Integration of EDM within a CIM Environment

Keynote Papers

Integration of EDM within a CIM Environment M. F. DeVries (1), N. A. Duffie (2), University of Wisconsin-Madison/USA; J. P. Kruth (2), Katholieke Universiteit Leuven, Leuven/Belgium; D. F. Dauw (2), Charmilles Technologies SA, Geneva/Switzerland; B. Schumacher (2). AGlE Ltd., Losone/Switzerland

ABSTRACT This paper has as its focus the integration of Electrical Discharge Machining (EDM) within a Computer Integrated Manufacturing (CIM) environment. Ckarly, the i n d u c t i o n of EDM into advanced manufacturing system with high levels of computer integration and automated material handlinghas pmpssed at a much slower rate than the integration of conventional machining pmcesscs such as milling and turning. However. recent developments in communications. controls and CAD/CAM system for EDM have created the potential for bringing EDM into the mainstream of automated machining opuations in modem manufacturing systems. Following a brief review of CIM, the paper shows that EDM is a v a y promising candidate for integration within a CIM environment because of its inninsic process conml and intelligence when compared to many rraditional processing techniques. Examples of several rather complete experimental EDWCIM systems set up within research facilities are described. Conclusions art drawn based upon the experiences gathered to date with these experimental systems.

KEYWORDS Electrical Discharge Machining. Computer IntegratedManufacturing

INTRODUCTION Computer Integnted Manufacturing (CIM) is a term that is commonly used to represent a technological umbrella of computer based activities involving the organization of data flow, mass flow and human interaction in a manufacturing enterprise. There is frequent misuse of the CIM concept especially for commercial purposes as some products are claimed to be ready for CIM when, in reality. these products are being sold with only a few elements matching the broad CIM philosophy. Computer Integrated Manufacturing must also be considered as an approach that may or may not be appropriate for a particular situation depending on human resources, the capability for making significant financial investments and other factors. For a CIM installation to succeed, it is important that there is a will to continuously learn, understand and keep pace with the “dynamic” aspects of this concept. It is obvious that CIM ideas must constantly evolve in order to improve the realizations that go along with them. Figure 1 presents the Computer Integrated Manufacturing philosophy. This figure illustrates the ultimate CIM objective: Inregmion of the enrire company organizaiion. In CIM, General Management, Manufacturing. R&D. Customer Support, Marketing, Finance, Sales, and Human Resources art linked together by a communication network making available shared data among the factory departments. CIM should lead to shorter production times, reduced inventory, consistent quality. less need for human intervention and increased management flexibility to respond quickly to market changes. At the present time, there is a small but growing amount of research underway that is related to EDMKIM integration. This activity is underway in several universities; in addition, there are several large international cooperative projects, being conducted, involving both academic and industrial establishmcnts. that are strongly related to this research theme. Four examples are enumerated below. At the University of Wisconsin-Madison, research is directed towards the integration of CNC-EDM in a multi-manufacturing cell environment [I]. * The Catholic University of Leuven, Belgium is focusing on software aspects including geometrical design (CAD), CAD-integrated programming of CNC EDM-machines (CAM). computer-aided pmcess planning for EDM (CAPP). and NC data communication [2,14]. * The European Strategic Program for Research and Development in Information Technology (ESPRIT) recently announced a large research project “Integrated Product Design System” (IPDES), ESPRIT Project #2590 131.

Annals of the ClRP Vol. 39/2/1990

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The Federal Republic of Germany is supporting a large research project on “Data Processing in Production.” One of its topics, related to this paper, is named “Werkstatt Orientierte Rogrammierung” (WOP), or “Shop Floor Oriented Pmgramming,” (41. These four projects all include indusaial partners and will be discussed later in this paper.

EXPECTATIONS OF EDM INTEGRATION WITHIN A CIM ENVIRONMENT The non-traditional machining processes of Electrical Discharge Machining (EDM), Laser Beam Machining (LBM), Electro Chemical Machining (ECM). Ultrasonic Machining (USM) and Electron Beam Machining (EBM) have always been technologically advanced as far as process control and automation are concerned. This is because these machining techniques arc based on elecuical. chemical, or thermal removal principles [ 5 ] involving a cutting tool and the workpiece to be machined that are separated by a controlled working gap when the physical removal process takes place. This is quite different from the more traditional metal cutting techniques where the material removal is based on shear (e.g.. in turning, drilling and milling) or abrasive removal principles (e.g.. in grinding). Thus. p m s s conml and optimization are inherent parts of the system for the non-traditional machining techniques, in particular EDM, which often include sophisticated intelligent background supervisoty systems 1301. EDM is particularly suited for CIM integration for the following reasons: * the level of automation currently existing on EDM units.

