1. Izici ze-EDM zezinto ze-graphite.
1.1. Isivinini somshini wokukhipha ishaja.
I-Graphite iyinto engeyona eyensimbi enephuzu lokuncibilika eliphakeme kakhulu elingu-3,650 ° C, kuyilapho ithusi linephuzu lokuncibilika elingu-1,083 ° C, ngakho-ke i-electrode ye-graphite ingamelana nezimo zokusetha zamanje ezinkulu.
Uma indawo yokukhipha kanye nobukhulu be-electrode kukhulu, izinzuzo zomshini wokugaya osebenza kahle kakhulu wezinto ze-graphite zisobala kakhulu.
Ukushisa kwe-graphite kungu-1/3 kokushisa kwethusi, futhi ukushisa okukhiqizwa ngesikhathi senqubo yokukhipha kungasetshenziswa ukususa izinto zensimbi ngempumelelo enkulu. Ngakho-ke, ukusebenza kahle kokucubungula kwe-graphite kuphakeme kunokwe-electrode yethusi ekucutshungulweni okuphakathi nokuncane.
Ngokwesipiliyoni sokucubungula, isivinini sokucubungula ukukhishwa kwe-graphite electrode sishesha ngokuphindwe ka-1.5 ~ 2 kunese-copper electrode ngaphansi kwezimo ezifanele zokusetshenziswa.
1.2. Ukusetshenziswa kwe-electrode.
I-electrode ye-graphite inobuntu obungamelana nezimo zamanje eziphezulu, ngaphezu kwalokho, ngaphansi kwesimo sokusetha okufanele kwe-roughing, kufaka phakathi izingcezu zomsebenzi zensimbi yekhabhoni ezikhiqizwa ngesikhathi sokususwa komshini wokugaya okuqukethwe kanye noketshezi olusebenzayo ekuqhekekeni kwezinhlayiya zekhabhoni ekushiseni okuphezulu, umphumela we-polarity, ngaphansi kwesenzo sokususwa okuyingxenye kokuqukethwe, izinhlayiya zekhabhoni zizonamathela ebusweni be-electrode ukuze zakhe ungqimba oluvikelayo, ziqinisekise ukuthi i-electrode ye-graphite ilahlekelwa kancane ekusetshenzisweni kokugaya okungafanele, noma ngisho "nemfucuza engekho".
Ukulahleka kwe-electrode okuyinhloko ku-EDM kuvela ekusetshenzisweni kwemishini okungahleliwe. Nakuba izinga lokulahlekelwa liphezulu ezimweni zokuhlela zokuqedwa, ukulahlekelwa okuphelele nakho kuphansi ngenxa yesibonelelo esincane sokusetshenziswa kwemishini esigcinelwe izingxenye.
Ngokuvamile, ukulahleka kwe-electrode ye-graphite kuncane kunokwe-electrode yethusi ekucubunguleni okuqinile komshini omkhulu wamandla futhi kukhulu kancane kunokwe-electrode yethusi ekuqedeni ukucubungulwa. Ukulahleka kwe-electrode ye-electrode ye-graphite kuyafana.
1.3. Ikhwalithi yobuso.
Ububanzi bezinhlayiya zezinto ze-graphite buthinta ngqo ubulukhuni bomphezulu we-EDM. Uma ububanzi bubuncane, ubulukhuni bomphezulu bungatholakala buphansi.
Eminyakeni embalwa edlule kusetshenziswa izinto ze-graphite ezingama-particle phi 5 microns ububanzi, ubuso obuhle kakhulu bungafinyelela kuphela i-VDI18 edm (Ra0.8 microns), kulezi zinsuku ububanzi bezinhlamvu zezinto ze-graphite bukwazile ukufeza ngaphakathi kwama-microns amathathu e-phi, ubuso obuhle kakhulu bungafinyelela i-VDI12 edm ezinzile (Ra0.4 mu m) noma izinga eliyinkimbinkimbi kakhulu, kodwa i-electrode ye-graphite ikwazi ukulingisa i-edm.
Izinto zethusi azinamandla okumelana nesakhiwo esincane, futhi zingacutshungulwa kahle ngaphansi kwezimo ezinzima. Ubulukhuni bomphezulu bungaba ngaphansi kuka-Ra0.1 m, futhi bungacutshungulwa ngesibuko.
