浅谈组合夹具在现代生产中的应用

随着现代工业生产技术的飞速发展,数字化信息的广泛普及,产品的设计信息、制造信息等都关联到了产品的模型中。在保证加工质量的前提下,合理设计及应用组合夹具替代部分专角夹具,可以大大降低生产成本,缩短生产准备周期,加快新产品的研制及生产速度;应用组合夹具还可以大量减少专用夹具的存储空间,有利手现场管理。同时．组合夹具元件可以重复使用,符合可持续发展战略。     

机床夹具定位元件图形库的开发与实现

本系统用Auto CAD内嵌语言AutoLISP为机床夹具CAD建立了夹具定位元件的参数图形库。 本软件运用数据库文件与LISP图形图程序相分离的方式,运用参数化设计,根据零件的主参数值及必要的信息,由CAD系统自动查询或计算出该零件其余各参数并绘出图形。用参数化程序建库既可大量节省存储空间,明显地提高设计效率和设计质量,又便于用户随需要对程序或数据库中的数据作灵活改动。 在设计方法上,对系统中图形库和数据库之间的数据传递、图形制作及尺寸标注等运用了简洁的程序设计方式。由于考虑到零件图与装配图有所不同,本系统在制作中也为这两种方式的转换和修改提供了途径。 本系统利用弹出式菜单或图标菜单与用户对话,使用极为方便,随时可以调用。 本课题的研究,体现了现代CAD的主要思想——参数化设计。从理论和实践上都为夹具CAD系统的开发提供了一条方便之路。     

计算机辅助成组夹具管理系统

本文介绍了一个简明、实用的计算机辅助成组夹具管理(CAGFM)系统。该系统为计算机辅助成组夹具设计(CAGFD)系统的配套软件。系统针对CAGFD系统中夹具识别的需要,对成组夹具进行了编码,并建立了成组夹具数据库和图形库。系统利用编码实现了成组夹具信息(数据和图形)的检索和统计。系统功能完善,维护简单、方便。CAGFM系统已用于我们开发的CAGFD系统中,运行效果良好。     

机床夹具信息分析

简述了机床夹具分类,具体分析了基于Web的机床夹具管理信息系统中夹具在设计、生产、管理过程中的信息需求,设计了机床夹具信息管理数据流程图,提出了夹具管理信息系统的E-R模型,为夹具信息管理系统的开发奠定了基础.     

可靠性强化试验通用夹具研究

针对可靠性强化试验中全轴随机振动试验的通用夹具问题展开研究，首先提出了基于全轴随机振动环境多轴非比例加载，非高斯幅值分布、宽频带等特性的全新夹具设计要求，然后通过理论分析得出了夹具设计的一般原则，最后设计实现了一种可靠性强化试验通用夹具，并对该夹具进行了测试验证，全轴随机振动试验的夹具设计是可靠性强化试验在工程应用中的关键技术，该文的研究可以为可靠性强化试验的推广应用提供广泛借鉴．     

基于最小响应偏离度的振动夹具优化设计

为了解决夹具传递给试件的振动量级的输入严重不均匀和偏离参考谱加速度均方根值的现象,依据电动振动台多点控制原理和夹具频响函数特性,建立夹具优化计算模型。以某试件夹具设计为实例,依据Nastran软件计算夹具频响函数值,根据所建优化计算模型,求出夹具最优设计参数。优化结果表明,优化后夹具传力点处的响应均方偏离度及加速度均方根值的变动范围均小于传统方法设计的夹具所求值;同时,优化后的夹具振动试验测试结果表明,传力点处实测加速度均方根值的变动范围与夹具设计阶段优化后的计算值变动范围基本一致,这就证明该优化方法是可行的和实用的,可以为振动试验实施和夹具设计提供实践和理论指导。     

某导弹发动机振动试验夹具设计

根据某导弹发动机的结构形状,设计了振动试验夹具.利用I-DEAS软件,建立了夹具的有限元模型并进行了模态分析,为改进夹具的动力学性能提供了设计依据,缩短了设计周期,提高了设计质量.改进后的夹具基本满足美国圣地亚试验室对振动试验夹具的动力学性能要求,保证了试验的顺利实施.     