the relatively low production rate of EDM compared to traditional machining processes. the availability of advanced softwarc in the areas of “Pan Geometry” (CAD), “Process Technology” (CAPP) and “Machining” (PRODUCTION). These three technologies can be dealt with independently, but have to be integrated of CLM to be guaranteed. for complete SUCC~SS A growing shortage of highly skilled EDM operators, for whom a fairly good understanding of the physical process is a pnrcquisite. CIM integration can free EDM from its island of automation, achieving more efficient and cost effective production. Figure 2 illustrates what might be expected from EDM/CIM integration. In this graph, it is shown that higher skilled machinists are required as job complexity increases. In this context. job complexity implies workpiece complexity

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(geometrical), as well as the complexity introduced by material properties. manufacturing process requirements. quality aspects and assembly constraints.

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ELECTRICAL MACHINING

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DlTlONAL D-CONTROL

REOUIRED OPERATORSKILL

NCCONTROL

Reduced labor costs (80 to 95%). Lower design and development costs (70 to 85%). * Shorter delivery time and i-sed flexibility at the organizational as well as at the part geometry level (40to 75%). This implies a shorter and quicker response to customer demands, i.e., the just in time concept (JIT).

Negathre Fedon: Risk of lowerquality. especially for small batch sizes. Substanrial financial investments nquired. Scarceness of machinability data, especially when various machining techniques are being considered. Electrical discharge machining will typically not show immediate quality improvements with CIM, because single jobs yield limited manufacturing P ~ C S and S product fd-back.

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Table 1 Results of a Market Analysis: What Can be Expected from CIM Innoduction [61 Figure 2 Required “Operator Skill” as a Function of Job Complexity. However, Figure 2 also shows that with CIM integration, the required skill of the operator is reduced as one moves from traditional hand-controlled machines to machines equipped with Numerical Control, to those in a CIM environnlcnt. Figure 3 depicts that with increasing job complexity the overall product throughput time and the amount of production control will increase but to a lesser degree for a CIM environment than in the case of traditional production. The figure suggests that CIMconml would be an effective technique for complex jobs to be performed; hence, the Elecnical Machining methods are g o d candidates for this type of production. ELECTRICAL I MACHINING

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Figure 3: Throughput T i m and Production Control versus Job Complexity. If the cost per pan is analyzed as a function of production lot volume, then the introduction of CIM has a positive effect on reducing costs. Indeed, as Figure 4 illusuates, CIM controlled production yields smaller costs per part for small batch sizes; the drop in cost pcr part has less of an effect when CIM integration and control are introduced for large production volumes. Hence, CIM-controlled production is an attractive alternative when EDM is being considered.

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PART A

The imponant positive effect obtained through the inuoduction of EDM into a CIM environment deals with the economics. This is obvious when one realizes that “manufacturing jobs” can now be handled in one or more shifts. For instance, the design and development concepts could run in the first shift, i.e.. the standard day shift. Additional production shifts can then be introduced because a CIM environment has a 24 hour operational availability. This allows for increases in productivity, shorter delivery times (the JIT concept), shorter pay-back periods, and more flexibility in setting schedules, all of benefit to the end customer. Figure 5 illustrates a potentially important negative side effect. Quite clearly, CIM implementation will require more overall attention than that needed for h e application of traditional plant concepts. The figure suggests that intensive training will be required for those who work in a CIM environment where important additional investments in computer networks, data sharing. communicarions and standardization will be required. These factors would typically increase with increasing job complexity. ELECTRICAL

ELECTRICAL MACHINING INCREASING: PLANT INVESTMENT

COMPUTER-STRUCTURE NETWORKING STANDARMSATlON REQ.

JOB-COMPLEXITY

PRODUCTION-LOT-VOLUME Figure 4: Cost Per Pan versus Production Lot Volume

SPECIAL CONSIDERATIONSWHEN INTRODUCING CIM The introduction of the CIM concept on the shop floor level is seldom achieved with ease. To implement CIM requires a basic understanding of its advantages and disadvantages. as well as the influence and persuasiveness to overcome prejudices. An overview of the results of a market analysis on what can be expected from the introduction of CIM is given in Table 1, [6,7]. The table shows expected improvements and negative impacts when CIM concepts are i n d u c e d in comparison to adopting traditional concepts. The following positive and negative factors can be drawn from Table 1.

Positha Factors: Substantially higher shop floor availability (200 to 30046 increase). This is a result of“24 hour availability.” Higher throughput rate (140 to 170%).