Ngakho-ke, uma umshini wokukhipha ulandela indawo encane kakhulu, kufaneleka kakhulu ukusebenzisa izinto zethusi njenge-electrode, okuyinzuzo enkulu ye-electrode yethusi kune-electrode ye-graphite.
Kodwa i-electrode yethusi ngaphansi kwesimo sokusethwa kwamanje okukhulu, ubuso be-electrode kulula ukuba bube buqinile, buvele buqhekeke ngisho, futhi izinto ze-graphite bezingeke zibe nale nkinga, imfuneko yobulukhuni bobuso be-VDI26 (Ra2.0 microns) mayelana nokucubungula isikhunta, ukusebenzisa i-electrode ye-graphite kungenziwa kusukela ekucubungulweni okuqinile kuya kokuncane, kuqaphela umphumela wobuso obufanayo, amaphutha obuso.
Ngaphezu kwalokho, ngenxa yesakhiwo esihlukile se-graphite nethusi, iphuzu lokugqwala kokukhishwa kobuso be-graphite electrode livame kakhulu kunele-electrode yethusi. Ngakho-ke, lapho ukugoba okufanayo kobuso be-VDI20 noma ngaphezulu kucutshungulwa, ubulukhuni bobuso bento yokusebenza ecutshungulwa yi-graphite electrode buhluke kakhulu, futhi lo mphumela wobuso bezinhlamvu ungcono kunomphumela wokukhishwa kobuso be-electrode yethusi.
1.4. Ukunemba komshini.
I-coefficient yokwanda kokushisa kwezinto ze-graphite incane, i-coefficient yokwanda kokushisa kwezinto zethusi iphindwe kane kunezinto ze-graphite, ngakho-ke ekucubungulweni kokukhishwa, i-graphite electrode ayithambekele kakhulu ekuguqukeni kune-electrode yethusi, engathola ukunemba kokucubungula okuzinzile nokuthembekile.
Ikakhulukazi uma ubambo olujulile noluncane lucutshungulwa, izinga lokushisa eliphezulu lendawo lenza i-electrode yethusi igobe kalula, kodwa i-electrode ye-graphite ayigobi.
Ku-electrode yethusi enesilinganiso esikhulu sobubanzi bokujula, inani elithile lokunwetshwa kokushisa kufanele linxeshezelwe ukuze kulungiswe usayizi ngesikhathi sokusetha imishini, kuyilapho i-electrode ye-graphite ingadingeki.
1.5. Isisindo se-electrode.
Izinto ze-graphite aziqinile kakhulu kunethusi, futhi isisindo se-electrode ye-graphite enomthamo ofanayo siyi-1/5 kuphela ye-electrode yethusi.
Kungabonakala ukuthi ukusetshenziswa kwe-graphite kufaneleka kakhulu kwi-electrode enomthamo omkhulu, okunciphisa kakhulu umthwalo we-spindle yethuluzi lomshini we-EDM. I-electrode ngeke ibangele ukuphazamiseka ekubambeni ngenxa yesisindo sayo esikhulu, futhi izokhiqiza ukuphambuka ekucutshungulweni, njll. Kungabonakala ukuthi kubaluleke kakhulu ukusebenzisa i-graphite electrode ekucutshungulweni kwesikhunta esikhulu.
1.6. Ubunzima bokukhiqiza ama-electrode.
Ukusebenza kahle kwemishini yezinto ze-graphite kuhle. Ukumelana nokusika kungama-1/4 kuphela kunokwethusi. Ngaphansi kwezimo ezifanele zokucubungula, ukusebenza kahle kwe-electrode ye-graphite yokugaya kuphindwe ka-2-3 kunokwe-electrode yethusi.
I-electrode ye-graphite kulula ukuyisula i-Angle, futhi ingasetshenziswa ukucubungula umsebenzi okufanele uqedwe ngama-electrode amaningi ube yi-electrode eyodwa.
Isakhiwo sezinhlayiya eziyingqayizivele zezinto ze-graphite sivimbela ama-burrs ukuthi angenzeki ngemva kokugaya nokwakheka kwe-electrode, okungahlangabezana ngqo nezidingo zokusetshenziswa lapho ama-burrs engasuswa kalula ekubumbeni okuyinkimbinkimbi, ngaleyo ndlela kuqedwe inqubo yokupholisha ngesandla i-electrode futhi kugwenywe ushintsho lwesimo kanye nephutha losayizi elibangelwa ukupholisha.
