Machining Planning for Tolerance Synthesis

The present paper deals with the preliminary study and the prototypical implementation of an expert system to quickly define an high level manufacturing sequence able to produce the assigned part tolerances. To do so, the expert system simulates the human reasoning process by applying specific knowledge and inferences. An assembly that is widely used to test the performances of different design methods represents the case study. This module belongs to a flexible and integrated environment that aims to automatically define both the tolerance specifications and the related process plan. Its aim is to support the designer during the definition of a functional project.     

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.     

基于特征的公差分析与综合中尺寸链的自动建立

在特征造型基础上阐明了零件和装配体中尺寸、公差的表达和记录，并讨论了尺寸、公差链自动建立的一种方法，以便进行公差分析与综合，使产品成本和精度最佳协调。在产品的三维实体模型上，设计者只需捡取待分析的封闭环的两个端元素，程序就会在零件模型和装配模型中自动搜索建立与此封闭环有关的尺寸链，并确定尺寸链各环的增减性。     

面向STEP-NC控制器的数控加工工艺规划模型

STEP-NC是欧美提出的一种用以取代ISO 6983的新数控接口标准(ISO 14649)。分析了STEP-NC数据模型及其对数控系统的影响，基于STEP-NC的基本思想将数控加工中的工艺规划划分为离线规划、在线规划和实时规划，重点研究了基于STEP-NC控制器的在线规划问题。为了避免过多地占用加工时间，提出了按工步级规划→特征级规划→零件级规划的在线规划模式，并据此分别给出了工步级铣削用量的优化模型、特征级工艺路线的筛选方法以及基于启发式算法的工步排序方法。     

Evaluating Multiple Feature-Based Machining Methods Using an Activity-Based Cost Analysis Model

For a designed part, if different sets of features are used for machining, the manufacturing costs may vary. In this research, the different manufacturing costs for the different feature-based machining methods are analyzed using an activity-based cost model. First, the activities required for machining a set of features are analyzed. Second, the activity-related cost for each activity is evaluated based on a consistent time scale. The summation of costs of the activities equals the manufacturing cost for producing the part. Finally, the different manufacturing costs corresponding to the multiple feature-based machining methods are evaluated. The set of features that can be machined with the lowest manufacturing cost is considered a good way to produce the part. Example parts are tested and discussed.     

制造系统中的公差与成本

公差设计是产品设计中的重要组成部分。公差设计的优劣,对产品制造加工过程有直接影响。文章详细分析了产品公差设计的类型和过程及产品成本的各项因素,提出了公差—成本关系的基本模型,为基于成本最低的公差设计优化提供了基础理论依据。     

公差优化中的制造成本估算

以公差优化为目标进行制造成本估算是对公差———成本关系进行建模的基础问题。文章分析比较了传统的制造成本的计算方法,提出了已知制造系统状态时对公差———制造成 本关系的建模 方法———多参数公式法,详细阐述了该方法的使用环境以及提出该方法的必要性及合理性,并以实例对其可用性进行了说明和验证。     

绿色机械加工的研究现状及其发展

以绿色制造为基础提出了绿色机械加工的概念 ,并阐述了其内涵 ,概述了绿色机械加工的特点及其应用 ,指出尚待解决的主要问题 ,并探讨了其发展趋势     

螺旋铣孔工艺的切削稳定性及工艺参数规划

以螺旋铣孔工艺时域解析切削力建模、时域与频域切削过程动力学建模、切削颤振及切削稳定性建模为基础,研究了螺旋铣孔的切削参数工艺规划模型和方法。切削力模型同时考虑了刀具周向进给和轴向进给,沿刀具螺旋进给方向综合了侧刃和底刃的瞬时受力特性;动力学模型中同时包含了主轴自转和螺旋进给两种周期对系统动力学特性的影响,并分别建立了轴向切削稳定域和径向切削稳定域的预测模型,求解了相关工艺条件下的切削稳定域叶瓣图。在切削力和动力学模型基础之上,研究了包括轴向切削深度、径向切削深度、主轴转速、周向进给率、轴向进给率等切削工艺参数的多目标工艺参数规划方法。最后通过试验对所规划的工艺参数进行了验证,试验过程中未出现颤振现象,表面粗糙度、圆度、圆柱度可以达到镗孔工艺的加工精度。     

数控车削虚拟加工环境全景仿真技术

指出目前数控加工仿真的缺陷并提出解决方法 ,实现含有整个数控车削加工环境的全景仿真 ,可表达几何仿真、加工过程仿真及加工质量仿真。作为基层关键技术 ,为解决当今切削加工仿真及其运行模式所存在的问题提供了一条有效的新途径。     

智能寻位加工技术中一种新的寻位方法

智能寻位加工中的关键技术是工件寻位。文章对现有的工件寻位方法进行了分析,指出了它们的优缺点,并在此基础上提出了一种适合常规工件寻位的新方法,实验证明这种方法简洁实用,能够应用到寻位加工系统中去,实现常规工件的敏感制造。     

某型手枪击发机构装配公差分析与信息化集成研究

针对轻武器行业人工修锉问题和企业数字化设计与制造需求,利用VSA软件进行了某手枪击发机构三维装配公差分析,得到了与实际装配情况一致的结果,说明基于三维模型的计算机辅助公差设计技术适用于轻武器设计制造公差控制,在轻武器数字化设计制造过程中可以为实际设计、制造提供支持,减少工程更改。在此基础上提出了CAT在数字化协同设计和制造环境下系统信息化集成框架、应用模式、数据模型和数据交互方式等,为后续系统的开发、集成与应用提供了参考。     

高速转体零件的加工工艺改进

介绍了加工高速转体零件分散工序与集中工序的工艺对比,及其完工零件对成套产品的影响.     

