一、鎢極(ji)脈(mo)沖氬弧焊(han)工作原理

  鎢(wu)極脈(mo)(mo)沖(chong)氬(ya)弧(hu)(hu)焊(han)(han)(han)是在普通鎢(wu)極氬(ya)弧(hu)(hu)焊(han)(han)(han)基礎上發展起(qi)來(lai)的(de)(de)一種(zhong)新(xin)(xin)的(de)(de)焊(han)(han)(han)接工(gong)藝，通過(guo)(guo)控制(zhi)焊(han)(han)(han)接電(dian)(dian)(dian)流(liu)按一定頻(pin)率周期地變化(hua)。每一次脈(mo)(mo)沖(chong)電(dian)(dian)(dian)流(liu)通過(guo)(guo)時(shi)，焊(han)(han)(han)件(jian)被加熱熔(rong)化(hua)，形(xing)成一個點狀的(de)(de)熔(rong)池。脈(mo)(mo)沖(chong)電(dian)(dian)(dian)流(liu)處于停歇(xie)(xie)期間(jian)，點狀熔(rong)池冷(leng)凝(ning)，電(dian)(dian)(dian)弧(hu)(hu)由基值(zhi)電(dian)(dian)(dian)流(liu)維(wei)持(chi)燃燒（輸入(ru)給焊(han)(han)(han)件(jian)的(de)(de)能量(liang)很小），即以(yi)一個較小的(de)(de)基值(zhi)電(dian)(dian)(dian)流(liu)來(lai)維(wei)持(chi)一個電(dian)(dian)(dian)弧(hu)(hu)的(de)(de)電(dian)(dian)(dian)離(li)通道，以(yi)便下(xia)一次脈(mo)(mo)沖(chong)電(dian)(dian)(dian)流(liu)導通時(shi)，脈(mo)(mo)沖(chong)電(dian)(dian)(dian)弧(hu)(hu)能可靠(kao)地燃燒，熔(rong)化(hua)金屬，形(xing)成一個新(xin)(xin)的(de)(de)焊(han)(han)(han)點。只要合理地調節間(jian)歇(xie)(xie)時(shi)間(jian)和適當的(de)(de)焊(han)(han)(han)槍移(yi)動(dong)速度，保證相鄰兩焊(han)(han)(han)點之(zhi)間(jian)有一定的(de)(de)相互重疊量(liang)，就可獲得一條連續致密的(de)(de)焊(han)(han)(han)縫。脈(mo)(mo)沖(chong)電(dian)(dian)(dian)路原理見圖4-41。

二(er)、鎢極脈沖氬弧焊工藝特(te)點及(ji)其適用范(fan)圍

  在焊接厚度小于1mm奧氏體不銹鋼箔片和金屬軟管管坯時，若采用普通氬鎢極弧焊，焊接電流只允許用到幾安培或十幾安培。雖然所選用的鎢極直徑可以相應減小，但是電流密度仍然太小，導致鎢極局部的極斑飄移、電弧不穩；如果焊接電流調得大些，會使焊件過熱而燒穿。為了克服上述缺點，且又能保證連續焊接，在20世紀60年代研制成功了氣體保護脈沖電弧焊。它的工藝特點及其適用范圍如下。

   ①. 可(ke)(ke)調工藝(yi)參(can)數多，可(ke)(ke)以精確地控制待焊(han)(han)(han)件的熱輸入和熔池的形狀及尺寸。因而可(ke)(ke)提高焊(han)(han)(han)縫抗燒穿和熔池的保持能力(li)，易獲得均勻熔深。所(suo)以特別(bie)適用于薄板（薄至0.1mm）焊(han)(han)(han)接和全位置焊(han)(han)(han)接以及單面焊(han)(han)(han)背面成形的焊(han)(han)(han)接工藝(yi)。

   ②. 可(ke)以(yi)用較低的熱輸入獲得較大的熔深，這樣可(ke)以(yi)減少焊接熱影響區和(he)焊件變形。

   ③. 在焊(han)接過程中(zhong)，脈沖電(dian)流對(dui)點狀熔池(chi)(chi)有(you)較強的攪拌作用(yong)，而(er)且熔池(chi)(chi)金屬冷(leng)凝快，高(gao)溫停留時間短，焊(han)縫金屬組織(zhi)致密，可以減少敏感(gan)材料(liao)產生裂紋的傾向。對(dui)于奧(ao)氏體(ti)不銹鋼還(huan)能(neng)提高(gao)焊(han)接接頭的耐腐(fu)蝕性能(neng)。

