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PPT2_Welding.ppt

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PPT2_Welding.ppt

  1. 1. COURSE: MANUFACTURING PROCESSS CODE: AMEB05 III Semester Regulation: IARE R18 Institute of Aeronautical Engineering (Autonomous) Dundigal, Hyderabad- 500043 G.Praveen Kumar Assistant Professor Mechanical Engineering Prepared by
  2. 2. ARC WELDING  The arc welding is a fusion welding process in which the heat required to fuse the metal is obtained from an electric arc between the base metal and an electrode.  The electric arc is produced when two conductors are touches together and then separated by a small gap of 2 to 4 mm, such that the current continues to flow, through the air. The temperature produced by the electric arc is about 4000°C to 6000°C. 2 11/30/2022
  3. 3. ARC WELDING 3  A metal electrode is used which supplies the filler metal. The electrode may be flux coated or bare. In case of bare electrode, extra flux material is supplied. Both direct current (D.C.) and alternating current (A.C.) are used for arc welding.  The alternating current for arc is obtained from a step down transformer. The transformer receives current from the main supply at 220 to 440 volts and step down to required voltage i.e., 80 to 100 volts. The direct current for arc is usually obtained from a generator driven by either an electric motor, or patrol or diesel engine.  An open circuit voltage (for striking of arc) in case of D.C. welding is 60 to 80 volts while a closed circuit voltage (for maintaining the arc) is 15 to 25 volts
  4. 4. PROCEDURE OF ELECTRIC ARC WELDING 4  First of all, metal pieces to be weld are thoroughly cleaned to remove the dust, dirt, grease, oil, etc. Then the work piece should be firmly held in suitable fixtures. Insert a suitable electrode in the electrode holder at an angle of 60 to 80° with the work piece.  Select the proper current and polarity. The spot are marked by the arc at the places where welding is to be done. The welding is done by making contact of the electrode with the work and then separating the electrode to a proper distance to produce an arc.
  5. 5. PROCEDURE OF ELECTRIC ARC WELDING ARC WELDING  When the arc is obtained, intense heat so produced, melts the work below the arc, and forming a molten metal pool. A small depression is formed in the work and the molten metal is deposited around the edge of this depression. It is called arc crator. The slag is brushed off easily after the joint has cooled. After welding is over, the electrode holder should be taken out quickly to break the arc and the supply of current is switched off. 5 11/30/2022
  6. 6. ELECTRIC CURRENT FOR WELDING 6 Both D.C. (direct current) and A.C. (alternating current) are used to produce an arc in electric arc welding. Both have their own advantages and applications. The D.C. welding machine obtains their power from an A.C. motor or diesel/petrol generator or from a solid state rectifier. The capacities of D.C. machine are: Current: Up to 600 amperes. Open Circuit Voltage: 50 to 90 volts, (to produce arc). Closed Circuit Voltage: 18 to 25 volts, (to maintain arc The A.C. welding machine has a step down transformer which receives current from main A.C. supply. This transformer step down the voltage from 220 V-440V to normal open circuit voltage of 80 to 100 volts. The current range available up to 400 amperes in the steps of 50 ampere. 11/30/2022
  7. 7. The capacities of A.C. welding machine are: Current Range: Up to 400 ampere in steps of 50 ampere. Input Voltage: 220V- 440V Actual Required Voltage: 80 – 100 volts. Frequency: 50/60 HZ. 7 ELECTRIC CURRENT FOR WELDING 11/30/2022
  8. 8. SIGNIFICANCE OF POLARITY 8 When D.C. current is used for welding, the following two types of polarity are available: (i)Straight or positive polarity. (ii)Reverse or negative polarity. When the work is made positive and electrode as negative then polarity is called straight or positive polarity. In straight polarity, about 67% of heat is distributed at the work (positive terminal) and 33% on the electrode (negative terminal). The straight polarity is used where more heat is required at the work. The ferrous metal such as mild steel, with faster speed and sound weld, uses this polarity. 11/30/2022
  9. 9. SIGNIFICANCE OF POLARITY On the other hand, when the work is made negative and electrode as positive then polarity is known as reverse or negative polarity, as shown in Fig. 7.16 (b). In reverse polarity, about 67% of heat is liberated at the electrode (positive terminal) and 33% on the work (negative terminal). The reverse polarity is used where less heat is required at the work as in case of thin sheet metal weld. The non-ferrous metals such as aluminum, brass, and bronze nickel are welded with reverse polarity. 9 11/30/2022
