1.石墨电极的制作

模具制(zhi)(zhi)造中的(de)(de)石(shi)墨电(dian)极主要(yao)用铣削(xue)加工的(de)(de)方法制(zhi)(zhi)作完(wan)成。从加工工艺的(de)(de)角(jiao)度看，石(shi)墨与(yu)铜是2种(zhong)不(bu)同(tong)的(de)(de)材料，应该掌握它(ta)们不(bu)同(tong)的(de)(de)切(qie)削(xue)特(te)性。如(ru)(ru)果使(shi)用加工铜电(dian)极的(de)(de)工艺来加工石(shi)墨电(dian)极，必然会出(chu)现(xian)问题，如(ru)(ru)薄片(pian)经常发生(sheng)断裂，这就要(yao)求采用合适(shi)的(de)(de)切(qie)削(xue)刀(dao)具与(yu)切(qie)削(xue)参数。

加(jia)(jia)(jia)工(gong)(gong)(gong)石(shi)(shi)墨电(dian)极比铜电(dian)极的(de)刀(dao)(dao)(dao)具(ju)(ju)磨损要大(da)(da)，就经济(ji)(ji)(ji)性考虑，选用(yong)(yong)硬质合金(jin)刀(dao)(dao)(dao)具(ju)(ju)是(shi)最经济(ji)(ji)(ji)的(de)，选择金(jin)刚石(shi)(shi)涂(tu)层(ceng)刀(dao)(dao)(dao)具(ju)(ju)（称石(shi)(shi)墨刀(dao)(dao)(dao)）价格(ge)较昂贵(gui)，但金(jin)刚石(shi)(shi)涂(tu)层(ceng)刀(dao)(dao)(dao)具(ju)(ju)使用(yong)(yong)寿命长，加(jia)(jia)(jia)工(gong)(gong)(gong)精(jing)度高(gao)，整体经济(ji)(ji)(ji)效益不(bu)错。刀(dao)(dao)(dao)具(ju)(ju)的(de)前(qian)角(jiao)(jiao)大(da)(da)小也影响其使用(yong)(yong)寿命，前(qian)角(jiao)(jiao)0°的(de)刀(dao)(dao)(dao)具(ju)(ju)会比前(qian)角(jiao)(jiao)15°的(de)刀(dao)(dao)(dao)具(ju)(ju)高(gao)出(chu)多达50%的(de)使用(yong)(yong)寿命，切(qie)削的(de)稳定性也较好，但是(shi)斜角(jiao)(jiao)越大(da)(da)，加(jia)(jia)(jia)工(gong)(gong)(gong)表面越好，使用(yong)(yong)15°斜角(jiao)(jiao)的(de)刀(dao)(dao)(dao)具(ju)(ju)能达到最佳的(de)加(jia)(jia)(jia)工(gong)(gong)(gong)表面。加(jia)(jia)(jia)工(gong)(gong)(gong)时的(de)走刀(dao)(dao)(dao)速度可按电(dian)极的(de)形状来(lai)调整，通(tong)常为10m／min，与加(jia)(jia)(jia)工(gong)(gong)(gong)铝或(huo)塑料类似，粗加(jia)(jia)(jia)工(gong)(gong)(gong)时刀(dao)(dao)(dao)具(ju)(ju)可直接在工(gong)(gong)(gong)件上(shang)下刀(dao)(dao)(dao)，精(jing)加(jia)(jia)(jia)工(gong)(gong)(gong)易(yi)发生崩(beng)角(jiao)(jiao)、碎裂的(de)现象，常采(cai)用(yong)(yong)轻刀(dao)(dao)(dao)快走的(de)方式(shi)。

石(shi)墨电(dian)极(ji)(ji)在(zai)切削加工中会产生大量的(de)粉尘(chen)，为(wei)避免石(shi)墨颗粒吸(xi)入机床主(zhu)轴和丝杠，目前解决方案主(zhu)要有2种(zhong)，一(yi)种(zhong)是使用专(zhuan)(zhuan)门的(de)石(shi)墨加工机，另一(yi)种(zhong)是将普通的(de)加工中心改装，配置(zhi)专(zhuan)(zhuan)门的(de)吸(xi)尘(chen)装置(zhi)。市场(chang)上专(zhuan)(zhuan)门的(de)石(shi)墨高速铣削机床铣削效(xiao)率(lv)高，可轻松完成复(fu)杂电(dian)极(ji)(ji)的(de)制(zhi)造，电(dian)极(ji)(ji)精度高，表面质量佳。

