小型臥式數(shù)控銑床的結構設計及應用含NX三維及14張CAD圖帶開題,小型,臥式,數(shù)控,銑床,結構設計,應用,利用,運用,nx,三維,14,cad,開題 Manufact discharge ,S. Wolfson gh, accepted WEDMutilisesacontinuouslytravellingwireelectrode (HSTR)materialsandeliminatethegeometrical chan- Thedevelopmen atechni inEDM. author. Tel.: l-line folls.t.newmanlboro.ac.u C3 Corresponding 227648. E-mailaddress: 0890-6955/$-seefrontmatter doi:10.1016/j.ijmachtools.2004.04.017 cesswastheresultofseeking machinedelectrodeused bohn applied the optica +44-1509-227660; fax: +44-1509- k(S.T.Newman). #2004ElsevierLtd.Allrightsreserved. the manufacturing tofthepro- quetoreplacethe In1974,D.H.Dule- ower systemto capableofachievingverysmall WEDM was rst introd industryinthelate1960s. made of thin copper, brass or tungsten of diameter 0.050.3mm,whichis gesoccurringinthemachiningofheat-treatedsteels. uced to 1. Introduction Wire electrical discharge machining (WEDM) is a widely accepted non-traditional material removal pro- cess used to manufacture components with intricate shapesandproles.Itisconsideredasauniqueadap- tationoftheconventionalEDMprocess,whichusesan electrode to initialise the sparking process. However, cornerradii.Thewireiskeptintensionusingamech- anical tensioning device reducing the tendency of pro- ducing inaccurate parts. During the WEDM process, thematerialiserodedaheadofthewireandthereisno direct contact between the workpiece and the wire, eliminating the mechanical stresses during machining. In addition, the WEDM process is able to machine exotic and high strength and temperature resistive Abstract Wireelectricaldischargemachining(WEDM)isaspecialisedthermalmachiningprocesscapableofaccuratelymachiningparts with varying hardness or complex shapes, which have sharp edges that are very dicult to be machined by the main stream machiningprocesses.ThispracticaltechnologyoftheWEDMprocessisbasedontheconventionalEDMsparkingphenomenon utilising the widely accepted non-contact technique of material removal. Since the introduction of the process, WEDM has evolved from a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degreeofdimensionalaccuracyandsurfacenishquality. Overtheyears,theWEDMprocesshasremainedasacompetitiveandeconomicalmachiningoptionfulllingthedemanding machiningrequirementsimposedbytheshortproductdevelopmentcyclesandthegrowingcostpressures.However,theriskof wirebreakageandbendinghasunderminedthefullpotentialoftheprocessdrasticallyreducingtheeciencyandaccuracyofthe WEDMoperation.AsignicantamountofresearchhasexploredthedierentmethodologiesofachievingtheultimateWEDM goalsofoptimisingthenumerousprocessparametersanalyticallywiththetotaleliminationofthewirebreakagestherebyalso improvingtheoverallmachiningreliability. Thispaperreviewsthevastarrayofresearchworkcarriedoutfromthespin-ofromtheEDMprocesstothedevelopmentof theWEDM.ItreportsontheWEDMresearchinvolvingtheoptimisationoftheprocessparameterssurveyingtheinuenceof thevariousfactorsaectingthemachiningperformanceandproductivity.Thepaperalsohighlightstheadaptivemonitoringand controloftheprocessinvestigatingthefeasibilityofthedierentcontrolstrategiesofobtainingtheoptimalmachiningconditions. AwiderangeofWEDMindustrialapplicationsarereportedtogetherwiththedevelopmentofthehybridmachiningprocesses. ThenalpartofthepaperdiscussesthesedevelopmentsandoutlinesthepossibletrendsforfutureWEDMresearch. #2004ElsevierLtd.Allrightsreserved. Keywords: Wireelectricaldischargemachining(WEDM);Hybridmachiningprocess;Processoptimisation;Cuttingrate;Matenalremovalrate; Surfacenish InternationalJournalofMachineTools ure44(2004)12471259 machining(WEDM) Rahimifard,R.D.Allen SchoolofMechanicalandManufacturingEngineering, LeicestershireLE113TU,UK 29April2004 duction and highlights some of its applications. The researchdirection. whichvariesfrom0.025to0.05mm 2.WEDMelim- 1248 K.H.Hoetal./InternationalJournalofMachineTools&Manufacture44(2004)12471259 2. WEDM This section provides the basic principle of the WEDMprocessandthevariationsoftheprocesscom- biningothermaterialremovaltechniques. 