點焊(han)(han)是(shi)指將焊(han)(han)件裝配成搭(da)接(jie)接(jie)頭,并壓緊在兩電極(ji)之(zhi)間,利用電阻(zu)熱熔化母材金屬,形(xing)成焊(han)(han)點的(de)電阻(zu)焊(han)(han)方法,見圖6-21。


圖 21.jpg



一、焊點形成過(guo)程


  焊(han)點形成過程是由預壓、通電加熱和(he)冷卻結晶三個連續(xu)階段所組(zu)成。


 1. 預(yu)壓階段


  焊件(jian)在(zai)(zai)點(dian)(dian)焊機(ji)電(dian)(dian)(dian)極間頂先擠壓(ya),其(qi)作用是在(zai)(zai)焊件(jian)的焊接(jie)處(chu)形(xing)成緊密(mi)的接(jie)觸(chu)點(dian)(dian),為此(ci),電(dian)(dian)(dian)極壓(ya)力(li)在(zai)(zai)焊接(jie)電(dian)(dian)(dian)流接(jie)通前(qian)即應達到滿值(zhi)。如果在(zai)(zai)通電(dian)(dian)(dian)加(jia)熱時的電(dian)(dian)(dian)極壓(ya)力(li)不夠大(da),則(ze)接(jie)觸(chu)電(dian)(dian)(dian)阻(zu)很(hen)大(da),接(jie)觸(chu)點(dian)(dian)處(chu)的金(jin)屬很(hen)快(kuai)熔化,以火花形(xing)式飛濺出來,產生所謂初期(qi)飛濺。這時工件(jian)可(ke)能被燒穿(chuan),電(dian)(dian)(dian)極可(ke)能被燒壞。


2. 通電加熱階(jie)段


  被擠壓在(zai)(zai)電(dian)極之間(jian)的焊(han)件,靠(kao)電(dian)流通過接觸(chu)電(dian)阻及工件本身(shen)電(dian)阻所產(chan)生的熱量加熱。這時,在(zai)(zai)熱和機械(力)作(zuo)用下形(xing)(xing)成塑性環、熔(rong)(rong)核,并隨著通電(dian)加熱的進(jin)行(xing)而(er)長大,直到(dao)獲得需(xu)要的熔(rong)(rong)核尺寸。在(zai)(zai)焊(han)點核心內的熔(rong)(rong)化金屬(shu)被塑性環包圍,如(ru)果這個環不夠緊(jin),部(bu)分(fen)液態(tai)金屬(shu)就會(hui)溢出,形(xing)(xing)成金屬(shu)飛濺。


3. 冷卻結晶(jing)階(jie)段


  該階段又稱(cheng)鍛壓階段。當熔(rong)(rong)核(he)(he)達到合格的形狀與尺寸后(hou)(hou),切斷焊(han)接電(dian)(dian)流,液態(tai)熔(rong)(rong)核(he)(he)在電(dian)(dian)極壓力作(zuo)用下(xia)冷卻結(jie)(jie)晶(jing)。熔(rong)(rong)核(he)(he)結(jie)(jie)晶(jing)是在封(feng)閉的金屬(shu)模內進行的,結(jie)(jie)晶(jing)時不能(neng)自由收(shou)縮,用電(dian)(dian)極擠(ji)壓就可使正在結(jie)(jie)晶(jing)的金屬(shu)變(bian)得(de)致密,使之不易產生縮孔(kong)或(huo)裂縫。因此,電(dian)(dian)極壓力在焊(han)接電(dian)(dian)流斷開、熔(rong)(rong)核(he)(he)金屬(shu)全部(bu)結(jie)(jie)晶(jing)后(hou)(hou)才能(neng)解除。


由于材(cai)質和焊接規范特(te)征的(de)不同,熔(rong)核的(de)凝固(gu)組(zu)(zu)織(zhi)(zhi)可有三種(zhong):柱(zhu)狀組(zu)(zu)織(zhi)(zhi)、等(deng)(deng)軸(zhou)(zhou)(zhou)組(zu)(zu)織(zhi)(zhi)、柱(zhu)狀+等(deng)(deng)軸(zhou)(zhou)(zhou)組(zu)(zu)織(zhi)(zhi)。純金(jin)(jin)屬(如鎳、鉬等(deng)(deng))和結晶溫度區間窄的(de)合金(jin)(jin)(碳鋼、合金(jin)(jin)鋼、鈦合金(jin)(jin)等(deng)(deng)),其熔(rong)核組(zu)(zu)織(zhi)(zhi)為柱(zhu)狀組(zu)(zu)織(zhi)(zhi);鋁合金(jin)(jin)等(deng)(deng)其熔(rong)核為“柱(zhu)狀十(shi)等(deng)(deng)軸(zhou)(zhou)(zhou)”組(zu)(zu)織(zhi)(zhi),熔(rong)核完全是等(deng)(deng)軸(zhou)(zhou)(zhou)組(zu)(zu)織(zhi)(zhi)的(de)情況極(ji)少。