如果需(xu)要使(shi)用电火(huo)花(hua)线(xian)切割(ge)来制作石墨(mo)(mo)电极，推荐使(shi)用颗粒直(zhi)径(jing)更(geng)小的细石墨(mo)(mo)材(cai)料。石墨(mo)(mo)材(cai)料的电火(huo)花(hua)线(xian)切割(ge)加工性能较差，其颗粒直(zhi)径(jing)越小时可获得(de)相对较高(gao)的切割(ge)效率，避免(mian)出现频繁断丝、表(biao)面(mian)条纹等(deng)异常(chang)问题。

2.石墨电极的电火花加工参数

石墨与铜材料的(de)电火花加(jia)工参(can)数选(xuan)用(yong)有较大差异。电火花加(jia)工参(can)数主要(yao)包括(kuo)电流(liu)、脉(mai)冲(chong)宽度、脉(mai)冲(chong)间隙、极(ji)性。以下介(jie)绍合理使用(yong)这些主要(yao)参(can)数的(de)依据。

石(shi)墨(mo)电(dian)(dian)(dian)(dian)极的电(dian)(dian)(dian)(dian)流(liu)密度一般(ban)为10~12 A/cm2，比(bi)铜电(dian)(dian)(dian)(dian)极要大(da)得多，因此(ci)在对应面(mian)积允许的电(dian)(dian)(dian)(dian)流(liu)大(da)小(xiao)范围(wei)内，电(dian)(dian)(dian)(dian)流(liu)选用越(yue)大(da)，则石(shi)墨(mo)放电(dian)(dian)(dian)(dian)加工(gong)速度越(yue)快(kuai)，电(dian)(dian)(dian)(dian)极损耗(hao)越(yue)小(xiao)，但表面(mian)粗糙度会变粗。

脉(mai)(mai)(mai)冲(chong)(chong)宽(kuan)(kuan)度(du)选(xuan)(xuan)用越(yue)大，电(dian)极损耗会降低(di)。但(dan)较(jiao)大的(de)脉(mai)(mai)(mai)冲(chong)(chong)宽(kuan)(kuan)度(du)会使(shi)(shi)加(jia)(jia)工稳定(ding)性变(bian)差，同(tong)时(shi)使(shi)(shi)加(jia)(jia)工速度(du)变(bian)慢，表面变(bian)粗糙。粗加(jia)(jia)工时(shi)为保证电(dian)极低(di)损耗，通常使(shi)(shi)用较(jiao)大的(de)脉(mai)(mai)(mai)冲(chong)(chong)宽(kuan)(kuan)度(du)，其取值在100～300 us时(shi)可有效实现(xian)石墨电(dian)极的(de)低(di)损耗加(jia)(jia)工。精加(jia)(jia)工时(shi)，为获(huo)得精细表面与稳定(ding)的(de)放(fang)电(dian)效果(guo)，宜(yi)选(xuan)(xuan)用较(jiao)小的(de)脉(mai)(mai)(mai)冲(chong)(chong)宽(kuan)(kuan)度(du)。一般石墨电(dian)极比铜(tong)电(dian)极加(jia)(jia)工时(shi)选(xuan)(xuan)取的(de)脉(mai)(mai)(mai)冲(chong)(chong)宽(kuan)(kuan)度(du)要(yao)减少约40%

