Laser cutting: An overview
Cutting is one of the most common and widely known applications of materials processing lasers. It is used widely in industries such as automotive, aerospace, solar, electronics, textiles, jewellery, and medical device manufacturing.
The process comprises a laser beam – the power and wavelength of which depends on the thickness and type of material being cut – being directed through a set of optics and manipulated in a pattern over a workpiece via computer numerical control (CNC). The beam is focused to hit the workpiece in a single spot typically measuring less than 500µm in diameter, with the intensity of the beam causing the material to heat up. The material then either burns, melts, vaporises or is blown away by a jet of gas to leave a high-quality surface finished edge. Once the beam completely penetrates through to the other side of the material, the cutting process has begun.
Many laser cutting applications are assisted by either an active or inert gas delivered coaxially through the same nozzle as the beam. Oxygen is the standard active assist gas used, for example, when cutting mild and carbon steels, while nitrogen is the typical choice of inert gas when cutting, for example, stainless steels, aluminium and its alloys. When cutting with oxygen, the material is burned and vapourised after being heated up to ignition temperature by the laser beam. The reaction between the oxygen and the metal creates additional energy in the form of heat, which supports the cutting process. The liquid metal is then removed from the kerf by the shear force of the oxygen jet. Cutting with an inert gas such as nitrogen on the other hand – also referred to as clean or high-pressure cutting – instead involves the material being melted solely by the laser. The melted material is then blown out of the cut kerf via the force of the gas jet.
What are the advantages of laser cutting?
Laser cutting is often favoured over alternative cutting methods such as plasma, waterjet, flame and mechanical cutting due to its exceptional speed, flexibility, repeatability, precision, efficiency, affordability and quality, as well as its minimal post-processing requirements.
Being a non-contact process, laser cutting usually results in little work piece distortion or warping. No hard tools are required, meaning there is no need for tool storage, changeover, or sharpening – reducing setup requirements and costly downtime between jobs, as well as inefficiencies throughout longer jobs. Being a highly automatable process simplified via CNC manipulators and robots, users are left with the tasks of programming the machines and loading and unloading the material accordingly.
The highly focused spot results in a small heat-affected zone, resulting in clean edges, precise cuts, and the rest of the workpiece only being subject to minimal thermal stresses. Consequently the technology can be used to cut intricate shapes, free of burrs, enabling parts to be nested close together in the sheet of material being cut. This provides the ability to either reduce or even eliminate scrap entirely.
Laser cutting can be used to process a wide range of materials up to hundreds of millimetres in thickness. These include many metals common to industry – copper, brass, aluminium, mild steel, stainless steel, titanium etc – as well as non-metal materials such as plastic, leather, ceramic, wood, laminate, acrylic, cork, foam, wax, textiles, and paper.
What lasers are used for cutting?
Two types of laser commonly used for cutting applications are CO2 lasers and fibre lasers, each presenting their own set of advantages and disadvantages.
CO2 lasers can be found at wavelengths 9.3, 10.25 and 10.6µm, and at powers typically ranging from tens to hundreds of watts. They carry the advantage of being able to cut a wide range of materials with exceptional edge quality, and particularly excel at cutting non-metals such as those previously mentioned. They also perform well in terms of piercing speed, cutting speed and edge quality when processing thicker (>8mm) sheets of mild and stainless-steel. The downsides of CO2 laser systems are that they require more servicing and consume more power than other cutting lasers, incurring relatively high maintenance and running costs. In addition, they are outperformed by fibre lasers when processing thinner metals, as well as reflective metals.
Fibre lasers operate at approximately 1.064µm and can be found at powers extending well into the kilowatt range – up to 40kW cutting systems are now available. They offer a considerably smaller spot size compared to CO2 lasers, meaning they achieve higher-precision cutting and higher-optical densities at the workpiece. Consequently they excel in speed particularly when cutting thinner (<8mm) sheets of mild and stainless steels, as well as when processing reflective metals. Despite requiring a higher initial investment than their CO2 counterparts, fibre lasers offer a compact, highly efficient solid-state design that results in next to no maintenance and a much lower cost of operation.
Cutting sees continual advancement
Despite having been an application of laser technology since the 1960s, cutting continues to see further development from machine and source manufacturers each year.
