The Tooling Instructor Software A New Approach For Decision Support In Tool Design

Transcription

1 The Toolig Istructor Software A New Approach For Decisio Support I Tool Desig Axel Selk 1, Peter Ket 2, Chris Gilboure 3 1 Breme Istitute of Idustrial Techology ad Applied Work Sciece (BIBA) Hochschulrig 20, D Breme, Germay Phoe: +49-(0) Fax: +49-(0) sel@biba.ui-breme.de 2 Walter Frak & Sos Ltd., Wakefield Road, Barsley, South Yorkshire S71 3LU, UK 3 Castig Techology Iteratioal, 7 East Bak Road, Sheffield S2 3PT, UK Abstract The paper describes the developmet of software which supports tool desigers i the derivatio of a appropriate mould desig from the castig geometry. This system is to be used i cojuctio with a CAD/CAM software. BIBA is developig this software withi the Europea Commuity fuded GROWTH project GRD DIRECTOOL. The mai focus of the work cocers castig applicatios. I co-operatio with project parters from the castigs idustry toolig desig kowledge has bee acquired which forms the basis for the software. A large variety of tool desigs from ijectio mouldig to gravity die castig has bee aalysed with regard to the relevat toolig characteristics. The results have bee used to develop a referece model which is capable of mappig tool desigs relatig their relevat features. The paper describes, how this referece model has bee used for the implemetatio of decisio support software for gravity die desigs. The two-step-decisio-support cosistig of Case Based Reasoig (CBR) ad iteractive desig support is preseted usig a case study. First experieces have bee made with the software prototype at Walter Frak & Sos Ltd., a UK foudry which specialises i gravity die castig alumiium. Itroductio The maufacture of dies ad moulds forms a sigificat part of the ecoomy ad commuity activities as there are more tha 5000 foudries ad ijectio moulders i Europe. I 1999 the Europea tool makig busiess reached a aual turover of more tha 8 billio Euro [1]. Small ad medium size foudries have to keep their processes competitive, whe it comes to desig ad data maagemet. Implemetig 3D CAD systems ivolves a lot of difficulties for small compaies. A major draw-back of curret CAD systems is, that they lack a kowledge-based iteractio durig the tool or mould desig phase. To set up a appropriate mould desig for a evisaged castig process is a difficult task as it requires a lot of kowledge about castig processes. I cotrast to other fields of techology the mould desig for castig applicatios has ot bee aalysed ad documeted i a

2 detailed way [2]. The approach preseted aims at providig a solutio to the problem described through the developmet of a software system for computer aided decisio support. Approach The software provides the tool desiger with decisio support i two steps. I the first step a similar toolig desig case ca be retrieved from a database for referece purposes through the techique of Case Based Reasoig (CBR). CBR is a method for desigig itelliget systems. It solves ew problems by retrievig similar problems which have already bee solved successfully [3]. The acquired solutio is adapted to solve the ew problem i a secod step. This techique has already bee applied to several CAD egieerig problems, such as the desig of stampig parts [4] ad the failure aalysis of mechaical uits [5]. Takig ito accout the referece toolig the tool desiger is assisted i all steps of desig. This support is provided i a secod step by usig a multimedia eviromet, which provides all fuctioality required. I the first support step CBR is applied to determie a tool desig solutio which best matches the curret problem. Cases are represeted by a set of sigificat attributes. For the evisaged applicatio these attributes must accurately describe the castig as they are the meas of compariso. Therefore the attributes describig the castig s geometry as well as material ad process requiremets eed to be determied. This is described for gravity die castig i the followig chapter. Through the applicatio of advaced database techiques eve large umbers of cases ca easily be maaged. The key fuctio of a CBR system is the determiatio of similarity betwee the ew problem ad previously solved cases. With a growig umber of stored cases the system should improve its ow performace. I order to obtai a fial tool desig the referece toolig solutio proposed by CBR eeds to be adapted for the ew castig. The detailed derivatio of toolig features is a complex task which ivolves a lot of kowledge of partig strategies, feeder ad gatig desig, oly to ame a few. For this task the desiger has to look up certai material ad process figures from charts ad to calculate additioal figures, such as the fill rate ad gatig cross-sectios. All this should be simplified through the applicatio of software. The implemetatio i a multimedia software eviromet seems to be the most efficiet way. This eviromet offers all kids of iteractios required, such as automated calculatio of toolig features ad database coectivity. All the results obtaied i the secod support step will be added to the actual case descriptio. Oce, the ew tool desig has bee prove, it will serve as a ew case for future CBR retrievals. Processig of toolig desig kowledge I order to develop a CBR represetatio scheme for toolig desig cases the required kowledge has bee acquired ad prepared for use withi CBR ad the multimedia support system. Gravity die desigs have bee coducted ad moitored with regard to relevat desig decisios. This ivestigatio resulted i the defiitio of certai stages of die desig, startig with the castig descriptio ad edig with the fial gravity die desig. The structure has bee set up based upo geeral stadards for gravity die desig as well as o best practice at Walter Frak & Sos Ltd. The parters agreed o a die desig process structure comprisig 10 stages. A large variety of aspects ifluecig gravity die desig has bee take ito cosideratio for this developmet. Iitially the castig is specified with regard to the material, the evisaged castig process ad the quality requiremets. Subsequet stages comprise the partig strategy as well as the feeder ad gatig desig for the die. Beside the pure mould-flow-related cosideratios also the machie iterface for the die has also bee itroduced to the structure. This iterface should esure the

