连接座体的机械加工工艺设计及夹具设计【含CAD图纸、说明书】
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毕 业 设 计(论 文)外 文 参 考 资 料 及 译 文译文题目: Prediction of workpiece deformation in a fixture systemusing the finite element method 利用有限元法预测夹具系统的工件变形 学生姓名: 学 号: 专 业: 所在学院: 指导教师: 职 称: 20xx年 2月 27日 Prediction of workpiece deformation in a fixture system using the finite element method1. Introduction Methods for analyzing fixtures are essential to the practice and economics of machining. In particular, the ability to model and accurately predict workpiece deformation induced by fixturing loads and/or predict the unknown fixtureworkpiece contact forces are crucial for designing functional fixtures. The most common modeling and analysis approaches used for fixtureworkpiece systems include the rigid body approach, thecontact mechanics based approach and the finite element modeling approach. Of these approaches, the rigid body modeling approach 13 is by definition incapable of predicting workpiece deformations and is therefore unsuitable for analysis of the impact of fixturing on part quality. The contact mechanics approach, although attractive from astandpoint of computational effort, is limited to parts that can be approximated as elastic half-spaces. Models derived fromthis approach are capable of accurately predicting unknown locator reaction forces and localized contact deformations 46. However, they are not applicable for thin, compliant parts. Finite element models on the other hand are very powerful and are capable of accounting for all compliances and nonlinearities present in the system. Although use of finite element models has been widely reported in the literature and employed in practice, a clear understanding of the role of the different fixture compliances on the prediction accuracy of workpiece deformation is lacking. Also knowledge of the effects of different finite element model parameters on workpiece deformation is lacking. A common assumption in application of Finite Element Analysis (FEA) to analyze a fixtureworkpiece system is that the fixture is completely rigid since it is much stiffer than the workpiece in many applications. In most such cases, the workpiece is modeled and nodes at the location of fixture contact are completely restrained. This formulation is commonly referred to as a single-point contact 712. Omitting fixture elements does not allow for the model to account for compliance in the fixture and neglects frictional contact effects between the fixture and workpiece. Other researchers 1316 have utilized linear springs to approximate the stiffness of the fixture components. However, such an approach requires the stiffness to be measured or approximated, adding time and introducing potential error into the analysis.Recent work 1719 has explored the use of surface-tosurface contact elements. Such an approach allows frictional effects to be modeled. This methodology was used for the work reported in this paper. Liao et al. 17 used FEA with contact elements to model a multiple-contact fixture system. They, however, did not investigate the effects of friction and meshing parameters on the results. Satyanarayanas 18,19 work was limited to a single fixtureworkpiece contact. More importantly, these studies did not analyze the contribution of fixture body compliance to the overall deformation. This paper investigates the effects of various finite element modeling parameters, such as friction and mesh density, on workpiece deformation. In addition to modeling the workpiece and fixture tips, as is common, the effect ofcompliance of other fixture components such as support blocks, base plate, etc. on workpiece deformation is also examined. The FEA predictions of workpiece deformation and locator reactions are experimentally verified. 2. Model development Finite element models were constructed using ANSYSw Version 5.7. Solid models were assembled of the prismatic block and fixture tips. All components in the system were modeled as isotropic elastic bodies. The fixture tips, shown in Fig. 2, were modeled as cylinders with either planar (clamp and locator circular contact areas 60 and 127 mm2,respectively) or spherical (35 mm radius of curvature) end caps. The axial lengths of the planar and spherical tips were 6.4 and 10.2 mm, respectively. The 10-node tetrahedral element Solid92 was used to mesh all solid bodies. Contact between the workpiece and fixture was simulated using the quadratic surface-to-surface contact elements Targe170 and Conta174. A constant static coefficient of friction was used to establish contact properties at the interfaces. To simulate the locators being rigidly fixed in place, the surface of each locator tip opposite to thecontact was restrained in all three translational degrees of freedom. A uniformly distributed pressure was applied over the surface of both clamps in opposite contact to simulate the desired clamping force.The deformation of the workpiece, analyzed in the subsequent sections, was found at two points on the workpiece. The positive directions of these two points, dC1 and dC2, are shown in Fig. 3. The selection of points was based upon locations on the workpiece that underwent themost deformation due to clamping. 