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  11. 11. Equipments Required for Electric Arc Welding 11 The various equipment's required for electric arc welding are: 1. Welding Machine:  The welding machine used can be A.C. or D.C. welding machine. The A.C. welding machine has a step-down transformer to reduce the input voltage of 220- 440V to 80-100V.  The D.C. welding machine consists of an A.C. motor-generator set or diesel/petrol engine-generator set or a transformer-rectifier welding set.  A.C. machine usually works with 50 hertz or 60 hertz power supply.  The efficiency of A.C. welding transformer varies from 80% to 85%. The energy consumed per Kg. of deposited metal is 3 to 4 kWh for A.C. welding while 6 to 10 kWh for D.C. welding. 11/30/2022
  12. 12. 62 Equipments Required for Electric Arc Welding 2. Electrode Holders: The function of electrode holder is to hold the electrode at desired angle. These are available in different sizes, according to the ampere rating from 50 to 500 amperes. 3. Cables or Leads: The function of cables or leads is to carry the current from machine to the work. These are flexible and made of copper or aluminum. The cables are made of 900 to 2000 very fine wires twisted together so as to provide flexibility and greater strength. The wires are insulated by a rubber covering, a reinforced fibre covering and further with a heavy rubber coating. 4. Cable Connectors and Lugs: The functions of cable connectors are to make a connection between machine switches and welding electrode holder. Mechanical type connectors are used; as they can he assembled and removed very easily. Connectors are designed according to the current capacity of the cables used. 5. Chipping Hammer: The function of chipping hammer is to remove the slag after the weld metal has solidified. It has chisel shape and is pointed at one end. 11/30/2022 12
  13. 13. Equipments Required for Electric Arc Welding 13 6. Wire Brush, Power Wire Wheel: The function of wire brush is to remove the slag particles after chipping by chipping hammer. Sometimes, if available a power wire wheel is used in place manual wire brush. 7. Protective Clothing: The functions of protective clothing's used are to protect the hands and clothes of the welder from the heat, spark, ultraviolet and infrared rays. Protective clothing used are leather apron, cap, leather hand gloves, leather sleeves, etc. The high ankle leather shoes must be wear by the welder. 8. Screen or Face Shield: The function of screen and face shield is to protect the eyes and face of the welder from the harmful ultraviolet and infrared radiations produced during welding. The shielding may be achieved from head helmet or hand helmet 11/30/2022
  14. 14. ARC WELDING ELECTRODES 14 Arc welding electrodes can be classified into two broad categories: 1.Non-Consumable electrodes. 2.Consumable electrodes. 1.Non-Consumable Electrodes: These electrodes do not consumed during the welding operation, hence they named, non-consumable electrodes. They are generally made of carbon, graphite or tungsten. Carbon electrodes are softer while tungsten and graphite electrodes are hard and brittle. Carbon and graphite electrodes can be used only for D.C. welding, while tungston electrodes can be used for both D.C. and A.C. welding. The filler material is added separately when these types of electrodes are used. Since, the electrodes do not consumed, the arc obtained is stable. 2.Consumable Electrodes: These electrodes get melted during welding operation, and supply the filler material. They are generally made with similar composition as the metal to be welded. 11/30/2022
  15. 15. 15 Arc Welding Consumable Electrodes Mild Steel Electrodes Copper Electrodes
  16. 16. 16 Arc Welding Non Consumable Electrodes Carbon Electrodes Tungsten Electrodes
  17. 17. There are a number of advantages to using arc welding compared with many other formats: 17 ARC WELDING PROS AND CONS 11/30/2022 •It is suitable for high-speed welds. •It is a simple welding apparatus. •It can work on AC or DC. •Superior temperatures. •Less smoke or sparks are involved. •Portability as a result of the simple equipment. •It offers strong joints. •Produces very little distortion. •High corrosion resistance. •It has the ability to weld on porous and dirty metal. •It is the equipment that is inexpensive. •Its operation can be performed during wind or rain. •Its power supply can be used where there is electricity and the alternative can use be if there is no electricity but generators. •Smooth welding is achieved. •It is a good impact strength. •Arc welding beads can be used to create designed on fine metals. •It can be carried out in any atmosphere.
