Laser Cutting Technology
Laser cutting is an advanced and widely applied thermal cutting technology method in materials processing industry. It uses laser beams of high energy density as “cutting tool” to carry out thermal cutting of materials. The focused high-power and high-density laser beam radiates onto the workpiece, causing the radiated are to be instantaneously molten, vaporized or ablate or causing the radiated are to instantaneously rise to the burning point, and at the same time, high-speed air flow which is coaxial with the laser beam blows away the dross produced there from, thereby cutting of the work piece.
Laser cutting can be classified into four types: Laser vaporization cutting, Laser fusion cutting, Laser oxygen-boosted fusion cutting and controllable break cutting.
Laser vaporization cutting
High-energy-density laser beams are used to heat workpiece and cause temperature to rise rapidly, and in a very short time, the temperature comes up the boiling point of the workpiece material, resulting in vaporization of the material and producing a vapour. This vapour is jetted at extremely high speed, leaving a cutting seam on the material. Heat of the material vaporization is usually very high, so high power and power density are required during lase vaporization cutting.
Laser vaporization cutting it usually applied to cutting of extreme-thin metal and non-metal material.
Laser oxygen-boosted cutting
The principle of laser oxygen cutting is similar to that of oxyacetylene cutting. Laser is used as the source for preheating, and oxygen as cutting gas. The jet gas interacts with metal, producing oxidation reaction and discharging a large amount of heat, and at the same time, the melted oxides and dross are blown away out of the reaction area, producing a cutting seam in the metal.
Laser Fusion Cutting
The fusion cutting technique uses nitrogen as an assist gas. The gas does not take part in the chemical reaction. The nitrogen is used to blow the slag, created during cutting, from the kerf. This laser cutting technique requires considerably higher gas pressure than the combustion technique. Fusion is slightly quicker when laser cutting thin steel sheet metal. An important advantage of fusing is that no oxide film is formed on the metal. A disadvantage of laser cutting with nitrogen is that gas consumption is high. This technique is normally used for non-ferrous metal and stainless steel. Controllable break cuttingWith heating of laser beam, brittle material is cutting of at very high speed and under controllable conditions. Its principle is as follows: laser beam heats a small area of a brittle material, causing thermal gradient and resulting severe mechanical distortion, and thus causing crack on the material. Controllable cutting has the feature of high cutting speed and requires very low laser power. If laser power is to high, it may cause surface melting on the workpiece and damage the cutting edges. The controllable parameters of controllable break cutting are laser power and laser spot size.
Stationary Cutting Bed
The laser cutting machine consists of a cutting head and a cutting bed. There are two types of cutting beds: stationary cutting beds and movable cutting beds. Machines with a stationary cutting bed have been designed in such a way that the laser, including the cutting head and the source, moves across the bed. The advantage of a laser cutting machine with a stationary cutting bed is that the bed can be very long. The rapid traverse speed of this machine is lower because the cutting head, including the source, is moved on a rail.
Movable Cutting Bed
The second type of machine has a movable cutting bed. The cutting head is moved across the bed, but the source is stationary. This means that the rapid traverse speed is higher. As a movable cutting bed consists of two different work beds, the cutting machine can be working on one bed, while the second bed is being loaded or unloaded.
CNC Laser Cutting
The laser cutting machine is controlled by a CNC program. The cutting head moves along two axes (length and width); the depth of the cutting head is set along a third axis. This depth depends on the thickness of the sheet. The advantage of laser cutting using CNC technology is that the tolerances are extremely tight. In addition, it is possible to load several programs consecutively, so that the machine can be constantly operative.
Laser Cutting Techniques
Engraving techniques are suitable for preparing sheets for further machining. They can be used for marking margins and drilling holes, but also for making identification marks. Adding batch or drawing numbers may facilitate construction or traceability. Evaporation is similar to engraving.
A micro-joint is a technique for keeping small products fixed within the sheet while laser cutting. By leaving a small part of the contours intact, the entire sheet can be removed from the cutting table in one go. This makes it easier and quicker to remove sheets from the table.
Laser Cutting – Limitations
Rust may affect the result of laser cutting. Rust on a sheet must therefore first be removed. If it is not removed, laser cutting will not produce a clean cut. Rust must be removed from the entire contour. The Heat-Affected Zone Laser cutting is a thermal process that creates a heat-affected zone The structure of the cut edge is different from that of the rest of the sheet. Laser cutting will harden material that is high in carbon. This makes the cut edge hard and brittle. This hard and brittle structure hinders subsequent drilling, tapping or milling. In laser cutting, the heat-affected zone is very small(0.04mm-0.06mm) in comparison to flame cutting and plasma cutting (0.5mm-1mm) Oxidation during Burning Techniques When making a cut using the combustion technique, a chemical reaction takes place between the steel and oxygen that is added. This reaction is called oxidation and it leaves an oxide film that can affect subsequent welding. Oxidation may be prevented by using nitrogen as an assist gas. Limitations due to the Kerf Laser cutting creates a kerf The kerf is wider at the top than at the bottom. The kerf is formed at the focal point of the laser beam. The shape of the cutting head is elliptical. It is possible to create a straight kerf by adjusting the height of the laser.
Tolerances for Laser Cutting Sheet Metal
Laser cutting allows the possibility of cutting holes in sheet metal. The minimum diameter of a hole depends on the thickness of the material. In general, the following diameters (in mm) apply to the corresponding sheet thicknesses (in mm):
Tolerances are often crucial when laser cutting sheet metal. In general, the larger and thicker the sheet metal, the larger the deviation in the cut. The table below shows the deviations for laser cutting at Tubecon Laser.