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外文翻譯1 焊接 美國焊接協(xié)會將焊接定義為：“金屬的局部結(jié)合”。在這部分金屬中，結(jié)合區(qū)是由加熱到適當(dāng)溫度而得到的，而這種適當(dāng)溫度的獲得，可以通過使用壓力或不使用壓力，使用填料金屬或不使用填料金屬。使用的填料金屬或者有與焊件相同或相近的熔點，或者熔點在其焊件以下，但必須在800℉以上。有34鐘焊接方法，它們分別如下： 氣焊 氣焊是一組焊接工藝方法的組合。說到這種焊接方法，其焊區(qū)是通過用一束氣體火焰或多束氣體火焰加熱，加壓或者不加壓，利用填料金屬材料或不使用填料材料而獲得的。 在所有氣焊方法中，人們最常使用的是氧乙炔焊。這種方法是利用氧氣和乙炔的混合氣體來產(chǎn)生熱量，利用焊劑可以降低焊區(qū)的氧化程度，從而獲得一個更好的焊點。這種焊接方法適用于黑色金屬（其中包括鑄鐵）和有色金屬，同時也能夠勝任比較厚的金屬焊件。 氫氧焊適用于熔點比較低的金屬。比如，鋁·鎂·和鉛。 加壓氣焊利用氧乙炔火焰作為熱源，但是，不需要填料金屬。相反，焊接熔合區(qū)一般通過對被加熱的構(gòu)件施加壓力獲得，或者在被加熱的過程中，或者在構(gòu)件加熱后，得到這種熔合區(qū)。這種焊接方法能夠用于黑色金屬和有色金屬當(dāng)中。 電弧焊 電弧焊是這樣一種焊接工藝方法：焊接區(qū)通過一束電弧或多束電弧加熱產(chǎn)生。在這過程中可以施加壓力，也可以不施加壓力；可以使用填料金屬，或不使用填料金屬獲得。有八種不同的電弧焊方法。它們是：（1）碳弧焊，（2）保護(hù)金屬電弧焊，（3）焊芯電弧焊，（4）氣保護(hù)金屬極電弧焊，（5）氣保護(hù)鎢極電弧焊，（6）埋弧焊，（7）等離子焊接，（8）電栓焊 。 在這些方法中，最常用的是保護(hù)金屬電弧焊。 它被定義為這樣一種焊接方法，在焊接過程中，焊接區(qū)是通過電弧焊產(chǎn)生的熱量而融化形成的，而這種電弧是在工件和覆蓋金屬藥皮的焊條中產(chǎn)生。這種保護(hù)來源于覆蓋電極的分解，其中并未施加壓力，填料金屬也來源于電極。 在人工和自動化生產(chǎn)裝備中，保護(hù)金屬電弧焊這種工藝方法都會用到。電極也可以用于黑色金屬（包括鑄鐵），所有不同型號的碳鋼，軸承鋼，銅合金鋼，鋁，鎳，鎳合金，和其他銅制品。這種焊接技術(shù)用于很多領(lǐng)域，尤其用在機(jī)械，交通設(shè)備，管道系統(tǒng)的生產(chǎn)和不同的結(jié)構(gòu)中。例如，建筑，機(jī)座，構(gòu)架等等。下面介紹的兩種廣泛使用的焊接方法是埋弧焊工藝方法和等離子焊工藝方法。 埋弧焊 它是這樣一種電弧焊工藝方法：其中，焊接區(qū)通過加熱產(chǎn)生，而這種加熱是通過一束或多束電弧實現(xiàn)的，電弧又是由一個單金屬極或多個金屬極和工件之間產(chǎn)生的。這種電弧由位于工件上的粒狀的可熔化地材料所保護(hù)，在這個過程中，可以不施加力，也可以施加力，而所需要的填料金屬，可以從電極中獲得。當(dāng)然，有時可以從附加的材料中獲得。 這種工藝方法能夠用于所有自動化設(shè)備中。在這種設(shè)備中，電極和粒狀焊劑的進(jìn)給量是被控制的。這種方法同樣也適用于半自動化生產(chǎn)裝備中，在這些半自動化生產(chǎn)裝備中，電極和粒狀焊劑的進(jìn)給量是有人工所控制的。既然，這種粒狀焊劑必須覆蓋焊接點，那么這種方法將被限制在只能用于水平位置的焊件，尤其適合那種比較長而又比較直的焊接點。同樣，比起其他焊接方法，人類通常需要保護(hù)金屬電弧焊去焊接那些比較厚的金屬。 埋弧焊可用于那些低碳鋼，高強(qiáng)度低合金鋼，烙合金鋼，烙鎳合金鋼。如果采用某些特別方法，那么也有可能焊接高合金鋼。 等離子焊 它是這樣一種焊接方法：其中焊接區(qū)已由加熱產(chǎn)生，而所需要的熱量是由一種壓縮電弧供應(yīng)，而這種壓縮電弧是在一個電極和工件（傳導(dǎo)電?。┊a(chǎn)生的，或者是在一個電極和壓縮噴嘴（非傳導(dǎo)電?。┊a(chǎn)生的。這種保護(hù)作用由一種熱的電離氣體實現(xiàn)的。這種氣體是從金屬環(huán)發(fā)射端發(fā)射出來，或者是由外加的輔助保護(hù)氣所提供。而這種保護(hù)氣或許是由一種插入式氣體，或是一種氣體混合物。外加壓力可以用，也可以不用，而且填料也可以用也可以不用。 等離子焊用于要求焊接質(zhì)量要求較高的焊接場所中，能夠焊接5英尺厚的鋁構(gòu)件中，或無縫鋼可以達(dá)到4英尺厚。既然沒有燃燒的物體供熱，那么焊接點便沒有高強(qiáng)度，不能夠承受高壓和沖擊載荷。 這種等離子電弧由處于一個金屬環(huán)中的電極所引導(dǎo)，而這個金屬環(huán)能夠通過電極引導(dǎo)內(nèi)部氣流。在這些等離子束中金屬環(huán)的發(fā)射末端在尺寸上比金屬環(huán)的上端尺寸小。這樣一個發(fā)射噴嘴便產(chǎn)生了較大氣流，另外一個噴嘴內(nèi)壁線性排列在一種陶瓷材料上。 雖然等離子束能夠由多種氣體產(chǎn)生，但必須保證這些氣體不被氧化，否則不應(yīng)該被使用。對這種要求較高的便是這種氣體的比熱容（熱量傳遞率），而不是它所能獲得的溫度。因此，較高比熱容的氣體能夠傳遞較多的熱量，這種特性使該氣體更使用于焊接，較大的構(gòu)件也可以。氬氣，氦氣，氫氣，也是比較常用的氣體。相比氬氣和氦氣，氫氣有比較高的比熱容，能夠產(chǎn)生溫度較高的電弧。 其它形式的電弧焊，即是：碳弧焊，焊芯電弧焊，氣保護(hù)金屬極電弧焊，氣保護(hù)鎢極電弧焊和電栓焊。這些焊接方法常用在一些特定場合中，或者批量生產(chǎn)。例如，碳弧焊被用于鍍鋅的薄片鋼，黃銅，青銅和鉛。然而，盡管焊芯電弧焊使用一種焊芯電極，但在批量生產(chǎn)中仍持續(xù)的需要從卷軸焊料中獲得。 電栓焊 它借助電栓焊槍來實現(xiàn)。電栓焊搶能夠?qū)⒁粋€電栓焊接到一個工件的表面。