Research On Swinging Punch Multi-point Forming Process For The Large Slab Parts

Diversified,rapid and accurate forming in the sheet metal forming industry has always been a difficulty in this field,especially for the formation of parts which are large and thick.The existing processing methods have disadvantages such as high labor intensity,long production cycle and low forming accuracy.Multi-point forming(MPF),as a flexible forming technology with discrete and reconfigurable mold profiles,can achieve rapid forming of various workpieces with complicated shapes and sizes.The swinging punch multi-point forming(SPMPF)on the basis of it for the optimization design of punch.By means of the self-adaptively attaching between them during the forming process,it further improves the surface quality and precision of the parts,and widens the forming limit of multi-point forming(MPF)on the parts' thickness and curve.It is of great significance for the development of automobile,ship,construction and other industries to study the forming characteristics of large slab parts on the swinging punch multi-point equipment.The main research contents of this article are as follows:1.Principle of swinging punch multi-point forming and establishment of finite element model.Based on the characteristics of multi-point forming equipment,this paper mainly introduced the swinging punch on the swinging punch multi-point equipment.The elasticplastic finite element theory of plate and bending deformation theory of thick plate are described.By taking large slab parts with double-curvature and spherical parts as examples,the finite element models of swinging punch multi-point forming are established,and the problems involved in the model are discussed,including material mechanical properties,contact properties,load control,constraint conditions,elements meshing,etc.2.Research on sectional forming technology of large hull part.The effects of overlap zone's size,transition zone design and forming sequence on the quality of a large hull part with double-curvature are studied when it is segmented on the swinging punch multi-point equipment.The simulation results show that overlap zone with reasonable length can reduce the severe degree of plastic deformation at the stage of ensuring production efficiency.A transition zone is designed between the effective forming zone and undeformed zone.By controlling the curvature radius and height difference of the transition zone,a smoother connection can be achieved to make the sheet flow more uniform,and effectively eliminate the defects such as wrinkles and junction marks that are prone to occur when the transition zone is not designed.Based on the designed deformationharmonized transition zone,unidirectional forming of thick plate is performed,the part appears to be work hardened and it is difficult to form.While the sectional forming from both ends to the middle can obtain a part with low residual stress and strain,high shape precision,and fully formed.Experiment in this way,the part obtained is consistent with the simulation results.3.The straight edge effect and its control method in forming slab parts.Taking cylindrical part as an example,the reason for the straight edge effect of the part after forming is analyzed,and the control effect of the residual material,the swinging punches' size and the basic bodies' arrangement on the straight edge effect are studied by numerical simulation.The results show that the straight edge effect comes from the unbalanced force of the upper and lower swinging punches,and this phenomenon will become more obvious as the thickness and curvature increase.Increasing the residual material on the basis of ensuring the target shape can improve the accuracy at the edges of the required part,but the accuracy cannot be improved after the size of residual material reaches a certain value.The swinging punches with different cross-section radius are used for forming.When the effective forming area produced by swinging punch of different sizes is close,the straight edge effect is not improved significantly.Forming the part under two kinds of asymmetrically arranged basic bodies can achieve the purpose of improving the straight edge effect by optimizing the stress state and increasing the continuity of the surface contour of the parts.4.Springback analysis of slab parts formed by swinging punch multi-point equipment.Numerical simulation of springback is carried out on the variable curvature parts with different materials and thicknesses and spherical parts with different thicknesses and curvature radius,then the variation trend of the maximum springback at the parts' feature position are compared.Explore the influence of different repeated forming paths on the springback of spherical parts.Calculate the springback of double curvature parts and take the saddle-shaped part as an example to simulate.The results show that with the increase of thickness,the amplitude of the springback decreases slowly between the adjacent thicknesses.Keeping the shape of the variable curvature parts unchanged,the maximum springback of Q345 parts with corresponding thickness is far less than that of high-strength steel parts.Moreover,with the increase of thickness,the variation trend of the springback difference between the edge and the middle of Q345 parts in the x direction is different from that of high-strength steel parts.The springback of spherical parts with different curvature increases with the decrease of curvature.The method of repeated forming can effectively reduce the springback,and the optimal repeated forming path can meet the technical requirements of part.By calculating and simulating the springback compensation of saddle parts,the high forming precision is obtained.