几何公差中最大实体要求的分析探讨及应用

根据《产品几何技术规范(GPS)几何公差最大实体要求、最小实体要求和可逆要求》标准要求规定,阐述最大实体要求的概念、应用最大实体要求时,形状公差与尺寸的补偿情况和相互关系;测量和控制最大实体要求下极限尺寸的方法。     

不同公差要求下极限尺寸含义的探讨

等效采用国际标准的国家标准《形状和位置公差 最大实体要求、最小实体要求和可逆要求》(以下简称《公差要求》)已经发布。与旧的《形状和位置公差》、《公差原则》相比,《公差要求》主要增加了最小实体要求和可逆要求(即反补偿原则),以及由此涉及到的一些新术语、新概念,如:体外作用尺寸、体内作用尺寸等等。     

基于公差原则的圆柱特征位置度公差数学模型研究

提出了基于最小实体要求(LMR)、最大实体要求(MMR)的圆柱特征位置度公差数学模型.将小位移矢量簇(SDT)引入到公差数学建模中,系统地研究了轴孔特征位置度公差在MMR、LMR下的不同约束条件及相应的位置度公差数学模型.该数学模型可以完整地表示出位置度公差的工程语义,便于公差的计算机处理及在各阶段的数据传递.实例验证了该模型的有效性.     

对三例GB标准中未于定义的形位公差的探讨

在引进Ｇ公司的产品图样中 ,碰到三个ＧＢ标准未于定义的形位公差代号。撰文阐述个人的理解。实例一 :螺孔的 ○Ｐ ○Ｍ 公差图 1为一简化了的机油泵体。图 1图中 4×Ｍ6螺孔对平面Ｆ位置度代号框格内公差值的后面标注了符号 ○Ｍ 。ＧＢ中 ○Ｍ 的意思是要求被测要素实际轮廓不越出形位公差的最大实体实效边界。螺孔是复杂曲面 ,其形状 (中径、螺距、半角 )误差由螺纹公差控制。对螺孔而言 ,小于塞规通端的“最大实体实效边界”也毫无意义。鉴于此 ,图1位置度代号框格下方标注了符号 ○Ｐ ,表示被测要素不是螺孔本身 ,而是它的指定延伸部分…     

设计与制造中的统计几何公差建模及应用

几何与尺寸公差(形位公差GD&T)广泛用于机械工程设计与制造中重要几何特征的偏差控制.相对较成熟和简单的尺度公差建模与分析,几何公差统计建模与分析更具挑战性,是当前CAD技术中尚未但亟待解决的课题之一.现提出采用统计几何模态模型(SMA)方法解决这一问题.SMA可识别刻划与解释测量数据中的几何特征信号模式及其变化,从而服务于制造中的(公差)质量检验、诊断及变化模式的统计建模.在设计中SMA可进行模态重组综合,从而再现或仿真几何特征偏差的随机变化进行统计几何公差分析.     

链槽类零件公差设计一致性的评价工具——软件量规

通过对漂移模型、虚拟边界要求及条件公差理论的剖析,在ＩＳＯ和国家标准的公差原则基础上,给出与标准相一致的,可用于键槽类零件公差一致性验证的软件量规数学等效式。它为基于约束的参数化ＣＡＤ系统中,计算机辅助公差设计的评价提供了理论依据,对于促进ＣＡＤ／ＣＡＭ集成,特别是并行工程的发展具有重要的科学意义和应用价值。     

键槽类零件公差设计一致性的评价工具——软件量规

通过对漂移模型、虚拟边界要求及条件公差理论的剖析，在ISO和国家标准的公差原则基础上，给出与标准相一致的，可用于键槽类零件公差一致性验证的软件量规数学等效式。它为基于约束的参数化CAD系统中，计算机辅助公差设计的评价提供了理论依据，对于促进CAD/CAM集成，特别是并行工程的发展具有重要的科学意义和应用价值。     

