The shipbuilding industry is a significant player in metal welding and cutting, with its main processes being cutting and welding. In recent years, the industry has experienced rapid expansion followed by a sudden contraction.
According to the Shipbuilding Industry Association, the market adjustment has resulted in some new developments in the industry. Although the overall economic aggregate of the shipbuilding industry remained unchanged, profits decreased to some extent, but export orders increased as the global order decreased.
Furthermore, the concentration of the shipbuilding industry has increased further, with the top ten companies now occupying more than 53.4% of the market in China. With intense market competition, decreasing profits and increasing quality requirements, the shipbuilding industry has placed greater emphasis on manufacturing quality.
Laser cutting, being an efficient, green, high-quality and high-precision technology, has become even more crucial in promoting the development and optimization of the shipbuilding industry. It plays a crucial role in weight reduction, remanufacturing, cost reduction, labor hour reduction, energy saving and environmental protection in the shipbuilding industry.
Furthermore, the laser cutting process is an ideal method for preparing the ship's frontal plate, aligning with the current trend of large-scale naval structures, precision manufacturing and efficient construction.
1. Laser cutting technology
(1) Laser cutting principle
Laser cutting is a common thermal cutting technique. It works by using a laser to produce a high-density laser beam, which is then focused by a group of laser lenses onto the workpiece. The beam repeatedly heats the workpiece material, causing it to melt, vaporize, and form holes quickly.
As cutting occurs, a high-velocity airflow coaxial with the light beam removes molten debris from the incision, completing the cutting and separation of the part.
Laser cutting principle
(2) Laser cutting capabilities
Good cutting quality:
Laser cutting offers excellent cutting quality with its small laser spot and high energy density, resulting in fast cutting speed and a narrow, flat incision. The cutting surface is smooth and attractive, with surface roughness of just a few tens of micrometers. The dimensional accuracy of cut parts can reach ±0.05mm.
The part undergoes minimal deformation and has a small heat-affected zone, making it highly adaptable and flexible. This allows laser cutting to be used as the final processing step, eliminating the need for secondary processing and reducing processing costs.
High cutting efficiency:
Laser cutting is highly efficient due to its optical and transmission characteristics, which can be carried out on a laser cutting machine with multiple numerical control operating tables. Furthermore, cutting of multiple shapes and parts can be achieved by modifying the NC program, including 2D and 3D cutting.
Reduced tooling costs:
Laser cutting is different from traditional cutting methods because the cutting torch does not contact the workpiece, eliminating the need for tool changes and reducing tool wear. The laser can be adjusted to cut different thicknesses or shapes of parts simply by changing the laser output parameters.
Green and environmentally friendly:
Laser cutting is an environmentally friendly and environmentally friendly processing method with low noise, vibration and no pollution. It is also a low-impact process that does not produce waste.
Quick Cutting of Various Materials:
Laser cutting can be performed on a wide variety of materials, including metals, non-metals, composite materials and wood. The cutting speed is fast, with a 4,000W laser cutting through 12mm thick low carbon steel with a 30° bevel at a speed of 2,200mm per minute. A 6000W laser can cut 8mm thick stainless steel with a 22.5° bevel at a speed of 1500mm per minute.
2. Application of laser cutting technology in shipbuilding
(1) Features of Ship Cutting
The shipbuilding industry requires high precision in hull segmentation and transfer accuracy, and the structure transfer gap must be kept within 1 mm. In the past, plasma was commonly used to cut ribs by shipbuilding companies, which required manual cutting during field assembly due to cutting tolerances set on ribs to ensure assembly clearance. Poor cutting quality would result in increased residual oxide in the cutting groove, leading to increased assembly workload and prolongation of the assembly cycle, affecting the entire segmented construction cycle.
However, using a laser cutting machine to eliminate assembly allowance reduces the need for on-site cutting and minimizes wasted labor and materials. This leads to faster assembly of the structure and better assembly quality.
