Automatic gas tungsten arc welding experiments of 5083 aluminum alloy were completed, to analyze the weld microstructure and mechanical properties. The influences of welding current, travel speed, frequency, and arc length on weld forming and mechanical properties were studied. When the welding current was 160 A, the travel speed was 380 mm/min, the frequency was 100 Hz, the arc length was 4 mm, and the maximum tensile strength of the welded joint was 296.9 MPa, which was 86.8% of the base metal’s tensile strength. The fracture elongation was 7.8%. No porosity was formed in the weld, but there were poor fusion problems. ER5356 welding wire can improve the problem of poor weld fusion and accommodate Mg element vaporization losses. When the wire feeding speed was 1200 mm/min, the tensile strength of the welded joint can be improved to 315.2 MPa, which was 92.2% of the base material’s tensile strength, and the fracture elongation was 8.5%. The tensile specimens fractured in the heat-affected zone. The fracture surface was characterized as plastic fracture.

Hot cracking is one of the major challenges in laser welding of Invar alloy. In this study, welding hot cracking susceptibility experiments are conducted with fish-bone-type Invar alloy sheets under pulsed laser welding condition. The pulse wave consists of two distinct power levels: welding pulse and post-heating pulse. The welding temperature field can be controlled by changing the duration of the post-heating pulse. The results of experimental measurements and finite element method calculation show that increasing of the post-heating pulse duration leads to a decline in the cooling rate of weld metal within the brittle temperature range, although the welding hot cracking susceptibility decreases at first and then increases. Neither the heat input nor the cooling rate is the only decisive factor for hot cracking during the welding process. 1. Introduction Invar alloy is widely applied in precision measurement devices and low-temperature-resistant structures for its low linear expansion coefficient at ambient temperature, which is less than 1.6 × 10 —6 k —1 , about 1/10 of the low carbon steel, and it changes very little within a large temperature range (Corbacho et al. 1998; Park et al. 2011; Zhao et al. 2015; Qiu et al. 2016). With the increase in demand for natural gas, the liquefied natural gas (LNG) carrier has been developed rapidly as a means of long-distance transport. The material of primary and secondary barriers on the containment insulation system of membrane-type LNG carrier is welded Invar alloy with a thickness of .7 mm, which directly contacts the — 163°C LNG (American Bureau of Shipping 2006; Bureau Veritas 2011; Wang et al. 2006). The total weld length of Invar alloy on an LNG carrier over 13 million cubic meters can reach up to 100 km according to statistics. Hot cracking is the major problem in the welding of Invar alloy, and currently Tungsten inert gas (TIG) arc welding is commonly used. However, the problem of hot cracking cannot be solved completely, and requires that the operator have good technical knowledge. Invar alloy has high hot cracking susceptibility during the welding process because of its single-phase austenite structure and high content of Ni (Kou 2003). Studies show that the welding hot cracking susceptibility of Invar alloy can be reduced when elements such as Ti, Mn, and Mo are added (Hirata et al. 2001), but these alloying elements will increase the linear expansion coefficient of the weld, resulting in the deterioration of mechanical properties at low temperature. Thus, laser welding and friction stir welding are proposed by researchers to solve the welding hot cracking problem of Invar alloy from the aspect of reducing welding heat input.

Nowadays in most shipyards, line heating techniques are widely used in the forming process of hull plates. The precision and efficiency of the process are greatly influenced by the determination of technical parameters, including heating length, heating velocity, and the arrangement of heating line. Previous studies on this, which considered only local shrinkage, produced large errors in the calculation of thick and large curvature plates because the whole deformation was ignored. In this article, new mathematical formulas are proposed to indicate the relationship between the whole deflection and shrinkage during the plate-forming process by line heating. The numerical models were established based on the thermoelastic plastic finite element method considering the deflection. The reliability of the numerical models was verified by the comparison of temperature fields and displacement. Based on the analysis of forming regularity, a new concept named influence factor of deflection (IFD) was proposed from the analysis between deflection and shrinkage. The formulas were derived, which establishes the relation between the IFD and technical parameters. Finally, the experimental results showed that the relative percentage error is 5.13% for IFD, and the forming formulas were verified. The research lays a foundation for the technique of parameter prediction of thick and big curvature plates considering the deflection. 1. Introduction The procedure of lofting, marking-off, pretreatment of steel plates, cutting, and welding has been automated in shipbuilding. Hull plate forming is the bottleneck of shipbuilding. There are numerous curved hull plates that need to be formed within the shipbuilding industry. Precision and efficiency are the technical difficulties in hull plate forming. It is very important to realize the automatic forming of curved hull plate. Line heating is an important method in hull plate forming, which mainly relies on the experience of the workers (Seong et al. 2013). The general processes are as follows. First, the technical parameters of hull plate forming are obtained based on the workers' experience. Then, hull plate forming is carried out manually by the workers. Last, plate forming quality is detected by using detection templates or a detection box. If plate forming cannot meet the requirements of the standards, the workers need to reform the plate, until it can meet the requirements. These procedures cause low efficiency and great fluctuation in forming quality. Therefore, it is essential to perform automatic line heating research.

