An integrated fixture planning system for minimum tolerances

Fixture planning is an important aspect of process planning. The steps involved in automatic fixture planning are manufacturing feature recognition, setup planning and fixture configuration planning. In the present work, an integrated setup and fixture planning system is developed for minimum tolerances at critical regions using a data exchanged part model as an input. A platform-independent STEP-based automatic feature recognition system that can recognize both design and manufacturing features, including intersecting features is implemented. An automatic setup planning module is developed for generating setup plans for complete machining of a given component. A fixture planning module is developed applying the criteria of uniqueness, stability, accessibility and tolerance minimization. A case study is presented to demonstrate the capabilities and integration between the various modules of the system.     

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.     

特征在加工过程中的变异性研究

从加工工艺角度分析特征在加工过程中的演变规律。提出了变异特征的概念,探讨了变异特征在结构、属性、类型等方面的变特点。给出了变异特征属性邻接图和边面关联矩阵, 表达了变异特征组成成面之间的有机联系。通过一般产品上特征的变异性定义,实现了基于变异特征的零件建模,并在夹具安装规划自动设计系统中初步应用,得到了较理想的夹具装夹方案。     

加工余量的自动确定

为使机床夹具自动设计系统能够快速、准确地自动确定加工余量,分别对影响加工余量的八种因素作了详细的分析和推导,给出了一套实用、准确的计算公式,并成功地应用于夹具安装规划自动系统.     

An intelligent fixture design method based on smart modular fixture unit

Fixture is an important assisting resource for manufacturing. Its design is under the combined influence of workpiece, machining methods, material performances, etc. and demands rich experience of the designer, which leads to significant increase in design cycle and costs. This paper researches on a new automatic fixture design methodology based on inheriting and reusing design knowledge. Traditional fixture model is changed to smart fixture model, which is not only a geometric model but also appending geometric knowledge, process planning knowledge, and performance knowledge. On the other hand, the ontology of workpiece’s machining requirement is established for driving smart fixture automatically. Based on the above ontology, the self-selection reasoning method is proposed, for machining planner, which can push unit selection scope and drive its size actively. To drive fixture unit assembly automatically, the self-assembly reasoning method is proposed according to typical feature’s assembly mode. By these ways, the geometric consistency among units as well as unit/workpiece is maintained. In the end, design efficiency and quality is expected to be improved more automatically.     

定位基准的自动优选原理与算法

为了在CAD CAPP自动系统中确保加工精度 ,研究并导出了特征综合定位能力计算的量化公式。给出了系统算法流程图。解决了特征与面的信息转换和数据结构等问题。在夹具安装规划系统FSPS上成功实现了定位面的自动优选和细分     

Workpiece locating error prediction and compensation in fixtures

In machining process, fixture is used to keep the position and orientation of a workpiece with respect to machine tool frame. However, the workpiece always cannot be at its ideal position because of the setup error and geometric inaccuracy of the locators, clamping force, cutting force, and so on. It is necessary to predict and control the workpiece locating error which will result in machining error of parts. This paper presents a prediction model of a workpiece locating error caused by the setup error and geometric inaccuracy of locaters for the fixtures with one locating surface and two locating pins. Error parameters along 6 degrees of freedom can be calculated by the proposed model and then compensated by either using the “frame transformation” function of a numerical control (NC) system or modifying NC codes in post-processing. In addition, machining error caused by the workpiece locating error can be predicted based on a multi-body system and homogeneous transfer matrix. This is meaningful to fixture design and machining process planning. Finally, a cutting test has shown that the proposed method is practicable and effective.     

