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1、出处：Journal of Materials Processing TechnologyVolume 201, Issues 13, 26 May 2008, Pages 24725110th International Conference on Advances in Materials and Processing TechnologiesAMPT 2007题目：笔记本顶盖的镁合金板材冲压模具设计蔡恒光，廖浩钦，陈复国摘要：在本文章中，对LZ91镁锂合金板材在室温下制造笔记本顶盖时的冲压工艺进行了检查，同时使用了实验方法和有限元分析。四步工序冲压工艺的开发，以消在冲压顶盖的工艺的情况下
2、产生裂缝和起皱缺陷。为了验证有限元分析，进行实际操作冲压工艺与使用0.6毫米厚的LZ91的空白。厚度分布在不同地点之间的实验数据和有限元计算结果吻合良好，证实了有限元分析的准确性和效率。 LZ91板材在室温成形性能优越，也表明目前的笔记本顶盖的成功制造研究。适合的四步操作过程本身操作程序数量少，比在目前的实践要求，形成在笔记本铰链的有效途径。这也印证了在制造笔记本盖的情况下，可以用LZ91镁合金板材的冲压工艺生产。它提供了一个在电子行业替代镁合金的应用。关键字笔记本电脑情况下;LZ91镁锂合金板材;多工序冲压;成形性1. 介绍在EMI中由于重量轻，性能良好，在电子行业镁合金已被广泛用于结构部件
3、，如手机和笔记本电脑。虽然现行的镁合金产品制造过程一直压铸，镁合金板材的冲压行业，因为其有竞争力的生产力和有效的薄壁结构构件生产性能已制定的利益。由于它的六角形密堆积（HCP的形成）晶体结构（陈等，2003和陈和黄，2003），即使它需要高温，常用冲压工艺中镁合金（铝3，锌1）已在目前的形成过程中应用。最近，镁，锂（LZ）合金也已研制成功，以提高镁合金的室温成形性。镁合金的延展性，可以改善锂此外，开发形成体心立方（BCC）晶体结构（Takuda等人。，1999，Takuda等。，1999和Drozd等，2004）。在本研究中，一个笔记本顶盖使用LZ表的情况下的冲压工艺进行了检查。笔记本顶盖的两
4、个铰链的形成，如图1所示（a和b），是由于在冲压过程中最困难的操作之间的法兰和图中显示在小角落半径小的距离。 如图1（c）。造成这种几何复杂圆角半径的一个戏剧性的变化时，铰链法兰太接近笔记本的边缘，这很容易造成周围的铰链法兰断裂缺损，并要求多操作，克服这一问题。在本研究中，LZ镁合金板的成形性能和最佳的多工序冲压工艺开发，以减少同时使用的实验方法和有限元分析的操作程序。图1 在笔记本顶盖的铰链法兰 （a）铰链，（b）顶盖情况和（c）法兰。2。镁合金板材的力学性能在室温下进行拉伸试验，比较其机械性能，在高温下对AZ31张镁锂合金板材LZ61（锂6，锌1），LZ91，LZ101。图2（a）显示LZ
5、表在室温和那些对AZ31张在室温和200C的应力应变关系据悉，应力 - 应变曲线趋于增加锂的含量较低。图（2）也显示，LZ91板材在室温和AZ31镁板在200C是彼此接近。 LZ101板材在室温下具有更延性比LZ91和AZ31在200C由于锂的成本是非常昂贵，而不是LZ101板材LZ91板材，可被视为一个合适的LZ镁合金板材在室温下呈现良好的成形性。出于这个原因，本研究采用LZ91板材的笔记本顶盖的空白，并试图探讨在室温成形性LZ91。以确定是否断裂将发生在有限元分析，为0.6毫米厚的LZ91板材成形极限图还建立了如图2（b）所示。 图2 镁合金的力学性能 （a）镁合金的应力应变关系; （b）
6、LZ91板材的（FLD）成形极限图3。有限元模型如图3（a）所示，使用软件DELTAMESH，由CAD软件，PRO / E的模具几何构造，被转换成有限元网格。被视为刚体的工具，并采用四节点壳单元建设空白网。从实验中获得的材料特性和成形极限图中使用的有限元模拟。在初始运行中使用的其他模拟参数为：冲压力5毫米/秒，压边力3千牛，库仑摩擦系数为0.1。采用有限元软件PAM_STAMP进行分析，并在台式电脑上进行模拟。 图3 有限元模拟 （a）有限元网格和（b）在角落断裂。首次构建了有限元模型研究的一个铰链的形成过程。由于对称性，只有一个顶盖的情况下的一半是模拟，如图3（a）所示。仿真结果如图3（b）
7、所示，表明断裂发生在法兰的角落，最小厚度小于0.35毫米。这意味着断裂问题非常严重，是只通过扩大在法兰圆角半径是不能解决的。对有限元模拟进行研究的参数，影响断裂的发生以及避免断裂，提出了几种方法。4. 多工序冲压工艺设计为了避免发生断裂，多工序冲压过程是必需的。在当前的工业实践中，形成顶盖的情况下，使用镁合金板材，通常需要至少十步的运作程序。在本研究中，尝试了减少运作程序。对避免断裂，提出了几种方法，断裂问题的一个可行的解决方案是四个操作冲压工艺。为了限制这个文件的长度，在下面只对两个操作和四个操作冲压工艺进行了描述。4.1 两步操作冲压工艺第一是在两个操作冲压工艺侧壁形成如图4（a），第二是
8、在图4（b）提出的铰链法兰成型，铰链法兰的高度为5毫米。图4（c）所示的厚度分布的有限元模拟得到。变形板材的最小厚度为0.41毫米及以上的成形极限图的菌株。这意味着可避免断裂缺损。此外，法兰的高度符合要达到的目标。然而，这个过程是产生起皱缺陷的关键，如图4（d）所示，法兰上的铰链，导致在随后的修剪操作中出现问题。因此，即使两个操作冲压工艺解决在角落和底部的铰链法兰断裂问题，更好的形成过程仍有望解决铰链法兰起皱。图4 两个操作冲压工艺 （a）形成的侧壁，（b）铰链，（c）厚度分布和（d）皱纹的形成4.2 四步操作冲压工艺如图5（a）所示，四部操作在本研究中提出的形成过程三个侧壁和慷慨的角半径的铰
