Numerical Simulation Study On Flexible-bending Process Of Typical Shipbuilding Profiles

Profiles are indispensable materials in the field of production and manufacturing and affect all aspects of our lives.In shipbuilding,many profiles are widely used.Profiles,especially asymmetric section profiles,provide strong support for the construction of ship ribs and the design of frame structures.The tube is a kind of profiles with special section.Because of its hollow section,light weight,high specific strength and absorbable impact,it is widely used in various liquid transportation systems and structural parts on the shipbuilding.Therefore,the study of bending technology is of great significance to the industrial application of profiles.Flexible-bending technology is a relatively new bending-profiles technology.The principle is that traditional fixed die is replaced by bending die with real-time adjustable position and we can bend profiles with different curvatures by adjusting and controlling the offset of the die.Therefore,it has the advantages of strong versatility,short production cycle and low cost,which satisfies the production demand such as multi-curvature and small batch of customers.Using numerical simulation method can well analyze the stress and strain when bending profiles,help to judge the bending trend,predict and eliminate the forming defects.It has an important assistant and guiding role for the actual bending profiles.In this paper,finite element software was used to simulate the flexible-bending process of tubs and flat-bulb steel.At the same time,stress and strain were analyzed and a series of process parameters were studied.The related forming defects were discussed and the solutions were put forward.The main contents and conclusions of this paper are as follows:(1)Analysis of flexible-bending and establishment of finite element modelThe development,forming principle,bending process and advantages of flexible-bending technology were analyzed.The finite element models of flexible-bending of tubes and flat-bulb steel were established.The selection and division of mesh elements,selection of material parameters,setting of boundary conditions and friction were discussed.(2)Analysis of bending-moment of bent tubes and simulation results of flexible-bendingThe bending-moment formula of bent tubes was deduced through mechanical analysis.The formula shows that the bending-moment is closely related to the specific size,material performance and bending curvature of bent tubes.The experimental equipment and forming principle of flexible-bending of tubes were introduced.The force of pusher and stress-strain distribution were analyzed by numerical simulation method.The results show that the force of pusher has good stability and increases with the increase of the offset of the bending die.The distribution of stress and strain in the circumference of the cross-section of the bent tubes has certain regularity and symmetry.(3)Study on springback of flexible-bending of tubesThe springback problem of 304 stainless steel tubes when flexible-bending was studied.The influence of wall thickness and bending radii on springback were discussed and analyzed.The springback compensation method was adopted to solve the problem,and the compensation amount under different parameters was further explored.The results show that with the increase of wall thickness,the springback decreases rapidly and then tends to be flat;with the increase of bending radii,the springback increases linearly.The method of springback compensation can effectively solve the problem of forming error and then improve the forming accuracy of bent tubes.The variation trend of springback compensation under different wall thickness and bending radii is similar to that of springback.(4)Study on flexible-bending of flat-bulb steel and relevant technological parametersTaking Q345 flat-bulb steel as the research object,the section characteristics,bending forms and the principle and process of flexible-bending were analyzed.The forming stability,stress-strain distribution and the influence of related parameters on the bending curvature were studied by numerical simulation.The results show that the flexible-bending process of flat-bulb steel has good forming stability,the distribution of stress and strain is uniform and regular,the offset of bending die and the distance parameter l between the guide and the bending die have important effects on the bending curvature.The effects of friction coefficient,clearance between profiles and forming device and guide device on forming process and forming effect were investigated.The results show that the increase of friction coefficient will increase the forming resistance and aggravate stress concentration;the existence of clearance has a certain effect on the bending curvature;the fillet of guide can effectively reduce the forming difficulty and improve the stress concentration of the profiles.(5)Research and elimination of side bending defects of flat-bulb steelBy means of numerical simulation,the side bending defect of flat-bulb steel in positive bending was studied and the solution was put forward.The results show that the cross-section asymmetry of flat-bulb steel is the intrinsic cause of the side bending defect.The relative bending radii has a great influence on the side-bending defect,and the side bending amount increases with the decrease of the relative bending radii.The side bending defect can be effectively suppressed or even eliminated by adjusting the offset of the die.