2.1. WEDMprocess ThematerialremovalmechanismofWEDMisvery similartotheconventionalEDMprocessinvolvingthe erosion eect produced by the electrical discharges (sparks).InWEDM,materialiserodedfromthework- piece by a series of discrete sparks occurring between the workpiece and the wire separated by a streamof dielectric uid, which is continuously fed to the machiningzone4.However,todaysWEDMprocess iscommonlyconductedonworkpiecesthataretotally submergedinatanklledwithdielectricuid.Sucha submerged method of WEDM promotes temperature stabilisation and ecient ushing especially in cases where the workpiece has varying thickness. The WEDMprocessmakesuseofelectricalenergygenerat- ing a channel of plasma between the cathode and anode5,andturnsitintothermalenergy6atatem- peratureintherangeof800012,000 v C7orashigh as 20,000 v C 8 initialising a substantial amount of heatingandmeltingofmaterialonthesurfaceofeach main section of the paper focuses on the major WEDM research activities, which include the WEDM processoptimisationtogetherwiththeWEDMprocess monitoringandcontrol.Thenalpartofthepaperdis- cusses these topics and suggests the future WEDM automaticallycontroltheshapeofthecomponenttobe machined by the WEDM process 1. By 1975, its popularity was rapidly increasing, as the process and its capabilities were better understood by the industry 2. It was only towards the end of the 1970s, when computer numerical control (CNC) system was initi- ated into WEDM that brought about a major evol- utionofthemachiningprocess.Asaresult,thebroad capabilities of the WEDM process were extensively exploitedforanythrough-holemachiningowingtothe wire, which has to pass through the part to be machined. The common applications of WEDM include the fabrication of the stamping and extrusion toolsanddies,xturesandgauges,prototypes,aircraft andmedicalparts,andgrindingwheelformtools. Thispaperprovidesareviewonthevariousacadem- icresearchareasinvolvingtheWEDMprocess,andis thesisterpapertoareviewbyHoandNewman3on die-sinkingEDM.Itrstpresentstheprocessoverview basedonthewidelyacceptedprincipleofthermalcon- inates the need for elaborate pre-shaped electrodes, whicharecommonlyrequiredinEDMtoperformthe roughing and nishing operations. In the case of WEDM,thewirehastomakeseveralmachiningpasses alongtheproletobemachinedtoattaintherequired dimensional accuracy and surface nish (SF) quality. KuniedaandFurudate10testedthefeasibilityofcon- ductingdryWEDMtoimprovetheaccuracyofthen- ishing operations, which was conducted in a gas atmosphere without using dielectric uid. The typical WEDM cutting rates (CRs) are 300 mm 2 /min for a 50 mm thick D2 tool steel and 750 mm 2 /min for a 150mmthickaluminium11,andSFqualityisasne as 0.040.25 lRa. In addition, WEDM uses deionised waterinsteadofhydrocarbonoilasthedielectricuid andcontainsitwithinthesparkingzone.Thedeionised waterisnotsuitableforconventionalEDMasitcauses rapid electrode wear, but its low viscosity and rapid coolingratemakeitidealforWEDM12. 2.2. Hybridmachiningprocesses There are a number of hybrid machining processes (HMPs) seeking the combined advantage of WEDM with other machining techniques. One such combi- nation is wire electrical discharge grinding (WEDG), which is commonly used for the micro-machining of ne rods utilized in the electronic circuitry. WEDG employsasinglewireguidetoconnethewiretension withinthedischargeareabetweentherodandthefront edge of the wire and to minimise the wire vibration. Therefore,itispossibletogrindarodthatisassmall as 5 lmin diameter 13 with high accuracy, good repeatability and satisfactory straightness 14. Other advantagesofWEDGincludetheabilitytomachinea rod with alarge aspect ratio, maintainingthe concen- tricityoftherodandprovidingawiderchoiceofcom- plex shapes such as tapered and stepped shapes at pole. When the pulsating direct current power supply occurring between 20,000 and 30,000 Hz 9 is turned o, the plasma channel breaks down. This causes a suddenreductioninthetemperatureallowingthecircu- lating