這種方法廣泛用于汽車，造船，鐵路及工廠基礎(chǔ)設(shè)施機(jī)構(gòu)建設(shè)。 電阻焊 它是一組焊接工藝方法的組合。在這種方法中，焊接區(qū)由加熱形成，而這些熱量來源于回路電阻。在電流回路中，工件作為電流回路的一部分，或者還要使用壓力。共有六種電阻焊工藝。它們是：（1）電阻電焊，（2）電阻縫焊，（3）凸焊，（4）閃光焊，（5）電阻對焊，（6）儲能焊。電阻焊應(yīng)用于批量生產(chǎn)中，借助合理的工具及控制系統(tǒng)，他很方便的適用于自動化生產(chǎn)當(dāng)中，其中也包括焊接后需要進(jìn)行預(yù)熱和進(jìn)行熱處理的任何工件中。在電阻焊中，使用最為廣泛的是電阻點焊，電阻縫焊以及凸焊。 電阻點焊： 電阻點焊是這樣一種焊接工藝方法，在接合面處的熔合區(qū)通過加熱而產(chǎn)生，其中這些熱量來源于通電電阻。通電回路是由在壓力作用下，通過幾個電極將工件連接在一起形成的。因此，所形成的焊接產(chǎn)品的形狀和尺寸主要有電極的尺寸和輪廓形狀所限制。電阻點焊僅僅局限于比較薄的金屬焊接當(dāng)中（例如，厚度在0.001英寸到0.125英寸的鋼和鎂，0.16英寸厚的鋁片）即是，鋼，鋁，鎂，鎳，鎳合金，青銅和黃銅。一些特性不相近的金屬可以進(jìn)行點焊，但是有困難。 電阻縫焊 他是這樣一種電焊工藝方法：在這種方法中，結(jié)合區(qū)的焊接由加熱產(chǎn)生，這種熱量來源于通電電阻，這種通電回路是由在壓力作用下，多個電極將工件連接起來的結(jié)果。最終的焊接有一系列的重疊的電阻焊接點所組成，而這些電阻焊接點是通過旋轉(zhuǎn)各電極逐次沿著某一條焊縫而形成的。原則上，電阻點焊與電阻縫焊是相近的。 電阻縫焊主要用于焊接質(zhì)量要球較高的焊件上，但這中焊接方法僅僅局限于焊接標(biāo)準(zhǔn)厚度的金屬版，而這些金屬板的厚度往往比那些用于點焊的金屬板的厚度要薄的多。而電阻縫焊所能勝任的標(biāo)準(zhǔn)焊件厚度范圍位于英寸0.100——0.125之間。 凸焊 它定義為這樣一種焊接方法：在這種焊接方法中，結(jié)合面處的焊接區(qū)由加熱產(chǎn)生，而這種熱量來源于通電電阻，這種通電回路是由在壓力作用下，多個電極將工件連接起來的結(jié)果。最終的焊接點位于預(yù)先決定的位置點上，而這些位置點往往由突出的隆起的部分以及相互接觸的位置所決定。 凸焊是和點焊相似的一種焊接方法。其不同點在于，凸焊往往使提供的熱量局部化，細(xì)化，從而使得這種方法能夠焊接比較厚的金屬材料。那么，由此以來，多處工件位置將可以進(jìn)行同時焊接。這樣，其最終結(jié)果便是在焊接結(jié)構(gòu)的強(qiáng)度上，該種方法將比電阻點焊大。 閃光焊 在這種工藝方法中，兩個對焊表面被固定地夾住，同時讓它們相距很近。結(jié)果將在這兩個對焊表面產(chǎn)生電弧，這樣產(chǎn)生的電弧將促使它們加熱到熔化溫度。在這個焊件上，兩個焊接表面通過外力結(jié)合在一起，完成了焊接。強(qiáng)加外力使得它們結(jié)合，這樣會使焊接金屬發(fā)生膨脹，將會向焊接點外部膨脹。在焊接完畢后，這部分多出來的金屬往往被除掉。預(yù)熱（對于大部分構(gòu)件來說）和過后熱處理（也就是熱處理），完全可以作為整個焊接程序的一部分。 能夠用于電阻點焊的材料，往往也能夠用于閃光焊，雖然這種方法大部分用于黑色金屬中，如銅，銅合金，還有一些鉛制品。不能夠使用這種方法獲得令人滿意的焊接點。但是，特性不相近的金屬卻可以使用這種工藝方法進(jìn)行焊接，甚至包括一些難熔的金屬，例如，鎢，鉬，以及鈦。 電阻對焊 電阻對焊這種工藝方法和閃光焊很相似，除了有一點不同，那就是在電路切斷之前，要焊接的工件彼此的緊密相接觸，因此在這種方法中，便沒有電弧光。電阻對焊廣泛用于管狀構(gòu)件的連接，銅管，大型銅環(huán)。當(dāng)然它也用于連接黑色和有色金屬條。 儲能焊（沖擊焊） 儲能焊是這樣一種焊接工藝方法：在這種工藝方法，焊接熔合區(qū)是通過熱量同時在整個對焊表面產(chǎn)生，而這種熱量來源于一束電弧，而這種電弧是由伴隨壓力突然間施加，電能快速釋放而產(chǎn)生的，這種力地施加，要么在電能釋放期間，要么緊跟其后。 儲能焊被用于特殊的焊接場合，（例如，焊接那些用閃光焊不經(jīng)濟(jì)的，特性不同的金屬）。這種焊接方法也被用于焊接針狀金屬，電栓，螺栓等等，以及焊接其他的零部件。例如，管道，金屬棒，或者細(xì)長管等它們之間的焊接或者它們與一些焊件的平面焊接。 釬焊 釬焊是這樣一種焊接工藝方法：在這種工藝方法中，焊接熔合區(qū)通過加熱到合適的溫度，以及用一種填料金屬而獲得的，而這種填料金屬擁有高于800℉的熔點，但是小于焊接件的凝固點。這種填料金屬通過毛細(xì)作用被放置在兩個距離很近的焊接件的表面?？偣灿辛N釬焊焊接工藝方法，它們是：（1）紅外線釬焊，（2）焊炬釬焊，（3）爐中釬焊，（4）感應(yīng)釬焊，（5）電阻加熱釬焊或者說接觸釬焊，（6）浸漬釬焊。在這些釬焊方法中，最主要的不同點，便是要焊接的金屬件其加熱的方式。同時，六種方法中，也只有四種方法對工業(yè)具有一定的重要性，即是:爐中釬焊，感應(yīng)加熱釬焊，和浸漬釬焊。這些方法的定義及其簡短的描述，在以下的段落中有所體現(xiàn)： 焊炬釬焊 這種焊接工藝方法可能會使用乙炔，天然氣，丁烷，或者再結(jié)合空氣，或者說氧氣用以供應(yīng)熱量，這種熱量用以熔化填料金屬并將填充于焊接件的兩表面，這種焊接技術(shù)并沒有廣泛的用于持續(xù)批量生產(chǎn)之中。 爐中釬焊 爐中釬焊是一種高生產(chǎn)率的焊接生產(chǎn)方法在這種方法中熱量有燃燒的氣體或者有電力加熱的汽油所供應(yīng)，這種爐具有盒子形狀或持續(xù)的曲線形狀。他是用一種線形網(wǎng)狀帶來傳送要被釬焊的工件。在焊接件被送入爐中之前，爐中釬焊要求預(yù)先成型的填料金屬，應(yīng)該放置在被焊接的工件上。這種釬焊方法非常適用于大量生產(chǎn)中，他能夠通過維持爐中的內(nèi)部環(huán)境而避免焊劑的使用。 