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Figure 5: Importance of CIM Related Parametm versus Job Complexity

REQUIREMENTSFOR EDWCIM INTEGRATION Electrical Discharge Machining (EDM) is shifting, more than ever, from its island of “Non-Traditional Machining” towards the broad sea of factory automation. Spark erosion, often appreciated by mechanical engineers and machinists for its unique removal principles. now has its own niche in the mechanical engineering business. EDM sometimes has been criticized for its relatively slow stock removal rate and the skills required to master the equipment and machines properly. Nevertheless, EDM is often the only technically attractive machining alternative. Indeed. there are a number of common applications today that would be too expensive and almost impossible to cany out if EDM did not exist. Irrespective of the fact that EDM is commonly classified as a “non-traditional machining” process. it is now breaking this image by its entrance and integration onto the machine shop floor. One implication is that tool preparation must be put at the same level of importance as production planning in order to organize the entire manufacturing environment as efficiently as possible. Another current implication is that EDM machining centers must be designed that resolve existing communication problems. This aspect is discussed at some length in the section of

this paper dealing with standardization. Clearly, the final objective is to improve the overall machining efficiency of the EDM process, a major goal of most customers. High overall efficiency implies that EDM units run independently and reliably, have their own supervision system for tool and workpiece flow and handling, incorporate EDM skills and experience (stored in internal data banks), and have internal and external communication capabilities. In brief, its autonomy must be assured [8.9]. An EDM cell must, therefore. be able to communicate with other machines; hence, suitable communication standards must be introduced 110.1 1.121.

department. They can. of course, be shared by other depanments as is often the case. Since integration is one of the principle aims of ClM, the concept shown in Figure 9 illusnates that the R&D facilities communicate with the manufacturing and assembly facilities.

Current Organization Figure 6 gives an overview of how EDM jobs are performed today. The tool design is performed either by the classical approach using drawing rulers and tables or through a Computer Aided Design (CAD) system. Considerable skill has already been introduced at this level, because it is often the EDM operator who performs this whole tool design cycle. The manufacturing of the EDM tool (electrode) is then accomplished using several production processes including milling, turning, drilling and grinding. Finally, the tool arrives at the EDM machine in its chuck holder, perhaps with the assistance of a flexible tooVworkpiece transportation system which, in turn, may have received its information from a Computer Assisted Rocess Planner (CAPP).

TOOL MANUFACTURINO

ANALYSIS

EDM MACHlNlNO

Figure 6: Product Flow During Work Preparation A CIM concept is shown in Figure 7 in which EDM machining centers are integrated on the shop floor with other machining centers. In this configuration, the EDM production machines are integrated into a Computer Aided Design / Computer Aided Manufacturing (CAD/CAM) system that already exists on the customer’s shop floor. The central CAD/CAM system essentially operates as a programming center. The EDM machines, as well as the NC milling, turning and drilling machines communicate with the cenwdl CAD/CAM system by means of a multi-user interface or Local Area Network.(LAh?.

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Figure 8: Example of Distinguishing Among CAD, CAPP and Production Figure 9 also depicts that the Computer Aided Process Planning unit (CAPP) is connected to the CAD/CAM system, as well as the CAE and CAA units. The CAPP element conmls the data flow as well as the transportation of the workpiece and tool to the proper machining stations; in this example, the turning. milling. grinding and EDM machines. In fact, the CAPP element can bc seen as the “plant manager”. assuring a reliable and flexible plant organization. A Computer Aided Tool Design (CATD) cell, which may well be part of the Computer Aided Engineering unit, may also have the capability for electrode-tool design. Funhermore, the connection path enables bi-diitional machine communication. Lastly, Figure 9 also shows an automatic warchousdstock (tooling center) which receives and sends tools to each machine in use. This task is accomplished by an appropriate mobile unit (AGV). Today. integration is being introduced into EDM machining centers by providing several machine options that assure that:

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programming of die sinking can be performed completely and automatically, tool and workpiece measurements can be made, * particular machining modes can be introduced with ease. and * tool and workpiece handling can bc incorporated. The Need for Stendardizetion

Figure 7: Integration of EDM Machining Centers and Others into a CAD-CAM

In the example of Figure 7. entities other than EDM machines arc also shown, such as a Programming Station (Personal Computer). Each machine is connected to the network by means of a serial interface. and program prepantion may be done on the CAD/CAM system or on the programming unit linked to the network. Personal and standard EDM data banks are available to complement the CIM system. Figure 8 shows that the EDM process can be easier understood if one distinguishes between the “Pan Geometry” (CAD), the “Process Technology” (CAPP) and the “Machining” (PRODUCTION). It is in the machining simulation sequence that the three entities of CAD, CAPP and PRODUCTION must be linked properly in order to guarantee complete job success.