dielectric uid to implore the plasma channel andushthemoltenparticlesfromthepolesurfacesin theformofmicroscopicdebris. While the material removal mechanisms of EDM andWEDMaresimilar,theirfunctionalcharacteristics arenotidentical.WEDMusesathinwirecontinuously feeding through the workpiece by a microprocessor, which enableparts of complex shapes tobemachined with exceptional high accuracy. A varying degree of taperrangingfrom15 v fora100mmthickto30 v fora 400 mm thick workpiece can also be obtained on the cut surface. The microprocessor also constantly main- tains the gap between the wire and the workpiece, tries 21,22. The eects of the various process para- 3. WEDM applications tatethesparkingofhighlyelectrical-resistiveceramics. K.H.Hoetal./InternationalJournalofMachineTools&Manufacture44(2004)12471259 1249 This section discusses the viability of the WEDM processinthemachiningofthevariousmaterialsused particularlyintoolingapplications. 3.1. Moderntoolingapplications WEDM has been gaining wide acceptance in the machining of the various materials used in modern toolingapplications.Severalauthors24,25haveinves- tigated the machining performance of WEDM in the wafering of silicon and machining of compacting dies madeofsinteredcarbide.Thefeasibilityofusingcylin- dricalWEDMfordressingarotatingmetalbonddia- mond wheel used for the precision form grinding of ceramics has also been studied 22. The results show that the WEDM process is capable of generating pre- ciseandintricateproleswithsmallcornerradiibuta highwearrateisobservedonthediamondwheeldur- ing the rst grinding pass. Such an initial high wheel wear rate is due to the over-protruding diamond grains, whichdo not bond strongly to the wheel after the WEDM process 26. The WEDM of permanent NdFeB and soft MnZn ferrite magnetic materials used in miniature systems, which requires small mag- netic parts, was studied by comparing it with the laser-cutting process 27. It was found that the meterssuchaspartrotationalspeed,wirefeedrateand pulseon-timeonthesurfaceintegrityandroundnessof the part produced have been investigated in the same feasibilitystudy23. various sections 15. Several authors 1619 have employed the WEDG process in the micro-machining of ne electrodes or pins with a large aspect-ratio, which are dicult to be machined by traditional pre- cision micro-machining methods such as Micro-EDM, LIGAandexcimerlaserdrilling. SomeoftheHMPsseektoimprovetheWEDMper- formance measures such as the surface integrity and the CR. For example, the ultrasonic vibration is appliedtothewireelectrodetoimprovetheSFquality togetherwiththeCRandtoreducetheresidualstress on the machined surface 20. On the other hand, the wireelectrochemicalgrinding(WECG)processreplaces theelectricaldischargeusedinWEDGwithanelectro- chemicalsolutiontoproducehighSFqualitypartfora wide range of machining condition 15. Masuzawa et al. 13,15 compared the SF quality obtained from theWECGwithWEDG,whichissuitablefornishing micro-parts.ArotaryaxisisalsoaddedtoWEDMto achieve higher material removal rate (MRR) and to enable the generation of free-formcylindrical geome- Both the EDM and WEDM processes have been suc- cessfully tested diusing conductive particles from assistingelectrodesontothesurfaceofsialonceramics assisting thefeedingthe electrode through the insulat- ingmaterial.Thesametechniquehasalsobeenexperi- mented on other types of insulating ceramic materials including oxide ceramics such as ZrO 2 and Al 2 O 3 , which have very limiting electrical conductive proper- ties37. WEDMprocessyieldsbetterdimensionalaccuracyand SFqualitybuthasaslowCR,5.5mm/minforNdFeB and0.17mm/minforMnZnferrite.Astudywasalso done to investigate the machining performance of micro-WEDM used to machine a high aspect ratio meso-scale part using a variety of metals including stainless steel, nitronic austentic stainless, beryllium copperandtitanium28. 