Discussion on the mechanism and process of the hot

2022-09-22
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Discussion on the mechanism and process of CO2 laser texturing and electrospark texturing

I. Introduction Jinan new era Gold Testing Instrument Co., Ltd. tensile winding film tensile testing machine is mainly used to test the tensile properties of tensile winding film used for transportation and packaging of non-direct contact food:

the Chinese government in the mid-1980s In the early 1990s, the National Key Laboratory of laser technology (to study the theory of the interaction between laser and matter) and the national laser processing engineering center (to study the application of laser processing) were established in Wuhan Huazhong University of science and technology. Under the guidance of these two sources, the "China Optics Valley" was born. Under the guidance of market economy, China Optics Valley has created the first in dozens of laser technology fields and even the first in the world in just a few years

high power CO2 laser texturing technology and equipment belong to the international leading technology with independent intellectual property rights. This technology can not only complete high-quality laser texturing morphology, but also has the special function of laser quenching, which can increase the service life of rolls by more than twice. Its comprehensive economic benefits can recover the investment of users within a year and bring long-term, stable and obvious economic benefits

II. CO2 laser texturing mechanism

laser texturing technology and equipment is a national science and Technology (Key Research) program of the "Eighth Five Year Plan" in China. It was launched in 91 and put into production in WISCO in 1996, and has achieved certain results. Limited by the technical conditions of various units in the late 1980s and early 1990s, some problems are inevitable in the first CO2 laser texturing machine tool developed as a domestic key scientific research project. Although it is temporarily discontinued now, we should see the foresight and market prospect of this technology in the international texturing field. At present, plastic bags are used as little as possible when buying vegetables. Under the implementation of Huagong laser company of Huazhong University of science and technology, Kunming Iron and steel company, Jinan Iron and steel company, Tangshan Jianlong iron and steel company and Chongqing Iron and steel company have adopted this technology and equipment, and obtained new intellectual property patents

1) CO2 laser texturing mechanism (with texturing and hardening functions)

as shown in Figure 1: during texturing, the chopping disc 2 rotates counterclockwise, the roller 1 rotates clockwise, and the laser beam 3 irradiates the rear tooth surface of the front tooth through the focusing lens 4, reflects the front tooth surface of the rear tooth, and then incident on the q-point on the surface of the rolling roller. Its incident area is less than 0.5mm2, and its power density is 104 ~ 105W/cm2, The metal material structure on the roll surface changes phase rapidly (the temperature is below the melting point)

figure 1

as shown in Figure 2: martensite, carbide, residual austenite, etc. are formed in the transformation hardening zone, and due to its extremely fast processing heating speed and cooling speed, various components obtained in the transformation hardening zone are extremely small and produce a large number of dislocation, which are very beneficial to improving the hardness and wear resistance of the roll surface, making the roll surface structure after laser transformation have better wear resistance than conventional quenching, At the same time, it has done preheating for the next step of laser coagulation modeling

as shown in Figure 3: when the front and rear teeth of the chopping disc 2 move to the position shown in the figure, the laser beam 3 is directly focused and incident on the roll surface Q 'point of the roll 1 through the through hole between the front and rear teeth, with an incident area of 0.02mm2 and a power density of more than 107w/cm2, so that the metal material on the roll surface can quickly dissolve into a solution pool, Under the action of side blowing gas 5 and centrifugal force, the dissolved substances in the dissolving pool accumulate to the edge of the dissolving pool in a certain direction and form ordered pits and bosses with high hardness through rapid condensation to complete the texturing process. The side blowing gas with given direction, flow and pressure 5 has three functions in addition to completing the modeling task: 1 Avoid the interaction between the roll surface and oxygen in the air during hot working, resulting in decarburization and affecting the strength of the boss

2) CO2 laser texturing process

according to the rolling process requirements of cold rolled plates and the subsequent processing process requirements: such as common plate, household appliance plate, automobile plate, anti-counterfeiting plate, annealing, deep drawing, ultra deep drawing, galvanizing, color coating, etc., select the process indicators of roll surface roughness value, density value, flatness value, as well as the process indicators of roughness copy rate and attenuation rate (these two indicators are very important to users in actual production), The main process parameters that determine the process index are laser power, laser pulse frequency, scanning speed, spot diameter and focusing distance. The higher the power used, the greater the roughness value (RA), and the power value can be continuously and automatically adjusted; The pulse frequency is determined by the speed of the chopping disc and the number of teeth of the chopping disc, which is generally about 20kHz, that is, 20000 points of textured morphology can be produced per second; That is, the higher the pulse frequency, the higher the density value (peak value PC). The scanning speed is determined by the roll speed, roll surface diameter and the moving speed of the texturing device, which is generally 6.5 m/s. reducing the scanning speed by 5 and the relative humidity by no more than 80% can improve the RA and PC values; The spot diameter and focal length are determined by the external light path. These variables can be accurately executed by 840D numerical control system, detection system and special process software. The operator only needs to be responsible for hoisting and inputting the selected roughness value, density value and flatness value, which is very convenient. Because all process parameters can be accurately controlled, CO2 laser texturing can reproduce the required processing process and results, which is very beneficial to summarizing the texturing effect and developing new products (the first generation of shot peening and the second generation of EDM have the defects that they can't obviously harden and reproduce functions)