感應(yīng)加熱釬焊 正如爐中釬焊的那樣，感應(yīng)加熱釬焊也要求使用成型的填料金屬。熱量是通過將需釬焊的零件放置在高頻感應(yīng)油當(dāng)中，焊接的工件被渦流加熱。因為焊接件提供電磁阻，用以改變其感應(yīng)區(qū)，加熱非常迅速，通過在感應(yīng)油中的合理成型，那么產(chǎn)生的熱量便能夠用于釬焊的主要焊接區(qū)域。當(dāng)設(shè)計合理的加工工具和進(jìn)給裝置安裝在生產(chǎn)設(shè)備中，那么感應(yīng)釬焊便能用于機(jī)械生產(chǎn)。 浸漬釬焊 工件可以通過兩種方法中的一種進(jìn)行釬焊。在化學(xué)浸漬釬焊中，要焊接的工件必須與預(yù)先成型的填料金屬同時準(zhǔn)備好，準(zhǔn)備好之后，將它們放進(jìn)一個裝有釬焊劑的熔池里。在金屬在熔池里進(jìn)行溶化的這道工序里，組裝的零件第一次被重新融化，然后進(jìn)漬在裝有填料金屬的金屬池里。釬焊的后一種方法主要用于焊接小的零件；然而，前一種方法便適用于焊接大的零件。 其他焊接工藝 除了前述的一些方法之外，還有一些固態(tài)的焊接技術(shù)和其他的焊接工藝方法。這些方法被美國工藝學(xué)會定義如下： 超聲波焊 一種焊接區(qū)域處于固態(tài)時的焊接工藝方法，而這種熔合區(qū)的獲得，是通過外加高頻振動能量實現(xiàn)的，而工件是通過外加壓力連接在一起。 摩擦焊 摩擦焊是一種固態(tài)焊接工藝方法，其熔合區(qū)的熱量獲得是從相互摩擦的兩表面的機(jī)械感應(yīng)的相對運(yùn)動中實現(xiàn)的。這些工件的連接也是通過施加外力實現(xiàn)的。 鍛焊 鍛焊它是一種固態(tài)焊接方法，其熔合區(qū)的熱量獲得是通過加熱或或使用壓力或充分的錘擊而在相互接觸的兩表面形成永久性的變形。 爆炸焊 爆炸焊它是一種固態(tài)焊接方法，其焊接熔合區(qū)受到高速運(yùn)動的影響。 擴(kuò)散焊 擴(kuò)散焊它是一種固態(tài)焊接方法，其兩接觸表面熔合區(qū)的獲得是通過壓力的使用和逐步升高的溫度。這種工藝方法并沒有牽扯到宏觀變形和工件的相對運(yùn)動。固態(tài)填料金屬可以使用也可以不使用。 冷焊 冷焊它是一種固態(tài)焊接方法，其兩接觸表面熔合區(qū)的獲得是僅僅通過外加機(jī)械壓力實現(xiàn)的。 熱劑焊 熱劑焊它是一系列的焊接工藝方法的組合，其兩接觸表面熔合區(qū)的獲得是通過加熱而實現(xiàn)的，熱量來源于溫度很高的液態(tài)金屬，或者來源于一種化學(xué)反應(yīng)的熱量。這種化學(xué)反應(yīng)是在一種金屬氧化物和鋁之間實現(xiàn)的。整個過程可以施加壓力也可以不施加壓力。當(dāng)使用這種方法時填料金屬是從液態(tài)金屬中獲得。 激光束焊 激光束焊是這樣的一種焊接方法，其兩接觸表面熔合區(qū)的獲得是通過加熱而實現(xiàn)的，熱量來源于固有激光束的使用，而這種激光束固在其金屬表面。 電子束焊 電子束焊是這樣的一種焊接方法，其兩接觸表面熔合區(qū)的獲得是通過加熱而實現(xiàn)的，熱量來源于高速電子運(yùn)動。 Welding The American Welding Society defines welding as “a localized coalescence of metals wherein coalescence is produced by heating to suitable temperatures with or without the application of pressure and with or without the use of the filler metal. The filler metal either has a melting point approximately the same as the base metals or has a melting point below that of the base metals but above 800 ℉.” There are 34 different welding processes. Gas Welding Gas welding is “a group of welding processes wherein coalescence is produced by heating with a gas flame or flames with or without the application of pressure and with or without the use of the filler material.” There are 3 different gas welding processes:oxyacetylene welding(OAW), oxhydrogen welding(OHW),pressure gas welding(PGW).Of the 3 types of gas welding, oxyacetylene welding(OAW) is the one most frequently employed.This method uses a mixture of oxygen and acetylene to produce heating.Fluxes may be used to reduce oxidation and to promote a better welding point.This type of welding is suitable for both ferrous (including cast iron) and nonferrous metals and is capable of welding thick metals sections. Oxyhydrogen welding(OHW) is used for low melting point metals such as