The shipbuilding industry is a major player in metal welding and cutting. The main processes involved in manufacturing are cutting and welding. In recent years, the shipbuilding industry has experienced rapid expansion and a sudden contraction.
According to the statistics of the Shipbuilding Industry Association, after the market adjustment, some new features have appeared in the shipbuilding industry.
Under the circumstances that the overall economic aggregate of the shipbuilding industry has not changed much, profits have fallen to a certain extent. With the overall order falling, export orders picked up.
At the same time, the industry concentration of the shipbuilding industry has further increased. Currently, the top ten shipbuilding companies occupy more than 53.4% of the market in China.
With the fierce market competition, the decline in profits and the increase in quality requirements, the shipbuilding industry has paid more attention to manufacturing quality. As a big cutting role, laser cutting has further ushered in the new situation.
Laser cutting, as an efficient, green, high-quality, high-precision technology, is the cornerstone of promoting the development of the shipbuilding industry and the optimization of shipbuilding.
It plays an important role in realizing reduction, light weight, re-manufacturing, cost reduction, reduction of man-hours, energy saving and environmental protection in the shipbuilding industry.
In addition, the laser cutting process is also an ideal way to prepare the ship’s front plate. It complies with the current development trend of large-scale ship structures, manufacturing precision, and efficient construction.
1. Laser cutting technology
(1) Laser cutting principle
Laser cutting is a typical thermal cutting method. It uses a laser to generate a high-energy-density laser beam, uses a laser lens group to focus the beam, irradiates the work piece, and heats the work piece material in a continuous and repetitive pulse operation mode so that the work piece rapidly melts, vaporizes, and forms holes.
At the same time, the high-speed air flow coaxial with the light beam blows away the molten waste at the incision to complete the cutting and separation of the work piece.
Laser cutting principle
(2) Features of laser cutting
Good cutting quality
Small laser spot, high energy density, fast cutting speed, narrow and flat laser cutting incision. The cut surface is smooth and beautiful, the surface roughness is only tens of microns, and the dimensional accuracy of the cut parts can reach ± 0.05mm.
The workpiece has small deformation, small heat affected zone, high adaptability and flexibility, and can be used as the last processing step without secondary processing as well as reducing the processing costs.
High cutting efficiency
Based on the optical and transmission characteristics of the laser, laser cutting can be performed on a laser cutting machine equipped with multiple numerical control operating tables.
At the same time, the cutting of multi-shape parts can be realized by modifying the NC program, including 2D and 3D cutting.
Non-contact cutting reduces tool costs
Laser cutting is not like traditional cutting methods. Its cutting torch does not contact the work piece, there is no need to change the “tool”, and there is no tool wear. Machining parts with multiple thicknesses or shapes can be achieved by simply changing the laser output parameters of the laser.
Therefore, laser cutting is a green and environmentally friendly processing method. The laser cutting process has low noise and vibration, and does not produce pollution.
Various types of cutting materials and in fast cutting speed
There are many types of laser cutting materials, including metal, non-metal, composite materials, wood, etc. And the laser cutting speed is fast, with a 4000W laser to cut 12mm thick low carbon steel with a 30 ° bevel, the cutting speed of the bevel can reach 2200mm per minute.
Using a 6000W laser to cut 8mm thick stainless steel with a 22.5 ° bevel, the cutting speed of the bevel can reach 1500mm per minute.
2. Application of laser cutting technology in shipbuilding
(1) Characteristics of ship cutting
The ship industry has high requirements for the hull segmentation and transfer accuracy, and the frame transfer clearance must be controlled within 1mm.
In the past, when shipbuilding companies generally used plasma to cut the ribs, in order to ensure the assembly gap, trimming allowances were set on the ribs, which required manual trimming during field assembly.
If the cutting quality is uneven, the residual oxide in the cutting slot will increase the assembly workload and also the assembly cycle, and the entire segmented construction cycle will be extended.
In addition, the use of a laser cutting machine to cut off the assembly margin eliminates the phenomenon of on-site trimming and reduces labor and material waste. The speed of assembly of the structure is significantly accelerated, and the quality of assembly is significantly improved.
(2) Application advantages of laser cutting technology in shipbuilding
In recent years, “precision shipbuilding” and “rapid shipbuilding” have become the main trends in the development of the shipbuilding industry, and laser cutting technology has developed rapidly, accounting for more than 70% of the entire laser processing industry.
