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.     

A case-based reasoning approach for design of machining fixture

Appropriate fixture design could lower process time, lower cost, and improve the quality of products. This paper proposes a case-based reasoning (CBR) method, with improved indexing and retrieving approaches which are critical issues in machining fixture design systems. A case storage for fixture design case indexing approach is developed so that the database is constructed into two levels—to manage and categorize numerous related fixture designs. The data includes existing workpieces and associated fixture planning and unit depository as solutions. Based on this approach, a CBR method with a two-step case retrieval is presented. The objective is to improve searching results in database for machining fixture design. In this CBR-based fixture design method, the appropriate workpiece in the first level of database by using design requirement is found. Then, the proper conceptual fixture design can be achieved by retrieving related fixture case from the second level. This method facilitates the fixture designing by means of referencing past design cases to generate a conceptual fixture design quickly and easily. It also helps in the finishing design by suggesting some alternative fixture cases. Finally, several case studies are used to validate and present the applicability and usability of the proposed approach.     

EROWA电极定位夹头专用夹具设计

结合被加工零件的结构及加工工艺特点,设计制造了一款专用铣床气动多功能夹具。为保证夹具具有良好的强度,运用ANSYS Workbench软件对夹具工件系统进行了平面铣削和钻孔过程受力仿真分析。结果表明:装配件在钻削力和切削力作用下,产生的最大应力远小于材料的屈服强度,且最大位移值在加工公差范围内。经样品试制、现场实验检验,使用专用夹具生产出来的产品,其工件尺寸和几何误差均满足精度要求,达到预期目标。因此,该夹具结构设计合理,具有一定的推广应用价值。     

Development of a finite element analysis tool for fixture design integrity verification and optimisation

Machining fixtures are used to locate and constrain a workpiece during a machining operation. To ensure that the workpiece is manufactured according to specified dimensions and tolerances, it must be appropriately located and clamped. Minimising workpiece and fixture tooling deflections due to clamping and cutting forces in machining is critical to machining accuracy. An ideal fixture design maximises locating accuracy and workpiece stability, while minimising displacements.The purpose of this research is to develop a method for modelling workpiece boundary conditions and applied loads during a machining process, analyse modular fixture tool contact area deformation and optimise support locations, using finite element analysis (FEA). The workpiece boundary conditions are defined by locators and clamps. The locators are placed in a 3-2-1 fixture configuration, constraining all degrees of freedom of the workpiece and are modelled using linear spring-gap elements. The clamps are modelled as point loads. The workpiece is loaded to model cutting forces during drilling and milling machining operations. Fixture design integrity is verified. ANSYS parametric design language code is used to develop an algorithm to automatically optimise fixture support and clamp locations, and clamping forces, to minimise workpiece deformation, subsequently increasing machining accuracy. By implementing FEA in a computer-aided-fixture-design environment, unnecessary and uneconomical “trial and error” experimentation on the shop floor is eliminated.     

Automated setup and fixture planning system for box-shaped parts

The topic of the research is related to the domain of computer-aided manufacturing process planning. This paper deals with the problem of setup and fixture planning for the machining of box-shaped parts on the horizontal machining centres. The setup and fixture planning involves the definition of setups, the setup sequence and conceptual design of fixtures for each setup. The central topic of this research is the automation of the conceptual design of fixtures. This topic is interconnected with the setup planning, and accordingly, the aim of the author has been the integrated handling of tasks of setup and fixture planning and the finding of solution in an integrated system. Based on the workpiece model, the developed system automatically determines the setup sequence, the content of setups and the conceptual solution of fixture for each setup. The paper presents the problems of fixture solutions and the partial tasks of workpiece holding, the typical solution of partial tasks and the conditions of their application and finally offers a new method, which makes the integrated handling of tasks of setup and fixture planning and finding solution in an integrated system possible.     

Design and optimization of machining fixture layout using ANN and DOE

In machining fixtures, minimizing workpiece deformation due to clamping and cutting forces is essential to maintain the machining accuracy. This can be achieved by selecting the optimal location of fixturing elements such as locators and clamps. Many researches in the past decades described more efficient algorithms for fixture layout optimization. In this paper, artificial neural networks (ANN)-based algorithm with design of experiments (DOE) is proposed to design an optimum fixture layout in order to reduce the maximum elastic deformation of the workpiece caused by the clamping and machining forces acting on the workpiece while machining. Finite element method (FEM) is used to find out the maximum deformation of the workpiece for various fixture layouts. ANN is used as an optimization tool to find the optimal location of the locators and clamps. To train the ANN, sufficient sets of input and output are fed to the ANN system. The input includes the position of the locators and clamps. The output includes the maximum deformation of the workpiece for the corresponding fixture layout under the machining condition. In the testing phase, the ANN results are compared with the FEM results. After the testing process, the trained ANN is used to predict the maximum deformation for the possible fixture layouts. DOE is introduced as another optimization tool to find the solution region for all design variables to minimum deformation of the work piece. The maximum deformations of all possible fixture layouts within the solution region are predicted by ANN. Finally, the layout which shows the minimum deformation is selected as optimal fixture layout.     

