LASER WELDING
Laser welding: Precise, flexible, automatable
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A brief introduction to laser welding, the technologies involved, and the advantages it offers over other joining methods
Laser welding, also commonly known as laser beam welding (LBW), is the process by which materials such as metals and thermoplastics are fused together, using either a continuous-wave or pulsed beam of amplified light emitted from a laser source. The light is delivered to a workpiece through a system of glass lenses, mirrors and often a fibre optic cable. The process has gained
significant popularity over the years, developing a reputation for being a reliable joining technology with exceptional quality, precision, speed, flexibility and versatility. This makes it an excellent choice for performing the standard lap, fillet and butt welds commonly used in industries such as automotive, aerospace and shipbuilding. Laser welding is also well suited to automation on production lines, being easily integrated with a wide range of robotic technologies in remote welding applications. This has been particularly relevant in recent years, with the gradual transition into the fourth industrial revolution: Industry 4.0.
Types of laser welding Most laser welding techniques can be classified into two categories: heat conduction
welding and keyhole welding. In heat conduction welding, the energy is coupled into the workpiece solely through heat conduction. The material surface is heated above its melting point, but not so much to vaporise it, meaning the laser beam is absorbed only at the surface of the material rather than penetrating it. Such welds therefore typically exhibit a high width-to-depth ratio, with the depth being controllable by varying the duration of the pulse – heat conducts further down into the part the longer the pulse. Such welds are typically performed at energy densities around 105W/cm2
, using laser
powers of hundreds of watts. Due to the relatively low powers involved, weld depth typically ranges from only a few tenths of a millimetre to one millimetre. Heat conduction welding is generally used in applications where a particularly aesthetic weld is required, or when particulates may be a cause for concern, like in battery sealing. Keyhole welding, on the other hand, is used where deeper, stronger welds are required. In this process, the laser beam heats up the material until it vaporises, penetrating deep into the metal. This creates a cavity known as a keyhole, filled with either expanding vapour or plasma that prevents the collapse of the cavity walls, with temperatures rising well above 10,000K. Welding is achieved by traversing the keyhole along the joint to be welded, or moving the joint with respect to the laser beam. Surface tension then causes some of the molten material at the leading edge of
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Laser welding has gained in popularity for its quality, precision and speed
the keyhole to flow around the cavity to the back, which then cools and solidifies to form the weld. Keyhole welding results in welds with a high depth-to-width ratio, reaching depths up to tens of millimetres in thickness. Such welds are typically performed at energy densities of about 106-107W/cm2
using laser powers typically in the order of kilowatts.
Benefits over alternative welding methods Laser welding poses a number of advantages over conventional arc-based methods, such as MIG, TIG and MAG welding. Such processes input large amounts of heat into the weld seams, which can lead to defects such as distortion and twisting, meaning post-processing techniques like grinding are required to achieve a more aesthetically pleasing weld. This can be very time- consuming. Comparatively, laser welding delivers lower heat input, resulting in better looking welds with high repeatability, removing any need for post processing and thus improving the time efficiency of the whole process. The controlled heat input of laser welding also makes it
suitable for joining thin materials together – a task not typically achievable using arc-based welding methods. Arc welding is also somewhat restricted in the types of joint it can make, whereas laser welding can be used to perform a wide range of welds over complex geometries due to its light often being deliverable via a fibre optic cable, enabling it to access harder- to-reach areas of a workpiece. This is what also allows certain laser welding technologies to be easily integrated with robotics technologies. Electron beam welding is
an alternative remote joining method, involving an accelerated beam of electrons that can be magnetically deflected and focused to the workpiece. While the technique is generally suited to performing thicker welds than laser-based methods, to prevent the electrons scattering or reacting with gas molecules, it must take place in a vacuum chamber. In addition to having to wait for the chamber to be pumped down before welding can begin, this also limits the size of the parts that can be welded. Laser welding faces no
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