3 proper fit of the die o a certai machie. The whole schematic sequece of desig decisios is give i Figure 1. Resultig from the preseted structure for die desig decisios, the parters extracted characteristic attributes describig a castig with regard to the required toolig. Die/ cores producible? Productivity ok? Castig desig Clarificatio of the castig specificatio Partig Strategy/ Core requiremets Orietatio of the die Feeder Desig Gatig Desig Iserts/ Chills Castig ejectio Machie Selectio Check of die sequece Fialisatio of die desig Fial die desig Figure 1 Schematic sequece of die desig decisios These attributes eable the tool desiger to describe a castig i such a way, that a best matchig die desig solutio ca be provided by Case Based Reasoig. A importat outcome of this research is that all factors ifluecig toolig desig ca be assiged to the mai iflueces, geometry ad material. These two categories each comprise a set of attributes, which together form a complete case descriptio for a castig as illustrated i Figure 2. Geometry Attributes volume o. of material accumulatios hollow sectios surface area wall thickess height width legth o. of revolvig axes o. of flages Castig Case Descriptio Material Attributes specific material volumetric shrikage material coefficiet for max. feedig distace max. velocity of the molte metal at the igates solidificatio rage Figure 2 Characteristic attributes for the castig case descriptio It is importat to metio that for a CBR compariso of two castigs it is ot sufficiet oly to take the specific material ito accout. As show i Figure 2, there are castig specific properties such as the maximum gate velocity ad the solidificatio rage of a material. While the specific material might ot be the same for two compared castigs, those castig specific material properties might evertheless be very similar. This is ofte the case, whe slightly differig alloys are used. I this case the castig performace of the two materials is very similar ad so is the resultig toolig. I order to determie the degree of similarity betwee two castigs with regard to the toolig, formulae are eeded for the computatio. Therefore the three formulae have bee applied to determie the overall degree of similarity betwee two castigs followig the paired compariso of sigle attributes.

4 For Boolea attributes like e.g. hollow part the followig equatio provides the eeded results: sim[ a ; b ] = 1 a b cases a ad b regardig theattribute a : value for attribute i case a; b : value for attribute i case b; sim :degree of similarity betwee the two [1] Numerical attributes are covered by the followig equatio: a b sim[ a; b ] =1 [2] a + b The overall degree of similarity gets determied usig the followig formula: DS W * sim[ a ; b ] i= 1 = W i= 1 W : Weightig DS : Overall degree of similarity [3] The applicatio of [1] to [3] provides the overall degree of similarity betwee two cases. Havig defied the case descriptio of castigs for Case Based Reasoig ad the sequece of die desig decisios, the software ca be implemeted Software implemetatio For the Case Based Reasoig a database applicatio has bee set up usig the Java programmig laguage. The tool desiger describes the ew castig defiig its geometrical properties ad the desired material. The desiger does ot eed to fill i the process-related material properties as those are directly retrieved from the database. Furthermore the CAD/CAM system, which is applied withi the project, trasfers some of the geometry iformatio such as volume, surface area ad boudig box dimesios, automatically to the CBR system. Oce all iformatio has bee give for the ew castig, the system performs the compariso betwee this case ad all cases stored i the database. For each compariso the degree of similarity is computed through the formulae (1) to (3) preseted i the previous sectio. The case which provides the highest degree of similarity is retrieved from the database as a proposal for the tool desiger. Iformatio o the castig which has bee used for the compariso as well as iformatio o the correspodig toolig solutio is displayed o a spreadsheet. Furthermore a lik is provided to the correspodig CAD file of the toolig. The equatios (1) to (3) are stadard formulae for the computatio of similarities. First test rus of the system cofirmed that the set of attributes describig a case, seems to satisfy the CBR requiremets best. For detailed assistace i the adaptatio of the proposed solutio the multimedia support tool is ivoked by the tool desiger. This software has bee implemeted usig the multimedia authorig system Macromedia Director 8.5 Shockwave Studio. This eviromet allows the implemetatio of all the media which is eeded, such as: Images, showig toolig features, Viewig of 3D models, Database iteractio, Iteractive formulae for automatic calculatios. The program is a executable, that ca be ru i the free-of-charge Macromedia Shockwave Player. This player is already itegrated i most web browsers. The gravity die module of this software is structured accordig to the sequece of the desig process, give i Figure 1. I this way the tool desiger ca avigate through the differet stages of tool desig ad complete the actual desig step by step. Completig the tool desig requires multitaskig betwee the CAD system ad the multimedia support software. Case study The system was validated by the itroductio of a ew castig case. The part is a female couplig for fire fightig equipmet as show i Figure 3. It is to be cast from Al-Si7Mg ad has a weight of 0.5

