一、鎢極脈沖氬弧焊(han)工(gong)作(zuo)原理
鎢極(ji)脈(mo)沖(chong)氬弧(hu)(hu)(hu)焊(han)是在普通(tong)鎢極(ji)氬弧(hu)(hu)(hu)焊(han)基(ji)礎(chu)上(shang)發展起來的(de)一(yi)(yi)(yi)種新(xin)的(de)焊(han)接工藝(yi)，通(tong)過(guo)控制焊(han)接電(dian)(dian)(dian)(dian)流(liu)按一(yi)(yi)(yi)定頻率周期(qi)地變化。每一(yi)(yi)(yi)次(ci)(ci)脈(mo)沖(chong)電(dian)(dian)(dian)(dian)流(liu)通(tong)過(guo)時，焊(han)件被加(jia)熱熔(rong)化，形成一(yi)(yi)(yi)個(ge)點(dian)(dian)狀(zhuang)的(de)熔(rong)池。脈(mo)沖(chong)電(dian)(dian)(dian)(dian)流(liu)處于停歇(xie)(xie)期(qi)間，點(dian)(dian)狀(zhuang)熔(rong)池冷凝(ning)，電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)由(you)基(ji)值(zhi)電(dian)(dian)(dian)(dian)流(liu)維(wei)持燃燒（輸(shu)入給焊(han)件的(de)能(neng)量很小），即以(yi)一(yi)(yi)(yi)個(ge)較小的(de)基(ji)值(zhi)電(dian)(dian)(dian)(dian)流(liu)來維(wei)持一(yi)(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)的(de)電(dian)(dian)(dian)(dian)離通(tong)道(dao)，以(yi)便下一(yi)(yi)(yi)次(ci)(ci)脈(mo)沖(chong)電(dian)(dian)(dian)(dian)流(liu)導通(tong)時，脈(mo)沖(chong)電(dian)(dian)(dian)(dian)弧(hu)(hu)(hu)能(neng)可(ke)靠地燃燒，熔(rong)化金屬，形成一(yi)(yi)(yi)個(ge)新(xin)的(de)焊(han)點(dian)(dian)。只要合理地調節間歇(xie)(xie)時間和(he)適當的(de)焊(han)槍移動速度，保證相鄰兩焊(han)點(dian)(dian)之(zhi)間有一(yi)(yi)(yi)定的(de)相互重疊(die)量，就可(ke)獲(huo)得一(yi)(yi)(yi)條(tiao)連續致密的(de)焊(han)縫。脈(mo)沖(chong)電(dian)(dian)(dian)(dian)路原理見(jian)圖4-41。
二、鎢極脈沖氬(ya)弧焊工藝特點(dian)及其(qi)適用范(fan)圍
在焊接厚度小于1mm奧氏體(ti)不銹(xiu)鋼(gang)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)調工(gong)藝參數多，可(ke)以(yi)精確(que)地(di)控制待(dai)焊件(jian)的熱輸入和(he)熔池的形(xing)狀及尺寸。因而可(ke)提高(gao)焊縫抗燒穿和(he)熔池的保持能力(li)，易獲得均勻熔深。所以(yi)特別適用(yong)于(yu)薄板（薄至0.1mm）焊接(jie)和(he)全位(wei)置焊接(jie)以(yi)及單(dan)面(mian)焊背(bei)面(mian)成形(xing)的焊接(jie)工(gong)藝。
②. 可(ke)以用較低的熱輸入獲得較大(da)的熔(rong)深，這樣可(ke)以減少焊接熱影響區(qu)和焊件變(bian)形。
③. 在焊(han)接(jie)過程中，脈沖電流對點(dian)狀熔(rong)池有較強(qiang)的(de)攪拌作用(yong)，而且(qie)熔(rong)池金(jin)(jin)屬冷凝快，高溫(wen)停留時間短，焊(han)縫金(jin)(jin)屬組織致密(mi)，可以減少敏感材料產生裂(lie)紋的(de)傾向。對于奧(ao)氏體不銹鋼還(huan)能提高焊(han)接(jie)接(jie)頭的(de)耐腐蝕性(xing)能。
④. 每個(ge)焊點加熱和冷卻迅速，很(hen)適合于焊接(jie)導熱性能(neng)強或厚度特別大的焊件。
⑤. 焊縫成(cheng)形美(mei)觀，質(zhi)量(liang)穩定(ding)，焊接接頭(tou)力(li)學性能高于普通鎢極氬弧焊焊接接頭(tou)力(li)學性能。