9、链法兰成形开始。由于侧壁接近法兰开放和圆角半径大于所需的法兰成功形成无断裂。成功地避免了这样的过程，同时形成两个几何特征的难度，但增加了一张白纸的物质流。下一步是修剪外侧壁的空白，并校准所需的圆角半径4毫米到2.5毫米的值。铰链，从而形成，如图5（b）所示。第三步是开放的一面折叠，使侧壁可以围绕其周边完成，如图5（c）所示。研究修剪额外的表外侧壁在第二步第三步的效果。当额外的工作表不修剪，在拐角处的厚度为0.381毫米，如图5（d）所示。提高到0.473毫米厚度的角落，如图5（e）所示。如果修剪在第二个步骤实施。在第三步的折叠过程中产生过多的物质，然后根据零件设计，修剪掉。最后一步是醒目的过程
10、，是适用于校准所有的圆角半径设计值。在最终产品的角落的最小厚度为0.42毫米，和所有株以上的成形极限图。这是要注意，图5（a-c）只显示一个铰链的形成。相同的设计概念，然后扩展到完整的顶盖的冲压工艺。5。实验验证为了验证有限元分析，进行实际操作冲压工艺与使用0.6毫米厚的LZ91表的空白。毛坯尺寸和模具的几何形状设计，根据有限元模拟结果。然后制造一个完善的产品无断裂和皱纹，如图6（a）所示。为了进一步验证了有限元分析定量，厚度，在完善的产品的铰链周围的角落，如图6（b）所示，进行测量和对比获得的有限元模拟，如表1所列。表1中可以看出，实验数据和有限元计算结果是一致的。四步操作过程的有限元分析的
11、基础上设计，然后由实验数据证实。图6 完善的产品 （a）无断裂和皱纹（b）测量厚度的位置。表1。测量的厚度比较ABCD真实值0.42mm0.44mm0.49mm0.53mm理论值0.423mm0.448mm0.508mm0.532mm误差0.71%1.79%3.54%0.38%6。结束语在目前使用的实验方法和有限元分析对镁合金板材成形进行了研究。首先研究了AZ31和LZ的成形性。研究结果表明，LZ91板材在室温下有良好的成形性，类似于AZ31板材成形温度在200C。LZ91板材在室温成形性能优越，也表明在目前的笔记本顶盖制造的成功研究。四步的操作过程使其本身在笔记本比在目前的实践中需要较少的操
12、作程序，形成铰链的有效途径。同时证明了笔记本盖，可以用LZ91， LZ91镁合金板的冲压工艺生产。在电子行业它提供了一个替代镁合金的应用。Journal of Materials Processing TechnologyVolume 201, Issues 13, 26 May 2008, Pages 24725110th International Conference on Advances in Materials and Processing TechnologiesAMPT 2007Die design for stamping a notebook case with magne
13、sium alloy sheets Heng-Kuang Tsai, Chien-Chin Liao, Fuh-Kuo Chen, Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan, ROC Available online 8 December 2007. http:/dx.doi.org/10.1016/j.jmatprotec.2007.11.288, How to Cite or Link Using DOI Permissions & ReprintsAbstractIn
14、the present study, the stamping process for manufacturing a notebook top cover case with LZ91 magnesiumlithium alloy sheet at room temperature was examined using both the experimental approach and the finite element analysis. A four-operation stamping process was developed to eliminate both the frac
15、ture and wrinkle defects occurred in the stamping process of the top cover case. In order to validate the finite element analysis, an actual four-operation stamping process was conducted with the use of 0.6mm thick LZ91 sheet as the blank. A good agreement in the thickness distribution at various lo
16、cations between the experimental data and the finite element results confirmed the accuracy and efficiency of the finite element analysis. The superior formability of LZ91 sheet at room temperature was also demonstrated in the present study by successful manufacturing of the notebook top cover case.