二、點焊工藝


1. 點焊種類及選用


 點(dian)焊(han)(han)(han)(han)(han)的種類(lei)有:工頻、交(jiao)流(liu)(liu)點(dian)焊(han)(han)(han)(han)(han),用(yong)于(yu)各種鋼(gang)材、鋁及其合金(jin)一般件焊(han)(han)(han)(han)(han)接;電容儲能點(dian)焊(han)(han)(han)(han)(han),用(yong)于(yu)異(yi)種金(jin)屬(shu)、鋁及其合金(jin)不等(deng)厚度及精密件和重要件的焊(han)(han)(han)(han)(han)接;直(zhi)流(liu)(liu)沖(chong)擊波點(dian)焊(han)(han)(han)(han)(han),用(yong)于(yu)鋁及其合金(jin)焊(han)(han)(han)(han)(han)接;低頻交(jiao)流(liu)(liu)點(dian)焊(han)(han)(han)(han)(han),用(yong)于(yu)大型磁(ci)性件焊(han)(han)(han)(han)(han)接。


2. 點焊接(jie)頭類(lei)型(xing)


  點(dian)焊的(de)(de)(de)接(jie)頭(tou)類型要(yao)充分考(kao)慮到點(dian)焊機電(dian)(dian)極(ji)能接(jie)近(jin)焊件(jian),做到施焊方(fang)便,加熱可靠(kao)。如圖6-22(a)~(d)所示的(de)(de)(de)是(shi)合理的(de)(de)(de)接(jie)頭(tou);(e)、(g)所示的(de)(de)(de)接(jie)頭(tou)難以用一(yi)般電(dian)(dian)極(ji)施焊;(f)所示的(de)(de)(de)接(jie)頭(tou)必(bi)須將電(dian)(dian)極(ji)伸人工件(jian)內部,施焊困難;(h)所示的(de)(de)(de)接(jie)頭(tou)的(de)(de)(de)分流(liu)現象嚴重,會(hui)影響焊接(jie)質(zhi)量。


圖 22.jpg


3. 焊件(jian)表面(mian)清理


  焊(han)(han)件表(biao)面(mian)狀態對焊(han)(han)點(dian)大小、強度和表(biao)面(mian)質量以及(ji)電極壽命有(you)直接影響。電極與焊(han)(han)件、焊(han)(han)件與焊(han)(han)件的接觸面(mian)均需清理(li)(li)。各種鋼材可(ke)用酸洗(xi)、噴砂或機械(xie)法清理(li)(li)。鋁合金(jin)等有(you)色金(jin)屬(shu)經(jing)酸洗(xi)或機械(xie)清理(li)(li)后,焊(han)(han)件的接觸面(mian)應有(you)一定的接觸電阻。不銹鋼還可(ke)用電拋光清理(li)(li)待焊(han)(han)表(biao)面(mian)。


4. 點焊規范參數的選(xuan)擇


  點焊(han)(han)(han)(han)規范(fan)參數(shu)主(zhu)要(yao)有:焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)(dian)流、通(tong)電(dian)(dian)(dian)(dian)時(shi)(shi)間(jian)、電(dian)(dian)(dian)(dian)極(ji)壓力和電(dian)(dian)(dian)(dian)極(ji)頭(tou)尺(chi)寸。一般焊(han)(han)(han)(han)各種鋼用(yong)平頭(tou)電(dian)(dian)(dian)(dian)極(ji),焊(han)(han)(han)(han)鋁或(huo)鈦合金用(yong)球(qiu)面電(dian)(dian)(dian)(dian)極(ji)。當電(dian)(dian)(dian)(dian)極(ji)材料、端面形狀及尺(chi)寸選(xuan)定以后(hou),焊(han)(han)(han)(han)接(jie)規范(fan)的(de)選(xuan)擇主(zhu)要(yao)是考慮(lv)焊(han)(han)(han)(han)接(jie)電(dian)(dian)(dian)(dian)流、通(tong)電(dian)(dian)(dian)(dian)時(shi)(shi)間(jian)和電(dian)(dian)(dian)(dian)極(ji)壓力這三個(ge)參數(shu),它們(men)是形成(cheng)點焊(han)(han)(han)(han)接(jie)頭(tou)的(de)三大要(yao)素,其相互配合可(ke)有兩種方式。


  ①. 焊(han)接電(dian)流和通電(dian)時(shi)間的(de)配合


   這種配合以(yi)反(fan)映焊接區加熱道度快慢為主(zhu)要(yao)特征。當(dang)采(cai)用(yong)大焊接電(dian)(dian)流、短通電(dian)(dian)時間參數時稱(cheng)為項(xiang)規范;而采(cai)用(yong)小(xiao)焊接電(dian)(dian)流、長通電(dian)(dian)時間參數時稱(cheng)為軟規范。


