基于刚体运动学的工件自由度分析方法

夹具设计最主要的任务就是将工件精确定位。在定位过程中,首先必须合理地约束工件自由度;其次在自由度受到约束的方向上,工件也只能在规定的范围内变动。因此,分析工件的自由度约束情况是复杂定位方案设计甚至整个夹具设计的关键所在。基于刚体运动学,文章建立了定位原理的数学模型,以定量分析工件自由度的约束情况。从而使得传统的定位原理从定性描述上升为数学定量表示,为计算机辅助夹具设计系统的开发提供了基础理论,并首次在UG软件系统环境下实现了夹具约束工件自由度分析系统的二次开发。     

基于定位法线的工件最少定位点布局规划方法

以建立满足工序需求的工件定位点数量最少的定位布局为目标,以定位法线为介质,基于定位法线的工件定位的几何定理,推论出工件自由度与定位法线关系,获得自由度约束模型的定位法线信息;建立工件自由度数学模型,运用逻辑减运算法则建立工件各类型自由度之间关系,获得自由度模型的规划方案;根据规划方案中的定位法线信息,得出定位点初始布局。利用典型实例详细介绍了基于定位法线进行工件定位点布局规划的应用过程。该方法仅需自由度信息,规划过程简便,适用于各类工件,尤其是复杂工件的初步定位方案设计。     

一面两孔定位时定位元件的设计

在箱体、杠杆、盖板等类零件的加工中,工件常以一平面两圆孔作为定位基面,简称一面两孔定位。工件以一面两孔定位时,夹具上的定位元件是：与工件平面相接触的定位元件是支承板,用于两个定位圆孔的定位元件有两种情况：一种是两个短圆柱销,另一种是一短圆柱销与一短削边销。下面主要阐述这两种情况下两销的设计。回两个短圆柱绍如图1所示,采用两个短圆柱销与工件两定位孔配合时,短圆柱销1限制人于两个自由度,短圆柱销2限制多、X＼两个自由度,平面3限制叫、r＼和三三个自由度。两短圆柱销重复限制了多这个自由度,即沿两销连心线方…     

异型内齿轮加工插齿机夹具设计

为插齿机加工异型内齿设计夹具,该夹具采用内孔钢球定位,端面压紧。分析该夹具结构及原理、定位误差、夹紧力及工件切削力。该夹具定位精度稳定可靠,保证了齿轮径向跳动精度要求。     

电机转子激光焊接系统设计

针对电机转子中套筒、护盖的焊接,设计了激光焊接系统。由于整个工件组合后长度和位置的尺寸存在一定的尺寸公差,需设计特殊夹具吸收其公差。激光焊接夹具包括随行夹具、顶升组件、上止档组件及转盘夹具,将工件置于随行夹具内,顶升旋转组件将工件顶入上止挡组件,以转子的上端面作为定位基准面,实现对工件的精确定位焊接。     

精密阀芯径向孔钻床夹具设计

针对某精密阀芯外圆表面径向孔尺寸和位置精度高、加工质量不稳定的情况,设计一种采用V形槽反装定位、偏心轮装置快速夹紧的专用钻床夹具。详细分析了径向孔加工钻床夹具的定位和夹紧方案,计算出定位元件关键尺寸,阐述夹紧装置的原理和工作过程。经夹具精度分析与验算,发现所设计的夹具完全能满足精密阀芯径向钻孔的高精度要求。该夹具操作简便、适应性强、工件加工质量稳定,为机械行业销轴类零件高精度径向孔钻床夹具的设计提供了参考。     

“一面两销”定位时的定位尺寸设计

工件以一面两孔定位时,夹具上用一面两销对工件定位。对于定位元件的定位尺寸设计,常规方法存在一定的问题。提出一种理论与实际相结合的设计方法,解决了过去在夹具制造和应用中存在的问题。     

龙门刨床平面定位可调定位夹具的设计

针对龙门刨床采用压板螺栓和垫铁进行大型工件以平面为定位基准定位时难以找正、定位及装卸费时、工作效率低的弊端,设计了适用于龙门刨床BQ2020的多件加工以平面划线定位为基准的可调定位夹具.完成了定位元件的结构设计和工作原理分析.对定位元件的载荷进行分析并进行了强度校核,结果表明所设计的定位元件满足多件加工以平面为定位基准时快速定位装夹的要求,为类似T型工作台上以平面为定位基准的多件加工快速定位提供参考.     

离心风机蜗壳车夹具的改进设计

以铝合金蜗壳压铸件的车削加工为例,排除了径向夹持的可能性,介绍传统的压板式车夹具工作原理并分析其缺陷后,设计一种楔紧式车夹具,它不仅定位、夹紧可靠,而且装、拆工件方便、快捷,提高了生产效率。对同类薄壁零件的加工具有一定的参考价值。     

一种方圆两用的形封闭型柔性夹具

设计了一种方圆两用的形封闭型柔性夹具,并介绍了其工作原理.该柔性夹具能适用于圆柱形和长方体形工件的定位和夹紧.允许工件尺寸在较大范围内变化,能较好地适应多品种、小批量生产方式对夹具的要求.     

