Optimal Tolerance Allocation Based on Fuzzy Comprehensive Evaluation and Genetic Algorithm

It is very important to know how to allocate tolerances economically for parts in a CAD/CAM system because this directly affects the machining costs of the parts. A new approach based on fuzzy comprehensive evaluation (FCE) and a genetic algorithm (GA) is presented to obtain a rational tolerance allocation for the parts. First, the current methods for tolerance allocation are reviewed in detail. Then, FCE is used to evaluate the machinability of a part; a new optimal model, which can fully exploit DFA (design for assembly) and DFM (design for manufacturing), is established by combining the functional sensitivity factors and machinability factors of parts. A genetic algorithm (GA) is developed and used to verify the feasibility of the above method; the computed result shows that the method can produce tolerance allocations economically and accurately.     

Composite Planar Tolerance Allocation with Dimensional and Geometric Specifications

A new optimal approach for planar tolerance allocation is proposed in which dimensional and orientation geometric specifications are included. To deal with the increased complexity of planar tolerance analysis, a special relevance graph (SRG) is used to represent the relationships between manufactured elements and their size and tolerance information. In addition, the SRG is also applied for the geometric dimensions and tolerances. Using a suitable algorithm, planar tolerance chains that include geometric specifications can be generated automatically during process planning. Through a graph based analysis, stacks of tolerance zones are obtained. The resultant tolerance zone contains all of the composite links of the tolerance zones. The links are assigned according to the process capacities, which can be considered as constraints. A linear optimal model is established to solve the tolerance allocation problem. A practical example is used to demonstrate the feasibility and effectiveness of the proposed method.     

A Statistical Dimension and Tolerance Design for Mechanical Assembly Under Thermal Impact

Most materials change length as they change temperature. As a result of this change, the dimensions and tolerances of a product become at variance with the design values. Hence, thermal effects must be taken into account when designing a product that will undergo temperature cycling. In this regard, a simultaneous optimisation of component dimensions and tolerance values at various temperatures is needed. The approach first generates a set of experimental data through Monte Carlo simulation, based on various combinations of parameters and tolerance levels as inputs. Then, the data are converted into a total cost as response values before applying response surface methodology (RSM) for statistical analysis and optimisation. he response value includes quality loss, tolerance cost, and failure cost, which reflect the combined effect of the parameter and tolerance values assigned. The results provide designers with optimal component parameters and tolerance values, and the critical components and the response function. The approach can also guarantee that the parameter and tolerance values found remain within tolerance for the temperature variation. Then, the product can function as intended under a wide range of temperature conditions for the duration of its life. ID="A1"Correspondance and offprint requests to:Dr A. Jeang, The head of Department of Industrial Engineering, Feng Chia University, PO Box 25–150 Taichung, Taiwan. E-mail: ajeang@fcu.edu.tw     

Product Grouping and Resource Allocation in Multiline Manufacturing Systems

This paper studies the product grouping problem and the resource allocation problem in the design of manufacturing systems where multiple production lines are used to manufacture a range of products. Each production line in the product grouping problem is dedicated to manufacturing a group of products. A mathematical model is developed to determine the number of product groups and the composition of each product group in the manufacturing system. For the resource allocation problem, a mathematical model is developed to determine the optimal resource allocation scheme for each production line and the optimal inventory level for each product. A genetic-based algorithm is proposed to solve the product grouping problem and the resource allocation problem simultaneously, and its results are compared to those of the conventional heuristic approaches. The proposed genetic approach is a simple but effective means of solving these problems.     

系统可靠性退化的单元责任Shapley值分配模型

针对系统可靠性退化过程中其组成单元的责任追溯问题,基于合作博弈思想提出一种系统可靠性退化的单元责任Shapley值分配模型,并给出了模型的构建过程和求解步骤。在确定单元退化联盟的形成规则、种类和数量的基础上,求解出了每种单元退化联盟的责任分配权重;提出并证明了基于联盟组成单元结构关系的责任分配特征函数;运用仿真方法验证了模型求解结果的正确性和合理性。最后结合实例研究,说明了所提模型的可行性和有效性。     

某型手枪击发机构装配公差分析与信息化集成研究

针对轻武器行业人工修锉问题和企业数字化设计与制造需求,利用VSA软件进行了某手枪击发机构三维装配公差分析,得到了与实际装配情况一致的结果,说明基于三维模型的计算机辅助公差设计技术适用于轻武器设计制造公差控制,在轻武器数字化设计制造过程中可以为实际设计、制造提供支持,减少工程更改。在此基础上提出了CAT在数字化协同设计和制造环境下系统信息化集成框架、应用模式、数据模型和数据交互方式等,为后续系统的开发、集成与应用提供了参考。     

Unbalanced Tolerance Design and Manufacturing Setting with Asymmetrical Linear Loss Function

Taguchi has developed many loss functions, and many of the situations are approximated by the quadratic function. Using a quadratic loss function when the actual loss function is non-quadratic may cause the incorrect input parameter levels to be chosen. In certain situations, a linear loss function is more appropriate in industrial applications. If tolerance design is unbalanced, setting the process mean at the nominal will not minimise the expected quality loss. Thus, two specific models of linear loss function are discussed for unbalanced tolerance design. One is an asymmetrical linear loss function and the other is a truncated asymmetrical linear loss function. The optimal process means for these two loss functions are also compared with each other. The results show that the process mean should be shifted a little from the nominal such that the expected quality loss is minimised.     