3.2. Advancedceramicmaterials TheWEDM process hasalso evolved asoneof the most promising alternatives for the machining of the advanced ceramics. Sanchez et al. 29 provided a literature survey on the EDM of advanced ceramics, which have been commonly machined by diamond grinding andlapping. In the same paper, they studied the feasibility of machining boron carbide (B 4 C) and silicon inltrated silicon carbide (SiSiC) using EDM andWEDM.Chengetal.30alsoevaluatedthepossi- bility of machining ZrB 2 based materials using EDM andWEDM,whereasMatsuo andOshima31 exam- ined the eects of conductive carbide content, namely niobiumcarbide(NbC)andtitaniumcarbide(TiC),on the CR and surface roughness of zirconia ceramics (ZrO 2 )duringWEDM.LokandLee32havesuccess- fully WEDMed sialon 501 and aluminium oxide titaniumcarbide (Al 2 O 3 TiC). However, they realised thattheMRRisverylow ascomparedtothecutting of metals such as alloy steel SKD-11 and the surface roughnessisgenerallyinferiortotheoneobtainedwith the EDMprocess. Dauw et al. 33 explainedthat the MRR and surface roughness are not only dependent onthemachiningparameters butalsoonthematerial ofthepart. Aninnovativemethodofovercomingthetechnologi- cal limitation of the EDM and WEDM processes requiring the electrical resistivity of the material with threshold values of approximately 100 X/cm 34 or 300 X/cm 35 has recently been explored. There are dierent grades of engineering ceramics, which Konig et al. 34 classied as non-conductor, natural-conduc- tor and conductor, which is a result of doping non- conductorswithconductiveelements.Mohrietal.36 brought a new perspective to the traditional EDM phenomenon by using an assisting electrode to facili- formancemeasures.Itwasfoundthattheprocesspara- meters have little inuence on the surface roughness 1250 K.H.Hoetal./InternationalJournalofMachineTools&Manufacture44(2004)12471259 buthaveanadverseeectonCR. 4. Major areas of WEDM research The authors have organised the various WEDM researchintotwomajorareasnamelyWEDMprocess optimisationtogetherwithWEDMprocessmonitoring andcontrol. 4.1. WEDMprocessoptimisation Today, the most eective machining strategy is determinedbyidentifyingthedierentfactorsaecting the WEDM process and seeking the dierent ways of obtaining the optimal machining condition and per- formance.Thissectionprovidesastudyonthenumer- ous machining strategies involving the design of the processparameterandthemodellingoftheprocess. 4.1.1. Processparametersdesign The settings for the various process parameters required in the WEDM process play a crucial role in producing an optimal machining performance. This section shows some of the analytical and statistical methodsusedtostudytheeectsoftheparameterson thetypicalWEDMperformancemeasuressuchasCR, MRRandSF. processes performed on the MMC and experimented with the machining of Al 2 O 3 /6061Al composite using rotaryEDM coupled with adisk-like electrode. Other studies42,43havebeenconductedontheWEDMof Al 2 O 3 particulate reinforced composites investigating theeectoftheprocessparametersontheWEDMper- reinforced liquid crystal polymer composites. These studiesshowedthatWEDM yieldsbettercuttingedge quality and has better control of the process para- meters with fewer workpiece surface damages. How- ever,ithasaslowerMRRforallthetestedcomposite materials. Gadalla and Tsai 40 compared WEDM withconventionaldiamondsawinganddiscoveredthat itproducesaroughnessandhardnessthatiscompara- ble to a low speed diamond saw but with a higher MRR. Yan et al. 41 surveyed the various machining 3.3. Moderncompositematerials Among the dierent material removal processes, WEDM is considered as an eective and economical tool in the machining of modern composite materials. Several comparative studies 38,39 have been made betweenWEDMandlasercuttingintheprocessingof metal matrix composites (MMC), carbon bre and 4.1.1.1. Factors aecting the performance measures. WEDMisacomplexmachiningprocesscontrolledby alargenumberofprocessparameterssuchasthepulse duration, discharge frequency and discharge current intensity. Any slight