2.1 Sensitivity to friction coefficient Laboratory tests conducted by Satyanarayana 18 on thesame fixtureworkpiece system found an average static coefficient of friction (m) of 0.18 between the workpiece and fixture tips. The average was in a range of experimental values from 0.15 to 0.25. To test the effect of friction of workpiece deformation prediction, FEA models were constructed for workpiece wall thicknesses of 610 mm restrained in the fixture previously described. A spectrum of m from 0.15 to 0.30 was tested in combination with the various wall thicknesses. A summary of the deformation results is given in Table 2. An average difference of 3.1%in deformation prediction was found for a change in m of 0.05. These results show that the effect of small variations in the friction coefficient on the workpiece deformation is quite small. 2.2 Treatment of primary plane locators A series of models were constructed to determine the influence of the primary plane locators. For a properly designed 3-2-1 layout in which workpiece rotation is prevented, the only normal load taken by the three primary plane locators is the weight of the workpiece. The frictionalforce produced by such a small load is often dwarfed by the much larger clamping loads. An analysis was performed to determine if the frictional effects at these locators must be accounted for in a modeling approach.Two sets of boundary conditions were applied to blocks with wall thicknesses of 7, 8, and 9 mm. The first set, Case A, included all three primary plane locators subjected to the previously described surface-to-surface contact boundary conditions. A value of 0.18 was specified for m. The second configuration, Case B, removed all three ofthe primary plane locators and simply restrained the bottom surface of the workpiece from translating in the z-direction. A summary of the results is given in Table 3. The FEA showed that the predicted deformations differed between the two boundary condition sets by an average of only 1.31%. This small impact of the bottom locators allows the FEA models to be constructed without the primary plane locators,thus saving considerable computational time. This (Case B) boundary condition set used only 77 and 69% of the complete model computational time for the planar and spherical tips, respectively. The omission of the three primary plane locators coupled with restraining the bottomsurface of the workpiece was the configuration used for subsequent models. It should be pointed out that this approximation may not be valid when machining loads are also taken into account.利用有限元法预测夹具系统的工件形1. 介绍 分析装置的方法是必不可少的实践加工和经济学,尤其是能力模型。准确预测工件变形诱导夹具负载或预测未知的夹具工件。接触力是关键设计功能的装置。最常见的用于建模和分析方法。夹具 - 工件系统包括刚体方法,联系力学为基础的方法和有限元建模方法。这些建模方法 1-3 是无法通过的定义预测工件变形,因此不适宜夹具对零件质量的影响分析。 联系力学的方法,虽然从一个具有吸引力,计算努力的立场,零件可以是有限的,近似为弹性半空间。这种方法能够准确地预测未知,定位反应部队和本地化的接触变形4 - 6。然而,他们不适用兼容的零部件。另一方面,有限元模型是非常强大的,会计能为所有符合和非线性系统中存在。虽然利用有限元模型已beenwidely文献报道,受雇于在实践中,明确了不同的作用的认识.预测精度对工件的夹具符合变形是缺乏。也是知识的影响.不同的有限元模型参数对工件变形缺乏。在应用中的一个共同的假设的有限元分析(FEA)分析工件夹具系统是夹具是完全刚性的,因为它是远远高于围追堵截。在许多应用中的工件。在大多数这种情况下,是仿照工件夹具的位置和节点联系被完全抑制。这一提法普遍被称为单点接触 7-12 。夹具元件不允许帐户模型遵守夹具和忽略摩擦接触效果夹具和工件之间,其他研究人员 13-16 利用线性弹簧,近似夹具部件的刚度。然而,这种方法需要刚度测量或近似,添加时间和引入潜在的错误分析。最近的工作 17-19 探索的表面使用接触单元。这种做法使摩擦为蓝本的影响。这种方法被用于本文报道的工作等。 17 使用有限元分析接触单元来模拟多接触夹具系统。然而,没有调查摩擦的影响啮合参数的结果 18,19。工作仅限于一个单一夹具 - 工件接触。更多重要的,这些研究中没有分析的贡献夹具的身体符合整体变形。本文探讨各种有限的影响元建模参数,如摩擦和网密度工件变形。除了造型工件和夹具的秘诀,是常见的的效果。如支持符合其他夹具元件块底座工件变形等也是检查工件变形的有限元分析预测实验验证和定位反应。2模型开发有限元模型构建使用ANSYSw.版本5.7。实体模型组装的棱柱块夹具提示。系统中的所有组件为各向同性弹性体建模。夹具的秘诀显示图。 2无论是平面建模作为气瓶.(夹具和定位圆形接触面积的60和127 mm2的分别)或球( 35毫米的曲率半径)结束上限。平面和球面提示轴向长度分别为:6.4和10.2毫米, 10节点的四面体.元素SOLID92用于所有实体网格。 工件和夹具之间的接触进行了数值模拟使用二次曲面表面接触.元素TARGE170和CONTA174 。恒定的静态摩擦系数是用来建立联系的属性在接口。到模拟地方的定位器,每个定位器尖端对面的表面接触被限制在所有三个平移度自由。适用于一个均匀分布的压力超过双方夹相反的接触面模拟所需的锁模力工件变形,分析了随后的章节,被发现在两个点上工件。这两点正方向DC1和DC2,如图。 3点的选择.根据工件的位置,经历了因为要夹紧大部分变形。2.1 摩擦系数的敏感性Satyanarayana 18 进行的实验室测试.相同的工件夹具系统发现平均静态和工件之间的摩擦系数为0.18 (米)夹具的提示。在实验范围内的平均值从0.15至0.25 。为了测试摩擦的影响.工件变形预测,有限元模型构建工件壁的厚度6-10毫米在前面所述的夹具抑制。频谱从0.15到0.30 m的测试结合各种墙体的厚度。变形摘要结果列于表2 。 3.1的平均差异在变形预测中被发现为一米的变化0.05。这些结果表明,在小的变化的影响对工件变形的摩擦系数相当小。2.2 治疗的主要平面定位构建了一系列车型确定主平面定位的影响。对于正确.设计的3-2-1布局,工件旋转阻止,三个主要采取的正常负荷平面定位工件的重量。摩擦这样一个小负载所产生的力量往往相形见绌更大的夹持负荷。进行了分析,确定是否必须在这些定位器的摩擦效应占建模方法。两套边界条件被应用到块与壁厚7,8,9毫米。第一组,案件一,包括所有三个主要的飞机受到定位.先前所描述的表面到表面的接触边界条件。被指定为M值0.18 。 第二个配置,案例B,删除了所有三主平面定位,只是抑制了在翻译的工件表面底部z方向。表3给出了一个结果摘要。有限元分析结果显示,预测变形之间的不同两个边界条件设置由平均只有1.31 。这小的冲击,使有限元分析的底部定位无主平面定位将建造的模型从而节省了大量的计算时间。这个(案例B )边界条件设置使用的只有77和69 。完成平面模型的计算时间和球技巧,分别遗漏的三个加上主平面与制约的底部定位.工件表面是用于配置随后模型。应当指出,这逼近未必有效加工负载时还考虑到。
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