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180C柴油机活塞加工工艺规程及工装夹具设计【5张CAD图纸+毕业论文】【答辩通过】

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摘 要

在柴油机气缸内，活塞在一部分工作循环压缩气体，而在另一部分工作循环气缸内混合气体燃烧膨胀使活塞顶面承受高温（约569C）高压（约116～120Kgf/cm2）气体的作用，并把压力通过活塞销、连杆传给曲轴。可见，活塞是在高温高压下作长时间连续变负荷的往复运动，它的负荷和工作环境很恶劣。在本设计中将对活塞的加工工艺进行设计，以保证活塞长久稳定工作。现将设计中所做的工作简要介绍如下：

180C柴油机活塞加工工艺合理性是很重要的，通过对零件的作用及工艺方案分析，拟定毛坯的制造形式及工艺路线，通过分析、比较，采用了相对集中加工工艺方案，最终确定比较合理的机械加工工艺路线。制定工艺路线时主要考虑粗、精加工安排、加工方法选择、工序集中与分散、加工顺序等方面的要求。接着确定加工余量、工序尺寸，经过对工序特点的分析，恰当选择相应加工设备和工艺装备。接下来经过计算查表确定活塞各主要工序的切削用量并绘制工序卡片，最后设计夹具。设计夹具时，要多方面考虑，严格要求，机床夹具的好坏直接影响工件加工表面的位置精度。所以，机床夹具设计是装备设计中的一项重要的工作，是加工过程中最活跃的因素之一。在本毕业设计中特别设计了定位准确、结构简单和使用方便的精镗销孔夹具。


关键字：活塞；工艺路线；加工设备；切削用量；夹具


Abstract

In diesel engine cylinder, the piston part of the cycle in the compressed gases, and in another part of the work cycle of the combustion gas mixture within the cylinder so the piston top surface expansion high pressure (about 116 ~ 120Kgf/cm2)under high temperature (about 569°C) gas role, and the pressure through the piston pin, connecting rod to the crankshaft. Can be seen that the piston is a long time under high temperature and high pressure in continuous reciprocating motion of the load, its load and working conditions were appalling. During the design process of the piston will be designed to ensure long-term stability of the work piston. The design of the work done by a brief introduction as follows:

   Diesel Engine Piston 180C reasonable processing technology is important, the role of parts and technology program analysis, preparation of rough form and process manufacturing line, through the analysis, comparison, use of the relative concentration of processing programs, and ultimately more reasonable to determine the mechanical line processing. The development process of rough line the main consideration, finishing arrangements, choice of processing methods, centralized and decentralized processes, such as processing the order requirements. Then determine the allowance, process size, after the analysis of the characteristics of the process, select the appropriate processing equipment and technical equipment. Calculated look-up table to determine the next major piston cutting process and the mapping of processes card, the design of the final fixture. Fixture design, it is necessary to take various aspects into account, the strict requirements of the fixture a direct impact on the surface of the workpiece processing position accuracy. Therefore, the machine tool design fixture design is an important task is the processing of one of the most active. During the graduation project in a specially designed positioning accuracy, simple structure and easy-to-use precision pin hole boring jig.


Keywords: Piston; Technology; processing equipment; cutting; Fixture

目录

摘要……………………………………………………………………Ⅰ

Abstract………………………………………………………………Ⅱ

目录………………………………………………………………………Ⅲ

第1章  序论………………………………………………………… 1

1.1 180 C柴油机活塞的由来 ……………………………………………………1

1.2 机械加工工艺规程………………………………………………………………7

第2章 180C柴油机活塞零件图的分析 ………………………………8

2.1 活塞的功用……………………………………………………………………8

2.2 活塞的结构特点和技术要求  …………………………………………………8

2.3 180C活塞的工作情况 …………………………………………………………9

2.4 180C组合活塞结构 ……………………………………………………………10

第3章 活塞加工工艺制定 …………………………………………12

3.1 计算生产纲领确定生产类型 …………………………………………………12

3.2 审查零件图图样工艺性 ……………………………………………………12

3.3 选择毛坯 ………………………………………………………………………12

3.4 工艺过程设计 ………………………………………………………………13

3.5 确定加工余量及毛坯尺寸、设计毛坯图 …………………………………25

3.6 部分重要工序设计 ……………………………………………………………29

3.7 确定切削用量及基本用时 …………………………………………………33

第4章  夹具设计……………………………………………………50

4.1 机床夹具概述 ………………………………………………………………50

4.2 机床专用夹具设计的基本要求 ……………………………………………50

4.3 活塞夹具的设计思路 …………………………………………………………51

4.4 活塞裙精镗销孔夹具设计 ……………………………………………………51


结论…………………………………………………………………56

参考文献…………………………………………………………57

致谢…………………………………………………………………58

附件 1…………………………………………………………59

附件 2…………………………………………………………81


第1章 序论

1.1 180C柴油机活塞的由来    

180C柴油机是四方机车厂与奥地利AVL公司合作开发的。下面就四方机车厂和AVL公司的发展历史做一下介绍，从他们的发展过程中，我们能看到柴油机行业的一些趋势以及中国柴油机的发展历程。

（1）四方机车厂的光辉历史

四方厂在1958年9月22日试制成的东风型内燃动车的基础上，于1959年4月10日制成了国产第一台液力传动内燃机车--卫星型客运内燃机车。机车装用2台仿西德的12V175Z型柴油机，装车功率2×1000马力，最高速度140km/h。

