As an advanced material cutting method, laser processing has been more and more accepted by sheet metal producers. With the continuous progress of computer control technology and optical technology, people have higher and higher expectations for its processing ability. This expectation is not only to be able to cut, but also to cut well and quickly. What can be answered is of course inseparable from the performance of the processing machine, and the quality of the processed material also directly affects the effect of the answer.
In Europe, the United States and Japan, where laser processing started earlier, laser processing machine manufacturers began to put forward specific quality requirements for steel production in the 1980s, which led to the development of laser special steel that is different from ordinary steel but with high price. With the acceptance of laser processing as the main cutting method, ordinary steel plates less than 25mm will use laser professional materials as standard materials. However, due to China's rapid development, steel production has not been able to adapt, so there is a distinction between Chinese steel and imported steel. The main difference lies in a series of reasons, such as the content of impurities in the steel, the treatment of the steel surface, and the transportation and storage, which cause the current situation of difficult cutting of Chinese plates.
Today, China's crude steel output is not only the first in the world, but also exceeds 50% of the global output. Developing countries and even some developed countries such as Australia and South Korea are also using Chinese plates in large quantities to save costs. Therefore, instead of expecting Chinese steel to adapt to laser cutting, it is better to study and propose methods and proposals that can process inferior materials with high quality. This paper puts forward some of these thoughts in order to throw a brick and attract jade.
[problems encountered in plate processing]
1. The piercing problem of carbon steel thick plates accounts for a large proportion of the piercing time in thick plate processing. Various laser manufacturers have developed rapid piercing technology one after another. The more representative is high-energy piercing (blasting). The advantage of this method is that it is fast (1 second, taking t16mm as an example - the same below), but the defect is that it not only affects the processing of small shapes, The huge energy injected during piercing will raise the temperature of the plate and affect the next overall cutting process. However, if a low-power pulse is used to perforate, the time will be very long (12 seconds), which will lead to a decrease in cutting efficiency and an increase in unit cost.
2. Cutting surface quality problems Fig. 1 and Fig. 2 show the cutting sections often encountered when processing medium and thick plates. Such cutting not only challenges the quality of the finished products, but also is accompanied by overburning and serious slag adhesion, so that the value of high-priced laser processing machines from other cutting methods cannot be reflected.
3. Stability of whole plate processing in the whole plate processing of domestic steel, poor processing in local areas often occurs. This phenomenon is sometimes very random, even when the machining machine is in good condition. In order to deal with local faulty products, which greatly affected the whole work progress, here are also some analysis and Countermeasures for the processing failure of unknown reasons.
[solutions to the above problems]
As its name implies, the peak piercing (HPP) scheme uses the high peak pulse laser with a small duty cycle, supplemented by the non fuel injected on the surface of the material to remove the attachment at the opening edge, and controls the reasonable frequency of the pulse while cooling and piercing. It is characterized by a relatively long blasting time (3 seconds), but a small hole diameter (about φ 4mm) and there is no attachment on the edge of the opening and the heat input is low, which is convenient for the next normal cutting and processing, and the efficiency is improved by 4 times compared with the ordinary piercing. Fig. 3 shows the difference among ordinary perforation, HPP perforation and high-energy perforation.
2. Cutting section improvement scheme for carbon steel, the important factor to improve the cutting section is to control the heat input to the plate and ensure the full combustion of the laser irradiated part. The k-cut processing conditions developed by Mitsubishi Electric have better fulfilled this mission. Figure 4. The traditional strip is used on the same domestic plate
And k-cut conditions. For stainless steel, the important factors to improve the cutting section are the improvement of the beam (improving the focal depth) and the effective utilization of auxiliary gas. The bright surface cutting technology is the result of improving the vibrator and nozzle. Fig. 5 shows the improved effect. Roughness of upper section 8 μ、 Lower part 12 μ Comparable to machining.
3. Scheme to ensure processing stability at present, in order to improve the running speed of the processing machine, the laser machine mostly adopts the structure commonly known as flying light path, that is, the form of the material tray moving while the processing head moving in the whole Machinable area. In order to compensate for the change of the relative position between the processing head and the light source, manufacturers also try their best to ensure the consistency of the light spot within the processing range, and the use of a curvature variable refractive mirror is a common choice. Although the structure of this method is simple, it will change the depth of focus, which makes it difficult to cut the medium thick plate which is very sensitive to the depth of focus (both the spot and the depth of focus should be kept unchanged). The equal length optical path adopted by Mitsubishi Electric (the light propagation path between the light source and the processing head is equal in the machinable range) can avoid the change of focal depth, so that the spot and focal depth are consistent. In addition, the attention to heat input can control the accumulated heat of the plate, and better solve the stability problem. Fig. 6 shows the principle of equal length optical path and the processing effect at different positions in the processing area.
Take the problems in processing seriously, study their mechanism, and find solutions to the end problems. Through a series of exploration and improvement of traditional laser technology, new technologies have been developed for more complex medium and heavy plate cutting and applied to series of products such as ex plus, Rx, XL, etc., meeting the actual needs of customers in processing domestic medium and heavy plate materials, thus greatly improving production efficiency. We will also make further efforts to explore new technologies, solve more difficult problems in processing, and serve the vast number of users.