The shipbuilding industry mainly uses steel plate as the main raw material. The use of laser cutting plates can replace some die-cutting methods that require complex large molds, greatly reducing production cycles and reducing costs.
At present, the cutting method of hull plate parts in the shipbuilding industry mainly adopts flame cutting, plasma cutting, shear processing and laser cutting.
Other cutting methods have many disadvantages compared to laser cutting. For example, flame cutting and plasma cutting have wide slits, poor cutting accuracy, easy to generate harmful gases, and large environmental pollution.
For shipboard cutting, laser cutting has the advantages of high cutting accuracy, small thermal deformation, reduced secondary processing (such as milling, drilling, etc.), transfer and grinding, especially small circles, small holes, and curved surfaces. The hull sectional transfer accuracy requirements can fully ensure that the frame assembly clearance is controlled within the range of 1mm, but its practical cutting speed in steel is poor compared to plasma cutting.
The relationship between cutting speed and cutting thickness of low carbon steel under different cutting methods, and the cutting effect of low carbon steel under different cutting methods are shown in the figure.
Relationship between cutting speed and cutting thickness of low carbon steel under different cutting modes
Cutting effect of low carbon steel under different cutting methods
In the field of shipbuilding, when laser cutting prevents plasma from cutting the ribs, a cutting margin is set on the ribs in order to ensure the assembly gap.
And through manual trimming, uneven quality of cutting occurs. Thereby reducing assembly workload, assembly cycle, material and labor costs.
The laser-cut marine steel plate has good cutting quality, good verticality of the cut surface, no dross, thin oxide layer and smooth surface. No secondary processing is required, and can be directly welded.
And the thermal deformation is small, the curve cutting accuracy is high, and the coordination man-hour is reduced to realize the obstacle-free cutting of high-strength ship plates.
Deviation of structural gaps in ships
(3) Application status of laser cutting technology in shipbuilding
At present, CO2 laser cutting technology is the most common and worldwide manufacturing and processing technology used in shipbuilding.
The cutting speed of the commonly used 5 ~ 6kW CO2 laser is worse than that of plasma, which cannot meet the current speed and efficiency requirements of the shipbuilding industry. And its equipment and machinery maintenance costs are high, the return is small, can not meet the needs of the shipbuilding industry.
Although its application on ships is not ideal, it has also been gradually adopted for laser cutting in the field of shipbuilding.
And there are some new developments in related cutting and processing technologies.
The effect of 4 kW CO2 laser cutting
In recent years, a few domestic shipyards with strong capabilities, such as Jiangnan Changxing Shipbuilding Base, have also introduced the world’s advanced “carry-on (CO2) laser cutting machine”.
However, the laser cutting machine equipped with technology, at home and abroad, only Japan’s technology application is more optimistic. Its success or failure also provides valuable experience for the domestic shipbuilding industry.
At the same time, with the development of domestic manufacturing, fiber lasers have also developed rapidly. Its high power has excellent beam quality, high electro-optical conversion efficiency, small volume at the same power, and optical fiber transmission brings better working flexibility.
And the comprehensive advantages of almost maintenance-free high reliability have challenged traditional (CO2) laser cutting.
With the continuous improvement of the effect of fiber laser cutting in thick plates, many domestic manufacturers of cutting equipment have entered or are preparing to deploy fiber lasers.
And some universities, institutions, and scholars have been studying the cutting effect of fiber lasers.
For example: Jae Sung Shin has used a 6kW fiber laser to study the cutting performance of high-speed fiber lasers on stainless steel plates. The maximum cutting speed can reach 72mm per minute. It can cut 60mm thick stainless steel plate with excellent cut shape and slit width, as shown in the figure.
Cutting speed for cutting 60mm thick stainless steel plate
AnttiSalminen has used a 5kW fiber laser to perform inert gas-assisted laser cutting of 10mm stainless steel plates and 4mm aluminum plates. The effects of laser power, cutting speed, focus position and auxiliary gas pressure on cutting performance and cutting quality were studied.
The maximum cutting speed was determined at different laser powers, and the combination of different cutting parameters was studied to optimize the cutting effect and obtain high-quality cuts.
The laser power parameter is 4kW, the cutting speed is 1m per minute, and the cutting effect of a 10mm thick stainless steel plate with 2MPa nitrogen is shown in the figure.
