Active variation compensation in vehicle body conceptual assembly

In this paper, an intelligent heuristic optimization algorithm in active variation compensation is proposed to improve the dimension accuracy in the assembly of a vehicle body by finding the optimal configuration of joint types and the corresponding assembly sequence to compensate variation accumulation in the conceptual assembly process. The authors develop and apply the algorithm to predict variation accumulation and then develop compensating assembly schemes to accomplish optimal joint configuration and assembly sequence compensating for the unnecessary or surplus variation. The essence of the active variation compensation algorithm means measuring and correcting assembling variations during the assembly conceptual process. The paper employs the design of experiment (DOE) approach to verify the heuristic optimization method in the simple application case.     

FLEXIBLE ASSEMBLY FIXTURING LAYOUT MODELING AND OPTIMIZATION BASED ON GENETIC ALGORITHM

There are many welding fixture layout design problems of flexible parts in body-in-white assembly process, which directly cause body assemble variation. The fixture layout design quality is mainly influenced by the position and quantity of fixture locators and clamps. A general analysis model of flexible assembles deformation caused by fixture is set up based on "N-2-1" locating principle, in which the locator and clamper are treated as the same fixture layout elements. An analysis model for the flexible part deformation in fixturing is set up in order to obtain the optimization object function and constraints accordingly. The final fixture element layout could be obtained through global optimal research by using improved genetic algorithm, which effectively decreases fixture elements layout influence on flexible assembles deformation.     

基于敏感度分析的多工位薄板装配过程测点优化设计

提出了一种多工位薄板装配过程测点优化设计方法。该方法利用薄板装配偏差流传递的状态空间模型确定优化设计的目标函数,采用遗传算法实现测点在多工位间坐标位置的优化设计。装配过程实验表明,该优化方法显著提高了测量数据对夹具定位偏差反应的敏感度,有助于在夹具定位偏差产生的早期发现问题,避免因夹具定位偏差引起的产品质量缺陷。     

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。     

装配型架定位器推理设计技术研究与实现

针对装配型架接头定位器设计步骤繁琐、效率低下等问题,在深入分析接头定位器结构和归纳总结接头定位器类型的基础上,提出并实现了接头定位器推理设计算法以及"紧密-松散"装配约束模式,建立了接头定位器推理设计流程.开发了基于CATIA平台的接头定位器推理设计系统,提高了定位器设计效率,缩短了设计周期,取得了良好的效果.     

面向装配系统可靠性分析的车身夹具系统优化设计

为描述多工位车身装配系统的渐进衰退特性,建立了面向车身产品尺寸质量和夹具系统要素的装配系统可靠性模型。结合夹具设计稳定性参数约束,提出了面向白车身装配系统可靠性的车身多工位焊装过程的夹具布局优化方法;在给定夹具布局下构建了定位销制造成本函数,提出多工位夹具定位销磨损率的优化模型并对其进行优化分配。将上述方法应用于侧围装配案例,分析发现优化后装配系统可靠性衰退过程得到较大改善,并有效提升了夹具系统的使用寿命。     

基于UG的车身零件组合检具自动装配方法研究

在UG二次开发平台上,采用模块化设计方法,研究虚拟车身坐标系装配空间确定方法等关键技术,通过定位约束映射和规则推理,给出了在三维模型空间中对检具各组合元件实施坐标变换并进行自动装配的过程,研究实例表明:计算机辅助技术的应用,能有效提高检具自动装配的效率.     

LOCATORS OPTIMIZATION FOR MEASURING FIXTURE DESIGN

"N-2-1" principle is widely recognized in the fixture design for deformable sheet metal workpieces, where N, the locators on primary datum, is the key to sheet metal fixture design. However, little research is done on how to determine the positions and the number of N locators. In practice, the N locators are frequently designed from experience, which is often unsatisfactory for achieving the precision requirement in fixture design. A new method to lay out the N locators for measuring fixture of deformable sheet metal workpiece is presented, given the fixed number of N. Finite-element method is used to model and analysis the deformation of different locator layouts. A knowledge based genetic algorithm (KBGA) is applied to identify the optimum locator layout for measuring fixture design. An example of a door outer is used to verify the optimization approach.     

