Robust fixture layout with the multi-objective non-dominated ACO/GA approach

Fixture design is an important procedure in many manufacturing operations in terms of maintaining product quality, consistency and assisting the assembly, machining and inspection processes. A robust fixture design approach is presented in this study. It treats fixture layout as a multi-objective optimization problem, which considers both the mean and the variation of the mean localization errors of the machining features in a set-up, and the distance of the location points among the locators to ensure the location is stable and reliable. The non-dominated ACO and GA are proposed to solve this multi-objective problem, and their performances are compared.     

A novel approach to fixture layout optimization on maximizing dynamic machinability

In the aerospace industry, the reasonable layout of fixture can efficiently suppresses machining vibration of thin-walled aerospace structure during machining. Based on the analysis of typical structural components encountered in the aerospace industry, a general frame-structure workpiece with fixture constraints can be equivalent as Mindlin plates with simultaneous elastic edges and internal supports. On basis of the equivalent models, the powerful pb-2 Ritz method defined by the product of a two-dimensional polynomial and basic functions can be introduced to be taken as trial functions. Substituting displacement functions into energy functional and minimizing total energy by differentiation leads to eigenfrequency equations of the workpiece–fixture system. Consequently, a novel nonlinear programming problem based on the frequency sensitivity can be built to optimize the layout of fixture supports to maximize the fundamental nature frequency of the workpiece–fixture system. The feasibility of the proposed approach is validated by a machining case.     

Experimental determination of the friction coefficient on the workpiece-fixture contact surface in workholding applications

Surface flatness, geometric integrity and micro-surface finish characteristics are crucial for automotive industry to properly seal joints, reduce leakage and consequently increasing engines efficiency and reducing emissions. Optimum fixture layout is a key element in achieving this goal. Machining of flexible parts impose further challenges to the selection of a proper fixture scenario.Workpiece motion arising from localized elastic deformation at the workpiece/fixture contacts due to machining and clamping forces significantly affect the workpiece location accuracy and hence the machined part quality. The tangential friction force plays an important role in fixture configuration design as it can be utilized to reduce the number of fixture components, thereby the workpiece features accessibility to machining operations and providing a damping mechanism to dissipate input energy from machining forces out of the workpiece/fixture system.Although the literature is full of research on friction and its application, it lacks research that relates to the contact found in workpiece/fixture systems. This paper presents the results of an experimental investigation of the workpiece/fixture contact characteristics.     

一种大型薄壁件的多点柔性定位工装与装夹优化技术

针对航空航天制造中经常会用到的一些尺寸大、刚度低、易变形的大型薄壁件,开发出了一种多点柔性定位工装,根据这种柔性工装和工件的特点,提出了一种能够对这类零件的定位/支承布局方式进行有效优化的方法,提高了零件的加工质量,节省了这类零件制造的工装成本。     

发动机进排气导管座圈锪铰专用机床设计

针对企业摩托车发动机缸体现有工艺存在加工精度、合格率低及生产效率跟不上市场需求的问题,在分析现有加工手段优劣的基础上,利用工序集中原则,将缸体进排气座圈孔、导管孔及平面的精加工集中于一台设备上进行加工,提出了两次装夹、多工件、多工位、多刀具复合加工的全新工艺方案。根据工件加工姿态确定了双工位、双夹具,每个夹具装夹两个工件的整体布局方案,工位一、二相互协作完成缸体工序加工内容;最后,根据整体方案对专用夹具、专用刀具及专用主轴箱等关键零部件进行了详细设计及阐述。     

An investigation into the use of spatial coordinates for the genetic algorithm based solution of the fixture layout optimization problem

The fixture layout optimization problem is highly modal. It has been shown that layout optimization methods that use the genetic algorithm (GA) are effective at finding high quality solutions. To date, such methods have used FEA node numbers to represent the locations of fixture elements. This paper presents a new GA based optimization method that uses spatial coordinates to represent the locations of fixture elements. This method integrates a number of important GA concepts such as real encoding, increased mutation, and sharing. Test results show that the new method provides higher quality solutions with substantially less numbers of generations than the old method. These results also show that the use of increased mutation and sharing significantly improves the performance of the new method.     