(2) Advantages of laser cutting technology in shipbuilding
In recent years, precision and rapid shipbuilding have become the main trends in 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 plates as the main raw material, and laser cutting plates can replace some die-cutting methods that require large and complex molds, significantly reducing production cycles and costs.
At present, the cutting method of hull plate parts in the shipbuilding industry mainly involves flame cutting, plasma cutting, shear processing and laser cutting. However, other cutting methods have several disadvantages compared to laser cutting. For example, flame and plasma cutting have wide slots, low cutting precision, produce harmful gases, and cause significant environmental pollution.
In board cutting, laser cutting has the advantages of high precision, minimal thermal deformation, reduced secondary processing (such as milling, drilling, etc.), transfer and grinding, especially for small circles, small holes and curved surfaces. It can fully meet the accuracy requirements of hull sectional transfer and control the gap of the frame assembly within 1mm, but its practical cutting speed for steel is slower compared to plasma cutting.
The figure shows the relationship between the 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.
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 shipbuilding, laser cutting is used to ensure assembly clearance by establishing a cutting margin on the ribs, which prevents plasma cutting. However, manual cutting leads to uneven cutting quality.
When using laser cutting, the cutting quality is improved, resulting in a good verticality of the cutting surface, no slag, a thin oxide layer and a smooth surface. This eliminates the need for secondary processing and allows direct welding.
Furthermore, laser cutting minimizes thermal deformation, ensuring high precision in curved cutting. This reduces coordination labor hours and enables unhindered cutting of high-strength ship plates, reducing assembly workload, cycle time, and material and labor costs.
Diversion of structural gaps in ships
(3) Application status of laser cutting technology in shipbuilding
Currently, CO 2 laser cutting technology is the most widespread and globally used manufacturing and processing technology in the shipbuilding industry.
However, the cutting speed of the commonly used 5-6kW CO 2 laser falls short of plasma and does not meet the current speed and efficiency requirements of the shipbuilding industry. Furthermore, the high maintenance costs of equipment and machinery, together with low returns, make it difficult to meet the needs of the shipbuilding industry.
Despite its limitations in shipbuilding applications, laser cutting technology has gradually been adopted in the field.
Furthermore, there have been new advances in related cutting and processing technologies.
The effect of 4 kW CO 2 laser cutting
In recent years, several domestic shipyards with strong capabilities, such as Jiangnan Changxing Shipbuilding Base, have introduced the advanced “CO 2 laser cutting machine” to the world.
However, the application of laser cutting machine technology is more optimistic only in Japan. Its success or failure provides valuable experience for the domestic shipping industry.
With the growth of national manufacturing, fiber lasers have also seen rapid development. The high power of fiber lasers, combined with their excellent beam quality, high electro-optical conversion efficiency, compact size and transmission capacity through optical fibers, provide greater working flexibility and are practically maintenance-free and with high reliability . This challenged traditional CO 2 laser cutting technology.
As the effectiveness of fiber laser cutting on thick plates continues to improve, many domestic cutting equipment manufacturers have entered or are preparing to enter the fiber laser market.
Universities, institutions and academics are also studying the cutting effect of fiber lasers. For example, Jae Sung Shin used a 6 kW fiber laser to examine the cutting performance of high-speed fiber lasers on stainless steel plates. The maximum cutting speed achieved was 72 mm per minute, and the study showed that the fiber laser was capable of cutting 60 mm thick stainless steel plates with excellent cutting shape and slot width.
Cutting speed for cutting 60 mm thick stainless steel sheet
Antti Salminen used a 5 kW fiber laser to perform inert gas-assisted laser cutting on 10 mm stainless steel plates and 4 mm aluminum plates. The study investigated the effects of laser power, cutting speed, focus position and auxiliary gas pressure on cutting performance and quality.
The maximum cutting speed was determined at different laser powers and the combination of various cutting parameters was studied to optimize the cutting performance and obtain high quality cuts.
