基于产品配合图的装配顺序自动规划

装配顺序规划( ASP) 是基于装配建模的装配工艺顺序的自动规划生成, 是DFA( 面向装配的设计) 的关键技术之一。本文采用配合条件法进行装配顺序求解, 装配体采用其部件与部件间的配合关系来描述, 从部件间的配合关系可得到其装配体配合图。本文还在原算法的基础上添加了一些约束来降低算法的计算量, 使得算法更为简洁。该法在AutoCAD®设计平台上实现, 并采用装配体实例加以检验。     

基于功能尺寸最短路径的零件尺寸标注模式的设计

机械零件的尺寸标注模式有多种。尺寸标注模式影响着机械产品的精度和制造成本。为获得零件尺寸合理的标注模式,建立了包含零件尺寸标注所有可能模式的装配尺寸联系路径图;以满足装配体功能尺寸形成路径最短为目标,基于装配尺寸链最短路径原则和最短路径问题的求解,通过2种方法建立了装配体功能尺寸最短路径生成树。功能尺寸最短路径生成树确定了该装配体所有零件唯一合理的尺寸标注模式。研究结果为零件尺寸标注的合理设计提供了新途径,且其易于计算机辅助实现。     

面向功能的三维装配公差链的自动生成

 基于TTRS理论,提出了3类变动几何约束.由CAD中的装配信息可唯一确定配合树(MT),分析了配合树的性质,配合树之间通过互参考变动几何约束彼此连接构成回路.基于配合树,给出了的回路和三维装配公差链的生成方法.实例分析验证了此方法的有效性.     

配制配合在精密散装轴承轴系中的应用

大型光测仪器中采用的精密散装轴承轴系尺寸较大,精度要求很高,如果仍然采用互换性生产,则会因加工和检验设备的限制而无法保证配合公差的要求.本文叙述了大尺寸精密散装轴承轴系在加工、测量、装配、维修和生产组织等方面的特点,以及在生产方式上采用的配制配合.同时还结合公差带图和配合公差带图说明了先加工件的选择原则、配制件制造公差的计算方法和精密测试在保证配合性质方面的重要作用.     

航空发动机装配尺寸链公差设计方法研究

介绍了航空发动机装配尺寸链的概念以及封闭环的特征,详细分析了3种适用于航空发动机的典型公差设计分析方法.通过几种典型的航空发动机装配精度要求算例,研究了公差设计分析方法的特点,并结合航空发动机结构和装配特点,提出了3种公差设计分析方法在航空发动机领域的适用性,以及对发动机公差设计运用的展望.     

工序尺寸换算中假废品的判定及补救措施研究

在工艺基准和设计基准不重合的情况下,在零件加工过程中采用极值法计算工艺尺寸链时经常会出现工序尺寸不合格而最终设计尺寸可能合格的“假废品”现象。为此,以工艺尺寸链极值法计算的特点为基础,对假废品产生的原因进行了分析。为了便于在零件加工过程中判定假废品,通过将工序尺寸作为封闭环尺寸,建立并计算新的尺寸链,得到间接保证设计尺寸合格的必要不充分条件,并结合先于工序尺寸生成的组成环尺寸的实际偏差,提出了一种新的判定假废品工序尺寸公差范围的计算方法和流程。为了避免假废品转化为设计尺寸不合格的真废品,提出了一种对后续加工尺寸进行公差压缩的补救措施。根据工艺尺寸链中各组成环尺寸的相互补偿关系,分析了后续加工工序中公差压缩后尺寸极限偏差和公差的计算方法和流程。研究结果可为实际生产中假废品的判定和补救提供指导。     

基于SDT的平面尺寸公差模型研究及应用

公差建模是在CAD系统中进行准确无误的公差表述,并对其语义作出正确合理的解释.为了在CAD系统中表示出公差的工程语义,提出一种基于SDT(small displacement torsor)的平面尺寸公差建模方法.根据约束条件将平面尺寸公差分为2类,研究了不同类型尺寸公差的约束关系,建立相应的尺寸公差数学模型,完整地表示出尺寸公差的工程语义.最后用此模型对公差综合进行验证,在满足装配要求的条件下,给出SDT中各个分量,得出平面尺寸的公差值,结果表明该方法合理有效.     

