1.石墨電極的制作

模具(ju)(ju)制造中的石(shi)墨電(dian)極(ji)主要用(yong)銑削(xue)加(jia)工(gong)(gong)的方法(fa)制作完成。從加(jia)工(gong)(gong)工(gong)(gong)藝的角度看(kan)，石(shi)墨與銅是2種不同(tong)的材(cai)料，應(ying)該掌(zhang)握(wo)它(ta)們不同(tong)的切(qie)(qie)削(xue)特性。如果使用(yong)加(jia)工(gong)(gong)銅電(dian)極(ji)的工(gong)(gong)藝來加(jia)工(gong)(gong)石(shi)墨電(dian)極(ji)，必然會出(chu)現問題，如薄片經常發生斷裂，這(zhe)就要求采用(yong)合適(shi)的切(qie)(qie)削(xue)刀(dao)具(ju)(ju)與切(qie)(qie)削(xue)參數。

加(jia)工(gong)(gong)(gong)(gong)石墨電極(ji)比(bi)銅(tong)電極(ji)的(de)(de)刀(dao)(dao)(dao)(dao)具(ju)(ju)磨損(sun)要大(da)，就經濟性考慮，選用硬質合金刀(dao)(dao)(dao)(dao)具(ju)(ju)是(shi)最(zui)經濟的(de)(de)，選擇金剛(gang)石涂層(ceng)刀(dao)(dao)(dao)(dao)具(ju)(ju)（稱(cheng)石墨刀(dao)(dao)(dao)(dao)）價格較(jiao)(jiao)昂貴，但金剛(gang)石涂層(ceng)刀(dao)(dao)(dao)(dao)具(ju)(ju)使(shi)用壽命(ming)長，加(jia)工(gong)(gong)(gong)(gong)精度(du)高(gao)，整體(ti)經濟效(xiao)益不錯。刀(dao)(dao)(dao)(dao)具(ju)(ju)的(de)(de)前角大(da)小也影(ying)響其(qi)使(shi)用壽命(ming)，前角0°的(de)(de)刀(dao)(dao)(dao)(dao)具(ju)(ju)會比(bi)前角15°的(de)(de)刀(dao)(dao)(dao)(dao)具(ju)(ju)高(gao)出(chu)多(duo)達(da)50%的(de)(de)使(shi)用壽命(ming)，切削的(de)(de)穩定性也較(jiao)(jiao)好，但是(shi)斜角越(yue)大(da)，加(jia)工(gong)(gong)(gong)(gong)表面(mian)越(yue)好，使(shi)用15°斜角的(de)(de)刀(dao)(dao)(dao)(dao)具(ju)(ju)能達(da)到最(zui)佳的(de)(de)加(jia)工(gong)(gong)(gong)(gong)表面(mian)。加(jia)工(gong)(gong)(gong)(gong)時的(de)(de)走(zou)刀(dao)(dao)(dao)(dao)速度(du)可按電極(ji)的(de)(de)形(xing)狀來調整，通常為10m／min，與加(jia)工(gong)(gong)(gong)(gong)鋁或塑料類似，粗加(jia)工(gong)(gong)(gong)(gong)時刀(dao)(dao)(dao)(dao)具(ju)(ju)可直接在工(gong)(gong)(gong)(gong)件上(shang)下刀(dao)(dao)(dao)(dao)，精加(jia)工(gong)(gong)(gong)(gong)易發(fa)生崩(beng)角、碎裂的(de)(de)現象，常采用輕刀(dao)(dao)(dao)(dao)快走(zou)的(de)(de)方式(shi)。

