a cad-cae integrated injection molding design system

Engineering with Computers (2002) 18: 80–92Ownership and Copyright 2002 Springer-Verlag London Limited

A CAD-CAE Integrated Injection Molding Design System

Y.-M. Deng, Y. C. Lam, S. B. Tor and G. A. BrittonCAD/CAM Lab, School of Mechanical and Production Engineering, Nanyang Technological University, Singapore

Abstract. In the injection molding design process, interac-tion between design and analysis is very intensive. This isto ensure that the plastic part being designed is manufactur-able by the injection molding process. However, such interac-tion is not supported by current computer-aided systems(CAD and CAE), because design and analysis are realizedas isolated modules. Although most of CAE systems providebuilt-in modeling tools, these are only meant for developingan analysis model with very limited CAD functionality. Onthe other hand, some CAD systems have allowed certainCAE systems to run under their environments, but inherentlythey use different data models, thus communication betweenthem is poor. This paper presents an innovative, CAD-CAEintegrated, injection molding design system. This system usesan integrated data model for both design and analysis. Thesystem is built on top of existing CAD and CAE systems,which not only greatly saves development effort, but alsomakes full use of the strong functionality of commercialcomputer aided systems. The system architecture consists offour layers: a CAD and CAE platform layer; a CAD-CAEfeature layer; a model layer; and a GUI layer. Two designcases were studied to illustrate the iterative design-analysisprocess and use of the developed system.

Keywords. CAD-CAE integration; Design-analysisprocess; Injection molding

1. Introduction

Injection molding design is characterized by the factthat there is intensive interaction between designand analysis. This, however, is not supported bycurrent computer-aided systems. There are variouscommercialized general-purpose CAD packages aswell as those specifically designed for injectionmolding design. These CAD systems enable thedesigner to quickly develop a geometric model of

Correspondence and offprint requests to: Dr. Deng Yimin,CAD/CAM Lab, School of Mechanical and Production Engineer-ing, Nanyang Technological University, Nanyang Avenue, Singa-pore 639798. E-mail: mymdeng�ntu.edu.sg

the design. On the other hand, injection moldingCAE systems provide the designer with analysisresults regarding the moldability of the design, thecost of the manufacturing process, the quality of theproduct, and so on. However, despite the advancedfunctionality of these systems, one problem is yetto be solved: CAD and CAE systems use differentmodels to describe a design, and they run undertheir own environments. Injection molding designand analysis are still not integrated.

Some commercial computer-aided system pro-viders have tried to tackle the problem. To compen-sate for the lack of CAD functionality, most CAEsystems provide built-in modeling tools to users.However, these are only meant for developing ananalysis model, so are of very limited CAD func-tionality. On the other hand, some CAD systemsallow certain CAE systems to run under their ownenvironments, such as the integration of SolidWorkswith COSMOS, AutoCAD with ANSYS, and Uni-graphics with MSC [1]. However, they only providean integrated environment, not an integrated system.Designers still need to create their design model,transfer the model to analysis model, and then spec-ify their analysis-related information over the analy-sis model. They inherently use different data models,thus are in effect not integrated.

There have been quite a lot of research workaddressing this problem from different perspectives.One earlier scheme is on the idealization of a CADmodel for CAE analysis and automatic mesh gener-ation. This includes techniques to support idealiz-ation and abstraction [2–4], as well as geometricreasoning for enabling idealization and abstraction,such as midsurface abstraction [5–7]. However,model idealization and automatic mesh generationonly support transformation from the CAD modelto the CAE model in terms of geometry. The derivedidealization models (either with or without meshgeneration) still need to be provided with infor-mation such as material type, manufacturing process

81A CAD-CAE Integrated Injection Molding Design System

or physical behavioral process, boundary conditions,and so on. That is, the model still lacks informationessential for CAE analysis.

There are in general two approaches for achievingCAD-CAE integration. One is through the developmentof an integrated environment with built-in CAD andCAE functionality. For example, Kim [8] developedan injection molding synthesis system, which integratesboth design synthesis and melt flow analysis, wheremelt flow analysis is used as a design evaluation tool.Irani et al [9] developed a framework for integratingCAE and iterative design/redesign of injection moldingfeed system. Kagan and Fischer [1] have developedan integrated mechanically-based CAE system by usinga B-spline finite element model for both design andanalysis stages.