   ④. 每個焊點加熱和冷(leng)卻迅(xun)速，很適(shi)合于焊接導熱性能強或厚(hou)度特別大的焊件。

   ⑤. 焊(han)縫成形美觀，質量(liang)穩定，焊(han)接(jie)接(jie)頭力(li)學(xue)性能高于(yu)普通鎢極氬(ya)弧(hu)焊(han)焊(han)接(jie)接(jie)頭力(li)學(xue)性能。

  根據(ju)脈(mo)沖(chong)頻率不同(tong)，可(ke)分為(wei)(wei)低頻脈(mo)沖(chong)氬弧焊和(he)高(gao)頻脈(mo)沖(chong)氬弧焊。鎢極脈(mo)沖(chong)氬弧焊可(ke)根據(ju)焊件的厚薄來選擇是否填加焊絲，也可(ke)以用氦氣(qi)作為(wei)(wei)保護氣(qi)體。

三、低頻脈沖氬弧焊(han)

  ①. 基(ji)本(ben)原理

    焊(han)(han)(han)接(jie)(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)大小(xiao)（直流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)或交流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)有效(xiao)值）呈周期(qi)性(xing)脈(mo)(mo)沖(chong)(chong)(chong)(chong)變(bian)(bian)化(hua)(hua)，脈(mo)(mo)沖(chong)(chong)(chong)(chong)的(de)頻(pin)率(lv)，從每秒(miao)接(jie)(jie)(jie)(jie)近于(yu)(yu)一次(ci)至(zhi)幾次(ci)，至(zhi)多不(bu)(bu)過(guo)十幾次(ci)，即以(yi)低頻(pin)脈(mo)(mo)沖(chong)(chong)(chong)(chong)的(de)方法供給電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)脈(mo)(mo)沖(chong)(chong)(chong)(chong)。圖4-42為常見的(de)脈(mo)(mo)沖(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)波形(xing)，從圖中可以(yi)看出脈(mo)(mo)沖(chong)(chong)(chong)(chong)焊(han)(han)(han)時(shi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)由兩(liang)個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)組成(cheng)：脈(mo)(mo)沖(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和(he)基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)；焊(han)(han)(han)接(jie)(jie)(jie)(jie)時(shi)間(jian)(jian)也是(shi)由脈(mo)(mo)沖(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)持續(xu)時(shi)間(jian)(jian)和(he)基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)持續(xu)時(shi)間(jian)(jian)兩(liang)部分組成(cheng)。它們是(shi)用(yong)來調節和(he)控(kong)制焊(han)(han)(han)縫熱輸入的(de)主(zhu)要參(can)數。在一個(ge)脈(mo)(mo)沖(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)期(qi)間(jian)(jian)，基(ji)(ji)本金屬熔(rong)(rong)(rong)化(hua)(hua)到(dao)一定的(de)熔(rong)(rong)(rong)深(shen)；隨之(zhi)，馬上轉變(bian)(bian)為一個(ge)小(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)（基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)），它的(de)主(zhu)要作(zuo)用(yong)是(shi)維持電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)不(bu)(bu)至(zhi)于(yu)(yu)熄滅，也提(ti)供一個(ge)熔(rong)(rong)(rong)池(chi)冷(leng)卻凝固條(tiao)件(jian)、使(shi)焊(han)(han)(han)件(jian)不(bu)(bu)至(zhi)于(yu)(yu)燒穿。其(qi)實，脈(mo)(mo)沖(chong)(chong)(chong)(chong)氬弧(hu)焊(han)(han)(han)所(suo)(suo)完成(cheng)的(de)連續(xu)焊(han)(han)(han)縫是(shi)由許多焊(han)(han)(han)點搭(da)接(jie)(jie)(jie)(jie)而(er)成(cheng)的(de)。焊(han)(han)(han)接(jie)(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)周期(qi)性(xing)變(bian)(bian)化(hua)(hua)，不(bu)(bu)僅能保證(zheng)得到(dao)一定的(de)熔(rong)(rong)(rong)深(shen)，又不(bu)(bu)至(zhi)于(yu)(yu)焊(han)(han)(han)穿工件(jian)，而(er)且隨著頻(pin)率(lv)節奏可以(yi)得到(dao)波紋美(mei)觀的(de)焊(han)(han)(han)縫。通(tong)過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)弧(hu)脈(mo)(mo)沖(chong)(chong)(chong)(chong)變(bian)(bian)化(hua)(hua)，使(shi)焊(han)(han)(han)接(jie)(jie)(jie)(jie)接(jie)(jie)(jie)(jie)頭金相組織(zhi)變(bian)(bian)得均(jun)勻，還細(xi)化(hua)(hua)了晶粒，從而(er)提(ti)高了焊(han)(han)(han)接(jie)(jie)(jie)(jie)接(jie)(jie)(jie)(jie)頭的(de)力學性(xing)能和(he)耐腐蝕能力。所(suo)(suo)以(yi)用(yong)脈(mo)(mo)沖(chong)(chong)(chong)(chong)氬弧(hu)焊(han)(han)(han)焊(han)(han)(han)接(jie)(jie)(jie)(jie)奧氏體(ti)型不(bu)(bu)銹鋼薄件(jian)和(he)中厚件(jian)是(shi)非常有益的(de)。