根據脈沖(chong)(chong)頻率不同，可分為低頻脈沖(chong)(chong)氬(ya)弧(hu)(hu)焊(han)(han)和高頻脈沖(chong)(chong)氬(ya)弧(hu)(hu)焊(han)(han)。鎢極(ji)脈沖(chong)(chong)氬(ya)弧(hu)(hu)焊(han)(han)可根據焊(han)(han)件(jian)的厚薄來選(xuan)擇是否(fou)填加焊(han)(han)絲，也(ye)可以用氦氣(qi)作為保護氣(qi)體。
三、低頻脈沖氬弧焊
①. 基本原理
焊(han)(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)大小（直流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)或交流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)的(de)有效值）呈周期(qi)性(xing)脈(mo)沖(chong)(chong)(chong)變化，脈(mo)沖(chong)(chong)(chong)的(de)頻率(lv)，從(cong)每秒(miao)接(jie)(jie)(jie)近于一(yi)次(ci)至(zhi)幾次(ci)，至(zhi)多不(bu)過十幾次(ci)，即以(yi)低頻脈(mo)沖(chong)(chong)(chong)的(de)方法供(gong)給電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)脈(mo)沖(chong)(chong)(chong)。圖4-42為常見的(de)脈(mo)沖(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)波形，從(cong)圖中(zhong)(zhong)可以(yi)看出脈(mo)沖(chong)(chong)(chong)焊(han)(han)(han)(han)時(shi)的(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)由兩個(ge)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)組成(cheng)：脈(mo)沖(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和(he)基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)；焊(han)(han)(han)(han)接(jie)(jie)(jie)時(shi)間(jian)也(ye)是(shi)(shi)由脈(mo)沖(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)持(chi)(chi)續時(shi)間(jian)和(he)基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)持(chi)(chi)續時(shi)間(jian)兩部分組成(cheng)。它們是(shi)(shi)用來(lai)調節(jie)和(he)控(kong)制焊(han)(han)(han)(han)縫熱輸入的(de)主(zhu)要(yao)參數(shu)。在一(yi)個(ge)脈(mo)沖(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)期(qi)間(jian)，基(ji)(ji)本金屬熔(rong)化到一(yi)定的(de)熔(rong)深；隨(sui)之，馬(ma)上轉(zhuan)變為一(yi)個(ge)小電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)（基(ji)(ji)值電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)），它的(de)主(zhu)要(yao)作用是(shi)(shi)維持(chi)(chi)電(dian)(dian)(dian)(dian)(dian)弧(hu)不(bu)至(zhi)于熄滅，也(ye)提供(gong)一(yi)個(ge)熔(rong)池冷卻凝固條件(jian)(jian)、使焊(han)(han)(han)(han)件(jian)(jian)不(bu)至(zhi)于燒穿(chuan)。其實，脈(mo)沖(chong)(chong)(chong)氬弧(hu)焊(han)(han)(han)(han)所(suo)完成(cheng)的(de)連續焊(han)(han)(han)(han)縫是(shi)(shi)由許多焊(han)(han)(han)(han)點搭接(jie)(jie)(jie)而成(cheng)的(de)。