Production Technology Lect. 3: Welding Processes PDF

Production Technology Lect. 3: Welding Processes Associate Prof. Mohamed A. Bhlol  Welding Processes Classification American Welding Society (AWS) has classified the welding processes as shown in Figure 1.  Shielded–metal Arc Welding (SMAW) SMAW is the most common type of...

Production Technology Lect. 3: Welding Processes Associate Prof. Mohamed A. Bhlol  Welding Processes Classification American Welding Society (AWS) has classified the welding processes as shown in Figure 1.  Shielded–metal Arc Welding (SMAW) SMAW is the most common type of arc welding. It uses a consumable covered electrode (metal wire). The electrode consisting of a core wire around which a flux coating is extruded. Electrode flux melts and forms a shield to protect the weld area from atmospheric contamination. The metal electrode also melts, and it combines with the molten base metal in the weld area as a filler metal.  Shielded–metal Arc Welding (SMAW) Principle and equipment  Shielded–metal Arc Welding (SMAW) Principle and equipment The electrode and the work are part of an electric circuit. Two cables come out from the power source. One is connected to the workpiece and the other to the electrode holder. To strike the electric arc, the electrode is brought into contact with the workpiece by a very light touch with the electrode to the base metal then is pulled back slightly. This initiates the arc and thus the melting of the workpiece and the consumable electrode and causes droplets of the electrode to be passed from the electrode to the weld pool.  Shielded–metal Arc Welding (SMAW) SMAW equipment components: A welding generator (D.C.) or Transformer (A.C.) Two cables- one for work and one for electrode a ground clamp Electrode holder Electrode Protective shield Gloves Wire brush Chipping hammer  Shielded–metal Arc Welding (SMAW) Polarity: The term polarity in welding may be attributed to the fact that every electrical circuit have negative and a positive terminals or pole. In a DC circuit the current flows in one direction only. The cable that carries current from the supply is called the positive side. The welding circuit in arc welding may be one of two types: 1) Direct current straight polarity (DCSP) or (DCEN) 2) Direct current reverse polarity (DCRP) or (DCEP)  Shielded–metal Arc Welding (SMAW) 1) Direct current straight polarity (DCSP) or (DCEN) Workpiece is connected to the positive side of the circuit and the electrode is attached to the negative side. more power (about two- thirds) is located at the work end of the arc and less (about one-third) at the electrode End. narrow and deep weld  Shielded–metal Arc Welding (SMAW) 2) Direct current reverse polarity (DCRP) or (DCEP) The work is made negative and the electrode positive Heating effect of electrons is now at the electrode Shallow weld Used for welding thin sheets materials  Shielded–metal Arc Welding (SMAW) Alternating current (AC) Alternating current combines the characteristics of both the deep penetration and the shallow penetration, yielding a penetration depth that is approximately halfway between that achieved by the DC straight and reverse polarity  Types of Welding joints Welded joints Edge Lap Tee Butt Corner joint joint joint joint joint it is used to is used to join is used to join this joint is is used to join join two two members the edges of made by two members members located at two or more lapping one located at aligned in the right angles to members piece of metal right angles to same plane. each other. lying in the over another. each other. same plane. Types of Welding joints  Types of welds used to join the pieces that form the joints: 1. Fillet Weld: * Used to fill in the edges of plates created by corner, lap, and tee joints. * Filler metal used to provide cross section in approximate shape of a right triangle. * Most common weld type in arc and oxyfuel welding. * Requires minimum edge preparation.  Types of welds used to join the pieces that form the joints: Various forms of fillet welds (a) inside single fillet corner joint; (b) outside single fillet corner joint; (c) double fillet lap joint; (d) double fillet tee joint.  Types of welds used to join the pieces that form the joints: 2. Groove Weld: Usually requires part edges to be shaped into a groove to facilitate weld penetration. Grooved shapes include square, bevel, V, U, and J, in single or double sides. Most closely associated with butt joints.  Types of welds used to join the pieces that form the joints: Some groove welds * square groove weld, one side; * single bevel groove weld; * single V-groove weld; * single U-groove weld; * single J-groove weld; * double V-groove weld for thicker sections.  Welding Defects 1. Slag inclusions 2. Gas porosity 3. Incomplete fusion 4. Incomplete penetration 5. Excessive penetration 6. Spatter 7. Cracks 8. Undercut 9. Underfill  Welding Terminology There is some special technical language that is used in welding. The basic terms of the welding language include: 1) Filler Material: When welding two pieces of metal together, we often have to leave a space between the joint. The material that is added to fill this space during the welding process is known as the filler material (or filler metal). Two types of filler metals are commonly used in welding are welding rods and welding electrodes.  Welding Terminology 2) Welding Rod: It is a form of filler metal that does not conduct an electric current during the welding process. The only purpose of a welding rod is to supply filler metal to the joint. 3) Electrode: It is the component that conducts the current from the electrode holder to the metal being welded. Electrodes are classified into two groups: consumable and nonconsumable.  Welding Terminology 4) Consumable Electrode: Consumable electrodes not only provide a path for the current but they also supply filler metal to the joint. An example is the electrode used in shielded metal-arc welding. 5) Nonconsumable Electrode: Non-consumable electrodes are only used as a conductor for the electrical current, such as in gas tungsten arc welding. The filler metal for gas tungsten arc welding is a hand fed consumable welding rod.  Welding Terminology 6) Flux: The term flux refers to a material used to dissolve oxides and release trapped gases and slag (impurities) from the base metal such that the filler metal and the base metal can be fused together. Fluxes come in the form of a paste, powder, or liquid. 7) Deposited Metal: Material which is added, either from the electrode or filler wire, to build up the weld profile  Welding Terminology 8) Base Metal: is the material to be welded, soldered, or cut. 9) Weld Metal: That portion of a weld that has been melted during welding. 10) Weld pool: commonly refers to the workable portion of a weld where the base metal has reached its melting point and is ready to melt with filler material.  Welding Terminology 11) Heat-affected zone (HAZ): That portion of the base metal that does not melt but its structure or properties have been changed by the heat of welding or cutting. Thank you