基于Solid Edge的尺寸链公差分配研究

Solid Edge是易学、高效、易用的机械计算机辅助设计系统，支持从三维到二维工程图的自动生成。但尺寸链的计算与分配仍需要手工进行，用VC 在Solid Edge的基础上进行开发，编制了尺寸链计算与分配模块，实现了计算机完成尺寸链的计算与分配，并且在二维工程图中自动标注尺寸公差，为基于尺寸链的加工精度分配提供依据，增强了Solid Edge机械产品的设计能力。     

公差设计特征专家系统

介绍了一个服务于公差分析与综合的特征专家系统。该特征专家系统应用在设计环境中,与公差设计中包括尺寸链、公差分析、公差综合各个环节的密切关联,很好地支持了公差分析与公差综合的进行。论文最后给出了运行实例。     

计辅工艺设计中工序尺寸处理自动化

本文介绍了PGCAPP系统中轴套类零件轴向工序尺寸及公差计算程序模块。该模块设计采用尺寸跟踪法原理。本文较详细介绍了设计方法与步骤,并给出一些数学模型和制定原则。PGCAPP系统通过对零件轴向尺寸和公差、加工端面粗糙度等信息描述后,由该模块自动计算获得各工序尺寸与公差,当工序图生成时自动标注于所定部位。     

Optimisation of assembly sequences for compliant body assemblies

Multi-sequence modelling is proposed to optimise assembly sequences for compliant body assemblies such as automotive and aircraft bodies. Multi-sequence modelling is composed of assembly modelling, assembly sequences, tolerance analysis, and assembly operations. Assembly modelling describes the geometric modelling through the liaison graph, which is based on assembly sequence optimisation. Assembly sequences provide information for assembly sequence optimisation. Three-dimensional tolerance analysis is employed to evaluate assembly operations, which is different from previous conceptual tolerance analysis. A genetic algorithm is presented to optimise assembly operations among components. Results show that different sequences lead to a different tolerance of key product characteristics because assembly operations among components are not identical. This paper provides the flowchart of optimising assembly sequences according to the tolerance of key product characteristics.     

Modelling and analysis of selective assembly using Taguchi's loss function

An assembly is the integrative process of joining components to make a completed product. It brings together the upstream process of design, engineering and manufacturing processes. The functional performance of an assembled product and its manufacturing cost are directly affected by the individual component tolerances. But, the selective assembly method can achieve tight assembly tolerance through the components manufactured with wider tolerances. The components are segregated by the selective groups (bins) and mated according to a purposeful strategy rather than being at random, so that small clearances are obtained at the assembly level at lower manufacturing cost. In this paper, the effect of mean shift in the manufacturing of the mating components and the selection of number of groups for selective assembly are analysed. A new model is proposed based on their effect to obtain the minimum assembly clearance within the specification range. However, according to Taguchi's concept, manufacturing a product within the specification may not be sufficient. Rather, it must be manufactured to the target dimension. The concept of Taguchi's loss function is applied into the selective assembly method to evaluate the deviation from the mean. Subsequently, a genetic algorithm is used to obtain the best combination of selective groups with minimum clearance and least loss value within the clearance specification. The effect of the ratio between the mating part quality characteristic's dimensional distributions is also analysed in this paper.     

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．     

A New Method in Selective Assembly to Minimize Clearance Variation for a Radial Assembly Using Genetic Algorithm

Selective assembly is the method of obtaining high-precision assemblies from relatively low-precision components. A relatively smaller clearance variation is achieved than in interchangeable assembly, with the components manufactured with wider tolerance. In selective assembly, the mating parts are partitioned to form selective groups with smaller tolerance, and the corresponding groups are assembled interchangeably. The mating parts are manufactured in different machines, using different processes, and with different standard deviations. Therefore, the dimensional distributions of the mating parts are not similar. In selective assembly, the number of parts in the corresponding selective groups is not similar and will result in surplus parts. The clearance variation is also very high. In this article, a new method is proposed in selective assembly. Instead of assembling components from corresponding selective groups, the components from different combination of selective groups can be assembled to achieve minimum clearance variation. Genetic algorithm is used to find the best combination of the selective groups for minimizing the clearance variation. A case of hole and shaft (radial) assembly is analyzed in this article, and the best combination is obtained to minimize assembly clearance variation. The assembly is done in three stages to completely use all the components. The best combination for the selective groups and the resulting clearance variations are tabulated. The surplus parts are minimized to a large extent.     