aluminum,magnesium and lead. Pressure gas welding(PGW) uses an oxyacetylene flame for a heat source but does not require a filler rod.Instead,fusion is obtained by applying pressure to the heated parts,either while being heated or after the parts are heated.This form of welding can be used for jointing both ferrous and nonferrous metals. Arc Welding Arc welding is “a welding processes wherein coalescence is produced by heating with an arc or arcs with or without the application of pressure and with or without the use of filler metals.”There are eight different arc welding processes:(1) carbon-arc welding,(2) shielded metal-arc welding,(3) flux cored arc welding,(4) gas metal-arc welding,(5) gas tungsten-arc welding,(6) submerged arc welding,(7) plasma-arc welding,and (8)stud welding. The most widely used of these methods is the shielded metal-arc welding(SMAW) process. It is defined as an arc welding process wherein coalescence is produced by heating with an arc between a covered metal electrode and the work.Shielding is obtained from decomposition of the electrode covering.Pressure is not used and filler metal is obtained from the electrode. The shielded metal-arc process is employed in both manual and automated production setups.Electrodes are available that permit the welding of ferrous metals (including cast iron) ,all grades of carbon steels ,low-alloy high-strength steels,stainless steels,copper bearing steels, copper alloys,aluminum,nickel,nickel alloys, and bronze.This welding technique is used in many fields,particularly in the manufacture of machinery,transportation equipment,piping systems and in various strctures (for example,buildings,trusses,machine bases,and so on ). The next two most widely used arc welding methods are the submerged arc welding(SAW) process and the plasma-arc welding (PAW) process. Submerged arc welding (SAW) is “an arc welding process wherein coalescence is produced by heating with an arc or arcs between a bare metal electrodes and the work.The arc is shielded by a blanket of granular fuseable material on the work.Pressure is not used and filler metal is obtaind from the electrode and sometimes from a supplyementay welding rod. ” This method can be used in fully automated equipment where the feeds of both the electrode and granular flux are controlled.The method is also adaptable for semiautomatic equipment where the feeds of the electrode and granular flux are contolled manually .Since the granular flux must cover the joint to be welded, this method is restricted to parts in horizontal position and is particularly suited for welding long straight joints .Also,fewer