Four point bending setup for characterization of semiconductor piezoresistance

We present a four point bending setup suitable for high precision characterization of piezoresistance in semiconductors. The compact setup has a total size of 635 cm(3). Thermal stability is ensured by an aluminum housing wherein the actual four point bending fixture is located. The four point bending fixture is manufactured in polyetheretherketon and a dedicated silicon chip with embedded piezoresistors fits in the fixture. The fixture is actuated by a microstepper actuator and a high sensitivity force sensor measures the applied force on the fixture and chip. The setup includes heaters embedded in the housing and controlled by a thermocouple feedback loop to ensure characterization at different temperature settings. We present three-dimensional finite element modeling simulations of the fixture and discuss the possible contributions to the uncertainty of the piezoresistance characterization. As a proof of concept, we show measurements of the piezocoefficient pi(44) in p-type silicon at three different doping concentrations in the temperature range from T=30 degrees C to T=80 degrees C. The extracted piezocoefficients are determined with an uncertainty of 1.8%.     

A systems approach to fixture planning and design

Within the last decade, the manufacturing research community has addressed many of the micro issues of automating the fixture design process using computers. Most of this research has concentrated on the geometric and kinematic factors that determine the configuration of a computer-aided fixture design (CAFXD) system. However, before the implementation of any of the researched micro issues can be accomplished, a systematic approach to fixture planning and design must be recognised that considers the macro issues (process planning and fixture design) of the complete design to manufacturing process. In order to improve the effectiveness and implementation of researched micro issues in fixture design, a generic model of the functional activities can provide an understanding of the process and information exchanged between process planning and fixture design. This paper presents such a generic IDEF working model that promotes the functional integration of these two functions — developed from a systems perspective.     

Design for economic manufacture of small sheet metal parts

Arguments are presented for a consideration of the DEM of pressed parts on a basis of equipment and tooling used to produce the parts rather than consider a categorisation based on ‘type’ by industry. It is also suggested that a combination of both generative and variant techniques of process planning, in conjunction with a good classification system and data base, should be used by the designer to develop, store and retrieve the type of information used in cost-optimising the design of pressed parts. This paper outlines the elements of cost involved in the production of pressed parts and presents details of a computer-aided process planning system which will assist the designer to quickly obtain the information necessary to optimise the designs. Typical computer program inputs and outputs are presented together with rules that have emerged in pressing design to reduce the number of tooling stages required and therefore the component manufacturing cost.     

基于网络的夹具设计信息模型与应用研究

根据夹具设计特点论述了集成工艺设计中夹具设计信息数据结构，应用面向对象的方法描述了夹具设计的制造工艺信息类和制造资源信息类体系结构，建立了数据结构中夹具设计的装夹工艺模型和夹具资源模型，根据建立的信息模型开发了装夹工艺信息子系统和夹具资源信息子系统，并在网络环境下得到了应用。     

由机器人调整的可重构汽车车身焊接夹具的设计研究

介绍了一种全新的由机器人调整的可重构汽车车身焊接夹具,该夹具充分利用了焊装生产线上工业机器人的高精度与柔性自动化能力,并采用"一步直拉式"夹具定位调整方法,实现夹具的快速自动化构建与调整.     

夹具规划技术研究

在计算机辅助夹具设计过程中,探讨了夹具规划的实施方法。考虑了从早期概念设计阶段到后期结构设计阶段多方面的因素,提出了夹具单元构形设计的概念,由此讨论了给定定位表面后夹具结构多方案的生成和优化。这种设计过程为夹具设计自动化提供了一种新的、自顶向下的设计途径。最后通过实例进行了分析验证。     

基于MDT的组合夹具CAD系统中元件选择及精度计算实现

组合夹具由不同形状、不同规格尺寸的标准元件组装而成。夹具设计过程中工艺人员在组装角度夹具和一些基本功能结构时,通过选取同类元件的多个不同系列尺寸装配形成一个组合尺寸。基于MDT软件和组合夹具CAD系统,开发了夹具设计中组合尺寸元件选择和精度检验的实现方法。     

Concept design of checking fixture for auto-body parts based on neural networks

The concept design of checking fixtures for auto-body parts is a highly complex process that requires a human designer to draw from his rich experience. By exploiting recent advances in CAD/CAM and artificial intelligence techniques, one may constrain multiple solutions such that only good designs are considered. In this paper, a method of selecting type for checking fixtures is proposed that harnesses advantages of neural networks. This method attempts to capture relevant domain knowledge and is used to produce acceptable solutions. The method is applied to a case problem and the suggested checking fixture type is compared to one offered by a human designer. The agreement between the two solutions is very close.     

