Numerical simulation on the local stress and local deformation in multi-point stretch forming process

Abstract

Multi-point stretch forming (MPSF) is a new flexible forming technique to form aircraft outer skin parts. The multi-point stretching die (MPSD) replaces the traditional fixed shape stretching die, and the sheet metal is formed over a MPSD composed by the punch element. The MPSD is a discontinuous surface of discrete stretching die, and the stress concentration and local strain occur on formed parts. These lead to generate dimples on the surface of formed part. In this paper, a series of numerical simulations on MPSF processes for stretching parabolic cylindrical, spherical, and saddle-shaped parts were carried out. The local stress and local strain in thickness distribution of MPSF part were analyzed by dispersed the blank into solid elements. The forming results of MPSF were compared with those that use traditional stretch forming, and the influences of thickness of elastic cushion and the size of punch element on the stress concentration and local strain were surveyed. The simulation results show the distribution of local stress and local deformation in different layers, and the elastic cushion and the small size of punch element can reduce the stress concentration and local deformation. The results may understand the stress distribution on the sheet and prevent the defect of dimple.

Multipoint forming using mesh-type elastic cushion: modelling and experimentation

“…The sheet and elastic cushion were modelled as deformable bodies and C3D8R quadratic element type was used. Five elements through the sheet thickness have been used as recommended by Wang, S. et al [22]. The element size is 1 mm and a total of 182,250 elements were used to mesh one-quarter of the sheet, while a total of 49,140 elements were used for the elastic cushion.…”

Effect of Flexible 3D Multipoint Stretch Bending Dies on the Shape Accuracy and the Optimal Design

“…In the past decades, stretch bending was the main production method for 2D parts. At present, it is mainly used in high-volume production of the profile and is also widely used in aircraft, high-speed railway, and automobile and shipbuilding industries [12]. However, the traditional stretch bending is only suitable for mass production rather than small batch production.…”

Optimization of Mechanical Anisotropy of Cover Sheets to Minimize the Polythickness When Stretch-Wrap Forming

“…Имеются работы последних лет, посвященные решению частных технологических задач по совершен-ствованию процессов формообразования обтяжкой, в которых вопрос о влиянии анизотропии механических свойств затрагивается слабо либо не затрагивается со-всем. Так, в работах [1][2][3] описываются особенности применения упругих элементов при формообразовании обтяжкой. В работах [3][4][5] рассматриваются вопросы учета влияния пружинения при применении многосек-ционного пуансона.…”

“…Так, в работах [1][2][3] описываются особенности применения упругих элементов при формообразовании обтяжкой. В работах [3][4][5] рассматриваются вопросы учета влияния пружинения при применении многосек-ционного пуансона. Дифференциальной обтяжке с кон-тролем зоны наибольшего напряжения и деформации посвящены работы [6; 7].…”