1. Makhalidwe a EDM a zipangizo za graphite.
1.1. Liwiro la makina otulutsa mphamvu.
Graphite ndi chinthu chosakhala chachitsulo chomwe chimasungunuka kwambiri ndi 3,650 ° C, pomwe mkuwa uli ndi 1,083 ° C, kotero electrode ya graphite imatha kupirira mikhalidwe yabwino kwambiri yamagetsi.
Pamene malo otulutsira ndi kukula kwa ma electrode kuli kwakukulu, ubwino wa makina opangidwa ndi graphite ndi woonekera bwino.
Mphamvu ya kutentha ya graphite ndi 1/3 ya mkuwa, ndipo kutentha komwe kumapangidwa panthawi yotulutsa madzi kungagwiritsidwe ntchito kuchotsa zitsulo bwino kwambiri. Chifukwa chake, mphamvu ya graphite yokonza ndi yayikulu kuposa ya electrode yamkuwa pokonza zinthu zapakatikati ndi zazing'ono.
Malinga ndi zomwe zachitika pokonza, liwiro lokonza ma electrode a graphite ndi lofulumira nthawi 1.5 ~ 2 kuposa la electrode yamkuwa pansi pa mikhalidwe yoyenera yogwiritsira ntchito.
1.2. Kugwiritsa ntchito ma elekitirodi.
Ma electrode a graphite ali ndi mawonekedwe omwe amatha kupirira mikhalidwe yamagetsi yapamwamba, kuphatikiza apo, pansi pa malo oyenera okonzera, kuphatikiza zida zogwirira ntchito zachitsulo cha kaboni zomwe zimapangidwa panthawi yochotsa zinthu zomwe zili mkati ndi madzi ogwirira ntchito pa kutentha kwakukulu kwa tinthu ta kaboni, zotsatira za polarity, pansi pa kuchotsedwa pang'ono kwa zinthu zomwe zili mkati, tinthu ta kaboni tidzamamatira pamwamba pa electrode kuti tipange wosanjikiza woteteza, ndikuwonetsetsa kuti electrode ya graphite ikutayika pang'ono mu makina ovuta, kapena ngakhale "zinyalala zero".
Kutayika kwakukulu kwa ma electrode mu EDM kumachokera ku makina opangidwa mopanda dongosolo. Ngakhale kuti kutayika kwa ma electrode kumakhala kwakukulu pakukonzekera, kutayika konsekonse kumakhala kochepa chifukwa cha ndalama zochepa zogwiritsira ntchito makina zomwe zimasungidwa pazigawo zina.
Kawirikawiri, kutayika kwa electrode ya graphite kumakhala kochepa kuposa kwa electrode yamkuwa mu makina osakanikirana amagetsi akuluakulu komanso kochulukirapo pang'ono kuposa kwa electrode yamkuwa mumakina omalizidwa. Kutayika kwa electrode ya graphite electrode ndi kofanana.
1.3. Ubwino wa pamwamba.
Kukula kwa tinthu tating'onoting'ono ta graphite kumakhudza mwachindunji kuuma kwa pamwamba pa EDM. Kukula kwa pamwamba kukakhala kochepa, kuuma kwa pamwamba kumakhala kochepa.
Zaka zingapo zapitazo pogwiritsa ntchito tinthu tating'onoting'ono ta graphite ta 5 microns m'mimba mwake, pamwamba pabwino kwambiri pamatha kufika pa VDI18 edm (Ra0.8 microns), masiku ano m'mimba mwake wa zinthu za graphite wakwanitsa kufika mkati mwa ma microns atatu a phi, pamwamba pake pamatha kufika pa VDI12 edm yokhazikika (Ra0.4 mu m) kapena mulingo wapamwamba kwambiri, koma graphite electrode imayimira edm.
Zinthu zamkuwa zili ndi mphamvu yochepa komanso kapangidwe kakang'ono, ndipo zimatha kukonzedwa bwino pansi pa zovuta. Kukhwima kwa pamwamba kumatha kukhala kochepera Ra0.1 m, ndipo kumatha kukonzedwa ndi galasi.
Choncho, ngati makina otulutsira zinthu akutsatira malo abwino kwambiri, ndibwino kugwiritsa ntchito zinthu zamkuwa ngati ma electrode, zomwe ndi ubwino waukulu wa ma electrode amkuwa kuposa ma electrode a graphite.
