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Application and development of high-tech cutting technology in China's shipbuilding industry

Abstract: This paper reviews the application of NC cutting technology in China's shipbuilding industry, and reveals the significance of vigorously promoting high-tech cutting technology for the future development of shipbuilding industry

key words: NC cutting; Flame cutting; Plasma arc cutting; Laser cutting; Profile cutting

1 NC cutting

in 1958, British oxygen company successfully trial produced the world's first NC cutting machine, creating a new era of NC cutting. Subsequently, developed countries have successively carried out in-depth development and Research on NC cutting technology, process, related supporting software and equipment. After more than 40 years of unremitting efforts, thanks to the continuous progress of the computer industry, they have launched various types of serial NC cutting products with complete functions to the market. Nowadays, for different workpiece objects, people can use CNC, robot cutting and other cutting methods; In order to meet the cutting performance and accuracy requirements of various materials, flame, plasma, laser and other appropriate cutting processes can be selected, which truly provides users with a comprehensive solution to the problem

the development of CNC cutting technology in China began in the early 1980s, with the maturity of microelectronics technology and its wide application. After more than 20 years of continuous development, it has finally made gratifying achievements. At present, the types and specifications of domestic CNC cutting products are quite complete, and some of them have approached or reached the level of similar products in the world in terms of technology, performance, indicators and functions

shipbuilding industry is the industry that introduced CNC cutting technology in China the earliest and benefited the most. Over the past 20 years, CNC cutting has been rapidly developed and widely used in domestic shipyards, completely changing the low efficiency of manual and semi-automatic cutting in the past, fundamentally solving the bottleneck problem that has plagued the cutting section in the process of ship construction for a long time, and becoming a booster to promote the rapid growth of China's shipbuilding total. This paper reviews the application of NC cutting technology in China's shipbuilding industry, and puts forward some opinions on its future development trend

2 NC flame cutting

2.1 start

in the mid-1970s, China's shipbuilding industry, aiming at the lofting process in the process of ship construction, studied the computer-aided design program for the mathematical smoothing of ship hull lines and the expansion of curved surface outer plates. The output results produced by the program system can be used for NC machining, Thus, the hull steel plate cutting does not need to go through so many cumbersome processes such as full-scale setting out - making templates - drawing lines on the steel plate - manual or semi-automatic cutting. From this, the advantages of using numerical control to cut marine steel plates immediately show up, which not only saves man hours, setting out platform sites and template materials, but also reduces workers' labor intensity and greatly improves work efficiency. It is in this context that CNC flame cutting machines began to enter China's shipyards for steel plate cutting and blanking

2.2 advantages of CNC flame cutting machine

a. full function and high degree of automation

b. multiple cutting torches are configured to work, and the effective cutting time is long and the production efficiency is high

c. adopting nesting cutting procedure can improve the utilization rate of steel plate and reduce thermal deformation

d. cutting information is easy to prepare, modify and save

e. high machining accuracy and good cutting quality

f. the machine is stable and reliable, and easy to operate

the market promotion of NC cold bending technology should be engaged in NC cutting technology services

2.3 the characteristics of shipyard NC flame cutting machine

the most obvious is the large gauge, which generally exceeds 6500 mm, so that the cutting of large-scale steel plates is not limited. In recent years, with the enlargement of ship type and the widening of marine steel plate, large machines with gauge of 7500 mm and 9000 mm or even wider have been preferred. In addition, the machine has the function of high-speed spraying (zinc) powder scribing, so as to provide convenience for assembly and welding after cutting; Because there is a large amount of welding workload of panel, the flame straight-line three cutting torches with stable and reliable performance and capable of cutting grooves of various shapes are usually listed in the order list of shipyards; The CNC system with the function of nesting and cutting of surplus materials can simplify the operation and improve the utilization rate of steel plate

in order to meet the requirements of large span and high speed, the CNC flame cutting machine selected by shipyards generally adopts the high rigidity gantry type frame to clear the working site and the driving mode of gear and rack bilateral synchronization. In addition, the CNC cutting machine used for cutting hull steel plates must also be equipped with a shipbuilding cad/cam

software system from hull line smoothing, outer plate deployment, structural part generation, typesetting and nesting, and output cutting instructions

2.4 application and development trend

since the 1980s, numerical control flame cutting machine has been widely used in China's shipbuilding industry because of its many advantages. By the mid-1990s, when the CNC plasma cutting machine appeared on the stage, its role gradually changed, but this does not mean that it will withdraw from the stage of history and be abandoned or eliminated. After all, the CNC flame cutting machine has many advantages that can not be ignored when cutting steel plates with a thickness of more than 30 mm, cutting and processing grooves of various shapes, and cutting straight steel plates in large quantities with multiple cutting torches. It can be predicted that the CNC flame cutting machine will continue to play its due role in the shipbuilding industry as a supplement to the CNC plasma cutting machine and other advanced equipment for a long time in the future, and will exist in the cutting equipment of shipyards for a long time

