1、第一章第一章材料連接技術的發(fā)展狀況材料連接技術的發(fā)展狀況2Categories of Joining Technologies Mechanical Joining Adhesive Bonding Welding 45%3連接技術的分類（1） 機械連接 膠接 焊接 45%4連接技術的分類（連接技術的分類（2） 機械連接機械連接 鉚接鉚接-使用鉚釘連接兩件或兩件以上的工件叫鉚接。使用鉚釘連接兩件或兩件以上的工件叫鉚接。 螺栓連接。螺栓連接。5連接技術的分類（連接技術的分類（3） 機械連接機械連接 實例照片實例照片6 膠接膠接 膠接技術是借助膠粘劑在固體表面上所產生的粘合膠接技術是借助膠粘劑在固

2、體表面上所產生的粘合力力,將同種或不同種材料牢固地連接在一起的方法。將同種或不同種材料牢固地連接在一起的方法。連接技術的分類（連接技術的分類（4）7 焊接焊接 通過加熱或加壓或二者并用，使被焊材料達到原子通過加熱或加壓或二者并用，使被焊材料達到原子間的結合，從而形成永久性連接的工藝。間的結合，從而形成永久性連接的工藝。連接技術的分類（連接技術的分類（5）89Applications of Friction Stir WeldingLeft top: the 2195 Al-Li Space Shuttle external tankLeft bottom: The Eclipse 500 bu

3、siness class jetRight: Mazda RX-8 rear doorFrom Welding Journal 200810Definition of Welding The process of joining together two pieces of metal so that bonding accompanied by appreciable interatomic penetration takes place at their original boundary surfaces. The boundaries more or less disappear at

4、 the weld, and integrating crystals develop across them. Welding is carried out by the use of heat or pressure or both and with or without added metal.11焊接的定義焊接的定義 焊接技術是指將兩種或兩種以上的（同種或異焊接技術是指將兩種或兩種以上的（同種或異種）材料通過種）材料通過原子或分子之間的結合和擴散原子或分子之間的結合和擴散造造成成永久性連接永久性連接的工藝過程。的工藝過程。 宏觀上：永久性聯(lián)系宏觀上：永久性聯(lián)系 微觀上：組織之間的內部聯(lián)

5、系微觀上：組織之間的內部聯(lián)系12Advantages and disadvantages of weldingAdvantagesJoints are permanent, precluding accidental (or even intentional) disassembly and looseningWide variety of process embodimentsApplicability to many materials within a fundamental classCan be portableReasonable overall cost, usuallyProv

6、ides leak tightness with continuous weldsDisadvantagesPrevents/precludes disassembly for any purposeHeat of some welding (especially involving fusion) disrupts base material propertiesPrecludes joining between materials from different classesUnbalanced heat input leads to distortion or residual stre

7、ssesRequires considerable operator skillCan be expensive due to skilled labor rates or due to labor intensity for thick, long, or critical weldsCapital equipment can be expensive, especially for some automated processes13Schematic illustration of the various microstructural zones in a typical fusion

8、 weld14Types of jointsWelding joints variationsWelding positions15Classification of Welding Processes Fusion welding gas welding, shielded metal arc welding, gas metal arc welding (aka. MIG), gas tungsten arc welding (aka. TIG), plasma arc welding, submerged arc welding, electroslag welding, electro

9、n beam welding, laser beam welding, etc. Pressure welding resistance welding, friction welding, diffusion welding, flash welding, explosion welding, ultrasonic welding, friction stir welding, etc. Brazing and Soldering 450 oC (840 oF) induction, furnace, dip, torch, resistance, etc.How many more wel