  上述早期试制内燃机车的特征：一是机车或柴油机基本是仿制国外的产品：二是直流电力传动匹配二冲程中速柴油机和四冲 程高速柴油机；三是液力传动匹配高速四冲程柴油机；四是设计技术水平较低，可靠性较差。

   早期内燃机车的试制及尔后各工厂、研究所进行的大量试验研究和设计改进工作，为国产第一代内燃机车的设计和生产奠定了基础，也为我国铁路内燃化拉开了序幕。


内容简介：
青岛理工大学本科毕业设计（论文）说明书通过识别功能的自动分割表面一代注塑模具K Chung1 ，K Lee2 *和T Kim31R&D的研发团队， INUS科技，韩国2School的机械航空工程系，汉城国立大学，韩国3Department的数字内容，世宗大学，韩国摘要本文提出了一种拓扑结构为基础的识别算法通道功能使用概念多面孔环。该多面孔环是一个概念是循环形成几个连接面孔和充当入口或出口的通道。因此一个通道功能由两个多面孔环相应的入口和出口所确定认识到。至创造的型芯和腔的注塑模具的部分通道的功能，无论是入口或出口的每个通道必须涵盖的面，这面构成分型面。该算法，本文提出了检查连接两个多面孔环承认通道特征。在一个零件上通道特征的数量是通过Euler方程计算的，并且验证程序一直在运行直到验证通道特征等于这个数字。为了找到某一零件所有多面洞环，该提出的方法考虑了所有的组合连接的面。凸边使用用来判断多面洞环的正确性。利用本文所提出的算法，通道特征会被有效地识别出来。提出的方法被很多实例所验证。 关键词：通道特征，特征识别，多面洞环，注塑模具一、引言注塑成型是生产热塑性聚合物部分最普遍的进程。在这过程中，热塑性聚合物注入腔所形成的型芯和腔。这模具腔的形状确定的塑料零件。一般注塑模具的构造如图1所示。图1展现了一个简化的注塑模具和显示板，型芯和腔。除了上面展示的那些，实际注塑模具有许多标准件，喷射器，流动和冷却系统。从历史上看，模具设计师使用二维计算机辅助设计（ CAD ）系统在二维图纸画出一个模具。然而，最近企图注塑模具的设计使用三维CAD系统在个人电脑上广泛使用。 利用三维CAD系统进行模具设计，许多设计任务可以自动或便利。 特别是，分型面可以自动生成或至少更方便 1 - 4 。 分型面是用来切断外部块内附部分被塑造成两块，即型芯和腔。当这部分有通道，无论其入口或出口都必须被表面所覆盖。即使零件表面通过延长零件到外面而非常容易产生，对于复杂零件来说验证所有的通道特征和用恰当表面覆盖它们是有错误倾向的任务。在本文中，提出了通过多面分析通道特征的算法。如图2所示。二、背景和动机图1 铸造模型的基本配置在注塑模具设计系统，是基于三维CAD系统，设计过程开始于零件的三维CAD模型。型芯区块分为型芯的腔。这个过程如图3所示。型芯和腔的生成如图4所示。首先，设计师设计一个能包含零件模型的立方块，在图 5中表示 。这个矩形块被称为型芯区块，这将最终成为型芯的腔。其次，分型面， 而分裂的型芯区块的型芯和空腔，会产生沿外边界部分模型如图6a所示。在分型面，如果要求，也可以产生的一端通道特征如图 6b所示。图2 贯穿多面的通道特征图3 制作型芯和空腔的流程型芯块通过零件和模型的表面被分离出型芯和空腔。型芯在型芯块的较低部分，空腔在上部。型芯和空腔的制造过程如图7所示。如图6b所显示的，分型面应产生的一端每个通道功能分裂型芯区块完全变成两件，即型芯和腔。范例中所示，对于一个简单的通道特征，在分型面的通道特征是很容易产生。但是在复杂通道特征形成多个面的例子中如图8所示，识别环路包围的两端通道特征和表面是非常困难和费时的任务。 图9显示零件表面带有通行特征的一个零件模型。以及图 10 显示通过覆盖通道特征所形成的表面。如图10所示 ， 这些表面分离通过区域包括许多复杂的面。 图4，具有一个通道特征的典型零件上表面和下表面图5 型芯快 图6 产生分型面图7 型芯和空腔的形成图8 听力装置外壳的简化图 大多数通过注塑成型的塑料零件在很多面孔上具有通道特征。 这使自动识别通道特征和创建零件表面变得困难。在本文中，一种检测通道特征的方法在自动生成零件表面的基础上被提出来。2.1相关工作自基普里亚努在CAD系统在他的博士论文 5 指出形状分类的必要性， 特征识别中实体模型一直是热门研究课题。到现在为止，从CAD数据提取加工特征一直是主要研究议题，而且特征识别技术已被衍生提取加工功能，如孔， 插槽和口袋特征 6 。有四种不同的特征识别的方法： （a）在图形模式匹配的方法 7 ， （b）凸包分解方法 8 ， 9 ， （c）基于细胞的分解方法 10 ，（d）在暗示为基础的推理方法 11 。 Joshi和 Chang所发现的图形模式匹配方法在特征识别领域已被证明是最流行的。这种的做法，在一个零件的B -Rep数据结构的被映射到一个节点代表面孔其分支机构代表边缘的图上。该图被称为面对邻接图（ FAG ） 。然后，一个子图同构是用来搜索匹配的子图功能模板。然而，在具有交叉功能的例子中，子图部分的变形，这使特征识别是不可能的。 Woo9提出了凸包分解方法.这种方法确认特征之间的布尔运算的一部分模型和凸包周边零件模型。布尔部分之间的运作模式和凸包是采用递归。当输出布尔操作是空的，行动是终止。不幸地是， 分解过程不一定收敛。为克服这一问题，Kim提出了交替之卷分区（ ASVP ） 分解 9 ，其中确认功能比较零件模型面临的凸包的面。 图9 构成分型面的通道特征所形成表面图10 覆盖通道特征的表面Sakurai 和 Chin 提出了基于细胞分解方法， 这种方法确认特征分解三角洲量到最低限度细胞，然后将这些细胞结合。三角洲量同股票和零件模型是不同的。 使用这种方法，由分解三角洲量所产生的细胞数量很大。因此，大量的组合必须识别相结合的细胞的特征。Vandenbrande 11 提出了暗示推理的方法。这种做法，提出了是为了识别交叉特征，这是图形模式匹配的方法主要问题。 这种技术识别特征源于传统的轨迹特征。例如，一个插槽提示生成，当一对平面平行相交时， 对应于槽壁。有了这样的提示， 该算法识别槽特征通过搜索槽壁之间的缝隙。 正如所建议的上述情况，研究加工特征识别目前正在积极进行。一些研究也已完成对特别与模具有关特征识别，例如削弱特征 13 。然而，就目前作者所知，没有识别分型面产生的通道特征数据的研究。三、概述一个通道特征由一对孔环和连接孔环的面组成的，从而通道特征识别是一个寻找配对孔环的程序。由于通道特征可以通过几个连接的面孔，孔环附着的连接面应该首先被识别出来。 当一个洞环被发现，其配对孔环会被搜查。如果这对孔环满足构成一个通道条件，它将被记为一个通道特征。 3.1定义由于通道特征通过的连接面是被识别的目标特征，一个特别孔环，称为多面孔环，形成多个面，在本文中定义如下： 对于任何一对连接的面，两面所有共享的边缘被消除，扩展面生成。如果内部环的扩展面边缘存在，这些内部环被定义为多面孔环。 一个说明多面孔环的例子如图11所示。图11 多面孔环的一个例子3.2基本概念 一个通道特征由两个孔环组成包括多面孔环和与其相连的面。这些面被称为内面。因此，寻找通行特征的过程，可以在概念上 简化寻找两个相连接孔环。详细过程的解释请看第4节。四、算法 在本节中提出的算法将详细说明解释 。识别简单的通道特征详细的算法将首先被解释，然后识别多连接面孔环所采用的办法将被叙述。一个通道特征被简单定义如果其入口和出口位于在单一的面。最后，多面孔环组成通道必要的条件以及找到结合的连接面方法，将加以解释。 4.1通过特征识别算法如前所述，一个通道特征由两个孔环通过连接面互相结合组成。 将使用下面的例子描述通道特征识别详细的程序。在图12中显示的样本零件拥有一个通道特征，每个对象定义如下：图12 应用简单通道特征的例子a=样本的上表面b=连接上下表面的面c=样本的下表面e1=a、b面共有的边e2=b、c面共有的边L1=a面上的孔环L2=b面上的孔环在这个样本零件中，由环组成通道特征是L1和L2 ，和面，如b面 ，连接这些环。一般来说，面（面b）组成一个拥有相邻面（a面和c面）共同边的通道特征，而且这些边在相邻面（a面和c面）上形成了孔环。也就是说，b面是组成通道特征的面并命名为侧面。a面和c面分别被命名为入口面和出口面。寻找通道特征的程序如下： 1 在一个面内搜索孔环（通道入口面） 。 2 搜索组成孔环的边，在第1步中搜索。 3 搜索分享的边缘面（侧面），在第2步中搜索。 4 如果在第3步中所寻找面（侧面）的边缘形成了一个孔环内另一面（出口面），这孔环和在第1步中的孔环形成一个通道特征。上面对算法的解释是在一个单独的面上识别通道特征。 为了在多个面上识别通道特征，就必须用到多面孔环的概念。4.2多连接面孔环的识别如前所述，一个多面孔环形成一个通过消除连接面共同边缘形成扩展的面。在多个连接面识别孔环需要三个步骤： （a）消除连接面共有的边（b ）用余下的边建造环 （c ）验证内部环。 识别多面孔环的程序描述如下。用于多面孔环的样本零件如图13，灰色面的连接面在调查中。灰色面共享边e1和e2 。如果两面共享边被删除并且两面被认为是一个面对如图 13b所示，两个环形成，即L1和L2 。环L1对应内环和环L2对应于外环。因此，在这个例子中多面孔是环L1。同样，内部环形成多个随意连接面被定义为多面孔环如果当连接面共享边被消除后内环存在。一旦多面孔环被验证，先前已描述的寻找简单通道的程序就能用来识别多面中的通道特征。4.3多面孔环形成通道的必要条件多面孔环形成通道特征有两个必需条件。首先，组成多面孔环所有的边必须是凸的。例如，对于零件如图 14 说明，在面F1中环L1是一个孔环，但组成的边孔环L1并不是通道特征，因为它们是凹。这可能是一个自然的结论考虑到多面孔环的边成为无论是入口或出口的通道，唯有凸边可以形成入口或出口。因此，一个程序来判断凸边是必要的。Kyprianou对边的分类如图15 14 所示 。边通过两个面共享边所组成的夹角分类，例如， 如果测量内部角度小于180 ，边是凸的。同样，如果大于180 ，边是凹的。如果两面连接顺利如图中c或d ，边通过实际的曲率来分类 14 。通过判断边的凹凸，组成多面孔环的凹面或顺利凹边缘在程序识别通道特征中被排除。 图13 识别通道特征的例子 图14 不能构成通道特征的孔环图15 Kyprianou角的分类即使所有的边满足第一条件，有的情况下，通道特征因为组成模型的多面孔环和其他面的关系而不能组成。在这里，第二条件下发挥作用。该多面孔环可以被看作是一个边的集合，将约束后来的分型面的相应通道特征。由于表面生成临别不得重叠的面的一部分，其多面孔环内部重叠区域表面必须考虑排除。 一个多面孔环满足这样的条件如图16，图17所显示多面孔环违反条件。换言之，多面孔环L2生成的零件表面如图16b所示， 这是从复合面衍化出来如图16a，组成零件的面没有任何重叠的。图16 可用多面孔环举例 图17 不可用多面孔环举例在复合面是一组连接的面孔，其中多面孔环被搜查。但是， 多面孔环L2生成的零件表面如图17b，这是在复合面寻找图17a，重叠的部分面孔。 因此，图17这种情况必须在寻找通道特征中排除考虑。不可用的多面体环具有详细条件如下。