Classification of Shipbuilding

The division of workshops often varies based on the production scale, nature, and habits of shipyards.

In the past, in addition to steel processing, hull assembly, welding and equipment system installation, many shipyards also had certain casting, forging and mechanical processing capabilities. While manufacturing the hull, they also manufactured the main engine, auxiliary engine, boiler and other equipment. Since the 1950s, with the development of shipbuilding and its supporting industries, shipyards have shifted towards the direction of final assembly, mainly focusing on building ship hulls. A large amount of mechanical and electrical equipment and outfitting parts are provided by professional or non professional cooperative factories, and shipyards only carry out installation to improve shipbuilding quality and efficiency.

The main process flow of shipbuilding can be represented by the following block diagram.

Steel pre-treatment refers to the correction, rust removal, and primer application of steel before material marking. Marine steel often undergoes various deformations due to uneven rolling, uneven cooling shrinkage after rolling, or other factors during transportation and storage. For this purpose, after the plates and profiles are taken out from the steel yard, they are first straightened using a multi roll steel plate leveler and a section steel straightener respectively to ensure the normal progress of material marking, edge and forming processing. The corrected steel is generally first polished and rust removed, and finally sprayed with primer and dried. The processed steel can be sent to the designated material. These processes often form a pre-treatment automatic assembly line, which is connected to the transportation lines of subsequent processes such as steel lifting, marking, and edge processing in the steel yard through the use of conveyor rollers, in order to achieve comprehensive mechanization and automation of ship parts preparation and processing.

The layout and marking of the hull shape are usually smooth spatial surfaces. The outline diagram of the ship, represented by a three-dimensional projection line provided by the design department, is called a profile diagram and is generally drawn at a scale of 1:50 or 1:100. Due to the large scale ratio, there is a certain degree of error in the three-dimensional smoothness of the profile, so it is not possible to directly carry out ship construction according to the profile diagram. Instead, it is necessary to carry out 1:1 full scale layout or 1:5, 1:10 ratio layout on the layout platform of the shipyard to smooth the profile, obtain the correct shape value and the actual shape, size, and position of each component required during construction, and provide necessary construction information for subsequent processes. Ship layout is a fundamental process in ship construction.

Material marking is the process of drawing the actual shape and dimensions of the ship's hull parts obtained after layout, using templates, samples, or sketches, onto plates or profiles, and marking them with marks for processing and assembly. The earliest methods of laying out and marking materials were full scale laying out and manual marking. In the early 1940s, proportional layout and projection marking emerged, which involved laying out at a ratio of 1:5 or 1:10 to create a projection base map, which was then enlarged to the actual size using a corresponding low magnification projection device; Alternatively, the projection film can be reduced to 1/5~1/10 to create a projection film, and then magnified 50-100 times using a high magnification projection device to create a solid shape of the part. Then, a line can be drawn on the steel. Proportional layout can also provide a profile diagram for the photoelectric tracking cutting machine to directly cut steel plates, thereby omitting the marking process. Although projection marking has made significant improvements on the basis of manual marking, it still cannot break free from manual operation. In the early 1960s, the application of electroprinting materials began, which utilized the principle of electrostatic photography to first spray photosensitive conductive powder on the surface of steel plates for positive projection exposure. After development and fixation, part graphics were developed on the steel plates. The large-scale electroprinting marking device suitable for large-sized steel plates adopts a synchronous continuous exposure projection method, that is, the base image and the steel plate move synchronously, and continuously project and expose during the movement process. A small electric marking device suitable for small-sized steel plates, which projects all the graphics on the steel plate at once. This marking method has been widely used. With the application of electronic computers in shipbuilding, mathematical layout methods have emerged again. Using mathematical equations to represent the hull line or surface of the ship, using the design value table and necessary boundary condition values as raw data, using a computer for repeated verification and calculation, to achieve the modification and smoothing of the hull line, in order to obtain accurate smoothing and corresponding projection points that are completely consistent with the hull line. Each profile of the ship is represented by a characteristic mathematical spline curve equation and can be drawn using a CNC drawing machine (see drawing tool). Mathematical layout can eliminate traditional full scale layout work and provide control information for subsequent processes such as cutting and forming. It plays a crucial role in the automation of the shipbuilding process and is an important development in shipbuilding technology.

The processing of ship parts includes edge processing and forming processing. Edge processing is the process of cutting the actual shape of the ship's hull parts on the steel after marking, using a shearing machine, oxygen acetylene gas cutting, or plasma cutting. The edges of some parts still need to be processed with gas cutting machines or edge planers for weld groove preparation. The photoelectric tracking gas cutting machine in the gas cutting equipment automatically tracks the lines on the scale diagram and cuts the steel plate through a synchronous servo system. It can be used in conjunction with manual marking and projection marking. The use of CNC gas cutting machines not only has high cutting accuracy, but also directly cuts based on mathematical layout data, which can skip the material marking process and achieve automation in the layout and cutting process.