Genetic algorithm for minimizing assembly variation in selective assembly

Selective assembly is a method of obtaining high-precision assemblies from relatively low-precision components. In selective assembly, the mating parts are manufactured with wide tolerances. The mating part population is partitioned to form selective groups, and corresponding selective groups are then assembled interchangeably. If the mating parts are manufactured in different processes and in different machines, their standard deviations will be different. It is impossible that the number of parts in the selective group will be the same. A large number of surplus parts are expected according to the difference in the standard deviations of the mating parts. A method is proposed to find the selective groups to minimize the assembly variation and surplus parts when the parts are assembled linearly. A genetic algorithm is used to find the best combination of the selective groups to minimize the assembly variation. Selective assembly is successfully applied using a genetic algorithm to achieve high-precision assemblies without sacrificing the benefit of wider tolerance in manufacturing.     

Maximising manufacturing system efficiency for multi-characteristic linear assembly by using particle swarm optimisation in batch selective assembly

Quality of an assembly is mainly based on the quality of mating parts. Due to random variation in sources such as materials, machines, operators and measurements, even those mating parts manufactured by the same process vary in their dimensions. When mating parts are assembled linearly, the resulting variation will be the sum of the mating part tolerances. Many assemblies are not able to meet the assembly specification in the available assembly methods. This will decrease the manufacturing system efficiency. Batch selective assembly is helpful to keep the assembly requirement and also to increase the manufacturing system efficiency. In traditional selective assembly, the mating part population is partitioned to form selective groups, and the parts of corresponding selective groups are assembled interchangeably. After the invention of advanced dimension measuring devices and the computer, today batch selective assembly plays a vital role in the manufacturing system. In batch selective assembly, all dimensions of a batch of mating parts are measured and stored in a computer. Instead of forming selective groups, each and every part is assigned to its best matching part. In this work, a particle swarm optimisation based algorithm is proposed by applying the batch selective assembly methodology to a multi-characteristic assembly environment, to maximise the assembly efficiency and thereby maximising the manufacturing system efficiency. The proposed algorithm is tested with a set of experimental problem data sets and is found to outperform the traditional selective assembly and sequential assembly methods, in producing solutions with higher manufacturing system efficiency.     

CAD-based integrated tolerancing system

Assembly tolerance analysis involves the determination of tolerances of critical dimensions. This paper addresses two basic areas in tolerance analysis and allocation. (1) Dimension normalization, which identifies the relevant functional dimensions. A new algorithm called the dimension block diagram (DBD) algorithm for dimension normalization is presented. (2) Dimension representation, which provides a robust framework for representing the tolerance chain. A new dimension representation framework using Assembly Dimensional Tolerance (ADT) tree is presented. The two methodologies are automated and integrated within the framework of a CAD system using an Expert System. A computer test bed software has been developed demonstrating the viability of this approach.     

Liaison concatenation – A method to obtain feasible assembly sequences from 3D-CAD product

Selection of optimized assembly sequence from the available feasible assembly sequences is significantly essential to achieve cost-effective manufacturing process. To achieve this, at the outset, generation of feasible assembly sequences with topological, geometrical, precedence and stability conditions should be generated. The increase of part count in a product results huge number of assembly sequences, the Liaison matrix/Liaison graph generated based on the connections between the assembly components eliminates non-possible assembly sequences at the initial phase. There exist methods namely cut-set method to eliminate the non-possible assembly sequences using liaison graph. In this paper a new approach to eliminate the non-possible assembly sequences based on liaisons is described and the correctness of the methodology is illustrated with an example. The methodology to obtain the feasible assembly sequences is also briefly described and presented. An algorithm to interface with the CAD environment is described briefly.     

Integration of geometric variation and part deformation into variation propagation of 3-D assemblies

This paper introduces a novel modelling method for variation propagation calculation of 3-D assemblies taking into account geometric variation and part deformation, which are neglected in most models in tolerance analysis. Initially, numerical studies are carried out in order to illustrate the characteristics of strain distribution in components and contact forces on the mating surfaces of a 3-D assembly. According to these characteristics, a linear equivalent model using springs to represent the elastic mating surfaces with geometric variation was presented. Then, the equilibrium criterions corresponding to actual contact situations and iterative searching algorithm of the equilibrium status of contacting were developed. The proposed modelling and calculation method were finally applied to the assembly of two machined parts, on which finite-element analyses and experimental tests were conducted to validate the effectiveness and accuracy. This linear contact model also shows an important advantage on modelling and calculating efficiency, which enable the practical application to variation propagation calculation in both tolerance design and assembly process.