Kufanele kuqashelwe ukuthi, ngenxa yokuthi i-graphite iwukuqongelela uthuli, i-graphite yokugaya izokhiqiza uthuli oluningi, ngakho-ke umshini wokugaya kumele ube nedivayisi yokuvala nokuqoqa uthuli.
Uma kudingeka ukusebenzisa i-edM ukucubungula i-electrode ye-graphite, ukusebenza kwayo kokucubungula akukuhle njengezinto zethusi, isivinini sokusika sihamba kancane cishe ngo-40% kunethusi.
1.7. Ukufakwa nokusetshenziswa kwe-electrode.
Izinto ze-graphite zinomumo omuhle wokubopha. Zingasetshenziswa ukubopha i-graphite nesixhumi ngokugaya i-electrode bese zikhipha, okungonga inqubo yokugaya imbobo yesikulufu ezintweni ze-electrode futhi konge isikhathi sokusebenza.
Izinto ze-graphite ziyaphuka kancane, ikakhulukazi i-electrode encane, encane futhi ende, okulula ukuyiphula uma isetshenziswa ngaphandle, kodwa ingazi ngokushesha ukuthi i-electrode yonakele.
Uma kuyi-electrode yethusi, izogoba kuphela futhi ingaphuki, okuyingozi kakhulu futhi okunzima ukuyithola enkambisweni yokusebenzisa, futhi izoholela kalula ekulimaleni kwento yokusebenza.
1.8. Intengo.
Izinto zethusi ziwumthombo ongavuseleleki, ukuthambekela kwentengo kuzobiza kakhulu, kuyilapho intengo yezinto ze-graphite ivame ukuzinza.
Intengo yezinto zethusi ikhuphuka eminyakeni yamuva nje, abakhiqizi abakhulu be-graphite abathuthukisa inqubo ekukhiqizweni kwe-graphite benza inzuzo yayo yokuncintisana, manje, ngaphansi komthamo ofanayo, ukujwayelekile kwentengo yezinto ze-graphite electrode kanye nentengo yezinto ze-electrode zethusi kukhulu impela, kodwa i-graphite ingafinyelela ukucubungula okuphumelelayo, kunokusebenzisa i-electrode yethusi ukonga inani elikhulu lamahora okusebenza, okulingana nokunciphisa izindleko zokukhiqiza ngqo.
Ngamafuphi, phakathi kwezici ezingu-8 ze-edM ze-graphite electrode, izinzuzo zayo zisobala: ukusebenza kahle kwe-electrode yokugaya kanye nokucubungula ukukhishwa kungcono kakhulu kunokwe-electrode yethusi; i-electrode enkulu inesisindo esincane, ukuzinza okuhle kobukhulu, i-electrode encane akulula ukuyishintsha, futhi ukuthungwa kwendawo kungcono kune-electrode yethusi.
Ububi bezinto ze-graphite ukuthi azifaneleki ukucutshungulwa kokukhishwa kobuso obuhle ngaphansi kwe-VDI12 (Ra0.4 m), futhi ukusebenza kahle kokusebenzisa i-edM ukwenza i-electrode kuphansi.
Kodwa-ke, ngokombono ongokoqobo, esinye sezizathu ezibalulekile ezithinta ukukhuthazwa okuphumelelayo kwezinto ze-graphite eShayina ukuthi kudingeka umshini wokucubungula i-graphite okhethekile kuma-electrode okugaya, okubeka phambili izidingo ezintsha zemishini yokucubungula yamabhizinisi okubumba, amanye amabhizinisi amancane angase angabi nalesi simo.
Ngokuvamile, izinzuzo zama-electrode e-graphite zihlanganisa iningi lezikhathi zokucubungula i-edM, futhi zifanele ukuthandwa nokusetshenziswa, ngezinzuzo ezinkulu zesikhathi eside. Ukuntuleka kokucubungula ubuso obuhle kungenziwa ngokusebenzisa ama-electrode ethusi.
2. Ukukhethwa kwezinto ze-graphite electrode ze-EDM
Ngezinto ze-graphite, kunezinkomba ezine ezilandelayo ezinquma ngqo ukusebenza kwezinto:
1) Ububanzi obumaphakathi bezinhlayiya zezinto
Ububanzi obumaphakathi bezinhlayiya zezinto buthinta ngqo isimo sokukhishwa kwezinto.