10、ding processes can you name?Arc weldingLaser beam weldingSoldering 16焊接方法的分類焊接方法的分類 熔焊熔焊 氣焊、焊條電弧焊、熔化極氣體保護焊（氣焊、焊條電弧焊、熔化極氣體保護焊（MIG）、鎢極氣）、鎢極氣體保護焊（體保護焊（TIG）、等離子弧焊、埋弧焊、電子束焊、激）、等離子弧焊、埋弧焊、電子束焊、激光焊、電渣焊等光焊、電渣焊等 壓焊壓焊 電阻焊、摩擦焊、擴散焊、冷壓焊、爆炸焊、超聲波焊、電阻焊、摩擦焊、擴散焊、冷壓焊、爆炸焊、超聲波焊、攪拌摩擦焊等攪拌摩擦焊等 釬焊釬焊 軟釬焊、硬釬焊軟釬焊、硬釬焊 感應釬焊、爐中釬焊、

11、浸沾釬焊、火焰釬焊、電阻釬焊等感應釬焊、爐中釬焊、浸沾釬焊、火焰釬焊、電阻釬焊等17Gas Welding Gas welding is a welding process that melts and joins metals by heating them with a flame caused by the reaction between a fuel gas and oxygen. Fuel gases: acetylene (乙炔), propane (丙烷), propylene (丙烯), hydrogen (氫氣), etc. Oxyacetylene welding (OA

12、W, 氧乙炔焊氧乙炔焊) is the most commonly used gas welding process because of its high flame temperature or source energy.18氣焊氣焊 氣焊是金屬熔焊方法的一種，所需要的熱源由氣氣焊是金屬熔焊方法的一種，所需要的熱源由氣體火焰提供。體火焰提供。 所用燃氣有乙炔、丙烷、丙烯、氫氣等，但乙炔所用燃氣有乙炔、丙烷、丙烯、氫氣等，但乙炔在氣焊中占主導地位。氧在氣焊中占主導地位。氧-乙炔氣焊最常用乙炔氣焊最常用（Oxy-Acetylene Welding ）。）。 氣焊的應用范圍越來越小。常用于黑色

13、金屬焊接。氣焊的應用范圍越來越小。常用于黑色金屬焊接。在建筑、安裝、裝修及野外施工等沒有電源的場在建筑、安裝、裝修及野外施工等沒有電源的場所，無法進行電焊時常使用氣焊。所，無法進行電焊時常使用氣焊。 與氣割的區(qū)別。與氣割的區(qū)別。19Gas Welding20氣焊設備氣焊設備 氧氣瓶氧氣瓶 氧氣減壓器氧氣減壓器 乙炔瓶乙炔瓶 回火保險器回火保險器 焊炬（槍）焊炬（槍） 橡皮管橡皮管氣焊氣焊焊炬構造圖焊炬構造圖21Three types of flames in oxyacetylene welding(a 中性火焰中性火焰, b 碳化火焰碳化火焰, c 氧化火焰氧化火焰)O2:C2H2=1:1O

14、2:C2H21:1for brassfor aluminum,high-carbon steelsfor most metalsGas Welding22Gas WeldingChemical reactions and temperature distribution in a neutral oxyacetylene flame23Advantages The equipment is simple, portable, and inexpensive The temperature in the weld pool is controllable For all-position wel

15、ding Field construction without electrical source Convenient for maintenance and repair applicationsDisadvantages Limited power density, low welding speed, high total heat input per unit length of the weld Large heat-affected zones Severe distortion Mostly operated manually, high requirements of lab

16、or skills Poor working conditionsGas Welding24氣焊優(yōu)點氣焊優(yōu)點 焊接熔池溫度易于控制，焊接熔池溫度易于控制，可以全位置焊接可以全位置焊接 不需要電源，可在野外施不需要電源，可在野外施工工 設備簡單，移動方便設備簡單，移動方便 通用性強，可用于熔焊、通用性強，可用于熔焊、釬焊，可改裝成氣割設備釬焊，可改裝成氣割設備 適于薄件、小件焊接和熔適于薄件、小件焊接和熔點較低的金屬焊接點較低的金屬焊接氣焊氣焊氣焊缺點氣焊缺點 與電弧相比，氣體火焰與電弧相比，氣體火焰溫度低，熱量分散溫度低，熱量分散 生產率低，焊件變形嚴生產率低，焊件變形嚴重，接頭熱影響區(qū)寬，重