Tolerance control for dimensional and geometrical specifications

The development of tolerance charts has come a long way from the past manual methods to the current computer-aided models. As a result, many techniques have emerged over the years. However, the area of geometrical tolerance charting has not been given much attention. In view of this, this paper addresses both linear and geometrical tolerance control.The method proposed in this paper allows the user to construct a model directly from the process plan. The relevant process links between any two planes which are required to satisfy both the linear and geometrical requirements are easily obtained from the model. Having established all the appropriate constraints, the linear programming optimisation software is used for the determination of the unknown working dimensions and tolerances.In essence, this paper presents a new methodology for deriving the process links from the process plan and also highlights the significance of the use of linear programming in achieving the optimal tolerance mix or combination.     

Optimum manufacturing tolerance to selective assembly technique for different assembly specifications by using genetic algorithm

Tolerance on parts dimension plays a vital role as the quality of the product depends on sub components tolerance. Thus, precision products that are manufactured reflect at high manufacturing cost. To overcome this situation, sub components of an assembly may be manufactured with wider tolerance, measured (using latest technologies like image processing) and grouped in partition and corresponding group components may be mated randomly. This present work is to obtain an optimum manufacturing tolerance to selective assembly technique using GA and to obtain maximum number of closer assembly specification products from wider tolerance sub components. A two components product (fan shaft assembly) is considered as an example problem, in which the subcomponents are manufactured with wide tolerance and partitioned into three to ten groups. A combination of best groups is obtained for the various assembly specifications with different manufacturing tolerances. The proposed method resulted nearly 965 assemblies produced out of one thousand parts with 15.86% of savings in manufacturing cost.     

A 2D Tolerance Chart for Machining Angular Features

tolerance chart illustrates visually the manufacturing sequence of all operations to make a product. In this paper the difficulties of dealing with angular features in a tolerance chart are analysed. A 2D angular tolerance chart is constructed and presented. Then, the algebraic approach is used to determine the working dimensions and to check the tolerances. This 2D tolerance chart can deal with angular features, as well as square-shouldered features. A 2D tolerance chart can be simplified to be a 1D tolerance chart when the features are all square-shouldered.     

多工位装配过程夹具系统公差和维护综合优化设计

提出一种面向二维多工位装配过程、综合考虑装配夹具系统全寿命周期成本、产品零件孔制造成本和产品质量损失成本的公差和维护综合优化方法。分析多工位装配尺寸偏差传递关系,建立多工位装配过程产品质量损失模型。然后根据4-2-1夹具定位原则,构建考虑夹具磨损过程损失的夹具定位销副偏差统计数字特征模型。继而发展了以夹具系统全寿命周期成本、零件孔制造成本和和产品质量损失成本为装配总成本最小化的定位销公差、零件孔公差与更换周期优化模型。以汽车侧围装配过程为例,分别研究定位销公差、零件孔公差、定位销更换周期、配合间隙、平均磨损率和磨损率方差对装配总成本的影响,并优化设计定位销公差、零件孔公差和定位销更换周期。所提出的综合优化设计方法比采用定位销等公差设计、零件孔等公差设计、定位销与零件孔等公差设计和定周期更换设计的装配总成本分别减少了16.25%、11.31%、39.93%和13.54%。该方法为产品装配夹具系统高质量低成本设计提供了一种新的途径。     

仿真加工的网络远程监控系统研究

在网络化制造模式下,需要加工设备具有和网络进行交互的功能,以实现远程的监视和控制.在这种背景下,文章提出了以客户/服务器模式为基础,以数控铣床仿真加工为监控对象的远程监控系统,来模拟实际铣床加工的远程监控过程.建立了监控系统的体系结构模型,设计了客户端和服务器的功能模块和界面,开发了专门的应用层协议,并取得了很好的远程监控效果.     

Tolerance synthesis adopting a nonlinear programming approach

One of the main objectives in tolerance charting is to determine the working dimensions and tolerances at the lowest cost without violating the blueprint specifications. In view of this, this paper presents a simple dimensional chains identification method. After establishing all necessary equations and constraints, a nonlinear objective function is formulated. Subsequently, all these relationships are submitted to an optimisation software, OPTIVAR written in FORTRAN for the determination of the unknown variables. In addition, an example is incorporated to demonstrate the effectiveness of this proposed methodology.     

基于知识工程的大型复杂冲压件工艺方案设计

运用知识工程和特征技术实现了大型复杂冲压件工艺知识的完整表述及其知识模型的建立,并通过冲压工艺知识驱动对应的智能决策机制完成了工艺特征的映射及工艺方案的智能设计,有效地解决了基于图形、规则及经验知识的决策判断,以及计算、分析与推理判断的融合问题.基于知识工程的工艺设计提升了大型复杂冲压件工艺方案设计的智能化程度,提高了设计的质量和效率,减少了工艺设计对设计人员经验的依赖.