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PCB機械加工:數(shu)控銑定位 時間:【2018-08-21】 共閱【3738】次 【打印】【返回

所謂數控(kong)銑(xian)(xian)的定(ding)(ding)位(wei),就是用(yong)定(ding)(ding)位(wei)銷將待加工(gong)(gong)的印制板(ban)(ban)定(ding)(ding)位(wei)到銑(xian)(xian)床(chuang)的工(gong)(gong)作(zuo)臺(tai)上,從而方便、準(zhun)確(que)地加工(gong)(gong)印制板(ban)(ban)外(wai)形。要求(qiu)定(ding)(ding)位(wei)簡單(dan)可靠,能快速裝(zhuang)(zhuang)、卸(xie)板(ban)(ban)同時能排除切屑。定(ding)(ding)位(wei)方法(fa)有(you)多(duo)種,如有(you)的數銑(xian)(xian)床(chuang)設計了往復式工(gong)(gong)作(zuo)臺(tai),當一個工(gong)(gong)作(zuo)臺(tai)在加工(gong)(gong)時,另(ling)一個工(gong)(gong)作(zuo)臺(tai)裝(zhuang)(zhuang)、卸(xie)板(ban)(ban)。還(huan)有(you)用(yong)兩套銑(xian)(xian)定(ding)(ding)位(wei)墊(dian)板(ban)(ban)的方法(fa),當一個銑(xian)(xian)定(ding)(ding)位(wei)墊(dian)板(ban)(ban)在數控(kong)銑(xian)(xian)工(gong)(gong)作(zuo)臺(tai)上加工(gong)(gong)時,另(ling)一個銑(xian)(xian)定(ding)(ding)位(wei)墊(dian)板(ban)(ban)在平臺(tai)上裝(zhuang)(zhuang)、卸(xie)板(ban)(ban)。兩者交換(huan)只需(xu)幾秒鐘。

  數控銑(xian)(xian)工(gong)(gong)作(zuo)臺(tai)本身就(jiu)是(shi)一(yi)(yi)(yi)塊定(ding)位(wei)(wei)(wei)板(ban)(ban),它是(shi)一(yi)(yi)(yi)塊以(yi)銷(xiao)釘定(ding)位(wei)(wei)(wei),螺(luo)釘固定(ding)的(de)鋁合(he)金板(ban)(ban)。在(zai)每個數控銑(xian)(xian)的(de)主(zhu)軸(zhou)之(zhi)下工(gong)(gong)作(zuo)臺(tai)面上有一(yi)(yi)(yi)孔一(yi)(yi)(yi)槽(cao)(cao)(cao)(cao)式定(ding)位(wei)(wei)(wei)系統。銑(xian)(xian)墊板(ban)(ban)實際上是(shi)中間(jian)定(ding)位(wei)(wei)(wei)夾(jia)具,有時(shi)稱為“軟定(ding)位(wei)(wei)(wei)”。要(yao)求其既能(neng)可靠的(de)定(ding)位(wei)(wei)(wei)又能(neng)快(kuai)速卸板(ban)(ban),減少輔助時(shi)間(jian),提高生產(chan)效率。在(zai)銑(xian)(xian)外形之(zhi)前,在(zai)銑(xian)(xian)墊板(ban)(ban)上預(yu)先銑(xian)(xian)出和印制板(ban)(ban)外形尺(chi)寸一(yi)(yi)(yi)樣(yang)的(de)溝槽(cao)(cao)(cao)(cao)。一(yi)(yi)(yi)般,槽(cao)(cao)(cao)(cao)寬的(de)尺(chi)寸是(shi)實際加(jia)(jia)工(gong)(gong)用銑(xian)(xian)刀(dao)(dao)直(zhi)徑加(jia)(jia)0。5mm。槽(cao)(cao)(cao)(cao)深是(shi)2。5mm。在(zai)加(jia)(jia)工(gong)(gong)過(guo)程中,它是(shi)銑(xian)(xian)刀(dao)(dao)運動軌(gui)跡(ji)的(de)一(yi)(yi)(yi)條通路。由于(yu)(yu)吸塵器吸塵,在(zai)溝槽(cao)(cao)(cao)(cao)里產(chan)生一(yi)(yi)(yi)股(gu)氣流,排除切屑,使(shi)被加(jia)(jia)工(gong)(gong)更光(guang)潔,防止切屑堵塞銑(xian)(xian)刀(dao)(dao)排屑槽(cao)(cao)(cao)(cao),降低鋒。加(jia)(jia)工(gong)(gong)時(shi),要(yao)使(shi)銑(xian)(xian)刀(dao)(dao)伸進(jin)溝槽(cao)(cao)(cao)(cao)1。5~2mm。這(zhe)樣(yang)可防止由于(yu)(yu)銑(xian)(xian)刀(dao)(dao)連續切入板(ban)(ban)材(cai)使(shi)末(mo)端磨損,直(zhi)徑減小以(yi)及由于(yu)(yu)銑(xian)(xian)刀(dao)(dao)制造允(yun)許的(de)末(mo)端直(zhi)徑減小等造成印制板(ban)(ban)加(jia)(jia)工(gong)(gong)尺(chi)寸的(de)偏差(cha)。