  18. 18. 18 ARC WELDING PROS AND CONS 11/30/2022 Disadvantages •Cannot be used for reactive metal like AI or Ti. •Not all thin metal can weld on arc welding. •Well trained and skillful operator is needed for the task. • More waste is generally produced during arc welding than many other types, which can increase project costs in some cases
  19. 19. 19 TUNGSTEN INERT GAS WELDING (TIG)
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  23. 23. 23 METAL INERT GAS WELDING (MIG)
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  31. 31. 31 Resistance Welding The welding process studied so far are fusion-welding processes where only heat is applied in the joint. In contrast, resistance welding process is a fusion-welding process where both heat and pressure applied on the joint but no filler metal or flux is added. The heat necessary for the melting of the joint is obtained by the heating effect of the electrical resistance of the joint and hence, the name resistance welding.
  32. 32. 32 Resistance Welding Principle In resistance welding (RW), a low voltage (typically 1-10 V) and very high current (typically 15000 A) is passed through the joint for a very short time (typically 0.25 Sec). This high amperage heats the joint, due to the contact resistance at the joint and melts it. The pressure on the joint is continuously maintained and the metal fuses together under this pressure. The heat generated in resistance welding can be expressed as: H = k I² R t
  33. 33. 33 Resistance Welding H = k I² R t Where, H = the total heat generated in the work, J I = electric current, A R = the resistance of the joint, ohms t = time for which the electric current is passing through the joint, Sec k = a constant to account for the heat losses from the weld joint. The resistance of the joint, R, is a complex factor to know because it is composed of the a) Resistance of the electrode, b) Contact resistance between the electrode and the workpiece, c) Contact resistance between the two workpiece plates, and d) Resistance of the workpiece plates.
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  36. 36. 37 Types of Resistance Welding Following are the 5 different types of resistance welding: 1. Spot resistance welding 2. Projection resistance welding 3. Seam resistance welding 4. Flash resistance welding 5. Butt resistance welding
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  52. 52. 53 Resistance Welding The Process of Resistance Welding
  53. 53. 54 Electron beam welding
  54. 54. 55 Principle
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  56. 56. 57 Electron beam setup
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  58. 58. 59 Process parameters
  59. 59. 60 Applications
  60. 60. 61 Advantages
  61. 61. 62 Disadvantages
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  71. 71. 72 Forge Welding 1. Forge welding (FOW) is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. 2. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. 3. The process is one of the simplest methods of joining metals and has been used since ancient times. 4. Forge welding is versatile, being able to join a host of similar and dissimilar metals. 5. With the invention of electrical and gas welding methods during the industrial revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process.
  72. 72. 73 Forge Welding Steps in Forge Welding There are several skills and processes that blacksmiths need to familiarize themselves with. Aside from the fact that these skills are essential in many blacksmithing processes, they are also crucial in minimizing the wastage of resources. Forge welding is undoubtedly one of these crucial skills and processing. It only requires excellent eye-hand coordination, as well as speed, meticulousness and loads of practice. Likewise, it requires you to understand the welding temperature of the material you are using. Also, the mode of welding will be dependent on the size and iron you are trying to create.