Development of a novel coordinate transposing fixture system

A novel quick action flexible fixture for two-dimensional clamping is fitted with sensors for automatically measuring the positions of the clamping surfaces and the vice opening. An algorithm is proposed to determine the location and orientation of the workpiece on the fixture. The NC codes preprogrammed with a given origin and orientation can then be modified with these data to appropriately transposed coordinates, which can then be downloaded to the NC controller for NC machining. With this system, the time and cost of fixturing will be greatly reduced.     

A mathematical approach to analysis and optimal design of a fixture locating scheme

In manufacturing engineering, localization accuracy is a key concern in the design of a fixture to specify a locating scheme and tolerance allocation. This paper presents a general analysis methodology that is able to characterize the effects of localization source errors based on the position and orientation of the workpiece. From this methodology, a fixture model is formulated by taking into account the overall errors among the system consisting of the workpiece and the fixture in the design of the fixture locating scheme. With this model, the locating principle and a criterion of the robust optimal design are then proposed to improve the localization quality of the fixture. Some examples are provided and allow for a detailed discussion about how to carry out the optimal design of the locating scheme. A comparative study is also made between the optimal solution and the empirical one. Finally, an experiment is made to validate the fixture locating scheme for a cylindrical workpiece. We conclude that this robust design method effectively achieves stable machining precision in workpieces.     

几何增强的装配工艺本体建模

包含产品几何与非几何信息的产品装配要求是装配工艺设计的主要依据,对装配工艺设计决策结果具有决定性的影响。在装配工艺模型中描述产品的几何相关信息能够更好地表达如装配顺序,装配路径等内容,同时可以更好地辅助装配工艺决策,提高决策的自动化水平。提出一种几何增强的装配工艺本体模型,利用语义本体技术,建立产品几何信息在装配工艺中的描述方法,数据结构与关系描述。并以该模型为基础,建立基于几何增强装配工艺本体的装配工艺决策框架。该框架分为两部分：一是采用几何增强的装配工艺本体模型描述产品几何信息和装配工艺信息的数据结构和相互关系;二是为了让几何信息与装配工艺信息之间存在的丰富的隐含关系显性化,对语义本体推理机制进行增强,提出推理单元的概念,使决策框架具有从产品几何信息中推理装配工艺相关信息的能力,有效地支持装配工艺决策。以针对某传动器产品装配顺序决策的过程,验证所提出的几何增强装配工艺本体模型与框架的有效性。     

Design and optimization of machining fixture layout for end-milling operation

High product quality and productivity are the important objectives of manufacturing industries. They are greatly affected by the fixture layout design, and it requires modeling and analysis of fixture-workpiece interactions. In particular, the position of fixture elements has explicit influence on the deformation of the workpiece which needs to be minimized during machining. In order to ensure effective fixture layout design, the relationship between the position of fixture elements and workpiece deformation has to be modeled and optimized. In this research paper, workpiece deformation is modeled using response surface methodology. The developed model is tested for model adequacy, and the results obtained are matched with the simulated data. Then, it is used to minimize the workpiece deformation by determining the appropriate positions of locators and clamps using sequential approximation optimization and LINGO solver. It is found that integration of response surface methodology, with sequential approximation optimization, produces better results than LINGO solver.     

FIX-DES: A computer-aided modular fixture configuration design system

This paper presents a computer-aided modular fixture configuration design system: FIX-DES. When fixturing requirements are specified as locating/clamping surfaces and points, a fixture configuration will be automatically generated by

1. Selecting fixture elements from a fixture element database to form fixture units based on fixture element assembly relationships.
2. Placing the fixture units and elements into position on a baseplate while the fixturing requirements and assembly relationships (e.g. hole alignments) are maintained.

