鎢極(ji)(ji)氬(ya)弧焊(han)(han)(han)雖然能(neng)獲得優良的焊(han)(han)(han)接(jie)(jie)(jie)(jie)質量，但由(you)于(yu)受(shou)到鎢極(ji)(ji)許用(yong)電(dian)流的限(xian)制，焊(han)(han)(han)接(jie)(jie)(jie)(jie)電(dian)流不(bu)能(neng)用(yong)得太大。一般情況下(xia)，不(bu)開坡(po)口(kou)對(dui)接(jie)(jie)(jie)(jie)鎢極(ji)(ji)氬(ya)弧焊(han)(han)(han)時，可以焊(han)(han)(han)透(tou)厚(hou)度小于(yu)3mm的母(mu)材(cai)，超過此(ci)厚(hou)度的焊(han)(han)(han)件如要(yao)全焊(han)(han)(han)透(tou)，需對(dui)母(mu)材(cai)開坡(po)口(kou)。由(you)于(yu)鎢極(ji)(ji)氬(ya)弧焊(han)(han)(han)焊(han)(han)(han)接(jie)(jie)(jie)(jie)速(su)度慢，導致焊(han)(han)(han)接(jie)(jie)(jie)(jie)變形增加(jia)、焊(han)(han)(han)接(jie)(jie)(jie)(jie)接(jie)(jie)(jie)(jie)頭(tou)抗(kang)腐蝕性能(neng)下(xia)降，而且鎢極(ji)(ji)氬(ya)弧焊(han)(han)(han)焊(han)(han)(han)接(jie)(jie)(jie)(jie)時產生一定量的放射線對(dui)人(ren)體有一定的損害(hai)，因(yin)此(ci)焊(han)(han)(han)接(jie)(jie)(jie)(jie)中、厚(hou)板奧氏體不(bu)銹鋼時已不(bu)能(neng)很好的滿足實際(ji)生產的需求。

  熔(rong)(rong)化極(ji)(ji)(ji)氣體保護焊用(yong)焊絲作為電(dian)極(ji)(ji)(ji)（和填充金屬），焊接電(dian)流可以大(da)大(da)提(ti)高。由于熔(rong)(rong)深(shen)大(da)，焊絲熔(rong)(rong)敷(fu)速度(du)快，提(ti)高了生產效率，改善了勞(lao)動條(tiao)件，減少(shao)了焊接變形，同(tong)時(shi)還(huan)有利于提(ti)高焊接接頭耐腐蝕性能。熔(rong)(rong)化極(ji)(ji)(ji)氣體保護焊適(shi)用(yong)于中等和大(da)厚度(du)母材的焊接。

  熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)極(ji)氣體(ti)保(bao)護(hu)焊(han)(han)(han)，是用可(ke)熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)的焊(han)(han)(han)絲(si)(si)(si)與被(bei)焊(han)(han)(han)工(gong)件之間的電(dian)(dian)(dian)(dian)弧(hu)(hu)作(zuo)為熱源來熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)焊(han)(han)(han)絲(si)(si)(si)和母材金屬(shu)，并向(xiang)焊(han)(han)(han)接區輸送(song)保(bao)護(hu)氣體(ti)，使(shi)電(dian)(dian)(dian)(dian)弧(hu)(hu)、熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)的焊(han)(han)(han)絲(si)(si)(si)、熔(rong)(rong)(rong)(rong)(rong)(rong)池(chi)(chi)及附(fu)近金屬(shu)免受周(zhou)圍(wei)空氣的有害作(zuo)用，通過(guo)(guo)(guo)連續(xu)送(song)進焊(han)(han)(han)絲(si)(si)(si)不斷熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)并過(guo)(guo)(guo)渡(du)到熔(rong)(rong)(rong)(rong)(rong)(rong)池(chi)(chi)，形(xing)成焊(han)(han)(han)縫金屬(shu)。熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)極(ji)氣體(ti)保(bao)護(hu)焊(han)(han)(han)焊(han)(han)(han)接奧氏體(ti)型不銹鋼時的熔(rong)(rong)(rong)(rong)(rong)(rong)滴(di)(di)過(guo)(guo)(guo)渡(du)有滴(di)(di)狀過(guo)(guo)(guo)渡(du)、短路過(guo)(guo)(guo)渡(du)和噴(pen)(pen)射(she)(she)過(guo)(guo)(guo)渡(du)3種(zhong)。其中滴(di)(di)狀過(guo)(guo)(guo)渡(du)時，熔(rong)(rong)(rong)(rong)(rong)(rong)滴(di)(di)直徑比(bi)焊(han)(han)(han)絲(si)(si)(si)直徑大，飛濺較大，導致焊(han)(han)(han)接過(guo)(guo)(guo)程不穩(wen)定(ding)(ding)，在生產上極(ji)少使(shi)用。短路過(guo)(guo)(guo)渡(du)電(dian)(dian)(dian)(dian)弧(hu)(hu)間隙小，電(dian)(dian)(dian)(dian)弧(hu)(hu)電(dian)(dian)(dian)(dian)壓(ya)較低(di)，電(dian)(dian)(dian)(dian)弧(hu)(hu)功率比(bi)較小，適用于(yu)薄板焊(han)(han)(han)接。生產中應用最(zui)為廣泛的是噴(pen)(pen)射(she)(she)過(guo)(guo)(guo)渡(du)，對于(yu)一(yi)定(ding)(ding)的焊(han)(han)(han)絲(si)(si)(si)和保(bao)護(hu)氣體(ti)，當焊(han)(han)(han)接電(dian)(dian)(dian)(dian)流(liu)(liu)增大到臨界電(dian)(dian)(dian)(dian)流(liu)(liu)值時（圖4-44），焊(han)(han)(han)絲(si)(si)(si)端頭(tou)熔(rong)(rong)(rong)(rong)(rong)(rong)化(hua)的金屬(shu)被(bei)壓(ya)縮成筆尖(jian)狀，以細小熔(rong)(rong)(rong)(rong)(rong)(rong)滴(di)(di)從(cong)液柱尖(jian)端高(gao)速(su)軸向(xiang)射(she)(she)入熔(rong)(rong)(rong)(rong)(rong)(rong)池(chi)(chi)，即噴(pen)(pen)射(she)(she)過(guo)(guo)(guo)渡(du)，如圖4-45所(suo)示(shi)。