一种有效加工筒环类零件夹具的优化

指出某种加工筒环类零件(壁薄、外观和尺寸精度要求高)夹具在实际应用中出现的问题,针对这些问题,提出该夹具的优化方法;并对该整体式夹具进行改进,设计一套整体镶拼式夹具,说明其优点、加工可行性和适用性。     

驱动桥主动轮夹具问题的分析与解决

针对延伸外摆线螺旋锥齿轮主动轮在干式切削加工中,出现的齿面振纹的现象进行分析,通过有目标的实际加工测试和过程监测,发现产品精加工过程中,振纹的产生与产品加工过程中的发热而导致夹具的夹紧、定位状态发生变化密切相关;分析表明可以通过夹具的设计优化排除或减小发热的影响。提出了典型夹具的优化设计方案,并进行了夹具改良后的试验验证,验证结果证明了改进后的效果良好。     

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.     

伺服阀套的精密电火花加工及组合夹具的设计

阀套是液压伺服系统中的一重要零件,圆柱面上方孔电火花加工及内环槽电磨削精度要求很高,加工难度大,加工合格率通常不足60％.通过对加工过程进行优化,稳定了环槽加工尺寸,设计了与设备相连接带油路的组合夹具之后,有效地改善了电火花加工方孔时的“烧伤”缺陷,一次加工合格率能达到92％.由于组合夹具一次装夹,能同时加工六个阀套零件,单件加工时间也缩短了30min.该电火花加工方法和组合夹具的结构对类似零件的加工具有一定的借鉴作用.     

卧式加工中心配置回转夹具回转中心位置误差的检验

在卧式加工中心上配置回转夹具是国内外机床制造技术的发展方向。卧式加工中心配置回转夹具主要是由夹具体、伺服电机、转台和液压系统等装置组成的一种复杂的夹紧结构，适用于汽车行业缸体、缸盖等零件的加工，在卧式加工中心装配调试工作中，经常遇到卧式加工中心配置回转夹具（转台＋夹具）专机，而确定回转夹具回转中心位置成为该专机调试工作的技术关键，该文主要研究回转夹具回转中心的确定，夹具主定位面（合定位销）误差的判断、调整及其机床三个坐标轴运动之间的关系。     

An investigation of the effectiveness of fixture layout optimization methods

Deriving the optimal layout of fixture elements is critical to minimizing the impact of fixture–workpiece deformation on machined feature error. Various optimization methods for solving this problem have been reported. Unfortunately no investigation has been executed to compare their relative performance. This paper presents the methodology and results of an extensive investigation into the relative effectiveness of the main elements of these competing methods. All methods were tested over a broad range of conditions. Performance measures that were tracked included solution quality, solution repeatability, and computation time. The results of this investigation show that the best overall performance is provided by optimization methods that use both the genetic algorithm and continuous interpolation for the distribution of boundary conditions.     

附加质量块对机床结构动态特性的影响研究

结构动力学优化设计是提高机床加工精度的有效途径,而机床结构各组成部件的合理化布局又是影响机床动态性能的关键因素.本文首先对XH786立式数控加工中心整机进行优化建模,然后采用附加质量块方法,对机床在同一位置处添加不同的质量块以及在不同位置添加相同质量块对整机动态特性的影响进行了研究,结果表明:不同的质量块安放在机床同一位置,对机床整机的动态特性前几阶影响较大,高阶影响较小;相同的质量块安装在机床不同位置,位置变化对机床的整体动态性能有较大影响.本研究为机床结构各组成部件的质量与位置布局优化提供了理论基础.     