Development of Automated Fixture Planning Systems

Fixturing is an important manufacturing activity. The computeraided fixture design technique is being rapidly developed to reduce the lead time involved in manufacturing planning. An automated fixture configuration design system has been developed to select automatically modular fixture components and place them in position with satisfactory assembly relationships In this paper, an automated fixturing planning system is presented in which fixturing surfaces and points are automatically determined based on workpiece geometry and operational information. Fixturing surface accessibility, feature accuracy, and fixturing stability are the main concerns in the fixture planning. The system development, the fixture planning decision procedure, and an implementation example are presented in the paper.     

Aspects of computer-aided fixture design

Computer software developed for the design of a modular fixture device for use in a computer-integrated manufacturing system is described. The software can guide a designer towards the optimum design of a fixture device by taking account of external forces and their positions, thus preventing obstacles from being placed in the cutting path, or the deflection of a workpiece. The flexibility of the modular system, which is known as SPUD, has been utilized and supported by the Computer-Aided FIXture Design (CAFIXD) system, which offers a high level of automation within the manufacturing process, and the economic benefits which a flexible manufacturing system brings.     

Rigorous Application of Tolerance Analysis in Setup Planning

Decades of computer-aided process planning research has resulted in techniques that automate portions of the process planning task such as operation sequencing and cutter path optimisation. Nonetheless, solutions to other areas such as setup planning and fixturing remain elusive. Setup planning research has received increased attention in recent years. The importance of tolerance analysis in setup planning has been recognised. However, due to the lack of a common measure for different types of tolerances, the analysis is carried out in an ad hoc fashion and often results in suboptimal setup plans. In this paper, a tolerance normalisation approach is presented to provide an accurate means for direct comparison of different types of geometric tolerances and dimensional tolerances. A normalised tolerance is an angle representing the maximum permissible rotation error when locating a component. It is calculated based on rigorous analysis of manufacturing errors involved in component setups. The formulae for tolerance normalisation are derived and the use of normalised tolerance in setup planning is illustrated.     

Computer aided manufacturing planning for mass customization: part 2, automated setup planning

Setup planning plays a crucial role in CAPP to ensure product quality while maintaining acceptable manufacturing cost. The tasks of setup planning include identifying manufacturing features and corresponding manufacturing processes, determining the number of setups, part orientation, locating datum and process sequence in each setup, and selecting machine tools and fixtures. An automated setup planning technique and system has been developed based on not only the tolerance analysis, but also the manufacturing resource capability analysis. The automated setup planning is divided into two levels: setup planning in single part level and in machine station level. Algorithms for setup generation and process sequencing have been developed and a case study of setup planning is presented.     

An integration of assembly planning by design into supply chain planning

A supply chain needs to consider the quality of a product as well as the quality of manufacturing process to satisfy customer requirements at efficient resources planning in terms of safety stock allocation and vendor–buyer coordination. The objective of this article is to use an axiomatic approach to make assembly planning by designing and integrating assembly into supply chain planning, particularly during supply chain reconfiguration. The effect of fixture layout planning, the accuracy of demand forecast, and the supplier capability of providing the required material quality are studied. An optimum supply chain network is configured by combining the product, assembly, and supply chain planning. Heuristic-based optimization is used to validate the proposed solution. The performance of the system is measured in terms of lead time variability, the number of backorders, and the level of safety stock. The results and analysis indicate that the axiomatic approach is capable of reducing the assembly variation and employing necessary fixture layout planning to deliver product intents. In addition, the reduction of assembly variation also reduces the safety stock, lead time variability, and backorders. Finally, management decision making is discussed among other concluding remarks.