  在每(mei)個批(pi)量生產(chan)之前,在數(shu)控銑工作臺上裝好銑墊(dian)板,擰上新的(de)尼龍螺紋塞(sai)。在螺紋塞(sai)上鉆(zhan)孔,裝上定(ding)位(wei)銷即可使(shi)(shi)(shi)用。銑墊(dian)板上的(de)排屑槽(cao),銑的(de)更(geng)深更(geng)寬一些,會更(geng)利(li)于(yu)氣流暢(chang)通,排屑,使(shi)(shi)(shi)被加(jia)工表面更(geng)光潔(jie)。但是(shi),卻減弱了支(zhi)撐面,特別是(shi)排屑槽(cao)靠近定(ding)位(wei)銷時,將使(shi)(shi)(shi)定(ding)位(wei)不牢固(gu)。

  大多數(shu)銑墊(dian)板采用(yong)(yong)非金(jin)屬層壓板。材料相對是軟的。當銷釘反復的裝(zhuang)、卸,定(ding)位孔磨損、擴(kuo)大。如半專(zhuan)用(yong)(yong)性、消耗性銑墊(dian)板就是在這(zhe)樣的條件(jian)下工作(zuo)的。

  通常,銷(xiao)釘(ding)在(zai)銑墊(dian)板(ban)(ban)(ban)(ban)(ban)上壓(ya)配,過盈(ying)量0.005~0.01mm。如果是專用(yong)(yong)(yong)性(xing)銑墊(dian)板(ban)(ban)(ban)(ban)(ban)或采用(yong)(yong)(yong)高密(mi)纖維板(ban)(ban)(ban)(ban)(ban)作銑墊(dian)板(ban)(ban)(ban)(ban)(ban),則采用(yong)(yong)(yong)更緊的(de)(de)(de)(de)配合為(wei)好(hao)。但半專用(yong)(yong)(yong)性(xing)銑墊(dian)板(ban)(ban)(ban)(ban)(ban)或消耗性(xing)銑墊(dian)板(ban)(ban)(ban)(ban)(ban),過盈(ying)量大(da)(da)于0.007mm,在(zai)壓(ya)配銷(xiao)釘(ding)時,有可能使銷(xiao)孔內的(de)(de)(de)(de)部分(fen)(fen)基(ji)材切(qie)下,形成(cheng)深的(de)(de)(de)(de)槽(cao)或空(kong)隙。銷(xiao)子(zi)反復(fu)的(de)(de)(de)(de)裝(zhuang)、卸,層壓(ya)板(ban)(ban)(ban)(ban)(ban)的(de)(de)(de)(de)銷(xiao)孔也產生分(fen)(fen)層或碎裂。在(zai)銑印(yin)制(zhi)板(ban)(ban)(ban)(ban)(ban)時,切(qie)銷(xiao)力(li)大(da)(da)部分(fen)(fen)由定(ding)位銷(xiao)承受,這(zhe)種(zhong)側(ce)向壓(ya)力(li)擠(ji)壓(ya)銷(xiao)孔再加上孔內缺(que)陷,使銷(xiao)釘(ding)一個一個的(de)(de)(de)(de)松動偏斜。它(ta)直接影響印(yin)制(zhi)板(ban)(ban)(ban)(ban)(ban)的(de)(de)(de)(de)外形尺(chi)寸(cun),不能保證嚴格的(de)(de)(de)(de)公差(cha)。

