1. ELECTRIC ARC WELDING1

2. Definition Electric arc welding: A group of fusion welding processes that use an electric arc to produce the heat required for melting the metal and filler material.2 3. Common Electric Arc Welding Processes 1. SMAWShielded Metal Arc Welding2. GMAWGas metal arc welding3. FCAWFlux core arc welding4. GTAWGas tungsten arc welding3 4. 4 5. Additional Arc Welding Processes 1. SAWSubmerged Arc Welding2. ESWElectroslag Welding3. EGWElectrogas Welding4. PAWPlasma Arc Welding5. ASWArc Stud Welding5 6. Arc Welding Requirements How do these arc welding processes meet the three requirements of arc welding?HeatShieldingFiller MaterialSMAWElectric arcInert gas-fluxConsumable electrodeGMAWElectric arcInert gasConsumable wireFCAWElectric arcInert gascylinderConsumable wireGTAWElectric arcInert gascylinderManual rod6 7. Heat 7 8. Arc Welding Electrical Terms To understand how an electric arc welder produces the correct heat for arc welding, you must understand the following fourteen (14) electrical terms.1. Electrical Circuit8.Constant potential2. Direct current (DC)9.Constant current3. Alternating current (AC)10.Voltage drop4. Ampere11.Open circuit voltage5. Volt12.Arc voltage6. Resistance13.Polarity7. Ohms Law14.Watt 8 9. Terms 1 - ElectricalCircuit An electrical circuit is a completepath for electricity. Establishing an arc completes an electric circuit .9 10. Terms 2 - Direct Current Direct current: Atype of current where the flow of electrons is in one direction. the direction In arc welding of flow is called the polarity. Recommended for out of position welding and low hydrogen electrodes. Electricity flows from negative to positive. The positive terminal will be hotter. 10 11. Terms 3 Alternating Current Alternating current: Thetype of current where the flow of electrons reverses direction at regular intervals. Recommended currentfor SMAW general purpose electrodes and flat position.11 12. Terms 4 - Ampere Amperes: the unit of measure forcurrent flow. One ampere is equal to 6.241509481018 electrons passing by a point per second. Electricity passing through a resistance causes heat. Change the amperage or change the resistance. An air gap is a high resistance Excessive amperage for the diameter of the electrode (current density) over heats the electrode, excessive penetration. Insufficient amperage for the diameter of electrode makes the electrode hard to start, reduced penetration. 12 13. Terms 5 Voltage Voltage is the measure ofelectromotive force (Emf). Emf is measured in units of volts Voltage is adjustable the electrode The voltage at on dual control machines. for SMAW determines the ease of starting and the harshness of the arc.13 14. Terms 6 Resistance Resistance is the characteristic of a material that impedes the flow of an electrical current. Measured in units of Ohms ( ) When an electrical current passes through a resistance heat (BTU) is produced.14 15. Terms 7 - Ohms Law Commonly expressed as:E=IR Voltage is equal to amps xresistance For arc welding rearranged as: Amperage is the voltagedivided by the resistance.E I= R 15 16. Terms 7 - Ohms Lawcont. Ohms law also be used to teach a principle of electrical safety. Amperage is the harmful portion of electrical current. Rearranging Ohms Law for amperage shows that amperage (current flow) is determined by the voltage divided by the resistance. Voltage is fixed by the circuit design.E I= R What should you do to keep you resistance high when arc welding? The higher the resistance, the less current that will flow for a given voltage. If you accidently come in contact with electric current while arc welding the severity of the shock is determined by the voltage in the circuit and your resistance. 16 17. Terms Constant Potential & Constant Current In the normal operation of a transformer, the amperage and voltage change in opposite direction. As amperage is increased, the voltage decreases, and vies versa. Electrical arc welding power supplies are designed to limit this effect.17 18. Terms 8 - Constant Potential18A constant potential power supply is designed to produce a relatively constant voltage over a range of amperage changes. Primarily used for GMAW FCAW 19. Terms 8 - Constant Potentialcont. 8070 60Volts50 40 3020 10 0 050100150200250AnperesIn the short circuiting process, the voltage stays constant as the amperage changes. Helps with restarting of the arc after it is broken.19 20. Terms 9 - Constant Current In a constant current power supply, the current (amperage) stays relatively constant over a narrow range of voltages. Primarily used for: SMAW TIG20 21. Terms 9 - Constant Current-cont. Increasing the voltage from 20 to 25 volts (25 %) causes the amperage to change from 123 to 132 Amp (4.8%). The voltage is not adjustable for most constant current power supplies. Is it possible to change the voltage while welding with a SMAW power supply? Yes How?21 22. Terms 10 - Voltage Drop Voltage drop is the reduction in voltage in an electrical circuitbetween the source and the load. Primary