  ②. 工藝參數的選(xuan)擇

    脈(mo)(mo)(mo)沖(chong)(chong)鎢極氬弧焊的工藝(yi)參數(shu)主要有(you)脈(mo)(mo)(mo)沖(chong)(chong)電流(liu)幅值（Ip或(huo)ip）、基值電流(liu)（Ib或(huo)ib）、脈(mo)(mo)(mo)沖(chong)(chong)電流(liu)持續時(shi)(shi)(shi)間(jian)（tp）、基值電流(liu)持續時(shi)(shi)(shi)間(jian)（tb），其中(zhong)交流(liu)脈(mo)(mo)(mo)沖(chong)(chong)參數(shu)ip、ib分(fen)別指脈(mo)(mo)(mo)沖(chong)(chong)電流(liu)和基值電流(liu)在持續時(shi)(shi)(shi)間(jian)內的有(you)效值。此(ci)外還(huan)有(you)脈(mo)(mo)(mo)幅比(bi)RA、脈(mo)(mo)(mo)寬比(bi)Rw、脈(mo)(mo)(mo)沖(chong)(chong)周期T、脈(mo)(mo)(mo)沖(chong)(chong)頻率f，各參數(shu)之間(jian)的關(guan)系如(ru)下：

   脈沖鎢極氬弧焊的工藝參數，通常按下述(shu)原(yuan)則和步(bu)驟選擇。

     a. 對(dui)于一定的(de)(de)母材(cai)厚(hou)度(du)，脈沖電流Ip（或(huo)ip）取決(jue)于被焊母材(cai)的(de)(de)種類，而與母材(cai)厚(hou)度(du)無關，所以通常先(xian)按被焊材(cai)料選擇Ip（或(huo)ip），然后再按母材(cai)厚(hou)度(du)決(jue)定脈沖電流維持時間tp,不同材(cai)料及(ji)厚(hou)度(du)的(de)(de)Ip（或(huo)ip）及(ji)tp值(zhi)(zhi)可參(can)考(kao)圖4-43進行選擇。當(dang)焊接薄(bo)件時，Ip（或(huo)ip）值(zhi)(zhi)應選低于圖示(shi)的(de)(de)數(shu)值(zhi)(zhi)，同時適當(dang)延(yan)長tp值(zhi)(zhi)；焊接厚(hou)件時，Ip或(huo)i，值(zhi)(zhi)應稍(shao)高(gao)于圖示(shi)的(de)(de)數(shu)值(zhi)(zhi)，并(bing)適當(dang)縮短tp值(zhi)(zhi)。

     b. 基(ji)值(zhi)(zhi)電(dian)(dian)流(liu)(liu)Ib（或ib）與基(ji)值(zhi)(zhi)電(dian)(dian)流(liu)(liu)維(wei)持(chi)時(shi)間(jian)tb相互要(yao)匹配，應保證(zheng)電(dian)(dian)弧不(bu)熄弧和熔池在基(ji)值(zhi)(zhi)電(dian)(dian)流(liu)(liu)期間(jian)得以凝固。通常基(ji)值(zhi)(zhi)電(dian)(dian)流(liu)(liu)Ib是脈(mo)沖(chong)電(dian)(dian)流(liu)(liu)Ip（或ip）的10％～20％，基(ji)值(zhi)(zhi)電(dian)(dian)流(liu)(liu)維(wei)持(chi)時(shi)間(jian)tb為(wei)脈(mo)沖(chong)電(dian)(dian)流(liu)(liu)持(chi)續時(shi)間(jian)tp的1～3倍(bei)。