基于偏差传递的二维多工位装配夹具系统公差可行稳健设计

提出一种基于偏差传递的二维多工位装配夹具系统公差可行稳健设计方法。分析二维多工位装配尺寸偏差传递关系,建立由定位销和零件定位孔(槽)公差引起夹具定位偏差的偏差流状态空间模型。采用数论网格方法对定位销和零件定位孔(槽)公差进行采样,将得到的公差样本代入夹具定位偏差模型,求得夹具定位偏差样本空间,将夹具定位偏差作为状态空间模型的输入偏差,提出基于状态空间模型的二维多工位装配成功率计算方法。继而应用Taguchi正交试验直观分析方法,分析得到影响装配成功率的主要因素即夹具系统定位销副关键公差,运用回归正交组合设计拟合得到二维多工位装配成功率与夹具系统定位销副关键公差的响应面模型。以定位销、零件定位孔(槽)制造成本所构成的装配成本最小化为目标,二维多工位装配成功率为约束,建立二维多工位装配夹具系统定位销和零件定位孔(槽)公差可行稳健设计模型。以汽车车身地板二维三工位装配为例,建立其公差可行稳健设计模型并对该模型进行计算与分析,结果表明在装配成本增幅较小的情况下,采用稳健约束后可显著提高公差设计的可行稳健性。该方法为二维多工位装配夹具系统公差稳健设计提供了一种新途径。     

An integration of assembly planning by design into supply chain planning

A supply chain needs to consider the quality of a product as well as the quality of manufacturing process to satisfy customer requirements at efficient resources planning in terms of safety stock allocation and vendor–buyer coordination. The objective of this article is to use an axiomatic approach to make assembly planning by designing and integrating assembly into supply chain planning, particularly during supply chain reconfiguration. The effect of fixture layout planning, the accuracy of demand forecast, and the supplier capability of providing the required material quality are studied. An optimum supply chain network is configured by combining the product, assembly, and supply chain planning. Heuristic-based optimization is used to validate the proposed solution. The performance of the system is measured in terms of lead time variability, the number of backorders, and the level of safety stock. The results and analysis indicate that the axiomatic approach is capable of reducing the assembly variation and employing necessary fixture layout planning to deliver product intents. In addition, the reduction of assembly variation also reduces the safety stock, lead time variability, and backorders. Finally, management decision making is discussed among other concluding remarks.     

用GAAA优化多阶段装配过程中的夹具布局

改进了遗传算法与蚁群算法的融合（GAAA）算法,利用它来解决多阶段装配过程中二维刚性零件的夹具布局优化问题,合理选择定位销的位置使得灵敏度指标最小化。通过改变遗传算法的变异算子,变异长度以及交叉、变异在蚁群算法中发生的位置,提高了GAAA的稳定性和收敛性。以汽车侧边装配为例验证了改进算法的有效性,结果表明改进后的GAAA比基本的GAAA和蚁群算法求得的结果要好,且收敛速度更快,稳定性更好。     

Selection of preliminary locating and clamping positions on a workpiece for an automatic fixture design system

This paper focuses on the development of heuristic algorithms for selecting the locating and clamping positions on an automatic fixture configuration for a given workpiece for an automatic fixture design (AFD) system. It discusses several issues regarding (i) an informationally complete product model, and (ii) the development of necessary computational modules coupled with a knowledge based system to reason about the workpiece's geometric characteristics for determining the locating and clamping positions. The motivation of the work is to develop a fixturing subsystem as an integral part of the complete CIM environment. A prototype AFD system has been completed in the object oriented programming platform of Wisdom's Concept Modeller. It has used several geometric reasoning mechanisms based on the traditional fixture design principles, and on the principles of collision-free assembly. The system exploits the power of Wisdom's advanced geometric modelling (AGM), and it implements the basic architecture of the proposed knowledge based fixture design system.     

基于夹具配置的薄板件装配偏差分析模型

为提高当前柔性薄板零件装配偏差分析的效率,提出了一种考虑夹具配置的装配偏差分析模型。通过对柔性薄板的定位装配过程的研究,分析了零件偏差、夹具偏差和装配偏差在各个步骤中的变化过程,建立了N-2-1和3-2-1两种夹具定位规则下的装配前后偏差之间的线性关系;根据装配后夹具定位点的释放模式的不同,建立了过定位释放和完全释放两种模式下的装配偏差分析模型。最后,通过分析实例薄板的装配偏差,表明了该装配偏差分析模型的有效性。     

面向大规模定制的夹具优化设计系统

针对大规模定制生产环境下夹具相似性的特点,提出了以工件的加工变形最小和变形最均匀为目标的夹具优化设计方法.基于SolidWorks平台,以VC为开发工具,采用遗传算法和有限元方法相结合的优化方法,开发了参数化夹具优化设计系统,并进行了验证.     

