A brief description of Laser Welding and Laser Cutting from Westermans
Lasers - Welding and Cutting
Many variants of laser technology are currently used in production processes including cutting, welding, marking, surface engineering and direct parts fabrication. The range of applications covers metals, plastics, semiconductors and ceramics on a scale from sub-micron to several metres. Many industries, including the automotive, shipbuilding and aerospace sectors are using laser welding and laser cutting technology.
Deep Penetration Laser Welding
Deep penetration laser welding is a non-contact joining process characterised by its high focused energy density, which is capable of producing high aspect ratio welds (weld width : weld depth) in many metallic materials. It can be performed at atmospheric pressure and with a relatively low heat input, compared with inert gas arc welding processes.
Deep penetration laser welding is a versatile fusion welding process, which has found wide application in industry; from spot welding of razor blades to welding of aerospace and marine structures. The process can be used to weld a variety of materials including, carbon steel, stainless steel, titanium, aluminium, nickel alloys. The industrial uptake of laser welding is driven by a requirement for high volume production and/or high weld quality.
The high focussability of laser beams enables power densities in the range 10^3 – 10^7 W/mm^2 to be applied to the joint. These power densities are sufficient to form a ‘keyhole’ (see video) below the laser beam impingement point. Efficient absorption of the laser beam by this keyhole allows low heat-input welds to be produced at fast processing speeds. These fast processing speeds combined with the ease of automation of industrial laser sources, lead to reliable, repeatable, and autonomous high volume production.
Heat inputs are ordinarily an order of magnitude lower than arc welding processes, promoting the adoption of deep penetration laser welding in components requiring minimal thermal distortion.
TWI has considerable experience in the successful development and qualification of deep penetration laser welding procedures for a variety of different applications, across numerous industry sectors.
• Deep narrow welds
• Low heat input, and consequently minimal thermally induced distortion
• Ease of automation
• Joint design flexibility
• High repeatability
• Joint design flexibility
• Aesthetically pleasing welds
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Hybrid Laser Arc Welding
Hybrid laser-arc welding is a joining process whereby arc welding and deep penetration laser welding are carried out simultaneously in the same process. In theory, the beam from any laser source (CO2, Nd:YAG, diode, Yb fibre, Yb:YAG disk etc) can be combined with any arc welding process (MIG/MAG, TIG, SAW, plasma), although hybrid laser-MIG/MAG and laser-TIG are perhaps the most common combinations. As a consequence of this, the process has the individual advantages of both laser and arc welding combined.
Deep penetration welds comparable with laser welds can be made, at the same time having a tolerance to joint fit-up more comparable with arc welds. Furthermore, arc welding consumables can be used, giving a degree of control over weld quality and properties greater than that possible with autogenous laser welds.
Hybrid welding is already being used, or under consideration, by the following industries:
• Road transport – the high welding speed of hybrid welding is attractive to the high production volume environments found in the automotive industry, especially so as the part fit-up tolerance is greater than that of autogenous laser welding.
• Shipbuilding – the low distortion of hybrid welding when compared with processes such as MAG welding or SAW reduces the amount of, and hence costs associated with, distortion correction and rework. Conventional joining methods have been estimated to take up to 20-30% of overall manufacturing costs.
• Rail transport – as in shipbuilding, the low distortion that can result from hybrid railcar seam welding compared with conventional arc welding processes is of interest as a means of reducing fabrication costs.
• Oil and gas – hybrid orbital girth welding and longitudinal welding of pipes has been demonstrated, and with further developments could be of interest in the oil and gas sector as a means of increasing root pass and overall joint completion rates, depending on the pipe steel grades used and operating environment requirements
TWI has over a decade of experience of hybrid laser-arc welding processes and their development. This includes experience of combining a variety of industrial lasers used for metals welding (principally CO2, Nd:YAG and, most recently, Yb fibre lasers) with MIG/MAG and TIG arc welding.
Furthermore, TWI’s research and development in this area has covered a broad base of engineering alloys, including C-Mn steels used for structural and pipeline applications, conventional (austenitic) and higher strength (duplex and ferritic) stainless steels, as well as a wide range of aluminium alloys.
The chief benefits of hybrid laser-arc welding can be summarised as:
• Improved tolerance to joint fit-up: for example, hybrid welding can extend the tolerance to joint gap by a factor of 2-3 over laser welding.
• Improved weld quality: hot cracking (e.g. in some higher strength Al alloys) can be avoided, and internal porosity content reduced, with respect to laser welds.
• Increase in single pass penetration depth: this is controlled by the choice of laser and welding parameters used, but single pass penetrations of up to at least 6-12mm can be achieved using higher power lasers.
• Increase in welding speed: this is dependent on the laser source used and materials being welded, but speeds of up to at least 5m/min are possible in thinner sections.
• The increases in penetration depth and/or welding speed are particularly significant as the net heat input is reduced. This results in lower distortion welding, suitable for long seam welds between plates, box sections, plates and attachments etc
Over the past decade, TWI has been carrying out developments of the hybrid welding process on a range of materials, within the Core Research Programme (CRP) and Group Sponsored Projects, as well as for its Industrial Members.
Examples of TWI’s work in hybrid welding include:
• CO2 laser-MAG welding of butt joints between C-Mn steel plates, including assessments of joint gap bridging ability and weld qualities and properties.
• Nd:YAG laser-MAG welding of T joints between C-Mn steels, and resulting properties, for shipbuilding applications.
• High speed, low distortion hybrid welding of aluminium alloys using latest generation fibre lasers.
• Low internal porosity content hybrid welding of aerospace aluminium alloys using fibre-delivered lasers.
• Hybrid welding of higher strength stainless steels.
• Real-time process control when hybrid welding butt joints in steels, stainless steels or aluminium alloys
Laser cutting is the largest industrial application of high power lasers; ranging from profile cutting of thick-section sheet materials for large industrial applications, to medical stents. The process lends itself to automation with offline CAD/CAM systems controlling 3-axis flatbed, 6-axis robots, or remote systems. Traditionally, CO2 laser sources have dominated the laser cutting industry. However, recent advances in fibre-delivered, solid-state laser technologies has enhanced the benefits of laser cutting, by providing the end-user with increased cutting speeds and decreased operating costs.
The recent improvements in fibre-delivered, solid-state laser technologies have stimulated competition with the well-established CO2 laser cutting process. The cut edge quality, in terms of nominal surface roughness, possible with solid-state lasers in thin sheets matches CO2 laser performance. However, the cut edge quality noticeably degrades with the sheet thickness. The cut edge quality can be improved with correct optical configuration and efficient delivery of the assist gas jet. TWI has the capabilities to assist its members by implementing these designs changes.
TWI has the necessary equipment, knowledge and expertise to perform R&D activities in the field of laser cutting with fibre delivered laser sources. TWI can provide support to its members from the specification and procurement of laser cutting systems, to the development of cutting procedures by addressing material, optical and gas-jet design issues.
The specific benefits of laser cutting are:
• High quality cut – no post cutting finishing is required.
• Flexibility – simple or complex parts can easily be processed.
• High precision – narrow cut kerfs are possible.
• High cutting speed – resulting in low operating costs.
• Non-contact – no marks.
• Quick set up – small batches and fast turn around.
• Materials - most can be cut
• Low heat input – low distortion.
Trumpf, Bystronic, Amada, LCD and ESAB are great makes of Laser machinery
If you buy a Laser cutter - does that mean you no longer have a need or the space for your CNC plasma cutte? Sell your surplus machine to us and we will pay you over the odds for it.
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