Lecture 1 Introduction to welding processes

1. Lecture 1 Introduction to welding processes 助理教授：王惠森 huei@mail.isu.edu.tw 您可以在以下的網址 Down Load 本檔案http://140.127.180.27/www/index.htm

2. Add the joint law welds and makes use of and adds the joint material or the work piece connects the law.

3. Fluid Flow and Surface Deformation in Weld Pool

4. cross-section of a welded butt joint,

6. Arc Welding • Arc welding is a process utilizing the concentrated heat of an electric arc to join metal by fusion o f the parent metal and the addition of metal to joint usually provided by a consumable electrode. Eit her direct or alternating current may be used for the arc, depending upon the material to be welded and the electrode used.

7. Power supplies of Arc Welding • The most common classification is constant current power supplies and constant voltage power supplies. • In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. • Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. • manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. • for automated welding processes arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. • The polarity of the electric current affects the heat transfer to the joined pieces. Normally the pos itive (+) pole is connected to the electrode. When welding very thin material or single-sided welding, the negative ( −)pole of an DC source is connected to the electrode.

8. 電弧焊 Shielded-Metal Arc Welding 用手工操縱焊條﹑用電弧作為熱源的焊接方法,又稱手弧焊(見圖)。焊條與工件各為一個電極,電弧引燃於其間。焊芯與工件的熔化金屬形成焊縫金屬,焊條藥皮產生的氣體和熔渣起保護熔池﹑穩定電弧和滲入合金的作用。使用不同的焊條可以焊接各類碳鋼﹑低合金鋼﹑不鏽鋼﹑鑄鐵﹑鎳和鎳合金﹑銅和銅合金﹑鋁和鋁合金等材料。焊條直徑有2～6毫米的一系列規格。小直徑焊條適用於薄板(1～3毫米)和各種位置的焊接;大直徑焊條適用於厚板的平焊和橫焊位置。

10. Difficulties in MMA welding • Because of the 'Slag' that covers the weld bead, the welder using this technique doesn't get much visual feedback until s/he removes the layer of slag and makes a visual inspection. Common problems encountered by people learning this technique include slag inclusion, poor fusion, excessive penetration, and electrode sticking, often all at once.

11. GTAW Welding • Gas Tungsten Arc Welding (GTAW) is frequently referred to as TIG welding.  TIG welding is a commonly used high quality welding process.  TIG welding has become a popular choice of welding processes when high quality, precision welding is required.  • In TIG welding an arc is formed between a nonconsumable tungsten electrode and the metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool.  If filler wire is used, it is added to the weld pool separately. 

12. Shielding Gas • ionization potentials for argon and heliumare 15.7 and 24.5 eV arc initiation is easier and • the voltage drop across the arc is lower with argon. • argon also has a greater oxide cleaning action than helium. • These advantages plus the lower cost of argon make it more attractive for GTAW than helium.

13. 鎢極惰性氣體保護焊 簡稱TIG焊。用鎢棒作為電極,用氬或氦作為保護氣體。電弧熔化母材形成接頭,必要時還可加入填充焊絲(圖1)。鎢極惰性氣體保護焊的特點是電弧穩定,輸入能量易於控制。因此多用於焊接呎吋精度要求較高﹑材料易於過熱脆化和在空氣中易於氧化的工件。

15. Characteristics of TIG TIG Welding Benefits  Superior quality welds  Welds can be made with or without filler metal  Precise control of welding variables (heat)  Free of spatter  Low distortion Shielding Gases  Argon  Argon + Hydrogen  Argon/Helium Helium is generally added to increase heat input (increase welding speed or weld penetration).  Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.

16. Common GTAW Welding Concerns •  Requires greater welder dexterity than MIG or stick welding •  Lower deposition rates •  More costly for welding thick sections

17. 熔化極氣體保護焊(MIG) Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. 用連續送進的焊絲作為電極,用氬﹑二氧化碳或混合氣體作為保護氣體。與鎢極惰性氣體保護焊相比,這種保護焊生產率較高,應用較廣,僅次於手工電弧焊和埋弧焊,有進一步發展的趨勢。焊絲可用實心焊絲,也可用藥芯焊絲。熔化極氣體保護焊按保護氣體種類不同又可分為惰性氣體保護焊﹑二氧化碳氣體保護焊和混合氣體保護焊。

18. GMAW torch nozzle cutaway image. (1) Torch handle, (2) Molded phenolic合成樹脂dielectric (shown in white) and threaded metal nut insert (yellow), (3) Shielding gas nozzle, (4) Contact tip, (5) Nozzle output face

19. GMAW Circuit diagram. (1) Welding torch, (2) Workpiece, (3) Power source, (4) Wire feed unit, (5) Electrode source, (6) Shielding gas supply.