磨料流加工中夹具设计的研究

磨料流加工(AFM)是光整加工领域的一项新技术。磨料流加工由磨料流加工机床,夹具和流体磨料三部分组成。当用磨料流加工形状较复杂的零件时,夹具设计的好坏对表面加工质量和加工效率有重要的影响。本文分析了磨料通过工件孔道的特性。介绍了用于研究材料去除量与加工距离和形状关系的实验。材料去除量在通道两端比中间小是磨料流加工的一基本特性。本文讨论了如何避免因此而产生的工件变形以及如何利用这一特性来获取某种特殊效果。最后,给出了一个用于加工某不锈钢三通体的夹具。     

Optimisation of machining fixture layout under multi-constraints

Fixture layout including locator layout and clamp layout plays a vital role in fixture performance. Current researches have been focused on fixtures for components with regular geometry, the results of which are not always applicable for components with complex geometry. This paper presents a methodology of fixture layout optimisation carried out in consideration of the repeatability, immobility and stability of fixturing. The locator layout is optimised based on the criteria of workpiece repeatability and location accuracy. The clamp layout optimisation offers a method to minimize the magnitude of the clamping force. The procedure of clamp optimisation is (1) to find the feasible clamping position in terms of the immobility requirement; (2) to get the best clamp among the feasible clamping positions under constraint of the stability. The optimal fixture layout is considered in a global range and is especially suitable for the workpiece with complex surfaces. A fixture layout design for the aerofoil of a turbine blade is analysed as an example, and the optimal fixture layout is demonstrated.     

摩托车发动机缸体三面加工专用机床设计

针对某摩托车发动机缸体某工序三面八孔加工精度及生产任务要求,在分析传统加工工艺及装备存在不足的基础上,提出了一次装夹完成所有工序内容的工艺方案,并根据工艺方案确定了缸体加工时的姿态,进而确定了机床整体布局方案;最后对专用机床关键部件如专用夹具,专用主轴箱等的工作原理及结构做了详细设计说明。设计的工艺及专用机床在发动机缸体机加生产线上实际应用显示:单台设备年生产纲领达到35万件左右,合格率提升至99. 9%以上,缸体三面八孔的各项精度指标均达到或超过企业要求。     

Analysis–synthesis of dimensional deviation of the machining feature for discrete-part manufacturing processes

Dimensional deviation analysis has been an active and important research topic in mechanical design, manufacturing processes, and manufacturing systems. This paper proposes a comprehensive dimensional deviation evaluation framework for discrete-part manufacturing processes (DMP). A generic, explicit, and transmission model is developed to describe the dimensional deviation accumulation of machining processes by means of kinematic analysis of relationships between fixture error, datum error, machine tool geometric error, fixturing force inducing error and the dimensional quality of the product. The developed modeling technology can deal with general fixture configurations. In addition, the local contact deformations of the workpiece–fixture system are determined by solving a nonlinear programming problem of minimizing the total complementary energy of the frictional workpiece–fixture subsystem in machining system. Moreover, the deviation of an arbitrary point on machining feature can be also evaluated based on a point deviation model with prediction dimension deviation from the transmission model. The dimensional error transmission within the machining process is quantitatively described in this model. A systematic procedure to construct the model is presented and validated. This model can be also applied to process design evaluation for complicated machining processes.     

一种新的卧式加工中心工作台常压系统的研究

介绍了一种卧式加工中心常压工作台结构,卧式加工中心是机床中自动化程度较高、工序较为集中的机床之一。应用传统的夹具在一定程度上限制了卧式加工中心优越性的发挥,采用工作台通油技术,为夹具提供动力,保证夹具动作的完成,从而增加了卧式加工中心的使用范围及自动化程度。实践证明:该技术设计合理、实用性强、可靠性高。     

五轴联动数控加工的装夹误差动态补偿方法

五轴联动数控加工中,由于工件装夹误差引起的实际加工基准与CAM编程基准不一致,其旋转中心偏差造成旋转附加运动无法由传统三轴加工中的坐标偏置方法补偿。文章提出五轴数控的装夹误差寻位补偿方法,在旋转轴转动过程中通过坐标变换和机床逆运动变换动态修正加工路径,使加工结果与设计一致。试验表明,采用该方法降低了五轴机床工件装夹要求,消除了装夹误差带来的精度问题,满足精密五轴数控加工要求。     

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。