17、 The proposed four-operation process lends itself to an efficient approach to form the hinge in the notebook with less number of operational procedures than that required in the current practice. It also confirms that the notebook cover cases can be produced with LZ91 magnesium alloy sheet by the st
18、amping process. It provides an alternative to the electronics industry in the application of magnesium alloys.Keywords Notebook case; LZ91 magnesiumlithium alloy sheet; Multi-operation stamping; Formability1. IntroductionDue to its lightweight and good performance in EMI resistance, magnesium alloy
19、has been widely used for structural components in the electronics industry, such as cellular phones and notebook cases. Although the prevailing manufacturing process of magnesium alloy products has been die casting, the stamping of magnesium alloy sheet has drawn interests from industry because of i
20、ts competitive productivity and performance in the effective production of thin-walled structural components. As for stamping process, AZ31 magnesium alloy (aluminum 3%, zinc 1%) sheet has been commonly used for the forming process at the present time, even though it needs to be formed at elevated t
21、emperature due to its hexagonal closed-packed (HCP) crystal structure ( Chen et al., 2003andChen and Huang, 2003). Recently, the magnesiumlithium (LZ) alloy has also been successfully developed to improve the formability of magnesium alloy at room temperature. The ductility of magnesium alloy can be
22、 improved with the addition of lithium that develops the formation of body centered-cubic (BCC) crystal structure ( Takuda et al., 1999a, Takuda et al., 1999bandDrozd et al., 2004).In the present study, the stamping process of a notebook top cover case with the use of LZ sheet was examined. The form
23、ing of the two hinges in the top cover of a notebook, as shown in Fig. 1(a and b), is the most difficult operation in the stamping process due to the small distance between the flanges and the small corner radii at the flanges, as displayed in Fig. 1(c). This geometric complexity was caused by a dra
24、matic change in the corner radius when the flange of hinge gets too close to the edge of the notebook, which would easily cause fracture defect around the flange of hinge and require a multi-operation stamping process to overcome this problem. In the present study, the formability of LZ magnesium al
25、loy sheets was investigated and an optimum multi-operation stamping process was developed to reduce the number of operational procedures using both the experimental approach and the finite element analysis.Fig. 1.Flange of hinges at notebook top cover case. (a) Hinge, (b) top cover case and (c) flan
26、ges of hinge.View thumbnail images2. Mechanical properties of magnesium alloy sheetsThe tensile tests were performed for magnesiumlithium alloy sheets of LZ61 (lithium 6%, zinc 1%), LZ91, and LZ101 at room temperature to compare their mechanical properties to those of AZ31 sheets at elevated tempera
27、tures. Fig. 2(a) shows the stressstrain relations of LZ sheets at room temperature and those of AZ31 sheets at both room temperature and 200C. It is noted that the stressstrain curve tends to be lower as the content of lithium increases. It is also observed from Fig. 2(a) that the curves of LZ91 she
28、et at room temperature and AZ31 sheet at 200C are close to each other. LZ101 sheet at room temperature exhibits even better ductility than LZ91 and AZ31 do at 200C. Since the cost of lithium is very expensive, LZ91 sheet, instead of LZ101 sheet, can be considered as a suitable LZ magnesium alloy she
29、et to render favorable formability at room temperature. For this reason, the present study adopted LZ91 sheet as the blank for the notebook top cover case and attempted to examine the formability of LZ91 at room temperature. In order to determine if the fracture would occur in the finite element ana
30、lysis, the forming limit diagram for the 0.6mm thick LZ91 sheet was also established as shown in Fig. 2(b).Fig. 2.Mechanical properties of magnesium alloy. (a) The stressstrain relations of magnesium alloy; (b) forming limit diagram (FLD) of LZ91 sheet.View thumbnail images3. The finite element mode
31、lThe tooling geometries were constructed by a CAD software, PRO/E, and were converted into the finite element mesh, as shown in Fig. 3(a), using the software DELTAMESH. The tooling was treated as rigid bodies, and the four-node shell element was adopted to construct the mesh for blank. The material
32、properties and forming limit diagrams obtained from the experiments were used in the finite element simulations. The other simulation parameters used in the initial run were: punch velocity of 5mm/s, blank-holder force of 3kN, and Coulomb friction coefficient of 0.1. The finite element software PAM_