passes are needed to weld thick metal sections than are usually required by shielded metal-arc welding. Submerged arc welding can be used to weld low carbon steels,high-strength low-alloy steels,chromium steels and austenitic chromium-nickle steels.With special methods, it is also possible to weld high-alloy air-hardening steels. Plasma-arc welding (PAW) is “an arc welding process wherein coalescence is produced by heating with a constricted arc between an electrode and the workpiece ( transferred arc ) or the electrode and the constricting nozzle ( nontransferred arc ) Shielding is obtained from the hot,ionized gas issuing from the orifice ,which may be supplemented by an auxiliary source of shielding gas.shielding gas may be an inert gas or a mixture of gases. Pressure may or may not be used ,and filler may or may not be used,and filler may or may not be supplied .” Plasma-arc welding is used for quality welding and can easily weld 5-in. thick aluminum sections or stainless sections up to 4-in.thick.Since there are no products of combustion,the welded joints have no porosity and display a strong resistance to high stresses and impact loading. The plasma torch is constructed with an electrode centrally within a metal cup that guides an inert streaming gas past the electrode.In the plasma-arc torch the discharge end of the cup is smaller in diameter than the upper diameter so that a discharge noozle is created.In addition ,the inner wall of the nozzle is lined with a ceramic material . Although a plasma stream can be created with any gas ,a gas that is nonoxidizing should be used .Another important requirement is thermal conductivity of the gas rather than the temperature it attains .Thus ,gases of the conductivity can transfer more heat ,making it possible to weld bulky sections more easily .Argon ,helium,and hydrogen,are the gases mostly frequently used. Hydrogen has the higher thermal conductivity and produces hotter arcs than those produced by argon or helium. Other forms of arc welding,namely, carbon-arc ,flux cored arc ,gas metal –arc,gas tungsten-arc ,and stud welding ,are used for joining particular metals or for mass production. For example ,whereas flux cored arc welding uses a flux cored electrode,continuously fed from a spool for quantity production. Stud welding is accomplished by means of a stud-welding gun,which welds a stud to the surface of a workpiece.The method is extensively employed in the automotive,shipbuildng,railroad,and building construction industries. Resistance Welding Resistance welding is “a group of welding processes wherein coalescence is produced by the heat obtained