机械设计中形状位置公差的确定

机械产品设计中,保证机械零件的精度是关系到实现设计的目的和生产经济性的问题.形位公差是控制零件几何精度技术的条件,就工程界在设计、制造及质量控制等方面优化产品质量过程中如何合理选用形位公差做一些探讨.     

形位误差的统计分析与统计公差

论证了形位误差的两种基本分布－折叠正态分布和瑞利分布，并在此基础上提出了形位误差的统计分析方法和形位公差的统计分差确定方法。     

对凸轮评定现行采用公差标准的商榷

在建立了形位公差标准之后 ,凸轮的评定究竟应采用什么公差标准 ,在认识上是不统一的。有的认为即使是在建立了形位公差概念之后 ,仍应采用尺寸公差 ;有的认为在建立了形位公差标准之后 ,应采用轮廓度公差 ;笔者则认为应采用跳动公差概念的控制方法 ,并希望本文论点能引起同行的共鸣。     

尺寸公差与形位公差优化设计的模型研究

在分析计算机辅助公差设计现状的基础上,引入不匹配率,研究尺寸公差与形位公差在产品性能要求上的互相约束关系,从而提出包括尺寸公差和形位公差的综合公差优化设计模型。     

机械零件设计中形位公差的确定研究

正确地选择和确定形位公差的项目、基准及数值对机械零件的设计是十分重要的.依据机械零件的功能要求.并考虑其使用性、工艺性和经济性的综合效果,详细分析了确定形位公差时公差项目、基准和公差数值的选择方法.零件的功能特性是选择形位公差项目、基准和公差数值的基础;公差间的关系可作为进一步精选它们的依据;同时还应兼顾经济性和测量的方便性.     

形位公差的编码描述方法

在计算机集成制造环境中,形位公差是构成零件工艺信息的主要组成部分之一,是零件设计、制造等过程中所必需的重要信息。本文研究了形位公差的编码描述方法,提出了形位公差的信息描述层次结构和编码结构,它能够详细地描述形位公差特征信息,便于由特征设计(CAD)中直接生成形位公差特征编码,易于实现形位公差的信息共享。     

推荐采用径向圆跳动公差 控制凸轮的升程误差

在建立了形位公差标准之后,凸轮的评定究竟庆采用什么公差标准,在认识上并不一致,有的认为,即使在建立了形位公差概念之后,亦应采用尺寸公差,有的认为应用用轮廓公差,笔者认为应采用跳动公差概念控制方法,并希望该论点能引起共鸣。     

《公差原则》国标在精度设计中的应用

在机械零件的精度设计中,《公差原则》标准的应用是比较复杂的问题。 公差原则,是指在应用尺寸公差及形位公差时所应遵循的原则。它分为独立原则及相关原则二种。独立原则——图纸上标注的尺寸公差与形位公差相互无关,在检测时用普通计量器具分别对尺寸形位误差进行测量,其标注如图1所示。相关原则——图纸上标注的尺寸公差与形     

“跳动”概念探讨

一、问题的提出 八十年代初，刚开始宣贯形位公差标准，曾有人提出：（１）形位公差特征符号固其对被测要素理想形状约束程度的不同分为形状公差、方向公差、位置公差。端面跳动等同于垂直度，当属方向公差，而径向跳动又属位置公差，跳动究竟该划归哪一类？（２）几何公差带区别于贴切概念，是现行形位公差标准的“理论基础”，然而跳动只是量表示值之变化幅度，它也有几何公差带吗？ 随着形位公差标准的广泛推行，又有人就跳动的标注实践提出：“跳动”是否一定得旋转？旋转轴线是否一定有固定位置？旋转轴线是否就是基准？等等。 笔者认…     

关于对同轴度测量的商榷

《计量技术》杂志 2 0 0 0年第 11期 (总第 315期 )第51页中刊载的《自制同轴度测量装置》一文 ,我认为存在以下问题 ,值得商榷。1 出现新、旧形位公差术语混用情况。我认为在文章中 ,不应同时出现同轴度和不同轴度术语。因为同轴度为形位公差现行国标的术语 ,而不同轴度为旧的形位公差国标中用过的术语 ,早已被淘汰不应再使用 ,也不应该将其混用。2 存在对新、旧形位公差带的理解偏差。在文章中提到 :“将被测件旋转一周 ,记录下指示表的示值变化 ,其值的 1/2即为同轴度误差” ,我认为是错误的。因为形位公差现行国标中规定 ,同轴度公差带…     

