基于TAD聚类的零件装夹规划方法研究

为实现零件加工时的自动装夹分组及定位面、装夹面的自动选择,从定义特征、加工面、装夹方案及它们之间的关系出发,采用聚类的思想求解装夹规划问题.在划分加工阶段的基础上,提出用"找相同元素法"获得刀具进入方向(TAD)相同的特征组合.对特征——TAD矩阵做变换,得到TAD可行解,进一步对TAD可行解寻找装夹面、定位面,并生成装夹可行解,即可形成装夹方案.以CATIA平台为基础,用CAA开发软件验证了该方法的可行性.该方法对实现零件的装夹分组有重要作用.     

联接盘零件的加工精度及变形问题研究

联接盘是卷烟机刀头组件中最关键的零件之一,由于需要高速旋转,因此,该零件的形位公差精度要求特别高,对零件各部分形状的对称性也有特殊要求。该零件属于薄壁件,不易装夹,易变形。通过自制专用工装来装夹,适当集中了加工工艺,并合理编制数控程序,有效提高了该零件的加工精度、解决了零件变形问题,保证了零件的加工质量。     

基于有限元分析的薄壁圆环零件加工工艺研究

目的 针对薄壁圆环零件刚性差、强度弱、加工过程中易发生受力变形的难题,基于薄壁圆环零件加工成形工艺,优化零件的加工工艺和装夹方式。方法 考虑到工艺对零件加工质量的影响,对零件的加工方法和装夹方式进行研究,提出一种新的加工工装,运用ANSYS软件对零件装夹受力情况和振动变形进行有限元模拟仿真分析。结果 该工装不仅能够防止零件发生应力集中,还提升了零件加工精度和表面质量,工装设计为一夹一顶方式,只需调整顶尖压紧力便可确保圆环件在加工中不会发生变形,同时拆装方便,提高了生产效率。结论 对于薄壁圆环件的数控加工,可通过科学设计零件加工工艺流程和装夹工装,解决零件受力变形问题,保证薄壁圆环零件的尺寸、形位公差和表面粗糙度符合要求,提高了生产加工效率,满足产品批量生产使用要求,为类似薄壁件的加工提供了参考。     

篦齿盘机械加工变形控制研究

篦齿盘是航空发动机的关键零件之一,该零件刚性较差,加工变形比较严重,具有很高的加工难度。该文通过对零件特点以及变形规律进行分析,依据以往的加工经验探索加工变形控制方法,分别从工艺路线安排、装夹方式、数控程序走刀路线以及加工参数等方面进行改进,以达到控制零件变形,提高零件质量的目的。     

典型薄壁零件在数控车床上的装夹与加工

薄壁零件在装夹和加工会存在较大的变形,很难保证零件的尺寸和形状精度。针对这一特点,我们结合在数控车床上的装夹与加工根据经验设计出了一套简单实用的夹具,通过实践该夹具解决了在加工中产品变形的问题,保证了产品的尺寸和形状精度。现就该产品的加工方法和夹具设计进行相应地阐述。     

大直径薄壁件的加工工艺研究

加工大直径特种材料薄壁零件极易产生变形问题,本文研究了一种材料为4J32的低膨胀合金的大直径薄壁零件,分析了薄壁零件加工变形主要是由装夹引起,提出采用端面压紧加工内孔和弹性胀套装夹加工外圆,可以有效地保证该零件的加工精度。最后通过对几批零件的质量跟踪,验证了该方法可有效控制零件的椭圆变形。     

活塞式发动机安装节加工工艺研究

在活塞式发动机零部件加工中,安装节属于异形结构件,其材料特殊,形状奇异,尺寸精度要求高、公差小,难以装夹及加工,本文通过对零件的加工工艺分析,选择合适的热表处理方式,摸索合理的加工参数,来提高生产合格率和产品质量水平。     

汽车空压机缸体缸孔加工用成组夹具的设计与应用

针对汽车空压机缸体缸孔加工中可调夹具装夹效率低、间隙不一致而导致装夹偏斜、加工孔与机床主轴不平行等问题,通过优化夹具结构、增设工艺安装板和随行压紧机构等,设计了一种用于汽车空压机缸体缸孔加工的成组夹具。将该成组夹具装在某汽车空压机制造企业的立式数控珩磨机上进行试验,结果表明：使用该成组夹具,一次最少能装夹2个工件,安装效率大幅提高,每件可减少辅助工时60 s,同时能够提高零件的加工精度,满足企业生产要求,对于解决异形零件内孔加工问题具有一定的参考价值。     

