1 Principle of Laser Cutting
Laser is the product of stimulated radiation. Its production is inseparable from three key elements: working material, pump and resonant cavity. After absorbing energy, low-energy level particles will transition to high-energy level orbits, but the state of high-energy level particles is It is unstable and will fall to a low energy level orbit at any time and emit photons. Laser is generated when many particles emit photons with high consistency at the same time. Laser processing can be divided into hot processing and cold processing according to the size of photon energy. Cold processing is generally used in the laser marking process of plastic parts. The laser completes the separation of molecules and substances by destroying the molecular bonds of the material. During this process, the material will not cause thermal damage, thermal deformation and other problems. Thermal processing is more widely used, such as laser cladding, laser welding, laser cutting, etc. During the laser cutting process, the laser beam forms a small focus on the material surface under the action of the focusing mirror, and the material around the focus absorbs the laser. The energy is quickly heated to melting, and the molten metal separates from the material under the blowing of the auxiliary gas to form a slit, thus completing the entire cutting process.
В соответствии с различными физическими проявлениями резки материалов, лазерную резку можно условно разделить на: лазерную резку плавлением, лазерную резку паром, лазерную резку реакцией плавления и лазерную резку контролируемым разрушением.
(1) Лазерная резка плавлением относится к тому, что во время процесса лазерной резки сфокусированный лазерный луч вызывает испарение внутри материала, образуя отверстия. Полученное отверстие выглядит как черное тело, что приводит к быстрому увеличению скорости поглощения лазера, и металлическая стенка маленького отверстия расплавляется. Окружение, увеличивается и углубляется, а затем выдувается под действием коаксиального газа высокого давления.
(2) Laser gasification cutting means that the material to be cut is heated to vaporize in a very short time, and the vaporized material is blown away from the cutting surface under the action of the auxiliary gas flow. Gas cutting can only be used for materials that are difficult to melt, such as wood, carbon and certain plastic materials. Materials processed in this way can often achieve very high cutting quality.
(3) Laser reaction melting cutting, also called laser oxygen-assisted cutting, is a special melting cutting method that uses oxygen as an auxiliary gas. During the cutting process, the high-energy laser beam heats the material to the ignition point temperature. At this time, the material has not yet melted. However, when the material reaches the ignition point, oxygen will react violently with the material, releasing a large amount of oxidation reaction heat. After that, the material begins to The melting forms a metal molten substance accompanied by the formation of a large amount of oxides. The molten substance is blown away from the surface of the cutting seam by the auxiliary gas flow, and the cutting process is completed. In the laser oxygen cutting process, the main reason for using oxygen as an auxiliary gas is that oxygen is one of the important substances involved in the oxidation and combustion reaction of the material. The combustion reaction will not occur when using other types of auxiliary gases. To complete the cutting, the laser beam is required to provide more More energy to ensure that the metal becomes molten. In the laser oxygen cutting process, the additional energy provided through the combustion reaction can reach 70% of the total cutting energy. In the reactive melting cutting of titanium alloy, it provides nearly 90% of the energy. The iron-oxygen combustion reaction will generate many oxidized melts. These melts generally have low viscosity and are easy to be removed under the action of auxiliary gas. Most of them are ferrous oxide, and there are also a small amount of iron oxide and ferric oxide. Due to the low viscosity of the melt, it is easier to be blown away from the bottom of the material by the auxiliary gas, reducing the possibility of slag adhering to the bottom of the cutting. At the same time, the oxides generated by the combustion reaction increase the laser absorption rate, which is beneficial to absorbing more laser energy.
(4) In laser controlled fracture cutting, cracks are caused by the material absorbing laser energy and heating up. Stress near the laser focus changes due to high temperatures. When the laser beam passes through, these compressive stresses relax to form local residual tensile stresses. Under the action of stress, the cracks will continue to extend in the direction of laser movement, and the material will fracture and separate along the path of the laser beam. This cutting method is particularly suitable for cutting brittle materials such as ceramics.