For the laser power parameter set at 4 kW and cutting speed at 1 m per minute, the figure shows the cutting effect on a 10 mm thick stainless steel plate with 2 MPa nitrogen.
10mm thick stainless steel plate with 4kw laser power, lm/min cutting speed and 2MPa nitrogen
The output power of a fiber laser on a 10 mm thick stainless steel plate with a laser power of 4 kW, cutting speed of 1 m/min and nitrogen pressure of 2 MPa reached 50 kW. Currently, the development focus is still on 1-4kW lasers, with 10kW lasers being developed based on this.
Laser technology was industrialized and solved cutting and welding problems in shipbuilding, aerospace and automobile manufacturing.
The shipbuilding industry has fully utilized laser cutting technology, incorporating it into robots to form robotic cutting systems. Since 2000, robot companies such as KUKA in Germany, ABB in Switzerland and FANUC in Japan have developed a range of laser robots and laser cutting robots.
The integration of robotics and laser technology is the current trend in the shipbuilding industry and throughout the manufacturing industry.
3. Laser cutting trends and suggestions in the marine industry
As mentioned previously, laser cutting technology has significant advantages in quality and has been widely adopted in industries such as automotive, sheet metal and machinery.
Currently, large shipbuilding companies such as Jiangnan Shipyard and Wuhan Shipyard use laser cutting to process ship plates.
However, objectively speaking, laser cutting has not yet dominated the domestic shipbuilding industry for the following reasons:
- The cost of laser cutting is higher than traditional cutting methods.
- The large scale of laser cutting equipment is not suitable for the manufacturing characteristics of the shipbuilding industry, such as on-site construction, segmented operations, and challenging work environments.
- There is no significant advantage in cutting efficiency, especially for cutting thick plates in the marine industry.
- Maintenance of laser equipment is complex and requires highly qualified workers, resulting in high costs.
According to the current state of the industry, laser cutting technology is expected to be widely used in shipbuilding due to the drop in laser prices and the increase in the level of intelligence. Following are the main reasons for this:
(1) Cost-effective
Cost reduction is a crucial issue in the shipbuilding industry. At present, traditional processes involve multiple steps, including plate entry, flame or plasma cutting, artificial deburring, artificial groove or cutting machine opening groove and rocker, drill, etc. However, if laser cutting is used, the process can be simplified to plate entry and laser cutting, which significantly reduces time, labor and site costs.
(2) Flexibility and intelligence of laser equipment
In recent years, there has been a significant advance in the level of intelligence of domestic equipment. CNC and robot-based equipment has several modular and intelligent technologies. For example, Nantong COSCO Kawasaki's intelligent production line can adapt to complex manufacturing systems. This adaptability is crucial to the shipbuilding industry's segmented manufacturing, offsite operations and complex production environments.
The process plays a crucial role in determining the effectiveness of the equipment. Therefore, technical personnel must monitor and control the mechanical cutting process in real time to collect and analyze process information. The integration of various energy fields and processes can simplify the cutting process, improve the laser cutting effect, reduce the construction period and cost.
(3) Reduced equipment and maintenance costs
The rapid development of high-power fiber laser and semiconductor laser manufacturing technology and the improvement of corresponding processing technology have led to precise, high-efficiency and energy-saving cutting characteristics. This meets market demand and the current development direction of laser manufacturing technology.
Fiber lasers and semiconductor lasers must be industrialized and commercialized, and corresponding equipment and control technologies must be developed and improved. Equipment progress has further improved equipment integration and flexibility.
For the special requirements of cutting machine for ship stern plate work and the diversity of hull structure shapes, laser cutting head multi-degree of freedom optimization designs, development of rotation control methods are required and control systems. Attention should also be paid to the application research of robots and machine vision detection systems in the laser field to achieve cutting path monitoring, high-precision cutting and unmanned automatic operation to improve the quality and efficiency of operations.
Effective cutting quality control can reduce production costs and safety risks.
