Research On Pivotal Techniques For Automatic Line-Heating Process

For a long time, the double-curved hull plate forming in shipyards depends on skilled workers performing the line-heating process by their empirical intuition and handwork. With the development of modern shipbuilding technique and the transformation of shipbuilding mode, the manual and experiential technique patterns of line-heating can not meet the requirement of modern shipbuilding in processing speed and product quality. Therefore, line-heating technique has to be innovated exigently. If automatic line-heating process can be realized by utilizing computer and numerical control techniques, there are important economic significances for increasing labor productivity, relieving workers' labor intensity, reducing reworking expenditure and improving manufacturing accuracy. Furthermore, it can provide technical reserve for the fabrication of double-curved plate in other fields.A comprehensive closed-loop system of automatic line-heating process includes the components of hull plate development, technique parameters prediction, automatic inspection and reformation, which is a complex system consisted of many disciplines such as shipbuilding, machinery, mathematics, computer and so on. Several pivotal techniques in the closed-loop system of automatic line-heating process have been investigated in this thesis.(1) Research on the flux boundary conditions in the numerical simulation of line-heating processWith the development of computer technique in recent years, the numerical simulation method has been applied more and more widely for the research of distortional mechanism and regulation in line-heating process. In the simulation of line-heating process, the selection and definition of flux boundary conditions will affect the solution of temperature field and its coupled deformation field directly, and have great influence on the precision of simulation results. The flux boundary conditions in the numerical simulation of line-heating process have been researched systematically including the fluxes of heat input, air convection, radiation convection and forced convection of subcooled water. Moreover, the forced convection boundary condition has been developed by utilizing the theories of forced convection boiling. This new boundary condition can improve the precision of simulation results and establish the foundation of numerical analysis of line-heating process.(2) Research on the technique parameters prediction of line-heating processBased on the analyses of factors affecting the deformation in line-heating process by using the methods of numerical simulation and experiment, the mathematical models for deformation disciplines of multi-factors have been remodeled to those of single factor, which can not only improve the precision and extend the application of models but express the deformation disciplines of factors more accurately and directly. And then, according to the local deformation obtained from ship hull plate development, the method for technique parameters prediction of line-heating process has been investigated and the corresponding software system has been developed by using the relation between local deformation and the needed energy. The method takes the practical experience in shipyard into consideration and avoids the disadvantage of considering the total energy constraint but ignoring the energy needed by local deformation. It has been testified to be effective by the applications in shipyard and that can improve the production efficiency. The accuracy reaches the requirement.(3) Research on algorithms for inspection and reforming of double-curved plates in line-heating processBased on the measurements and mathematical expressions of the fabricated double-curved plate surface, algorithms for automatic inspection and reforming of both longitudinal and transverse shape haven been studied. The process of forming a double-curved plate by line heating is regarded as a reverse process of plate development. The longitudinal shape of a plate surface is inspected by developing the formed plate surface onto the inspecting surface, while the transverse shape is inspected by the error analyses of transverse curvature radiuses on the measuring lines. Combining the inspection results of longitudinal shape with those of transverse shape, it is determined whether the plate is formed successfully or not. Moreover, it can provide explicit guidance to the reforming of unformed plate. Discussions are made on how to use the inspection results to reform unformed plates and the corresponding algorithms for the reheating technique parameters prediction have been developed, which can calculate the reheating technical parameters of both longitudinal and transverse shape and be suited for automated operation in line heating process.(4) Research on design of cantilever robot for line-heating processThe development of the automated line-heating machine is an important component of automatic line-heating process. According to technique characters and requirements of practical line-heating process, the design requirements of cantilever robot with better mobility have been established by referring to the existing automated line-heating machine. The performance parameters, structural parameters, topological structure and design project have been determined. By combining the structure design with the static analysis and modal analysis, the structure has been optimized to reduce the weight of robot in the condition of structural strength and rigidity having been satisfied. Furthermore, the kinematics analyses can be helpful to the research on motion control.