variations in the process para- meterscanaectthemachiningperformancemeasures such as surface roughness and CR, which are two of the most signicant aspects of the WEDM operation 44.SuzikiandKishi45studiedthereductionofdis- chargeenergytoyieldabettersurfaceroughness,while Luo 46 discovered the additional need for a high- energy eciency to maintain a high machining rate without damaging the wire. Several authors 47 have alsostudiedtheevolutionofthewiretoolperformance aecting the machining accuracy, costs and perform- ancemeasures. The selection of appropriate machining conditions fortheWEDMprocessisbasedontheanalysisrelat- ing the various process parameters to dierent per- formance measures namely the CR, MRR and SF. Traditionally,thiswascarriedoutbyrelyingheavilyon theoperatorsexperienceorconservativetechnological data provided by the WEDM equipment manu- facturers, which produced inconsistent machining per- formance.LevyandMaggi48demonstratedthatthe parametersettingsgivenbythemanufacturersareonly applicable for the common steel grades. The settings for machining new materials such as advanced cer- amicsandMMCshavetobefurtheroptimisedexper- imentally. 4.1.1.2. Eects of the process parameters on the cutting rate. Many dierent types of problem-solving quality tools havebeen used to investigate the signicant fac- torsanditsinter-relationshipswiththeothervariables inobtaininganoptimalWEDMCR.Kondaetal.49 classied the various potential factors aecting the WEDM performance measures into ve major cate- goriesnamelythedierentpropertiesoftheworkpiece material and dielectric uid, machine characteristics, adjustable machining parameters, and component geometry. In addition, they applied the design of experiments (DOE) technique to study and optimise the possible eects of variables during process design and development, and validated the experimental resultsusingnoise-to-signal(S/N)ratioanalysis.Tarng etal. 50 employed aneural network system with the application of a simulated annealing algorithm for solving the multi-response optimisation problem. It was found that the machining parameters such as the pulse on/o duration, peak current, open circuit volt- age,servoreferencevoltage,electricalcapacitance and table speed are the critical parameters for the esti- mation of the CR and SF. Huang et al. 51 argued that several published works 50,52,53 are concerned mostly with the optimisation of parameters for the K.H.Hoetal./InternationalJournalofMachineTools&Manufacture44(2004)12471259 1251 roughing cutting operations and proposed a practical strategyofprocessplanningfromroughingtonishing operations. The experimental results showed that the pulse on-time and the distance between the wire per- ipheryandtheworkpiecesurfaceaecttheCRandSF signicantly.Theeectsofthedischargeenergyonthe CRandSFofaMMChavealsobeeninvestigated54. 4.1.1.3. Eects of the machining parameters on the material removal rate. The eects of the machining parameters on the volumetric MRR have also been consideredasameasureofthemachiningperformance. Scottetal.52usedafactorialdesignrequiringanum- ber of experiments to determine the most favourable combination of the WEDM parameter. They found thatthedischargecurrent,pulsedurationandpulsefre- quency are the signicant control factors aecting the MRR and SF, while the wire speed, wire tension and dielectricowratehavetheleasteect.Liaoetal.53 proposed an approach of determining the parameter settings based on the Taguchi quality design method and the analysis of variance. The results showed that theMRRandSFareeasilyinuencedbythetablefeed rateandpulseon-time,whichcanalsobeusedtocon- trol the discharging frequency for the prevention of wirebreakage.HuangandLiao55presentedtheuse of Grey relational and S/N ratio analyses, which also display similar results demonstrating the inuence of tablefeedandpulseon-timeontheMRR.Anexperi- mentalstudytodeterminetheMRRandSFforvary- ingmachiningparametershasalsobeenconducted56. The results have been used with a