10mm thick stainless steel plate with laser power of 4kw, cutting speed of lm / min, and nitrogen of 2MPa
The output power of the fiber laser of a 10mm thick stainless steel plate with a laser power of 4kW, a cutting speed of 1m / min and a nitrogen pressure of 2MPa has already reached 50kW. However, the current development focus is still on 1-4kW lasers, and based on this, 10kW lasers are developed.
The industrialization of laser has been realized, and the cutting and welding problems of shipbuilding, aerospace and automobile manufacturing have been solved.
At the same time, in order to adapt to the cutting conditions and environment, laser cutting technology is fully utilized by the shipbuilding industry. It is combined with robots to form robot cutting systems.
Since the Year 2000, robot companies such as KUKA in Germany, ABB in Switzerland, and FANUC in Japan have developed a series of laser robots and laser cutting robots.
The combination of robotics and laser technology is the mainstream trend currently used in the shipbuilding industry or the entire manufacturing industry.
3. Trends and suggestions of laser cutting in the shipbuilding industry
As mentioned earlier, the laser cutting quality has obvious advantages and has been widely promoted in the automotive, sheet metal, machinery and other fields.
At present, large shipbuilding companies such as Jiangnan Shipyard and Wuhan Shipyard have used laser cutting to process ship plates.
But objectively speaking, in the domestic shipbuilding industry, laser cutting has not dominated. The main reasons include:
① Laser cutting cost is higher than traditional cutting methods.
② Large-scale equipment for laser cutting is not suitable for the manufacturing characteristics of the shipbuilding industry, such as on-site construction, segmented operations, and complex working environments.
③ There is no obvious advantage in cutting efficiency, especially for thick plate cutting in the shipping industry.
④ The maintenance of laser equipment is complex, which has high requirements for workers and high cost.
According to the current status of the industry, with the gradual decline in laser prices and the increase in the level of intelligence, laser cutting technology will gradually be widely used in the shipbuilding industry. The main reasons include:
(1) The cost
One of the most concerned issues in the shipbuilding industry is cutting costs. At present, traditional processes generally include: Board Entry + Flame cutting or plasma cutting + Artificial deburring + Artificial groove or trimming machine opening groove + Rocker, drill, etc. include about 5 processes + 4 times parts handling. The process is relatively complicated and costly;
If laser cutting is used instead, the process can be simplified to: Board Entry + Laser cutting (laser cutting + laser beveling + laser drilling), in terms of time cost, labor cost, site cost, etc. are all reduced.
(2) The flexibility and intelligence of laser equipment are gradually adapted to the development of the shipbuilding industry
In recent years, there has been a breakthrough in the intelligence level of large domestic equipment. Various types of equipment based on the combination of CNC and robot machines have many modular and intelligent practical technologies. For example, Nantong COSCO Kawasaki’s intelligent production line can adapt to manufacturing systems in complex situations. This has good adaptability to the segmented manufacturing, outdoor operations and complex production environments of the shipbuilding industry.
In addition to equipment, the process ultimately determines the effect of use. Therefore, scientific and technical personnel complete the collection and analysis of process information by monitoring and controlling the mechanical cutting process in real time.
Simultaneous integration of multiple energy fields and processes, an important means to achieve process improvement, thereby improving the laser cutting effect, simplifying the cutting process, reducing the construction period and cost.
(3) Laser development has reduced equipment and maintenance costs
With the rapid development of high-power fiber laser and semiconductor laser manufacturing technology as well as the improvement of the corresponding processing technology level, the high-efficiency, energy-saving and precise cutting characteristics of fiber laser and semiconductor laser meet the market demand and meet the current development direction of laser manufacturing technology.
We should vigorously promote the industrialization and marketization of fiber lasers and semiconductor lasers, and the development and improvement of corresponding equipment and control technologies.
The progress of the corresponding equipment has further improved the integration and flexibility of the equipment.
In view of the special requirements of the cutting machine for the ship’s stern plate work and the diversity of the shapes used in the processing of the hull structure, the multi-degree-of-freedom optimization design of the laser cutting head, the development of rotation control methods and control systems are urgent.
At the same time, attention is paid to the application research of robots and machine vision detection systems in the field of lasers to achieve monitoring of cutting paths, high-precision cutting, and unmanned automatic operation to improve the quality and efficiency of operations.
Effectively control cutting quality, reducing production costs and safety risks.