The traditional block lifting schemes often give rise to a host of problems such as the complexity of the lifting process, low degree of automation, and lack of theoretical guidance. To overcome the deficiencies, the authors of this paper have developed an automatic design system for the complex block lifting. Tribon is adopted as the data extraction method to identify the feature area of a block so as to lay out the lifting lugs properly and efficiently. Besides, Matlab is employed to analyze the stress on lifting wires and 3ds Max to simulate the block lifting process. In this way, the potential problems about mechanics and interference between the block and wires can be forecasted so as to enable the designers to improve the lifting scheme and ensure a safer and more reliable design. 1. Introduction Block lifting operation is a crucial process in shipbuilding since it determines the efficiency of the hull construction as well as the quality of the ship. The traditional artificial block lifting schemes often entail a host of problems such as the complexity of the lifting process, low degree of automationand lack of theoretical guidance. in recent years, scholars have studied the block lifting technologies for several types of ships including Very Large crude carrier (VLcc) and the container vessel. After analyzing the features of block lifting operation and the lifting environment, Li et al. (2013) summarized the principles and requirements of block lifting design, built models for the object to be lifted for the lifting equipment as well, designed an automatic layout algorithm for block lifting scheme and developed a design system for ship block lifting. Li et al. (2014) rebuilt the finite element model under ANSYS environment based on the extracted data of blocks. The calculation results can serve as a guidance for the design of structural reinforcement, which can save materials and reduce workload. In terms of the block lifting technologies used in the building of a 3500 TEU container vessel, Zhang (2010) studied on the lifting technologies employed in lifting some typical blocks such as the stern, broadside, and engine room. Based on the analysis and study on hull assembly method, Yu (2014) took use of computer to successfully simulate the process of hull assembly and save the relevant process information about the hull before shipbuilding. Kim et al. (2005) developed the virtual assembly simulation system for shipbuilding, which can simulate the operation of cranes and the installation of blocks in a virtual shipyard and evaluate the operations. Miura (2011) adopted the three-dimensional computer Aided Design (cAD) to develop a simulation system for block lifting and then he illustrated the features and functions of the system and stressed the importance of threedimensional model used in the process. Takola et al. (2013) established a mathematical model to analyze the constraint conditions in the block lifting process so as to optimize the lifting scheme and improve the efficiency of lifting operations. By applying the theory of combined discrete event and discrete time, Cha J.H. developed an integrated simulation framework for block lifting and erection process (Cha et al. 2010; Cha & Roh 2010). KuN. developed a crane system consists of several crane types, a scenario manager capable of creating and editing lifting process for multibody dynamics-based simulation is proposed (Ku et al. 2014a, 2014b). This study focuses on the complex ship block lifting with an attempt to build a system integrating the design of the complex block lifting scheme, the analysis on the mechanical characteristics in the lifting process and the simulation design of the block lifting operation together (Fig. 1).

In this article, the line heating forming technology by using the moveable induction heating is used to form a concave-type plate. In shipyard, it is necessary to get a bigger contraction deformation at the plate edge for the concave plate. However, the heat input of the metal near the plate edge is less than that of the internal metal along the heating line due to the decrease of heat power near the plate edge, thus causing smaller transverse shrinkage of the plate edge. To solve this problem, the paper investigates the suitable heating way of the inductor for the concave plate forming. An electromagnetic coupling finite element model is built to simulate the moveable induction heating process and reveal different heating and forming characteristic of different inductor heating ways. The simulation results are verified by experiments data. Research results showed that the heating way by which the inductor moves out of plate edge is an effective heating technology which meets the forming requirement of the concave plate.

Creating an access opening in ship structure through thermal cutting is an important process in ship repair and reconstruction. The flame cutting process typically leads to a nonuniform temperature distribution, generates residual thermal stress and localized plastic deformation. As openings are needed at various locations of ship hulls, it is also necessary to consider the effects of structural constraints in the immediate end of the plate where the plate is either welded or fixed to the ship frame or bulkhead. These are challenging tasks. This article presents a study based on the thermal elastoplastic analysis. By using the finite element techniques, a steel plate model undergoing flame cutting process to create an opening was studied in details. The numerical model was validated with experimental data. The study identified several key parameters that are 1) structural boundary condition, 2) steel plate size, 3) opening location, and 4) opening shape.

The hull job shop in a shipyard is a typical flexible manufacturing system (FMS), the flexibility and efficiency of which largely depends on the level of FMS scheduling. In this paper, the Object-Oriented Colored Petri Net (OOCPN) is used to build the FMS model for the hull job shop. A four-step modeling method of FMS has been developed to successfully simulate the scheduling of the hull job shop.

An automatic line-heating process for the double-curved shell plates is introduced. This process contains four subprocesses: calculating the heating information based on shell development and analysis of primary technological parameters, which is named as prediction system of heating information; heating the plate by an automated line-heating machine according to the calculated heating information; measuring and inspecting the plate surface to determine whether it matches the designed surface; and calculating the reheating information for the deformed plate and reheating the plate automatically until the designed shape is achieved. Therefore, an iterative loop system of an automated line-heating process can be developed based on the integration of these four components.

Line heating is an effective and economical method for forming metal plates into three-dimensional shaped plates for ships, trains, and airplanes. When a curved plate subject to deformation is formed in line-heating process, the deformed shape is repeatedly inspected and reformed to reach the designed shape. Efficient automatic inspection and reforming processes are essential to enhance productivity in the whole manufacturing process. In this paper, efficient algorithms for inspection and reforming of double-curved plates are introduced. These algorithms have been developed to automatically inspect the transverse and longitudinal shape of plate surfaces and provide technical parameters to reform the unformed plates. The longitudinal shape of the plate surface is examined based on a shell plate development with plastic deformation during the plate formation, and the transverse shape is inspected through error analyses of transverse curvature radiuses. How to use the inspection results to reform unformed plates is discussed. In the end, experiments are performed with comparison to the current industrial plate manufacture, and results show a prospective application of our algorithms to the practical manufacturing of doublecurved plates. The methods presented in this study may play a role in realizing the automation of the entire curved-plate manufacturing process.