Koma ma electrode amkuwa pansi pa malo akuluakulu amagetsi, pamwamba pa ma electrode ndi osavuta kukhala okhwima, amawoneka ngati ming'alu, ndipo zipangizo za graphite sizingakhale ndi vutoli, kufunika kwa kukhwima kwa pamwamba pa VDI26 (Ra2.0 microns) pa kukonza nkhungu, pogwiritsa ntchito electrode ya graphite kungachitike kuyambira pa kukonza kosalala mpaka kosalala, kuzindikira zotsatira zofanana pamwamba, zolakwika pamwamba.
Kuphatikiza apo, chifukwa cha kapangidwe kosiyana ka graphite ndi mkuwa, mfundo yotupa ya graphite electrode pamwamba imakhala yofanana kwambiri ndi ya electrode yamkuwa. Chifukwa chake, pamene kuuma komweko kwa VDI20 kapena kupitirira apo kukukonzedwa, kuchuluka kwa pamwamba pa workpiece yokonzedwa ndi graphite electrode kumakhala kosiyana kwambiri, ndipo zotsatira za pamwamba pa tiriguzi zimakhala bwino kuposa zotsatira za electrode yamkuwa.
1.4. Kulondola kwa makina.
Kuchuluka kwa kutentha kwa zinthu za graphite ndi kochepa, kuchuluka kwa kutentha kwa zinthu zamkuwa kumakhala kowirikiza kanayi kuposa kwa zinthu za graphite, kotero pokonza zotulutsa, graphite electrode siisintha kwambiri kuposa electrode yamkuwa, yomwe ingapeze kulondola kokhazikika komanso kodalirika pakukonza.
Makamaka pamene nthiti zakuya komanso zopapatiza zikukonzedwa, kutentha kwakukulu kwapafupi kumapangitsa kuti electrode yamkuwa ipinde mosavuta, koma electrode ya graphite siitero.
Pa ma electrode amkuwa okhala ndi chiŵerengero chachikulu cha kuya-m'mimba mwake, mtengo winawake wokulitsa kutentha uyenera kulipidwa kuti ukonze kukula kwake panthawi yokonza makina, pomwe ma electrode a graphite safunika.
1.5. Kulemera kwa ma elekitirodi.
Zipangizo za graphite n’zochepa kwambiri kuposa mkuwa, ndipo kulemera kwa electrode ya graphite ya voliyumu yomweyo ndi 1/5 yokha ya kulemera kwa electrode yamkuwa.
Zikuoneka kuti kugwiritsa ntchito graphite ndikoyenera kwambiri pa electrode yokhala ndi voliyumu yayikulu, zomwe zimachepetsa kwambiri katundu wa spindle ya chida cha makina cha EDM. Electrode sidzayambitsa zovuta pakumangirira chifukwa cha kulemera kwake kwakukulu, ndipo ipanga kusuntha kwa deflection pokonza, ndi zina zotero. Zikuoneka kuti ndikofunikira kwambiri kugwiritsa ntchito graphite electrode pokonza nkhungu yayikulu.
1.6. Kuvuta kwa kupanga ma elekitirodi.
Kagwiridwe ka ntchito ka graphite ndi kabwino. Kukana kudula ndi 1/4 yokha ya mkuwa. Pansi pa mikhalidwe yoyenera yokonza, mphamvu ya graphite electrode yopera ndi kuwirikiza kawiri mpaka katatu kuposa ya electrode yamkuwa.
Ma electrode a graphite ndi osavuta kuchotsa, ndipo angagwiritsidwe ntchito pokonza workpiece yomwe iyenera kumalizidwa ndi ma electrode angapo kukhala electrode imodzi.
Kapangidwe ka tinthu tating'onoting'ono ta graphite kamaletsa ma burrs kuchitika pambuyo pogaya ndi kupanga ma electrode, zomwe zimatha kukwaniritsa zofunikira zogwiritsidwa ntchito pamene ma burrs sachotsedwa mosavuta mu chitsanzo chovuta, motero zimachotsa njira yopukutira ma electrode ndi manja ndikupewa kusintha kwa mawonekedwe ndi kukula komwe kumachitika chifukwa cha kupukutira.