5 kg. First of all a best matchig die desig case was selected via Case Based Reasoig. The system suggested takig a male couplig for referece as show i Figure 4. This referece case is documeted with regard to its die desig through all desig stages as show i Figure 1. The tool desiger used this referece for the ew die desig. The software offers a iterface for the referece case as well as for the ew die desig. Both cases are displayed o oe scree. I this way the desiger ca have a look at the referece solutio while derivig the ew die desig. Figure 4 Castig proposed for die desig referece by the Toolig Istructor software Figure 3 New die desig case: Female couplig from Al-Si7Mg Geeral cocepts of partig, feedig ad gatig could easily be trasferred from the referece solutio to the ew die desig. The software eables the automatic calculatio of toolig-relevat figures, such as feedig distaces ad cross-sectios for sprue ad i-gates. The results were stored automatically i the database. I this way a die desig protocol was geerated for the female couplig which gives complemetary iformatio to the pure CAD file of the toolig. Figure 5 Oe die half for the female couplig, which has bee geerated i the CAD system i parallel with the die methodig i the Toolig Istructor. After the toolig had bee approved i the castig process, it was saved as a

6 additioal toolig solutio i the database system. I this way it will serve as a ew toolig solutio for future CBR requests. Coclusios The followig coclusios could be draw from the case study preseted. Gravity die desig cases ca be classified accordig to the eeds of Case Based Reasoig. The applicatio of CBR provided a satisfactory result i fidig a solutio to a similar problem. The retrieved die desig solutio could be adapted to the ew castig with little effort. The multimedia software for decisio support proved to be a helpful tool for die desigers. It provides guidace through all ecessary desig decisios. Furthermore it makes the die desig more trasparet ad comprehesible, as all desig decisios are stored i the database. Beside the pure CAD file of the die desig there is also a comprehesive toolig feature descriptio available from the database. The curret software system is beig istalled i the desig departmets of Walter & Sos Ltd ad Castig Techology Iteratioal. First test rus have bee performed. The desigers are satisfied with the geeral priciples ad fuctioig of the support offered by the software. A lot of work is still to be implemeted o detailig the secod step of support. This developmet is uderway i co-operatio with all parters i the DIRECTOOL project, so that this effort will result i a software tool, which ca be applied at a idustrial level. [3] Aamodt, A.; Plaza, E.: Case-Based Reasoig: Foudatioal Issues, Methodological Variatios ad System Approaches, I: AI Commuicatios, Vol.7 No 1, 1994, pp [4] Leake, D.; Birbaum, L.; Hammod, K.; Camero, M.; Hao, Y.: Itegratig diverse iformatio resources i a casebased desig eviromet, I: Egieerig Applicatios of Artificial Itelligece, 12 (1999), pp [5] Liao, T.W.; Zhag, Z.M.; Mout, C.R.: A Case-Based Reasoig System for Idetifyig Failure Mechaisms, I: Egieerig Applicatios of Artificial Itelligece, 13 (2000), pp Refereces [1] VDMA: Statistik zur Situatio des europäische Werkzeug- ud Formebaus im globale Umfeld, Brachestudie im Auftrag des VDMA 2000 [2] Müller, B: Gießtechische Gestaltug im Zeitalter der 3-D- Modellierug, Zeitschrifteaufsatz: Gießerei, Bad 85 (1998) Heft 2, Seite 56-60