Future Organlzatlon Improving machine integration without also improving machine autonomy does not make much sense and can not be commercially justified. Thus, EDM units, as well as other traditional machine tools, must be designed and equipped for a CIM environment.

A major objective for integrating a CAD/CAM system into a CIM environment is to enable the programming of numerically controlled (NC) machines. Cumnt CAD/CAM systems provide extensive capabilities for programming NC lathes and milling machines, but very few systems support the less common NC machines such as grinders, press brakes, punch presses, nibbling machines, laser cutters and EDM machines. A few systems offer some capabilities for programming wirccutting EDM machines. However, these systems only generate the geotncmcal NC program (i.e.. the wire cutter path). and do not generate the technological content for the NC program that would contain the proper machining parameters and generator settings. Examples of geometrical and technological NC programs are given in Figures 10 and 11. Recent breakthroughs in the area of die-sinking EDM, such as NC controlled planetary EDM or EDM contouring ( k . , vectorial tool movement) with noncylindrical electrodes, arc also not supported by commercial CAD/CAM systems. Additionally, CAD/CAM systems supporting wire-cutting EDM mostly offer dedicated solutions for programming only a specific type of EDM machine. A general solution. able to program a wide range of machines in a similar way as is done for NC lathes and milling machines. is more difficult to achieve because of the large inconsistencies in the way that various EDM machines arc programmed.

While a general overview of the ‘*Factoryof the Future” was presented in Figure I, Figure 9 illustrates a more specific layout of a possible shop-floor configuration. In Figure 1. the CAD (Computer Aided Design). CAM (Computer Aided Manufacturing), CAE (Computer Aided Engineering) and the CAA (Computer Aided Assembly) services were considercd to be part of the R&D

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GeometricalProgram RLD, EOI, S185, M8, F012, V3, P13. A6.. W7., L2., B.82, TOF. W1. -.I71 SFG.DEMO.IS0 Technological P r o w Rgun 1 0 NC Programs for a Charmilles Win-EDM Machine A major problem in the realization of such universal solutions is the lack of standardization. Standardization is nquired at different levels: EDM machine technology. NC cutter location file (SOAFT CL-file). Geometrical NC program (IS0 NC code), Technological NC program. These four items are major components of any CAD-based NC programming system for EDM each will now be considend in nun.

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In conventional machining, the relationship between machining parameters (cutting speed, feed, depth of cut) and machining results (material removal rate, roughness, workpiece deformation) is governed by “universal” rules: e.g.. Taylor’s tool life equation, empirical cutting force equations, analytical surface roughness quations, ctc. However, in EDM the relationship between machining parameters (e.g.. discharge current, discharge frequency. etc.) and machining results (e.g.. material removal rate. roughness, tool wear, etc.) differs from one machine to another. Even the parameters themselves are not the same for different machines. For example. some machines adjust a generator capacitance and the dielectric inlet pressure, while others control the pulse or discharge time and the dielectic flow. In order to overcomc those differences, each EDM machine is provided with a specific “technology”. This technology gives, for a particular machine, the controllable machining parameters and their influence on the machining results. The presentation of the technology also varies from machine to machine, and may be based on graphs, nomograms, formulae, tables or even software data bases.

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NC C u f f e r N - 6 6 2 1 5APT CL-fd@ As far as NC turning and milling are concerned. CAD/CAM systems are kept independent of any specific machine by using 1SD3592 CL-files as the NC output

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Figure 11: NC Rograms for an Agie Win-EDM Machine format. The CL-file consists of a sequence of records with each record containing a record number, a rccord type and subtype, and a set of data specific to the record type and subtype. Unfonunately, the ISO-3592 standard does not suppon EDM. One way to solve this problem is by defining additional subtypes of type 2000 records covering specific EDM functions [2]. A few examples of such type 2000 record definitions are given below: * Type 2000. subtype 1080: adjust taper angle in wire-cutting EDM. * Type 2000. subtype 1084: select set of predefined machining parameters

(e.g., discharge current and time). Type 2000. subtype 1096: generate special NC address words and values: e.g., generate “R40” NC code to define a reference plane on a wire-EDM machine. Other specific EDM functions, such as automatic wire insertion and cutting the wire electrode in wire-EDM. are confrolled by special auxiliary functions (Mfunctions) in the I S 0 coded KC program itself. This requires a CL-file rccord type 2000. subtype 1022 (i.e.. auxiliary function). ’

m 1150-6983/01N-66025 NC cade) Most NC controllers for conventional machine tools accept ISO-6983 NC coded programs and use the same code for identical functions; e.g.. GOO, GO1, GO2 and GO3 for the interpolation modes, M06 for a tool change, etc. The lack of standardization with respect to EDM has caused EDM machine builders to develop totally different solutions with respect to handling functions typical for EDM machining. For example, applying a taper angle of 5 degrees on a wire-cutting EDM machine is sometimes programmed within the geomeuical NC program by inserting “GO1 A5000”. On another machine, the same command has to be programmed within the technological NC program by including “PO1 5”. Several other examples are listed in Table 2.