33、STAMP was employed to perform the analysis, and the simulations were performed on a desktop PC.Fig. 3.The finite element simulations. (a) Finite element mesh and (b) fracture at the corners.View thumbnail imagesA finite element model was first constructed to examine the one-operation forming process
34、 of the hinge. Due to symmetry, only one half of the top cover case was simulated, as shown in Fig. 3(a). The simulation result, as shown in Fig. 3(b), indicates that fracture occurs at the corners of flanges, and the minimum thickness is less than 0.35mm. It implies that the fracture problem is ver
35、y serious and may not be solved just by enlarging the corner radii at the flanges. The finite element simulations were performed to study the parameters that affect the occurrence of fracture. Several approaches were proposed to avoid the fracture as well.4. Multi-operation stamping process designIn
36、 order to avoid the occurrence of fracture, a multi-operation stamping process is required. In the current industrial practice, it usually takes at least ten operational procedures to form the top cover case using the magnesium alloy sheet. In the present study, attempts were made to reduce the numb
37、er of operational procedures. Several approaches were proposed to avoid the fracture, and the four-operation stamping process had demonstrated itself as a feasible solution to the fracture problem. To limit the length of this paper, only the two-operation and the four-operation stamping processes we
38、re depicted in the following.4.1. Two-operation stamping processThe first operation in the two-operation stamping process was sidewall forming as shown in Fig. 4(a), and the second one was the forming of flange of hinge presented in Fig. 4(b), the height of the flange of hinge being 5mm. Fig. 4(c) s
39、hows the thickness distribution obtained from the finite element simulation. The minimum thickness of the deformed sheet was 0.41mm and the strains were all above the forming limit diagram. It means the fracture defect could be avoided. In addition, the height of the flange conformed to the target g
40、oal to be achieved. However, this process produced a critical defect of wrinkling, as shown in Fig. 4(d), on the flange of hinge, which induces a problem in the subsequent trimming operation. Hence, even though the two-operation stamping process solved the fracture problem at the corner of the botto
41、m and the flange of hinge, a better forming process is still expected to solve the wrinkling of flange of hinge.Fig. 4.Two-operation stamping process. (a) Formation of sidewalls, (b) formation of hinges, (c) thickness distribution and (d) wrinkle.View thumbnail images4.2. Four-operation stamping pro
42、cessThe four-operation forming process proposed in the present study starts with the forming of three sidewalls and the flange of the hinge with a generous corner radius, as shown in Fig. 5(a). Since the sidewall close to the flange was open and the corner radius was larger than the desired ones, th
43、e flange was successfully formed without fracture. Such process successfully avoided the difficulty of forming two geometric features simultaneously, but increased the material flow of the blank sheet. The next step was to trim the blank outside the sidewalls, and to calibrate the corner radius of 4
44、mm to the desired value of 2.5mm. The hinge was thus formed, as shown in Fig. 5(b). The third step was to fold the open side, so that the sidewall could be completed around its periphery, as shown in Fig. 5(c). The effect of trimming the extra sheet outside the sidewalls in the second step on the th
45、ird step was studied. When the extra sheet was not trimmed, the thickness at the corner was 0.381mm, as shown in Fig. 5(d). The thickness of the corner increased to 0.473mm, as shown in Fig. 5(e), if the trimming was implemented in the second step. The excessive material produced by the folding proc
46、ess in the third step was then trimmed off according to the parts design. The last step was the striking process that is applied to calibrate all the corner radii to the designed values. The minimum thickness at the corner of the final product was 0.42mm, and all the strains were above the forming l
47、imit diagram. It is to be noted that Fig. 5(ac) only shows the formation of one hinge. The same design concept was then extended to the stamping process of the complete top cover case.Fig. 5.Four-operation stamping process. (a) First operation, (b) second operation, (c) third operation, (d) without
48、trimming and (e) with trimming.View thumbnail images5. Experimental validationIn order to validate the finite element analysis, an actual four-operation stamping process was conducted with the use of 0.6mm thick LZ91 sheet as the blank. The blank dimension and the tooling geometries were designed according to the finite element simulation results. A sound product without fracture and wrinkle was then manufactured, as shown in Fig. 6(a). To further validate the finite element analysis quantitatively, the thickness at the corners around the hi