購買設(shè)計請充值后下載，，資源目錄下的文件所見即所得，都可以點開預(yù)覽，，資料完整，充值下載可得到資源目錄里的所有文件。。?！咀ⅰ浚篸wg后綴為CAD圖紙，doc,docx為WORD文檔，原稿無水印，可編輯。。。具體請見文件預(yù)覽，有不明白之處，可咨詢QQ:12401814
河南機電高等?？茖W(xué)校
畢業(yè)設(shè)計(論文)開題報告
學(xué)生姓名： 學(xué) 號：
專 業(yè)：
設(shè)計(論文)題目：
指導(dǎo)教師：
2006年03月08日
畢 業(yè) 設(shè) 計（論 文）開 題 報 告
1．結(jié)合畢業(yè)設(shè)計（論文）課題情況，根據(jù)所查閱的文獻資料，撰寫1500字左右（本科生200字左右）的文獻綜述(包括目前該課題在國內(nèi)外的研究狀況、發(fā)展趨勢以及對本人研究課題的啟發(fā))：
模具成型方法在現(xiàn)代工業(yè)的主要部門，機械、交通、電子、和國防工業(yè)中得到了廣泛的應(yīng)用。利用模具生產(chǎn)制品和零件已成為工業(yè)上進行成批和大批量生產(chǎn)的主要手段，其對產(chǎn)品的質(zhì)量，縮短試制周期，以及產(chǎn)品的更新?lián)Q代都具有決定性的意義。所以模具的設(shè)計與制造的水平高低可以代表一個國家的工業(yè)發(fā)展水平。
我國的模具工業(yè)發(fā)展現(xiàn)狀：解放前，由于工業(yè)基礎(chǔ)薄弱，根本談不上有什么模具工業(yè)；解放后，國家為了繁榮經(jīng)濟，組織了專門的技術(shù)力量對模具進行研發(fā)，并取得了很大的成功和發(fā)展。在以后的蘇聯(lián)等社會主義國家對我國進行的援助期間，有關(guān)的模具設(shè)備和模具設(shè)計開始輸入我國，對我國的模具工業(yè)發(fā)展起到了促進作用。十年動亂期間，模具工業(yè)停滯不前，沒有取得進展。1977年以來，國家模具工業(yè)發(fā)展迅速，可研制微米級精度的多工位級進模和多腔塑料成型模具。此外，精沖模具、沖裁模具和鍛模的計算機輔助設(shè)計（CAD）和計算機輔助制造（CAM）技術(shù)已開展了研究，并取得了初步的應(yīng)用成果。此時我國的模具工業(yè)才真正的得到較大的發(fā)展，模具工業(yè)初具規(guī)模。但與發(fā)達國家相比許多方面存在較大差距，主要表現(xiàn)在：
（1）總量供不應(yīng)求、產(chǎn)品結(jié)構(gòu)不夠合理。
其中中低檔模具供過于求，中高檔模具自配率嚴重不足，大量進口。國內(nèi)模具總量中屬大型、精密、復(fù)雜、長壽命模具的比例不足30%，國外在50%以上。
（2）企業(yè)組織結(jié)構(gòu)都不夠合理。
我國模具生產(chǎn)廠點中多數(shù)是自產(chǎn)自配的工模具車間（分廠），自產(chǎn)自配比例高達60%左右，國外70%以上是商品模具；專業(yè)模具廠也大多數(shù)是"大而全 "、"小而全"的組織形式，國外模具企業(yè)是"大而專"、"大而精"。
（3） 工藝裝備水平低，且配套性不好，利用率低，技術(shù)結(jié)構(gòu)、模具產(chǎn)品水平比國際水平低許多。而模具生產(chǎn)周期卻要比國際水平長許多。
（4）技術(shù)人才嚴重不足，經(jīng)濟效益欠佳。隨著時代的進步和技術(shù)的發(fā)展，能掌握和運用新技術(shù)的人才如模具結(jié)構(gòu)設(shè)計、模具工藝設(shè)計異常短缺，高級鉗工及企業(yè)管理人才也非常緊缺。
（5）與國際水平相比，模具企業(yè)的管理落后更甚于技術(shù)落后。
（6）專業(yè)化、標準化、商品化的程度低，協(xié)作差。
可見，未來我國模具工業(yè)和技術(shù)的主要發(fā)展方向?qū)⑹牵?
