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本文从机械精加工中常用的外圆磨削着手,寻求圆柱形零件的尺寸误差、圆度误差、表面粗糙度之间的内在联系;同时考虑零件的功能要求、加工方法和加工成本,建立计算机辅助确定几何参数公差的数学模型,为CAD/CAM系统及其它机械设计中合理选择零件几何参数公差提供依据。 相似文献
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1机械加工精度
机械加工精度是指零件加工后的实际几何参数(尺寸、形状和位置)与理想几何参数相符合的程度。它们之间的差异称为加工误差。加工误差的大小反映了加工精度的高低。误差越大加工精度越低,误差越小加工精度越高。加工精度包括三个方面内容:尺寸精度指加工后零件的实际尺寸与零件尺寸的公差带中心的相符合程度;形状精度指加工后的零件表面的实际几何形状与理想的几何形状的相符合程度;位置精度指加工后零件有关表面之间的实际位置与理想。在机械加工中总是存在一定的加工误差,误差都包括哪些方面以及怎样提高加工精度昵? 相似文献
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孔组位置度误差值用最小包容圆的直径φf表示。根据圆周分布孔组位置度的特性,各孔的公差带可集中在任一孔的理想位置上,最小包容圆的圆心必须与公差圆的圆心重合,所以最小包容圆是指以孔的理想位置为中心,包容孔组中各孔的实际位置的最小圆。而孔组各孔的理想位置取决于孔组几何框图相对于基准的位置。几何框图相对于基准固定与否,直接影响到φf的取值问题。本文就确定圆周分布孔组位置度误差最小包容圆作些探讨。一、基准圆心如图1所示零件,6孔圆周均布,以φT孔为基准A。用极坐标法测量能得出被测要素的径向误差△R和角向弧长误差△S。如果测得的角向误差△θ为角度值时,可根据△S=△θ×0.0029×R求出△S。其中△θ角向误差 相似文献
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《上海计量测试》2015,(3)
推广几何公差标准的目标是:(1)所有采用几何区域公差带概念的几何公差都能用框格代号标注。设计师应该根据功能需要提出几何公差要求,而不能囿于标准已有的示例。有些标准只有案例。这种情况下,须由这些案例推理得出普遍适用的规律,才能有效指导实践。(2)对符合规范的公差代号只有唯一确定的解释。同一项公差可能有多种误差测量方法(且总是近似的),所以只能根据对公差代号的解释选择误差测量方法,不可按误差测量方法解释公差代号。撰写此文,旨在凭借自己对标准的理解,帮助读者正确理解标准,用好标准。即使出于同样的功能需要,也可能有多种标注公差代号的方案。本文图中标注的公差代号未必是唯一的合理选择。公差值取决于多方面因素,本文实例中的公差值只求相对合理。本文的12个实例(关节球、球轴承内环、滚子轴承内环、沉头螺钉、开槽螺母、铰制孔用螺栓、55°角度规、V形槽、端盖、目镜套筒、前叉、轴辊)力求展示多种可能的几何公差要求。读者可以执行某项指定的未注公差标准,或者在图样技术要求栏规定图示零件的未注几何公差。部分图形选自沈阳市标准计量局、沈阳市机电工业局组织编著的《表面形状和位置公差标注示例图册》(技术标准出版社1978年8月版)和汪恺、刘巽尔主编的《新编形状和位置公差标注示例图册》(中国标准出版社1998年8月版)第五部分综合示例。 相似文献
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在测量以凸轮为代表的非整圆回转零件时,若转动中心偏离工件几何中心,就会给某些重要参数的测量结果带来误差。本文对测量过程进行了数学描述,并经严谨推导建立了修正的数学模型。 相似文献
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在测量以凸轮为代表的非整圆回转零件时,若转动中心偏离工件几何中心,就会给某些重要参数的测量结果带来误差.本文对测量过程进行了数学描述,并经严谨推导建立了偏心修正的数学模型. 相似文献
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本文根据国家标准GB/T 1182-2008《产品几何技术规范几何公差形状、方向、位置和跳动公差标注》,详细论述了圆度、圆柱度和直线度等几何公差之间的联系与区别,结合自已的工作经验,就生产中一些常见项目和常见问题进行说明. 相似文献
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为测量未知名义几何模型和参数的零件,提出了“免形状测量模式”.该测量模式通过高精度获取被测轮廓的“数据微粒”,建立典型几何要素及其内在不变量的理论模型,作为识别被测要素几何形状的准则;根据识别准则识别被测轮廓的名义几何形状;利用数据处理与误差分析软件,确定几何参数进而完成误差评定.论述了两个关键问题,即几何信息获取和几何形状识别.分析了几何信息获取的关键技术,阐述了对测量仪器的要求,介绍了结合内插和外插技术的自适应采样策略;提出了用于几何形状快速识别的6个算子;研制了测量仪器FormFree300,实现了“免形状测量”. 相似文献
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依据纤维丝束带复合材料的相关几何结构参数值和所确定的纤维丝束带特征体积单元(RVE)模型几何结构尺寸,以有限元软件MSC.Patran/Nastran为平台建立纤维丝束带复合材料RVE有限元模型并在模型中置入相应的制备缺陷。各类制备缺陷的置入均采用删除网格单元的方法,置入裂纹型制备缺陷时偏移裂纹两侧单元相对面以获得当前裂纹宽度,置入孔洞型制备缺陷时尽量模拟其真实形貌。根据复合材料力学关于材料各性能参数的定义和细观力学基本理论推导了有限元计算细观力学(FECM)方法预测复合材料有效弹性性能和有效热膨胀性能的过程。根据FECM方法预测了不含制备缺陷、含单一制备缺陷和含各类制备缺陷时的弹性常数和有效热膨胀系数。结果表明:各类制备缺陷的存在均会使弹性模量和剪切模量减小,泊松比和热膨胀系数可能增大也可能减小。通过与实验测试结果对比分析可知,数值预测结果普遍比实验测试结果偏大,但总体效果较为理想,最大相对误差为6.04%。 相似文献
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Xue-Cheng Ping Meng-Cheng Chen 《International Journal of Mechanics and Materials in Design》2009,5(3):231-242
A unit rectangular cell is usually cut out from a medium for investigating fracture mechanism and elastic properties of the
medium containing an array of irregularly shaped inclusions. It is desirable to clarify the geometrical parameters controlling
the elastic properties of heterogeneous materials because they are usually embedded with randomly distributed particulate.