from resistance of the work to electric current in a circuit of which the work in a part ,and by the application of pressure.”There are six types of resistance welding processes.these are (1)resistance spot welding,(2)resistance seam welding,(3)projection welding,(4)flash welding,(5)upset welding, and (6)percussion welding.Resistance welding is widely used for quantity production.By means of proper controls and tooling,it is readily adaptable to automation,including any required welding are the spot,seam,and projection forms of welding. Resistance Spot Welding (RSW).”A resistance welding process wherein coalescene at the faying surfaces is produced in the heat obtained from the resistance to electric current through the work parts held together under pressure by electrodes.The size and shape of the individually formed welds are limited primarily by the size and contour of the electrodes.” Spot welding is primarily restricted to thin metals (for example,0.001 in thick to 0.125 in.thick for steel and magnesium,0.16 in. thick for aluminum ) ,namely,steels,stainless steels,aluminum,nixkel,nickel alloys,bronze ,and brass.Some dissimilar metals can be spot welded,but with difficulty. Resistance Seam Welding (RSW) “A resistance welding process wherein coalescene at the faying surfaces is produced in the heat obtained from the resistance to electric current through the work parts held together under pressure by electrodes. The resulting weld is a series of overlapping resistance-spot welds made progressively along a joint by rotating the electrodes.” In principle, seam welding is similar to spot welding except that the weld is continuous by virtue of the rollers rather than discontinuous as in spot welding. Seam welding is primarily used for quantity production but is restricted to joining metal gages that are thinner than those which can be joined by spot welding .The normal range of thicknesses compatible with seam welding is 0.100-0.125 in. Projection Welding (RPW) “A resistance welding process wherein coalescene at the faying surfaces is produced in the heat obtained from the resistance to electric current through the work parts held together under pressure by electrodes. The resulting welds are localized at predetermined points by projections ,embossment,and intersections.” Projection welding is a process similar to spot welding except that the projections tend to localize the heat ,permitting thicker materials to be welded.Simultaneous welds are readily made by this method ,and result in a stronger welded struture than that obtained with spot welding. Flash Welding (FW).In this process abutting