Flexible Stretch Forming For Sheet Metal And Study Of Its Numerical Simulation

The process of flexible stretch forming is completed with multi-point forming die andflexible grippers. The whole process of stretch forming as follows: Firstly use the CADsoftware to create the shape of the workpiece, get spherical coordinate data by the specialsoftware of multi-point forming, and adjust the multi-point forming device to make thefundamental elements have the same height. then input the data of fundamental elements, thedevice will automatically control the fundamental elements to the corresponding location. Thestretch forming has a pre-tension process in the horizontal direction after clamping the sheet tomake the sheet touch the multi-point die. During the stretch forming, flexible grippers should beadjusted in order to complete stretching smoothly. Separate them after the sheet and themulti-point mould entirely die, finally release the grippers to finish the stretching.The overall gripper appearing earlier, many experts and scholars have done thecorresponding research. The flexible grippers appear much more later, and there is only a fewexpert who have done the research, therefore it is a new technology. The concept of flexiblegrippers technology is that the overall gripper is divided into some small grippers which havethe same size. Each small gripper can move and roll easily in a certain range. They will beadjusted according to the contact of the sheet and fundamental elements. The flexible gripperusually forms certain curve shape in order to coordinate with multi-point die.They coordinatewith each other so that the flow of the material increases very much and the force of theforming tend to average. Flexible stretch forming of sheet metal often appear dimples, whichaffects the quality of forming parts seriously. After adding the elastic cushion, the extent ofdamage to reduce. This paper mainly uses the method of numerical simulation to gripperparameters and elastic cushion parameters act on the quality of the forming. To find out theoptimal process parameters. Though the research it can get a conclusion:1、Numerical simulations on flexible stretch forming using different grippers number.Establish flexible forming numerical model of spherical part. Seen form the chart ofstress and strain with different gripper number. The forming will be more uniform when thegripper number increases. The sheet avoids drawing breakage in transition region. It can beknown from thickness plot that forming region of the sheet metal with ten group of grippers ismore even. In general,forming quality is improved when the gripper number increase. 2、Compared with different grippers arrangement on flexible stretch forming.Because of many flexible grippers, there are a lot of gripper arrangement, each kind ofarrangement would have a certain impact on the workpiece quality of stretch forming. Thispaper study a group of four gripper, and put forward three method of gripper arrangement. Afteranalysis the method which two group of gripper is arranged in a square is the best. Forrequirement of stretching parts with high precision, the third method of gripper arrangementshould be adopted.3、Study on influence of gripper force on the stretch forming.Establish flexible forming numerical model of saddle part. Through the analysis of sheetmetal strain,it can be known that with the increase of the gripper force, the quality of theforming parts is better, which shows that the increase of gripper force make the sheet metalstrain tend to uniform distribution. But the gripper force can’t be too large, otherwise it willcrack the sheet metal.4、Numerical Simulations of the effect of elastic cushion parameters on the flexiblestretch formingEffect of elastic cushion materials on flexible stretch forming is very important. Seenfrom the stress-strain diagram，elastic cushion which use79polyurethane is the best one.Theelastic cushion which use83polyurethane material is better than that use89polyurethanematerial, so the best material of elastic cushion is79polyurethane. It also shows that as elasticcushion material the smaller hardness value of polyurethane is, the better effect of stretchforming is. At the same time, by the finite element analysis, spherical model using differentelastic cushion was simulated. Through the analysis of stress-strain diagram of sheet, it can beseen that,as the elastic cushion thickness increases, dimples of sheet metal forming have beenwell restrain.