A second, more promising, approach is to developan integration model on top of existing CAD andCAE packages. This model is different from the vari-ous neutral files such as DXF and IGES, in that itincorporates product lifecycle information rather thangeometry alone. These neutral files only provideinterfacing mechanism between different computer-aided systems. In this respect, the STEP standard (ISO10303) provides a promising model paradigm. STEPwas initially proposed for the integration of differentapplications within the product development process,such as design, manufacturing, economy, numericalanalysis, and so on. It has several partial modelsconcerning the Finite Element Analysis (FEA) method(part 104) and the CAD-FEA link (parts 209/214)[10]. However, these partial models are still in draftstatus, and they are of limited application.

There is also some research focusing on the opti-mization of gate location [11, 12]. Although thesehave touched upon the problem of design-analysisinteraction, their focus is the specific problem ofthe gate location optimization algorithm. Such workonly shows the importance of design-analysis inter-action, and they have not addressed the generalproblem of enabling injection molding CAD-CAEintegration.

This paper presents strategies and methods for thedevelopment of a CAD-CAE integrated injectionmolding design system based on existing CAD/CAEsystems. The system uses an integrated feature modelfor both design and analysis, which is also referredto as an integration model. The next section brieflydiscusses the model, which is then followed by adescription of the proposed integrated, iterative,design-analysis process. The paper then continuesto discuss the system framework and methodsfor its development. A case study is presentedbefore concluding.

2. CAD-CAE Integration Model

The authors propose a set of CAD-CAE featuresthat are oriented to both the design and analysisprocesses of plastic part design [13]. These includea part feature and a collection of wall features, holefeatures, rib features, boss features and treatmentfeatures. These features can be decomposed into anumber of sub-features because designers may needto specify different analysis information over differ-ent parts of a feature (either a wall feature, or a ribfeature or a boss feature). Therefore, there are alsocollections of sub-features.

The part feature contains the overall informationof a plastic part. Wall features are the base of theplastic part. Other features are developed from wallfeatures, so are referred to as development features.Rib features are developed from two adjacent wallfeatures. Hole features refer to any cutouts in aplastic part. Boss features refer to any protrusionsfrom a plastic part. Treatment features are used asa treatment of other features, such as a chamfer,round and fillet. These features are organized intoa hierarchical structure called a feature tree (Fig. 1).At the root of the feature tree is the part feature.The second level of the feature tree contains collec-tions of wall features and development features. Thethird level contains individual features. The fourthlevel contains sub-features, such as sub-wall, sub-rib and sub-boss features.

Each feature contains design and analysis relateddata, which are called feature attributes (Table 1).Most of the attributes are self-explanatory, exceptfor the attributes of pointer, constraint and sup-pressibility. All features have a pointer attribute,which describes the relationship between the fea-tures. The constraints relating to part features referto the relevant analysis criteria. The constraints relat-ing to other features include gate location con-straints, which act on the edges and surfaces of thefeature geometry. The suppressibility attribute of rib,boss, hole and treatment features allows the designerto suppress these features when abstracting theanalysis model.

This feature-based scheme has been implementedusing Object Oriented technology [13] and a com-mercial CAD platform (Solid Edge).

3. Integrated Injection MoldingDesign-Analysis Process

Figure 2 shows the proposed injection moldingdesign and analysis process. The process consists

82 Y.-M. Deng et al.

Fig. 1. CAD-CAE feature tree.

Table 1. Feature attributes

Feature type Feature attributes

Part part identifier, thickness, material,constraints, analysis type, boundaryconditions, processing conditions,pointers to wall features

Wall wall identifier, wall geometry, thickness,constraints, pointers to children sub-walls, pointers to embedded rib/boss/hole/treatment features

Hole hole identifier, hole geometry,constraints, suppressibility, pointer toparent feature, pointers to embeddedtreatment features

Rib rib identifier, rib geometry, thickness,constraints, suppressibility, pointers toparent wall features, pointers to childrensub-ribs, pointers to embedded hole andtreatment features

Boss boss identifier, boss geometry, thickness,constraints, suppressibility, pointer toparent wall feature, pointers to childrensub-bosses, pointers to embedded holeand treatment features

Treatment treatment identifier, treatment geometry,constraints, suppressibility, pointer toparent feature

Sub-Wall sub-wall identifier, sub-wall geometry,constraints, pointer to parent wallfeature

Sub-Rib sub-rib identifier, sub-rib geometry,constraints, pointer to parent rib feature

Sub-Boss sub-boss identifier, sub-boss geometry,constraints, pointer to parent bossfeature

of several steps, such as creating individualCAD-CAE features, constructing an integrationmodel, abstracting information to create an analysismodel and activating the analysis.

