注塑模具自动装配造型外文文献翻译英文原文（可编辑）

注塑模具自动装配造型外文文献翻译英文原文（可编辑） Int J Adv Manuf Technol 2000 16:739?7472000 Springer-Verlag London Limited Automated Assembly Modelling for Plastic Injection Moulds X. GYe, JY. HFuh and K. SLee Department of Mechanical and Production Engineering, National University of Singapore, Singapore An injection mould is a mechanical assembly that consists of product-dependent parts and product-independent partsThis paper addresses the two keyissues of assembly modelling for injection moulds, namely, representing an injection mould assembly in a computerand determining the position and orientation of a product-independent part in an assemblyA feature-based and object-oriented representation is proposed to represent the hierarchical assembly of injectionmoulds. 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 whyThus, it provides an opportunity for designers to design for assembly DFAA simpli?ed symbolic geometric approach is also presented to infer the con?gurations of assembly objects in an assembly according to the mating conditions. Based on the proposed representation and the simpli?ed symbolic geometric approach, automatic assembly modelling is further discussed. 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, productrefers 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 ful?l a number of tasks such as thedistribution of melt, cooling the molten material, ejection of the moulded product, transmitting motion, guiding, and aligning the mould halvesThe functional parts to ful?l these tasks are usually similar in structure and geo- metrical shape for different injection moulds. Their structures and geometrical shapes are independent of the plastic moulded products, but their sizescan be changed according to the plastic products. Therefore, it can be concluded that an injection mould isactually a mechanicalassembly that consistsof 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 thegeometry fromtheplastic product Inrecentyears, CAD/CAM technology hasbeen successfully used to help mould designers to design the product-dependent partsThe Keywords: Assembly moulds; Object-oriented modelling; Feature-based; Injection CA-plate 1 Introduction Fixed-half Guild-bush Injection moulding is the most important process for manufac- turing plastic moulded products. The necessary equipment con- sists 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 forplastic parts withdifferent geometries canbe mounted, within certain dimension limits,but the injection mould design has to change with plastic products. For different moulding geometries, different mould con?gurations are usually necessary. The primary task of an injection mould is to shape the molten material into thenal shape of the plastic product. This task is ful?lled by the cavity system that consists of core, cavity, inserts, and slider/lifter headsThe geometrical shapes TCP-plate Mouldbase Bep-plate Cb-plate Move-half Ea-plate Mould Eb-plate Plug Guid-pin Cool Socket Ip-plate head Fill Ret-pin Slider Core body Cav_1 Cav_2 guide Layout Stop-blk Heel-blk Cavity Correspondence and offprint requests to: Dr Jerry Y. HFuh, Depart- ment of Mechanical and Production Engineering, National University of Singapore NUS, 10 KentRidge Crescent, Singapore 119260. E-mail: mpefuhyh?//0>. Product-independent part Product-dependent part Fig. 1. Assembly structure of an injection mould. 740 X. G. Ye et al. 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 dif?cult- ies 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 constraintsIt is time-consuming for the designer toorient and position thecomponents 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 solidsTherefore, it is necessary to develop an automatic assembly modelling system for injection moulds to solve these two problemsIn this paper, we address the follow- ing two key issues for automatic assembly modelling: rep- resenting a product-independent part and a mould assembly in a computer; and determining the position and orientation of a component part in an assembly. 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 “?t” 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 equationsThis technique has twodisadvantages: ?rst, 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 comput- ing the required rotation and translation for each component to satisfy the spatial relationships between the components in anassembly Six variablesthreetranslationsandthree rotations for each component are solved to be consistent with the spatial relationshipsThis method requires a vast amount of programming and computation to rewrite related equations in a solvable formatAlso, 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 constraintsReasoning 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 DOFThe 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 de?ned. For a problem involving a single object and constraints between markers on that body, and markers which have invariant attri- butes, action analysis [7] is used to obtain a solution. Action analysis decides thenal con?guration of a geometric object, step by step. At each step in solving the object con?guration, degrees of freedom analysis decides what action will satisfy one of the body’s as yet unsatis?edconstraints, given the available degrees of freedomIt 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 signi?cant development for assembly modellingThis symbolic geometric approach can locate all solutionsto constraintconditions,and iscomputationally 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 fea- ture based assembly modellingfor injection mould design. Kruth et al[9] developed a design supportsystem for an injection mould. Their system supported the assembly design forinjection mouldsthroughhigh-level functionalmould objects components and featuresBecause their system was This papergives a briefreview ofrelated research in assembly modelling, and presents an integrated representation for the injection mould assembly. A simpli?ed geometric sym- bolic method is proposed to determine the position and orien- tation of a part in the mould assembly. An example of auto- matic assembly modelling of an injection mould is illustrated. 