Numerical Simulation On Compensation Of Elastic Cushion For Shape Adjusting Of Multi-point Stretch Forming

Multi-point stretch forming technology is a flexible processing method for sheet metalforming of 3d surface, and a casting die consisting of a series of fundamental element ( orpunch) regularly arranged. In the whole die forming process, the sheet metal 3d surfaceparts are formed by mould, and it is completed through the fundamental element ball headof envelope noodles( or fundamental element group of forming surface) in the multi-pointstretch forming. Each fundamental element's formation is controlled by computer, adjustingthe height of each fundamental element according to the target shape parts to construct theforming surface accurately and rapidly, and that means realizing the rapid flexible partsforming. All fundamental elements in multi-point stretch forming can independently adjustand change the height of each fundamental element, which is exactly the same thing asre-structuring the forming surface.Dimples is the peculiar forming defect of multipoint pull form, decreasing the formingquality seriously, so it is the main problem to be solved in multi-point stretch forming. Thedimples are caused by local plastic deformation on the concentrated load of thefundamental element. The most efficient way to inhibit the dimples is the elastic cushiontechnology. Large elastic deformation can be produced when the elastic cushion betweenthe fundamental element and the panel veneer is added, for the elastic cushion is oftenmade by polyurethane rubber material full of good elasticity. Thus the gap between thefundamental element can be filled, and the concentrated load on the fundamental elementget scattered, which makes the stress of the plank more even, inhibiting the dimpleseffectively.Elastic cushion has certain thickness. The envelope formed by fundamental elementdon't directly contact with the noodles. The thickness of the elastic cushion must beconsidered when aiming to form the target surface. On the other hand, in order to obtain the accurate curved surface, the deformation of elastic cushion should be considered. The deformation is uneven, and greatly influences the forming precision, so it is important parameter of form surface correction in shape adjusting. Simulate the stretch forming process through the finite element software and study the different results of various elastic cushions and sheet metal with different parameters to compare the correction of shaped surface under different parameters. The main research contents are as follows:(1) Simulation on the compensation value of the elastic cushion in different shape adjustingVertical and pull shape direction is from the inside out when the sphere part was formed. At first compression value does not change much, however, contact molding on the edge perpendicular to the pull shape direction is not so easy, and the load of elastic cushion from the punch are relatively minor, and the thickness change of the elastic cushion is relatively minor, thus the decrement calculated is also relatively minor. The height of the fundamental element to be adjusted increases gradually positively first and increases gradually negatively. In the pull shape direction, the load continuously increase from center to verge, and the stress of the elastic cushion increases, with the thickness change, the decrement and the height to be adjusted increased. The curvature in the vertical and pull shape the direction is 0 when to form the paraboloid part. Thus the load perpendicular to pull shape direction of the elastic cushion don't change much, and the decrement changes very little, so the adjustment needn't be carried out in the direction. The height correction is magnified with the decrement continuously increased from center to verge.(2) Research on elastic cushion compensation in shape adjusting for panel veneers with different parameters.The thickness of the panel veneer to the elastic cushion influence is: the increased thickness of the panel veneer causes the increased ability of resisting deformation, so greater force is needed to form the same shape. The forming force of the whole panel veneer is increased because of the increased thickness, so, in the conditions of the same other parameters, the nonaffine deformation of the elastic cushion will be intensified and fundamental element height adjustment will be increased when the panel veneer becomes thicker, no matter in x, y or the slash direction.The influence of the forming radius of curvature is: the displacement constraint loading varies with the radius of curvature, and the smaller the radius is, the greater the curvature will be, thus the displacement constraint loading tends to be growing when to form the same size of the plank. The load of the elastic cushion is also increased, with the bigger decrement, but the AB line does not change much, and the adjustment of the fundamental element is smaller. In the fringing field perpendicular to the pull shape direction, the smaller the radius is, the less obvious the load area of the punch to the elastic cushion will be, which is because contact molding is more difficult with the smaller radius and the bigger curvature. The decrement perpendicular to the pull shape direction decreases more quickly with the smaller radius, while the height adjustment of the fundamental element will be greater.The influence of elastic cushion thickness deformation for different materials is mainly that every kind of material has its own stress-strain curve, and the yield point and the density are different, so the forming force of the materials is also different. Of the two models, the non-uniform deformation of elastic cushion is bigger, with the more compensation for elastic cushion, and the aluminium alloy is relatively small.(3) Parameters change of the elastic cushion on the compensation impact studyWhen the elastic cushion is thicker, the fundamental element adjustment will highly greaten. Comparison of the flexibility and superelasticity elastic cushion models shows us the shape change of the hyperelastic model is less than that of the elastic model, and the adjustment of the fundamental element is relatively less.