One of the more immediate advancements users can see in cutting systems is the continual increase in maximum power they can offer to deliver faster cutting speeds, quicker piercing times, and in turn, lower cost-per-part. Over the past three years, for example, system manufacturers Amada, BLM Group, Bodor Laser, Bystronic, and Mazak Optonics (to name a few) have all upped the maximum power offered by their systems.
Mazak Optonics introduced a 10kW offering for its Optiplex Fiber III systems, enabling it to achieve increased cutting speeds and greater throughput. In addition, the system can cut larger thicknesses than its predecessors – up to 25.4mm mild steel, 31.75mm stainless steel and 31.75mm aluminium – with the part edge quality also being visibly smoother and cleaner. The system also offers a number of intelligent features to optimise operation, such as beam diameter control, focus detection and auto focus positioning.
BLM Group USA added more processing power to its LS5 and LC5 flat sheet laser cutters, with the new option of a 12kW fibre laser source. These machines can now cut steel, stainless steel, iron, copper, brass, and aluminium sheets in thicknesses from 1 to 34.7mm, depending upon the material.
BLM Group added the option for a 12kW fibre laser source in its LS5 and LC5 flat sheet laser cutters last year. (Image: BLM Group USA)
Amada also added a 12kW source to its Ensis-AJ system, designed for manufacturers needing fast piercing and cutting across a wide range of materials. The system can cut up to 25mm of aluminium, mild and stainless steel, 18mm of brass and 12mm of copper. The system incorporates Amada’s Variable Beam Control to adjust the laser mode, allowing it to process different materials and thicknesses with a single cutting lens. It also features auto collimation technologies to deliver increased beam spot control.
Bystronic increased the power of its ByStar Fiber systems to 15kW, which delivers speed increases of up to 50 per cent compared to a system with a 10kW laser source. The firm noted that the higher power would enable its ByStar Fiber systems to cut steel, aluminium, and stainless steel precisely and reliably in thicknesses between 1 and 30mm, and brass and copper in thicknesses up to 20mm. This is aided by a new ‘BeamShaper’ function that adapts the shape of the laser beam optimally to thicker sheets and fluctuating sheet metal qualities. In thicknesses between 20 and 30mm, the new function enhances the quality of the cutting edges and increases the cutting speed by up to 50 per cent compared to conventional 10kW machines.
Bodor Laser took cutting power a step further and unveiled what it says is the world’s first 40kW fibre laser cutting machine. According to the firm, 40kW laser cutting will ‘break through the bottleneck of cutting thickness, create new standards and redefine laser cutting to achieve a new high point in the laser cutting industry.’ At release Bodor claimed the system is able to cut 20mm carbon steel at a rate of 6m/min and 30mm carbon steel at 2.4m/min. The firm also has systems in the 10, 20 and 30kW range, with its 10kW+ system sales having reached over 1,000 units in 2021.
Bodor's new 40kW machine was unveiled at the Bodor Laser Innovation and Research Center in Jinan in 2020. (Image: Bodor Laser)
As hinted by some of the additional features offered by these cutting machines, power isn’t the only aspect of laser cutting being improved. In recent years for example, fibre laser source manufacturers such as Coherent, NLight, Trumpf, SPI Lasers, IPG, and others have all released lasers with variable beam quality – the shape of the output beam can be adjusted – which has been shown to provide better cutting results across different materials and thicknesses.
Coherent's ARM technology offers variable beam quality to provide better cutting results across different materials and thicknesses. (Image: Coherent)
Even already in 2022 cutting has since new technology released to further its capability. Trumpf has just introduced BrightLine Speed, which enables cutting speed to be increased up to 60 per cent for sheets up to 4mm thick. The technology also consumes around 50 per cent less cutting gas per part than conventional laser cutting, and makes the cutting process up to 15 per cent more productive with the same laser power, meaning each part requires correspondingly less energy to fabricate.
Described in this article are just a few examples of the many ways in which laser cutting is being developed and optimised. The progress will no doubt continue, bringing continual power gains and efficiency benefits to users on the factory floor in the years to come.
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Complex cuts and contours have led to the rise of using lasers for cutting. For most metals, the small focus diameters of lasers provide a low distortion, fast cutting tool with small kerf widths. Aspheric lenses enable laser cutting systems to achieve very small and precise beams for precision cutting.
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