基于虚拟现实的组合夹具组装系统研究

针对计算机辅助组合夹具设计存在的问题,提出了一个基于虚拟现实的组合夹具组装系统。给出了系统的功能模型和体系结构,研究了组合夹具虚拟装配模型、虚拟环境下组合夹具元件的装配定位等关键技术和解决方案。提出了基于多视图的组合夹具虚拟装配模型,该模型便于信息表达和管理,符合虚拟环境的表达和组织原则,解决了元件重复使用问题。提出了基于模糊评判的几何约束自动识别方法,对待装配件与装配基准件的装配特征进行匹配和优化选择,实现装配操作意图的准确捕捉。应用实例表明,原型系统能够很好地支持组合夹具组装设计。     

A systematic method of adaptive joint design considering different assembly sequence in sheet metal product

In sheet metal assembly, not only the component variations and tool errors, but also the component structure (joint type) and assembly process (assembly sequence) affect the final dimensional quality. In this paper, a systematic method for adaptive joint design considering different assembly sequence is proposed to meet the in-process dimensional adjustability of KCs (key characteristics). First, the adaptive characteristic of the sheet metal joint is depicted. Then, the mathematical model in order for concurrently optimizing both joint type and different assembly sequence is presented. How to evaluate the combination of joint type and assembly sequence is carried out according to two conditions: (1) for single KC, and (2) for multiple KCs. The KC confliction is considered to ensure the important KCs. Genetic algorithm is used to resolve the optimization of joint design. An example is chosen to demonstrate our method finally, and various joint designs are acquired according to different assembly sequences by this means. The proposed methods make it possible for us to improve the dimensional quality of product in the design stage.     

基于矢量角度和优化技术的定位误差新算法

在夹具设计中,为了分析与计算定位误差,保证工件的加工精度,提出了基于矢量角度和优化技术的定位误差自动算法.首先通过工件与央具的装配结构关系,建立了经过接触点的定位误差尺寸链搜索方法;然后基于矢量角度的推算,将定位误差尺寸链转化为有约束优化问题,以实现定位误差的自动计算.该方法为计算机辅助夹具设计系统的开发提供了基础理论.     

Assembly Root Cause Analysis: A Way to Reduce Dimensional Variation in Assembled Products

The objective of root cause analysis (RCA) is to make the trouble shooting dimensional error efforts in an assembly plant more efficient and successful by pinpointing the underlying reasons for variation. The result of eliminating or limiting these sources of variation is a real and long term process improvement. Complex products are manufactured in multileveled hierarchical assembly processes using positioning fixtures. A general approach for diagnosing fixture related errors using routine measurement on products, rather than from special measurements on fixtures, is presented. The assembly variation is effectively tracked down into variation in the fixture tooling elements, referred to as locators. In this way, the process engineers can focus on adjusting the locators affected by most variation. However, depending on the assembly process configuration, inspection strategy, and the type of locator error, it can be impossible to completely sort out the variation caused by an individual locator. The reason for this is that faults in different locators can cause identical dimensional deviation in the inspection station. Conditions guaranteeing diagnosability are derived by considering multiple uncoupled locator faults, in contrast to previous research focusing on single or multiple coupled locator faults. Furthermore, even if an assembly is not diagnosable, it is still possible to gain information for diagnosis by using a novel approach to find an interval for each locator containing the true underlying locator variation. In this way, some locators can be excluded from further analysis, some can be picked out for adjustment, and others remain as potential reason for assembly variation. Another way around the problem of diagnosability is to make a higher level diagnosis by calculating the amount of variation originating from different assembly stations. Also, a design for diagnosis approach is discussed, where assembly and inspection concepts allowing for root cause analysis are the objective.     

Machining fixture layout design using ant colony algorithm based continuous optimization method

In any machining fixture, the workpiece elastic deformation caused during machining influences the dimensional and form errors of the workpiece. Placing each locator and clamp in an optimal place can minimize the elastic deformation of the workpiece, which in turn minimizes the dimensional and form errors of the workpiece. Design of fixture configuration (layout) is a procedure to establish the workpiece–fixture contact through optimal positioning of clamping and locating elements. In this paper, an ant colony algorithm (ACA) based discrete and continuous optimization methods are applied for optimizing the machining fixture layout so that the workpiece elastic deformation is minimized. The finite element method (FEM) is used for determining the dynamic response of the workpiece caused due to machining and clamping forces. The dynamic response of the workpiece is simulated for all ACA runs. This paper proves that the ACA-based continuous fixture layout optimization method exhibits the better results than that of ACA-based discrete fixture layout optimization method.     

电阻点焊焊装夹具定位点的优化设计

提出一种适用于电阻点焊焊装夹具的定位点优化设计方法.该方法基于"N-2-1"定位原理,利用有限元计算工件第一基准面上的变形,在建立目标函数时综合考虑夹具工作过程中的多工位状况,并且采用全局收敛效果很好的隔代映射遗传算法作为优化工具来寻找最优点.通过算例分析Ⅳ取不同数值时的夹具定位精度,并将隔代映射遗传算法与小种群遗传算法的收敛效果进行比较,验证了方法的有效性.