The stress and strain relationship of the rectangular cell is obtained by an ad hoc hybrid-stress finite element method. By
matching the boundary condition requirements, the effective elastic properties of composite materials are then calculated,
and the effect of shape and arrangement of inclusions on the effective elastic properties is subsequently considered by the
application of the ad hoc hybrid-stress finite element method through examining three types of rectangular cell models assuming
rectangular arrays of rectangular or diamond inclusions. It is found that the area fraction (the ratio of the inclusion area
over the rectangular cell area) is one dominant parameter controlling the effective elastic properties. 相似文献
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Markel VA Shalaev VM 《Journal of the Optical Society of America. A, Optics, image science, and vision》2001,18(5):1112-1121
We develop a theoretical approach to calculating optical properties of carbonaceous soot in the long-wavelength limit. Our method is based on geometrical renormalization of clusters; it avoids both the inaccuracy of the dipole approximation in its pure form and the numerical complexity of rigorous direct methods of solving the EM boundary problem. The results are verified by comparison with the experimental measurements for specific extinction of diesel soot in the spectral region from 0.488 microm to 0.857 cm that were performed by Bruce et al. [Appl. Opt. 30, 1537 (1991)]. The theory leads to analytical expressions that are applicable to different soots, with various geometrical properties and optical constants. We show that the functional form of the long-wavelength asymptote of the specific extinction can depend critically on a parameter characterizing the sample geometry, and we identify the critical value of this parameter. 相似文献
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A. Fischer P. Z. Bar‐Yoseph 《International journal for numerical methods in engineering》2000,48(11):1571-1582
An advanced CAD model is required for efficient, real‐time adaptive generation of FE meshes. In this paper, a discrete level of detail (LOD) method for reconstructing progressive multiresolution models is proposed. With this approach, the model is reconstructed a priori so that any level of detail can be accessed directly, in real time, according to application requirements. The mesh is generated adaptively according to geometrical or analysis error indicators, where even at lower levels of resolution, critical areas are preserved. The method has been extended to progressive time and geometrical models for simulation and is demonstrated by several examples. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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We propose in this paper a geometrical equivalence between a shape described by a power law and a conical geometry. A theoretical and numerical study has allowed us to generalize an equivalence between the conical geometrical parameter tanβ and the spherical or power law shape geometrical parameter ac/R. Moreover, in order to superpose indentation data whatever the geometry, a new pile-up parameter Δ has been introduced. For one set of mechanical properties of the tested sample, this new formulation leads to a perfect superposition between conical, power law shape and spherical indentation data. At the end of this paper, we propose a comparison between the results proposed in literature and the present formulation. 相似文献
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A. Petriccione D. Annicchiarico V. Antonucci M. Giordano A. Riccio F. Scaramuzzino M. Zarrelli 《Composites Science and Technology》2012
A representative volume element (RVE) based model to evaluate the mechanical performance of non-crimp fabric (NCF) composites has been developed and presented hereafter. By means of the stiffness averaging method, the modelling procedure is able to simulate the NCF’s elastic properties taking into account the effects of process-induced defects and final geometrical configuration. Microscopy analysis has been used to quantitatively evaluate the effects of tow waviness, stitching geometrical parameters and matrix porosity; these features have been included as sub-models into the final model. Numerical predictions have been compared to the results of tensile tests performed on composite coupons. A geometrical parameter characterising the undulation of the tows has been introduced and a sensitivity analysis has been performed on the model with different undulations. 相似文献
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有关三维编织复合材料的理论分析研究归纳为:基于细观结构几何模型的物理性能研究和力学性能研究两部分.纤维体积分数是物理性能研究的最主要参数,力学分析以复合材料的弹性性能为主.合理的几何模型决定了力学性能分析与试验结果的一致性.建立在代表性体积单元尺度的几何模型应用最为广泛,得到了力学性能的试验验证.三维编织复合材料的力学性能的数值仿真主要以有限元方法为主,然而仅仅依赖于对其弹性性能的研究结果还远远不能满足三维编织复合材料作为关键结构部件的使用要求,建立完善的断裂准则是编织复合材料大量使用的理论依据.特殊形状的一次性编织复合材料的力学性能研究有待进一步深入. 相似文献