石(shi)(shi)墨(mo)(mo)(mo)電(dian)極(ji)在切削加工中(zhong)會(hui)產(chan)生大量的(de)粉塵，為避免石(shi)(shi)墨(mo)(mo)(mo)顆粒吸入機床主軸和絲杠(gang)，目(mu)前解決方(fang)案主要(yao)有2種(zhong)，一(yi)種(zhong)是(shi)使用專門(men)(men)的(de)石(shi)(shi)墨(mo)(mo)(mo)加工機，另(ling)一(yi)種(zhong)是(shi)將(jiang)普通的(de)加工中(zhong)心(xin)改裝，配置(zhi)專門(men)(men)的(de)吸塵裝置(zhi)。市場(chang)上專門(men)(men)的(de)石(shi)(shi)墨(mo)(mo)(mo)高(gao)速銑(xian)削機床銑(xian)削效率高(gao)，可輕松完成復雜電(dian)極(ji)的(de)制造，電(dian)極(ji)精度高(gao)，表面質量佳。

如果需要使用電(dian)火(huo)花(hua)線(xian)切(qie)(qie)割(ge)來制作(zuo)石墨(mo)電(dian)極，推薦使用顆粒(li)直徑(jing)(jing)更小的細石墨(mo)材料。石墨(mo)材料的電(dian)火(huo)花(hua)線(xian)切(qie)(qie)割(ge)加工性能較差，其顆粒(li)直徑(jing)(jing)越小時(shi)可獲得相(xiang)對較高的切(qie)(qie)割(ge)效率，避免(mian)出現頻繁斷絲(si)、表面條(tiao)紋等異常問(wen)題。

2.石墨電極的電火花加工參數

石墨與(yu)銅材(cai)料的電火(huo)(huo)花(hua)加工參(can)(can)(can)數選用有較大差異(yi)。電火(huo)(huo)花(hua)加工參(can)(can)(can)數主(zhu)要(yao)包(bao)括電流、脈沖(chong)寬度、脈沖(chong)間隙、極性。以下(xia)介紹合(he)理(li)使用這些主(zhu)要(yao)參(can)(can)(can)數的依據。

石墨(mo)電(dian)(dian)極(ji)的電(dian)(dian)流密度一般為10~12 A/cm2，比銅電(dian)(dian)極(ji)要(yao)大得多，因此(ci)在對應面積允許的電(dian)(dian)流大小范圍(wei)內(nei)，電(dian)(dian)流選用越大，則石墨(mo)放電(dian)(dian)加工速度越快，電(dian)(dian)極(ji)損耗越小，但表面粗糙度會變粗。

脈沖(chong)(chong)寬(kuan)(kuan)度選(xuan)用(yong)越大(da)，電(dian)(dian)極損(sun)耗(hao)會降低。但較(jiao)大(da)的(de)(de)脈沖(chong)(chong)寬(kuan)(kuan)度會使加(jia)(jia)工(gong)穩定(ding)(ding)性(xing)變差(cha)，同(tong)時使加(jia)(jia)工(gong)速(su)度變慢，表面變粗(cu)糙。粗(cu)加(jia)(jia)工(gong)時為(wei)保證電(dian)(dian)極低損(sun)耗(hao)，通(tong)常使用(yong)較(jiao)大(da)的(de)(de)脈沖(chong)(chong)寬(kuan)(kuan)度，其取(qu)值在100～300 us時可(ke)有效(xiao)實現石墨(mo)電(dian)(dian)極的(de)(de)低損(sun)耗(hao)加(jia)(jia)工(gong)。精(jing)加(jia)(jia)工(gong)時，為(wei)獲得精(jing)細表面與穩定(ding)(ding)的(de)(de)放電(dian)(dian)效(xiao)果(guo)，宜選(xuan)用(yong)較(jiao)小的(de)(de)脈沖(chong)(chong)寬(kuan)(kuan)度。一(yi)般石墨(mo)電(dian)(dian)極比銅(tong)電(dian)(dian)極加(jia)(jia)工(gong)時選(xuan)取(qu)的(de)(de)脈沖(chong)(chong)寬(kuan)(kuan)度要減少約40%

脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)主(zhu)要(yao)影響(xiang)放電(dian)加(jia)工(gong)(gong)速度和加(jia)工(gong)(gong)穩(wen)定性，其值越大(da)加(jia)工(gong)(gong)穩(wen)定性越好，對獲(huo)得(de)(de)較(jiao)(jiao)好的(de)(de)(de)(de)表(biao)面(mian)均勻性有(you)幫助，但加(jia)工(gong)(gong)速度會(hui)降(jiang)低。在(zai)(zai)保證(zheng)加(jia)工(gong)(gong)穩(wen)定的(de)(de)(de)(de)情(qing)況下，選用較(jiao)(jiao)小的(de)(de)(de)(de)脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)可獲(huo)得(de)(de)較(jiao)(jiao)高的(de)(de)(de)(de)加(jia)工(gong)(gong)效率，但放電(dian)狀態不穩(wen)定時，脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)選取(qu)較(jiao)(jiao)大(da)些可獲(huo)得(de)(de)更高的(de)(de)(de)(de)加(jia)工(gong)(gong)效率。石墨(mo)電(dian)極放電(dian)加(jia)工(gong)(gong)中通常(chang)將脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)與(yu)脈(mo)(mo)寬寬度按1:1來設定，而通常(chang)銅電(dian)極加(jia)工(gong)(gong)中脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)與(yu)脈(mo)(mo)寬寬度按1:3來設定。在(zai)(zai)石墨(mo)加(jia)工(gong)(gong)穩(wen)定的(de)(de)(de)(de)情(qing)況下，可以將脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)與(yu)脈(mo)(mo)寬寬度的(de)(de)(de)(de)搭配比例調(diao)整到(dao)2:3。脈(mo)(mo)沖(chong)(chong)間(jian)隙(xi)較(jiao)(jiao)小的(de)(de)(de)(de)情(qing)況下，有(you)利于在(zai)(zai)電(dian)極表(biao)面(mian)形成覆蓋層(ceng)，對降(jiang)低電(dian)極損耗(hao)有(you)一(yi)定的(de)(de)(de)(de)幫助。

石(shi)墨電(dian)(dian)極(ji)(ji)電(dian)(dian)火花(hua)(hua)加工中極(ji)(ji)性(xing)(xing)的(de)(de)選(xuan)(xuan)(xuan)用(yong)與銅電(dian)(dian)極(ji)(ji)基本(ben)相同。根據電(dian)(dian)火花(hua)(hua)加工的(de)(de)極(ji)(ji)性(xing)(xing)效應，在加工模(mo)具鋼時通常(chang)選(xuan)(xuan)(xuan)用(yong)正極(ji)(ji)性(xing)(xing)加工，也(ye)就(jiu)是電(dian)(dian)極(ji)(ji)接電(dian)(dian)源(yuan)的(de)(de)正極(ji)(ji)，工件接電(dian)(dian)源(yuan)的(de)(de)負極(ji)(ji)。使用(yong)較大(da)電(dian)(dian)流(liu)和脈沖(chong)寬(kuan)度(du)，選(xuan)(xuan)(xuan)擇(ze)正極(ji)(ji)性(xing)(xing)加工可以獲得(de)(de)極(ji)(ji)低的(de)(de)電(dian)(dian)極(ji)(ji)損(sun)耗(hao)效果(guo)，如(ru)果(guo)將極(ji)(ji)性(xing)(xing)選(xuan)(xuan)(xuan)錯將會導致電(dian)(dian)極(ji)(ji)損(sun)耗(hao)變(bian)得(de)(de)非常(chang)大(da)。只有在表(biao)面(mian)要求小(xiao)于(yu)VDI18（Ra0.8μm）的(de)(de)精(jing)細加工，采用(yong)極(ji)(ji)小(xiao)的(de)(de)脈沖(chong)寬(kuan)度(du)，才選(xuan)(xuan)(xuan)用(yong)負極(ji)(ji)性(xing)(xing)加工以獲得(de)(de)較好(hao)的(de)(de)表(biao)面(mian)質量，但電(dian)(dian)極(ji)(ji)損(sun)耗(hao)較大(da)。