某发动机多个机匣零件通用铣槽夹具设计与应用

本文针对一组结构类似的发动机机匣零件,对零件的结构和尺寸和装夹特点进行分析,设计了一套5个机匣零件通用的型槽铣加工夹具,满足各不同尺寸零件的装夹和定位要求,通过零件的加工试验,验证了该夹具结构方案的可行性。     

精密盘类零件车削加工方法解析

本论文主要论述的是某机平衡用夹具的关键零件安装边的加工工艺分析。此零件技术条件要求严,圆柱度为0.003和全部跳动公差为0.02,属于高精度零件之列。通过改进材料及合理安排加工方法,使车削加工变更方便,最终保证最终图纸要求。     

Alternative tolerance allocations for machining parts represented with multiple sets of features

In a feature-based model, if feature interactions occur, there may exist multiple sets of features that can be used to represent the same part. The multiple sets of features represent different ways for machining the same part. In tolerance charting, the different sets of features represent alternative ways that the working dimensions and working tolerances can be allocated to achieve the specified blueprint dimensions and tolerances. This paper presents a feature-based tolerance charting approach to evaluate the multiple sets of features from the tolerance allocating point of view. A feature-based tolerance charting methodology is developed for automatically allocating the working dimensions and tolerances for 3D prismatic parts represented in boundary representation data. The tolerance charting methodology is used as a basis for evaluating the multiple sets of features. The objective is to find the set of features that is capable of maximizing the cumulative sum of working tolerances and minimizing the cost functions. Under a consistent tolerance charting methodology, different sets of features are analysed and evaluated. The set of features that fully utilizes the blueprint tolerances to achieve the objective functions is considered 'better' for machining. The developed method is implemented on a personal computer. Example parts are tested and discussed.     

Identification of machining features based on available resources of cutting tools

In research on machining feature recognition, the problems of interacting features and availability of cutting tools are considered two major obstacles for developing industrial applications. In this research, a new machining feature recognition approach is developed to address these problems. In this work, a new concept called cutting mode is introduced to associate generic machining surfaces and cutting motions. In the feature recognition process, the machining surfaces of a part are first mapped to cutting modes, and these cutting modes are further mapped to available cutting tools. Among all the created candidate machining processes, heuristic rules are employed to identify the optimal solution that requires the minimum number of setups. When a number of machining surfaces are associated with a cutting tool in the same setup, these surfaces are grouped as a machining feature. Therefore the interacting features are recognised by the different cutting tools to produce these features. A database of available cutting tools is used to avoid the identification of features which cannot be machined in a machine shop. Three mechanical parts with interacting features are selected in the case studies to demonstrate the effectiveness of the developed approach.     

Geometry-based machining precedence reasoning for feature-based process planning

This paper presents a method to generate machining precedence relations systematically based on the geometric information of the part. The feature recognition method using Alternating Sum of Volumes with Partitioning (ASVP) Decomposition is applied to obtain a Form Feature Decomposition (FFD) of a part model. Form features are classified into a taxonomy of atomic machining features to which machining process information has been associated. Geometry-based precedence relations between features are systematically generated using the face dependency information obtained by ASVP Decomposition and the features' associated machining process information. Multiple sets of precedence relations are generated as alternative precedence trees based on the feature types and machining process considerations. These precedence trees can be further enhanced with precedence relations from tolerance specifications and machining expertise. Machining sequence planning can be performed for each of these precedence trees while minimizing the number of tool changes. The precedence trees may then be evaluated based on machining cost and other criteria. The precedence-reasoning module is currently being implemented within a comprehensive computer-aided process planning system.     

Setup planning using Hopfield net and simulated annealing

This paper reports a new approach to setup planning of prismatic parts using Hopfield neural net coupled with simulated annealing. The approach deals with setup planning in two stages, i.e.: (1) sequence all the features of a workpiece according to geometric and technological constraints; and (2) identify setups from the sequenced features. In the first stage, the task of feature sequencing is converted to a constraint optimization problem (COP) which is similar to the travelling salesman problem (TSP). The setup time due to setup and tool changes is incorporated into the 'distance' between features, while the precedence and critical tolerance relationships between features are treated as constraints. The Hopfield neural net approach for TSP, i.e. energy function, is adopted to model the COP mathematically where the constraints are attached as additional penalty functions. Simulated annealing is then used to search for the minimum energy state of the net while avoiding the local minima. The feature sequence obtained aims at minimizing the number of setups and tool changes while ensuring little or no violation of feature precedence relationship, thus keeping critical tolerance violation to a minimum. In the second stage, setups are generated from the sequenced features using a vector intersection approach based on common tool approach directions. A case study is presented to demonstrate the effectiveness of this approach. A comparison study between this approach and an existing integer programming setup planning system is also given which indicates the superior efficiency of the proposed approach when dealing with problems with large number of features.     