读者可能会问为什么考虑这样奇怪的例子。所有可能的多面孔环必须考虑，因为它们是由复合连接的面自动生成的。共边的面组成了多面孔环和不参加的复合过程的是侧面。如果边的起点和终点被多面孔环中两个侧面共有，这条边可以和多面孔环的其他边组成环。使用此环生成的分型面应该是侧面中的一个，这使分型面的重叠零件表面。 图18b代表18a零件二维布局图。面F1、F2、F3和F4对应复合面，面S1、S2、S3、S4、S5对应侧面。多面孔环的边界边用粗线表示。 图18b所示边a一条是侧面所共有的边，a的起点和终点都在多面孔环上。因此，边a 形成一个回路连同其他边S5，也属于多面孔环。由这一回路产生成的分型面因为S5的存在也属于多面孔环。因此，分型面重叠S5。通过这种方式，识别多面孔环屈服无效分型面，可避免调查多面孔环与侧面共有边的终点的关系。 4.4找到所有连接面组合的程序为了在一个零件中寻找多面孔环，验证并复合连接面是需要。有二种方法可用于生成一组连接面。第一种方法涉及到通过判断面组中面的连接性选取一组用来复合的面。然而，这一做法，当总数是很大的随意生成的组合面数量增加了可能性。在此X=结合的数量n=面的总数r=将要复合的面的数量例如，如果面的总数是200 ， 当四个面被复合时待定面组合数量是64 684 950 因此，这种做法在一组连接面复合时是低效的。图8 Planar组成面展示第二种方法涉及产生通过已经验证过设定一个可行的面组的连接面面组。 在此方法中，已记录的面组中各成员面都存储在堆栈。然后，它搜索能连接最新登记面的面。如果没有面连接到最新记录面，那么最后记录的面将被从堆栈中移除和继续搜索与移除面下面的记录面。这种方法可以有效地缩短生成仅仅通过结合面找面组时间，而第一办法搜寻所有可能的组合和检查连接性。 所产生用来复合的面组被用于寻找模型中的多面孔环。五、执行5.1程序结构提出算法的基本概念如下。到现在被搜索到的通道特征等于一个模型中通道特征的数量，用于复合的面增加到表2.用Euler方程得到通道特征的总数。每一步，通过搜索相连接的多面孔环，多面孔环和通道特征被找到并识别。因此，执行程序有四个子程序，即找到通道特征总数的路径 ， 寻找所有组合面的结合，识别多面孔环和通道特征。这个项目是在Windows NT上用Unigraphics V15.0 API开发的。 5.2运行时间分析本文中提出的算法搜索拥有越来越多的结合面通道特征。因此，模型中识别通道特征运行时间由连接面最大数量确定。因此，运行时间可由最大复合面数表示。 如前所述，产生用于复合的面组程序涉及到多面与一面和再次进行搜寻面与已搜查面，直至连接面组所有成员等于给定连接的面数。如果在一个零件中的面数是n，平均连接面的数量是m,用于复合的面数是r，那么随意组合的面组是数列n mr1:X O(n mr1)一般而言，一个零件中平均连接面数到远小于面的总数。 图8所示这个零件，总面数是286平均连接面数是5 。在这种情况下，预计用于复合的面数在表1中显示 。 六、举例6.1样本部分样本零件如图19a条有很多凹台面， 孔和通道特征边界的孔环形成一个面。图19b显示6个通道特征识别。图19 拥有环槽和通孔的典型零件6.2 L形部分图20a显示的样本零件中是L形，有一个通过特征组成孔环形成多面加上样本特征通道。在这种情况下，形成多面孔环的面数是4 。被识别的通道特征如图20b。图20 L型零件6.3套管的手机图21a显示样本零件是一个手机封面并拥有14个通道特征。识别的通道特征如图21b。 图21 典型手机表面6.4 小型组成封面样本零件如图 22a的是一个小型部分封面 ，并拥有多面通道特征。这部分有15个通道特征。识别的通道特征如图22b。 上述4例的运行时间在表2中列出。图22 听力装置表面七、结论本文提出了一种算法，使用多面孔环概念自动识别通道特征。分型面的自动产生是用三维CAD系统设计模具最自然的目标任务。当零件的边界产生之后分型面很容易生成。但是，如果被制造零件具有通道特征，其入口和出口应该被分型面覆盖。有时，当零件有一个复杂的形状时验证所有通道特征是一个乏味和容易出错的任务。在本文该算法通过自动识别多面的通道特征缩短设计时间。 本文中该算法提出了识别通道特征，增加可复合面数量。因此，识别通道特征时间受多面孔环形成通道特征的面的最大数量影响。随着复合面的增多，选择用于复合面的时间也因为面组数量的增加随之增加。因此，该算法生成复合的面组需要首先通过排除不实际的情况。此外，基于通道特征自动生成分型面算法需要开发。分型面位于入口和出口的通道时生成分型面会更加困难。当通道的侧面有一个凸曲率这种情况就会发生。21Recognition of pass features for automatic partingsurface generation in injection mouldsK Chung1, K Lee2* and T Kim31R&D Team, INUS Technology, Korea2School of Mechanical and Aerospace Engineering, Seoul National University, Korea3Department of Digital Contents, Sejong University, KoreaAbstract: This paper proposes a topology-based algorithm for recognizing passage features using theconcept of a multiface hole loop. The multiface hole loop is a conceptual hole loop that is formed overseveral connected faces and serves as an entrance or an exit of a passage. A passage feature is thusrecognized by identifying two multiface hole loops corresponding to its entrance and exit. Togenerate the core and the cavity of an injection mould for a part with passage features, either theentrance or the exit of each passage must be covered by a surface, and this surface constitutes theparting surfaces. The algorithm proposed in this paper checks the connectivity of the two multifacehole loops to recognize passage features. The total number of passage features in a part iscalculated from the Euler equation, and the identication procedure continues until the number ofidentied passage features equals this number. To nd all of the multiface hole loops in a part, theproposed approach considers all of the combinations of connected faces. The edge convexity is usedto judge the validity of multiface hole loops. By using the algorithm proposed in this paper, thepassage features could be recognized eVectively. The approach proposed is illustrated with severalexample cases.Keywords: passage feature, feature recognition, multiface hole loop, injection mould1INTRODUCTIONInjection moulding is the most prevalent process for theproduction of thermoplastic polymer parts. In thisprocess, a thermoplastic polymer is injected into thecavity formed by the core and the cavity. This mouldcavity determines the shape of the plastic part. Thegeneral conguration of an injection mould is shown inFig. 1.Figure 1 represents a simplied conguration of aninjection mould and illustrates the plates, the core andthe cavity. The actual injection mould has manystandard parts, ejectors, a slide system and a coolingsystem, in addition to those shown. Historically, moulddesigners have generated the two-dimensional drawingsof a mould using a two-dimensional computer aideddesign (CAD) system. Recently, however, attempts todesign injection moulds using three-dimensional CADsystems have been made as three-dimensional CADsystems running on personal computers have becomewidely available.By using a three-dimensional CAD system for moulddesign, many design tasks can be automated or facili-tated. In particular, the parting surfaces can be generatedautomatically