2 Related Research Assembly modelling has been the subject of research in diverse ?elds, such as, kinematics, AI, and geometric modellingLib- ardi et al[3] compiled a research review of assembly model- lingThey reported thatmany researchers had used graph structures to model assembly topologyIn this graph scheme, the components are represented by nodes, and transformation matrices are attachedto arcsHowever, the transformation matrices are not coupled together, which seriously affects the transformation procedure, i.eif a subassembly is moved, all its constituent parts do not move correspondinglyLee and Gossard [4] developed a system that supported a hierarchical assembly datastructure containing morebasic information about assemblies such as “mating feature” between the compo- nentsThe transformation matrices are derived automatically from the associations of virtuallinks, but this hierarchical topology model represents only “part-of” relations effectively. Automatically inferring the con?guration of components in an assembly means that designers can avoid specifying the transformation matrices directlyMoreover, the position of a component will change whenever the size and position of its reference component are modi?ed. There exist three techniques to infer the position and orientation of a component in the assembly: iterativenumerical technique, symbolic algebraic technique, and symbolic geometric technique. Lee and Gossard [5] proposed an iterative numerical technique to compute the Automated Assembly Modelling 741 based on AutoCAD, it could only accommodate wire-frame and simple solid models. oriented representationof assemblies makesit easy fora “child” object to inherit information from its “parent”. Figure 2 shows the feature-based and object-oriented hier- archical representation of an injection mouldThe represen- tation is a hierarchical structure at multiple levels of abstraction, from low-level geometric entities form feature to high-level subassembliesTheitems enclosed inthe boxesrepresent “assembly objects” SUBFAs, PARTs and FFs; the solid lines represent “part-of” relation; andthe dashed lines represent other relationshipsSubassembly SUBFA consists of parts PARTs. A part can be thought of as an “assembly” of form features FFsThe representation combines the strengths of a feature-based geometric model with those of object-oriented modelsIt 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 de?nition of an assembly object, and detailed relations between assembly objects are presented in Section 3.2. 3 Representation of Injection Mould Assemblies The two keyissues of automated assemblymodelling for injection moulds are, representing a mould assembly in com- puters, and determining the position and orientation of a pro- duct-independent part in theassemblyIn this section, we present an object-oriented and feature-based representation for assemblies of injection moulds. The representation of assemblies in acomputer involves structural and spatial relationships between individual parts. Such a representation mustsupport 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: 3.1 De?nition of Assembly Objects 1It should be possible to have high-level objects ready to use while moulddesigners think onthe level ofreal- world objects. In our work, an assembly object, O, is de?ned as a unique, identi?able entity in the following form: 2The representation of assemblies should encapsulate oper- ational functions toautomate routine processes suchas pocketing and interference checks. O Oid, A, M, R 1 Where: 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 componentsA hierarchy implies a de?nite assembly sequence. In addition, a hierarchical model can provide an explicit representation of the dependency of the position of one part on another. Oid is a unique identi?er 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, tcEach element of M is a function that uniquely identi?es a method. The symbol m represents a method name; and methods de?ne operations on objects. The symbol tci i Feature-based design [10] allows designers to work at a somewhat higher level of abstraction than that possible with the directuse ofsolid modellersGeometricfeatures 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 datastructureof featuremodellersWithoutfeatures, designers have to be concerned with all the details of geometric construction procedures required by solid modellers, and design changes have to be strictly speci?ed for every entity affected by the change. Moreover, the feature-based representation will provide high-level assembly objects for designers to useFor example, while mould designers think on the level of a real- world object, e.ga 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 con- ceptsThe 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 anddatabasesIn addition, the object- Fig. 2. Feature-based, object-oriented hierarchical representation. 742 X. G. Ye et al. 1, 2,%, n speci?es the argument type and tc speci?es the returned value type. Among all the elements of an assembly object, the relation- ships are most important for assembly designThe relationships between assembly objects will not only determine the position of objects in an assembly, but also maintain the associativities between assembly objectsIn the following sub-sections, we will illustrate the relationships at the same assembly level with the help of examples. R is a set of relationships among O and other assembly objects There aresixtypesof basicrelationships between assembly objects, i.ePart-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 speci?ed as: 3.2.1 Relationships Between Form Features 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. 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 partsfrom formfeatures The moul