外翼翼盒对接面装配协调的容差分析及工艺优化

随着飞机结构和工艺的发展,飞机制造的协调准确度要求越来越严格,因此利用数字化手段进行容差分析,实现工艺优化己成为必然趋势。通过对飞机部件装配的误差累计分析与容差优化理论进行研究,提出了基于软件仿真分析解决实际制造中尺寸工程问题的方法,并利用基准统一原则,对某机型外翼翼盒对接面的装配协调要求进行优化分析。结果表明,该理论与技术方法的应用改善了翼盒对接面的工程及工艺方案,提高了装配协调准确度分析的效率,具有一定的工程应用价值。     

产品变型主模型的参数标定与容差划分方法

为了提高变型设计结果的有效性,提出对变型设计主模型中的参数进行标定与容差划分的思想。针对参数标定问题,通过构建定制产品相关的质量特性指标及其综合模型,并基于定制产品实例数据得到的关键参数取值区间作为约束条件,运用多目标优化的遗传算法,计算得到使综合指标取值最佳的参数标定值。针对容差划分问题,基于田口式三步设计方法,分析参数变化造成的产品成本损失以及性能偏移,在综合指标允许的范围内,得到参数允许的容差区间。通过参数标定和容差划分,使得基于产品变型设计主模型派生得到的定制产品实例都能满足质量特性指标的需求,从而提高成功派生变型设计实例的比率。最后,通过一个实例对上述原理和方法进行验证。     

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。     

Datum-Hierarchy Tree Method for Tolerance Analysis of Plating and Heat Treatment Operations

This paper presents a new method for the tolerance analysis of plating and heat treatment operations. It is suitable for both manual and computerised tolerance analysis. The new method uses a datum-hierarchy tree to identify tolerance stacks and a stock removal set matrix to calculate the positions of surfaces created during the manufacturing sequence. A tolerance chart is used to associate stock removal sets with the geometry of the workpiece, to show the manufacturing sequence, and to record the operation data and the tolerance analysis results. Plating and heat treatment operations are represented as edges in the tree, so that for each operation (edge) the input and output nodes represent consecutive surfaces in a stock removal set. Rules are given for calculating the tolerance stackups and the positions of the surfaces in the stock removal sets. The method is illustrated with an example.     

The Adaptive Branch and Bound Method of Tolerance Synthesis Based on the Reliability Index

Tolerance synthesis is a stochastic optimisation problem. It can be converted into deterministic optimisation by replacing stochastic design function constraints with deterministic reliability index constraints. This problem was first approached and solved with both a heuristic algorithm TOL-M and a feasible directional method. In this paper, we propose an adaptive branch and bound method, which is a coarse to fine positioning technique, to resolve it. The proposed heuristic algorithm significantly outperforms the previous algorithms for the optimum solution. Although the adaptive branch and bound algorithm is heuristic and does not guarantee a global optimum, we give a theoretical reason why it provides a superior local minimum to both the TOL-M and the feasible directional method. Issues of the relationship between yield and reliability index are addressed. Various related results in the literature are compared with ours to show that some reliability indices are less important than others and can be violated without suffering too much loss of yield.     

基于价值工程与模糊可靠度装配尺寸链公差优化分配

将模糊数学原理引入到装配尺寸链公差分配中,提出了装配尺寸链装配模糊可靠度的概念。从公差与制造成本之间的关系出发,建立了以制造成本为目标函数、装配尺寸链装配模糊可靠度为约束条件的公差优化分配数学模型,并给出一实例。     

Concurrent Optimisation of Parameter and Tolerance Design via Computer Simulation and Statistical Method

This study optimises component parameters and component tolerances simultaneously via computer simulation and response surface methodology (RSM). The approach first generates a set of experimental data through computer simulation, then the data are converted to a total cost as a response value before applying RSM for statistical analysis and mathematical optimisation. The response value (total cost) includes quality and related costs which reflect the combined effect of the parameter and tolerance values being assigned. The results provide designers with the optimal component design values, the critical components, and the response function of a product or process design, which are very important to know during design activities as they give designers information about repeated applications, accurate feedback and appropriate suggestions, particularly under uncertain design conditions. Three examples are provided: They are mechanical assembly design, machining process planning, and electronic circuit design.     

考虑路面附着和自适应时间系数影响的车道保持控制

分析了路面附着系数对车辆控制的影响,根据车辆线性二自由度模型与一定的预瞄信息获得车辆-道路动力学模型,并给出了基于Brush轮胎模型的路面附着系数估计算法。针对车道保持转向过程中的车身横摆角速度与转向角的时间延迟现象,提出与路面附着系数有关的自适应时间系数,并加入到车辆-道路动力学模型中。在此基础上,基于滑模控制理论设计横摆角速度滑模控制器来跟踪期望车辆状态,获得理想的转向角。最后,进行了基于CarSim/Simulink的仿真计算和硬件在环台架试验,研究结果表明,在不同路面附着系数下考虑自适应时间系数可改善车道保持控制效果。