Setup planning for machining the features of prismatic parts

This paper focus on the development of a formalized procedure for automatic generation of feasible setups and then to select an optimal setup plan for machining the features of a given prismatic part. The proposed work simultaneously considers the basic concepts of setup planning from both machining and fixturing viewpoints in order to formulate feasible setup plans. The tasks that are performed are: (a) identifying groups of features that can be machined in a single setup, (b) determining a suitable work piece orientation, i.e. the suitable datum planes for each setup, (c) determining all the feasible setup plans to machine the given set of features of prismatic parts, and (d) evaluating the feasible setup plans on the basis of technological (available tolerance) and economical conditions (total setup time). For the proposed work the authors have introduced four new concepts namely, ‘surface fit for location’, ‘primary group’ ‘secondary group’, and ‘eligible group’. The first concept plays an important role in the identification of suitable faces of the part for positioning, clamping and supporting. The other three help in clustering of features, which can be converted in to candidate setups.     

Evaluating the manufacturability of machined parts and their setup plans

Design-for-manufacturability is an approach that requires product designers to consider the manufacturing issues of a product concurrently with the geometrical and design aspects. This paper presents a manufacturability evaluation methodology that incorporates design, machining and work-holding issues. The evaluation is carried out in two parts. The first part is related to the machinability of the features of the part, whereas the second part is concerned about the fixturability of the part with regards to its planar faces. The methodology uses the fuzzy sets theory and the analytical hierarchy process method to evaluate the accessibility, orientation, dimensional tolerances, and surface finish specifications of a part. The former is used to model the various ill-defined boundaries of the criteria, while the latter allows for differences in opinions from designers/machinists to be incorporated into the evaluation process. The quantitative machinability and fixturability indices found can be used to evaluate designs and generate redesign suggestions. A setup plans evaluation module has been developed to determine the merit indices of setup plans for machining a part using these machinability and fixturability indices.     

飞机结构件加工域单元分层识别及构造方法

加工域的自动识别是自动数控加工编程的关键技术之一。为实现飞机结构件自动数控加工程序编制过程中工序件加工域的自动识别,建立了加工域模型,提出了一种实用、可行的域元分层识别方法。首先,根据工序件构建分层面,截切零件和毛坯;其次,依据层交结果构建层域元轮廓,生成层域元;然后,建立规则合并层域元生成域元;最后,通过匹配域元间纵向关系,构建域元树状模型。通过对飞机结构件的测试,证明了该方法的有效性和实用性。     

Tolerance analysis for setup planning: A graph theoretical approach

Setup planning is the act of preparing detailed work instructions for setting up a part. The purpose of setting up a part is to ensure its stability during machining and, more importantly, the precision of the machining processes. Therefore, tolerance control can be achieved proactively via setup planning. This fact was somewhat overlooked in the computer-aided process planning (CAPP) research community. While many researchers focused their attention on tolerance chart analysis, the issue of tolerance analysis for setup planning was relatively unexplored. To systematically solve the setup planning problem, a graph theoretical approach is proposed. The design specification of a part is represented as a graph. The problem of identifying the optimal setup plan is transformed into a graph search problem. A setup planning algorithm for rotational parts was then developed. The algorithm was evaluated and found to be both efficient and effective.     

Recognizing generalized pockets for optimizing machining time in process planningPart 1

In this two-part paper, a new methodology for feature recognition (FR) and machining planning is described. Most of the earlier FR work was aimed at facilitation of machining planning by extraction of simple shaped features. Our method deviates from earlier strategies, attempting to recognize relatively complex shaped features that are not only machinable, but also allow smart machining planning to reduce total machining time. This new approach has two advantages: allowing complex-shaped features leads to computational advantages, simplifying the recognition; also, the ability to generate near-optimal machining plans for complex pockets results in reduced total machining time for parts. The first part of this paper concentrates on the details of the machining feature extraction procedures. The algorithms are presented, and examples provided. The recognition system has been tested successfully for over 70 parts from the NIST part repository, including most benchmark parts from research and industry. The second part of the paper will describe a multiple-tool milling planning technique. Results will be presented to prove the viability of this system.