Flange wrinkling is one of the most common defects in conventional spinning. A lot of work has been done to find the reason for the flange wrinkling and the way to avoid it. However, the theoretical prediction of flange wrinkling is limited for the non-uniformly distributed stresses and complicated boundary conditions of the flange. In this paper, a FE (Finite element) model is established to study the deformation characteristic of the material in conventional spinning, two stable compressive stress rings distributed at the middle surface of the formed part are found, and the outer stress ring distributed at the flange is considered to be the key factor of flange wrinkling. A theoretical flange wrinkling prediction method is proposed based on the plastic buckling theory and the energy method with the boundary conditions extracted from the FE simulation results. Experiments are designed to research the flange wrinkling phenomenon and verify the proposed theoretical flange wrinkling prediction method. At last, effects of feed ratio on flange wrinkling are analyzed by this method, it is concluded that the decrease of the circumferential compressive stresses distributed in the flange caused by low feed ratio reduces the risk of flange wrinkling.

Flange wrinkling is one of the most common defects in conventional spinning. Slight wrinkles can be eliminated by a reasonable design of the spinning process parameters or assisted process, while severe wrinkles lead to low forming quality or even defective products. A lot of work has been done to find the reason for flange wrinkling and the way to avoid it, while limited research has been done to study the severe flange wrinkling phenomenon in conventional spinning process. In this paper, the severe flange wrinkling phenomenon in first-pass conventional spinning of the hemispherical part has been studied through FE (finite element) simulations and experiments. A double curved surface buckling prediction model based on the energy method is proposed in order to predict severe flange wrinkling. Experiments are designed to verify the theoretical severe flange wrinkling prediction method. It turns out that the wrinkling of the inner compressive stress ring leads to the severe fluctuations of the spinning force, and it can be taken as a sign of severe flange wrinkling in the conventional spinning process. Furthermore, the effects of flange wrinkling on the spinning qualities of the final formed hemispherical parts are researched. It is concluded that slight flange wrinkles in the first-pass have little effects on thickness distribution and geometry accuracy of the final formed part, while severe flange wrinkles lead to failed products. Severe flange wrinkling prediction is significant for the conventional spinning of the hemispherical part.

The purpose of this work is to establish the forming limit diagram (FLD) for a seamed tube hydroforming. A new theoretical model is developed to predict the FLD for a seamed tube hydroforming. Based on this theoretical model, the FLD for a seamed tube made of QSTE340 sheet metal is calculated by using the Hosford yield criterion. Some forming limit experiments are performed. A classical free hydroforming tool set is used for obtaining the left hand side forming limit strains, and a novel hydroforming tool set is designed for the right hand side of FLD. The novel device required the simultaneous application of lateral compression force and internal pressure to control the material flow under tension–tension strain states. Furthermore, the suitable loading paths for the left hand side of FLD by theoretical formulas and for the right hand side of FLD by finite element (FE) simulations are calculated. Finally, a comparison between the theoretical results and experimental data is performed. The theoretical predicting results show good agreement with the experimental results.

In finite element simulation of auto-body panels forming, an accurate forming limit criterion is very important. To evaluate accurately the formability of automotive aluminium alloy sheet, in this paper, a ductile fracture criterion developed by the author is introduced in finite element simulation. Based on Barlat’s yield function and Hollomon’s hardening equation, the simulations of aluminium alloy sheet forming are carried out. Material constants in the ductile fracture criterion are determined by means of uniaxial tension and hemispherical punch stretching tests. The critical punch strokes of the aluminium alloy sheets X611-T4, 6111-T4 and 5754-O in cylindrical complex forming, which includes deep drawing and stretching modes, are calculated by the ductile fracture criterion. The comparison of the calculated results with the experimental values shows that the critical punch strokes of the three sheets mentioned above are predicted successfully by the ductile fracture criterion.