This is a CAD-CAE integrated process – designand analysis use the same data model, and operateunder the same computational environment. Byusing the same data model, the authors mean thatthe design process aims at developing a model thatconsists of both design and analysis information.This same model is then directly used by the analy-sis process. Hence, this model is not a geometricmodel (CSG or B-Rep) for both design and analysis,but rather an integration model, which can incorpor-ate any geometric models as long as the CADsystem supports them.

Note that, although the process requires ananalysis model, this model is abstracted from theintegration model, not converted from a CADgeometric model, as is current practice. The inte-grated model captures essential analysis infor-mation during the design process, which is thenused to automatically set the boundary conditionsand processing conditions for analysis. On theother hand, current practice requires designers tomanually specify the boundary conditions andother analysis data over an analysis model, notthe design model.

3.1. Create CAD-CAE Features

The creation of feature geometry is dependent onthe functionality of the CAD system platform. If aCAD system supports feature-based modeling, as isthe case for most commercial CAD systems, theCAD geometry will be referred to as ‘features’ in


Fig. 2. Flowchart of the integrated design-analysis process.

the CAD system (CAD features). However, thesefeatures are CAM-oriented and, in general, cannotbe directly mapped into CAE-oriented features.These CAD features provide the geometry for theproposed CAD-CAE features. Assignment of CADgeometry to a CAD-CAE feature may involve selec-

tion of a complete CAD feature, combining severalfeatures, and/or decomposing a feature so part of itcan be selected. After the geometry has been definednon-geometric information can be added.

The part feature is created after the individualCAD-CAE features. Its geometry is assigned throughthe assignment of the constituent wall features.Overall product information relating to design andanalysis can be specified over the part feature. Forexample, for flow analysis, it is necessary to specifythe injection location(s) as part of the boundaryconditions. CAD tools are used to create gatelocation markers for this purpose. These markerscan also be regarded as CAD-CAE features.

3.2. Construct Integration Model

The integration model is constructed from the fea-tures. This includes constructing the geometry of aplastic part by Boolean operations, as well as estab-lishing relationship information between features. Ifa CAD system supports automatic Boolean oper-ations during geometric feature creation, then onlythe second task is required. For example, in theSolid Edge environment, the creation of a ‘Cutout’feature will automatically invoke the Boolean ‘Sub-traction’ operation between the created feature andthe base feature. Other CAD systems, such as Auto-CAD, require users to manually activate Booleanoperations during the model construction process.

3.3. Abstract Information to Create AnalysisModel

Abstraction depends upon the type of analysis andthe strategy of the optimization routines. Theabstraction process involves abstracting an idealizedgeometric model as well as non-geometric analysisinformation, such as material type, boundary con-ditions, processing conditions and constraint infor-mation. In this paper, idealization refers to simplify-ing the geometric model to suppress non-significantfeatures. This is a very subjective process whichrelies heavily on a designer’s experience and expert-ise. Hence, the system allows designers to specifywhether a feature can be suppressed or not.

3.4. Activate CAE Analysis Routines

With all of the information is available, the under-lying CAE system can be activated to conduct aCAE analysis. The analysis results are then examined


to check whether any of the pre-defined criteria –which are in the form of part feature constraints inthe integration model – are violated. If they arethen the CAD-CAE features need to be modified.After modification, a new integration model will beconstructed and an analysis model abstracted, sothat another CAE analysis can be activated. Theprocess iterates until all criteria have been satisfied.

If the design requires optimization of some para-meters, then designers need to have a predefinedoptimization routine. This routine can take fulladvantage of the integration model. For example, ifa designer needs to search for an optimized gatelocation over a restricted area of the plastic part,the optimization routine will only need to changethe gate location attribute of the part feature inthe integration model for each iteration process.Furthermore, the gate location constraint of the cor-responding wall feature can be utilized to reducethe optimization search space.

