基于伪随机点的薄壁件装配公差的有限元分析

针对金属薄壁件刚性小、易变形等特点，提出了基于伪随机点和有限元方法对薄壁件的装配公差进行计算的方法。计算过程中，利用基于数论方法所产生的少量伪随机点代替随机点。算例结果表明，与影响系数法相比，计算精度基本相同。由于计算过程中不需要单独计算刚度矩阵，因此利用该方法可以同时考虑零件装配过程中的弹塑性变形。该方法与Monte Carlo法计算精度基本一致，而计算量仅为Monte Carlo法的1／15。     

一种面向薄壁件装配的公差优化分配方法

为实现薄壁件装配的公差分配优化,提出了一种面向制造和变形的公差优化方法。首先,针对薄壁件变形,采用有限元方法将尺寸链环表示为单元,建立了有限元模型。然后,根据单元有限元模型推导了整体有限元模型,并得到封闭环与组成环变形满足的关系。最后,将变形关系作为公差优化的约束条件,推导了薄壁件装配的公差优化模型。以某型飞机登机门外形组件作为实例,验证了该优化模型的合理性和有效性。     

虚拟装配中装配公差的检验分析

装配性能分析的主要内容之一是装配公差的分析。阐述了虚拟装配系统中公差并行设计的过程，建立了零件尺寸公差与装配体配合公差的模型，利用约束关系图表达了零件尺寸信息与装配体配合关系信息，利用尺寸公差模型与约束关系图通过有关算法生成装配尺寸链。介绍了公差分析的两种方法，并以孔轴的径向配合为例，利用极值法进行装配公差检验，针对检验时出现的各种不合理结果进行了详细分析，并提出了设计公差相应的修改意见。     

柔性件装配偏差的有限元分析

利用有限元法对两个刚性小、形状不同且易变形的柔性件进行装配偏差分析。采用"6-2-1"定位方式对柔性件进行定位,通过影响系数法对柔性件装配偏差进行建模,分析在焊接装配中产生的偏差。结合有限元软件Workbench和MATLAB进行仿真计算,与CATIA TAA分析结果进行对比。研究结果表明:薄板A中测量点偏差的分析结果与CATIA TAA仿真结果存在偏差,而薄板B中测量值与CATIA TAA仿真结果基本相同,验证了分析结果的有效性,为产品分析提供了方便。最后,研究了焊接点个数对柔性件装配偏差的影响,得出柔性件装配偏差随着焊接点个数的增加呈先减小、后增加的趋势。     

公差分析与综合的进展

公差分析与综合是产品设计阶段的一项重要内容，对产品装配质量及成本有直接的影响。详细介绍了公差分析过程中所采用的三种主要方法：极值公差法、统计公差法和Monte Carl仿真方法，以及公差综合过程中目标函数的确定、优化方法的选择等问题。同时指出，为实现公差分析与综合的自动化，提高计算效率，需要更为有效的公差综合与分析算法。     

一种面向可装配性的公差分析方法

基于新一代产品的几何技术规范,分析了装配体的几何信息构成,给出了基于自由度分析的变动域建模原理和变动域-SDT(small displacement torsor)映射关系,采用齐次坐标变换描述了特征几何变动在装配体中的传播和累积,建立了包含零件公差信息和装配间隙信息的装配公差累积模型;构建了公差回路的矩阵表达式,用两个简单装配公差分析实例说明了零件可装配性条件及分析过程;最后以一个工程计算分析实例验证了方法的正确性。     

综合受力变形的薄壁零件公差设计与分析

为了缩短设计周期、降低计算成本、提高产品竞争力,将有限元分析和公差设计相结合的方法应用于薄壁零件的公差设计。根据实际工况下薄壁零件的受力,对详细设计阶段的薄壁零件系统进行静态有限元分析,并将有限元分析的结果带入公差分析,检验实际工况下的薄壁零件的尺寸公差是否满足设计要求,识别出影响实际工况下车门配合最敏感的因素,选出最优方案。试验结果表明,通过该种方法获得的设计方案,在较大程度上提高了车门品质,在达到产品性能要求的同时使设计的目的性更强,并缩短了设计的周期。     

基于有限元法的柔性件装配偏差分析

传统柔性件装配偏差分析所使用的超元刚度矩阵以文件形式存在,导致装配偏差计算流程操作复杂,分析人工成本大大增加。使用有限元法封装装配偏差计算,根据边界条件直接输出装配偏差,从而简化装配偏差计算流程。开展薄板装配试验,通过与仿真装配偏差数据进行对比,验证了该装配偏差计算方法的正确性。     

尺寸公差及装配零件公差的CAD系统

为了保证产品的装配精度,必须合理地确定零件的公差。本文较为详细地介绍了尺寸公差的程序设计,并对装配零件公差的概率计算法作了深入的探讨,编制了该计算方法的软件。     

薄壁件多点柔性加工变形的有限元分析

针对开发薄壁件多点柔性工装系统的需求.研究了薄壁件多点柔性数控加工中的变形问题.通过建立工件加工的有限元模型,利用ANSYS对变形进行静态非线性分析.得到了不同受力、不同间距情况下最大变形量随工件厚度变化的规律,以及不同受力、不同工件厚度情况下最大变形量随支撑间距变化的规律,同时还得到了不同厚度、不同间距情况下最大变形量随切削力变化的规律.分析结果表明:工件厚度变化时,最大变形量近似呈指数规律变化;支撑距离和切削力变化时.最大变形量近似呈线性规律变化.研究结果为更有效解决柔性工装的优化设计和控制问题提供了必要依据.     

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.     

