This paper mainly introduces the selection, application, installation precautions, quality control principles and future development direction of laser cutting machine in the sheet metal laser cutting of railway freight cars.

As a common processing equipment for sheet metal parts, laser cutting machine has the advantages of high precision, small edge heat affected zone, good cutting section quality, narrow cutting seam, smooth cutting section, etc., and is often the preferred equipment for enterprises to purchase.
 

With the development of railway freight cars, heavy-load, fast and lightweight have become its main development direction. The design of railway freight car products is diversified and the structural characteristics are becoming more and more complex, resulting in more and more special-shaped sheet metal parts in terms of type and quantity. In terms of economy, cutting and blanking can only be used for processing. Especially in recent years, stainless steel, aluminum alloy and other materials have been widely used in the new products of railway freight cars, and the requirements for section quality and heat affected zone are extremely high, which also aggravates the current situation of insufficient cutting capacity and low manufacturing technology level in the railway freight car manufacturing industry. Therefore, many railway freight car manufacturers also urgently need to purchase laser cutting machines and other key equipment to solve the current capacity bottleneck and improve quality and efficiency.

Selection of laser cutting machine

At present, there are two major types of laser cutting machines on the market: CO2 laser cutting machines and fiber laser cutting machines. CO2 laser cutting machine is to pass carbon dioxide, nitrogen and helium through a pair of positive and negative electrodes in proportion at several thousand times of atmospheric pressure to generate laser, and then use the resonator to derive the available laser beam, which is transmitted to the cutting head through the flight optical path, and then focus the laser on the workpiece through the focusing lens, and use the simplicity of the laser beam and high temperature to melt, vaporize, and ionize the material, and then cooperate with the auxiliary cutting gas to blow off the melting, vaporization The ionized material generates slits to realize cutting processing. (The optical fiber laser cutting machine is to excite a large number of semiconductor tubes in a concentrated way, and then couple several laser beams generated from them and transmit them to the cutting head through the optical fiber.)

At present, the power of CO2 laser cutting machines on the market in China is no more than 6kW, and the range of cutting head movement is no more than 2mx6m (because the laser beam with a flying optical path of more than 9m will attenuate and affect the focusing modulus, thus affecting the cutting quality). The mode is generally TM01 (some manufacturers promise to reach TM00), and the photoelectric conversion rate is general. The water cooling system is required to take away excess heat, and the compressed air is also required=protect and air cool the flying optical path and other parts. Due to its early entry into the Chinese market, this kind of equipment has the advantages of reliable and mature technology, wide cutting thickness range, easy procurement of consumable parts, perfect auxiliary gas supply chain, and numerous manufacturers, which occupy the vast majority of the market share. The time of commercialization of fiber laser cutting machine is relatively short, and the market share is small. The main reason is that the wavelength is relatively short, which is only 1/10 of that of CO2 laser cutting machine. This is easier for the material to absorb heat and produce heat affected zone. The common thickness of railway freight car sheet metal parts ranges from 2 to 10 mm, and the material types include carbon steel, stainless steel (ferrite and austenite), aluminum alloy, etc. The dimensional accuracy requirements are high, and the size of cutting heat affected zone is particularly important. Therefore, this disadvantage is unacceptable for the manufacturing of railway wagons, and the procurement of railway wagons should be based on CO2 laser cutting machines.

Precautions for installation of laser cutting machine

Many enterprises think that the CO2 laser cutting machine can be used after it is purchased and connected with electricity, but it is not. The equipment also needs compressed air, cooling water, stabilized power supply, pressure reducing valve, three kinds of laser generating gas and two kinds of auxiliary cutting gas, and constant temperature room and other supporting facilities. If dewar bottles are used, pressure reducing vaporization device and filtration device are also required.

Laser cutting machines have high requirements for environment. The vibration of surrounding equipment will have a great impact on its processing accuracy. Therefore, it is necessary to set a ring of vibration reduction ditch at the outermost part of the foundation during civil construction. In northern cities, the winter is cold, the summer is hot, and the temperature difference between morning and evening is large, which has a great impact on the lens and other components. Therefore, it is often necessary to install its main body in the constant temperature room. However, due to the need for loading and unloading, the external exchange workbench must be arranged outside the constant temperature room through the wall.

Quality control of laser cutting machine

The reference cutting parameter values of various materials and thicknesses are preset in the laser cutting machine, which can be directly selected for cutting after calling the cutting program. However, because the railway wagons are all medium and thick plates, the cutting quality is often poor, and the phenomenon of incomplete cutting and slagging occurs. For this situation, the operators have a headache, so how can we improve the quality? The general factors are divided into four categories:

(1) Laser generator: output power, laser mode, laser polarization, beam parallelism, laser straightness; Only the output power can be properly adjusted within the rated range, and the other influencing factors mainly depend on the factory quality and specific type selection of the equipment.

(2) Cutting head: appropriate cutting lens, clean cutting lens, accurate focus position, nozzle type, nozzle size, and whether the beam is in the center of the nozzle.

(3) Programming: reliable cutting path, pre-cutting. The cutting program setting path should be as simple as possible, and pay attention to the setting of micro-connection and other functions; It is better to conduct a pre-cutting before cutting to determine whether it is correct.

(4) Suitable process parameters: puncture point, nozzle height, power, cutting speed, auxiliary gas purity and outlet pressure.

In fact, the CO2 laser cutting machine has basically developed to the limit due to the restriction of output power and other factors, while the high-power laser generator of the fiber laser cutting machine is gradually commercialized and the technology is constantly mature. In the future, the shortcomings of short wavelength will be compensated, the harmful light in the coupling beam will also be controlled, and the slag phenomenon will be improved. In addition, in addition to the consumption of auxiliary gas and a small amount of lenses, only electric energy is needed, With the advantages of high electro-optical conversion rate, it is bound to become the main force of cutting equipment in the future. Especially in the cutting of medium and thick plates of railway freight cars, it is fully capable of replacing the plasma cutting machine and flame cutting machine. Of course, its application field will be more extensive, and it will truly become the main force of laser cutting equipment with high quality, efficiency and energy saving.

About HGTECH: HGTECH is the pioneer and leader of laser industrial application in China, and the authoritative provider of global laser processing solutions. We have comprehensively arranged laser intelligent machine, measurement and automation production lines, and smart factory construction to provide overall solutions for intelligent manufacturing.