surfaces to be welded are clamped in futures and brought within close proximity ( or light contact ) of each other so that an electric arc is surfaces are forced together, completing the weld .Forcing the two surfaces together causes the metal to be displaced ( that is ,bulge) outward from the welded joint. This upset metal is usually removed after welding. Preheating ( for large bulky parts ) and postheating ( that is heat treatment ) can readily be made part of the overall welding cycle. Materials that are easily welded by spot welding are also weldable by flash welding ,although the method is used mostly with ferrous metals. Copper, copper alloys and some aluminums can not be relied upon to produce satisfactorily welded joints. However, dissimilar metals can readily be welded by this methods, including even refractory metals such as tungsten , molybdenum ,and tantalum. Upset Welding (UW).A process similar to flash welding except the parts to be welded are held in close contact with each other before the electric circuit is cloded .Thus ,there is no flashing in this method. Upset welding is extensively used in the fabrication of tubular sections ,pipe,and heavy steel rings ;it is also used for joining small ferrous and nonferrous strips. Percussion Welding (PW). “A resistance welding process wherein coalescence is produced simultaneously over the entire abutting surfaces by heat obtained from an arc produced by a repaid discharge of electrical energe with pressure percussively applied during or immediately following the electrical discharge.” Percussion welding is used for special joining situations ( for example ,joining dissimalar metals that can not be welded economically by flash welding ).This welding method is also used to weld pins ,studs,bolts,and so on,to other components as well as to join sections of pipe,rod ,or tube to each other or to flat sections. Brazing Brazing is “a group of welding processes wherein coalescence is produced by the heat and by using a filler metal having a liquidus above 800 ℉ and below the solidus of the base metals .The filler metal is distributed between the closely fitted surfaces of the joint by capillary attraction”.There are six brazing welding methods .Those are (1)infrared brazing,(2)torch brazing,(3)furnace brazing ,(4)induction brazing,(5)resistance brazing ,(6)dip brazing. Among these methods ,the primary difference is the manner in which the metal to be joint are heated .Also ,only four of the six methods are of industrial importance ,torch brazing, furnace brazing,induction brazing,and dip brazing. These methods are defined and briefly described in the following paragraphs. Torch Brazing. (TB) A joint process that may employ acetylene ,natural gas ,butane,or propane in combination with air or oxygen to supply the heat required to melt the filler rod and diffuse it into the surface of the base metal.This technique is not extensively used for continuous mass production . Furnace Brazing .