Tiyenera kudziwa kuti, chifukwa graphite ndi fumbi lochuluka, graphite yophwanyira imapanga fumbi lambiri, choncho makina ophwanyira ayenera kukhala ndi chipangizo chosindikizira ndi chosonkhanitsira fumbi.
Ngati pakufunika kugwiritsa ntchito edM pokonza ma electrode a graphite, ntchito yake yokonza siili bwino ngati zinthu zamkuwa, liwiro lodulira limachepa ndi pafupifupi 40% kuposa mkuwa.
1.7. Kukhazikitsa ndi kugwiritsa ntchito ma elekitirodi.
Zinthu za graphite zili ndi mphamvu yabwino yolumikizirana. Zingagwiritsidwe ntchito kulumikiza graphite ndi chogwirira mwa kugaya electrode ndikutulutsa, zomwe zingapulumutse njira yopangira dzenje la screw pa zinthu za electrode ndikusunga nthawi yogwira ntchito.
Zipangizo za graphite zimakhala zofooka pang'ono, makamaka electrode yaying'ono, yopapatiza komanso yayitali, yomwe ndi yosavuta kusweka ikagwiritsidwa ntchito ndi mphamvu zakunja, koma imatha kudziwa nthawi yomweyo kuti electrodeyo yawonongeka.
Ngati ndi electrode yamkuwa, imapindika yokha osasweka, zomwe ndi zoopsa kwambiri komanso zovuta kuzipeza mukugwiritsa ntchito, ndipo zingayambitse mosavuta zidutswa za workpiece.
1.8. Mtengo.
Zinthu zamkuwa sizingabwezeretsedwe, mitengo idzakhala yokwera mtengo kwambiri, pomwe mtengo wa zinthu za graphite umakhala wokhazikika.
Mtengo wa zinthu zamkuwa ukukwera m'zaka zaposachedwa, opanga akuluakulu a graphite omwe akukonza njira yopangira graphite akupeza mwayi wopikisana, tsopano, pansi pa voliyumu yomweyo, mtengo wa zinthu za graphite electrode ndi mtengo wa zinthu za electrode zamkuwa ndi wokwanira, koma graphite imatha kukwaniritsa ntchito yabwino, kuposa kugwiritsa ntchito electrode yamkuwa kuti isunge maola ambiri ogwirira ntchito, zomwe zimafanana ndi kuchepetsa mtengo wopangira mwachindunji.
Mwachidule, pakati pa makhalidwe 8 a electrode ya graphite, ubwino wake ndi woonekeratu: kugwira ntchito bwino kwa electrode yopera ndi kukonza zotulutsa ndikwabwino kwambiri kuposa kwa electrode yamkuwa; electrode yayikulu ili ndi kulemera kochepa, kukhazikika kwabwino, electrode yopyapyala sikophweka kuisintha, ndipo kapangidwe ka pamwamba ndi kabwino kuposa electrode yamkuwa.
Kuipa kwa zinthu za graphite ndikuti sizoyenera kutsukidwa bwino pamwamba pa VDI12 (Ra0.4 m), ndipo kugwiritsa ntchito edM popanga ma electrode ndikochepa.
Komabe, malinga ndi mfundo yeniyeni, chimodzi mwa zifukwa zofunika kwambiri zomwe zimakhudza kukwezedwa bwino kwa zipangizo za graphite ku China ndichakuti makina apadera opangira graphite amafunika ma electrode opera, zomwe zimapangitsa kuti pakhale zofunikira zatsopano zogwiritsira ntchito zida zogwirira ntchito zamakampani opanga nkhungu, mabizinesi ena ang'onoang'ono sangakhale ndi vutoli.
Kawirikawiri, ubwino wa ma electrode a graphite umakhudza nthawi zambiri zogwirira ntchito za edM, ndipo ndi woyenera kutchuka ndikugwiritsidwa ntchito, ndipo ubwino wake ndi wautali. Kusowa kwa kukonza bwino pamwamba kungapangidwe pogwiritsa ntchito ma electrode amkuwa.
2. Kusankha zipangizo za graphite electrode za EDM
Pa zinthu za graphite, pali zizindikiro zinayi zotsatirazi zomwe zimatsimikizira mwachindunji momwe zinthuzo zimagwirira ntchito:
1) Avereji ya tinthu tating'onoting'ono ta zinthuzo
Kukula kwa tinthu tating'onoting'ono ta zinthuzo kumakhudza mwachindunji momwe zinthuzo zimatulutsidwira.