成组夹具CAD系统的研究与开发

本文介绍了在微机上开发的成组夹具CAD系统(WCJJCAD)的一般构成原理和设计方法。本文讨论了图形库的建立和开发技术,夹具元件数据库结构设计,及夹具设计应用程序设计。探讨了AutoLisp图形库、FoxBasc数据库、C语言应用程序等不同软件环境下数据传递和集成管理的方法。     

环境振动试验传感器布置优化方法研究

为了快速获得最优的加速度传感器布置位置,依据电动振动台多点控制原理和夹具传递函数特性,建立了传感器布置优化计算模型。以一夹具为实例建立有限元模型,利用nastran软件求出传递函数,然后,根据所建优化模型获得传感器最优布置位置,最后,通过夹具振动试验测试夹具与试品连接部位处的响应。测试结果表明优化方法所得的响应加速度均方偏离度明显小于传统方法,证明了该优化方法是实用和可行的,并能为环境振动试验中的传感器布置和夹具设计提供实践与理论指导。     

回转体零件成组夹具的CAD系统

计算机辅助成组夹具设计系统——(CAGFD系统)采用信息检索方式,根据用户输入的被加工零件的信息,由计算机自动地查找合适的夹具类型,并完成整套夹具的设计工作。 该系统夹具设计模块的构思,应用了成组技术的设计思想,用形体要素来合成复杂的零件图,使较复杂图形的描述问题得以解决;用图形与文字结合的方式,提高菜单的形象和使用的方便性;应用菜单上开窗口,监控图形的构成,该系统为计算机辅助夹具设计探索出一条新路。     

基于实例推理的航空产品机加工工装设计相似性研究

针对航空产品的零件结构特点,将实例推理应用于航空结构零件机械加工工装设计.提出考虑工件信息、工艺信息和装夹信息的工装设计信息表示方法,来表达设计任务信息和以往设计实例信息.将工装设计实例分解为各属性,并按照一定方法对属性间的相似度进行量化,计算实例间的相似度值.结合分层检索的相似性评价算法,得到与设计任务匹配程度高的实例方案,并通过实例修正,达到新设计任务的快速实现.     

Fixture design information support for integrated design and manufacturing

Although a vast amount of research has been conducted on developing computer-aided fixture design systems, the need for information exchange between the fixture design domain and other manufacturing domains has not been thoroughly dealt with. This paper addresses this gap in fixture design research through the development of appropriate information models for computer-aided fixture design systems to support integrated design and manufacturing. A fixture design activity model is presented that relates fixture design to other design and manufacturing activities. The implementation of the information models in XML and the exchange of the information models based on an XML messaging approach are also discussed.     

Defining specialized design similarity measures

Similar product designs resemble each other and have similar attributes and characteristics. When examining a product design to create its process plan, design its fixture, or estimate its manufacturing cost, manufacturing engineers often identify one or more similar products that the factory has manufactured in the past. They may do this from memory, from a file cabinet, or from a database (in a product data management system). Then, they retrieve the process plan (or fixture or cost estimate) for the similar product and modify it for the new product. Manufacturing and process planning experts use a complex set of rules, guidelines, and other knowledge to determine how similar two products are. Computer-aided process planning tools, however, generally use simpler, less sophisticated procedures for determining similarity. These traditional procedures may be inappropriate for specific settings. This paper presents an approach for developing function-specific design similarity measures. Such a measure explicitly exploits the specific need for similar products and thus improves variant approaches for process planning, fixture planning, and manufacturability evaluation. The approach is applied to a specific fixture planning domain.     

Field and Thermal Characteristics of Magnetizing Fixture

1. IlltroductionA capacitor discharge impulse magnetizer is usedto produce a high current impulse of short durationin a magnetizing fixture for magnets of the variousshapes[1-3]. The problem of designing custom fixturesfor magnetization has often been considered more ofan art than a science. The problem of designing custom fixtures for magnetization fixtures has ulltil recently been a "cut and try" process. Especially, computation of the temperature rise of a magnetizing fixture is very import…     

Robust fixture layout design for multi-station sheet metal assembly processes using a genetic algorithm

The optimal fixture layout is crucial to product quality assurance in the multi-station sheet metal assembly processes. Poor fixture layout may lead to product variation during the assembly processes. In this paper, a genetic algorithm (GA)-based optimisation approach has been presented for the robust fixture layout design in the multi-station assembly processes. The robust fixture layout is developed to minimise the sensitivity of product variation to fixture errors by selecting the appropriate coordinate locations of pins and slot orientations. In this paper, a modified state space model for variation propagation in the multi-station sheet metal assembly is developed for the first time, which is the mathematical foundation of optimal algorithm. An e-optimal is applied as the robust design criteria. Based on the state space model and design criteria, a genetic algorithm is used to find the optimal fixture layout design. The proposed method can greatly reduce the sensitivity level of product variation. A four-station assembly process of an inner-panel complete for a station wagon (estate car) is used to illustrate this method.     