Assembly tolerance allocation using a coalitional game method

Assembly tolerance allocation in modern manufacturing industries is important because it directly affects product quality and manufacturing cost. Loose tolerances may cause quality deficiency while tight tolerances can increase the cost. It is significant to develop a reasonable tolerance allocation strategy for every assembly component combining the cost and quality demands. Traditionally, designers often adopt the single objective optimization with some kind of constraint or establish a comprehensive evaluation function combining several optimization objectives with different weights to solve the tolerance allocation problem. These approaches may not be desirable as it is difficult to adequately consider the interaction and conflict between the cost and quality demands. In this article, an assembly tolerance allocation method using coalitional game theory is proposed in an attempt to find a trade-off between the assembly cost and the assembly quality. First, the assembly tolerance allocation problem is formulated as a multi-objective optimization problem and the concept of the Pareto-optimal solution is introduced. Then, how the assembly tolerance allocation model is transformed into a coalitional game model is discussed, and a key technique of transforming the tolerance design variables into the game strategies is presented. Further, the Shapley value method of coalitional game based on each player's contribution evaluation to the profit of the whole coalition is given. Finally, the feasibility of the procedure is demonstrated through an example of vehicle front structure assembly.     

基于关键测量特征的机翼对接容差分配

针对在飞机装配过程中机翼对接准确度难以保证而影响飞机的气动外形和飞行平稳性的问题,建立了一种以关键测量特征的测量数据为节点的容差分配模型。基于测量辅助装配技术,对装配过程中飞机的关键测量特征进行定义。分析了机翼对接中关键测量特征间的几何关系,考虑了现场测量设备的测量不确定度,在此基础上建立了以关键测量特征的测量数据为节点的容差分配模型。试验结果表明,利用容差分配模型对机翼的安装角、上反角和对称性等进行容差分配,将分配的容差信息融入数字化装配系统,可以显著提高飞机装配的质量和效率。研究结果可以为飞机机翼对接过程中装配特征的定义和容差分配提供一定的理论指导。     

Concurrent optimization of assembly tolerances for quality with position control using scatter search approach

Tolerance allocation to individual parts in any assembly should be a vital design function with which both the design and manufacturing engineers are concerned. Generally design engineers prefer to have tighter tolerances to ensure the quality of their design, whereas manufacturing engineers prefer loose tolerances for ease of production and the need to be economical. This paper introduces a concurrent tolerance approach, which determines optimal product tolerances and minimizes combined manufacturing and quality related costs in the early stages of design. A non-linear multivariable optimization model is formulated here for assembly. A combinatorial optimization problem by treating cost minimization as the objective function and stack-up conditions as the constraints are solved using scatter search algorithm. In order to further explore the influence of geometric tolerances in quality as well as in the manufacturing cost, position control is included in the model. The results show how position control enhances quality and reduces cost.     

Integrating the Lambert W Function to a Tolerance Optimization Problem

This paper explores the integration of the Lambert W function to a tolerance optimization problem with the assessment of costs incurred by both the customer and a manufacturer. By trading off manufacturing and rejection costs, and a quality loss, this paper shows how the Lambert W function, widely used in physics, can be efficiently applied to the tolerance optimization problem, which may be the first attempt in the literature related to tolerance optimization and synthesis. Using the concept of the Lambert W function, a closed‐form solution is derived, which may serve as a means for quality practitioners to make a quick decision on their optimal tolerance without resorting to rigorous optimization procedures using numerical methods. A numerical example is illustrated and a sensitivity analysis is performed. Copyright © 2005 John Wiley & Sons, Ltd.     

