Application of laser cutting in sheet metal processing

Traditional processing methods in the sheet metal workshop include technological processes such as plate shearing, punching and bending. Among them, the blanking process requires a large number of molds, and has the characteristics of less cutting and no cutting process. When a product is processed, dozens of molds are usually equipped, and some products may even require hundreds of molds. From an economic point of view, with a large number of molds, the cost of the product will increase correspondingly, resulting in a waste of funds. In order to adapt to modern sheet metal processing, reduce production costs and improve processing technology, laser processing technology came into being.

Classification of laser cutting machines

According to the different laser generators, there are currently three types of laser cutting machines on the market: CO2 laser cutting machines, YAG (solid) laser cutting machines, and fiber laser cutting machines.

CO2 laser cutting machine

The CO2 laser cutting machine is equipped with a nozzle for blowing oxygen, compressed air or inert gas N2 at the beam exit to increase the cutting speed and ensure the smoothness of the cut. In order to improve the stability and life of the power supply, the CO2 gas laser must solve the discharge stability of the high-power laser. According to international safety standards, the laser hazard level is divided into 4 levels, and the CO2 laser is the least hazardous level.

YAG (solid) laser cutting machine

YAG solid-state laser cutting machine has the characteristics of low price and good stability, but the energy efficiency is generally less than 3%. At present, the output power of products is mostly below 800W. Due to the small output energy, they are mainly used for punching, spot welding and thin plate cutting. Its green laser beam can be applied under pulse or continuous wave conditions. It has the characteristics of short wavelength and good light concentration. It is suitable for precision machining, especially hole machining under pulse. It can also be used for cutting, welding and lithography. Wait. The wavelength of the YAG solid-state laser cutting machine laser is not easily absorbed by non-metals, so non-metallic materials cannot be cut, and the YAG solid-state laser cutting machine needs to improve the stability and life of the power supply. It is necessary to develop a large-capacity, long-life optical pump excitation light source, and the use of semiconductor optical pumps can greatly increase the energy efficiency.

Fiber laser cutting machine

Fiber laser cutting machine can be transmitted through optical fiber, the degree of flexibility is unprecedentedly improved, the failure point is less, the maintenance is convenient, and the speed is fast. It has great advantages when cutting thin plates within 4mm. However, it is affected by the wavelength of the solid laser when cutting thick plates. The quality is poor. The wavelength of fiber laser cutting machine is 1.06μm, which is not easily absorbed by non-metal, so it cannot cut non-metal materials. The photoelectric conversion rate of fiber laser is as high as 25%, and fiber laser has obvious advantages in terms of electricity consumption and supporting cooling system parameters. According to international safety standards, fiber lasers are the most harmful to the eyes due to their short wavelength. For safety reasons, fiber laser processing needs to be carried out in a fully enclosed environment. As an emerging laser technology, fiber laser cutting machine is far less popular than CO2 laser cutting machine.

Laser cutting method

Laser melting and cutting

⑴In laser melting and cutting, the workpiece is partially melted and the melted material is sprayed out with the help of airflow. Because the transfer of the material only occurs in its liquid state, the process is called laser melting and cutting.

⑵The laser beam is equipped with high-purity inert cutting gas to promote the melted material to leave the kerf, and the gas itself does not participate in the cutting.

⑶Laser melting cutting can get higher cutting speed than gasification cutting. The energy required for gasification is usually higher than the energy required to melt the material. In laser melting and cutting, the laser beam is only partially absorbed.

⑷ The maximum cutting speed increases with the increase of the laser power, and decreases inversely proportionally with the increase of the sheet thickness and the increase of the melting temperature of the material. In the case of a certain laser power, the limiting factors are the air pressure at the slit and the thermal conductivity of the material.

⑸Laser melting and cutting can obtain non-oxidized incisions for iron materials and titanium metals. For steel materials, the laser power density will be melted but not vaporized, and the laser power density is between 104W/cm2～105W/cm2.

Laser flame cutting

The difference between laser flame cutting and laser melting cutting is that it uses oxygen as the cutting gas. With the help of the interaction between oxygen and the heated metal, a chemical reaction occurs to further heat the material. For structural steel of the same thickness, the cutting rate that can be obtained by this method is higher than that of melting cutting.

On the other hand, this method is worse than fusion cutting. In fact, a wider slit, obvious roughness, increased heat-affected zone area and worse edge quality are produced.

⑴ Laser flame cutting is defective when processing precision models and sharp corners (there is a danger of burning off the sharp corners). A pulsed mode laser can be used to limit the heat-affected zone.

⑵The laser power used determines the cutting speed. In the case of a certain laser power, the limiting factor is the supply of oxygen and the thermal conductivity of the material.

Laser gasification cutting

During the laser gasification cutting process, the material gasifies at the kerf. In this case, very high laser power is required. In order to prevent material vapor from condensing on the slit wall, the thickness of the material must not greatly exceed the diameter of the laser beam. Therefore, this process is only suitable for use when there is no discharge of molten material. This processing is actually only used in areas where iron-based alloys are very small.

This processing cannot be used for wood and certain ceramics, which usually require thicker cuts.

⑴In laser gasification cutting, the optimal beam focus depends on the material thickness and beam quality.

⑵The laser power and the heat of vaporization have a certain influence on the optimal focus position.

⑶When the thickness of the sheet is constant, the maximum cutting speed is inversely proportional to the material vaporization temperature.

⑷The required laser power density is greater than 108W/cm2, depending on the material, cutting depth and beam focus position.

⑸In the case of a certain thickness of the plate. Assuming sufficient laser power, the maximum cutting speed is limited by the gas jet speed.

With the application of laser cutting machines, sheet metal processing technology has developed rapidly, and has brought revolutionary concepts to sheet metal manufacturing and processing. Laser cutting technology and laser cutting machine equipment are being familiar and accepted by the majority of plate processing enterprises.

Laser processing technology has a very important position in the sheet metal processing technology, which improves the labor productivity of the sheet metal process and promotes the development of the sheet metal process. The high degree of flexibility of the laser cutting machine can greatly reduce the processing cycle, the cutting speed is fast, the production efficiency is high, the processing accuracy is improved, and the product development speed is accelerated. These advantages are paid attention to by many manufacturing companies.