21. GMAW weld area. (1) Direction of travel, (2) Contact tube, (3) Electrode, (4) Shielding gas, (5) Molten weld metal, (6) Solidified weld metal, (7) Workpiece.

22. MIG welding process.

23. MIG Welding Benefits •  All position capability •  Higher deposition rates than SMAW •  Less operator skill required •  Long welds can be made without starts and stops •  Minimal post weld cleaning is required • The primary shielding gasses used are: • Argon •  Argon - 1 to 5% Oxygen •  Argon - 3 to 25% CO2 •  Argon/Helium

24. Flux Cored Arc Welding • Flux cored arc welding (FCAW) is an electric arc welding process that uses an arc between a continuously fed flux-filled electrode and the weld pool. The process is used with shielded gas from a flux contained within the tubular electrode with or without additional shielding from an externally supplied gas. 

25. Submerged Arc Welding SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the workpiece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high as 60% (compared with 25% for manual metal arc). There is no visible arc light, welding is spatter-free and there is no need for fume extraction.

26. Electroslag Welding • Electroslag Welding (ESW)deposits the weld metal into the weld cavity between the two plates to be joined. This space is enclosed by water cooled copper dams or shoes to prevent molten slag from running off. The weld metal is produced from a filler wire that forms an initial arc with the workpiece until a sufficient pool of liquid metal is formed to use the electrical resistance of the molten slag. • This process requires special equipment used primarily for horizontal welds of very large plates up to 36 inches or more by welding them in one pass as in large machinery and nuclear reactor vessels.

27. 電漿弧熔接 (Plasma arc welding) • Plasma gases are normally argon. The torch also uses a secondary gas, argon, argon/hydrogen or helium which assists in shielding the molten weld puddle thus minimizing oxidation of the weld. • Plasma is ionized gas at very high temperatures (30.000 C). The plasma is generated by sending a jet of gas through an electric arc. Plasma welding is only done on automatic machines. and stops, thanks to a pilot arc.

28. Deposition Rate of the Welding Processes

29. Soldering /Brazing

30. 軟焊及硬焊(Soldering and Brazing) 軟焊(Soldering)係指在溫度不超過50oC下，以一金屬熔溶狀態介入兩擬焊接元件之間達成焊合者。最常用的鉛及錫合金，熔點範圍為180oC ~370oC，黏接強度以該合金的黏接品質而定。可用熱浸爐子火炬電阻電感或超音波來加熱或使用烙鐵。助焊劑有助於清潔母材表面，惟易於生成化合物。軟焊法容易使用的母材有銅、錫、鉛、銀及金。硬焊(Brazing)係使非鐵合金呈熔化狀態，並放於母材表面間隨之即凝固而接合。此填充材料之熔化溫度高於450oC，不過卻低於焊件主材料之熔點，焊料藉毛細作用分佈於焊件表面。銅合金銀合金及鋁合金是一般最常用的硬焊填充金屬。硬焊使用於管路及接頭，碳化物刀尖及刀具及鑄造之修補。

31. Brazing using a laser as the heat source.

32. Induction Soldering • Inductive heating was discovered by Michael Faraday in 1881 and for a long time was regarded as an undesirable side effect in transformer construction. Nowadays inductive heating is used for all types of metal heating in many areas of industry and is in use throughout the world. • The principle of inductive heating is based on eddy currents which are induced in the workpiece and heat this within a very short time by continuous polarity reversal. • A high eddy current frequency and the necessary power are required for this.

33. Induction Heating The basic components of an induction heating system are an AC power supply, induction coil, and workpiece (material to be heated or treated). The power supply sends alternating current through the coil, generating a magnetic field. When the workpiece is placed in the coil, the magnetic field induces eddy currents in the workpiece, generating precise amounts of clean, localized heat without any physical contact between the coil and the workpiece.

34. Wave Soldering • Wave Soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The name is derived from the fact that the process uses a tank to hold a quanitity of molten solder; the components are inserted into or placed on the PCB and the loaded PCB is run across a pumped wave or cascade of solder.

