Effect of Draw-In on Formability in Axisymmetrical Sheet Metal Forming
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Abstract:
In the formability of sheet metal, distinction is made between the formability at the critical section, the formability of the material, and process efficiency. It is shown that draw-in has an adverse effect on the formability at the critical section, but greatly improves the gross process efficiency, which measures the extent to which the formability of the material is exploited in a particular process. The effect of draw-in on the strain distribution in the workpiece is shown in a triangular coordinate system for strains.Keywords:
Forming limit diagram
Forming Limit Diagram (FLD) is a resourceful tool to study the formability of sheet metals. Research on the formability of Perforated Sheet Metal is growing over the years as perforated sheet metal finds its applications in various fields. But finding FLD of perforated sheet metals is complex due to the presence of holes. Also, the hole size, shape and pattern, ligament ratio, thickness of the blank, percentage of open area influence the formability of a perforated sheet metal.In the present scenario, various simulation softwares have made the process of plotting FLD much easier, saving time and money. This paper is an attempt to predict the formability of mild steel perforated sheet metal through simulation software package LS Dyna. Also, Parametric analysis is performed to determine the influence of geometric parameters on the drawability of the perforated sheet metal.
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This paper attempts to optimize the forming quality of sheet metal by drawing the formability region diagram based on the forming limit diagram of sheet metal, which provides a method for rapid adjustment of stamping process parameters in production. Fristly, the strain of sheet metal forming limit was quantized to obtained the standard of sheet metal forming quality. Secondly, the formability region diagram of sheet metal is got by using the method of orthogonal test, finite element numerical simulation and BP neural network. Finally, taking an automotive rear end panel reinforcement as an example, the stamping test was carried out by selecting the process parameters corresponding to different points in the stamping formability region diagram, and the test results were consistent with the results reflected in the formability region diagram. This paper provides a method to improve the quality of sheet metal forming and quickly optimize the stamping process parameters, which has important engineering application value.
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The forming limit curve (FLC) has been used to represent the stretchability of sheet metal under various forming modes. However, the formability window in stamping depends not only on the material's forming limit, but also on its strain distribution ability. In the present work, a total forming capacity (TFC) index is introduced to describe the global formability of sheet metals, which accounts for the contributions of both forming limit and strain distribution ability in the material during forming. Essentially, this index is constructed by integrating the instantaneous n-value from zero to the effective strain limit of the material. The usefulness of this new index is demonstrated through a comparison of the overall global formability between a cold-rolled (CR) 590DP steel and a CR980GEN3 steel via a dome test coupled with digital image correlation (DIC). Contradicting of its lower forming limit, the 980GEN3 can be formed to a higher limiting dome height (LDH) than the 590DP under a near plane strain condition. This superior overall global formability of 980GEN3 is attributed to its capability to dissipate strain uniformly during forming, resulting in lower strain gradient and delayed strain concentration. While revealing the limitation of using the FLC alone, findings in this study evince the strength and effectiveness of this new index in assessing the overall global formability of sheet metals. The higher index is successfully correlated to the higher LDH of the 980GEN3. Further, the TFC concept is applied to evaluate the global formability of a multitude of high strength steels at different thicknesses. An explicit relationship is established between the calculated index and experimental LDH results. The development and application of the TFC indices promise a straightforward way to assess the overall global formability of a material. It also serves as a more precise yet simple tool for material comparisons and selections.
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NC incremental sheet metal forming is a flexible process which forms the parts point by point with NC forming machine according to the prepared program.The experimental tests about the formability,namely the maximum forming limit angle and the forming limit diagram,was done for hot galvanized automotive steel sheets H180YD+Z.The experimental results show that,in the incremental sheet metal forming process,the thickness distribution obeys the cosine law t=t0cosθ.The material H180YD+Z,which can be used in incremental forming for automotive sheet parts,has good formability.This paper provides a theoretical basis on sheet incremental forming.
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