4. Framework of a PrototypeInjection Molding Design System

4.1. System Architecture

A prototype injection molding design system hasbeen developed to provide designers with an inte-grated environment for design and analysis. Thesystem architecture is organized into four layers: aCAD and CAE platform layer, a CAD-CAE featurelayer, a model layer and a GUI layer. The CADplatform (Solid Edge was used) provides modelingtools and algorithms for specifying geometric infor-mation of the plastic part, while CAE platform(Moldflow was used) provides analysis routinesfor the CAE analysis. The feature layer comprisespredefined features and user-defined features basedon the proposed CAD-CAE feature definition. Themodel layer is used to develop the feature modeland to abstract the required CAE analysis model.Figure 3 shows the system architecture.

4.2. CAD System and ActiveX Automation

A commercial CAD system provides the modelingtools and geometric processing algorithms for cre-ating and editing feature geometry. This geometrywill be incorporated in the CAD-CAE features asgeometry objects. Solid Edge was selected as CAD

Fig. 3. System architecture of the software prototype.

platform because it supports ActiveX automation1.By using a CAD system that supports ActiveXautomation, users and other applications can accessthe CAD functionality of the system via its exposedActiveX objects and ActiveX controls (components).

For example, Table 2 lists the information of anobject ‘ExtrudedProtrusion’ (representing the geo-metric feature of extruded protrusion) exposed bySolid Edge. Obviously, outside applications can eas-ily create, modify, delete, display and query a geo-metric feature using this kind of object. Hence, theexposed ActiveX objects can be directly used as thegeometry objects of the CAD-CAE features.

4.3. GUI of the System

Figure 4 shows the graphical user interface of theprototype system. The upper panel shows the system

1 ActiveX is the term used to describe the Microsoft componentobject technology. Components are independent (both language-independent and hardware independent) software modules. Thecomponent object technology provides the means to make anapplication expose its functionality to the other applications [14].The technology is based on a communicating protocol calledComponent Object Model (COM). COM is a software architecturethat allows applications to be built from binary software compo-nents. It is the underlying architecture that forms the foundationfor higher-level software services.


Table 2. An ActiveX object ‘ExtrudedProtrusion’ exposedby Solid Edge

Properties Application, AttributeSets, BottomCap,BottomCaps, Depth, Edges, ExtentSide,ExtentType, Faces, FacesByRay,FromPlane, IsAttributeSetPresent, Name,Parent, Profile, ProfileSide,ShowDimensions, SideFaces, Status,Suppress, ToCap, ToCaps, ToPlane, Type

Methods Delete, GetProfiles, Range, Reorder,SetProfiles

Table 3. Iterative design-analysis results of the design case

Node No. Pressure Pressure�20? Pressure(gate (MPa) (1 for yes, increaselocation) 0 for no) over the

minimum

484 17.536 1 11.20%485 17.2083 1 9.10%486 16.838 1 6.80%488 17.1707 1 8.90%493 20.221 0 28.20%494 18.6344 1 18.20%495 17.3293 1 9.90%496 17.0481 1 8.10%497 18.1478 1 15.10%498 19.609 1 24.30%499 17.6907 1 12.20%500 16.9489 1 7.50%504 18.5845 1 17.90%507 18.1689 1 15.20%508 19.4148 1 23.10%510 17.6612 1 12.00%512 20.6822 0 31.20%514 18.4319 1 16.90%515 19.8195 1 25.70%516 18.5524 1 17.60%517 18.5423 1 17.60%519 15.7696 1 0.00%520 16.1881 1 2.70%521 15.8102 1 0.30%522 16.2429 1 3.00%523 16.4471 1 4.30%524 17.0368 1 8.00%534 20.5398 0 30.20%535 20.5571 0 30.40%536 18.0001 1 14.10%537 18.5524 1 17.60%538 19.0828 1 21.00%539 20.1463 0 27.80%578 20.9275 0 32.70%582 17.126 1 8.60%

menus and tool bars and the panel on the left showsthe feature tree of a plastic part, which is beingdesigned. The graphics window is shown on theright.

The primary menu structure of the system is givenin Fig. 5. Figure 6 shows the popup menu structureof the feature tree operation.

4.4. Feature Creation and Modification

The software contains a library of CAD-CAE featureprototypes which can be used to create features.Features are created by first using the modelingtools provided by the CAD platform to create thefeature geometry. After that, the CAD geometry isassigned to a feature using the feature prototypes.Finally, non-geometric information is added to thefeature.