cause is resistance. Excessive voltage drop reduces the heat of the arc.22 23. Terms 11 - Open Circuit Voltage Open circuit voltage is the potential voltage between theelectrode and the work when the arc is not present. The higher the OCV the easier the arc is to start. The higher the OCV the steeper the volt amp curve.Is the OCV on a welding power supply adjustable?23 24. Terms 12 - Arc VoltageArc voltage is the electrical potential between the electrode and the metal after the arc has started. Which will have the higher value, OCV or arc voltage?Is the arc voltage constant once the arc has started?24 25. Terms 13 - Polarity Polarity (positive & negative) is present in all electrical circuits. Electricity flows from negative to positive Controlling the polarity allows the welder to influence the location of the heat. When the electrode is positive (+) it will be slightly hotter than the base metal. When the base metal is positive (+) the base metal will be slightly hotter than the electrode. What abbreviations are used to indicate the polarity of the electrode?25 26. Terms 14 - Watt Watts are a measure of the amount of electrical energy being consumed. Watts = Volts x Amps The greater the Watts of energy flowing across an air gap the greater the heat produced. Is the wattage for a weld controlled by adjusting the Volts or the amps? Both, depends upon the welding process SMAW amps GMAW volts GTAW amps26 27. Arc Welding Power Supplies--cont. The type of current and the polarity of the welding current are one of the differences between arc welding processes. SMAWConstant current (CC), AC, DC+ or DC- GMAWConstant voltage (CV) DC+ FCAWConstant voltage (CV) DC- GTAWConstant Current (CC) ), AC, DC+ or DC-What should be changed when switch a MIG welder between the GMAW and the FCAW process? 27 28. Safe Practices Arc welders need protection from: Arcs rays Welding fumes Sparks Contact with hot metal28 29. Twelve (12) Considerations When Selecting An Arc Welding Power Supply 1. Maximum Amperage 2. Duty cycle 3. Amperage range 4. Amperage adjustmentmechanism8. Future needs for a power supply 9. Available skills10. Safety5. Input power requirements11. Manufacturer's support6. Initial cost and operating cost12. Open circuit voltage7. Size and portability29 30. 1: Amperage Output The maximum output of the powersupply determines the thickness of metal that can be welded before joint beveling is required. 185 to 225 amps is a common size. For an individual weld, the optimum output amperage is determined by the Thickness of the metal, The type of joint, Welding position and Type of electrode. 30 31. 2: Duty cycle The amount of continuous welding time apower supply can be used is determined by the duty cycle of the power supply. Duty cycle is based on a 10 minute interval. Many power supplies have a sloping duty cycle. Note in the picture there is a circle around the 75 amp setting. Why is it there?What is the guaranteed outcome of exceeding a power supply duty cycle? 31 32. Joints, Welds & Positions Electric arc welding uses the five (5) types of joints and five (5) types of welds and five (5) positions. The five (5) types of joints are; 1-butt 2-corner 3-edge 4-lap 5-T The five (5) types of welds are: 1-Surface 2-groove 3-fillet 4-plug 5-slot The five (5) welding positions. 1-Flat 2-horizontal 3-vertical up 4-vertical down 5-overhead32 33. Weld Defects A weld defect is any physical characteristic in the completed weld that reduces the strength and/or affects the appearance of the weld. The mark of a good welder is the ability to identify weld defects and adjust the welding parameters to eliminate them. Defects that are not visible must be detect by using destructive or nondestructive testing. If the defects in a weld exceed the specifications, the weld must be removed and redone. Welds are removed by grinding, gouging and cutting. Eliminating a weld defect is time consuming and expensive -- you must be able to complete the weld correctly the first time.33 34. Common Defects and Causes DescriptionCause(s)The depth of the weld is less than specifications.Excessive heat Excessive speed.The weld metal is not completely fused to base metal or passes are not completely fused.Incorrect angle Incorrect manipulation Insufficient heatWeld material flows over, but is not fused with the base metal.Slow speed34 35. Common Defects and Causes--cont. DescriptionCause(s)Weld bead does not extend to the desired depth.Low heat Long arc Incorrect joint designSmall indentions in the surface of the weldExcessive gas in the weld zone.Small voids throughout the weld material.Accelerated coolingMoisture Rust Dirt35 36. Common Defects and Causes--cont. DescriptionCause(s)Usually visible cracks on the surface or through the weldAccelerated cooling Constrained joint Small weld volumeCracks in the transition zone between the weld and base metalInduced hydrogen Incompatible electrode or wire Accelerated coolingMisshapen and/or uneven ripplesInconstant speed Incorrect manipulation Incorrect welder settings 36