     c. 脈(mo)幅比(bi)RA和脈(mo)寬比(bi)Rw值較(jiao)大時(shi)，脈(mo)沖特點較(jiao)顯著，有利于克服熱(re)裂紋，但過大會增加咬邊傾向(xiang)。需(xu)在(zai)焊接過程中對焊接速度進(jin)行(xing)合(he)理調節(jie)來控(kong)制熔透率，避免(mian)產生(sheng)熱(re)裂紋和咬邊。

     d. 焊接速度要和脈(mo)沖(chong)頻(pin)率相匹配，以保證焊點(dian)間(jian)距的要求，它們(men)之間(jian)的關系是：

  Lw 不能太大，否則焊(han)點之間(jian)無重疊量(liang)，而得不到連(lian)續致(zhi)密的焊(han)縫，常用頻(pin)率一般低于10Hz，可參考表4-40選用。不銹鋼脈沖鎢(wu)極氬弧焊(han)焊(han)接工藝(yi)參數(shu)，可參考表4-41、表4-42。

四、高頻脈沖鎢極氬弧焊

   高(gao)(gao)頻(pin)(pin)脈(mo)(mo)沖(chong)鎢(wu)極(ji)氬(ya)弧(hu)(hu)(hu)焊(han)(han)(han)與(yu)低(di)頻(pin)(pin)脈(mo)(mo)沖(chong)氬(ya)弧(hu)(hu)(hu)焊(han)(han)(han)的(de)(de)(de)(de)不(bu)(bu)同之處(chu)，是焊(han)(han)(han)接(jie)(jie)電(dian)(dian)(dian)(dian)流以每秒鐘幾千次(ci)甚至幾萬(wan)次(ci)的(de)(de)(de)(de)極(ji)高(gao)(gao)頻(pin)(pin)率變化著。這(zhe)樣的(de)(de)(de)(de)高(gao)(gao)頻(pin)(pin)脈(mo)(mo)沖(chong)電(dian)(dian)(dian)(dian)流使電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)的(de)(de)(de)(de)磁收縮效應比較強(qiang)烈(lie)，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)直徑受到(dao)的(de)(de)(de)(de)壓縮更為激烈(lie)，增強(qiang)了電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)的(de)(de)(de)(de)挺度。同時(shi)使熔池能很好地攪拌，改善了焊(han)(han)(han)縫的(de)(de)(de)(de)冶(ye)金性(xing)能，特別適合(he)鋁(lv)及鋁(lv)合(he)金的(de)(de)(de)(de)焊(han)(han)(han)接(jie)(jie)。高(gao)(gao)頻(pin)(pin)脈(mo)(mo)沖(chong)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)產生的(de)(de)(de)(de)壓力還(huan)導致超(chao)聲(sheng)振動，它可(ke)以增強(qiang)熔化金屬的(de)(de)(de)(de)流動性(xing)。這(zhe)些(xie)都(dou)有利于細化晶粒，減少焊(han)(han)(han)縫氣(qi)孔，使焊(han)(han)(han)縫成形美觀。在(zai)(zai)焊(han)(han)(han)接(jie)(jie)電(dian)(dian)(dian)(dian)流平(ping)均(jun)值相等的(de)(de)(de)(de)情況下，高(gao)(gao)頻(pin)(pin)脈(mo)(mo)沖(chong)鎢(wu)極(ji)氬(ya)弧(hu)(hu)(hu)焊(han)(han)(han)的(de)(de)(de)(de)焊(han)(han)(han)接(jie)(jie)速度可(ke)比普(pu)通鎢(wu)極(ji)氬(ya)弧(hu)(hu)(hu)焊(han)(han)(han)提(ti)高(gao)(gao)1倍，這(zhe)就必然會縮短(duan)焊(han)(han)(han)縫金屬的(de)(de)(de)(de)高(gao)(gao)溫停留時(shi)間，對改善奧氏體型不(bu)(bu)銹鋼的(de)(de)(de)(de)耐蝕性(xing)是有益的(de)(de)(de)(de)。但是，這(zhe)種焊(han)(han)(han)接(jie)(jie)方法在(zai)(zai)施焊(han)(han)(han)過程中有刺(ci)耳的(de)(de)(de)(de)噪聲(sheng)。

   有關脈沖鎢極氬弧焊機(ji)的型號很多，表4-43列(lie)出(chu)了國內幾種脈沖鎢極氬弧焊機(ji)型號及其主要技術性能，可供選(xuan)用。