脉(mai)(mai)冲(chong)间(jian)隙(xi)主要影(ying)响放电(dian)(dian)加(jia)(jia)工(gong)(gong)速度(du)(du)和加(jia)(jia)工(gong)(gong)稳(wen)定(ding)(ding)(ding)(ding)性，其值越(yue)大加(jia)(jia)工(gong)(gong)稳(wen)定(ding)(ding)(ding)(ding)性越(yue)好(hao)，对获(huo)得(de)较(jiao)好(hao)的(de)表面(mian)均(jun)匀性有(you)帮(bang)助(zhu)，但(dan)加(jia)(jia)工(gong)(gong)速度(du)(du)会降(jiang)低。在(zai)保证(zheng)加(jia)(jia)工(gong)(gong)稳(wen)定(ding)(ding)(ding)(ding)的(de)情(qing)况下(xia)，选用较(jiao)小的(de)脉(mai)(mai)冲(chong)间(jian)隙(xi)可(ke)获(huo)得(de)较(jiao)高(gao)的(de)加(jia)(jia)工(gong)(gong)效率(lv)，但(dan)放电(dian)(dian)状态不稳(wen)定(ding)(ding)(ding)(ding)时，脉(mai)(mai)冲(chong)间(jian)隙(xi)选取较(jiao)大些可(ke)获(huo)得(de)更(geng)高(gao)的(de)加(jia)(jia)工(gong)(gong)效率(lv)。石墨(mo)电(dian)(dian)极放电(dian)(dian)加(jia)(jia)工(gong)(gong)中通(tong)常(chang)将脉(mai)(mai)冲(chong)间(jian)隙(xi)与脉(mai)(mai)宽(kuan)(kuan)宽(kuan)(kuan)度(du)(du)按1:1来(lai)设定(ding)(ding)(ding)(ding)，而通(tong)常(chang)铜电(dian)(dian)极加(jia)(jia)工(gong)(gong)中脉(mai)(mai)冲(chong)间(jian)隙(xi)与脉(mai)(mai)宽(kuan)(kuan)宽(kuan)(kuan)度(du)(du)按1:3来(lai)设定(ding)(ding)(ding)(ding)。在(zai)石墨(mo)加(jia)(jia)工(gong)(gong)稳(wen)定(ding)(ding)(ding)(ding)的(de)情(qing)况下(xia)，可(ke)以将脉(mai)(mai)冲(chong)间(jian)隙(xi)与脉(mai)(mai)宽(kuan)(kuan)宽(kuan)(kuan)度(du)(du)的(de)搭(da)配比例调整(zheng)到2:3。脉(mai)(mai)冲(chong)间(jian)隙(xi)较(jiao)小的(de)情(qing)况下(xia)，有(you)利于在(zai)电(dian)(dian)极表面(mian)形成覆盖层，对降(jiang)低电(dian)(dian)极损(sun)耗有(you)一定(ding)(ding)(ding)(ding)的(de)帮(bang)助(zhu)。

石(shi)墨电(dian)(dian)(dian)极(ji)(ji)(ji)电(dian)(dian)(dian)火(huo)花(hua)(hua)加工中极(ji)(ji)(ji)性(xing)(xing)的(de)(de)选(xuan)(xuan)用(yong)(yong)与铜(tong)电(dian)(dian)(dian)极(ji)(ji)(ji)基本相同(tong)。根据电(dian)(dian)(dian)火(huo)花(hua)(hua)加工的(de)(de)极(ji)(ji)(ji)性(xing)(xing)效(xiao)应，在加工模具钢时通(tong)常选(xuan)(xuan)用(yong)(yong)正极(ji)(ji)(ji)性(xing)(xing)加工，也就是电(dian)(dian)(dian)极(ji)(ji)(ji)接电(dian)(dian)(dian)源的(de)(de)正极(ji)(ji)(ji)，工件接电(dian)(dian)(dian)源的(de)(de)负(fu)极(ji)(ji)(ji)。使用(yong)(yong)较大(da)电(dian)(dian)(dian)流和(he)脉冲宽度(du)，选(xuan)(xuan)择正极(ji)(ji)(ji)性(xing)(xing)加工可以获得极(ji)(ji)(ji)低的(de)(de)电(dian)(dian)(dian)极(ji)(ji)(ji)损耗(hao)效(xiao)果(guo)，如果(guo)将(jiang)极(ji)(ji)(ji)性(xing)(xing)选(xuan)(xuan)错将(jiang)会导致电(dian)(dian)(dian)极(ji)(ji)(ji)损耗(hao)变(bian)得非常大(da)。只有在表面要求小(xiao)于VDI18（Ra0.8μm）的(de)(de)精(jing)细(xi)加工，采用(yong)(yong)极(ji)(ji)(ji)小(xiao)的(de)(de)脉冲宽度(du)，才选(xuan)(xuan)用(yong)(yong)负(fu)极(ji)(ji)(ji)性(xing)(xing)加工以获得较好的(de)(de)表面质量(liang)，但电(dian)(dian)(dian)极(ji)(ji)(ji)损耗(hao)较大(da)。

