Laser welding

As in other laser material processing methods, the foundations of laser welding are in the interaction between laser radiation and the material. Compared to laser cutting, however, a great number of parameters must be taken into account, significantly increasing the complexity of the process.

When a laser beam hits a material, it is heated to its melting point. If the material is simply melted by the laser beam, this is referred to as heat conduction welding. By using higher intensities, the material is not only melted, but also vaporised, forming a vapour capillary. This is known as deep penetration welding.

• Restricted heat-affected zone: One advantage of laser welding is the low energy input compared to other methods. This results in a locally limited heat-affected zone and low thermal distortion.
• Flexibility: Laser welding offers high flexibility regarding feasible weld seam geometries. Plus, trajectory geometries can be easily adjusted.
• Precise application of energy: The precisely adjustable application of energy allows laser welding to meet particularly high quality requirements. Plus, it can be automated.
• Weld seam geometry: By creating a keyhole, laser welding can produce particularly slim and deep weld seams.
• Less rework: The need for rework is reduced thanks to smooth, narrow seams.
• Less preliminary work: Compared to other welding options, tedious preparation of weld seams is not necessary.
• Variety of materials: A large number of materials can be welded using laser welding. Even materials that are difficult or impossible to weld can be joined with this method.
• Welding environment: In contrast to electron beam welding, laser welding can also be done outside a vacuum. Process comparison also shows that laser welding offers improved weld seam quality.
• Contactless: Laser welding is contactless and can be performed from one side.

• Variety of parameters: Not every laser beam source is equally suitable for every welding job. The range of system parameters is also extensive. At BBW Lasertechnik, we have a wide selection of laser beam sources to provide our customers with the proper technology for every application.
• Investments: Even though costs may decrease in relation to output, investment in laser welding systems remains very high. With our machine pool, we provide customers with a wide variety of laser systems and reliable services. Customers don’t have to make their own investments, or take entrepreneurial risks.
• Know-how: The high technical complexity of laser welding requires special technical expertise. Suitable clamping techniques and professional quality control are musts for best practice. Our employees are qualified professionals whose work our customers can rely on.
• Safety: Working with laser radiation requires compliance with a vast number of safety criteria.

Whilst perhaps not obvious at first glance to consumers, laser welding is becoming increasingly attractive to manufacturers – for example those in the household appliances industry, the cooling and energy technology industry, and the e-mobility sector – due to its many advantages. Successful laser welding for products starts with design and development.

Metallographic tests are the standard method for assessing laser-welded seams – both in process development and during series production. This means that a number of parts per batch are subjected to destructive testing during series production. At the same time, visual inspections can also be carried out to immediately detect changes in the welding process. For automated production and large series, it is also wise to use online process monitoring. Such monitoring recognises changes in the welding process directly, without manual tests and without damaging anything. An ultrasonic inspection can also be carried out for jobs with especially strict requirements, such as those in the aerospace industry. 3D measurements can optionally be taken to detect welding distortion. In addition, product-specific tests – such as using certain inspection equipment – are also common to determine the mechanical strength of weld seams.

Gas, solid-state and disk lasers are typically used as laser beam sources. Today, fibre-bound guidance technology is preferred, although CO2 lasers, for example, are still guided by mirrors.

There is a difference between robot-guided systems and Cartesian axis systems when it comes to the kinematics of the machining head.

With regard to actual movement of the laser beam, there is a distinction between the use of fixed optics and scanner optics. Fixed optics are mainly used for small quantities and materials that can be easily welded. On the other hand, scanner optics are being used more and more for larger quantities and difficult materials. Scanner technology enables very high welding speeds and oscillations of the laser beam, whilst also optimising cycle time and quality of the weld seam. To make up for the disadvantages posed by fixed optics, there are now fixed optics with a wobble function available. Large gaps, for example, can be bridged with such optics.

Double-core fibres are also becoming increasingly important: they are used to increase the quality of weld seams in deep penetration welding.