焊(han)(han)(han)(han)接(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)周期(qi)性(xing)變化，不(bu)僅(jin)能(neng)保證得到一(yi)定的(de)熔(rong)深，又不(bu)至(zhi)于焊(han)(han)(han)(han)穿(chuan)工(gong)件(jian)(jian)，而且隨(sui)著頻率(lv)節(jie)奏可以(yi)得到波紋美(mei)觀的(de)焊(han)(han)(han)(han)縫。通(tong)過電(dian)(dian)(dian)(dian)(dian)弧(hu)脈(mo)沖(chong)(chong)(chong)變化，使焊(han)(han)(han)(han)接(jie)(jie)(jie)接(jie)(jie)(jie)頭(tou)金相組織變得均(jun)勻，還(huan)細化了晶粒，從(cong)而提高(gao)了焊(han)(han)(han)(han)接(jie)(jie)(jie)接(jie)(jie)(jie)頭(tou)的(de)力學(xue)性(xing)能(neng)和(he)耐腐蝕能(neng)力。所(suo)以(yi)用脈(mo)沖(chong)(chong)(chong)氬弧(hu)焊(han)(han)(han)(han)焊(han)(han)(han)(han)接(jie)(jie)(jie)奧氏體型不(bu)銹鋼薄件(jian)(jian)和(he)中(zhong)(zhong)厚件(jian)(jian)是(shi)(shi)非常有益的(de)。
②. 工藝參數(shu)的選擇
脈(mo)沖(chong)(chong)鎢極(ji)氬弧焊的(de)工藝(yi)參(can)數主要有脈(mo)沖(chong)(chong)電流(liu)幅(fu)值（Ip或ip）、基(ji)值電流(liu)（Ib或ib）、脈(mo)沖(chong)(chong)電流(liu)持(chi)(chi)續時間（tp）、基(ji)值電流(liu)持(chi)(chi)續時間（tb），其中交(jiao)流(liu)脈(mo)沖(chong)(chong)參(can)數ip、ib分別指脈(mo)沖(chong)(chong)電流(liu)和(he)基(ji)值電流(liu)在持(chi)(chi)續時間內的(de)有效值。此(ci)外還有脈(mo)幅(fu)比RA、脈(mo)寬比Rw、脈(mo)沖(chong)(chong)周(zhou)期T、脈(mo)沖(chong)(chong)頻率f，各參(can)數之間的(de)關系如下：
脈沖鎢(wu)極氬弧焊的工藝參數(shu)，通常(chang)按(an)下(xia)述原則和步驟選擇。
a. 對于一(yi)定(ding)的(de)母(mu)材(cai)厚(hou)度，脈沖(chong)電流Ip（或(huo)(huo)(huo)ip）取決(jue)于被(bei)焊(han)母(mu)材(cai)的(de)種(zhong)類，而與母(mu)材(cai)厚(hou)度無關，所以通常先按被(bei)焊(han)材(cai)料選(xuan)擇(ze)Ip（或(huo)(huo)(huo)ip），然(ran)后再按母(mu)材(cai)厚(hou)度決(jue)定(ding)脈沖(chong)電流維持時(shi)間tp,不同材(cai)料及(ji)厚(hou)度的(de)Ip（或(huo)(huo)(huo)ip）及(ji)tp值(zhi)(zhi)可參(can)考圖(tu)4-43進(jin)行選(xuan)擇(ze)。當(dang)焊(han)接(jie)薄件(jian)時(shi)，Ip（或(huo)(huo)(huo)ip）值(zhi)(zhi)應選(xuan)低于圖(tu)示(shi)的(de)數值(zhi)(zhi)，同時(shi)適當(dang)延(yan)長tp值(zhi)(zhi)；焊(han)接(jie)厚(hou)件(jian)時(shi)，Ip或(huo)(huo)(huo)i，值(zhi)(zhi)應稍高于圖(tu)示(shi)的(de)數值(zhi)(zhi)，并適當(dang)縮短tp值(zhi)(zhi)。
b. 基(ji)值(zhi)(zhi)電(dian)(dian)流Ib（或ib）與基(ji)值(zhi)(zhi)電(dian)(dian)流維持時(shi)(shi)間(jian)tb相(xiang)互要(yao)匹(pi)配，應保證電(dian)(dian)弧不熄(xi)弧和(he)熔池在基(ji)值(zhi)(zhi)電(dian)(dian)流期(qi)間(jian)得以凝固。通常基(ji)值(zhi)(zhi)電(dian)(dian)流Ib是脈(mo)沖(chong)電(dian)(dian)流Ip（或ip）的10％～20％，基(ji)值(zhi)(zhi)電(dian)(dian)流維持時(shi)(shi)間(jian)tb為脈(mo)沖(chong)電(dian)(dian)流持續(xu)時(shi)(shi)間(jian)tp的1～3倍。