现(xian)在的数(shu)(shu)控电火花加(jia)工(gong)(gong)机(ji)(ji)床(chuang)都配有石(shi)(shi)(shi)墨(mo)放电加(jia)工(gong)(gong)参(can)数(shu)(shu)。电参(can)数(shu)(shu)的使用是智能(neng)化的，可以通过机(ji)(ji)床(chuang)的专家系统来(lai)自动生(sheng)成。通常是在编程(cheng)时选(xuan)择(ze)材料对(dui)、应用类(lei)型(xing)(xing)、表面粗(cu)糙度(du)值，输入加(jia)工(gong)(gong)面积、加(jia)工(gong)(gong)深度(du)、电极(ji)尺(chi)寸缩放量等(deng)，机(ji)(ji)床(chuang)就能(neng)配置出优化的加(jia)工(gong)(gong)参(can)数(shu)(shu)。机(ji)(ji)床(chuang)针对(dui)石(shi)(shi)(shi)墨(mo)电极(ji)的放电加(jia)工(gong)(gong)设有丰富的加(jia)工(gong)(gong)参(can)数(shu)(shu)库，材料类(lei)型(xing)(xing)里可选(xuan)择(ze)粗(cu)石(shi)(shi)(shi)墨(mo)、中石(shi)(shi)(shi)墨(mo)、细(xi)石(shi)(shi)(shi)墨(mo)对(dui)应多(duo)种工(gong)(gong)件材料，将应用类(lei)型(xing)(xing)细(xi)分为标(biao)准(zhun)、深槽、尖点、大(da)(da)面积、大(da)(da)型(xing)(xing)腔、微(wei)细(xi)等(deng)，还提供(gong)了低损耗、标(biao)准(zhun)、高效率等(deng)多(duo)种加(jia)工(gong)(gong)优先(xian)权选(xuan)择(ze)。

3.石墨(mo)电(dian)极加工应(ying)用(yong)案例

下(xia)图(tu)所示手机模(mo)具零(ling)件的(de)(de)(de)材料(liao)S136钢料(liao)，加(jia)(jia)工(gong)(gong)(gong)形(xing)状(zhuang)包(bao)含形(xing)状(zhuang)复杂的(de)(de)(de)加(jia)(jia)强(qiang)筋。使(shi)(shi)用(yong)(yong)石墨(mo)电(dian)(dian)极(ji)(ji)，精加(jia)(jia)工(gong)(gong)(gong)电(dian)(dian)极(ji)(ji)使(shi)(shi)用(yong)(yong)TTK-4石墨(mo)，电(dian)(dian)极(ji)(ji)数量(liang)(liang)2个，粗(cu)加(jia)(jia)工(gong)(gong)(gong)电(dian)(dian)极(ji)(ji)尺寸缩放量(liang)(liang)单边0.08 mm，精加(jia)(jia)工(gong)(gong)(gong)电(dian)(dian)极(ji)(ji)尺寸缩放量(liang)(liang)单边0.08 mm。粗(cu)加(jia)(jia)工(gong)(gong)(gong)时间3H，精加(jia)(jia)工(gong)(gong)(gong)时间53 min，表面粗(cu)糙度VDI18（Ra 0.8μm）。加(jia)(jia)工(gong)(gong)(gong)说明：利(li)用(yong)(yong)石墨(mo)的(de)(de)(de)特(te)性将不(bu)同形(xing)状(zhuang)，将不(bu)同高低(di)的(de)(de)(de)众多(duo)薄(bo)加(jia)(jia)强(qiang)筋组合(he)在一个电(dian)(dian)极(ji)(ji)上进行(xing)放电(dian)(dian)加(jia)(jia)工(gong)(gong)(gong)，可减少电(dian)(dian)极(ji)(ji)原材料(liao)、夹具的(de)(de)(de)投入成本，降低(di)电(dian)(dian)极(ji)(ji)的(de)(de)(de)装夹次数和定(ding)位工(gong)(gong)(gong)作量(liang)(liang)，放电(dian)(dian)时间比使(shi)(shi)用(yong)(yong)铜电(dian)(dian)极(ji)(ji)加(jia)(jia)工(gong)(gong)(gong)缩短(duan)40%。