——大力普及、廣泛應(yīng)用CAD/CAE/CAM技術(shù)，逐步走向集成化?，F(xiàn)代模具設(shè)計制造不僅應(yīng)強調(diào)信息的集成，更應(yīng)該強調(diào)技術(shù)、人和管理的集成。
——提高大型、精密、復(fù)雜與長壽命模具的設(shè)計與制造技術(shù)，逐步減少模具的進口量，增加模具的出口量。
——在塑料注射成型模具中，積極應(yīng)用熱流道，推廣氣輔或水輔注射成型，以及高壓注射成型技術(shù)，滿足產(chǎn)品的成型需要。
——提高模具標準化水平和模具標準件的使用率。
——發(fā)展快速制造成型和快速制造模具，即快速成型制造技術(shù)，迅速制造出產(chǎn)品的原型與模具，降低成本推向市場。
——積極研究與開發(fā)模具的拋光技術(shù)、設(shè)備與材料，滿足特殊產(chǎn)品的需要。
——推廣應(yīng)用高速銑削、超精度加工和復(fù)雜加工技術(shù)與工藝，滿足模具制造的需要。
——開發(fā)優(yōu)質(zhì)模具材料和先進的表面處理技術(shù)，提高模具的可靠性。
——研究和應(yīng)用模具的高速測量技術(shù)、逆向工程與并行工程，最大限度地提高模具的開發(fā)效率與成功率。
——開發(fā)新的成型工藝與模具，以滿足未來的多學(xué)科多功能綜合產(chǎn)品開發(fā)設(shè)計技術(shù)。
設(shè)計啟發(fā)：通過此次的模具設(shè)計，感觸良多。深深感覺到要作為一個模具設(shè)計工作者的不易，模具設(shè)計者成功設(shè)計一套模具，需要付出大量的體力與腦力勞動，需查閱大量的參考文獻，在該設(shè)計中查閱了楊占堯教授主編的《塑料注塑模結(jié)構(gòu)與設(shè)計》；翟德梅教授編寫的《模具制造技術(shù)》；陳萬林教授主編的《實用注塑模設(shè)計與制造》；馬金俊老師主編的《注塑模具設(shè)計》；張克慧老師主編的《注塑模設(shè)計》等文獻，在文獻中學(xué)到了大量的模具知識。雖然此次的設(shè)計我認真的對待，付出了很大的努力，設(shè)計過程中也頻頻受到指導(dǎo)老師的指點和批正，但是作為模具設(shè)計的初學(xué)者，沒有足夠的設(shè)計與生產(chǎn)實踐，深深感覺到自身知識的缺乏，設(shè)計過程中屢有錯誤出現(xiàn)；也體會到，多與老師交流，多向老師請教，會從老師那里學(xué)來很多知識和經(jīng)驗。
敬請老師對本次設(shè)計批評指正。
畢 業(yè) 設(shè) 計（論 文）開 題 報 告
２．本課題的研究思路（包括要研究或解決的問題和擬采用的研究方法、手段（途徑）及進度安排等）：
該設(shè)計首先對塑件進行工藝分析，了解塑件的材料、形狀、尺寸及精度要求，參考工藝的可行性，選擇滿足要求的工藝方案。然后我按照設(shè)計要求對組成注塑模具的成型零部件、澆注系統(tǒng)、導(dǎo)向機構(gòu)、脫模結(jié)構(gòu)、側(cè)向分型與抽芯機構(gòu)、加熱與冷卻系統(tǒng)、排氣系統(tǒng)和其它零部件進行設(shè)計。由于塑件形狀比較簡單，沒有設(shè)計側(cè)抽芯結(jié)構(gòu)。設(shè)計過程中較多的考慮了模具結(jié)構(gòu)的調(diào)整性、易更換性及模具成本。模具零件設(shè)計完畢后，對重要的工作結(jié)構(gòu)和零件進行了校核。校核結(jié)束后對模具安裝并調(diào)試。從模具設(shè)計到零部件的加工工藝以及裝配工藝等進行詳細的闡述，并應(yīng)用CAD進行各零件和裝配圖的設(shè)計。畢業(yè)設(shè)計是塑料模設(shè)計課程重要的綜合性和實踐性教學(xué)環(huán)節(jié)?，F(xiàn)將本設(shè)計的進度表安排如下
（1）熟悉設(shè)計要求及分析制件圖…………………………………………1天
（2）借閱參考資料…………………………………………………………1天
（3）模具主要設(shè)計計算……………………………………………………2天
（4）模具總體設(shè)計…………………………………………………………2天
（5）模具主要零部件設(shè)計…………………………………………………4天
（6）模具裝配圖的確定及工作原理………………………………………2天
（7）注塑工藝確定及其過程中的問題及解決措施………………………1天
（8）電子文檔的制作………………………………………………………6天