For ship hull panels with spatial shapes such as curvature, bending angles, or edges, forming processing is required after cutting the steel plates, mainly using roller bending machines and rolling presses for cold bending; Alternatively, the processing method of water and fire forming can be adopted, which involves using an oxygen acetylene torch to locally heat the sheet according to a predetermined heating line, and using water to track and cool it, resulting in local deformation of the sheet and bending it into the desired curved shape. For profiles used as ribs, rib cold bending machines are often used to bend them into shape. With the development of digital control technology, digital control rib cold bending machines have been used, and further digital control bending machines have been developed. The processing of ship parts has progressed from mechanization to automation.

The process of assembling and welding the components of a ship's structure into the entire hull. The commonly used segmented construction method is divided into three stages: component assembly welding, segmented assembly welding, and slipway assembly welding.

① Component assembly welding: also known as small closure. The process of combining processed steel plates or profiles into plate columns, T-profiles, rib frames, or ship's bow and stern columns is carried out on the welding platform in the workshop.

② Assembly and welding of sub (total) sections: also known as middle closure. Combine components into flat, curved, or three-dimensional segments, such as bulkheads, bottoms, sides, and superstructure segments; Alternatively, it can be combined into a circular three-dimensional segment that cuts across the main hull in the direction of the captain, known as the main section, such as the bow section, stern section, etc. The assembly and welding of segments are carried out on the welding platform or tire frame. The division of sections mainly depends on the characteristics of the hull structure and the lifting and transportation conditions of the shipyard. With the increasing scale of ships and the increasing capacity of cranes, the number of sections and total sections is also increasing, with a weight of over 800 tons.

③ Shipway (dock) assembly welding: refers to the final assembly of the hull, also known as large closure. Finally assemble and weld the ship's components, sections, and sections onto the shipyard (or dock) to form the hull. Large ships with a displacement of over 100000 tons are often assembled in shipyards to ensure safe launching. The commonly used assembly methods include: using the main section as the assembly unit and lifting it from the middle to the bow and stern of the ship, known as the main section construction method, which is generally suitable for building small and medium-sized ships; The tower construction method involves first lifting a bottom section at the stern of the ship, and then using it as a construction reference to lift adjacent sections towards the bow, stern, and upper deck, with a lifting range in the shape of a pagoda; There are 2-3 construction benchmarks, which are constructed using the tower construction method and finally connected to the hull, known as the island construction method; When constructing the first ship at the end of the shipyard (or shipyard), the tail of the second ship is simultaneously constructed at the front end of the shipyard. After the first ship is launched, the tail of the second ship is moved to the end of the shipyard and other sections are continued to be lifted until the entire hull is assembled. At the same time, the tail of the third ship is also constructed at the front end of the shipyard. This method is called the series construction method; The two-stage construction method involves dividing the hull into two sections, the first and the second, which are built on the slipway and then launched, followed by a large closure on the water. The selection of various final assembly methods depends on the structural characteristics of the ship and the specific conditions of the shipyard.

The workload of ship assembly and welding accounts for more than 75% of the total workload of ship construction, with welding accounting for more than half. Welding is a crucial task in shipbuilding, as it not only directly affects the quality of ship construction, but also affects the efficiency of shipbuilding. Since the 1950s, welding methods have evolved from fully manual welding to submerged arc welding (see submerged arc welding), semi-automatic welding, slag welding, and gas shielded arc welding. Since the mid-1960s, there have been new technologies such as single-sided welding and double-sided forming, gravity welding, automatic corner welding, as well as vertical welding and horizontal automatic welding. Welding equipment and welding materials have also developed accordingly. Due to the complexity of the ship's structure, manual welding is still required in locations where automatic and semi-automatic welding is difficult to implement.

With the development of welding technology, since the 1960s, T-shaped welding assembly lines and flat segmented welding assembly lines have been used in ship components and segmented assembly, respectively. T-shaped profiles are the basic components that make up a planar segmented skeleton. Plane segmentation occupies a considerable proportion in ship structure, for example, on large bulk carriers and oil tankers, plane segmentation can account for more than 50% of the total weight of the ship. The planar segmented assembly and welding assembly line includes various specialized assembly and welding equipment. It uses conveying devices to continuously perform feeding, panel welding, and skeleton assembly operations, which can significantly improve the mechanization of segmented assembly and become one of the main contents of modern shipyard technological transformation. Some shipyards in the world also use assembly line production methods for welding and dock assembly of large-scale oil tankers produced in bulk.

After the final assembly of the hull is completed, a sealing test must be carried out on the hull, and then the shaft system and rudder system must be aligned at the tail, and the shaft system, propeller, and rudder must be installed. Prepare for launching after completing various underwater projects.

