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首页> 外文期刊>Journal of Manufacturing Processes >Effect of quasi-static prestrain on the formability of dual phase steels in electrohydraulic forming
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Effect of quasi-static prestrain on the formability of dual phase steels in electrohydraulic forming

机译：准静态预应变对电液压成形双相钢成形性的影响

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Dual phase steels derive their name from their microstructure, which consists of islands of martensite surrounded by a ferrite matrix. These steels are increasingly being used in automobile structures in order to reduce weight, improve fuel economy, and maintain crash safety performance. The higher strength grades of dual phase steels, such as DP780 and DP980, often present significant formability challenges in sheet stamping operations, and therefore any technologies which could alleviate these issues would be of significant value to the automotive industry. Electrohydraulic forming (EHF) is based upon the electro-hydraulic effect: a complex phenomenon related to the discharge of high voltage electrical current through a liquid. In EHF, electrical energy is stored in a bank of capacitors and is converted into the kinetic energy needed to form sheet metal by rapidly discharging that energy across a pair of electrodes submerged in a fluid. During such a discharge, a high pressure, high temperature plasma channel is created between the tips of the electrodes. The resulting Shockwave in the liquid, initiated by the expansion of the plasma channel, is propagated toward the blank at the acoustic velocity of the fluid, and the mass and momentum of the water in the shock wave accelerates the sheet metal blank toward the die. The objective of this paper is to report the results of formability testing of dual phase steels under three basic conditions: (1) conventional limiting dome height (LDH) testing; (2) starting with a flat blank and using one pulse of EHF to fill the desired die geometry; and (3) starting with a quasi-static preforming step to partially fill the die cavity and then using one pulse of EHF to fill the remaining area of the die cavity. A hybrid process which combines sheet hydroforming (HF) and EHF as described herein has the potential to reduce the cycle time of the EHF process by replacing the initial EHF forming increments with one quasi-static preforming step. Additionally, a numerical model was developed and employed in order to better understand the sheet deformation process within EHF. The numerical model consists of four distinct models that are integrated into one: (1) an electrical model of the discharge channel, (2) a model of the plasma, (3) a model of the liquid as a pressure-transmitting medium, and (4) a deformable sheet metal blank in contact with a rigid die. Significant improvements in formability were confirmed experimentally for DP780 and DP980 by forming into conical and v-shape dies using EHF from a flat sheet and by using EHF combined with a quasi-static preforming step. Numerical modeling showed that the peak strain rates occurring in both single-pulse EHF the hybrid HF-EHF process are approximately 17,000 units per second.
机译：双相钢的名字来自其微观结构，该微观结构由被铁素体基质包围的马氏体岛组成。这些钢越来越多地用于汽车结构中，以减轻重量，提高燃油经济性并保持碰撞安全性能。双相钢的较高强度等级，例如DP780和DP980，经常在板材冲压操作中面临重大的可成形性挑战，因此，任何可减轻这些问题的技术对汽车行业都将具有重大价值。电液压成形（EHF）基于电液压效应：一种复杂现象，与通过液体释放高压电流有关。在EHF中，电能被存储在电容器组中，并通过迅速地将能量跨过浸没在流体中的一对电极释放而转化为形成金属薄板所需的动能。在这种放电期间，在电极的尖端之间产生了高压高温等离子体通道。由等离子通道的膨胀引发的在液体中产生的冲击波以流体的声速向毛坯传播，并且冲击波中水的质量和动量使金属板毛坯向模具加速。本文的目的是报告在三种基本条件下双相钢的可成形性测试的结果：（1）常规极限拱顶高度（LDH）测试； （2）从平坦的坯料开始，并使用一个EHF脉冲填充所需的模具几何形状； （3）从准静态预成型步骤开始，以部分填充模腔，然后使用一个EHF脉冲填充模腔的其余区域。如本文所述，结合片材液压成型（HF）和EHF的混合工艺具有通过用一个准静态预成型步骤代替初始EHF成型增量来减少EHF工艺的循环时间的潜力。此外，为了更好地了解EHF中的板材变形过程，开发并采用了数值模型。数值模型由四个不同的模型组成，这些模型集成到一个模型中：（1）放电通道的电模型；（2）等离子体的模型；（3）作为压力传递介质的液体的模型；以及（4）与刚性模具接触的可变形钣金毛坯。实验证明，对于DP780和DP980，通过使用平板上的EHF将EHF成型为圆锥形和V形模具，以及将EHF与准静态预成型步骤结合使用，可成型性得到了显着改善。数值模型表明，在单脉冲EHF和HF-EHF混合过程中出现的峰值应变速率约为每秒17,000个单位。

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