   硬規范(fan)(fan)的特點:生產率(lv)高,電(dian)極磨損(sun)少,焊(han)件表面壓坑淺(qian),熱(re)影響區小(xiao),焊(han)接(jie)變形小(xiao)。但是由于焊(han)接(jie)電(dian)流大,對通電(dian)時(shi)間必須精確控制。如(ru)果通電(dian)時(shi)間稍發生變化,就有可能(neng)引起加(jia)熱(re)不足(zu)或過燒,嚴重影響焊(han)點強度。當焊(han)機功率(lv)不足(zu)和焊(han)接(jie)淬硬傾(qing)向(xiang)較大的材(cai)料(如(ru)低(di)合金高強度鋼)時(shi),均(jun)不宜用(yong)硬規范(fan)(fan)。


  軟(ruan)(ruan)(ruan)規(gui)(gui)范的(de)(de)特(te)點(dian)(dian)(dian):加(jia)熱平穩,焊(han)接質量(liang)對規(gui)(gui)范參數波動的(de)(de)敏感性低,焊(han)點(dian)(dian)(dian)強度(du)穩定;溫度(du)場分布平緩、塑性區寬,在壓力(li)作(zuo)用下易變形(xing),可減少(shao)熔核內(nei)噴濺、縮孔和裂紋傾(qing)向;對有淬(cui)硬傾(qing)向的(de)(de)材料(liao),軟(ruan)(ruan)(ruan)規(gui)(gui)范可減少(shao)接頭冷裂紋傾(qing)向;所用設備容量(liang)小(xiao),控制精度(du)不高,因(yin)而較便宜(yi)。但是,軟(ruan)(ruan)(ruan)規(gui)(gui)范易造(zao)成焊(han)點(dian)(dian)(dian)壓痕(hen)深、接頭變形(xing)大,表面質量(liang)差;電極磨(mo)損快、生產效率低。


  一般硬(ying)規范適用于(yu)鋁合(he)金(jin)、奧氏(shi)體(ti)不銹鋼(gang)、低(di)碳鋼(gang)及(ji)不等厚(hou)度板(ban)材的焊接,而(er)軟規范適用于(yu)低(di)合(he)金(jin)鋼(gang)、可(ke)淬硬(ying)鋼(gang)+耐熱合(he)金(jin)及(ji)鈦合(he)金(jin)等。


 ②. 焊接電(dian)流和電(dian)極壓力(Fo)的配(pei)合


  這(zhe)種配(pei)合以焊(han)(han)(han)接(jie)過程中不產(chan)生噴(pen)濺(jian)為主(zhu)要特征。根據這(zhe)一原(yuan)則制(zhi)定的焊(han)(han)(han)接(jie)電(dian)(dian)(dian)流(liu)(I)、電(dian)(dian)(dian)極(ji)(ji)壓力(Fw)關系(xi)曲(qu)線(xian)稱為噴(pen)濺(jian)臨界曲(qu)線(xian)(見(jian)圖6-23).曲(qu)線(xian)左半區(qu)為無噴(pen)濺(jian)區(qu),這(zhe)里Fw大(da)而I小,但(dan)焊(han)(han)(han)接(jie)壓力選擇過大(da)會造成固相焊(han)(han)(han)接(jie)(塑性環)范圍過寬,導致焊(han)(han)(han)接(jie)質量(liang)不穩定。曲(qu)線(xian)右半區(qu)為噴(pen)濺(jian)區(qu),因為電(dian)(dian)(dian)極(ji)(ji)壓力不足,加熱(re)過快而引起噴(pen)濺(jian)。當規范選在噴(pen)濺(jian)臨界曲(qu)線(xian)附(fu)近(無噴(pen)濺(jian)區(qu)內)時,可獲(huo)得(de)最(zui)大(da)熔核和最(zui)高拉伸載荷。同時,由于(yu)降(jiang)低(di)了焊(han)(han)(han)機機械功率,也提高了經濟效果。


圖 23.jpg


 焊接規范的最后(hou)確定主要是(shi)用(yong)實驗法(fa),即先借用(yong)經驗數據→試焊→檢驗→確定。


③. 應用范(fan)圍(wei)


  點(dian)(dian)焊(han)廣泛應用(yong)(yong)(yong)在電(dian)(dian)子、儀表、家用(yong)(yong)(yong)電(dian)(dian)器的組合件連接上,同(tong)時(shi)也(ye)大(da)量(liang)應用(yong)(yong)(yong)于建筑工(gong)程、交(jiao)通運輸及航(hang)(hang)空航(hang)(hang)天工(gong)業中的沖壓件、金屬構件和鋼筋網的焊(han)接。目前(qian),從以微米計的微型電(dian)(dian)子電(dian)(dian)路到厚達(3.0+0.0)mm的巨型房框架都(dou)可采(cai)用(yong)(yong)(yong)點(dian)(dian)焊(han)連接。