综合量规的设计计算——关于相关原则的检测

当被测要素或基准要素采用相关原则时,用综合量规进行检测。用这种量规检测,完全符合相关概念,能保证零件的完全互换性和功能要求,使用方便,操作简单,是在需要保证互换性的成批生产中的一种重要检测工具。本文以GB1958-80《形状和位置公差检测规定》为准则,分别举例说明:相关原则仅用于被测要素或基准要素以及相关原则同时用于被测要素和基准要素时综合量规的设计计算方法。一、当相关原则((M))仅用于被测要素时,综合量规(主要尺寸)的设计计算方法(见图1) 量规工作尺寸及公差:     

解析形位公差中的最大实体要求

最大实体要求在形位公差的相关要求中占有重要的位置,应用时要注意分析对多孔零件的成组要素遵守最大实体要求的情况。当被测要素、基准要素偏离最大实体状态时,正确理解几何图框中的中心要素变化将变得十分重要。     

浅析零件图的尺寸公差和形位公差

根据GB/T 4249-1996《公差原则》,本文通过具体实例,对机械零件图纸进行分析,详细地讲述了独立原则、包容要求和最大实体要求,为正确理解图纸要求提供了简单的方法.     

Generalization and evaluation of vectorial tolerances

In recent years, vectorial tolerancing has emerged as a new alternative for representing workpiece tolerances. In contrast to conventional geometric tolerances which originated from hard gauging practices, vectorial tolerancing follows the working principle of coordinate measuring machines and CAD/ CAM systems. Moreover it provides feedback from measurement directly to manufacturing process control. Many believe it is a better tolerancing method to tie design, manufacuturing, and measurement together. However, the current proposal of vectorial tolerancing has some limitations. First, the currently adopted orientation vector is not sufficient for representing true 3D orientations. As a result, the orientation of a free form surface cannot be properly established. Second, there is lacking a unified and consistent method for the evaluation of vectorial tolerances. This paper proposes a new orientation vector which provides a more general mathematical basis for representing vectorial tolerances. It enables true 3D orientation representation and relates tolerances to the functional requirement. With the improved mathematical definition, a systematic tolerance evaluation approach becomes possible for both analytical geometric elements and free-form surfaces. Computer simulations and real-world applications are studied to validate this new approach.     

Optimisation of a pyramidal geometric transition radar absorbing material loaded with a resistive frequency selective surface

Designs for an improved pyramidal geometric transition radar absorbing material incorporating frequency selective surfaces loaded with either distributed or lumped resistance are presented. It is shown, through full-field simulation, that for a given absorber, the inclusion of impedance loading can reduce the frequency at which a 240 dB reflectivity level is obtained from 6 to 2 GHz. Oblique incidence and variable tolerancing are also discussed.     

虚拟产品开发中的并行公差设计

并行公差设计能够有效解决VPD中的公差控制与公差分配问题，有利于VPD的全面集成以及面向加工和面向装配的实现。本文介绍了并行公差设计的内涵和特点，并提出了并行公差设计的系统结构。在此基础上开发的基于PDM的并行公差设计系统是虚拟开发平台的一个重要组成部分，已经通过863CIMS主题专家组的验收。     