4.4.1. Wall/Hole/Rib/Boss/Treatment featureFigure 7 shows the user interface for creating/modifying a wall feature. By clicking the ‘AssignGeometry’ button, the system will automaticallyaccess the CAD system and allow a designer toselect the desired geometry from the CAD environ-ment. The collection of ActiveX objects correspond-ing to the selected geometry is then used as thegeometry object of the wall feature. This geometryobject incorporates not only all the geometric entitiesof the feature, but also the topological relationshipscontained within the CAD system.

Using the interface, information relating to theconstraints of the wall feature can also be specified.A designer can drag the slider to specify a valuebetween 0 and 10 for the weight of the gate location.The value 0 indicates a gate is not to be locatedon this wall feature, while the value 10 indicatesthat the wall feature is highly desirable for locatinga gate.

If it is necessary to specify different constraintsover different areas of a wall feature, it can bedecomposed by selecting the decomposing geometry.The resulting sub-wall features can be assigned withindividual constraints as desired. Figure 4 shows anexample of a ‘U-shape Carrier’, where three wallfeatures have been created. The ‘Right plate’ hasbeen decomposed into two sub-wall features; theSolid Edge ‘sketch’ geometry is used as the decom-posing geometry.

Other features are created in a similar way.

4.4.2. Part FeatureThe boundary condition is specified through partfeature. The software uses a circle (a Solid Edge


Fig. 4. Graphical user interface of the developed prototype system. The two small circles represent gate locations, which are actuallyon the outside face of the wall geometry. The reason they appear on the inside face is for pedagogical convenience.

Fig. 5. Primary menu structure of the system.

sketch) as a gate location marker to represent therequired gate location. Similar to the creation ofother features, Solid Edge system is accessed viathe relevant ActiveX object to allow a designer tocreate the gate location markers. Figure 4 showsthat two gate locations have been specified.

Material type is also specified through part fea-ture, which will be discussed in the following sec-tion. Depending upon the type of analysis, infor-mation relating to the processing conditions canalso be specified, such as mold temperature, melttemperature and injection time.

4.5. Material Library

Material properties data are provided by Moldflow.However, a designer might wish to specify materialtype during the design process. Since Moldflow usesthe manufacturer and the trade name of a materialas the index to the material properties database, theauthors propose to use them as the material infor-mation.

To assist a designer specify this information, theprototype system has its own material library. Thus,a designer can simply choose the desired material


Fig. 6. Popup menu structure of the feature tree operation.

Fig. 7. User interface for creating a wall feature.

from the library without searching through the Mold-flow material database. The library uses materialtype as an indexing field, together with the fieldsof manufacturer and trade name. If two materialsare of the same type, then a serial number is auto-matically added to ensure unique representation, e.g.ABS-1 and ABS-2. The data stored in the libraryis extracted from Moldflow material database toensure that during CAE analysis, the relevantmaterial properties can be retrieved.

The material can be specified over the part featureduring design process. The following is an exampleof material data specified:

� Material type: PP-2.� Material manufacturer: ATC Inc. [ATC].

� Material trade name: ATX 759–39B [AT 001].

4.6. Integration Model Construction

Once all the CAD-CAE features have been createdthe integration model can be constructed. This is anautomatic process because the inter-feature relation-ships have been specified during feature creationprocess. For example, when a hole feature is createdon a wall feature, a pointer attribute is specified forboth the wall feature and the hole feature. As such,a relationship between the wall feature and thehole feature will be automatically established andcaptured in the integration model. Figure 8 showsthe algorithm for constructing the integration model.

4.7. Analysis Model Abstraction and CAEAnalysis

Of the two types of data for analysis model abstrac-tion, analysis model geometry can be easily idealizedbecause the integration model already has the speci-fied information about whether a feature can besuppressed or not. By using the ActiveX objects ofthe CAD geometry, the system can access the fea-ture geometry to be suppressed and change its sup-press attribute from ‘False’ to ‘True’.

The idealized analysis geometry is used to gener-ate finite element mesh. Moldflow supports threetypes of mesh model: midplane mesh model, surfacemesh model and 3D mesh model. A midplane meshis a web of three-noded triangular elements. Themidplane mesh model represents the solid modelusing the thickness information during an analysis.A surface mesh analysis works by simulating theflow of the melt on both the top and bottom surfacesof the mold cavity. The surface mesh consists of amixture of different types of mesh including regionswith traditional midplane elements and surface(double-skin) elements. A 3D mesh is made up ofsolid, tetrahedral shaped mesh elements. Tetrahedralelements have four nodes, four faces and six edgesand allow an accurate 3D flow simulation to becalculated [15].