（9）模具裝配圖及零件圖的繪制…………………………………………7天
（10）其他 …………………………………………………………………2天
畢 業(yè) 設(shè) 計（論 文）開 題 報 告
指導(dǎo)教師意見：
1．對“文獻綜述”的評語：
2．對本課題的研究思路、深度、廣度及工作量的意見和對設(shè)計（論文）結(jié)果的預(yù)測：
指導(dǎo)教師：
年 月 日
所在專業(yè)審查意見：
負責(zé)人：
年 月 日
畢業(yè)設(shè)計說明書/論文目錄
緒 論 1
第1章 模塑工藝規(guī)程的編制 3
1.1 塑件的工藝性分析 3
1.2 計算塑件的體積和質(zhì)量 4
1.3 塑件注塑工藝參數(shù)的確定 4
1.4注塑機的選用 5
第2章 注塑模的結(jié)構(gòu)設(shè)計 6
2.1 分型面的設(shè)計 6
2.2 模腔數(shù)量的確定 7
2.3 確定型腔的排列方式 7
2.4 澆注系統(tǒng)設(shè)計 8
2.5 成型零件結(jié)構(gòu)設(shè)計 9
第3章 模具設(shè)計的有關(guān)計算 11
3.1 型芯和型腔的工作尺寸計算 11
3.2 型腔側(cè)壁厚度計算 13
第4章 模具加熱與冷卻系統(tǒng)的計算 14
第5章 導(dǎo)向與定位機構(gòu)計算 15
5.1 導(dǎo)柱設(shè)計 15
5.2 導(dǎo)套的設(shè)計 15
第6章 脫模機構(gòu)設(shè)計 16
6.1 脫模力計算 16
6.2推件板厚度計算 16
第7章 模具閉合高度的確定 17
第8注 注塑機有關(guān)參數(shù)的校核與模架選取 18
8.1 注塑機校核 19
8.2 模架的選取 19
第9章 模具的安裝與試模 19
9.1 模具安裝 19
9.2本模具的工作原理 19
9.3試模 19
第10章 注塑模主要零件加工工藝規(guī)程的編制 22
小 結(jié) 23
致 謝 24
參考文獻 25
第 22 頁 共 23 頁
桂林電子科技大學(xué)畢業(yè)設(shè)計用紙
Automated Assembly Modelling for Plastic Injection Moulds
An injection mould is a mechanical assembly that consists of product-dependent parts and product-independent parts. This paper addresses the two key issues of assembly modelling for injection moulds, namely, representing an injection mould assembly in a computer and determining the position and orientation of a product-independent part in an assembly. A feature-based and object-oriented representation is proposed to represent the hierarchical assembly of injection moulds. This representation requires and permits a designer to think beyond the mere shape of a part and state explicitly what portions of a part are important and why. Thus, it provides an opportunity for designers to design for assembly (DFA). A simplified symbolic geometric approach is also presented to infer the configurations of assembly objects in an assembly according to the mating conditions. Based on the proposed representation and the simplified symbolic geometric approach, automatic assembly modelling is further discussed.
