Numerical Simulation Of Clamp Modes For Multi-Point Stretch-forming

Title of Dissertation:Numerical Simulation onmulti-Point Stretch-forming using discrete clampasSpecialty:material Processing EngineeringSupervisor:Prof Su ShizhongMulti-point stretch forming process is the basic body shape fitting ball instead of the wholemold surface, It is equivalent to re-construct the pull-shapedmold that the basic body of stroke can be adjusted independently to change the basic body position.multi-point stretch forming process is generally divided into the basic body adjustment, the level of pre-pull and the process of formingmold. Forming the former, the coMPauter based parts of the CAD data, through the surfacemodeling, the basic body to adjust to the target location, then formingmulti-pointmold. During the forming process, the basic body tomaintain the same relative position, which is the same as the traditionalmold. Clampa clampa sheetmetal,Pre-pull in the horizontal direction so that sheetmetal and diemore fit; then, table up until all of the fundamental group of sheetmetal and punch, sheetmetal forming to the required surface shape.Many conditions influence the forming of sheet quality, the sheet gripping way is a very iMPaortant factor, so there aremany domestic and foreign scholars studing on holdingmethod for sheet stretch forming process, the overall clampa, clampas were divided into two parts. Before stretching the skin, the first pull-shapedmold plate edge was placed between both sides of the jaw, and then applied bymeans of hydraulic clampaing device on the jaw to the jaw clampaing force, clampaing the next step only after pull action to coMPalete the process of stretch forming shape. Discrete clampaingmeans a flexible sheet form, The traditional discrete clampa divided into several small clampa, each clampa is a separate clampaing device, clampaing plates in the same time, the chuck can be achieved swing up and down and turning left. In sheetmetal forming process, the edge of plate-shaped pieces can be pulled with the curvature of the changing edge. In this way, the sheetmetal edge no longer applied when the overall clampa a straight line shape, but showed a certain degree of curvature,making clampaing device clampaing plate in the same time, gripping the edge and stretching to achievemode change of curvature closer to the end, this willmake the Board in the stretch forming process easier to punch, at the same time iMParove the sheet.stress state. Based on these two holdingmethod, a numerical simulationmethod is usedmainly by the following conclusions:1. The coMPaarison of forming quality of the discrete and the overall clampaIn the cylindrical part forming single rate, the various small clampa has no relative displacement between the discrete clampas, so it looks the same as overall clampa, as forming single rate of cylindrical parts, forming quality of the discrete clampa and the overall clampa is almost the same. Double curvature of the spherical in shape and saddle-shaped pieces of parts, the sheetmetal end of the curvature of themold will gradually tend to the curvature, discrete small clampa clampa between the various relatively small displacement occurs, so that the arrangement of the shape clampa curvature tends to die face, thus iMParoving the traditional shortcomings of punch clampa hard,Sharply reduced after the sheet forming the stress level so that stress and strain as well as thinning of the sheetmore uniform. Especially for the different curvature of the saddle-shaped pieces, the use of discrete clampa jaw position significantly reduces the thinning of serious regional thinning and stress.2.Study on the factors use discretemulti-point stretch forming when useing discretemulti-point stretch formingWith the decrease of friction coefficient and the free of hindeing flowing of sheetmetal elements inside is weakened,more andmore uniform thickness distribution of formed parts, indicating that the internal deformation of sheetmore easily and fully, while in the vacant area, with reduced friction, thickness also will become larger, as the region forming process easily produced in Latin fracture, so reducing friction is beneficial to decreasing the risk ofmaterial is pulled off. In the stretching force, the friction and the smaller, the required stretching force is also smaller, the largest sheet thinning is also smaller, so the actual production process in order to get better-quality stretching forming parts,must be on the contact surface to be lubricated.Clampaing force is iMPaortant for the quality of discrete Stretching clampa, stretching force can not be too big or too small, or will cause clampa can not exercise well or clampa fall off sheetmetal. In the allowed force range, the smaller clampaing force can iMParove the stress distribution in the workpiece, uniform thickness and iMParove the forming quality. Stretching in the actual process should be appropriate to give priority to choose a smaller clampaing force. In a certain range, the higher the degree of discreting, themore pull-shaped parts can iMParove the forming quality, the chapter simulation results show that the five clampa pull-shaped pieces forming quality is better than three clampa. The quality differencemade by five and seven clampas clampa is small in shape, taking into account the increase in the number of a corresponding increase in clampa fixture of themanufacturing cost, five clampas aremore appropriate.3. Clampaingmethods on the application of the two spherical parts and saddle-shaped pieces of ReboundingAs the use of discrete clampa the workpiece to iMParove the stress distribution within the state, so the rebound of stretching by discrete clampa in the OA, OB directions are significantly less than overall pull-shaped clampa parts, formingmore accurate. For controling rebound, the discrete clampaing clampa is better than the overall clampa. The overall amount of clampa rebound increasemore quickly than discrete clampas. And near the center of the area of sheet springback of discrete clampas is close to zero, while the overall clampa the workpiece contour line have undergone obvious rebound. As the sheet in the direction perpendicular to the stretching is less than the size of sheet stretching direction size in the process of stretch forming sheet to the deformation of the former than the latter, so the direction of springback OA significantly higher than the direction of OB, so in actual production determine the appropriate sheet size is an iMPaortant factor to ensure accuracy. Saddle-shaped piece of resilient, fully resilient with the spherical parts of the line, but the saddle-shaped pieces of spring was greater than that of spherical parts, produced bymeans of two clampaing springback differences in values larger than spherical pieces.