  定(ding)(ding)位銷(xiao)直(zhi)徑(jing)(jing)愈(yu)小(xiao),相(xiang)對的偏斜量(liang)也愈(yu)大(da)。所以,應(ying)盡可能采(cai)用大(da)直(zhi)徑(jing)(jing)的孔作(zuo)為(wei)定(ding)(ding)位孔。定(ding)(ding)位銷(xiao)直(zhi)徑(jing)(jing)和偏斜量(liang)也直(zhi)接影(ying)響生產率。例如,原(yuan)定(ding)(ding)一疊(die)四(si)塊,一次可銑完(wan)。由于銷(xiao)釘(ding)直(zhi)徑(jing)(jing)小(xiao),偏斜量(liang)大(da),那么(me)只好銑三塊,使效率降(jiang)低25%。

  在(zai)加工過程中,定位(wei)銷應緊密配合,使(shi)加工板(ban)可靠定位(wei)。而不應靠膠粘帶或(huo)膠粘劑(ji)的幫助,因為這要花時間去(qu)粘接、固化。緊密配合也(ye)(ye)意(yi)味著嚴格的公差,銑多(duo)層板(ban)或(huo)高質量(liang)雙面板(ban)也(ye)(ye)能保證精度(du)。

  通常(chang),鉆頭(tou)(tou)直(zhi)徑(jing)(jing)是(shi)下偏差(cha),一(yi)(yi)(yi)般是(shi)0~0.005mm,有(you)的(de)(de)(de)是(shi)0~0.01mm。大多(duo)數非金屬層壓(ya)板,鉆孔后有(you)一(yi)(yi)(yi)定的(de)(de)(de)收縮(suo)量(liang),一(yi)(yi)(yi)般為0.005~0.007mm。這樣的(de)(de)(de)下偏差(cha)為0.005~0.01mm的(de)(de)(de)孔配上標準(zhun)銷釘,可產生(sheng)0.005mm的(de)(de)(de)過盈量(liang)。因而不必考(kao)慮特別的(de)(de)(de)加工技術,也不必去逐個測量(liang)鉆頭(tou)(tou)直(zhi)徑(jing)(jing),挑選小直(zhi)徑(jing)(jing)鉆頭(tou)(tou),就可以達到壓(ya)配合的(de)(de)(de)要求,節省了時間(jian)。

  例如,某種1.6mm厚的(de)印制板,外形公差±0.013mm,每次(ci)銑四塊一疊。鉆孔(kong)位(wei)置公差+/-0.025mm,鉆孔(kong)直徑(jing)差±0.025mm,使(shi)用標準銷(xiao)(xiao)釘(ding)。那么裝(zhuang)、卸板困難,費時間。因為有可能使(shi)銷(xiao)(xiao)釘(ding)鎖緊在被銑板材里(li)。本例指出銷(xiao)(xiao)釘(ding)與被板配(pei)合,要(yao)采用較松(song)的(de)滑(hua)配(pei)合。當然,如果間隙太大(da),要(yao)影響加工精(jing)度和(he)邊緣光潔。

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