Concurrent optimal allocation of design and process tolerances for mechanical assemblies with interrelated dimension chains

Concurrent tolerance allocation has been the focus of extensive research, yet very few researchers have considered how to concurrently allocate design and process tolerances for mechanical assemblies with interrelated dimension chains. To address this question, this paper presents a new tolerance allocation method that applies the concept of concurrent engineering. The proposed method allocates the required functional assembly tolerances to the design and process tolerances by formulating the tolerance allocation problem into a comprehensive model and solving the model using a non-linear programming software package. A multivariate quality loss function of interrelated critical dimensions is first derived, each component design tolerance is formulated as the function of its related process tolerances according to the given process planning, both manufacturing cost and quality loss are further expressed as functions of process tolerances. And then, the objective function of the model, which is to minimize the sum of manufacturing cost and expected quality loss, is established and the constraints are formulated based on the assembly requirements and process constraints. The purpose of the model is to balance manufacturing cost and quality loss so that concurrent optimal allocation of design and process tolerances is realized and quality improvement and product cost reduction is achieved. The proposed method is tested on a practical example.     

Sequential algorithms for structural design optimization under tolerance conditions

A deterministic optimization usually ignores the effects of uncertainties in design variables or design parameters on the constraints. In practical applications, it is required that the optimum solution can endure some tolerance so that the constraints are still satisfied when the solution undergoes variations within the tolerance range. An optimization problem under tolerance conditions is formulated in this article. It is a kind of robust design and a special case of a generalized semi-infinite programming (GSIP) problem. To overcome the deficiency of directly solving the double loop optimization, two sequential algorithms are then proposed for obtaining the solution, i.e. the double loop optimization is solved by a sequence of cycles. In each cycle a deterministic optimization and a worst case analysis are performed in succession. In sequential algorithm 1 (SA1), a shifting factor is introduced to adjust the feasible region in the next cycle, while in sequential algorithm 2 (SA2), the shifting factor is replaced by a shifting vector. Several examples are presented to demonstrate the efficiency of the proposed methods. An optimal design result based on the presented method can endure certain variation of design variables without violating the constraints. For GSIP, it is shown that SA1 can obtain a solution with equivalent accuracy and efficiency to a local reduction method (LRM). Nevertheless, the LRM is not applicable to the tolerance design problem studied in this article.     

ROBUST TOLERANCE ALLOCATION USING STOCHASTIC PROGRAMMING

Abstract

Tolerance allocation in manufacturing is a prominent industrial task for enhancing productivity and reducing manufacturing costs. The classical tolerance allocation problem can be formulated as a stochastic program to determine the assignment of component tolerances such that the manufacturing cost is minimized. However, tolerance design is a prerequisite to the overall quality and cost of a product; robust tolerance design is particularly important and should be considered. In this paper, robustness is considered in formulating the tolerance allocation problem by minimizing the manufacturing cost's sensitivity. Moreover, from a practical perspective, the process capability index for each component and the upper bound of the manufacturing cost are also considered. To effectively and efficiently resolve the robust tolerance allocation problem, a sequential quadratic programming algorithm embedded with a Monte Carlo simulation is developed. To demonstrate this design method's robustness, two commonly used test problems are solved. The designs devised in this paper have lower manufacturing costs and smaller variations in manufacturing costs than those in previous studies, indicating that the proposed method is highly promising in the robust tolerance design.     

A new interval optimization method considering tolerance design

This study considers the design variable uncertainty in the actual manufacturing process for a product or structure and proposes a new interval optimization method based on tolerance design, which can provide not only an optimal design but also the allowable maximal manufacturing errors that the design can bear. The design variables' manufacturing errors are depicted using the interval method, and an interval optimization model for the structure is constructed. A dimensionless design tolerance index is defined to describe the overall uncertainty of all design variables, and by combining the nominal objective function, a deterministic two-objective optimization model is built. The possibility degree of interval is used to represent the reliability of the constraints under uncertainty, through which the model is transformed to a deterministic optimization problem. Three numerical examples are investigated to verify the effectiveness of the present method.     

形位误差对装配精度影响的定量分析

基于形位公差带的分布特征，对形状、位置要素变动情况进行研究，提出了一种在一维线性装配尺寸链下，判断模型中形住误差是否应当纳入装配误差累积计算的方法．在统计平方根模型的基础上，依据零件生产加工完毕后各形位要素变动的分布特性，提出了一种新的装配误差累积计算模型．采用此模型可实现包含形住误差的装配精度定量分析．给出的一个应用实例说明了所提出方法的有效性．