35. Infrared Soldering

36. 電阻焊接(Resistance Welding) • used extensively in electronic packaging & sensor/transducer assembly 通過電極對焊件施加壓力,同時利用電流通過接觸點產生的電阻熱進行焊接的方法, 又稱接觸焊。電阻焊的形式有點焊﹑ 凸焊﹑縫焊和對焊。電阻焊生產率高,容易實現機械化和自動化, 但所需焊機複雜而且耗用電功率大,主要用於大批量生產。

37. Resistance Welding

38. Flash welding • Flash welding is a development of resistance butt welding and is particularly suitable for butt welding complex or larger sections. It is used for a wide range of component shapes and sizes from bicycle wheel rims to rails. More efficient energy input, and a more localised and evenly heated zone can be achieved, compared with resistance butt welding

39. High frequency resistance welding (HFRW) • High frequency resistance welding (HFRW) is a resistance welding process which produces coalescence of metals with the heat generated from the resistance of the work pieces to a high-frequency alternating current in the 10,000 to 500,000 hertz range and the rapid application of an upsetting force after heating is substantially completed. The path of the current in the work piece is controlled by the proximity effect

40. 衝擊電阻焊 Percussion Welding Percussive arc welding, in its general form, is a high-speed welding process which can be used to produce either a fusion or forge (solid phase) weld. While other arc-based processes require an inert gas shroud or flux covering to avoid oxidation of the molten material, the extremely short arc duration in percussive arc welding means such measures are not required. The basics of percussive arc welding equipment are shown schematically in Fig.1. The component (in this case a fuse) is located in a jig with the metallic part connected to a power supply, whilst the pin to be welded to the fuse-cap is held in a moving clamp which is connected to the other side of the power supply. When the weld is initiated, by closing the switch, several things occur in a very short space of time

41. Solid State Welding

42. 磨擦壓接(FRICTION WELDING) • 磨擦熔接是一種固態熔接方法，是以磨擦發熱為熱源，透過機械摩擦運動及軸向壓力 ，使摩擦表面產生熱量，把工件表面旋轉加熱 到塑性熔化狀態，施以壓力頂鍛將同種或異種金屬牢固熔接起來。

44. Friction Stir Welding of Steel Pipes

46. force heat atomic movement force 擴散焊接(Diffusion Welding) 將焊件緊密貼合﹐在一定溫度和壓力下保持一段時間﹐使接觸面之間的原子相互擴散形成聯接的焊接方法。影響擴散焊過程和接頭質量的主要因素是溫度﹑壓力﹑擴散時間和表面粗糙度。焊接溫度越高﹐原子擴散越快。焊接溫度一般為材料熔點的0.5～0.8倍。根據材料類型和對接頭質量的要求﹐擴散焊可在真空﹑保護氣體或溶劑下進行﹐其中以真空擴散焊應用最廣。為了加速焊接過程﹑降低對焊接表面粗糙度的要求或防止接頭中出現有害的組織﹐常在焊接表面間添加特定成分的中間夾層材料﹐其厚度在0.01毫米左右。擴散焊接壓力較小﹐工件不產生宏觀塑性變形﹐適合焊後不再加工的精密零件。擴散焊可與其他熱加工工藝聯合形成組合工藝﹐如熱耗-擴散焊﹑粉末燒結-擴散焊和超塑性成形-擴散焊等。這些組合工藝不但能大大提高生產率﹐而且能解決單個工藝所不能解決的問題。

47. 超音波金屬熔接機 • 是利用超音波高頻率振動，產生相對摩擦振動能量，對非鐵金屬，異種金屬合金等，以每秒20,000次振動，使熔接面分子搓合，而牢固接合，並沒有熔化，所以沒有高溫退火等問題產生。而同種或異種合金分子的互相攙雜，產生穩定恆久的砌合，可在極短時間內完成，是工業應用的最新技術。

48. Oxyfuel Gas Welding

49. 氣體焊接(Gas Welding) 利用氣體燃燒的火焰作為熱源的焊接方法(見圖)。乙炔(C2H2)是最常用的可燃氣體。氧和乙炔燃燒的化學過程是2C2H2+CO2→4CO+2H2+3O2+熱量→4CO2+2H2O+熱量。形成的火焰可調節成4種形式,分別適用於不同金屬和合金的焊接(見表)。氧乙炔火焰生成的氫和二氧化碳對熔化金屬有一定的保護作用。氣焊一般是手工操作,常用於焊接6毫米以下的薄板和小直徑管材以及修補焊接。 氣焊適用於多種金屬材料的焊接,設備簡單﹑成本低廉﹑焊炬操作靈便,在小批量薄件(最薄0.5毫米)焊接﹑全位置安裝焊(如鍋爐低壓管安裝)和修補焊等方面應用較普遍。 。