Tolerancing of board-level-free-space optical interconnects

For optical interconnects to become a mature technology they must be amenable to electronic packaging technology. Two main obstacles to including free-space optical interconnects are alignment and heat-dissipation issues. Here we study the issues of alignment tolerancing that are due to assembly and manufacturing variations (passive-element tolerancing) over long board-level distances (>10 cm) for free-space optical interconnects. We also combine these variations with active optoelectronic device variations (active-element tolerancing). We demonstrate a computer-aided analysis procedure that permits one to determine both active- and passive-element tolerances needed to achieve some system-level specification, such as yield or cost. The procedure that we employ relies on developing a detailed design of the system to be studied in a standard optical design program, such as code v. Using information from this model, we can determine the integrated power falling on the detector, which we term optical throughput, by performing Gaussian propagation or general Fresnel propagation (if significant vignetting occurs). This optical throughput can be used to determine system-level performance criteria, such as bit-error rate. With this computer-aided analysis technique, a sensitivity analysis of all the variations under study is made on a system with realistic board-level interconnect distances to find each perturbation's relative effects (with other perturbations set to 0) on the power falling on the detector. This information is used to set initial tolerances for subsequent tolerancing analysis and design runs. A tolerancing analysis by Monte Carlo techniques is applied to determine if the yield or cost (yield is denned as the percentage of systems that have acceptable system performance) is acceptable. With a technique called parametric sampling, a subsequent tolerancing design run can be applied to optimize this yield or cost with little increase in computation. We study a design example and show that most of the tolerances can be achieved with current technology.     

Simultaneous tolerancing for design and manufacturing

This paper presents a new tolerance design theory—simultaneous tolerancing— which works in the concurrent engineering context. After stating the need to develop a simultaneous tolerancing theory by showing the shortcomings of conventional tolerancing technique, the concept of simultaneous tolerancing is given, and its elements are briefly presented. Then we focus our attention on the development of a general mathematical model of optimal tolerancing supporting concurrent engineering. Two commonly used models, worst-case and statistical, are discussed in detail. Next, a method of ‘interim tolerances’, which help to determine an appropriate machining process without using functional tolerances, is proposed. The simultaneous tolerancing theory presented in this paper permits of determining directly optimal machining tolerances in product design, reducing the manufacturing cost and improving the quality of products. Finally, an example is given, showing that the proposed theory is feasible in practice.     

Tolerancing techniques: the state-of-the-art

The intense global competition to produce quality products at a low cost has led many industrial nations to consider mechanical tolerances as a key factor to bring about cost saving as well as to remain competitive. In the last two decades, some work has been done in the area of tolerance techniques. In this paper a comprehensive summary of the state-of-the-art and the projection of future trends in tolerancing techniques is presented to describe improved techniques available today and to aid in guiding research for the future. This paper reviews the status of theory and practice of how manufacturing and assembly processes are characterized for relating tolerancing to process or production cost. The specification of tolerancing on the dimension of the manufactured part has a significant impact on the final production cost. Tight tolerances can result in excessive process cost, while loose tolerances may lead to increased waste and assembly problems. This paper systematically reviews the state-of-the-art by classifying more than 50 papers written so far into five categories. They are, the dimensional tolerances chain technique, geometrical modelling in tolerances, statistical and probabilistic methods in tolerancing, tolerances based on analysis and synthesis, tolerances based on cost-tolerance algorithms and design methods. Future areas of research and the unresolved issues have been presented that will serve as a springboard for researchers to investigate and produce solutions for the end of this century. The present problems and issues once resolved, will revolutionize the manufacturing industry as the year 2000 approaches!     

Rapid optimization of cost-based tolerancing

In this paper, a rapid optimization method of cost-based tolerancing is proposed. An example shows that only a few cases of the Monte Carlo simulation are necessary to find the best balance of the yield and the tolerance cost for the practical tolerancing problem.     

Tolerancing algebra: A building block for handling tolerance interactions in design and manufacturing Part 1: Concept and representation

As a fundamental building block for 3D tolerance transfer analysis, tolerancing algebra on a deviation space has been proposed and elaborated. Based on the investigation of the spatial characteristic and the propagation mechanism of geometric tolerances and manufacturing process dispersions, a set of primitives and operations has been defined, which forms the algebraic structure of tolerancing algebra. Some important algebraic properties have been derived that will be extensively used to establish a tolerance transfer technique for process planning. Companion papers present the idea of tolerancing algebra in two parts. Part 1 presents some important concepts and their representations. Part 2 endeavours to show the interactions between product tolerances and process dispersions by way of the basic algebraic operations on deviation volumes.