III. electric spark texturing mechanism

there is no professional manufacturer for the special equipment of electric spark texturing technology in China at present. Most steel enterprises just think that the uniformity and retention of its morphology are better than shot peening, and most of them have introduced foreign electric spark texturing equipment due to the psychological induction of conformity and outside. It should be said that EDM texturing technology was born on the basis of EDM Technology in the 1940s, which is decades behind laser processing technology. We should not follow the old path of introducing backward products and then introducing them, not to mention the cost performance difference of more than twice

China began to study and apply EDM Technology in the early 1950s, which is mainly used for mold forming and wire cutting. The Chinese government dares to be the first in the issue of texturing equipment in the metallurgical industry and enters the high-end market. Putting aside the follow-up development of EDM texturing equipment, it is undoubtedly the right direction to directly invest in the national key scientific research project of "large-scale CO2 laser texturing equipment and process" in WISCO

1) asynchronous mechanism of electric spark texturing two oil cylinders

electric spark is a kind of self-excited discharge, which is characterized by high voltage between the two electrodes before discharge. When the two electrodes are connected, the electrolyte in the gap is punctured, and then an instantaneous spark discharge occurs. With the breakdown process, the resistance between the two electrodes decreases rapidly, and the voltage decreases rapidly

as shown in Figure 5: the roughened part of roll 1 and electrode 3 are immersed in electrolyte 2, and the gap distance between them is about 0.1mm. The roll is grounded with zero line for low-speed rotation, and the speed is usually about 8rpm. Electrode 3 is installed on roughening head 4 for horizontal and linear movement. The electrical circuit includes a high voltage circuit 5 and a low voltage circuit 6. When electrolyte 2 is broken down, the low current of the high voltage circuit provides the initial pulse. The roughening of pits and needle spikes is caused by the electric spark discharge of low voltage pulse on the metal material on the roll surface through the electrode. The size of the current is achieved by selecting one or more resistance combinations, and its pulse frequency is set by adjusting the output of the oscillator. The size, quantity and shape of the pits and spikes on the roll surface are determined by the current and the duration of the electric spark (of course, when the roll is roughened, the electrode will also be roughened faster, which is a vulnerable part)

1. Roll 2 Electrolyte 3 Electrode 4 Texturing head 5 High voltage electric fire 6 Low voltage electric fire 7 Select current 8 Mechanical pulse

Figure 5

due to the limitation of EDM technology itself, it can not form a hill shaped boss with strong extrusion resistance. Due to the rapid attenuation of needle spikes, the surface roughness of the roll has poor morphology retention, and the wear speed is very fast in the initial wear stage, while the wear resistance in the normal wear stage is general. In order to prolong the service life of the roll, many steel enterprises have adopted the process of EDM roughening and hard chromium plating, that is, mechanically combining the chromium coating with higher hardness on the surface of the roll roughened by EDM. However, because chromium plating will produce trough filling, which will affect the texturing effect, and more importantly, because the mechanical combination is prone to local peeling of chromium plating layer in complex rolling, it is difficult to move forward. The texturing head 4 shown in Figure 5 is composed of a servo shaft and a dozen independent electrodes 3. An EDM texturing machine tool generally has several texturing heads

2) EDM texturing process

the important parameters that determine the process indicators of EDM texturing are various electrical parameters of pulse power supply, discharge gap and electrolyte. The higher the current, the deeper the spark crater, the higher the roughness value (RA) and the corresponding peak number (PC). The longer the current lasts, the wider the spark crater, and the corresponding peak value (PC) decreases, on the contrary, the PC value increases. The smaller the gap is, the higher the efficiency is. However, if the gap is too small, the waste generated in the process of electric spark will not be carried away by the flow of insulating oil. Generally, the clearance is about 0.1mm. The electrolyte consists of insulating oil and additives, in which the additives form a conductive bridge in the gap. The higher the dielectric coefficient of the additive, the smaller the gap. The particle size of the additive, the uniformity of distribution and the flow rate in the gap have a great impact on the roughening effect of electric cremation. In addition, it is impossible to keep the corresponding points between the arc surface of the electrode and the roller surface equidistant

electric spark texturing roller surface laser texturing roller surface

IV. conclusion

in conclusion, through the comparison of the mechanism and process of the two technologies, it is not difficult to see that the electric spark texturing technology originates from the electric spark technology in the 1940s, and it has many process parameters and factors that affect the texturing effect, which are extremely complex and highly random. Due to the limitation of its technical level, the reproducibility, retention and wear resistance of its textured morphology are behind the laser texturing based on laser technology, which is one of the four major inventions of the 20th century, especially in the hardening effect and process stability, and EDM texturing requires a large amount of electrolyte, which is polluting and energy consuming. In addition, imported EDM texturing equipment is times more expensive than domestic CO2 laser texturing equipment. Therefore, it is not difficult for us to know that the new high-power CO2 laser texturing equipment will become the third generation of leading products in the metallurgical industry at home and abroad

reference:

1 Laser processing technology manual China Metrology press

2 EDM Technology National Defense Industry Press (end)

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