerance by laser welding. The result is higher speeds and lower fuel consumption of the ships.

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Buy used laser welding machines

Thanks to the tool-free laser welding process, wear in the systems is comparatively low. In laser welding, the tool head moves along the desired path practically contact-free. The transfer to the workpiece takes place through the air. The guide and bearing of the robot arm are therefore hardly exposed to any significant wear. However, the laser optics are exposed to tremendous stress. The high temperatures applied here are generated by bundling the light. If particularly inexpensive systems for laser welding are offered, this is usually due to missing or defective optics. It then remains a matter of calculation: With a fresh look and an overhauled laser generator, a used laser welding system is almost as good as new one.

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This article was first published by belchnet.

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