or at least much more conveniently 14.Parting surfaces are used to cut the external block enclos-ing the part to be moulded into two pieces, i.e. the coreand the cavity. When the part has passages, either theirentrances or exits have to be covered by the partingsurfaces. Even though the parting surfaces are generatedfairly easily by extending the parting lines towards theoutside of the part, identifying all the passage featuresand covering them with proper surfaces are error-pronetasks when the shape of the part is complicated. In thispaper, an algorithm for nding such passage featurespassing through multiple faces, as shown in Fig. 2, isproposed.2BACKGROUND AND MOTIVATIONIn injection mould design systems that are based onthree-dimensional CAD systems, the design process783B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureThe MS was received on 21 May 2001 and was accepted after revisionfor publication on 21 December 2001.*Corresponding author: Department of Mechanical and AerospaceEngineering, Seoul National University, San56-1, Shillim-Dong,Kwanak-Gu, Seoul 151-742, Korea.starts from the three-dimensional CAD model of a part.Then, the core and the cavity are created from the partmodel. The procedure is shown in Fig. 3. The core andthe cavity of the part modelshown inFig. 4 aregeneratedas follows.Firstly, a designer creates a cubic block enclosing thepart model, as illustrated in Fig. 5. The rectangularblock is called the core block, which will eventuallybecome the core and the cavity. Next, the parting sur-faces, which split the core block into the core and thecavity, are generated along the outer boundaries of thepart model as shown in Fig. 6a. The parting surfaces, ifrequired, are also generated on one end of the passagefeature as shown in Fig. 6b.The core block is split into the core and the cavity bythe parting surfaces and the faces of the part model. Thecore is the lower portion of the core block, and the cavityis its upper portion. The created core and cavity areillustrated in Fig. 7.As illustrated in Fig. 6b, the parting surfaces should begenerated on one end of each passage feature to split thecore block completely into two pieces, i.e. the core andthe cavity. In the case of a simple passage feature, asshown in the example, the parting surface of the passagefeature is easily generated. However, in the case ofcomplicatedpassagefeaturesformedoverseveralfaces as illustrated in Fig. 8, the recognition of theloops bounding the ends of the passage feature and theFig. 1General conguration of an injection mouldFig. 2Passage feature passing through multiple facesFig. 3Procedure for generating the core and the cavity784K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 2002generation of the parting surfaces on them are verydi?cult and time consuming tasks.Figure 9 shows a part model with the parting surfaceswith the corresponding passage features, and Fig. 10shows the surfaces that will form the parting surface bycovering the passage features. As shown in Fig. 10,these surfaces for separating the passage region consistof many complicated faces.Most plastic parts fabricated by injection mouldinghave passage features passing through multiple faces.This makes it di?cult to recognize passage featuresand to generate the parting surfaces automatically. Inthis paper, an algorithm to detect passage features isproposed as the basis for automatic parting surfacegeneration.Fig. 4Top and bottom views of an example part with one passage featureFig. 5Core blockFig. 6Generation of parting surfacesRECOGNITION OF PASS FEATURES FOR AUTOMATIC PARTING SURFACE GENERATION785B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureFig. 7Generation of the core and the cavityFig. 8Simplied front cover of an audio system786K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 20022.1Related workSince Kyprianou pointed out the necessity for shapeclassication in CAD systems in his PhD thesis 5,feature recognition in solid models has been a popularresearch topic. Until now, the extraction of machiningfeatures from CAD data has been the main subject ofresearch, and feature recognition techniques have beenderived to extract machining features, such as holes,slots and pocket features 6. There are four distinctapproaches to feature recognition:(a) the graph pattern matching approach 7,(b) the convex hull decomposition approach 8, 9,(c) the cell-based decomposition approach 10,(d) the hint-based reasoning approach 11.The graph pattern matching approach was introduced byJoshi and Chang, and has proven to be the most popularmethod in the feature recognition eld 12. In thisapproach, the B-Rep data structure of a part ismapped onto a graph whose nodes represent faces andwhose branches represent edges. This graph is calledthe face adjacency graph (FAG). Then, a subgraph iso-morphism is used to search subgraphs that match thefeature templates. However, in the case of intersectingfeatures, the subgraphs in the part are deformed, whichmakes feature recognition impossible.The convex hull decomposition approach was pro-posed by Woo 9. This approach recognizes the featuresFig. 