點焊工件只在有限的接觸面上即所謂“點”上被焊接起來,并形成扁球形的熔核。點焊又分為單點焊和多點焊,多點焊時使用兩對以上的電極,在同一工序內形成多個熔核。點焊方法通常又分為雙面點焊和單面點焊兩大類。雙面點焊時,通常采用搭接接頭和折邊接頭兩種形式(圖6-11).接頭可以由兩個或兩個以上等厚度或不等厚度的工件組成。在設計點焊結構時,必須考慮電極的可達性,即電極必須能方便地抵達構件的焊接部位。同時還應考慮邊距、搭接量、點距、裝配間隔和焊點強度等因素。

由于不銹鋼的電阻率高、導熱性差,因此與低碳鋼相比,可采用較小的焊接電流和較短的焊接時間。不銹鋼有較高的高溫強度,必須采用較高的電極壓力,以防止產生縮孔、裂紋等缺陷。不銹鋼的熱敏感性強,通常采用較短的焊接時間、強有力的內部和外部水冷卻,并且要準確地控制加熱時間和焊接電流,以防熱影響區晶粒長大和出現晶(jing)間腐蝕現象。點焊不銹鋼的電極推薦用硬度較高的電極合金,滿足高電極壓力的需要。
馬氏體不銹鋼由于有淬火(huo)傾向,點焊(han)(han)時要求(qiu)采(cai)用較長(chang)焊(han)(han)接時間。為消除淬硬組織,最好(hao)采(cai)用焊(han)(han)后回火(huo)的雙脈(mo)沖點焊(han)(han)。點焊(han)(han)時一(yi)般(ban)不采(cai)用電極的外部水冷(leng)卻,以免因淬火(huo)而產生(sheng)裂(lie)紋。
單(dan)(dan)面(mian)點(dian)(dian)(dian)焊(han)(han)時(shi),電(dian)(dian)(dian)極(ji)(ji)由(you)工件(jian)的(de)(de)(de)(de)(de)同一(yi)側向焊(han)(han)接(jie)處饋電(dian)(dian)(dian)。典型(xing)的(de)(de)(de)(de)(de)單(dan)(dan)面(mian)點(dian)(dian)(dian)焊(han)(han)方式如(ru)圖6-12所示(shi)。圖中:(a)單(dan)(dan)面(mian)單(dan)(dan)點(dian)(dian)(dian)點(dian)(dian)(dian)焊(han)(han),不(bu)形(xing)成焊(han)(han)點(dian)(dian)(dian)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)極(ji)(ji)采用大(da)直徑和大(da)接(jie)觸面(mian)以減(jian)(jian)小電(dian)(dian)(dian)流(liu)密度(du)。(b)無(wu)分流(liu)的(de)(de)(de)(de)(de)單(dan)(dan)面(mian)雙(shuang)點(dian)(dian)(dian)點(dian)(dian)(dian)焊(han)(han),此時(shi)焊(han)(han)接(jie)電(dian)(dian)(dian)流(liu)全部流(liu)經焊(han)(han)接(jie)區(qu)。(c)有(you)分流(liu)的(de)(de)(de)(de)(de)單(dan)(dan)面(mian)雙(shuang)點(dian)(dian)(dian)點(dian)(dian)(dian)焊(han)(han),流(liu)經上面(mian)工件(jian)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)流(liu)不(bu)經過焊(han)(han)接(jie)區(qu),形(xing)成分流(liu)。為了(le)(le)給(gei)焊(han)(han)接(jie)電(dian)(dian)(dian)流(liu)提供低電(dian)(dian)(dian)阻的(de)(de)(de)(de)(de)通(tong)路。在工件(jian)下面(mian)墊(dian)有(you)銅墊(dian)板。(d)當(dang)兩焊(han)(han)點(dian)(dian)(dian)的(de)(de)(de)(de)(de)間(jian)距很大(da),如(ru)在進行骨架構件(jian)和復板的(de)(de)(de)(de)(de)焊(han)(han)接(jie)時(shi),為了(le)(le)避免不(bu)適當(dang)的(de)(de)(de)(de)(de)加(jia)熱引(yin)起翹曲和減(jian)(jian)小兩電(dian)(dian)(dian)極(ji)(ji)間(jian)電(dian)(dian)(dian)阻,采用了(le)(le)特殊的(de)(de)(de)(de)(de)銅橋A,與電(dian)(dian)(dian)極(ji)(ji)同時(shi)壓緊在工件(jian)上。