Tinthu tating'onoting'ono ta graphite tikakhala tating'onoting'ono, kutulutsa madzi kumakhala kofanana, ndipo kutuluka madzi kumakhala kokhazikika, ndipo pamwamba pake pamakhala bwino, ndipo kutayika kwake kumakhala kochepa.
Tinthu tating'onoting'ono tikakhala tambiri, timakhala ndi mwayi wabwino wochotsa zinthu pogwiritsa ntchito makina osakaniza, koma mphamvu ya pamwamba pa ntchito yomaliza ndi yotsika ndipo kutayika kwa ma elekitirodi kumakhala kwakukulu.
2) Mphamvu yopindika ya zinthuzo
Mphamvu yopindika ya chinthu imasonyeza mphamvu yake mwachindunji, zomwe zimasonyeza kulimba kwa kapangidwe kake ka mkati.
Zipangizo zomwe zili ndi mphamvu zambiri zimakhala ndi mphamvu yotsutsa kutulutsa madzi. Kwa elekitirodi yolondola kwambiri, zipangizo zomwe zili ndi mphamvu zabwino ziyenera kusankhidwa momwe zingathere.
3) Kulimba kwa gombe la zinthuzo
Graphite ndi yolimba kuposa zipangizo zachitsulo, ndipo kutayika kwa chida chodulirako kumakhala kwakukulu kuposa kutayika kwa chitsulo chodulirako.
Nthawi yomweyo, kuuma kwakukulu kwa zinthu za graphite mu ulamuliro wotaya zinthu zotayira kuli bwino.
4) Kukana kwachilengedwe kwa zinthuzo
Kuchuluka kwa kutulutsa kwa zinthu za graphite zokhala ndi resistivity yayikulu kudzakhala pang'onopang'ono kuposa komwe kumakhala ndi resistivity yochepa.
Kuchuluka kwa mphamvu yamagetsi yoteteza magetsi ikakwera, kutayika kwa ma elekitirodi kumakhala kochepa, koma kukwera kwa mphamvu yamagetsi yoteteza magetsi ikakwera, kukhazikika kwa mphamvu yamagetsi kumakhudzidwa.
Pakadali pano, pali mitundu yosiyanasiyana ya graphite yomwe imapezeka kuchokera kwa ogulitsa otsogola padziko lonse lapansi.
Kawirikawiri malinga ndi kukula kwa tinthu tating'onoting'ono ta zinthu za graphite zomwe ziyenera kugawidwa m'magulu, tinthu tating'onoting'ono ta ≤ 4 m timatanthauzidwa ngati graphite yabwino, tinthu tating'onoting'ono ta 5 ~ 10 m timatanthauzidwa ngati graphite yapakatikati, tinthu tating'onoting'ono ta 10 m pamwamba timatanthauzidwa ngati graphite yopyapyala.
Kaya tinthu tating'onoting'ono timakhala tating'onoting'ono, tinthu tating'onoting'ono timakhala tokwera mtengo kwambiri, ndiye kuti tinthu tating'onoting'ono toyenera kwambiri tingasankhidwe malinga ndi zofunikira komanso mtengo wa EDM.
3. Kupanga ma electrode a graphite
Ma electrode a graphite amapangidwa makamaka ndi mphero.
Malinga ndi ukadaulo wopangira zinthu, graphite ndi mkuwa ndi zinthu ziwiri zosiyana, ndipo makhalidwe awo osiyana odulira ayenera kudziwika bwino.
Ngati electrode ya graphite ikonzedwa pogwiritsa ntchito njira ya electrode yamkuwa, mavuto adzabuka mosalephera, monga kusweka kwa pepala pafupipafupi, komwe kumafuna kugwiritsa ntchito zida zoyenera zodulira ndi magawo odulira.
Kudula ma electrode a graphite kuposa kuvala kwa zida za electrode zamkuwa, poganizira zachuma, kusankha chida cha carbide ndikotsika mtengo kwambiri, kusankha chida chophikira diamondi (chotchedwa mpeni wa graphite) mtengo wake ndi wokwera mtengo, koma chida chophikira diamondi chimakhala ndi moyo wautali, kulondola kwambiri pakukonza, komanso phindu lonse lazachuma ndilabwino.