9Surfaces generated from passage features that constitute parting surfacesFig. 10Surfaces covering passage featuresRECOGNITION OF PASS FEATURES FOR AUTOMATIC PARTING SURFACE GENERATION787B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering Manufactureby Boolean operations between a part model and aconvex hull surrounding the part model. The Booleanoperation between the part model and convex hull isapplied recursively. When the output of the Booleanoperation is empty, the operation is terminated. Unfor-tunately, the decomposition process may not necessarilyconverge. To overcome this problem, Kim proposed thealternating sum of volumes with partitioning (ASVP)decomposition 9, which recognizes features by compar-ing the part model faces with its convex hull faces.The cell-based decomposition approach was proposedby Sakurai and Chin 10. This method recognizesfeatures by decomposing the delta volume into minimalcells and then combining these cells. The delta volumeis the diVerence between a stock and a part model.Using this approach, the number of cells derived fromthe decomposed delta volume is large. Consequently, alarge number of combinations are needed to recognizethe features by combining the cells.The hint-based reasoning approach was proposed byVandenbrande 11. This approach was proposed inorder to recognize intersecting features, which are themain problem of the graph pattern matching approach.The technique recognizes features from the traditionaltraces of features. For example, a slot hint is generatedwhen a pair of parallel opposing planar faces is encoun-tered, which correspond to slot walls. With such hints,the algorithm recognizes the slot feature by searchingthe slot oor between the slot walls.As is suggested by the above, research on machiningfeature recognition is being actively pursued. Someresearch has also been performed on feature recognitionspecically related to moulds, for example upon under-cut features 13. However, as far as the present authorsare aware, no research has been undertaken to date onthe recognition of passage features for parting surfacegeneration.3OVERVIEWA passage featureiscomposed of a pair of hole loops andthe faces connecting the hole loops, and thus passagefeature recognition is a process of nding paired holeloops. Because a passage feature can pass throughseveral connected faces, the hole loops lying over severalconnected faces should be identied at rst.When a hole loop is found, its pair hole loop issearched. If the pair of hole loops satises a certain con-dition to become a passage, it is registered as a passagefeature.3.1DenitionSince the passage features passing through many con-nected faces are the target features to be recognized, aspecial hole loop, called a multiface hole loop, formedover several faces, is dened in this paper as follows:For any pair of connected faces, allthe edges shared bytwo faces in the pair are eliminated and an expandedface is generated. If internal loops of edges inside theexpanded face exist, these internal loops are denedas multiface hole loops.An example of a multiface hole loop is illustrated inFig. 11.3.2Basic conceptsA passage feature is composed of two hole loops includ-ing multiface hole loops and the faces coupling these holeloops. These faces are called side faces. Thus, the pro-cedure for nding passage features can be conceptuallysimplied to nd two connected hole loops. The detailedprocedure will be explained in Section 4.4ALGORITHMIn this section the proposed algorithm will be explainedin detail. The detailed algorithm for recognizing thesimple passage feature will be explained rst, and thenthe approach used to recognize the hole loops onmultiply connected faces will be described. A passagefeature is dened as simple if its entrance and exit lieover a single face. Finally, the conditions necessary formultiface hole loops to compose a passage, and themethod for nding all the combinations of connectedfaces, will be explained.4.1Algorithm for passage feature recognitionAs explained earlier, a passage feature is composed oftwo hole loops connected to each other by side faces.The detailed procedure for passage feature recognitionis described using the following example.The