EXAMPLESOF EDWCIMINTEGRATION Machine A

Command Taper angle e.g. 5 degrees taper

Type of tapered mrner: a) Conral b) Sharp edge

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Machine B

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Goometricalpmgram: GO1 ASoOOX..Y..

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Technological program: PO15

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Reference to settings-register defined in technologicalprogram Definition of registers with associated settings (see Fa. 101

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Definitiin01 settings (seeFio. 111

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Through geometricalprogram: M6&?467/M68/M69

I NC Proarm For turning and milling, the technological commands are stored in the geometrical NC program using the S-code for the spindle speed, the F-code for the feed rate. the M-codes for functions such as flushing, tool changes, etc. Most EDM machine builders chose to store the technological commands in a separate “tcchnologicd~NC propm.”This may be justified by: the machine dependency of the technological information since the machining patameten differ from machine to machine. the lack of a standard format for representing technological NC commands for EDM (compared to the S or F codes for turning and milling), the large number of machining parameters (10 or more) whose definition in the geometrical program may be inappropriate. However, some machine builders introduced an E-code in the geometrical NC program. This code allows for the calling of machining parameters defined within the technological NC program; see, for example, the EOl-code in Figures 10a and lob. Due 10their machine dependency and the lack of standardization. technological programs are totally different from one machine to another. compare, for example, Figure 10b and 1Ib. Therefon, formatting the technological program can not be done by defining a machine-independent NC format (comparable to the binary APT CL-file format) and using a general NC post-processor as often done for turning or milling machines. Unless further standardization is accomplished. specific formatting program will be required for each individual EDM machine.

The Universityof Wlsconsln-Approach Research at the University of Wisconsin-Madison (UW) has led to the demonstration of an F M S for the automated production of molds for the injection molding of plastic pans. The system was configured as a group of cells which performed CAD/CAM. EDM, milling, finishing. and coordinate measurement functions. It is the latest of a number of experimental manufacturing systems which have been conshucted for use in research in the design. implementation and evaluation of heterarchical manufacturing system control architectuns [ 18,211. CAD-directed inspection [201, and integration of new pmesses such as EDM and automated surface finishing into automated manufacturing [16.19]. The system is illustrated in Figure 12 and supported a complete manufacturing cycle from the conception and detail design of a high-volume plastic pan, through mold manufacture, and the injection molding of the finished product. The system performed the following functions: computer-aided design of the plastic part, mold and elccp.ode geometry; computer-aided manufacturing of both electrodes and molds; * CAD-dincted inspection of elccuode, mold and plastic part geometry; and corn uter aided modification of mold cavity geometry based on inspection

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In order to facilitate the automated operation of the EDM machine used in the FMS,several hardware additions and modifications were necessary to provide the following capabilities: EDM communication with a host computer. robotic loading and unloading of pans, automatic pan fixnuing. automatic draining of the work mk.and post-EDM washing of parts and pallets. The F M S was driven by parts entering the system, and each pan was responsible for scheduling the processing resources required for its production. Each pan was also responsible for scheduling the transporters to move it to the appropriate . EDM host computer, therefore, had to be capable of nprocessing R S O ~ S The ceiving inquiries from parts, sending appropriate responses to parts, and communicating with the EDM machine and other cntitia in the manufacturing system. In order to use the EDM in an unattended environment, a method of access to fixturing inside the tank needed to be developed for loading and unloading pans. Several schemes were considered for accomplishing this task. and the method shown in Figure 13 was chosen [I]. The existing work tank door remained permanently clovd and pallets were loaded over the top of the work tank. In this choice, the disadvantage of increased complexity in the robot‘s movement in reaching into the tank was balanced by the fact that no modifications were required to be made to the tank or its door. Leaving the door permanently closed also decreased the chance of an accidental dielectric spill. The close proximity of the robot to the EDM is an advantage in terms of compactness of the cell, and is also a disadvantage in tcnns of potential damage to the EDM in the case of a robot malfunction.