Another type of data for analysis model abstrac-tion is non-geometric, analysis-related information.After the analysis mesh model is generated, theprototype system automatically generates the bound-ary condition file using the specified gate locationinformation from the integration model. After that,an analysis inputs file is generated for other non-geometric information such as material, processingconditions, and so on. This file contains all the


Fig. 8. Flowchart of constructing integration model fromindividual features.

necessary data, either directly or through pointers tothe relevant data files, for activating the correspond-ing analysis routines from Moldflow to conductthe desired analyses. Figure 9 is a flowchart ofabstracting the analysis model.

Fig. 9. Flowchart of abstracting analysis model from integrationmodel.

5. Case Study

5.1. Case No. 1

This case study illustrates the integrated CAD-CAEprocess and how the system can be used to specify


analysis information over a CAD design model. Thepart is a U-shape carrier (Fig. 4). Using the pre-defined feature prototypes from the system, threewall features are created first: ‘Base plate’, ‘Leftplate’ and ‘Right plate’. All design and analysisinformation relating to these walls are specified inthe corresponding wall features. System GUI toolsassist in the specification process. Assume that thedesigner wishes to specify that a certain part of theouter surface of the ‘Right plate’ wall feature notbe allowed to have gate location mark. To achievethis, the wall feature is decomposed into two sub-wall features: ‘Left sub-wall’ feature (allowed toput gate location) and ‘Right sub-wall’ feature (notallowed to put gate location) (Fig. 4).

After this, development features are created. Theseinclude a boss feature developed on the ‘Base plate’wall feature, named ‘Base boss’; two ribs on boththe ‘Base plate’ wall feature and the ‘Left plate’wall feature, named ‘Side rib’ and ‘Small rib’, aswell as two hole features on the ‘Base plate’ wallfeature, named ‘Base hole’ and ‘Square hole’. Twotreatment features, named ‘Left round’ and ‘Rightround’, are also created, which correspond to the‘Round’ features under the Solid Edge environment.Assume that the designer wants to specify that someof these development features can be suppressedduring CAE analysis. This is achieved by assigningthe ‘suppressibility’ attribute of the correspondingfeatures.

The part feature is created next. The part name

Fig. 10. Abstracting analysis geometry model of the design case.

is specified as ‘U-shape Carrier’. Material is speci-fied as: material type: ‘PP-2’; manufacturer: ‘ATCInc. [ATC]’; trade name: ‘ATX 759–39B [AT001]’.Assume that the designer has created two gatelocation markers (Fig. 4), which will later be usedto create the boundary condition file.

With all the features created and their relevantinformation specified, the system will automaticallyconstruct the desired integration model.

Based on this integration model, the designer canactivate the CAE package to carry out analysis. Thisis achieved by first abstracting an idealized analysisgeometry model from the integration model (Fig.10). As can be seen, a hole feature (‘Square hole’),a rib feature (‘Small rib’) and two treatment features(‘Left round’ and ‘Right round’) have been sup-pressed (their names are prefixed with a star in thefeature tree window).

The abstracted geometry model is used to createa surface mesh model. The system activates therelevant module of Moldflow to achieve this. Byextracting the coordinates of the gate location mark-ers from the integration model, and comparing themwith the node coordinates of the created meshmodel, the gate locations can be assigned to themesh model, hence a boundary condition file can beautomatically created. Figure 11 shows the generatedmesh model displayed under Moldflow PlasticInsight (MPI) environment (the two gate locationsare also displayed).

Next the non-geometric information is abstracted


Fig. 11. Surface mesh model of the design case under MPI environment.

to create the Moldflow analysis inputs file. Withthis file, the relevant Moldflow analysis routines areexecuted automatically. The whole process incorpor-ates both design and analysis. During this process,a same data model, namely the integration model,was created and used, which allows the designer tospecify analysis information over the CAD designmodel directly.