sample part illustrated in Fig. 12 has one passagefeature and each symbol is dened as follows:Fig. 11Example of a multiface hole loop788K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 2002a top face of the sample partb face connecting the top and bottom surfacesc bottom face of the sample parte1 edge shared by face a and face be2 edge shared by face c and face bL1 hole loop in face aL2 hole loop in face cIn the example part, the loops composing the passagefeature are L1 and L2, and the faces, such as face b, con-nect these loops. Generally, the face (face b) composing apassage feature has edges shared by the neighbouringfaces (face a and face c), and these edges form holeloops in the neighbouring faces (face a and face c).That is, face b is a face composing the passage featureand is named the side face. Faces a and c are namedthe entrance face and the exit face respectively. The pro-cedure for nding the passage features is as follows:1. Search for hole loops in a face (entrance face of apassage).2. Search for edges composing the hole loop searchedfor in step 1.3. Search for faces (side faces) sharing the edgessearched for in step 2.4. If the edges of the face (side face) searched for in step3 form a hole loop inside another face (exit face), thishole loop and the hole loop searched for in step 1form a passage feature.Thealgorithm explained above isfor recognizing passagefeatures composed of hole loops residing on a single face.To recognize the passage features composed of holeloops lying over multiple faces, the concept of the multi-face hole loop must be applied.4.2Recognition of hole loops on multiply connected facesAs described earlier, a multiface hole loop is dened asthe internal loop formed over an expanded face formedby removing edges shared by connected faces. Threesteps are needed in order to recognize the hole loopson multiply connected faces:(a) remove the edges shared by the connected faces,(b) construct loops with the remaining edges,(c) identify the internal loop.The procedure for recognizing a multiface hole loop canbe described as follows. A sample part for explaining themultiface hole loop is shown in Fig. 13, where the greyfaces are the connected faces being investigated. Thegrey faces share edges e1 and e2. If the shared edges inFig. 12Example using a simple passage featureFig. 13Example for recognizing a multiface hole loopRECOGNITION OF PASS FEATURES FOR AUTOMATIC PARTING SURFACE GENERATION789B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering Manufacturethe two faces are removed and the two faces are consid-ered as one face, as shown in Fig. 13b, two loops areformed, i.e. L1 and L2. Loop L1 corresponds to theinternal loop and loop L2 corresponds to the peripheralloop. Consequently, the multiface hole loop is loop L1 inthis case. Likewise, the internal loops formed over narbitrary connected faces are dened as multiface holeloops if internal loops exist when the shared edges ofconnected faces are removed. Once the multiface holeloops are identied, the procedure for nding a simplepassage described earlier can be applied in order torecognize the passage features in the multiple faces.4.3Conditions necessary for a multiface hole loop toform a passageFor the multiface hole loops to compose passage fea-tures, two conditions are required. First of all, all theedges composing the multiface hole loop must beconvex. For example, for the part illustrated in Fig. 14,loop L1 is a hole loop in face F1, but the edges compos-ing the hole loop L1 do not compose a passage featurebecause they are concave. This may be a natural conclu-sion considering that the edges of the multiface holeloops become either the entrance or exit of the passageand only convex edges may form the boundary of theentrance or the exit. Therefore, a procedure for judgingthe convexity of edges is required. The classication ofedges by Kyprianou is illustrated in Fig. 15 14.Edges are classied by the angle between the two facesthat share the corresponding edge; i.e. if the anglemeasured inside a part is smaller than 180 , the edge isconvex. Likewise, if it is larger than 180 , the edge isconcave. If the two faces are connected smoothly asshown in Figs 15c or d, the edges are classied by thelocal curvature 14. By judging the convexity of theedges, the multiface hole loops composed of concave orsmooth concave edges are excluded during the procedurefor recognizing passage features.Even if all the edges satisfy the rst condition, there arecases where passage features cannot be composed becauseof the relationship between the multiface hole loops andthe faces composing the model. Here,the secondcondition comes into play. The multiface hole loops canbe considered as a collection of edges that will boundthe parting surfaces later for the corresponding passageFig. 