NECWOKK

MANUFACTURING SYSTEMS LABORATORY Universig of Wisconsin-Madison

AUTOMATED MOLD PRODUCTION SYSTEM

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LOCAL AREA NETWORK

Figure 1 2 Experimental F M S for Automated Mold Manufacturing

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Mold Production Examole As illustrated in Figure 12, the flexible manufacturing system consisted of four cells: an EDM cell, a machining center/finishing cell, a CMM cell and a CAD/CAM cell. Mold cavities could be rough machined on either the EDM or the machining center. Finish machining could be done on the EDM, by hand, or by using the surface grinding capabilities added to the machining center 1191. Both the mold cavity and the produced pans could be analyzed for dimensional and shape accuracy in the coordinate measuring cell. Major components of the system were: * a Charmilles SYSTRID CAD/CAM system, * a Charmilles ROBOFORM 200 EDM machine.

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n of CAD/CAMlntp The UW FMS

A CAD/CAM system was integrated as a design cell in the U W FMS [24]. and played a crucial role in geometry modeling, database management and NC code generation. A key to database management in the FMS was the establishment of a unified data format and a single database entity in which geometric information was stored and could be accessed by other entities in the integrated system. Automated interfaces and file translators then linked the various cells and machines to this database in the integrated system. Database integration was aided by adhering to the VDAFS geometry data transfer standard. Through the use of a standardized data exchange format such as VDAFS, the database entity could communicate with other entities in a single format. Then, after data was transferred, the data could be convened locally by a translator program in the entity if necessary. Standard translators are particularly useful when a wellestablished application is being interfaced to external databases. In this case it may not be desirable or possible to rewrite the application code, and using a translator allows database access without modifying the application. In the UW FMS. VDAFS translators were used in the CAD/CAM system to convert internally stored geomemc data prior to data transfer to the database entity and after data transfer from the database entity back to the CAD/CAM system. &&,mchical

FMS C o w Svsten

Thc flexible manufacturing system developed at the University of Wisconsin Madison is unique in that a fully distributed, heterarchical control architecture was used instead of the more common, hierarchical control architecture [42,43]. This was implemented using mierocomputm for cell control and a network for cell-tocell communications. Each cornputexin the network had a multi-tasking operating system that concurrently supported multiple Pascal programs. These programs were responsible for all aspects of system operation. Principles developed for the design of heterarchical manufacturing system controls were applied in decomposing and partitioning the system into a set of independent, communicating entities [21]. These entities included: mold entities, machine entities (Mill, Wash, Inspection, EDM,CMM), mawrial handling entities (Robot, Pallet Mover). a CAD/CAM entity, * a gwmetric database entity, and input and output station entities. These entities were. disaibuted over five microcomputers on a local m a network. The interconnections between entities were established in the homogeneous fashion illustrated in Figure 14.

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The CAD/CAM system supported the mold cavity design. Once the shape of the cavity to be produced had been defined, a geometric database was created for the desired surface and transferred to a central geomeuic database for use in electrode and mold machining. NC files for the production of the electrodes could be downloaded to the milling machine and, once the required elecuodes were made, they were delivered to the EDM tool carousel. At this point. the instructions for producing the mold cavity could be downloaded to the EDM machine. After the mold cavity had been completed. it could be taken to the CMM and inspected using a program generated from the central geometric database. Results of this inspection could be compared against the geometric data and errors could be evaluated. These errors could then be brought back to the CAD system and used to generate additional NC files for modification of the mold cavity geometry. Similarly, injection-molded parts produced from the mold cavity could be inspected. and the inspection results could be compared against the geometric database and the errors brought back to the CAD/CAM system and displayed as shown in Figure 15. The mold cavity could then be modified to improve the shape accuracy of these parts.

Figure 15: Dimensional Error Analysis and Display on CAD/CAM System

Local Area Network

u Figure 14: Entities in the University of Wisconsin-Madison FMS

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a Cincinnati Milicron 5VC-CNC milling machine, a DEA PJM-0101 coordinate measuring machine, an automated surface finishing system (IJWdeveloped), two General Electric material handling robots, a high-speed overhead-track transportation system (UW developed), and the k t m h i c a l control system described abbe.