The process of launching a ship from land to water is carried out when the ship has completed the final assembly of the shipyard (dock). The direction of movement when a ship is launched, either parallel or perpendicular to the captain, is called longitudinal launch and transverse launch, respectively. The main types of launching slides are wooden beam slides and mechanized slides. The former relies on the weight of the ship to slide and launch, and is more commonly used; The latter uses a small car to carry the ship and pull it onto the track for launching, which is often used in small and medium-sized shipyards in inland rivers.

Before launching longitudinally, transfer the hull resting on the pier to the skateboard and slide, which have a certain inclination towards the direction of the ship's entry into the water. After releasing the braking device set between the skateboard and the slide, the ship slides into the water along with the skateboard and support due to its own weight, and then floats on the water surface by its own buoyancy. To reduce friction resistance during sliding, a certain thickness of grease is often applied between the skateboard and the slide; Steel balls can also be used instead of grease to change sliding friction to rolling friction, further reducing friction. The ship assembled in the dock can float as long as it is filled with water, and its launching operation is much simpler and safer than using a slide under the slipway.

Launching means that critical and major work has been completed in ship construction. According to traditional customs, a grand celebration ceremony is often held for the launch of large ships.

Dock installation (installation of equipment and systems): After the ship is launched, it often leans against the shipyard outfitting dock to install hull equipment, mechanical and electrical equipment, pipelines, and cables, and carry out cabin woodworking, insulation, and painting work. There are many types of work involved in dock installation, and their mutual influence is also significant. With the increasing complexity of ship equipment and systems, the requirements for installation quality are also constantly improving. Therefore, installation work is directly related to whether the ship can be quickly tested and delivered after launch. In order to shorten the installation cycle after launching, the above installation work should be carried out as early as possible in the stage of segmented assembly and overall hull assembly, which is called pre outfitting. Changing traditional single piece installation to unit assembly can greatly shorten the installation cycle, which determines the degree of composition of the installation unit based on the layout and composition characteristics of the engine room and other cabin equipment. For example, the main engine cooling unit can include heat exchangers, pumps, temperature regulators, relevant pipelines with accessories, and necessary electrical equipment for the unit. Forming installation units in the workshop and then hoisting them to sections, sections, or ships for installation can advance 18-25% of the installation workload from the ship to the inner field, and shorten the installation cycle on the ship by 15-20%.

Mooring and navigation tests must be conducted comprehensively and strictly after the completion of ship construction and installation work, in order to ensure the completeness of construction and the reliability of various equipment work. They are usually divided into two stages, namely mooring tests and navigation tests.

Mooring test, commonly known as dock test, is a series of practical tests conducted on the main engine, auxiliary engine, and other mechanical and electrical equipment of a ship in a mooring state to verify installation quality and operation. The mooring test is centered around the main engine test, which checks the working condition of the generator set and distribution equipment in order to create conditions for the testing of the main engine and other equipment. Reliability and safety tests are also required for coordination, emergency response, remote sensing, and automatic control of various relevant systems. During mooring tests, the ship is basically in a stationary state, and the main engine, shaft system, and related equipment systems cannot display the performance of full load operation, so navigation tests are also required.

Navigation test is a comprehensive inspection of the performance of the main engine, auxiliary engine, various electromechanical equipment and systems of a ship during navigation. Usually there are light load and heavy load trials. Measure the speed, engine power, maneuverability, turning ability, heading stability, inertia, and airworthiness of the vessel in the navigation test. After the test results are accepted by the ship organization and users, they will be officially delivered by the shipyard to the ordering party for use.

The development process of modern shipbuilding technology is a transition from manual operation to mechanization and automation. Since the 1950s, welding has replaced riveting in ship construction, which has greatly improved the efficiency of shipbuilding by replacing the previously used scattered bulk method with segmented assembly method. Due to the complex structure and shape of the ship, manual operations have always accounted for a significant proportion in ship construction. The application of electronic computers and numerical control technology is further changing the face of the shipbuilding industry. Electronic computers were first applied to mathematical layout, leading to the emergence of CNC drawing machines, CNC cutting machines, CNC rib cold bending machines, CNC propeller processing machines, and pipe processing machines with digital input and graphic output. At the same time, electronic computing technology is gradually being applied in production management, planning, material and equipment supply, and cost accounting in shipyards. In order to reduce information preparation work and eliminate the disconnection between design and production, a large-scale integrated numerical control system for shipbuilding has been developed. It includes universal information for all functions of ship design, production, and management, and can coordinate the entire work process from design to production. Therefore, continuing to expand the application of computers in shipbuilding is the main direction for modern development of shipbuilding technology and further improvement of shipbuilding automation.