Improved workpiece location accuracy through fixture layout optimization

Inaccuracies in workpiece location lead to errors in position and orientation of a machined feature on the workpiece. The ability to accurately locate a workpiece in a machining fixture is strongly influenced by rigid body displacements of the workpiece caused by elastic deformation of loaded fixture–workpiece contacts. This paper presents a model for improving workpiece location accuracy in fixturing. A discrete elastic contact model is used to represent each fixture–workpiece contact. Reduction in workpiece locating error due to rigid body displacements is achieved through optimal placement of locators and clamps around the workpiece. The layout optimization model is also shown to improve the overall workpiece deflection and reaction force characteristics.     

自动装夹设计中支承位置与工件变形的几何推理方法

定位支承设计是装夹设计过程的核心部分。描述了一种自动装夹设计系统体系结构，并建立了初始装夹设计方案中工件最大变形的分析模型，应用有限元分析工具对工件最大变形进行定量分析；用3-2-1定位原理和定性分析方法提出了最佳定位支承点的调整规则和用几何推理方法求解最小变形定位支承位置推理机制。为自动装夹设计系统提供一种用3-2-1定位原理确定定位支承位置的一般算法，使工件在自动装夹设计过程中具有严格准确的位置。     

多腔缸体零件端面铣削加工的高精密夹具设计及其优化

针对发动机多腔体缸体的结构复杂和刚度小的问题,对该缸体铣削端面加工工序确定高精密夹具的定位和夹紧方案.在初步分析夹具方案之后,运用有限元法对夹具的主要零件进行了变形分析和计算,并在此基础上对夹具结构进行了优化,最终确定了高精密夹具设计新方案.结果表明优化得到的设计方案优于经验设计方案,提高了夹具的定位和夹紧精度,从而保证了加工质量,在实际生产中效果良好.     

圆柱面组合定位误差计算新方法

圆柱面定位是广为采用的一种典型定位方式，其精度分析对于评价定位方案优劣，保证工件加工精度具有十分重要的意义。本文在认真分析传统计算方法的基础上，提出圆柱面定位时定位误差的统一解析表达计算公式，避免了因极限位置判断失误所造成的计算错误，大大简化了计算过程。经实例验证，该方法准确、高效。     

Prediction of workpiece deformation in a fixture system using the finite element method

Knowledge of workpiece deformations induced by loading in a fixture–workpiece system is important to ensure quality part production. Suitable methods for accurately predicting such deformations are essential to the design and operation of fixtures. In this regard, finite element modeling has been widely applied by researchers and practitioners. However, these studies generally neglect the role of compliance of the fixture body on workpiece deformation. Also lacking is knowledge of the effects of different finite element model parameters on workpiece deformation. This study uses finite element analysis (FEA) to model a fixture–workpiece system and to explore the influence of compliance of the fixture body on workpiece deformation. In addition, the effects of certain finite element model parameters on the prediction accuracy are also examined. Experimental verification of the workpiece deformations and locator reaction forces predicted by the FEA model shows agreement within 5% of the experimental data. For the fixture–workpiece system analyzed in this study, it was found that 98% of all system compliance is captured by modeling just the workpiece and fixture contact tips. The remainder of deformation occurred in the other fixture components. The accuracy and computational time tradeoffs are given for various fixture models.     

面向套类零件的成组夹具设计

依据套类零件的结构特点,通过合理设计夹具定位件和调换件,给出成组夹具的总体结构图。该夹具结构简单紧凑,使用方便,对工件特征在一定范围内变化的适应性很强,适用于形状相似的套类零件的多品种小批量生产。     

A unified framework of error evaluation and adjustment in machining

Errors of machine tool, fixture, and datum on workpiece to be machined influence the machining accuracy of the workpiece. The objective of this paper is to provide a framework for abstracting an error model that integrates three types of errors, i.e., machine tool, fixture, and datum errors, into a unified one. Differential motion theory is used to build the evaluation model of three types of errors. The resultant deviation model of the tool with respect to the workpiece is derived by using the model. For the purpose of eliminating the deviation, the resultant geometric variation is mapped into the locator errors on the fixture. Then the position and orientation errors of the tool with respect to the workpiece may be reduced by adjusting the length of locators. Finally, the effectiveness of the resultant deviation model is verified by examples.     

Analysis of the effects of fixture clamping sequence on part location errors

Several fixture-related error sources are known to contribute to part location error, which can lead to poor part quality. In addition to typical error sources, such as fixture geometric error and elastic deformation of the fixture and part due to clamping forces, the clamping sequence used can also influence part position and orientation. In this paper, the effect of clamping sequence on workpiece location error is modeled analytically for a fixture–workpiece system where all major compliance sources and fixture geometric error are considered. Part location error is quantified by the displacement of a response point on the part surface. An algorithmic procedure designed to understand how forces and deformations change as clamps are applied sequentially is presented. The effect of clamping sequence on part location error and locator reaction force is examined through model simulations and experiments via an example involving a 3-2-1 machining fixture.