17、，接頭熱影響區(qū)寬，顯微組織粗大，接頭性顯微組織粗大，接頭性能較差能較差 多為手工操作，對焊工多為手工操作，對焊工有較高的技巧要求有較高的技巧要求 勞動條件差勞動條件差25(1) Area of applicationMost ferrous and non-ferrous metalsOAW: carbon steels, cast iron, alloyed steels, copper, nickel, aluminum, etc.With other fuel gases: low-melting point metals and noble metals, e.g. aluminum,

18、 magnesium, zinc, lead, etc.Not recommended for refractory metals (niobium, molybdenum, wolfram) and reactive metals (titanium, zirconium). (2) Main applicationsThin sheets, thin-section tubesSmall batch production, field construction, repair, etc.Gas Welding26氣焊氣焊適用范圍氣焊適用范圍（1）可氣焊的金屬）可氣焊的金屬絕大多數的黑色和有

19、色金屬。絕大多數的黑色和有色金屬。用用氧氧-乙炔火焰乙炔火焰時，可焊接碳鋼、鑄鐵、時，可焊接碳鋼、鑄鐵、合金鋼、銅合金、鎳合金、鋁合金等。合金鋼、銅合金、鎳合金、鋁合金等。用用氫、天然氣、丙烷氫、天然氣、丙烷等其它可燃氣體等其它可燃氣體時，可焊接熔點較低的金屬和貴重金時，可焊接熔點較低的金屬和貴重金屬，如鋁、鎂、鋅、鉛等。屬，如鋁、鎂、鋅、鉛等。高熔點金屬如鈮、鉬、鎢等以及活性高熔點金屬如鈮、鉬、鎢等以及活性金屬如鈦、鋯等不宜采用氣焊。金屬如鈦、鋯等不宜采用氣焊。（2）主要用途）主要用途最適于焊接薄板或薄壁管子。隨著板最適于焊接薄板或薄壁管子。隨著板厚增加，焊接越不經濟。由于生產率厚增加，焊接

20、越不經濟。由于生產率低，故適用于小批生產、野外焊接、低，故適用于小批生產、野外焊接、修理和改建等場合。修理和改建等場合。27Shielded Metal Arc Welding (SMAW) Shielded metal arc welding (SMAW) is a process that melts and joins metals by heating them with an arc established between a sticklike covered electrode and the metals. It is often called stick welding.Th

21、e core of the covered electrode, the core wire, conducts the electric current to the arc and provides filler metal for the joint. For electrical contact, the top 1.5 cm of the core wire is bare and held by the electrode holder. The electrode holder is essentially a metal clamp with an electrically i

22、nsulated outside shell for the welder to hold safely.28焊條電弧焊（焊條電弧焊（SMAW） 焊條電弧焊是藥皮焊條手工電弧焊的簡稱（焊條電弧焊是藥皮焊條手工電弧焊的簡稱（SMAW, Shielded Metal Arc Welding）。是用手工操縱焊條施焊的電弧焊方法。）。是用手工操縱焊條施焊的電弧焊方法。它利用焊條與工件之間燃燒的電弧熱它利用焊條與工件之間燃燒的電弧熱熔化焊條端部和工件的局部，在焊條熔化焊條端部和工件的局部，在焊條端部迅速熔化的金屬以細小熔滴經弧端部迅速熔化的金屬以細小熔滴經弧柱過度到工件已經局部熔化的金屬中，柱過度到工件

23、已經局部熔化的金屬中，并與之融合一起形成熔池，隨著電弧并與之融合一起形成熔池，隨著電弧向前移動，熔池的液態(tài)金屬逐步冷卻向前移動，熔池的液態(tài)金屬逐步冷卻結晶而形成焊縫。焊接過程中，焊條結晶而形成焊縫。焊接過程中，焊條芯是焊接電弧的一個極，并作為填充芯是焊接電弧的一個極，并作為填充金屬熔化后就成為焊縫的組成部分；金屬熔化后就成為焊縫的組成部分；焊條的藥皮經電弧高溫分解和熔化而焊條的藥皮經電弧高溫分解和熔化而生成氣體和熔渣，對金屬熔滴和熔池生成氣體和熔渣，對金屬熔滴和熔池起防止大氣污染的保護作用和冶金反起防止大氣污染的保護作用和冶金反應作用；某些藥皮加入金屬粉末為焊應作用；某些藥皮加入金屬粉末為焊縫

