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Views: 0 Author: hu Publish Time: 2021-08-27 Origin: dapeng
On June 14th, the "OFweek 2019 (15th) China Laser Technology and Industrial Application Forum" hosted by the Chinese high-tech portal OFweek Veken Net and Hi-Tech Association and organized by OFweek Laser Net was officially held at the JW Marriott Hotel Qianhai Overseas Chinese Town, Shenzhen hold. Dr. Gao Hui, a laser application engineer from Wuhan Raycus Fiber Laser Technology Co., Ltd. attended the forum and gave a speech, introducing several important basic theories of laser processing and key factors to improve the quality of laser cutting and welding.
Tribute to the sages: Four key time points in the development of laser
When it comes to laser technology today, we have to mention four sages who have made important contributions to the development of laser science. The first topic of Dr. Gao's speech was to express his respect to the four sages.
The first is Einstein, who put forward the theory of stimulated emission in 1917; the second is Gordon Gould, who discovered that stimulated radiation can amplify a beam of light at Columbia University in 1959, and thus established the concept of laser; the third is Gordon Gould. Mayman, who invented the first ruby laser, was mainly used for distance measurement in the military field; the fourth was Kumar Patel, who invented the first industrial-grade carbon dioxide laser. Dr. Gao believes that 1963 was an epoch-making time node, and the invention of Kumar Patel opened the era of laser processing.
Engineers must understand geometric optics
Lasers are widely used, including aerospace, navigation, automobiles, nuclear energy, manufacturing, and processing industries. There are many materials that can be processed by laser, including metals, non-metals, plastics, glass, wood, ceramics, rubber and so on. Dr. Gao believes: "There is no possibility that fiber lasers will replace CO 2 lasers forever in the laser industry, because different lasers have their corresponding application fields."
According to statistics, from 2014 to 2018, the output value of laser processing has increased year by year, and material processing is the most important application sector. In the specific processing methods, cutting, welding, and marking occupy the main position of laser processing.
Currently, lasers are divided into two categories: continuous and pulsed. Dr. Gao said: “When using continuous laser or long-pulse laser for processing, the material often needs to go through the process of solid-state heating, melting, liquid heating and vaporization. If a short-pulse laser is used, these three changes will be skipped directly. Reach the last step to realize vaporized cutting."
Dr. Gao believes: “As a laser application engineer, you must understand geometric optics. Only in this way can you change the parameters reasonably and obtain the desired processing effect.” Dr. Gao explained several related concepts here. The two parameters of beam quality, BPP value and M², can be converted into each other by the formula and are directly proportional.
The second concept is the key word that everyone usually ignores-brightness. Dr. Gao explained: “Fiber lasers are high-brightness lasers, so the concept of brightness is very important. In fact, in the field of laser processing, the most important factor is not power, but power density and energy density. For this reason, we have introduced the size of the spot Concept. And the size of the spot determines the slit width of laser cutting. If you understand this principle, even if you change 100 cutting heads, the focus position is different, you can know at which spot position the best board is cut."
Afterwards, Dr. Gao showed the light spot changes of the two common cutting heads on the market (the defocusing amount is both -15～+15). It can be seen from the figure that the M1.5 cutting head has a smaller spot within the beam waist, but the greater the defocus, the larger the spot. For this reason, Dr. Gao said: “When the defocus is larger, the beam of the M2.0 cutting head is narrower, so the M1.5 cutting head has advantages in thin plate processing, but the M2.0 cutting head is better for processing thick plates. Or when the power is higher, the advantage is more obvious. Because this can not only suppress the nozzle heating phenomenon, but also obtain a better taper."
The key factors to improve the quality of laser cutting and welding
Dr. Gao believes: "There are four important points in laser cutting, namely: better materials, better nozzles, better processes, better lasers and beam quality." Regarding the nozzles, he focused on the Laval Ultra High speed nozzle. Traditional nozzles have higher requirements for the distance of the cutting head. The higher the height of the cutting head, the more turbulent the airflow changes, usually set to 0.5mm-2mm. The Laval nozzle can maintain a stable air flow in the range of 0-6mm of the cutting head height, and the end effect is better.
Subsequently, Dr. Gao also mentioned oxygen cutting. He said: "If you know the calculation method, adding the laser power required by the iron opening to the power provided by the oxygen during oxygen cutting is the most accurate power in the processing. And by calculating the slag spray speed, it can be reversed. To promote the best cutting speed."
As laser processing moves toward a high-power era, the requirements of laser processing are gradually changing. Dr. Gao summed up the current market's requirements for laser processing with the "three highs": "high power, high speed, and high quality". Dr. Gao said: "The effect of increased power is firstly reflected in the increase in cutting speed. The increase in speed means the increase in efficiency, and the increase in efficiency means the increase in profit.
Regarding laser welding, Dr. Gao introduced the important influence of the adjustable waveform on the laser welding effect. Dr. Gao believes: “For heat-sensitive materials, the use of rising edge waveforms is not good, but for materials with lower temperature sensitivity, the rising edge waveforms can have good results. Therefore, combined wave welding has the best effect. Good. In addition, for copper-aluminum welding and metal-plastic welding, different stacking sequences adapt to different waveforms."