Keywords: Assembly modelling; Feature-based; Injection moulds; Object-oriented
1. Introduction
Injection moulding is the most important process for manufacturing plastic moulded products. The necessary equipment consists of two main elements, the injection moulding machine and the injection mould. The injection moulding machines used today are so-called universal machines, onto which various moulds for plastic parts with different geometries can be mounted, within certain dimension limits, but the injection mould design has to change with plastic products. For different moulding geometries, different mould configurations are usually necessary. The primary task of an injection mould is to shape the molten material into the final shape of the plastic product. This task is fulfilled by the cavity system that consists of core, cavity, inserts, and slider/lifter heads. The geometrical shapes and sizes of a cavity system are determined directly by the plastic moulded product, so all components of a cavity system are called product-dependent parts. (Hereinafter, product refers to a plastic moulded product, part refers to the component of an injection mould.) Besides the primary task of shaping the product, an injection mould has also to fulfil a number oftasks such as the distribution of melt, cooling the molten material, ejection of the moulded product, transmitting motion, guiding, and aligning the mould halves. The functional parts to fulfil these tasks are usually similar in structure and geometrical shape for different injection moulds. Their structures and geometrical shapes are independent of the plastic moulded products, but their sizes can be changed according to the plastic products. Therefore, it can be concluded that an injection mould is actually a mechanical assembly that consists of product-dependent parts and product-independent parts. Figure 1 shows the assembly structure of an injection mould. The design of a product-dependent part is based on extracting the geometry from the plastic product. In recent years, CAD/CAM technology has been successfully used to help mould designers to design the product-dependent parts. The
Fig. 1. Assembly structure of an injection mould
automatic generation of the geometrical shape for a product-dependent part from the plastic product has also attracted a lot of research interest [1,2]. However, little work has been carried out on the assembly modelling of injection moulds, although it is as important as the design of product-dependent parts. The mould industry is facing the following two difficulties when use a CAD system to design product-independent parts and the whole assembly of an injection mould. First, there are usually around one hundred product-independent parts in a mould set, and these parts are associated with each other with different kinds of constraints. It is time-consuming for the designer to orient and position the components in an assembly. Secondly, while mould designers, most of the time, think on the level of real-world objects, such as screws, plates, and pins, the CAD system uses a totally different level of geometrical objects. As a result, high-level object-oriented ideas have to be translated to low-level CAD entities such as lines, surfaces, or solids. Therefore, it is necessary to develop an automatic assembly modelling system for injection moulds to solve these two problems. In this paper, we address the following two key issues for automatic assembly modelling: representing a product-independent part and a mould assembly in a computer; and determining the position and orientation of a component part in an assembly.
This paper gives a brief review of related research in assembly modelling, and presents an integrated representation for the injection mould assembly. A simplified geometric symbolic method is proposed to determine the position and orientation of a part in the mould assembly. An example of automatic assembly modelling of an injection mould is illustrated.
2. Related Research
Assembly modelling has been the subject of research in diverse fields, such as, kinematics, AI, and geometric modelling. Lib-ardi et al. [3] compiled a research review of assembly modelling. They reported that many researchers had used graph structures to model assembly topology. In this graph scheme, the components are represented by nodes, and transformation matrices are attached to arcs. However, the transformation matrices are not coupled together, which seriously affects the transformation procedure, i.e. if a subassembly is moved, all its constituent parts do not move correspondingly. Lee and Gossard [4] developed a system that supported a hierarchical assembly data structure containing more basic information about assemblies such as “mating feature” between the components. The transformation matrices are derived automatically from the associations of virtual links, but this hierarchical topology model represents only “part-of” relations effectively.
Automatically inferring the configuration of components in an assembly means that designers can avoid specifying the transformation matrices directly. Moreover, the position of a component will change whenever the size and position of its reference component are modified. There exist three techniques to infer the position and orientation of a component in the assembly: iterative numerical technique, symbolic algebraic technique, and symbolic geometric technique. Lee and Gossard [5] proposed an iterative numerical technique to compute the location and orientation of each component from the spatial relationships. Their method consists of three steps: generation of the constraint equations, reducing the number of equations, and solving the equations. There are 16 equations for “against” condition, 18 equations for “fit” condition, 6 property equations for each matrix, and 2 additional equations for a rotational part. Usually the number of equations exceeds the number of variables, so a method must be devised to remove the redundant equations. The Newton–Raphson iteration algorithm is used to solve the equations. This technique has two disadvantages: first, the solution is heavily dependent on the initial solution; secondly, the iterative numerical technique cannot distinguish between different roots in the solution space. Therefore, it is possible, in a purely spatial relationship problem, that a
mathematically valid, but physically unfeasible, solution can be obtained.
Ambler and Popplestone [6] suggested a method of computing the required rotation and translation for each component to satisfy the spatial relationships between the components in an assembly. Six variables (three translations and three rotations) for each component are solved to be consistent with the spatial relationships. This method requires a vast amount of programming and computation to rewrite related equations in a solvable format. Also, it does not guarantee a solution every time, especially when the equation cannot be rewritten in solvable forms.
