Research On The Press Forming Of Large-Size High Strength Steel Thick Curved-Shells

In recent years,with the rapid development of China’s chemical industry,nuclear power,shipbuilding,national defense and other fields,the demand for high strength steel curved parts is gradually increasing.As an important compression component,its forming quality not only affects the manufacturing cost and quality of the device,but also directly affects the safe use of the device.The traditional high strength steel double curvature thick plate forming process has some problems such as low forming precision,low strength and low productivity caused by point pressure.In order to solve this problem,this paper proposed the whole pressing forming process of large size asymmetric high strength steel double curvature thick shell,and studied its forming characteristics and key process parameters,especially established the optimization compensation method of asymmetric rebound.First of all,through the parts of the material and structure of the two aspects of analysis,explore the forming difficulties.The results show that due to the high yield strength and high yield ratio of Q890 high strength steel,the material itself has a large rebound and requires a large compression force.Due to the asymmetry of the structure of the parts,the springback situation is complicated and lateral force will be generated on the die.Then,through the finite element simulation of large size high strength steel curved thick shell molding process,the influence of pressing force on forming accuracy,die force analysis and parts rebound law during forming process were investigated.The results show that there is a surge stage of pressing force in the process of pressing forming,and the pressing force increases to 8885 T at the pressing moment.By analyzing the relationship between the pressing force and springback,the pressing force can meet the forming requirements when it is 400 T.Thus,the idea of low clamping force and high precision manufacturing is put forward.The lateral force can be reduced by 87.6% by optimizing the placement position of the slab in the die.In the process of pressing the die has obvious uneven force phenomenon,part of the contact stress is large;During the forming process,the stress distribution of the slab is not uniform,there is elastic deformation area,and obvious rebound phenomenon will occur after unloading.The mold surface with the same curvature as the design surface is used to press the whole forming,there is uneven springback phenomenon,the maximum springback amount is 43.9mm,the springback rate is 3.7%.Then,the results of finite element simulation are verified by the experiments of heavy shell forming with large size high strength steel curved surface.The results show that,corresponding to the finite element simulation results,the difference of pressing force is about100 t,and the difference of springback is only about 1.5mm in the state of close compression.At this stage,the change of pressing force has little influence on springback,which verifies the feasibility of low clamping force and high precision manufacturing scheme.The prediction accuracy of compression force and springback by finite element simulation can reach more than95%,so it is feasible to optimize the mold surface by finite element simulation.Finally,the mold surface was optimized by adjusting the ellipsoid section ellipticity,that is,iteratively compensating the radial springback on the warp and weft section line of the parts.By adjusting the flatness of the two ellipses,the sphere-bottom die is optimized into an ellipsoid die,the forming accuracy is greatly improved,and the deviation rate can be controlled at about0.3%.In conclusion,this paper proposes an asymmetric springback optimization compensation method with low clamping force,high precision manufacturing scheme and iterative compensation for radial springback of longitudes and weft sections,which can meet the forming requirements of thick shells with large size and high strength steel surfaces.