The Catholic Unkrersity of Leuven Approach Figure 16 shows the structure of the EDM/CIM concept established at the Catholic University of Leuven (K.U. Leuven). It was conceived to support EDM as well as conventional machining. I h e EDM/CIM system consists of: a standard (commercial) two or three. dimensional CAD/CAM system, with CAM modules for turning.milling and other operations. a system-independent interactive CAD programming interface [ 131, * a CAM module for wincutting EDM, a CAM module for die-sinking EDM, a CAPP module for process planning of turning, milling and EDM operations. a general 5-axes NC post-processor for turning, milling. wire-EDM and diesinking EDM machines, with associated machine data file [Zl.and an EDM technological data base. The neutral CAD programming interface allows the CAM modules for EDM and the CAPP application software to be integrated transparently into the basic CAD/CAM system while remaining totally independent of any specific CAD/CAM system. This allows the CAM and CAPP modules to use the internal data base of the CAD/CAM systems, as well as the graphical and alphanumeric user interfaces and many internal routines of the basic CAD/CAM system. Integration of the CAM and CAPP software into a different CAD/CAM system only requires this relative simple interface to be available or developed on the receiving system. The technology data file contains the technological information on the available EDM machines in a machine-independent format. No prerequisites are. defined in the data base with respect to the type and the number of machining parameters or

output parameters (results), nor with respect to which machining parameter influenceswhich output parameter. Machining parameters, output parameters and their relationships are defined within the technology data file. Upon initiation, the CAPP or CAM software will first identify the actual parameters before accessing tables containing quantitative data specifying the existing inputloutput relationships. Individual EDM machine technology data, whether it is provided in tables, nomograms, formulae or graphs, must be converted into the data file format. This lack of a standardized representation for EDM machine technologies is a major bottleneck to their integration into CIM environments. The following paragraphs desnibe the basic modules of the K.U. Leuven EDWCIM system. r’------‘-----------‘-------I I I

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routines also calculate the electrode wear as a function of the distance travelled and introduce appropriate tool changes or tool indexing for polygon shaped electrodes whenever the wear limit is reached. CAPP for FOM and Other Qoerabons

This module, which is still under development, is especially directed to mold making. It is a process planning system based on form features such as cylindrical and rectangular holes. 2D, 2.5D and 3D pockets, sculptured surfaces, etc. The software is intended to select the most appropriate or inexpensive operation sequence: planning, drilling. boring. rough milling, fine milling, EDM diesinking, planetary EDM die-sinking, EDM contouring, EDM pocketing. wirecutting EDM, etc. A cost calculation module for injection molds has been developed to complement the CAPP system. General Interactive 5-Axes NC Post-Processorand

The general post-processor for 2- to 5-axes NC turning, milling and EDM machines is described in [2]. This paper also describes the machine data file which contains a description of all available NC machines.

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Figure 16: ‘Ihe EDWCIM System of the K.U.Leuven . .m CAM Software for Wire-FOM A This module enables the generation of the technological and geometrical NC programs for 2- to 5-axes wire-cutting EDM machines. Duplication of CAM routines has been avoided by making use of the CAM routines available for milling, it., a basic 2- to 5-axes milling toolpath is generated first. The resulting “milling CL-fie” is then processed by the wire-EDM module. Records specific to milling are eliminated (e.g.. type 2000 records for the control of spindle speed or fced rate), while information specific to wire-EDM is added. Some information is added automatically, while other information can be inserted on an interactive basis. Information added automatically relates to the machining parameters (discharge current, discharge time, etc.) and wire offset (discharge gapwidth). The values to be assigned to those parameters are calculated by consulting the EDM machine technology stored in the technology data file. A process planning routine determines how many cutting passes are required (i.e.. the roughing and finishing cuts) and whether the parameter values are to be changed in the vicinity of sharp comers or fillets in order to improve the cutting accuracy. The NC programmer may at any time use the CAD/CAM user interface (e.g., a cursor, joy-stick, icons or menu) in order to command wire thrcading or wire cut-off, change of the w k inclination or w’m offset, the insertion of “glue stops’’ (i.e.. optional stops for fixing the workpiece core thereby avoiding the dropping of the core at the end of the cutting of the whole contour), etc. The technological NC program is written directly in the required format by a formatting routine dedicated to the specific EDM machine. The geometrical NC program is stored in an EDM &fie (1.50-3592 CL-file) for funher processing by the general NC post-processsor. ’Ihis EDM CL-file contains special type 2000 records, defined exclusively for wire-EDM applications as previously described in the section on standardization.