24、提供附加的填充金屬?？p提供附加的填充金屬。29Shielded Metal Arc Welding (SMAW) The electrode holder is connected through a welding cable to one terminal of the power source and the workpiece is connected through a second cable to the other terminal of the power source. The heat of the arc causes both the core wire and th

25、e flux covering at the electrode tip to melt off as droplets. The molten metal collects in the weld pool and solidifies into the weld metal.The lighter molten flux, on the other hand, floats on the pool surface and solidifies into a slag layer at the top of the weld metal.30Shielded Metal Arc Weldin

26、g (SMAW)Protection: It provides a gaseous shield to protect the molten metal from air.Deoxidation: It provides deoxidizers and fluxing agents to deoxidize and cleanse the weld metal. The solid slag formed also protects the already solidified but still hot weld metal from oxidation.Arc Stabilization:

27、 It provides arc stabilizers to help maintain a stable arc. Arc stabilizers are compounds that decompose readily into ions in the arc. They increase the electrical conductivity of the arc and help the arc conduct the electric current more smoothly.Metal Addition: It provides alloying elements and/or

28、 metal powder to the weld pool. The former helps control the composition of the weld metal while the latter helps increase the deposition rate. Functions of Electrode Covering31焊條電弧焊（焊條電弧焊（SMAW）工藝特點工藝特點1）設備簡單，操作靈活方便，適應性強，可達性好，不受場地和焊接位置的）設備簡單，操作靈活方便，適應性強，可達性好，不受場地和焊接位置的限制，在焊條能達到的地方一般都能施焊，這些都是被廣泛應用的重要

29、原因。限制，在焊條能達到的地方一般都能施焊，這些都是被廣泛應用的重要原因。2）可焊金屬廣，除難熔或極易氧化的金屬外，大部分工業(yè)用的金屬均能焊接。）可焊金屬廣，除難熔或極易氧化的金屬外，大部分工業(yè)用的金屬均能焊接。3）待焊接頭裝配要求較低，但對焊工操作技術要求高，焊接質量在一定程度）待焊接頭裝配要求較低，但對焊工操作技術要求高，焊接質量在一定程度上取決于焊工的操作水平。上取決于焊工的操作水平。4）勞動條件差，熔敷速度慢，生產效率低。因所用焊條尺寸一般已固定，每）勞動條件差，熔敷速度慢，生產效率低。因所用焊條尺寸一般已固定，每焊完一根焊條，必須更換焊條，并殘留下一截焊條頭，而未被充分利用，焊后焊完

30、一根焊條，必須更換焊條，并殘留下一截焊條頭，而未被充分利用，焊后還需清渣等，故生產率低。還需清渣等，故生產率低。32焊條電弧焊（焊條電弧焊（SMAW） 適用范圍與局限性適用范圍與局限性1. 可焊工件厚度范圍可焊工件厚度范圍1mm以下的薄板不宜用焊條電弧焊；采用坡口多層焊的厚度雖不受限以下的薄板不宜用焊條電弧焊；采用坡口多層焊的厚度雖不受限制，但效率低，填充金屬量大，經濟型下降，所以一般大多用在制，但效率低，填充金屬量大，經濟型下降，所以一般大多用在340mm之間。之間。2. 可焊金屬范圍可焊金屬范圍能焊的金屬有能焊的金屬有：碳鋼、低合金鋼、不銹鋼、耐熱鋼、銅、鋁及其合金；：碳鋼、低合金鋼、不銹