現在的(de)數控電(dian)(dian)(dian)火花(hua)加(jia)(jia)(jia)工(gong)機床(chuang)(chuang)都(dou)配有石(shi)墨放(fang)電(dian)(dian)(dian)加(jia)(jia)(jia)工(gong)參(can)數。電(dian)(dian)(dian)參(can)數的(de)使(shi)用(yong)是智能(neng)化的(de)，可以通過機床(chuang)(chuang)的(de)專家系統來自(zi)動(dong)生成。通常(chang)是在編程時選(xuan)擇材料(liao)對、應用(yong)類(lei)(lei)型、表(biao)面(mian)粗糙度值，輸入加(jia)(jia)(jia)工(gong)面(mian)積(ji)、加(jia)(jia)(jia)工(gong)深度、電(dian)(dian)(dian)極尺寸縮放(fang)量等(deng)，機床(chuang)(chuang)就能(neng)配置出優(you)化的(de)加(jia)(jia)(jia)工(gong)參(can)數。機床(chuang)(chuang)針對石(shi)墨電(dian)(dian)(dian)極的(de)放(fang)電(dian)(dian)(dian)加(jia)(jia)(jia)工(gong)設有豐富的(de)加(jia)(jia)(jia)工(gong)參(can)數庫(ku)，材料(liao)類(lei)(lei)型里(li)可選(xuan)擇粗石(shi)墨、中(zhong)石(shi)墨、細石(shi)墨對應多(duo)種工(gong)件(jian)材料(liao)，將應用(yong)類(lei)(lei)型細分(fen)為(wei)標(biao)準(zhun)、深槽、尖(jian)點(dian)、大面(mian)積(ji)、大型腔(qiang)、微細等(deng)，還提(ti)供了低損耗、標(biao)準(zhun)、高效率等(deng)多(duo)種加(jia)(jia)(jia)工(gong)優(you)先(xian)權選(xuan)擇。

3.石墨(mo)電極加工(gong)應用案例(li)

下(xia)圖所示(shi)手機模具(ju)零(ling)件的(de)材料S136鋼料，加(jia)(jia)(jia)工(gong)形(xing)狀包含形(xing)狀復雜的(de)加(jia)(jia)(jia)強(qiang)(qiang)筋。使用(yong)石(shi)墨(mo)電極(ji)，精(jing)加(jia)(jia)(jia)工(gong)電極(ji)使用(yong)TTK-4石(shi)墨(mo)，電極(ji)數量2個，粗加(jia)(jia)(jia)工(gong)電極(ji)尺(chi)(chi)寸縮(suo)放(fang)量單(dan)邊0.08 mm，精(jing)加(jia)(jia)(jia)工(gong)電極(ji)尺(chi)(chi)寸縮(suo)放(fang)量單(dan)邊0.08 mm。粗加(jia)(jia)(jia)工(gong)時間(jian)3H，精(jing)加(jia)(jia)(jia)工(gong)時間(jian)53 min，表(biao)面(mian)粗糙度VDI18（Ra 0.8μm）。加(jia)(jia)(jia)工(gong)說明：利(li)用(yong)石(shi)墨(mo)的(de)特性將不(bu)同形(xing)狀，將不(bu)同高(gao)低的(de)眾多薄(bo)加(jia)(jia)(jia)強(qiang)(qiang)筋組合在一個電極(ji)上進行放(fang)電加(jia)(jia)(jia)工(gong)，可減(jian)少電極(ji)原(yuan)材料、夾(jia)(jia)具(ju)的(de)投(tou)入成本，降低電極(ji)的(de)裝夾(jia)(jia)次數和定位工(gong)作量，放(fang)電時間(jian)比使用(yong)銅(tong)電極(ji)加(jia)(jia)(jia)工(gong)縮(suo)短40%。