喜歡這套資料就充值下載吧。。。資源目錄里展示的都可在線預覽哦。。。下載后都有，，請放心下載，，文件全都包含在內(nèi)，圖紙為CAD格式可編輯，【有疑問咨詢QQ:414951605 或 1304139763】 Recognition 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