Kramer [7] developed a symbolic geometric approach for determining the positions and orientations of rigid bodies that satisfy a set of geometric constraints. Reasoning about the geometric bodies is performed symbolically by generating a sequence of actions to satisfy each constraint incrementally, which results in the reduction of the object’s available degrees of freedom (DOF). The fundamental reference entity used by Kramer is called a “marker”, that is a point and two orthogonal axes. Seven constraints (coincident, in-line, in-plane, parallelFz, offsetFz, offsetFx and helical) between markers are defined. For a problem involving a single object and constraints between markers on that body, and markers which have invariant attributes, action analysis [7] is used to obtain a solution. Actionanalysis decides the final configuration of a geometric object, step by step. At each step in solving the object configuration, degrees of freedom analysis decides what action will satisfy one of the body’s as yet unsatisfied constraints, given the available degrees of freedom. It then calculates how that action further reduces the body’s degrees of freedom. At the end of each step, one appropriate action is added to the metaphorical assembly plan. According to Shah and Rogers [8], Kramer’s work represents the most significant development for assembly modelling. This symbolic geometric approach can locate all solutions to constraint conditions, and is computationally attractive compared to an iterative technique, but to implement this method, a large amount of programming is required.
Although many researchers have been actively involved in assembly modelling, little literature has been reported on feature based assembly modelling for injection mould design.Kruth et al. [9] developed a design support system for an injection mould. Their system supported the assembly design for injection moulds through high-level functional mould objects (components and features). Because their system was based on AutoCAD, it could only accommodate wire-frame and simple solid models.
3. Representation of Injection Mould
Assemblies The two key issues of automated assembly modelling for injection moulds are, representing a mould assembly in com- puters, and determining the position and orientation of a product-independent part in the assembly. In this section, we present an object-oriented and feature-based representation for assemblies of injection moulds.
The representation of assemblies in a computer involves structural and spatial relationships between individual parts. Such a representation must support the construction of an assembly from all the given parts, changes in the relative positioning of parts, and manipulation of the assembly as a whole. Moreover, the representations of assemblies must meet the following requirements from designers:
1. It should be possible to have high-level objects ready to use while mould designers think on the level of real-world objects.
2. The representation of assemblies should encapsulate operational functions to automate routine processes such as pocketing and interference checks.
To meet these requirements, a feature-based and object-oriented hierarchical model is proposed to represent injection moulds. An assembly may be divided into subassemblies, which in turn consists of subassemblies and/or individual components. Thus, a hierarchical model is most appropriate for representing the structural relations between components. A hierarchy implies a definite assembly sequence. In addition, a hierarchical model can provide an explicit representation of the dependency of the position of one part on another.
Feature-based design [10] allows designers to work at a somewhat higher level of abstraction than that possible with the direct use of solid modellers. Geometric features are instanced, sized, and located quickly by the user by specifying a minimum set of parameters, while the feature modeller works out the details. Also, it is easy to make design changes because of the associativities between geometric entities maintained in the data structure of feature modellers. Without features, designers have to be concerned with all the details of geometric construction procedures required by solid modellers, and design changes have to be strictly specified for every entity affected by the change. Moreover, the feature-based representation will provide high-level assembly objects for designers to use. For example, while mould designers think on the level of a real- world object, e.g. a counterbore hole, a feature object of a counterbore hole will be ready in the computer for use.
Object-oriented modelling [11,12] is a new way of thinking about problems using models organised around real-world concepts. The fundamental entity is the object, which combines both data structures and behaviour in a single entity. Object-
oriented models are useful for understanding problems and designing programs and databases. In addition, the object- oriented representation of assemblies makes it easy for a“child” object to inherit information from its “parent”.
Figure 2 shows the feature-based and object-oriented hier- archical representation of an injection mould. The representation is a hierarchical structure at multiple levels of abstraction, from low-level geometric entities (form feature) to high-level subassemblies. The items enclosed in the boxes represent “assembly objects” (SUBFAs, PARTs and FFs); the solid lines represent “part-of” relation; and the dashed lines represent other relationships. Subassembly (SUBFA) consists of parts (PARTs). A part can be thought of as an “assembly” of form features (FFs). The representation combines the strengths of a feature-based geometric model with those of object-oriented models. It not only contains the “part-of” relations between the parent object and the child object, but also includes a richer set of structural relations and a group of operational functions for assembly objects. In Section 3.1, there is further discussion on the definition of an assembly object, and detailed relations between assembly objects are presented in Section 3.2
Fig. 2. Feature-based, object-oriented hierarchical representation
3.1 Definition of Assembly Objects
In our work, an assembly object, O, is defined as a unique, identifiable entity in the following form:
O = (Oid, A, M, R) (1)
Where:
Oid is a unique identifier of an assembly object (O). A is a set of three-tuples, (t, a, v). Each a is called an attribute of O, associated with each attribute is a type,
t, and a value, v. M is a set of tuples, (m, tc1, tc2, %, tcn, tc). Each element of M is a function that uniquely identifies a method. The symbol m represents a method name; and methods define operations on objects. The symbol tci(i= 1, 2, %, n) specifies the argument type and tc specifies the returned value type.