Kukula kwa ngodya yakutsogolo kwa chida kumakhudzanso nthawi yake yogwirira ntchito, ngodya yakutsogolo ya 0° ya chida idzakhala yokwera ndi 50% kuposa ngodya yakutsogolo ya 15° ya nthawi yogwirira ntchito ya chida, kukhazikika kwa kudula nakonso kuli bwino, koma ngodya ikakhala yayikulu, malo opangira makina amakhala abwino, kugwiritsa ntchito ngodya ya 15° ya chida kungapangitse malo opangira makina kukhala abwino kwambiri.
Liwiro lodulira pokonza makina lingasinthidwe malinga ndi mawonekedwe a elekitirodi, nthawi zambiri 10m/min, mofanana ndi kupanga aluminiyamu kapena pulasitiki, chida choduliracho chikhoza kukhala mwachindunji pa workpiece pokonza makina okhwima, ndipo vuto la kugwa kwa ngodya ndi kugawikana n'kosavuta kuchitika pokonza makina, ndipo njira yoyenda mwachangu nthawi zambiri imagwiritsidwa ntchito pokonza mpeni wopepuka.
Maelekitirodi a graphite akamadulidwa amapanga fumbi lochuluka, kuti tipewe tinthu ta graphite tomwe timapumira makina opindika ndi screw, pali njira ziwiri zazikulu zomwe zilipo, imodzi ndi kugwiritsa ntchito makina apadera osinthira graphite, inayo ndi malo osinthira okhazikika, okhala ndi chipangizo chapadera chosonkhanitsira fumbi.
Makina apadera opukutira graphite omwe ali pamsika ali ndi mphamvu zambiri zopukutira ndipo amatha kupanga mosavuta ma electrode ovuta molondola kwambiri komanso bwino pamwamba.
Ngati EDM ikufunika popanga electrode ya graphite, ndi bwino kugwiritsa ntchito graphite yopyapyala yokhala ndi tinthu tating'onoting'ono.
Kagwiridwe ka ntchito ka graphite ndi koipa, tinthu tating'onoting'ono tikakhala tating'onoting'ono, timadula bwino kwambiri, ndipo mavuto osazolowereka monga kusweka kwa waya pafupipafupi ndi mphero ya pamwamba amatha kupewedwa.
4.EDM magawo a graphite electrode
Kusankhidwa kwa magawo a EDM a graphite ndi mkuwa n'kosiyana kwambiri.
Magawo a EDM makamaka amaphatikizapo mphamvu yamagetsi, m'lifupi mwa pulse, kusiyana kwa pulse ndi polarity.
Zotsatirazi zikufotokoza maziko ogwiritsira ntchito mwanzeru magawo akuluakulu awa.
Kuchuluka kwa magetsi a graphite electrode nthawi zambiri kumakhala 10 ~ 12 A/cm2, kwakukulu kwambiri kuposa kwa electrode yamkuwa. Chifukwa chake, mkati mwa mphamvu yololedwa m'dera lofanana, mphamvu yamagetsi ikasankhidwa yayikulu, liwiro lokonza kutulutsa kwa graphite lidzakhala lofulumira, kutayika kwa magetsi kudzakhala kochepa, koma kukhwima kwa pamwamba kudzakhala kokulirapo.
Kuchuluka kwa pulse kukakhala kwakukulu, kutayika kwa ma electrode kumakhala kochepa.
Komabe, kukula kwakukulu kwa kugunda kwa mtima kudzapangitsa kuti kukhazikika kwa processing kukhale koipa, ndipo liwiro la processing lidzakhala locheperako komanso pamwamba pake padzakhala paukali.
Pofuna kuonetsetsa kuti ma electrode otsika akutayika panthawi yokonza zinthu mopanda dongosolo, nthawi zambiri amagwiritsidwa ntchito ndi pulse width yayikulu, yomwe ingathandize kuti ma electrode a graphite awonongeke pang'ono pamene mtengo wake uli pakati pa 100 ndi 300 US.
Kuti mupeze malo abwino komanso mphamvu yotulutsa mpweya bwino, muyenera kusankha kugunda kwa mtima pang'ono.