CAM S a l w r e for DI‘,+sin-

lieations

Early applications of die-sinking EDM required specially designed and often complex electrodes for each particular job. The introduction of EDM machining centers with tool changers and point-tepoint NC control allowed the production of complex cavities with a set of simple electrodes. The recent introduction of 2- to 4-axes simultaneouscontour control further enhanced the EDM process making it possible to apply non-circular planetary movements around several axes (X.Y,Z). Very recently, “EDM contouring” was introduced, a technique in which inexpensive standard cylindrical or square electrodes are guided through the workpiece in order to generate complex cavities. The die-sinking CAM module, developed at the K.U.Leuven, uses the same principles as the wirecutting EDM module shown in Figure 16. Standard CAM milling modules may be used to generate toolpaths for cylindrical EDM electrodes. However, special CAM modules have also been developed for EDM contouring with non-cylindrical elecuodes (square. rectangular or triangular). Here too, a CAPP module is used in conjunction with the EDM technology file in order to calculate the required number of finishing steps, the correct settings for the machining parameters (e.g., discharge current and time) and the corresponding gap size. The settings ~ J C continuously adapted to the size of the active electmde surface (sparking surface), which is calculated by the CAM module. The same

An injection mold was produced within the KUL-CIM environment [ 141. NC milling was applied in order to produce the free-form graphite and copper electrodes for EDM die-sinking. The outer geomeay of the plastic part (in this case an aerodynamic cover for the back window wiper of an automobile) was introduced i n the CAD system and used as the basic input in the design and manufacture all of the elements needed for molding the part. Successively, the following geometries were derived, taking into account the appropriate corrections listed between brackets: outer mold shape (injection molding shrinkage compensation): 1 shape. inner mold shape (wall thickness of product and shrinkage): 2 shapes, mold cavity and mold c m plates (moldsplitting line): 2 shapcs, roughin and finishing electrodes for both the mold cavity and core (spark gapwidti and eccentricity of planetarj movement): 4 shapes, rough and fine milling shapes for each electrcde (rough milling overcut): 8 shapes, NC milling tFlpaths f o r m h and fine milling (tool radius compensation of ball-end milling cutter): 24 F$C programs.

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The ESPRIT Project #2590: Integrated Design System (IPDES) [3] ESPRIT (European Strategic Program for Research and Development in Information Technology) is a pre-competitive, industry-oriented, collaborative research and development program in information technology. The program is managed and co-funded by the European Community, and is organized in close liaison with industry. national adminisuations and the research community. It has the following focused goals: To provide the European information technology indushy with new basic technologies tomeet the competitive quirements of the 1990s. To promote European industrial cooperation in information technology, and To pave the way to standards. The ESPRIT Project #2590, named the Integrated Product Design System (IPDES), was started on November I , 1989 and is supported by a 12 million dollars (US)budget. Part of this funding is provided by the EEC (6.8 million); the remaining is to be provided by the industrial parmen. The IPDES program will run for four years. with ten full partners and three associate partners involved. The IPDES program has the following main objectives: Research on generic tools and methodologies, Research on the product level including the developing of a product modeler. Research on the part modeler, and Development of the part modeler. Three types of pan modelers are being analyzed a sheet metal pan modeler, a rotational part modeler, and a three dimensional part modeler. The three dimensional part modeler covers die-sinking EDM, wk-EDM. planetary EDM and three dimensional CAD/CAM systems as working tools.

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The Gerrnen Resewch Project: Workshop Wemted Programming 14) This research program, sponsored by the German Government, has the following goals: To simplify complete data input (not only geometry) at the shop floor level, To come to identical work preparation conditions either in the work-planning office or on the shop floor, and To work out a man/machine operating interface enabling full flexibility at the program level, including machine and process parameter selection and modification, geometrical data control. and the adaptation of job related setting conditions. Today EDM units can run fully automatically, assuring process autonomy and thmfore. fit perfectly into this CIM philosophy.

CONCLUSIONS The integration of Electrical Discharge Machining into Computer Integrated h4anufacturing systems demonstrates that unattended operation of the EDM process is a viable alternative to conventional machining pmesses in automated manufacturing. In the future, as the need for alternatives in the unattended processing of difficult to machine materials increases. EDM machines operating in CIM environments can be expected to provide that capability. The problems of integrating EDM into a CIM environment were shown to be considerably more difficult than that of the more common NC operations of turning, drilling and milling. The primary impediment is that OF a lack of standardization although progress is being made in this area.

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Several ongoing research projects were described and their characteristics were briefly discussed. It was also noted that several large projects an being iniriared with governmental support which should further enhance the integration of EDM into CIM environments.

ACKNOWLEDGMENTS The authors gratefully acknowledge communications and contributions received from: Professor T. Matsuo, Kumamoto University. Japan; Professor G. Spur. IPK, Berlin, W. G C ~ M YIr.; C.A. vanluttervelt. TU Delft. Netherlands; Professor B. Ravani. University of California-Davis, USA; and Ms. S. Moehring. Metcut Research Associates. Cincinnati, Ohio, USA.

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