(FB) A high production fabrication method where the heat is supplied by gas or electric heating coils. The furnace of the box type or the continuous type ,which employ a wire mesh belt to transport the part to be brazed. Furnace brazing requires that preformed shapes of filler metal be placed on the parts to be jointed prior to entering the furnace .This method of brazing is well suited to high production and can avoid the use of fluxing by maintaining an insert atmosphere in the furnace. Induction Brazing .Like furnace brazing ,induction brazing requires the use of preformed shapes of filler metal .Heat is produced by placing the parts to be brazed within the field of a high frequency induction coil, the heat can be applied in the local area of the joint to be brazed.Induction brazing can be used for mechanized production when properly designed tooling and feeding devices are incorporated into the production setup. Dip Brazing .(DB) Parts can be dip brazed by one of two methods. In chemical dip brazing,the parts to be jointed are prepared with preformed filler metal,after which they are placed into a molten bath brazing flux .In the molten metal bath process,the assembled parts are first refluxed and then immersed into a molten bath of filler metal. This latter method of brazing is restricted to small parts,whereas the former method is more adaptable for joining large parts. Other Welding Processes The master chart of welding processes shows,in addition to the aforementioned methods,a series of solid state welding techniques and some other processes. These methods are defined by the American Welding Society as following: Ultrasonic Welding (UW) A solid state welding process wherein coalescence is produced by the local application of high frequency vibratory energy as the work parts are held together under pressure . Friction Welding.(FW) A solid state welding process wherein coalescence is produced by the heat obtained from mechanically induced sliding motion between rubbing surfaces.The parts are held together under pressure.” Forge Welding .(FW) A solid state welding process wherein coalescence is produced by heating and by applying the pressure or blows sufficient to cause permanent deformation at the interface .” Explosion Welding .( EW ) A solid state