Uma inhlayiya evamile yezinto ze-graphite incane, lapho ukukhishwa kwayo kufana kakhulu, isimo sokukhishwa kwayo sizinzile, ikhwalithi yobuso iba ngcono, futhi ukulahlekelwa kwayo kuyancipha.
Uma ubukhulu bezinhlayiya ezimaphakathi bukhulu, izinga lokususa elingcono lingatholakala ekushiseni okungekuhle, kodwa umphumela womphezulu wokuqeda mubi futhi ukulahleka kwe-electrode kukhulu.
2) Amandla okugoba kwezinto
Amandla okugobeka kwezinto ezibonakalayo abonisa ngqo amandla azo, okubonisa ukuqina kwesakhiwo sangaphakathi sazo.
Izinto eziqinile kakhulu zisebenza kahle kakhulu ekumelaneni nokukhishwa. Ku-electrode enokunemba okuphezulu, izinto eziqinile kufanele zikhethwe ngangokunokwenzeka.
3) Ukuqina kogu lolwandle lwezinto
I-Graphite ilukhuni kunezinto zensimbi, futhi ukulahleka kwethuluzi lokusika kukhulu kunokwensimbi yokusika.
Ngesikhathi esifanayo, ubulukhuni obukhulu bezinto ze-graphite ekulawuleni ukulahlekelwa kokukhishwa bungcono.
4) Ukumelana okungokwemvelo kwezinto
Izinga lokukhishwa kwezinto ze-graphite ezinokumelana okuphezulu okungokwemvelo lizohamba kancane kunalelo elinokumelana okuphansi.
Uma ukumelana okungokwemvelo kuphakeme, ukulahlekelwa kwe-electrode kuncane, kodwa uma ukumelana okungokwemvelo kuphakeme, ukuzinza kokukhishwa kuzothinteka.
Njengamanje, kunezinhlobo eziningi ezahlukene ze-graphite ezitholakala kubaphakeli be-graphite abaphambili emhlabeni.
Ngokuvamile ngokwesilinganiso sobubanzi bezinhlayiya zezinto ze-graphite ezizohlukaniswa, ububanzi bezinhlayiya ≤ 4 m buchazwa njenge-graphite encane, izinhlayiya eziku-5 ~ 10 m zichazwa njenge-graphite ephakathi, izinhlayiya eziku-10 m ngaphezulu zichazwa njenge-graphite eqinile.
Uma ububanzi bezinhlayiya buncane, lapho izinto zibiza kakhulu, izinto ze-graphite ezifaneleka kakhulu zingakhethwa ngokuya ngezidingo kanye nezindleko ze-EDM.
3.Ukwenziwa kwe-electrode ye-graphite
I-electrode ye-graphite yenziwa kakhulu ngokugaya.
Ngokombono wobuchwepheshe bokucubungula, i-graphite nethusi kuyizinto ezimbili ezihlukene, futhi izici zazo zokusika ezahlukene kufanele zifundwe kahle.
Uma i-electrode ye-graphite icutshungulwa yinqubo ye-electrode yethusi, izinkinga zizovela ngokungenakugwenywa, njengokuqhekeka njalo kweshidi, okudinga ukusetshenziswa kwamathuluzi okusika afanele kanye nemingcele yokusika.
Umshini wokugaya i-graphite electrode kunokugqoka kwamathuluzi e-copper electrode, uma kucatshangelwa ezomnotho, ukukhetha ithuluzi le-carbide kuyonga kakhulu, ithuluzi lokukhetha idayimane (elibizwa ngokuthi ummese we-graphite) libiza kakhulu, kodwa ithuluzi lokugqoka idayimane impilo ende, ukunemba okuphezulu kokucubungula, inzuzo yezomnotho iyonke inhle.
Usayizi we-Engela engaphambili yethuluzi uthinta nokuphila kwalo kwesevisi, i-Engela engaphambili engu-0° yethuluzi izoba phezulu ngo-50% kune-Engela engaphambili engu-15° yempilo yesevisi yethuluzi, ukuzinza kokusika nakho kungcono, kodwa uma i-Engela inkulu, indawo yomshini iba ngcono, ukusetshenziswa kwe-Engela engu-15° yethuluzi kungafeza indawo yomshini engcono kakhulu.
