鎢(wu)極(ji)(ji)(ji)氬(ya)弧(hu)焊(han)(han)雖(sui)然(ran)能(neng)獲(huo)得優良的(de)焊(han)(han)接(jie)(jie)(jie)質量，但由于(yu)受到鎢(wu)極(ji)(ji)(ji)許用電流的(de)限制，焊(han)(han)接(jie)(jie)(jie)電流不能(neng)用得太大。一(yi)(yi)般(ban)情況下(xia)，不開(kai)坡口對接(jie)(jie)(jie)鎢(wu)極(ji)(ji)(ji)氬(ya)弧(hu)焊(han)(han)時(shi)(shi)，可以焊(han)(han)透厚度(du)小(xiao)于(yu)3mm的(de)母(mu)材，超過此(ci)厚度(du)的(de)焊(han)(han)件如要全焊(han)(han)透，需對母(mu)材開(kai)坡口。由于(yu)鎢(wu)極(ji)(ji)(ji)氬(ya)弧(hu)焊(han)(han)焊(han)(han)接(jie)(jie)(jie)速度(du)慢，導致焊(han)(han)接(jie)(jie)(jie)變形增加、焊(han)(han)接(jie)(jie)(jie)接(jie)(jie)(jie)頭抗腐蝕性能(neng)下(xia)降，而且鎢(wu)極(ji)(ji)(ji)氬(ya)弧(hu)焊(han)(han)焊(han)(han)接(jie)(jie)(jie)時(shi)(shi)產生一(yi)(yi)定量的(de)放射(she)線對人(ren)體有(you)一(yi)(yi)定的(de)損害，因此(ci)焊(han)(han)接(jie)(jie)(jie)中、厚板奧氏(shi)體不銹鋼時(shi)(shi)已不能(neng)很好的(de)滿足實際生產的(de)需求。

  熔(rong)(rong)化(hua)極(ji)氣體保護焊(han)用焊(han)絲作為電極(ji)（和(he)填(tian)充金屬），焊(han)接電流可以(yi)大大提(ti)高(gao)。由于熔(rong)(rong)深(shen)大，焊(han)絲熔(rong)(rong)敷(fu)速度快，提(ti)高(gao)了生(sheng)產效(xiao)率，改善了勞動條(tiao)件(jian)，減少(shao)了焊(han)接變形，同時還有利(li)于提(ti)高(gao)焊(han)接接頭耐腐蝕性能。熔(rong)(rong)化(hua)極(ji)氣體保護焊(han)適(shi)用于中等和(he)大厚度母(mu)材(cai)的焊(han)接。

  熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)極氣(qi)(qi)體(ti)保(bao)(bao)護焊(han)(han)(han)(han)(han)(han)(han)，是(shi)用(yong)(yong)可熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)的(de)焊(han)(han)(han)(han)(han)(han)(han)絲(si)與被(bei)(bei)焊(han)(han)(han)(han)(han)(han)(han)工件之間的(de)電(dian)弧(hu)作為(wei)熱源來熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)焊(han)(han)(han)(han)(han)(han)(han)絲(si)和母材金(jin)屬(shu)，并向(xiang)焊(han)(han)(han)(han)(han)(han)(han)接區輸送(song)保(bao)(bao)護氣(qi)(qi)體(ti)，使(shi)電(dian)弧(hu)、熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)的(de)焊(han)(han)(han)(han)(han)(han)(han)絲(si)、熔(rong)(rong)(rong)(rong)(rong)池及附近金(jin)屬(shu)免(mian)受周圍空氣(qi)(qi)的(de)有(you)害作用(yong)(yong)，通過連續送(song)進焊(han)(han)(han)(han)(han)(han)(han)絲(si)不斷熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)并過渡(du)(du)到(dao)(dao)熔(rong)(rong)(rong)(rong)(rong)池，形成(cheng)焊(han)(han)(han)(han)(han)(han)(han)縫金(jin)屬(shu)。熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)極氣(qi)(qi)體(ti)保(bao)(bao)護焊(han)(han)(han)(han)(han)(han)(han)焊(han)(han)(han)(han)(han)(han)(han)接奧氏體(ti)型(xing)不銹鋼時(shi)的(de)熔(rong)(rong)(rong)(rong)(rong)滴(di)過渡(du)(du)有(you)滴(di)狀(zhuang)過渡(du)(du)、短路過渡(du)(du)和噴(pen)(pen)射(she)過渡(du)(du)3種。其中滴(di)狀(zhuang)過渡(du)(du)時(shi)，熔(rong)(rong)(rong)(rong)(rong)滴(di)直徑(jing)比(bi)焊(han)(han)(han)(han)(han)(han)(han)絲(si)直徑(jing)大，飛濺較大，導致焊(han)(han)(han)(han)(han)(han)(han)接過程不穩定，在生產上(shang)極少(shao)使(shi)用(yong)(yong)。短路過渡(du)(du)電(dian)弧(hu)間隙小(xiao)(xiao)(xiao)，電(dian)弧(hu)電(dian)壓較低，電(dian)弧(hu)功率(lv)比(bi)較小(xiao)(xiao)(xiao)，適用(yong)(yong)于(yu)薄板(ban)焊(han)(han)(han)(han)(han)(han)(han)接。生產中應用(yong)(yong)最為(wei)廣泛的(de)是(shi)噴(pen)(pen)射(she)過渡(du)(du)，對于(yu)一定的(de)焊(han)(han)(han)(han)(han)(han)(han)絲(si)和保(bao)(bao)護氣(qi)(qi)體(ti)，當(dang)焊(han)(han)(han)(han)(han)(han)(han)接電(dian)流(liu)增大到(dao)(dao)臨界電(dian)流(liu)值時(shi)（圖4-44），焊(han)(han)(han)(han)(han)(han)(han)絲(si)端頭熔(rong)(rong)(rong)(rong)(rong)化(hua)(hua)的(de)金(jin)屬(shu)被(bei)(bei)壓縮(suo)成(cheng)筆尖狀(zhuang)，以細小(xiao)(xiao)(xiao)熔(rong)(rong)(rong)(rong)(rong)滴(di)從液柱尖端高(gao)速軸向(xiang)射(she)入(ru)熔(rong)(rong)(rong)(rong)(rong)池，即噴(pen)(pen)射(she)過渡(du)(du)，如(ru)圖4-45所示。