31、鋼、耐熱鋼、銅、鋁及其合金；能焊但可能需預熱、后熱或兩者兼有的金屬有能焊但可能需預熱、后熱或兩者兼有的金屬有：鑄鐵、高強度鋼、淬：鑄鐵、高強度鋼、淬火鋼等；火鋼等；不能焊的金屬主要有不能焊的金屬主要有：低熔點金屬如鋅、鉛、錫及其合金；難熔金屬：低熔點金屬如鋅、鉛、錫及其合金；難熔金屬如鎢、鉬等，活性金屬如鈦、鈮、鋯等。如鎢、鉬等，活性金屬如鈦、鈮、鋯等。3. 最合適的產品結構和生產性質最合適的產品結構和生產性質結構復雜的產品，在結構上具有很多短的或不規(guī)則的、具有各種空間結構復雜的產品，在結構上具有很多短的或不規(guī)則的、具有各種空間位置及其它不易實現機械化或自動化焊接的焊縫，最宜用焊條電弧焊。位置

32、及其它不易實現機械化或自動化焊接的焊縫，最宜用焊條電弧焊。單件或小批量的焊接產品多采用焊條電弧焊。在安裝或修理部門因焊單件或小批量的焊接產品多采用焊條電弧焊。在安裝或修理部門因焊接位置不定，焊接工作量相對較小，也宜采用焊條電弧焊。接位置不定，焊接工作量相對較小，也宜采用焊條電弧焊。33Advantages Simple, portable, and inexpensive All-position welding Maintenance, repair, and field constructionDisadvantages Limited deposition rate Limited le

33、ngth of the electrode (about 350mm) requires electrode changing which further reduces the overall production rate Operated manually, high requirements of labor skills Poor working conditionsShielded Metal Arc Welding (SMAW)34Shielded Metal Arc Welding (SMAW)(1) Applicable thickness of the workpiece:

34、 3-40mm. (2) Area of applicationApplicable metals: carbon steels, low alloy steels, stainless steels, heat-resistant steels, copper, aluminum.Pre- and/or post-heat treatment: cast iron, high-strength steel, quenched steels, etc.Not recommended for low-melting point metals (e.g. zinc, lead, tin, etc.

35、), refractory metals (molybdenum, wolfram, etc.) and reactive metals (titanium, niobium, zirconium).35(3) Most applicable structures and productsComplicated structures: short weld, irregular weld, all types of positions difficult for automatic welding Single piece or small batch productionRepair, ma

36、intenance, etc.Shielded Metal Arc Welding (SMAW)36Gas tungsten arc welding (GTAW) Gastungsten arc welding (GTAW) is a process that melts and joins metals by heating them with an arc established between a nonconsumable tungsten electrode and the metals。 The shielding gas goes through the torch body a

37、nd is directed by a nozzle toward the weld pool to protect it from the air.Gastungsten arc welding: (a) overall process; (b) welding area enlarged37鎢極氣體保護焊（TIG）在惰性氣體的保護下，利用鎢電極與工件之間產生的電弧熱熔化母材在惰性氣體的保護下，利用鎢電極與工件之間產生的電弧熱熔化母材和填充焊絲的焊接方法稱鎢極惰性氣體保護焊，簡稱和填充焊絲的焊接方法稱鎢極惰性氣體保護焊，簡稱TIG焊焊（Tungsten Inert Gas Welding)或

38、或GTAW（Gas Tungsten Arc Welding）。）。 TIG焊有手工焊、半自動焊和焊有手工焊、半自動焊和自動焊三種操作方式。手工焊自動焊三種操作方式。手工焊時，焊槍的運動和焊絲的送進時，焊槍的運動和焊絲的送進均由焊工左右手同時操作；半均由焊工左右手同時操作；半自動焊時，焊槍由手工操作，自動焊時，焊槍由手工操作，焊絲由專門的送絲機構等速地焊絲由專門的送絲機構等速地自動輸送；自動焊時，分別有自動輸送；自動焊時，分別有行走機構、送絲機構，完成這行走機構、送絲機構，完成這兩個動作。兩個動作。38鎢極氣體保護焊（鎢極氣體保護焊（TIG） TIG焊的工藝特點焊的工藝特點1）焊接時使用不熔化