Ijubane lokusika ekushiseni lingalungiswa ngokuya ngesimo se-electrode, ngokuvamile i-10m/min, kufana nomshini we-aluminium noma wepulasitiki, ithuluzi lokusika lingafakwa ngqo futhi liphume endaweni yokusebenza ekushiseni okuqinile, futhi isimo sokuwa kwe-Angle kanye nokuqhekeka kulula ukwenzeka ekushiseni okuqediwe, futhi indlela yokuhamba ngokushesha ngommese olula ivame ukusetshenziswa.
I-electrode ye-graphite enqubweni yokusika izokhiqiza uthuli oluningi, ukuze kugwenywe izinhlayiya ze-graphite eziphefumulayo ngomshini wokuphotha kanye nezikulufo, kunezixazululo ezimbili eziyinhloko njengamanje, esinye ukusebenzisa umshini wokucubungula i-graphite okhethekile, esinye isikhungo sokucubungula esijwayelekile, esifakwe idivayisi ekhethekile yokuqoqa uthuli.
Umshini wokugaya okhethekile we-graphite onesivinini esikhulu emakethe usebenza kahle kakhulu ekugayweni futhi ungaqedela kalula ukukhiqizwa kwama-electrode ayinkimbinkimbi ngokunemba okuphezulu kanye nekhwalithi enhle yobuso.
Uma i-EDM idingeka ukwenza i-electrode ye-graphite, kutuswa ukusebenzisa izinto ezincane ze-graphite ezinobubanzi obuncane bezinhlayiya.
Ukusebenza kahle kwe-graphite ekushiseni akubi, uma ububanzi bezinhlayiya buncane, kulapho ukusebenza kahle kokusika kungatholakala khona, futhi izinkinga ezingavamile njengokuqhekeka kwentambo njalo kanye nomphetho womphezulu zingagwenywa.
Amapharamitha e-EDM e-graphite electrode
Ukukhethwa kwamapharamitha e-EDM e-graphite nethusi kuhluke kakhulu.
Amapharamitha e-EDM afaka kakhulu amandla kagesi, ububanzi be-pulse, igebe le-pulse kanye ne-polarity.
Okulandelayo kuchaza isisekelo sokusetshenziswa okunengqondo kwalezi zinhlaka ezinkulu.
Ubuningi bamanje be-graphite electrode ngokuvamile buyi-10~12 A/cm2, bukhulu kakhulu kunobe-copper electrode. Ngakho-ke, ngaphakathi kobubanzi bamanje obuvunyelwe endaweni ehambisanayo, uma ugesi ukhethwa mkhulu, isivinini sokucubungula ukukhishwa kwe-graphite sizoba sishesha, ukulahleka kwe-electrode kuzoba kuncane, kodwa ubulukhuni bomphezulu buzoba bukhulu.
Uma ububanzi be-pulse bukhulu, ukulahlekelwa kwe-electrode kuzoba kuncane.
Kodwa-ke, ububanzi obukhulu be-pulse buzokwenza ukuzinza kokucubungula kube kubi kakhulu, futhi ijubane lokucubungula lihambe kancane kanye nendawo ebanzi.
Ukuze kuqinisekiswe ukulahleka okuphansi kwe-electrode ngesikhathi sokucubungula okungahleliwe, ngokuvamile kusetshenziswa ububanzi obukhulu be-pulse, obungenza ngempumelelo ukucubungula okuphansi kwe-graphite electrode uma inani liphakathi kuka-100 no-300 US.
Ukuze uthole indawo encane kanye nomphumela wokukhipha ozinzile, kufanele kukhethwe ububanzi obuncane bokushaya kwenhliziyo.
Ngokuvamile, ububanzi be-pulse ye-graphite electrode bungaphansi ngo-40% kunobe-electrode yethusi
Igebe lokushaya kwenhliziyo lithinta kakhulu isivinini sokukhishwa kwemishini kanye nokuqina kwemishini. Uma inani likhulu, kulapho ukuzinza kwemishini kuzoba ngcono, okuwusizo ekutholeni ukufana okungcono kwendawo, kodwa ijubane lomshini lizoncishiswa.