5.2. Case No. 2

This case study illustrates how an iterative design-analysis process can be carried out by using thedeveloped system. Specific targets for the analysisresults can be input as constraint information ofthe part feature during the design process, and theconstraints checked against the corresponding analy-sis results. If a constraint is not satisfied, then therelevant CAD-CAE features need to be modified inthe integration model. The designer can specifywhich parameter is to be changed in the integrationmodel, e.g. gate location. The CAD-CAE integrationprocess is then repeated. The process iterates auto-matically until all the constraints are satisfied. Ifthere is more than one design variant satisfying allconstraints, then an optimal one can be selectedwhich best satisfies these constraints.

To illustrate this process, a same CAD designmodel ‘U-shape Carrier’ from the above case studyis used. The part material remains unchanged. Theprocessing conditions are specified as:

� Melt temperature: 215°C.

� Mold temperature: 50°C.� Injection time: 2 sec.

Assume that this time the designer decides to usea single gate instead of the above two-gate design.The designer also wishes to constrain the single-gate location to a sub-wall feature ‘Left sub-wall’(Figs 4 or 10). This will automatically constrain thegate location to those mesh nodes located within thisarea. Figure 12 shows the surface mesh generated byMoldflow. This is the same mesh shown in Fig. 11but viewed from different perspective. The meshnodes for the constrained gate location are thosewithin the outlined area.

Another constraint is specified over the partfeature: the maximum pressure should be less than20 MPa. After all these data are specified, thedesign-analysis process is automatically iterated,with each iteration a new gate location is used.Table 3 lists the results from this process.

The results show that when nodes 493, 512, 534,535, 539, 578 are used as the gate location, thepressure constraint is not satisfied. These nodes formthe upper-side area of the constrained sub-wallfeature (Fig. 12). Of those successful nodes, node519 is the optimum because it best satisfies thepressure constraint (it has the minimum value ofthe maximum pressure). Node 578, which is at theupper left corner of the constrained area, has themaximum value of the maximum pressure, which is32.7% more than the value when node 519 is used.Figure 13 shows the contour plot of the maximumpressure versus the gate location within the con-strained area of the ‘Left sub-wall’ feature.


Fig. 12. Mesh nodes for the constrained gate location (within the outlined area).

Fig. 13. Contour plot of maximum pressure versus the constrained gate location.

An intuitive interpretation of these results is that,in general, a single-gate location should be approxi-mately in the geometric center of the plastic part,so as to minimize the requirement of pressure andto have a uniform flow pattern. Hence, for thecurrent design case, the gate location is required tobe positioned at the lower edge of the constrainedarea, which includes nodes 519–524 and 582.

Because of the presence of the ‘Base hole’ and‘Base boss’ feature, node 519 is nearest to thegeometric center among these candidate nodes.

6. Conclusions

The objective of this research is to develop a CAD-CAE integrated injection molding design system.


Integration is achieved through a feature-based inte-gration model and an iterative design-analysis pro-cess based on the model. The integration modelconsists of a number of CAD-CAE features and therelationships between them. The features captureboth geometric and non-geometric informationessential for CAE analysis.

A system framework for integrating design andanalysis was described. The system platform consistsof a commercial CAD system (Solid Edge) and acommercial CAE system (Moldflow). By using exist-ing CAD/CAE software as the system platform, devel-opment effort is reduced considerably and full advan-tage can be taken of the functionality of this software.The functionality of ActiveX automation of Solid Edgeis used for retrieving feature geometry and foraccessing Solid Edge itself. A prototype system hasbeen developed, which consists of a number of mod-ules organized into four layers: CAD and CAE plat-form layer, feature layer, model layer and GUI layer.A number of tools have been developed to assist inthe integrated design-analysis process.

Two design cases were studied which demonstratethat the system provides a unified data model forboth design and analysis. With this model, designerscan specify not only design information, but alsoanalysis-related information. This is especially usefulwhen a designer needs to specify design intentionsthat are analysis-related, such as gate location con-straints. The case study also shows that thedeveloped system supports iterative design-analysisprocess.

The results of this work are not limited to SolidEdge and Moldflow. The feature prototypes and theintegration model can be applied to other CADsoftware employing ActiveX automation technologyand to other CAE software.

Future research is aimed at developing automaticinterpretation of CAE analysis results based on pre-specified target criteria and providing design guidesfor modifying the integration model when criteriaare not satisfied.

Acknowledgments

This project is supported by the Academic ResearchFund, Ministry of Education, Singapore and MoldflowPty Ltd.

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a cad-cae integrated injection molding design system

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