39、的鎢電極，不存在電極熔化對弧長的影響）焊接時使用不熔化的鎢電極，不存在電極熔化對弧長的影響問題，故電弧長度易于控制。需要填充金屬時，可從側面向電弧問題，故電弧長度易于控制。需要填充金屬時，可從側面向電弧送進焊絲，焊接電流不受影響。送進焊絲，焊接電流不受影響。2）焊接時，保護焊接區(qū)的是惰性氣體，不需加入任何焊劑即可）焊接時，保護焊接區(qū)的是惰性氣體，不需加入任何焊劑即可獲得純凈的焊縫金屬。因此，幾乎可以焊接所有的金屬。獲得純凈的焊縫金屬。因此，幾乎可以焊接所有的金屬。3）為了避免鎢極被損壞和不致引起焊縫金屬被鎢污染，一般不）為了避免鎢極被損壞和不致引起焊縫金屬被鎢污染，一般不用接觸（短路）式引弧，

40、而采用非接觸式引弧。為此，需配備一用接觸（短路）式引弧，而采用非接觸式引弧。為此，需配備一個引弧裝置；對于普通交流個引弧裝置；對于普通交流TIG焊，還需配備穩(wěn)弧裝置，以使焊焊，還需配備穩(wěn)弧裝置，以使焊接過程電弧穩(wěn)定。接過程電弧穩(wěn)定。4）無論使用直流電源還是交流電源，都要求具有陡降或垂直下）無論使用直流電源還是交流電源，都要求具有陡降或垂直下降（即恒流）的外特性，以減小或排除因弧長變化引起焊接電流降（即恒流）的外特性，以減小或排除因弧長變化引起焊接電流的波動。的波動。39鎢極氣體保護焊（鎢極氣體保護焊（TIG）TIG焊的三種極性焊的三種極性40鎢極氣體保護焊（鎢極氣體保護焊（TIG） 陰極霧化或

41、陰極清理作用陰極霧化或陰極清理作用TIG焊接過程中，當母材為陰極時，電弧焊接過程中，當母材為陰極時，電弧中質量較大的正離子高速向母材表面撞擊，中質量較大的正離子高速向母材表面撞擊，就象噴砂的作用一樣，把母材表面的氧化就象噴砂的作用一樣，把母材表面的氧化膜打碎并清除掉，這種現象稱陰極清理作膜打碎并清除掉，這種現象稱陰極清理作用，又稱陰極破碎作用。如圖所示為鋁的用，又稱陰極破碎作用。如圖所示為鋁的TIG焊焊縫外觀示意圖。焊縫周圍的白邊，焊焊縫外觀示意圖。焊縫周圍的白邊，就是因清洗作用把母材表面氧化膜去除的就是因清洗作用把母材表面氧化膜去除的痕跡。發(fā)生陰極清洗作用的基本條件是母痕跡。發(fā)生陰極清洗作用

42、的基本條件是母材必須是負極，正極不能發(fā)生。因此，只材必須是負極，正極不能發(fā)生。因此，只有直流反接和交流負半周期內才能有這種有直流反接和交流負半周期內才能有這種作用。此外，發(fā)生的范圍是在惰性氣體充作用。此外，發(fā)生的范圍是在惰性氣體充分包圍的地方，混入空氣就不發(fā)生這種作分包圍的地方，混入空氣就不發(fā)生這種作用。惰性氣體流量不足，其作用范圍就會用。惰性氣體流量不足，其作用范圍就會減少。減少。41 AdvantagesGastungsten arc welding is suitable for joining thin sections because of its limited heat inpu

43、ts. The feeding rate of the filler metal is somewhat independent of the welding current, thus allowing a variation in the relative amount of the fusion of the base metal and the fusion of the filler metal. Therefore, the control of dilution and energy input to the weld can be achieved without changi