Quality design of fixture planning for sheet metal assembly

Fixturing plays an important role in enhancing weld quality of the sheet metal assembly process. However, traditional experience-based fixturing schemes and purely optimal fixturing schemes are often sensitive to location fluctuation of the designed locators. In this paper a mathematical representation of deterministic locating and total fixturing for a flexible workpiece is developed first, then a virtual beam model is proposed to evaluate the degree of flexibility of the locating points. A quality design model of fixture planning for sheet metal assembly with resistance spot welding is then developed; both the performance expectation and the variance are considered in the formulation of the objective function; a prescribed factor is used to weight the two objectives. The finite element model based on ANSYS software is set up with a spot weld feature employed and genetic algorithm is used in the optimization process. A simple example and an industrial case illustrate the feasibility of the developed model. This work provides a basis for improving the quality of sheet metal assembly in the design phase.     

A parametric study of sheet metal joints for dimensional integrity

The characteristics of joints between parts are one of the most critical issues in variation simulation analysis. This paper presents a parametric study of the dimensional variation characteristics of butt joints and slip joints. These two basic joints encompass the whole domain of joints used in sheet metal assemblies for structural extension. A geometrical model was proposed for predicting the assembly variation in order to take into consideration the possibility of part deformation and tool variation. Butt joints act like rigid bodies in the normal direction. For slip joints, the sensitivity coefficient in the slip direction is a function of tooling variations. The variation from individual part and tooling can be eliminated or substantially reduced if the product structure and assembly process is properly designed. A simple four-part assembly example shows the structure and assembly process. This result provides improved understanding of sheet metal assembly processes and provides a new idea for adaptive product and process design.     

A parametric study of sheet metal joints for dimensional integrity

The characteristics of joints between parts are one of the most critical issues in variation simulation analysis. This paper presents a parametric study of the dimensional variation characteristics of butt joints and slip joints. These two basic joints encompass the whole domain of joints used in sheet metal assemblies for structural extension. A geometrical model was proposed for predicting the assembly variation in order to take into consideration the possibility of part deformation and tool variation. Butt joints act like rigid bodies in the normal direction. For slip joints, the sensitivity coefficient in the slip direction is a function of tooling variations. The variation from individual part and tooling can be eliminated or substantially reduced if the product structure and assembly process is properly designed. A simple four-part assembly example shows the structure and assembly process. This result provides improved understanding of sheet metal assembly processes and provides a new idea for adaptive product and process design.     

金属薄板激光弯曲成形的工艺参数研究

以不锈钢薄板的激光弯曲成形为研究对象,研究其成形的工艺过程及影响因素;介绍实验设备和激光调焦方法。通过实验研究了激光能量因素、扫描速度因素、激光光斑大小和扫描次数等因素对弯曲成形角度的影响。     

Lubricant test methods for sheet metal forming

Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has proven successful and has in a number of examples assisted the substitution of environmentally hazardous lubricants by more friendly ones in industrial production.     

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。     

Simultaneous optimization of fixture and joint positions for non-rigid sheet metal assembly

This paper presents an optimization methodology for non-rigid sheet metal assembly variation by considering part variation, fixture variation, fixture layout, and joint positions, as well as the assembly spring back. The proposed algorithm integrates the finite element analysis (FEA) with a powerful global optimization algorithm, called the mode-pursuing sampling (MPS) method to simultaneously search for the optimal fixture and joint positions in order to minimize the assembly variation. An example application study is presented to demonstrate the optimization procedure and its effectiveness.     

Characterising material and process variation effects on springback robustness for a semi-cylindrical sheet metal forming process

Variation in the incoming sheet material and fluctuations in the press setup is unavoidable in many stamping plants. The effect of these variations can have a large influence on the quality of the final stamping, in particular, unpredictable springback of the sheet when the tooling is removed. While stochastic simulation techniques have been developed to simulate this problem, there has been little research that connects the influence of the noise sources to springback. This paper characterises the effect of material and process variation on the robustness of springback for a semi-cylindrical channel forming operation, which shares a similar cross-section profile as many automotive structural components. The study was conducted using the specialised sheet metal forming package AutoForm™ Sigma, for which a series of stochastic simulations were performed with each of the noise sources incrementally introduced. The effective stress and effective strain scatter in a critical location of the part was examined and a response window, which indicates the respective process robustness, was defined. The incremental introduction of the noise sources allows the change in size of the stress–strain response window to be tracked. The results showed that changes to process variation parameters, such as BHP and friction coefficient, directly affect the strain component of the stress–strain response window by altering the magnitude of external work applied to forming system. Material variation, on the other hand, directly affected the stress component of the response window. A relationship between the effective stress–strain response window and the variation in springback was also established.     

A general forming limit criterion for sheet metal forming

The forming limit of sheet metal is defined to be the state at which a localized thinning of the sheet initiates during forming, ultimately leading to a split in the sheet. The forming limit is conventionally described as a curve in a plot of major strain vs. minor strain. This curve was originally proposed to characterize the general forming limit of sheet metal, but it has been subsequently observed that this criterion is valid only for the case of proportional loading. Nevertheless, due to the convenience of measuring strain and the lack of a better criterion, the strain- based forming limit curve continues to play a primary role in judging forming severity. In this paper it is shown that the forming limit for both proportional loading and non-proportional loading can be explained from a single criterion which is based on the state of stress rather than the state of strain. This proposed criteria is validated using data from several non-proportional loading paths previously reported in the literature for both aluminum and steel alloys. In addition to significantly improving the gauging of forming severity, the new stress-based criterion is as easy to use as the strain-based criterion in the validation of die designs by the finite element method. However, it presents a challenge to the experimentalist and the stamping plant because the state of stress cannot be directly measured. This paper will also discuss several methods to deal with this challenge so that the more general measure of forming severity, as determined by the state of stress, can be determined in the stamping plant.