  73. 73. 74 Forge Welding STEP 1: Prepare the Materials: It is of utmost importance to note that welding heat varies based on the type of steel being used. It is best to heat the materials together to about 90% of their melting temperature. However, what you want to watch for is a yellow color. Once you get it to that color, you are at the right temperature; if you keep going after this point, your metal can turn into a sparkler. This forge welding temperature is when the carbon in the metal begins to oxidize, which will ruin your metal. So first bring your steel to good orange heat. The following are the six steps in Forge Weld:
  74. 74. 75 Forge Welding STEP 2: Fluxing: Then sprinkle with a flux (like a 20 Mule Team Borax). Forge welding of dirty or contaminated surfaces will yield poor weld and weak joints. It will also increase the melting temperature of the metal. Consequently, the forge welding flux serves as a low-temperature glassy shield that prevents the oxygen from the steel surface, which causes scales on the surface. Scales will prevent your metal from welding. It is advisable to use a flux because you need to have the right amount of skill and experience or an oxygen-free burner to weld without scaling your metals.
  75. 75. 76 Forge Welding STEP 3: Heating: After you have fluxed, place the steel back in the heart of the fire, while avoiding direct air blast as you do not want to oxidize your metal. You can weld the metals in a reducing environment. The most common reducing atmosphere is within the coal forge. Since the environment is short of oxygen, a layer of iron-oxide is formed on the surface of the metal. This iron-oxide layer is called wustite. The appropriate forge welding temperature is dependent on the types of materials involved in the process. Different materials have their required temperature, but the presence of impurities can alter it.
  76. 76. 77 Forge Welding STEP 4: Watch Out for Color Change: Allow the steel to get to a lemon-yellow color (IMPORTANT: do not look into the fire without using a pair of didymium glasses). It will appear shimmery and almost slippery. Once the material reaches an austenitizing temperature, there will be a rapid diffusion of iron through the metal. The rate of carbon diffusion will increase with increasing temperature.
  77. 77. 78 Forge Welding STEP 5: Remove Material from Forge: The pieces of steel should be removed from the heat now as this temperature is just below the spark causing temperature. Flashes mean that your iron is contaminated. The forge welding must be done rapidly before decarburization sets into the process. The fast operation will consequently prevent the material from becoming slightly too soft; thus, producing the appropriate amount of hardness.
  78. 78. 79 Forge Welding STEP 6: Joining and Hammering: Now, secure your pieces together with a bit of metal wire until the primary weld forms. After this step, simply use a power hammer or hydraulic press to hammer from one end to the other. You have to be careful not to hit the metal too hard; the hammer blows should be firm and reliable but not the same force you would use if you were changing bar shapes. It depends on the thickness of your pieces. Thicker ones would require more power. Also, you need to be careful not to miss any spots.
  79. 79. 80 Forge Welding
  80. 80. 81 Applications Forge Welding The significant applications of weld forging in blacksmithing include; 1. It is used to create a more substantial metal from smaller pieces by allowing blacksmiths to join metal and steel. 2. It is particularly useful in the welding process of weapons like swords. 3. It is crucial in creating architectural structures such as gates and prison cells. 4. It is useful in the welding barrels of shotguns. 5. Forge welding is usually employed in the production of various cookware.
  81. 81. 82 Advantages Forge Welding The advantages of forge welding include; 1. It is relatively straightforward and less complicated. 2. It can easily be carried out by most blacksmiths because it doesn’t cost much and requires only small pieces of metal. 3. Forge melting is sufficient to join both dissimilar and similar metals. 4. The weld joint usually takes most of its properties from the base material. 5. Forge welding of metals does not require any filler material to be reliable.
  82. 82. 83 Disadvantages Forge Welding The disadvantages of blacksmithing include; 1. It is not useful for mass production of materials. 2. It is preferable for steel and iron. 3. The forge welding process is relatively slow.
  83. 83. THERMIT WELDING 84
  84. 84. 85 THERMIT WELDING
  85. 85. THERMIT WELDING 86
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  87. 87.  A flux coating is a layer of a chemical which acts as a cleaning agent, a purifying agent or a flowing agent. The coating is used on electric welding rods and serves several functions. It protects the weld pool and solid metal from atmospheric contamination and helps in removing impurities from the weld pool 88
  88. 88. 89 Why do we use a Step Down Transformer ? A Step Down Transformer is designed to reduce the voltage from the primary winding to secondary winding. We use a Step Down Transformer as it converts a high voltage & low current alternating source to a low voltage & high current alternating supply.
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