Factors affecting laser cutting
(1) Мощность лазера: Мощность лазера - это энергетическая мощность, подаваемая на лазер. Интенсивность лазерного луча может быть рассчитана путем деления мощности на площадь лазерного пятна. Размер мощности лазера напрямую определяет способность к резке и эффективность резки. Однако чем больше мощность лазера, тем лучше. Слишком большая мощность лазера приведет к увеличению ширины пропила и зоны термического влияния, и даже к пережогу заготовки, что очень серьезно. Ухудшение качества обработки.
(2) Скорость резки: В лазерной резки, скорость резки напрямую связана с эффективностью обработки. Чем больше скорость резки, тем выше эффективность обработки. Однако скорость резки ограничивается качеством обработки. Чрезмерная скорость резки приведет к невозможности прорезать материал. Слишком маленькая скорость резания повлияет на эффективность обработки и приведет к снижению рентабельности предприятия. Поэтому очень важно определить скорость резки при выполнении лазерной резки.
(3) Давление газа: основная функция вспомогательного газа заключается в удалении расплавленного металла на шве резки для обеспечения плавного хода лазерной резки. Вообще говоря, чем больше давление газа, тем сильнее способность удаления расплавленного материала. Однако если давление газа слишком велико, скорость воздушного потока в сопле увеличится, и поток воздуха будет нарушен в щели, что снизит способность газа удалять расплавленный материал и увеличит охлаждающую способность. Таким образом, значительно увеличивается вероятность зависания шлака в щели. Использование азота в качестве вспомогательного газа для резки нержавеющей стали позволяет получить неокисляющиеся, яркие режущие кромки. Для низкоуглеродистой стали кислород может использоваться в качестве вспомогательного газа для повышения эффективности резки и использования меньшей мощности лазера для завершения резки.
(4) Laser frequency: When the average laser power is constant, the higher the laser frequency, the more laser pulses the laser emits per unit time, and the lower the energy carried by a single laser pulse. When cutting, it is like using a Use a dull knife to cut the material. (5) Laser duty cycle: The laser duty cycle will affect the peak power of the laser. For example, when the laser duty cycle is 10%, the peak power of the laser can reach 10 times the average power. When the average laser power is constant, the laser The larger the duty cycle, the smaller the laser peak power. When the laser duty cycle is 100%, the average laser power is equal to the peak power.
3 Advantages of laser cutting
Compared with conventional cutting methods, laser cutting has the following advantages:
(1) The cutting quality is good. The diameter of the focal point formed by the laser produced by the laser after being focused by the lens is very small. When cutting, the width of the cutting slit is generally ten to twenty filaments. Compared with traditional flame cutting, the accuracy is greatly improved. In addition, the laser machine has a positioning accuracy of five wires and a repeatable positioning accuracy of two wires, and can be used to process various precision parts.
(2) High processing efficiency. As an advanced processing method, the most prominent advantage of laser cutting technology is its high processing efficiency. Generally, the maximum cutting speed can reach 10m/min, and the processing speed is more than ten times that of traditional methods. Due to the small focus diameter, material loss can be reduced during cutting, and it is widely used in precious metal processing.
(3) Contactless processing. Laser cutting is a processing method that does not require mechanical contact. In traditional processing, there is a cutting tool, and there will be processing stress. The workpiece may be deformed or even scratched by the tool, affecting product quality. However, using laser cutting It can ensure no processing stress, and compared with plasma cutting, the heat affected zone during cutting is small, and the workpiece has almost no thermal deformation, which can reduce the subsequent processing steps of the workpiece and save costs.
(4) Wide selection of cutting materials. Laser can cut a wide variety of materials. From the beginning, it could only cut steel plates, but now it can cut most metal and non-metal materials. The principle of laser cutting is to vaporize or melt the material, so the hardness of the processed material can be ignored during cutting. In addition, The cutting precision is high, so it is becoming more and more popular in jewelry processing such as diamonds.
(5) High degree of flexibility. With the maturity of fiber laser technology, the flexibility of laser processing is getting stronger and stronger. The propagation of laser beams requires mirrors to reflect the light. Therefore, the structure of the laser cutting machine is complex and the processing range is limited. Fiber laser cutting using optical fibers for transmission The function can flexibly process parts of any shape, greatly reducing the adverse impact of the shape of the workpiece on cutting.