14Hole loop that does not constitute a passage featureFig. 15Kyprianous edge classication 14790K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 2002features. Since the generated parting surfaces must notoverlap the faces of a part, multiface hole loops whoseinside region overlaps the part surfaces must be excludedfrom consideration.A multiface hole loop that satises such a condition isshown in Fig. 16, and Fig. 17 shows a multiface hole loopthat violates the condition. In other words, the partingsurface to be generated using multiface hole loop L2shown in Fig. 16b, which is identied from the mergedfaces hatched in Fig. 16a, does not overlap the faces com-posing the part. Merged faces are a set of connected faceswithin which a multiface hole loop is searched for. How-ever, the parting surface to be generated using multifacehole loop L2in Fig. 17b, which issearched for among themerged faces hatched in Fig. 17a, overlaps the part faces.Therefore, the case in Fig. 17 must be excluded from con-sideration in nding the passage features. The detailedcondition for invalid multiface hole loops is as follows.The readers may wonder why an odd situation like thisis considered. All possible cases of multiface hole loopshave to be considered because they are generated auto-matically by merging connected faces.The faces that share the edges composing a multifacehole loop and do not participate in the merging processare side faces. If both the starting point and the end-point of an edge shared by two side faces are on themultiface hole loop, this edge can compose a loop withseveral other edges that belong to the multiface holeloop. A parting surface generated using this loopshould be the same face as one of the side faces, whichmakes the parting surface overlap the part face.Figure 18b represents a two-dimensional layout of thepart in Fig. 18a. Faces F1, F2, F3 and F4 correspond tothe merged faces, and faces S1, S2, S3, S4 and S5correspond to the side faces. The boundary edges ofthe multiface hole loop are indicated by thick lines.Edge a shown in Fig. 18b is an edge shared by the sidefaces, and both the starting point and the end-point ofedge a are on the multiface hole loop. Thus, edge aforms a loop together with other edges of S5 that alsobelong to the multiface hole loop. The parting surfacegenerated from this loop becomes the existing face S5,and thus the parting surface overlaps S5. In this way,Fig. 16Example of a valid multiface hole loopFig. 17Example of an invalid multiface hole loopRECOGNITION OF PASS FEATURES FOR AUTOMATIC PARTING SURFACE GENERATION791B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering Manufacturethe recognition of multiface hole loops yielding invalidparting surfaces can be avoided by investigating therelationship between the multiface hole loops and theend points of edges shared by the side faces.4.4Procedure for nding all sets of connected facesTo nd the multiface hole loops in a part, a process thatidenties and merges the connected faces is needed. Twoapproaches can be applied to generate the sets of con-nected faces. The rst approach involves selecting thesets of faces to be merged by judging the connectivitybetween the member faces out of face sets generatedarbitrarily. However, in this approach, the number ofsets generated arbitrarily increases approximately by anorder of nrwhen the total number of faces is large:?nrn!r!n r!nn 1n 2n r 1rr 1r 21X OnrwhereXnumber of combinationsntotal number of facesFig. 18Planar display of participating faces792K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 2002rnumber of faces to be mergedFor example, if the total number of faces is 200, thenumber of candidate face sets is 64684950 when fourfaces are to be merged. Thus, this approach is not e?-cient in generating the sets of connected faces to bemerged.The second approach involves generating face sets byidentifying faces connected to the faces that have beenalready identied as the elements of a feasible face set.In this approach, the member faces of a registered faceset are stored in a stack. Then, it searches faces connectedto the last registered face among the registered faces. Ifthere are no more faces connected to the last registeredface, the last registered face is removed from the stackand the searching process continues with the registeredface just below the removed face. This approach can e?