The fixture element assembly relationships can be established automatically when the geometric models and fixturing functions of the fixture elements are specified so that the FIX-DES system can be applied easily to different fixture systems. The system also provides the interactive design and design modification functions for human expert involvement. The system was developed with core programs in C and C++ and interface programs in a specific CAD environment. The system has been successfully applied in industry and can be transferred easily to other CAD systems. The overall structure of the FIX-DES system is introduced in the paper. The development of the automated fixture configuration design (AFCD) functions are presented in detail. Finally a fixture configuration design example is given to illustrate the application of the system.     

主减速器壳体车削工装夹具设计

针对主减速器壳体在立式多刀半自动车床上加工时,采用标准液压三爪卡盘无法有效定位夹紧工件的问题,依据工件的结构特点,设计制造一种能在一次装夹下完成粗精两序加工的专用车削工装夹具,彻底解决了由于多刀同时粗加工、车削抗力大,工件夹持不可靠的安全问题。通过夹紧力的高低压转换,有效防止工件夹紧变形。生产实践证明,该夹具简单可靠,便于操作,提高了生产效率,保证了加工精度。     

Modeling and compensation technology for the comprehensive errors of fixture system

Error modelling and compensating technology is an effective method to improve the processing precision.The position and orientation deviation of workpiece is caused by the fixing and manufacturing erro...     

Stability improvement and vibration suppression of the thin-walled workpiece in milling process via magnetorheological fluid flexible fixture

In aerospace industry, thin-walled workpiece milling is a critical task. Also, the machining vibration is a major issue for the accuracy of the final part. In this study, a new dynamic analytical model is proposed to determine the effect of damping factor on the dynamic response of thin-walled workpiece in machining. A complex structure workpiece is equivalent to a thin plate. The fixture constrains and the damping factor are crucial elements of this thin plate. Therefore, the magnetorheological fluid flexible fixture is designed to suppress the machining vibration in machining process. Then, the general dynamic cutting force model and the damping force model are proposed for the key dynamic equation for the prediction of dynamic response to evaluate the stability of the milling process with and without the damping control. Finally, the feasibility and effectiveness of the proposed model is validated by machining tests. The predicted values match on the experiment results.     

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.     

孔系组合夹具三维构形自动生成研究

采用ObjectARX语言开发了具有夹具特征和装配特征的参数化的孔系组合夹具元件库,并基于夹具特征和专家系统,建立了一种自动确定定位和夹紧区域的孔系组合夹具构形图自动生成系统,并阐述了有关算法主要思想.     

基于实例推理的机床专用夹具虚拟装配技术

针对传统的夹具设计存在着设计周期长、设计效率低等问题,实例推理的机床夹具虚拟装配技术大大提高了机床专用夹具的设计速度,减少了重复劳动,满足了现代制造系统灵活、快速的要求。采用基于典型实例推理机制的机床专用夹具设计方法,重点研究了机床专用夹具实例检索模型、实例组织模型、实例修改推理机制及基于Pro／E的机床专用夹具实例快速装配方法,实现了机床专用夹具实例快速装配。研究结果表明该方法有利于提高夹具设计效率,可以在机床夹具设计行业进行推广。     

Automated fixture configuration using projective geometry approach

The geometric and topological specification of a workpiece boundary is usually represented in a specific data format in a CAD database. To retrieve a set of workpiece data, to analyse its shape in addition to the machining requirements, and to determine the proper fixture configuration accordingly, are not trivial tasks when a part has a complicated shape. The real challenge is to recognise and synthesise the shape of a workpiece from its data representation. Consequently, the decision for fixturing can be made when the shape of a workpiece and the relationship of the shape and the fixturing configuration can be derived by a systematic methodology. In this paper, a projective spatial occupancy enumeration (PSOE) approach is applied as a representational and manipulating scheme for developing algorithms in automatic fixture configuration. The workpiece is projected onto the working plane of the fixture baseplate. A 2D projection is defined as a matrix of cells which can represent a workpiece with an arbitrary shape. Using a discrete search based upon the matrix of cells, the fixture types and their locations are generated according to a set of heuristic algorithms. This work is a generalisation and extension of previous works for prismatic parts. The same methodology is equally applicable in general robot grasping.     

机床夹具设计资源库构建方法研究

分解夹具设计过程中涉及的信息,分析机床夹具设计信息的数据结构,采用以夹具为主题的基于关系数据库的事实表/维表的多维数据组织结构,提出一种将知识和实例结合在一起的混合知识表达模型,建立了由工件信息库、制造信息库、夹具设计知识库以及参数化三维图库组成的夹具设计资源库。