Numerical Simulation Analysis On The Multi-Point Stretching For Aircraft Skin

Multi-point forming (MPF) is a flexible manufacturing technology for three-dimensional surface part of thin sheet metal. Its main idea is dividing the curvedsurface of the traditional stamping dies into rule arrange, high adjustable elementgroup, and then the three-dimensional shape of sheet metal is formed by thecurved surface of elements(element group forming surface). MPF controls thedisplacement and speed of elements through computer, to change the curvedsurface of elements and complete flexible manufacturing. Currently MPF isextensively applied in many realms, such as shipbuilding, orbit passenger car,medical science engineering and the large stadium building construction...etc. thereis extensively applied foreground in the aviation aerospace realm.Numerical analysis technology of sheet metal forming is an essential tool tooptimize die design, forecasting forming defects and analyzing forming quality.Finite element technology is the most valid method in the simulation methods. Inrecent decades, Finite element technology is applied more and more extensivelyin blank forming. Numerical analysis technology is not only used to typicalforming analysis and simulation , but also used to forecasting wrinkling ,dimpling defects , calculating spring and the original blank design. Because thecontact between the elements and blank is changing all the time, and thecomplicated applying load condition, adoptoing dynamic explicit finite elementcalculation has apparent advantage on the process of multi-point stretching foraircraft skin. Therefore, making numerical simulation analysis on the on theprocess of multi-point stretching for aircraft skin by dynamic explicit finite elementcalculation.The main contents are as follows:1)Building up finite element model of multi-point stretching for aircraft skinwith thin blank, simulating the wrinkling defect of the blank under differentHorizontal pulling force. By contrast with analysis on the practical stretching forceverified the accuracy of the calculating way indirectly without experiment.2)Building up finite element model of multi-point stretching with elasticcushion for aircraft skin and simulating the process. Simulation results show that,using elastic cushion on the process of multi-point stretching can suppress thedimpling defect effectively, and can improve the forming quality on the basis ofmeeting the accuracy request.3)Building up finite element model of repeated multi-point stretching foraircraft skin and simulating the process. Simulation results show that, repeatedmulti-point stretching can uppress the dimpling defect effectively . By contrastwith using elastic cushion , repeated multi-point stretching can improve theforming accuracy and efficiency doubly4)Simulating the wrinkling defect on the process of multi-point stretching,discussing the causes and solutions of the wrinkling defect. through horizontalpulling force, blank size and material etc. Simulation results show that, thewrinkling trend is decling as the blank thickness and horizontal pulling forceincrease, but too large horizontal pulling force can result in cracking defect.Make use of the hard aluminum plank of LY12 takes better result than usingindustry of L2Y2 aluminum plank and wrinkle appear easier as the stretchingcoefficient increase.5)Simulating the dimpling defect on the process of multi-point stretching,discussing the causes and solutions of the dimpling defect. Comparing the differentthickness of the elastic cushion effection to the dimpling defect. Simulation resultsshow that, the thickness of the elastic cushion does not affect the dimpling defectapparently. But when the thickness of the elastic cushion increases, the formingaccuracy decreases.Studying the multi-point stretching for aircraft skin systematically ,simulating the factors affecting the blank forming quality on the process of multi-point stretching, especially discussing and analyzing the influence of horizontalpulling force, blank thickness , different material and blank size etc on theblank forming quality.Putting forward the influence regulation of techniquefactors to the blank forming quality.