3 NC plasma cutting

3.1 overview

human beings have used plasma arc to cut metal materials for more than 40 years, and the application of NC plasma cutting in China's shipbuilding industry is only a matter of nearly 10 years. However, it is not difficult to find that this is a new technology that has grown and expanded very rapidly. It has brought great changes to the steel plates of shipyards in our country, and has had an extremely far-reaching impact. Up to now, the CNC plasma cutting machine has replaced the CNC flame cutting machine and occupied a leading position in the steel plate blanking of the shipyard. What's more, when ordering new ships, whether the shipyard has the means of NC plasma cutting has been included in the necessary conditions for whether it can undertake contract orders

3.2 historical review

the development of numerical control plasma cutting technology in China began on the basis of the maturity and wide application of numerical control flame cutting technology. In the late 1980s and early 1990s, the national economy entered the fast lane of development, and the cutting volume of steel plates and other metal materials increased sharply. The high-speed and high-efficiency NC plasma cutting technology has increasingly attracted the attention of the manufacturing industry, including shipbuilding. At that time, domestic equipment was not able to bear this responsibility for a while, and many large backbone shipyards had to spend a lot of money to take the lead in introducing NC plasma cutting machines from abroad, To solve the urgent need of production. The arrival of a large number of imported machines has greatly stimulated our domestic counterparts and stimulated our sense of mission and urgency to develop advanced equipment to replace imported equipment. On the other hand, the introduction of foreign advanced equipment also provides us with a rare opportunity to learn and learn from. After digesting and studying, concentrating on research, and taking measures of introduction and independent development in key technologies (it is worth mentioning that the grafting and introduction of internationally advanced plasma cutting system) has made a qualitative leap in the development level of China's CNC plasma cutting technology at a high starting point. Therefore, the domestic CNC plasma cutting machine has basically realized high automation, complete functions, reliable operation The development goal of high cost performance was soon recognized and accepted by China's shipbuilding industry, and has become a strong competitor of foreign imported equipment since then

3.3 characteristics and types of plasma arc cutting

3.3.1 characteristics

the plasma arc generated under the condition of high temperature and strong electric field, through mechanical compression, thermal compression and magnetic compression, makes the arc column current dense, and generates extremely high temperature and high-speed air flow. The high temperature and high-speed plasma arc flame flow melts the workpiece metal and is blown away from the matrix to form a slit. Because the temperature of the arc column greatly exceeds the melting point of metals and their oxides, plasma arc can also be used to cut stainless steel, aluminum, copper and other metals in addition to cutting carbon steel

3.3.2 type

a. conventional plasma arc cutting

b. double gas plasma arc cutting

the cutting torch uses plasma gas and shielding gas respectively. The function of shielding gas is to make the cutting area and the external shape bench can be assembled into an effective isolation within about 10 minutes, so as to obtain better cutting edge quality. According to the characteristics of the material to be cut, the combination of different gases can be changed to achieve the best cutting effect

c. water jet plasma arc cutting

during the cutting process, the cooling water is sprayed to the arc from the small hole in the cutting torch nozzle, and the plasma arc is compressed again to further increase its density and temperature, so as to improve the cutting speed and cutting quality

d. long life oxygen plasma arc cutting

long life oxygen plasma arc cutting is a novel plasma arc cutting technology for cutting carbon steel. The most prominent advantage is the long service life of the electrode. Compared with ordinary oxygen plasma, the average service life is prolonged by 4-6 times, and the number of perforations is increased by nearly 10 times

e. fine plasma arc cutting

the plasma arc current density is very high, so there is a very narrow and straight plasma flame. The slit is narrow, the cutting surface is smooth, the notch edge is vertical, and the cutting accuracy and surface quality are close to laser cutting

3.4 applicability and promotion of long-life oxygen plasma arc cutting technology in shipyards

in 1983, American hyper therm company successfully used oxygen as plasma gas to cut carbon steel [1]. Its main advantages are: A. no slag hanging, large cutting speed range, good cutting quality; b. The cutting speed can be increased by 30% under the same power supply; c. There is no nitriding problem on the cut surface, and the cut workpiece has good welding and processing properties

the long-life oxygen plasma arc cutting technology fundamentally overcomes the shortcomings of the short service life of electrodes and nozzles in the previous oxygen plasma arc cutting process, so that the oxygen plasma arc cutting greatly reduces the cost on the basis of high quality and high speed, and opens up a Xintiandi for those enterprises with large demand for steel plate cutting. In the past 10 years, due to the increase of the total shipbuilding volume and the shortening of the construction cycle, the workload of steel plate cutting has increased sharply. Therefore, many domestic backbone shipbuilding enterprises and local shipyards have added large-scale CNC cutting machines equipped with long-life oxygen plasma cutting system to cut medium and thick steel plates, which are the most used in the shipbuilding industry. The effect is remarkable, which also urges people to gradually reach a consensus in machine selection, That is, the long-life oxygen plasma cutting machine is the best suitable model for shipyards at present

another important reason for the rapid promotion and application of long-life oxygen plasma arc cutting technology in China's shipbuilding industry recently is that it benefits from the considerable economic benefits it brings after it is put into use. First of all, using NC plasma cutting, people can quickly and conveniently complete the cutting tasks of stainless steel, aluminum, copper, composite plates and complex parts that NC flame cutting is not competent, and its economy is better than other machining methods. Secondly, according to the current state

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