Modelling and compensation of fixture locators’ error in CNC milling

Fixture errors are one of the error sources in machining operations. The fixture errors consist of positioning inaccuracies and errors due to workpiece and fixture deformations. Fixture locators’ height error causes incorrect positioning of the workpiece in the fixture and inaccuracy in machined surfaces which can be much more than the locators’ height error. For machining precise workpieces, it is necessary to eliminate these errors. This paper presents a method for modelling and compensating the fixture locators’ height error effect on workpiece machined surfaces. In this method, the planes of workpiece actual coordinate system (ACS) are mathematically modelled in the workpiece theoretical coordinate system (TCS). Using the model, required homogenous transformation matrix for coinciding ACS with TCS and modifying machining toolpath for compensating the errors is generated. The presented model is used to develop a post-processing fixture locator error compensation module, which can modify CNC machining codes to eliminate the effect of fixture locators’ height error on the workpiece machined surfaces. For verifying the presented method, machining simulations and cutting experiments have been performed in this work. The results show that the method can eliminate the effect of fixture locators’ height error on the workpiece machined surfaces considerably.     

试验夹具动态设计

为考核汽车电器的可靠性,需对其进行振动可靠性实验。装夹和固定电器系统元件的夹具,是实验的重要组成部分,其动态性能对振动试验有重要影响。根据试件的外形及安装定位方式建立了夹具的三维模型,用有限元方法计算了夹具的模态频率与振型,依据分析结果对夹具的结构进行了改进,使夹具动态性能满足试验要求。     

Fixture modelling for an automotive assembly line

This paper proposes an efficient fixture modelling procedure for automotive body assembly lines. A fixture model consists of two sub-models; a geometric model and a kinetic model that should be remodelled frequently whenever design changes occur. We develop an algorithm extracting the kinetic model from the geometric model of a fixture to reduce the fixture modelling time and effort. Although the geometric models of fixtures used in automotive assembly lines vary, most follow the same kinetic mechanism, the so-called slider-crank mechanism; this is a four-axis system of three revolute and one prismatic joint. The prismatic axis of a fixture represents a pneumatic actuator involving a piston and a cylinder. It is very important to identify the prismatic axis from a given geometric model to extract the kinetic model of a fixture. We use the concept of the ‘moment of inertia’, which is a measure of an object's resistance to changes in its rotation rate, to identify the prismatic axis. Since the exact computation of the moment of inertia for an arbitrary solid model requires complicated computations, we introduce an approximating method for the moment of inertia. The proposed procedure has been implemented and tested with various examples.     

An integrated setup/fixture planning approach for machining prismatic parts

Setup/fixture planning for machining prismatic parts is usually carried out by grouping features/operations into setups, determining suitable locating surfaces for each setup, and sequencing setups and operations in each setup. The presently developed setup/fixture planning methods can be classified into three categories: multi-constraints, fixture driven, and tolerance analysis planning methods. The multi-constraints planning is theoretically sound, but very difficult to use. In fixture driven planning, the generated setup plans are highly practical, but may not be optimal. Tolerance analysis based planning cannot be used to generate the optimal solution by itself. In this research, a new integrated setup/fixture planning approach is developed to identify the optimal and practical setup/fixture plan. The planning is conducted in four steps. (1) The dissimilarity degree matrix (DDM), operation precedence graph (OPG), and hybrid graph are used to describe the requirements and constraints for setup/fixture planning. (2) A setup precedence graph (SPG) is used to describe precedence constraints between setups. The SPG is generated by the vertex clustering algorithm. Precedence loops among setups are avoided by checking whether two serial vertex clusters can generate a loop. (3) Suitable locating surfaces are selected for each setup in a SPG. When the fixture locating surface and design datum surface are different, two types of dimension recalculations are employed to obtain the dimensions against the locating surfaces. (4) All the candidate setup/fixture plans are evaluated based on the number of setups and recalculation of dimensions. An example is given to demonstrate the effectiveness of the developed approach.     

Optimizing workholding efficiency through fixture function simulation

In the past two decades, simulating workpiece–fixture interactions has remarkably drawn the attention of academia. However, many aspects of the workpiece–fixture system, specifically workpiece–fixture contact condition, still enjoy research effort. For the efficient use of Automated Fixture Design (AFD) systems, verification of their outputs is required. This paper presents a workholding simulation approach that considers assessment of AFD system outputs regarding different workholding parameters. The effect of friction forces on workholding and part rigid body stability is considered. Besides, determining deformation and stress in the workpiece, locators and clamps are modelled and their elastic deformation and stress distribution are computed. A procedure based on the application of contact elements in finite-element method is developed to quantify the status of contact between the workholding elements and the workpiece. Clamping tightness is modelled and its effect on the workpiece–fixture system performance is quantified. The central component of the verification tool is the use of nonlinear finite-element analysis to model the frictional interactions in workpiece–fixture system.