R is a set of relationships among O and other assembly objects. There are six types of basic relationships between assembly objects, i.e. Part-of, SR, SC, DOF, Lts, and Fit.
Table 1 shows an assembly object of injection moulds, e.g. ejector. The ejector in Table 1 is formally specified as:
(ejector-pinF1, {(string, purpose, ‘ejecting moulding’), (string, material, ‘nitride steel’), (string, catalogFno, ‘THX’)},
{(checkFinterference(), boolean), (pocketFplate(), boolean)}, {(part-of ejectionFsys), (SR Align EBFplate), (DOF Tx, Ty)}).
In this example, purpose, material and catalogFno are attributes with a data type of string; checkFinterference and pocketFplate are member functions; and Part-of, SR and DOF are relationships.
3.2 Assembly Relationships
There are six types of basic relationships between assembly objects, Part-of, SR, SC, DOF, Lts, and Fit.
Part-of An assembly object belongs to its ancestor object.
SR Spatial relations: explicitly specify the positions and orientations of assembly objects in an assembly. For a component part, its spatial relationship is derived from spatial constraints (SC).
SC Spatial constraints: implicitly locate a component part with respect to the other parts.
DOF Degrees of freedom: are allowable translational/ rotational directions of motion after assembly, with or without limits.
Lts Motion limits: because of obstructions/interferences, the DOF may have unilateral or bilateral limits.
Fit Size constraint: is applied to dimensions, in order to maintain a given class of fit.
Among all the elements of an assembly object, the relation-ships are most important for assembly design. The relationships between assembly objects will not only determine the position of objects in an assembly, but also maintain the associativities between assembly objects. In the following sub-sections, we will illustrate the relationships at the same assembly level with the help of examples.
3.2.1 Relationships Between Form Features
Mould design, in essence, is a mental process; mould designers most of the time think on the level of real-world objects such as plates, screws, grooves, chamfers, and counter-bore holes. Therefore, it is necessary to build the geometric models of all product-independent parts from form features. The mould designer can easily change the size and shape of a part, because of the relations between form features maintained in the part representation. Figure 3(a) shows a plate with a counter-bore hole. This part is defined by two form features, i.e. a block and a counter-bore hole. The counter-bore hole (FF2) is placed with reference to the block feature FF1, using their local coordinates F2and F1, respectively. Equations (2)–(5) show the spatial relationships between the counter-bore hole (FF2) and the block feature (FF1). For form features, there is no spatial constraint between them, so the spatial relationships are specified directly by the designer. The detailed assembly relationships between two form features are defined as follows:
Fig. 3. Assembly relationships.
F2k= F1k (4)
r2F= r1F+ b22*F1j+ AF1*F1i (5)
DOF:
ObjFhasF1FRDOF(FF2, F2j)
The counter-bore feature can rotate about axis F2j.
LTs(FF2, FF1):
AF1, b11? 0.5*b21 (6)
Fit (FF2, FF1):
b22= b12 (7)
Where
F and r are the orientation and position vectors of features.
F1= (F1i, F1j, F1k), F2= (F2i, F2j, F2k).
bij is the dimension of form features, Subscript i ifeature number, j is dimension number.
AF1is the dimension between form features.
Equations (2)–(7) present the relationships between the form feature FF1 and FF2. These relationships thus determine the position and orientation of a form feature in the part. Taking the part as an assembly, the form feature can be considered as “components” of the assembly.
The choice of form features is based on the shape characteristics of product-independent parts. Because the form features provided by the Unigraphics CAD/CAM system [13] can meet the shape requirements of parts for injection moulds and the spatial relationships between form features are also maintained, we choose them to build the required part models. In addition to the spatial relationships, we must record LTs, Fits relationships for form features, which are essential to c