Ngaphansi kwesimo sokuqinisekisa ukuzinza kokucubungula, ukusebenza kahle kokucubungula okuphezulu kungatholakala ngokukhetha igebe elincane lokushaya kwenhliziyo, kodwa lapho isimo sokukhishwa singazinzile, ukusebenza kahle kokucubungula okuphezulu kungatholakala ngokukhetha igebe elikhulu lokushaya kwenhliziyo.
Ekucubunguleni kokukhipha i-graphite electrode, igebe le-pulse kanye nobubanzi be-pulse ngokuvamile kubekwe ku-1:1, kuyilapho ekucubunguleni i-copper electrode, igebe le-pulse kanye nobubanzi be-pulse ngokuvamile kubekwe ku-1:3.
Ngaphansi kokucutshungulwa kwe-graphite okuzinzile, isilinganiso sokufanisa phakathi kwegebe lokushaya kwenhliziyo kanye nobubanzi bokushaya kwenhliziyo singalungiswa sibe ngu-2:3.
Uma i-pulse clearance encane, kuyazuzisa ukwakha ungqimba olumboza ubuso be-electrode, okuwusizo ekunciphiseni ukulahleka kwe-electrode.
Ukukhethwa kwe-polarity ye-graphite electrode ku-EDM ngokuyisisekelo kufana nokwe-electrode yethusi.
Ngokusho komphumela we-polarity we-EDM, i-positive polarity machining ivame ukusetshenziswa lapho kucutshungulwa insimbi edayiwe, okungukuthi, i-electrode ixhunywe epalini elihle lokunikezwa kwamandla, futhi umsebenzi uxhunywe epalini elibi lokunikezwa kwamandla.
Ukusebenzisa ububanzi obukhulu bamanje kanye nobubanzi be-pulse, ukukhetha imishini ye-polarity enhle kungaletha ukulahlekelwa kwe-electrode okuphansi kakhulu. Uma i-polarity ingalungile, ukulahlekelwa kwe-electrode kuzoba kukhulu kakhulu.
Kuphela uma indawo engaphansi komhlaba idingeka ukuthi icutshungulwe kahle ngaphansi kwe-VDI18 (Ra0.8 m) futhi ububanzi be-pulse buncane kakhulu, ukucubungula i-polarity engemihle kusetshenziswa ukuthola ikhwalithi engcono yendawo, kodwa ukulahleka kwe-electrode kukhulu.
Manje amathuluzi omshini we-CNC edM afakwe amapharamitha omshini wokukhipha i-graphite.
Ukusetshenziswa kwamapharamitha kagesi kuhlakaniphile futhi kungadalwa ngokuzenzakalelayo uhlelo lochwepheshe lwethuluzi lomshini.
Ngokuvamile, umshini ungalungiselela amapharamitha okucubungula alungiselelwe ngokukhetha i-pair yezinto ezibonakalayo, uhlobo lohlelo lokusebenza, inani lobulukhuni bendawo nokufaka indawo yokucubungula, ukujula kokucubungula, ukukala usayizi we-electrode, njll. Ngesikhathi sokuhlela.
Isethi ye-electrode ye-graphite yomtapo wolwazi we-edm machine tool inezici zokucubungula ezicebile, uhlobo lwezinto ezibonakalayo lungakhetha ku-graphite ecolekile, i-graphite, i-graphite ihambisana nezinto ezahlukahlukene zomsebenzi, ukuze kwahlukaniswe uhlobo lwesicelo se-groove ejwayelekile, ejulile, iphuzu elibukhali, indawo enkulu, umgodi omkhulu, njenge-fine, futhi inikeza ukulahlekelwa okuphansi, okujwayelekile, ukusebenza kahle okuphezulu nokunye okuningi.
5. Isiphetho
Izinto ezintsha ze-graphite electrode zifanele ukuthandwa kakhulu futhi izinzuzo zazo zizoqashelwa kancane kancane futhi zamukelwe embonini yokukhiqiza isikhunta yasekhaya.
Ukukhethwa okufanele kwezinto ze-graphite electrode kanye nokuthuthukiswa kwezixhumanisi zobuchwepheshe ezihlobene kuzoletha ukusebenza kahle okuphezulu, ikhwalithi ephezulu kanye nezinzuzo eziphansi emabhizinisini okukhiqiza isikhunta.
Isikhathi sokuthunyelwe: Disemba-04-2020