基于3DCS的RV减速器静态装配公差分析及优化

基于提高RV减速器装配成品率,结合其装配尺寸链设计零件公差,运用CATIA对RV减速器进行三维建模。运用三维公差分析软件3DCS给零件添加相关尺寸公差和几何公差,设定测量参数偏心距和齿侧间隙,模拟实际静态装配过程建立3DCS公差仿真模型,对零件公差进行优化和敏感性分析。优化后回差为0. 25′～1′,满足回差要求,摆线轮与针齿之间间隙≥0. 001 mm,且敏感性分析结果对RV减速器的零件公差设计有一定参考价值。     

串行布置的多装配尺寸链组公差分配优化设计

针对航天产品在装配过程中面临需同时满足多个装配要求而导致的公差分配不合理问题,通过构建串行布置的多装配尺寸链组,将多个装配要求分配给组内成员尺寸链,基于加工成本—公差模型和质量损失模型,以成员尺寸链公差,原装配尺寸链公差和加工能力为约束条件,建立了多装配尺寸链组的多目标公差优化分配数学模型。在Pareto机制下,采用非支配排序遗传算法（NSGA-Ⅱ）对数学模型进行求解,进而得到模型的Pareto前沿曲线图。以某航天企业产品复材箱体中纵筋与环筋的装配为例验证了公差优化分配模型的有效性和适用性,为公差优化分配提供更多的解决思路和理论依据。     

多工位装配过程夹具系统公差和维护综合优化设计

提出一种面向二维多工位装配过程、综合考虑装配夹具系统全寿命周期成本、产品零件孔制造成本和产品质量损失成本的公差和维护综合优化方法。分析多工位装配尺寸偏差传递关系,建立多工位装配过程产品质量损失模型。然后根据4-2-1夹具定位原则,构建考虑夹具磨损过程损失的夹具定位销副偏差统计数字特征模型。继而发展了以夹具系统全寿命周期成本、零件孔制造成本和和产品质量损失成本为装配总成本最小化的定位销公差、零件孔公差与更换周期优化模型。以汽车侧围装配过程为例,分别研究定位销公差、零件孔公差、定位销更换周期、配合间隙、平均磨损率和磨损率方差对装配总成本的影响,并优化设计定位销公差、零件孔公差和定位销更换周期。所提出的综合优化设计方法比采用定位销等公差设计、零件孔等公差设计、定位销与零件孔等公差设计和定周期更换设计的装配总成本分别减少了16.25%、11.31%、39.93%和13.54%。该方法为产品装配夹具系统高质量低成本设计提供了一种新的途径。     

装配尺寸路径图的建立与应用

用带下标的英文字母明确装配体中各个要素的所属零件及各个零件间的定位状况,为正确建立装配尺寸关系提供依据;提出目标尺寸概念,指出选取目标尺寸应遵循的"独立性"与"完整性"两个原则;在"路径最短"及"高精度优先"两项原则的基础上,提出建立路径图的两个基本要点,由此确定出各个目标尺寸的唯一形成路径——装配尺寸基础路径图;根据各零件的工艺特征及尺寸标注习惯等要求对基础路径图进行优化而建立最终的装配尺寸路径图,从而确定出装配体中各个零件的合理尺寸标注模式;根据装配尺寸路径图还能够建立全体目标尺寸的装配尺寸式系,从而得到完整的全相关装配尺寸模型,在全体目标尺寸及公差的驱动下,能求解出全部零件尺寸及公差,可更好地满足计算机辅助公差设计及参数化设计的需求。     

基于UG的装配公差图自动搜索算法的研究

当前装配公差分析和设计一般是基于尺寸链原理,只考虑了装配零件的尺寸公差,并未考虑装配零件的形位公差,因此基于尺寸链原理的装配公差分析方法是有缺陷的。如何能使装配公差分析更贴近实际零件的装配是要解决的问题。基于图论知识和UG二次开发平台,对三维装配体模型建立装配链图,在此基础上查找零件几何公差的传递路径,为进一步探究零件几何公差的积累效应、装配体公差分析和综合应用做准备。     

PRO/E CE/TOL在模具设计中的应用

三维设计软件以其卓越功能引领设计领域,PRO/E作为其中一种有着强大的功能。本文运用PRO/E软件对模具总成进行设计及装配,同时运用自带的PRO/E中的CE/TOL(公差分析)模块对所设计的模具零件及零件装配的全过程进行公差分析与综合优化,确定各零件的公差在装配过程中影响关键尺寸公差的约束及其敏感度,通过改变个别零件的关键尺寸的公差约束即公差的优化过程,达到模具装配后的合理间隙,减少发生干涉和精度超标的概率,提高模具精度。     

基于CE/TOL的滚刀轴部件公差分析与优化

为了合理地分配滚刀轴部件各零件的尺寸与公差,优化产品设计,利用Pro/E软件对滚刀轴部件进行三维设计。根据功能要求确定分析目标,将分析目标作为封闭环,借助装配模型确定尺寸回路。使用公差模块CE/TOL分析该尺寸链中各组成环对分析目标的影响程度,依据尺寸的贡献度和敏感度找出对封闭环影响最大的关键尺寸。优化关键尺寸及其公差,从而在满足功能的前提下扩大零件公差,提高零件合格率,降低生产成本。     