-ciently shorten the time for generating face sets by search-ing for connected faces only, whereas the rst approachsearches all possible sets and checks the connectivity.The generated sets of faces to be merged are used in themodule used for nding multiface hole loops.5IMPLEMENTATION5.1Program architectureThe basic concept of the proposed algorithm is asfollows. Up to the moment when the number of searchedpassage features equals the total number of passagefeatures in a model, the number of faces to be mergedis increased starting from 2. The total number of passagefeatures is derived using the Euler equation 15. In eachstep, the multiface hole loops are found and passagefeatures are recognized by searching for the connectedmultiface hole loops. Thus, the implemented programis composed of four subroutines, i.e. routines for ndingthe total number of passage features, nding all com-binations of connected faces, recognizing multifaceholeloopsandrecognizingpassagefeatures.Theprogram was developed with Unigraphics V15.0 APIon Windows NT.5.2Analysis of running timeThe algorithm proposed in this paper searches forpassage features with an increasing number of faces tobe merged. Thus, the running time for recognizing allpassage features in a model can be determined by thepassage feature involving the maximum number ofconnected faces. Therefore, the running time can berepresented by the maximum number of faces to bemerged.As mentioned earlier, theprocedure for generating setsof faces to be merged involves searching for the facesconnected to a face and searching again for the facesconnected to the searched faces until all members ofthe connected face sets of the given number of faces arecollected. If the total number of faces in a part is n, theaverage number of faces connected to each face is mand the number of faces to be merged is r, the numberof feasible face sets is of the order of nmr1:X Onmr1Generally, the average number of faces connected toeach face is much smaller than the total number offaces in a part.For the part illustrated in Fig. 8, the total number offaces is 286 and the average number of faces connectedto each face is 5. In this case, the expected number ofTable 1Order of combinations for the part in Fig. 8Number of faces to be mergedExpected number of combinations2143037150435750Fig. 19Example part with oorless pockets and throughholesRECOGNITION OF PASS FEATURES FOR AUTOMATIC PARTING SURFACE GENERATION793B05601IMechE 2002Proc Instn Mech Engrs Vol 216 Part B: J Engineering Manufacturecombinations according to the number of faces to bemerged is as shown in Table 1.6CASE STUDY6.1Example partThe example part shown in Fig. 19a has several pockets,holes and passage features bounded by the hole loopsformed over one face. Figure 19b shows the six passagefeatures recognized.6.2L-shaped partThe sample part shown in Fig. 20a is L-shaped and has apassage feature composed of hole loops formed overmultiple faces in addition to a simple passage feature.In this case, the number of faces forming the multifacehole loops is 4. The recognized passage features areillustrated in Fig. 20b.6.3Casing of a cellular phoneThe sample part shown in Fig. 21a is the front cover of acellular phone and has 14 passage features. The recog-nized passage features are illustrated in Fig. 21b.6.4Minicomponent front coverThe sample part shown in Fig. 22a is the front cover of aminicomponent and has passage features residing overmultiple faces. This part has 15 passage features. Therecognized passage features are shown in Fig. 22b.The running time for the four cases illustrated above isshown in Table 2.7CONCLUSIONSIn this paper, an algorithm is proposed for automaticrecognition of passage features using the concept of themultiface hole loop. The generation of the partingsurfaces is one of the most natural target tasks to beautomated in mould design using a three-dimensionalCAD system. The parting surfaces are easily generatedalong the boundaries of the part to be made. However,if the part to be made has passage features, their entranceFig. 20L-shaped example partFig. 21Example partcover of a cellular phone794K CHUNG, K LEE AND T KIMProc Instn Mech Engrs Vol 216 Part B: J Engineering ManufactureB05601IMechE 2002and exit areas should also be covered by the partingsurfaces. Sometimes, it is a tedious and error-pronetask to identify all the passage features when the parthas a complicated shape. The algorithm proposed inthis paper could shorten the time for designing injectionmoulds by automatically recognizing passage featurespassing through multiple faces.The algorithm proposed in this paper recognizespassage features with increase in the number of faces tobe merged. Thus, the time for recognizing passagefeatures is inuenced by the maximum
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