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Sheet metal forming limit diagram (FLD) is a comprehensive index used to evaluate sheet metal formability. In this paper, the forming limit curves of GH605 sheet materials with 0.2 mm and 2.5 mm thickness under three different heat treatment conditions were obtained by numerical simulation of bulging. Then, the simulated forming limit results of the three materials with 0.2 mm thickness were compared with the experimental results. The results show that the simulated FLDs can be in good agreement with the experimental FLDs. The influences of work hardening index (n value) and anisotropy index (r value) on the forming limit are analysed from the view of material property difference. The comprehensive simulated and experimental results show that the formability of the sheets after the two kinds of solution treatment is significantly better than that of the annealed sheets. The forming limit curve increases with the increase of n value and r value, and the influence of n value on the forming limit curve is more significant than that of r value. The forming limit diagram established by numerical simulation can provide a theoretical basis for material development and process selection.

In order to accurately predict the forming limit curve of DP780 steel sheet under the condition of warm forming,the ductile fracture prediction model was introduced into the numerical simulation. Based on the unidirectional tensile test results analysis of DP780 steel sheet in the temperature range of 573 K ～ 873 K and strain rate range of 6. 67×10-4 s-1～ 6. 67×10-3 s-1,the warm forming performance of DP780 steel sheet is better under the condition of temperature of 673 K and strain rate of3. 33×10-3 s-1 determined by the product of strength and ductility. And through the simple tensile test and simulation under this deformation condition,determined the main factors affecting the ductile fracture of DP780 steel sheet. Thus a model for predicting tensile fracture and shear fracture of DP780 steel under different strain paths was developed,by combining it with the warm forming constitutive model and the Hill ’48 yield criterion,the finite element simulation of the rigid mold bulging test was realized,and the forming limit curve of DP780 steel sheet at the temperature of 673 K was predicted,The mathematical model of forming limit was established. The results show that the forming limit results predicted by this method have better precision.

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Forming limit is an important performance index and process parameter in sheet metal processing. In this paper,A method for the thermal incremental forming of liquid while supporting and heating was proposed. An inverted cone was studied as a research object. The influence of process parameters such as the temperature,the distance between the layer and the diameter of the tool head on the thermal incremental forming was studied by means of orthogonal test,and the theoretical analysis is carried out. The results show that the forming limit angle increases obviously with the increase of the forming temperature,and the smaller the distance between the layers increases with the increase of the layer spacing. The limit angle of the tool head diameter is not significant.

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Deficiencies in formability and forming quality are the key factors to restrict the wide industrial application of single point incremental forming (SPIF) technology. Ultrasonic vibration is introduced into the single point incremental forming process to increase the forming limit of a material by changing its de¬formation mechanism. For 1060 aluminum sheet, the effects of vibration amplitude and frequency on the constitutive relation of material are analyzed. And the sidewall forming angle of a cone frustum part is taken as a measure standard. The influences of ultrasonic vibration parameters on the forming accuracy are studied through numerical simulation and experiment. The results show that the formability of 1060 a¬luminum sheet can be significantly changed by applying ultrasonic vibration, and the single point incre¬mental forming limit and the forming quality can be improved under the conditions of 120 W and 25 kHz. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper overviews the methods of predicting the forming limit stress diagram in sheet metal forming, the maximum forming ratio, the forming limit diagram, the ductile fracture criteria (DFC), and so on. Making use of DFC, the forming limit can be predicted in the metal sheet with low ductility, and can be predicted when the forming path varies. In the finite element method, DFC can be applied to incremental approaches with a fully coupled elastoplastic-damage model, and can be applied to the one-step inverse approach. In order to predict the forming limit exactly, a criterion that indicates the material ability in essence is expected to be worked out, including the improvement of finite element method. [ABSTRACT FROM AUTHOR]