提高无键过盈联接装配精度的方法

经过车、铣、刨、磨、镗、焊、锻及热等多道制作工序而成的零件,只要是符合图样的几何尺寸和形位公差要求的零件都是合格的零件,合格零件都可以进入装配工序进行装配。装配作业是机械制造过程的最后阶段,装配工作的好坏对生产进度,产品质量都有着很大的影响。百分之百合格的零件,尺寸也是在一个合格公差的范围内,由于装配工艺的不合理,累计误差的存在,有时就不能实现产品设计的要求。     

尺寸链仿真技术在精密装配中的应用试验

微系统产品对整机装配精度要求非常高,而装配精度直接受限于零件各配合尺寸的公差设计。如何既满足装配精度,又有效降低零件加工成本,成为公差设计急需研究的方向。针对上述问题,设计了典型样件,通过尺寸链仿真分析,将所需装配精度分解到各配合尺寸公差,检测结果表明该技术实现了设定的装配精度,可以作为公差设计的指导工具。     

基于制造公差的复杂机械产品精准选配方法

针对复杂机械产品多质量要求下的选配问题,提出一种基于遗传算法的选择装配方法。以装配精度和装配成功率作为质量要求的评价指标,建立了综合考虑形位公差与尺寸公差的装配质量综合优化模型,能够在保证尺寸公差装配精度的前提下,有效降低产品的形位公差。同时提出了基于影响度的选配优先级评价模型,有效地提高了遗传算法的收敛速度。根据复杂机械产品尺寸链的特点,提出一种以零部件为单元的编码方式,并建立了映射关联矩阵描述多个公差项间的关联关系,综合Pareto支配强度及密集度生成适应度函数作为个体评价规则,以某发动机曲柄连杆机构的装配为例验证了该方法的可行性和有效性。     

基于特征的公差表示方法与实现

公差的存储表示是公差分析和公差综合的基础 ,提出一种几何公差的计算机辅助表示方法。利用特征的几何公差结构块 ,建立各种公差带的空间表示函数 ,并计算其三维空间中相应自由度的允许变动量。通过图论方法给出公差图的形式化定义 ,设计公差图的数据结构 ,可实现零件公差的计算机存储表示。最后给出零件实例来验证所提出的方法。     

A hybrid method of artificial neural networks and simulated annealing in monitoring auto-correlated multi-attribute processes

In mechanical assemblies, individual components are placed together to deliver a certain function. The performance, quality, and cost of the mechanical assembly are significantly affected by its tolerances. Toleranced dimensions inherently generate an uncertain environment in a mechanical assembly. This paper presents a proper method for tolerance analysis of mechanical assemblies with asymmetric tolerances based on an uncertainty model. This mathematical approach is based on fuzzy logic and tolerance accumulation models such as worst-case and root-sum-square methods. A fuzzy-based tolerance representation is developed to model uncertainty of tolerance components in the mechanical assemblies. According to this scheme, toleranced components are described as fuzzy numbers with their membership functions constructed using the statistical distributions of manufactured variables. In this way, the uncertainty of assembly requirements and accumulation of tolerances are represented in the form of fuzzy number. In this paper, a new factor, the fuzzy factor, is introduced that helps converting the membership functions into fuzzy intervals that can be used for modal interval analysis. Equations for estimation of percent contributions of individual tolerances are introduced in terms of uncertainty parameter. These equations yield percent contributions of upper and lower bounds of independent variables (manufactured dimensions) on the upper and lower bounds of dependent variables (assembly dimensions). The proposed method is applied to an example, and its results are discussed.     

A continuous tolerance system

This paper analyzes the current ISO tolerance systems (ISO 286-1¹ and ISO 286-22) and presents new formulas that allow the aggregation of the tolerance system in a simple way. The approach used makes it possible to compute the tolerances in a continuous manner with respect to both dimension and grade of tolerance (quality). The results are always within the tolerances tabulated in the ISO 286-1' and 286-22 Standards. This continuous approach is suitable for optimization in design and automation in tolerancing on computer-assisted design (CAD) systems. The paper proposes a tolerancing approach closer to the modern tolerancing philosophy as given by the Taguchi methods.     

Tolerance analysis of mechanical assemblies based on modal interval and small degrees of freedom (MI-SDOF) concepts

Tolerance analysis is a key analytical tool for estimation of accumulating effects of the individual part tolerances on the design specifications of a mechanical assembly. This paper presents a new feature-based approach to tolerance analysis for mechanical assemblies with geometrical and dimensional tolerances. In this approach, geometrical and dimensional tolerances are expressed by small degrees of freedom (SDOF) of geometric entities (faces, feature axes, edges, and features of size) that are described by tolerance zones. The uncertainty of dimensions and geometrical form of features due to tolerances is mathematically described using modal interval arithmetic. The two concepts of modal interval analysis and SDOF are combined to describe the tolerance specifications. The algorithm is presented which explains the steps and the procedure of tolerance analysis. The proposed method is compatible with the current GD&T standards and can incorporate GD&T concepts such as various material modifiers (maximum material condition, least material condition, and regardless of feature size), envelope requirement, and bonus tolerances. This method can take into account multidimensional effects due to geometrical tolerances in tolerance analysis. The application of the proposed method is illustrated through presenting an example problem and comparing results with tolerance charting method.     