44、ng the size of the weld. It can also be used to weld butt joints of thin sheets by fusion alone, that is, without the addition of filler metals or autogenous welding. Since the GTAW process is a very clean welding process, it can be used to weld reactive metals, such as titanium and zirconium, alumi

45、num, and magnesium.Gas tungsten arc welding (GTAW)42 DisadvantagesHowever, the deposition rate in GTAW is low. Excessive welding currents can cause melting of the tungsten electrode and results in brittle tungsten inclusions in the weld metal. However, by using preheated filler metals, the depositio

46、n rate can be improved. In the hot-wire GTAW process, the wire is fed into and in contact with the weld pool so that resistance heating can be obtained by passing an electric current through the wire.Gas tungsten arc welding (GTAW)43鎢極氣體保護焊（鎢極氣體保護焊（TIG） TIG焊的優(yōu)點焊的優(yōu)點1）在惰性氣體保護下焊接，不需）在惰性氣體保護下焊接，不需使用焊劑就可

47、以焊接幾乎所有金使用焊劑就可以焊接幾乎所有金屬；特別適于焊接化學活性強和屬；特別適于焊接化學活性強和形成高熔點氧化物的鋁、鎂及其形成高熔點氧化物的鋁、鎂及其合金。合金。2）焊接工藝性能好。明弧，能觀）焊接工藝性能好。明弧，能觀察電弧及熔池；電弧燃燒穩(wěn)定，察電弧及熔池；電弧燃燒穩(wěn)定，無飛濺，焊后不須去渣，焊縫成無飛濺，焊后不須去渣，焊縫成型美觀；能進行全位置焊接。是型美觀；能進行全位置焊接。是實現單面焊背面成形的理想焊接實現單面焊背面成形的理想焊接方法。方法。3）能進行脈沖焊接，減少焊接熱）能進行脈沖焊接，減少焊接熱輸入，很適于薄板或對熱敏感材輸入，很適于薄板或對熱敏感材料的焊接。料的焊接。 T

48、IG焊的缺點焊的缺點1）熔深淺，熔敷速度小，焊接生產）熔深淺，熔敷速度小，焊接生產率較低。率較低。2）鎢極載流能力有限，過大焊接電）鎢極載流能力有限，過大焊接電流會引起鎢極熔化和蒸發(fā)，其微粒流會引起鎢極熔化和蒸發(fā)，其微粒可能進入熔池，造成對焊縫金屬的可能進入熔池，造成對焊縫金屬的污染。污染。3）焊接時，需采取防風措施。）焊接時，需采取防風措施。4）惰性氣體較貴，生產成本較高。）惰性氣體較貴，生產成本較高。44鎢極氣體保護焊（TIG）Manual TIG手工鎢極氬弧焊Automatic TIG全自動鎢極氬弧焊45鎢極氣體保護焊（鎢極氣體保護焊（TIG） 適用范圍適用范圍1. 適焊的材料適焊的材料

49、鎢極氬弧焊幾乎可焊接所有的金屬和合金，但因其成本較高，生產中主要用鎢極氬弧焊幾乎可焊接所有的金屬和合金，但因其成本較高，生產中主要用于焊接鋁、鎂、鈦、銅等有色金屬及其合金，不銹鋼和耐熱鋼。對于低熔點于焊接鋁、鎂、鈦、銅等有色金屬及其合金，不銹鋼和耐熱鋼。對于低熔點易蒸發(fā)的金屬如鉛、錫、鋅等因焊接操作困難，一般不用易蒸發(fā)的金屬如鉛、錫、鋅等因焊接操作困難，一般不用TIG焊。對已鍍有錫、焊。對已鍍有錫、鋅、鉛等低熔點金屬層的碳鋼，焊前需去掉鍍層，否則熔入焊縫金屬中生成鋅、鉛等低熔點金屬層的碳鋼，焊前需去掉鍍層，否則熔入焊縫金屬中生成中間合金會降低接頭性能。中間合金會降低接頭性能。2. 適焊的焊接接