c. 脈幅比(bi)RA和脈寬比(bi)Rw值較大(da)時，脈沖特點較顯著(zhu)，有利于克服熱裂紋(wen)，但過大(da)會增加咬(yao)邊傾向。需在焊接過程中對(dui)焊接速度進行(xing)合理調節來(lai)控制熔透率，避(bi)免產生熱裂紋(wen)和咬(yao)邊。
d. 焊接速度要和脈沖頻率(lv)相匹配，以保證焊點間距的要求，它們之間的關系是：
Lw 不(bu)能太大，否(fou)則(ze)焊點(dian)之間(jian)無重疊量，而得(de)不(bu)到連續致密(mi)的焊縫(feng)，常用頻率一般(ban)低(di)于10Hz，可(ke)參考(kao)表(biao)4-40選用。不(bu)銹鋼脈沖鎢極氬弧(hu)焊焊接工藝參數(shu)，可(ke)參考(kao)表(biao)4-41、表(biao)4-42。
四、高頻脈沖(chong)鎢極(ji)氬弧焊
高(gao)(gao)頻(pin)脈(mo)沖(chong)(chong)鎢(wu)(wu)極(ji)(ji)氬弧焊(han)(han)與低(di)頻(pin)脈(mo)沖(chong)(chong)氬弧焊(han)(han)的(de)(de)(de)不(bu)同(tong)之(zhi)處，是(shi)焊(han)(han)接(jie)電(dian)(dian)流(liu)以(yi)每秒鐘幾(ji)千次甚至幾(ji)萬次的(de)(de)(de)極(ji)(ji)高(gao)(gao)頻(pin)率變化著。這樣(yang)的(de)(de)(de)高(gao)(gao)頻(pin)脈(mo)沖(chong)(chong)電(dian)(dian)流(liu)使電(dian)(dian)弧的(de)(de)(de)磁收縮效應比(bi)較強(qiang)烈(lie)，電(dian)(dian)弧直徑受到的(de)(de)(de)壓縮更(geng)為激烈(lie)，增強(qiang)了電(dian)(dian)弧的(de)(de)(de)挺度。同(tong)時使熔(rong)池能(neng)很好(hao)地攪拌(ban)，改(gai)善(shan)了焊(han)(han)縫(feng)(feng)的(de)(de)(de)冶金(jin)(jin)性能(neng)，特別(bie)適合鋁(lv)及鋁(lv)合金(jin)(jin)的(de)(de)(de)焊(han)(han)接(jie)。高(gao)(gao)頻(pin)脈(mo)沖(chong)(chong)電(dian)(dian)弧產生的(de)(de)(de)壓力還(huan)導致(zhi)超(chao)聲振動(dong)，它(ta)可以(yi)增強(qiang)熔(rong)化金(jin)(jin)屬的(de)(de)(de)流(liu)動(dong)性。這些都有(you)利于(yu)細化晶粒，減少(shao)焊(han)(han)縫(feng)(feng)氣孔，使焊(han)(han)縫(feng)(feng)成形美觀(guan)。在(zai)焊(han)(han)接(jie)電(dian)(dian)流(liu)平均值(zhi)相等的(de)(de)(de)情況下，高(gao)(gao)頻(pin)脈(mo)沖(chong)(chong)鎢(wu)(wu)極(ji)(ji)氬弧焊(han)(han)的(de)(de)(de)焊(han)(han)接(jie)速度可比(bi)普通鎢(wu)(wu)極(ji)(ji)氬弧焊(han)(han)提高(gao)(gao)1倍，這就(jiu)必然會縮短(duan)焊(han)(han)縫(feng)(feng)金(jin)(jin)屬的(de)(de)(de)高(gao)(gao)溫停留(liu)時間(jian)，對改(gai)善(shan)奧氏體型不(bu)銹(xiu)鋼的(de)(de)(de)耐蝕性是(shi)有(you)益的(de)(de)(de)。但(dan)是(shi)，這種(zhong)焊(han)(han)接(jie)方(fang)法(fa)在(zai)施焊(han)(han)過程中有(you)刺耳的(de)(de)(de)噪聲。
有關脈(mo)沖(chong)鎢極氬(ya)弧焊機(ji)的(de)型號(hao)很多(duo)，表4-43列出了國內(nei)幾種(zhong)脈(mo)沖(chong)鎢極氬(ya)弧焊機(ji)型號(hao)及其主要(yao)技術性(xing)能(neng)，可供選(xuan)用。