尺寸公差与形位公差混合优化分配

为解决尺寸公差与形位公差混合优化分配问题,提出了一种公差优化分配方法.根据成本-公差函数和尺寸公差与形位公差的关系,建立了以最小制造总成本为目标的非线性公差混合优化分配模型.该模型的约束包括装配尺寸链的功能要求和加工能力.求解该模型能同时得到优化的尺寸公差和形位公差.最后,分别用公差混合优化分配法和传统方法对一个实例进行公差分配,结果表明所提方法比传统方法更优越.     

Closed-form solutions for multi-objective tolerance optimization

Component tolerances have important influence on the cost and performance of products. In order to obtain suitable component tolerances, multi-objective tolerance optimization model is studied, in which the combined polynomial and exponential functions are used to model manufacturing cost. In this paper, analytical methods are proposed to solve the multi-objective optimization model. In this model, the objective function is not a monotone function, and it is possible that the assembly tolerance constraint, including worst-case method and root sum square method, is inactive. Therefore, two closed-form solutions are proposed for each component tolerance in terms of the Lambert W function. When the assembly tolerance constraint is not considered, the component tolerances are obtained and named as the initial closed-form solutions. If the initial solutions satisfy assembly tolerance constraint, it is the final value of optimal tolerances. Otherwise, constrained optimization model is established and Lagrange multiplier method is applied to obtain the new closed-form solution of component tolerances as the final value of optimal tolerances. Several simulation examples are used to demonstrate the proposed method.     

Multibody approach for tolerance analysis and optimization of mechanical systems

A multibody approach is suitable for tolerance analysis of mechanical systems since multibody formulation can directly consider part-level tolerance variables. In this study, procedures for performing tolerance analysis and corresponding sensitivity analysis for spatial multibody systems are proposed. First, statistical formulation for performing multibody system tolerance analysis is developed to obtain system level tolerance for given part-level tolerances. One very useful aspect of the proposed formulation is that in the process of computing system tolerance, the sensitivity of system tolerance with respect to part-level tolerances can be additionally obtained. The kinematics of spatial multibody systems has been redefined in terms of both generalized coordinates and part-level tolerance variables. Tolerances in geometry of a body are specified in terms of the variations in relative locations of joint definition points and relative distance between them. Tolerances in the joint kinematics are defined through variations in vector closure equations and orthogonality equations that are two fundamental constraint equations for most kinematic joints. To demonstrate the validity and effectiveness of the proposed tolerance analysis procedure, tolerance analysis of a spatial 4-bar mechanism and tolerance optimization are performed.     

Dimensional and geometric tolerance design based on constraints

The paper presents a computer-aided approach of dimensional and geometric tolerance design. The method allows a designer to specify synthetically dimensional and geometric tolerances, including tolerance types and values. Firstly, tolerances are classified as self- and cross-referenced tolerances, and the rules for tolerance types design are presented. Secondly, the stack-up of 3D feature variation is formulated as a set of stack-up constraints (equation constraints), and the variation specified by tolerance forms tolerance constraints (inequality constraints). Tolerance value design is represented as the combinatorial optimization problem. The application of the variation and tolerance constraints to specify tolerance values is studied. Finally, a tolerance design example is used to illustrate the method.     

Dimensional and geometrical tolerance balancing in concurrent design

In conventional design, tolerancing is divided into two separated sequential stages, i.e., product tolerancing and process tolerancing. In product tolerancing stage, the assembly functional tolerances are allocated to BP component tolerances. In the process tolerancing stage, the obtained BP tolerances are further allocated to the process tolerances in terms of the given process planning. As a result, tolerance design often results in conflict and redesign. An optimal design methodology for both dimensional and geometrical tolerances (DGTs) is presented and validated in a concurrent design environment. We directly allocate the required functional assembly DGTs to the pertinent process DGTs by using the given process planning of the related components. Geometrical tolerances are treated as the equivalent bilateral dimensional tolerances or the additional tolerance constraints according to their functional roles and engineering semantics in manufacturing. When the process sequences of the related components have been determined in the assembly structure design stage, we formulate the concurrent tolerance chains to express the relations between the assembly DGTs and the related component process DGTs by using the integrated tolerance charts. Concurrent tolerancing which simultaneously optimizes the process tolerance based on the constraints of concurrent DGTs and the process accuracy is implemented by a linear programming approach. In the optimization model the objective is to maximize the total weight process DGTs while weight factor is used to evaluate the different manufacturing costs between different means of manufacturing operations corresponding to the same tolerance value. Economical tolerance bounds of related operations are given as constraints. Finally, an example is included to demonstrate the proposed methodology.