50、頭和位置適焊的焊接接頭和位置常規(guī)的對接、搭接、常規(guī)的對接、搭接、T形接和角接等接頭，處在任何位置（即全位置）只要結形接和角接等接頭，處在任何位置（即全位置）只要結構上具有可達性均能焊接。構上具有可達性均能焊接。3. 適焊的板厚與產品結構適焊的板厚與產品結構從生產率考慮以從生產率考慮以3mm以下的薄板焊接最適宜。重要厚壁結構件的根部熔透焊以下的薄板焊接最適宜。重要厚壁結構件的根部熔透焊道或其它結構窄間隙焊縫的打底焊道，為了保證焊接質量，有時采用道或其它結構窄間隙焊縫的打底焊道，為了保證焊接質量，有時采用TIG焊。焊。手工手工TIG焊宜用于結構形狀較復雜的焊件和難以接近的部位或間斷的短焊縫的焊宜用

51、于結構形狀較復雜的焊件和難以接近的部位或間斷的短焊縫的焊接；自動焊接；自動TIG焊適于焊接長焊縫，包括縱鋒、環(huán)鋒和曲線焊縫。焊適于焊接長焊縫，包括縱鋒、環(huán)鋒和曲線焊縫。46氬弧焊視頻氬弧焊視頻（319）47Gas metal arc welding (GMAW) Gasmetal arc welding (GMAW) is a process that melts and joins metals by heating them with an arc established between a continuously fed filler wire electrode and the me

52、tals. Shielding of the arc and the molten weld pool is often obtained by using inert gases such as argon and helium, and this is why GMAW is also called the metalinert gas (MIG) welding process. Since noninert gases, particularly CO2, are also used,GMAW seems a more appropriate name.48 Category of G

53、MAW processGas metal arc welding (GMAW)49Gas metal arc welding (GMAW)Gasmetal arc welding: (a) overall process; (b) welding area enlarged50Gas metal arc welding (GMAW) Modes of Metal TransferShallow weld,Thin workpieceIrregular weld,SpatteringDeep penetration,Stable transferShort-Circuiting Transfer

54、短路過渡Globular Transfer滴狀過渡Spray Transfer噴射過渡51熔化極氣體保護焊（熔化極氣體保護焊（MIG）熔滴過渡形式（熔滴過渡形式（a 滴狀過渡；滴狀過渡；b 噴射過渡）噴射過渡）52熔化極氣體保護焊（熔化極氣體保護焊（MIG）The is characterized by an axial transfer of fine, discrete molten particles or drops from the consumable electrode to the workpiece at rates of several hundred per second

55、. The metal transfer is very stable, directional, and essentially free of spatter. Spray transfer is produced by welding in the DC electrode positive mode at high voltages (typically 2730V) and amperages above some critical value related to the wires diameter. The high arc energy and heat associated

56、 with the spray transfer mode limits its effectiveness for joining sheet gauge metals, but the strong directional spray (often referred to as “arc stiffness”) can be useful for welding vertically up or down or overhead, all of which are said to be “” compared to downward or “down-hand” on a horizont

57、al plane.53熔化極氣體保護焊（熔化極氣體保護焊（MIG）The is characterized by large globules or drops of molten metal being formed at the tip of the consumable electrode and then being released and carried to the workpiece and weld by gravity and/or arc forces. Globule formation is usually from about one per second to f

58、ive per second. The large drop size tends to make out-of-position welding difficult, as there is no directed “push” to make the drops fight gravity. is usually considerable compared to spray transfer.54熔化極氣體保護焊（熔化極氣體保護焊（MIG）In the which is known as a “bridging” mode, welding currents and voltages ar

59、e kept low and the slow-forming globules at the tip of the consumable electrode are periodically touched to the weld puddle to cause their release through surface tension forces.This short-circuiting occurs at rates in excess of 50 per second and is best performed using specially designed power sour

60、ces. The low currents required for this mode enable the welding of thin sections without melting through or overwelding. Out-of-position welding is facilitated by the direct transfer of the molten metal through contact. Spatter is minimized with this transfer mode.It is possible to superimpose inter