Kawirikawiri, m'lifupi mwa graphite electrode ndi pafupifupi 40% poyerekeza ndi mkuwa electrode
Kusiyana kwa kugunda kwa mtima kumakhudza kwambiri liwiro la makina otulutsa ndi kukhazikika kwa makina. Mtengo ukakhala waukulu, kukhazikika kwa makina kudzakhala bwino, zomwe zimathandiza kuti pakhale kufanana kwabwino pamwamba, koma liwiro la makina lidzachepetsedwa.
Poonetsetsa kuti ntchito yokonza zinthu ikuyenda bwino, mphamvu yokonza zinthu ingapezeke posankha malo ocheperako ogunda, koma pamene malo otulutsira zinthu sakuyenda bwino, mphamvu yokonza zinthu ingapezeke posankha malo ogunda kwambiri.
Mu makina otulutsira ma electrode a graphite, kusiyana kwa pulse ndi m'lifupi mwa pulse nthawi zambiri zimayikidwa pa 1:1, pomwe mu makina a electrode yamkuwa, kusiyana kwa pulse ndi m'lifupi mwa pulse nthawi zambiri zimayikidwa pa 1:3.
Pogwiritsa ntchito graphite yokhazikika, chiŵerengero chofananira pakati pa kusiyana kwa kugunda kwa mtima ndi m'lifupi mwa kugunda kwa mtima chingasinthidwe kukhala 2:3.
Pankhani ya kugunda pang'ono kwa mtima, ndibwino kupanga chophimba pamwamba pa electrode, chomwe chingathandize kuchepetsa kutayika kwa electrode.
Kusankhidwa kwa polarity kwa graphite electrode mu EDM kwenikweni ndi kofanana ndi kwa electrode yamkuwa.
Malinga ndi mphamvu ya polarity ya EDM, makina opangira polarity abwino nthawi zambiri amagwiritsidwa ntchito popanga zitsulo, ndiko kuti, maelekitirodi amalumikizidwa ndi ndodo yabwino ya magetsi, ndipo chogwirira ntchito chimalumikizidwa ndi ndodo yoyipa ya magetsi.
Pogwiritsa ntchito mphamvu yayikulu yamagetsi ndi kugunda kwa mtima, kusankha makina abwino a polarity kungapangitse kuti ma electrode atayike pang'ono kwambiri. Ngati polarity ili yolakwika, kutayika kwa ma electrode kumakhala kwakukulu kwambiri.
Pokhapokha ngati pamwamba pakufunika kukonzedwa bwino osakwana VDI18 (Ra0.8 m) ndipo m'lifupi mwa pulse ndi pang'ono kwambiri, processing ya negative polarity imagwiritsidwa ntchito kuti pakhale bwino pamwamba, koma kutayika kwa electrode kumakhala kwakukulu.
Tsopano zida za makina a CNC edM zili ndi magawo oyeretsera graphite.
Kugwiritsa ntchito magawo amagetsi ndi kwanzeru ndipo kungapangidwe kokha ndi makina odziwa bwino ntchito.
Kawirikawiri, makina amatha kukonza magawo okonzedwa bwino posankha awiriawiri a zinthu, mtundu wa ntchito, kuchuluka kwa malo ogwirira ntchito ndikuyika malo ogwirira ntchito, kuya kwa ntchito, kukula kwa ma elekitirodi, ndi zina zotero. Pa nthawi yokonza mapulogalamu.
Chokhazikitsidwa cha ma electrode a graphite a laibulale ya zida zamakina a edm, cholemera pa magawo ogwiritsira ntchito, mtundu wa zinthuzo ungasankhidwe mu graphite yopyapyala, graphite, graphite ikugwirizana ndi zinthu zosiyanasiyana zogwirira ntchito, kuti igawanitse mtundu wa ntchito ya muyezo, groove yozama, mfundo yakuthwa, malo akuluakulu, m'mimba yayikulu, monga yabwino, komanso imapereka kutayika kochepa, muyezo, magwiridwe antchito apamwamba, ndi zina zotero.
5. Mapeto
Zipangizo zatsopano za graphite electrode ziyenera kutchuka kwambiri ndipo ubwino wake udzazindikirika pang'onopang'ono ndi makampani opanga nkhungu m'nyumba.
Kusankha bwino zipangizo za graphite electrode ndi kukonza maulalo okhudzana ndi ukadaulo kudzabweretsa phindu lalikulu, labwino komanso lotsika mtengo kwa mabizinesi opanga nkhungu.
Nthawi yotumizira: Disembala-04-2020