Study On Finite Element Numerical Simulation Of Stretch Forming Of Skin

Skin stretch forming(i.e. stretching) has become an important processing method in the aerospace industry because it has many advantages, for example,its mold is very simple and spring back is small. Nowadays, new aircraft is very harsh to improve its overall performance in the gas dynamic coordination and shape accuracy. However, the traditional stretching often appears defects, such as fracture, wrinkling, coarse grained and slip line etc. Therefore, many domestic aircraft manufacturing enterprises have introduced advanced NC stretch forming machine, such as FET1200, VTL1000 etc. to improve the quality of skin parts. In order to fundamentally change the current traditional aircraft skin stretch forming process based on experience and the method of trial, the advanced CNC stretch forming machine superior performance is given full play to ensure quality of skin stretch forming parts. Furthermore, the computer system and engineering is urgently needed to be applied into skin stretch forming process. The introduction of finite element simulation technology into the stretch forming process can not only effectively improve shape quality, reduce or eliminate try stretching frequency, but also can use finite element software to achieve virtual try stretching, significantly save raw materials and reduce the cost of research and development.In this paper, 3D software CATIA which is commonly used in aerospace field is utilized to set up geometric models and ANSYS/LS-DYNA software is utilized to analyze and simulate skin stretch forming process continuously and timely. The forming principle of the FET600 CNC horizontal machine which is introduced by an aviation manufacturing enterprises is combined with mould's type and characteristics to calculate and design the initial traveling path of the clamping jaw shape(stretching trajectory). Through the virtual test, the stretching trajectory was verified, the stretching forming defects was predicted, and the process parameters optimization was then adjusted according to the simulation result. Then carrying on the stretch forming finite element simulation analysis of obtained optimization data again until it met the forming process and quality requirements. Finally, conserving the optimal data into machine code so that the machine can woke according to the design of stretching trajectory and reach purposes of the scientization of the skin stretching forming process design and controllability of stretch forming process.In stretching production test, a series of initiatives to improve the forming quality was given. Practice has proved that stretching equivalent size and distribution of stress and strain, the reduction rate of the thickness size and distribution are in line with the requirements and fit ability is well. At last a qualified single convex hyperboloid Mongolian part was manufacture-red, and then the rationality and validity of the optimal trajectory were verified. The research of testing method and data can provide scientific basics for the designer to analyze of skin stretch forming process and improve the quality of the products. Furthermore, they can also contribute to the change of stretch forming manufacturing mode from tradition to digital.