Electric Arc Welding


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Electric Ars welding is explaing thogoughly for easy understanding and basic knowledge of this technique

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  • Stay dryWear appropriate welding apparelInspect equipment
  • In the short circuiting process, the voltage stays constant as the amperage changes. Helps with restarting of the arc after it is broken.
  • Yes and No. It is an option on some industrial rated machines, but usually fixed on consumer rated machines.
  • OCVNo. It will vary slightly with arc length, depending on if the power supply is constant current or constant potential.
  • DCEN or DCSP [direct current electrode negative or direct current straight polarity]DCEP or DCRP [direct current electrode positive or direct current reverse polarity]
  • Both, depends upon the welding process SMAW amps GMAW volts GTAW amps
  • Over heat power supply.
  • Electric Arc Welding

    2. 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. 3. Common Electric Arc Welding Processes 1. SMAW Shielded Metal Arc Welding 2. GMAW Gas metal arc welding 3. FCAW Flux core arc welding 4. GTAW Gas tungsten arc welding 3
    4. 4. 4
    5. 5. Additional Arc Welding Processes 1. SAW Submerged Arc Welding 2. ESW Electroslag Welding 3. EGW Electrogas Welding 4. PAW Plasma Arc Welding 5. ASW Arc Stud Welding 5
    6. 6. Arc Welding Requirements How do these arc welding processes meet the three requirements of arc welding? Heat Shielding Filler Material SMAW Electric arc Inert gas-flux Consumable electrode GMAW Electric arc Inert gas Consumable wire FCAW Electric arc Inert gascylinder Consumable wire GTAW Electric arc Inert gascylinder Manual rod 6
    7. 7. Heat 7
    8. 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 Circuit 8. Constant potential 2. Direct current (DC) 9. Constant current 3. Alternating current (AC) 10. Voltage drop 4. Ampere 11. Open circuit voltage 5. Volt 12. Arc voltage 6. Resistance 13. Polarity 7. Ohms Law 14. Watt 8
    9. 9. Terms 1 - Electrical Circuit  An electrical circuit is a complete path for electricity.  Establishing an arc completes an electric circuit . 9
    10. 10. Terms 2 - Direct Current • Direct current: A • type 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. 11. Terms 3 Alternating Current  Alternating current: The type of current where the flow of electrons reverses direction at regular intervals.  Recommended current for SMAW general purpose electrodes and flat position. 11
    12. 12. Terms 4 - Ampere • Amperes: the unit of measure for current flow. • One ampere is equal to 6.24150948×1018 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. 13. Terms 5 Voltage  Voltage is the measure of electromotive 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. 14. Terms 6 Resistance  Resistance is the characteristic of a material that impedes the flow of an electrical current.  Measured in units of Ohm’s ( )  When an electrical current passes through a resistance heat (BTU) is produced. 14
    15. 15. Terms 7 - Ohm’s Law  Commonly expressed as: E=IR  Voltage is equal to amps x resistance  For arc welding rearranged as:  Amperage is the voltage divided by the resistance. E I= R 15
    16. 16. Terms 7 - Ohm’s Law—cont. • Ohm’s law also be used to teach a principle of electrical safety.  Amperage is the harmful portion of electrical current.  Rearranging Ohm’s 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. 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. 18. Terms 8 - Constant Potential 18 A constant potential power supply is designed to produce a relatively constant voltage over a range of amperage changes. Primarily used for GMAW FCAW
    19. 19. Terms 8 - Constant Potential—cont. 80 70 60 Volts 50 40 30 20 10 0 0 50 100 150 200 250 Anperes In the short circuiting process, the voltage stays constant as the amperage changes. Helps with restarting of the arc after it is broken. 19
    20. 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 TIG 20
    21. 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. 22. Terms 10 - Voltage Drop  Voltage drop is the reduction in voltage in an electrical circuit between the source and the load.  Primary cause is resistance.  Excessive voltage drop reduces the heat of the arc. 22
    23. 23. Terms 11 - Open Circuit Voltage  Open circuit voltage is the potential voltage between the electrode 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. 24. Terms 12 - Arc Voltage Arc 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. 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. 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 amps 26
    27. 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.  SMAW Constant current (CC), AC, DC+ or DC-  GMAW Constant voltage (CV) DC+  FCAW Constant voltage (CV) DC-  GTAW Constant Current (CC) ), AC, DC+ or DC- What should be changed when switch a MIG welder between the GMAW and the FCAW process? 27
    28. 28. Safe Practices Arc welders need protection from: – Arc’s rays – Welding fumes – Sparks – Contact with hot metal 28
    29. 29. Twelve (12) Considerations When Selecting An Arc Welding Power Supply 1. Maximum Amperage 2. Duty cycle 3. Amperage range 4. Amperage adjustment mechanism 8. Future needs for a power supply 9. Available skills 10. Safety 5. Input power requirements 11. Manufacturer's support 6. Initial cost and operating cost 12. Open circuit voltage 7. Size and portability 29
    30. 30. 1: Amperage Output  The maximum output of the power supply 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. 31. 2: Duty cycle  The amount of continuous welding time a power 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. 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-overhead 32
    33. 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. 34. Common Defects and Causes Description Cause(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 heat Weld material flows over, but is not fused with the base metal. Slow speed 34
    35. 35. Common Defects and Causes--cont. Description Cause(s) Weld bead does not extend to the desired depth. Low heat Long arc Incorrect joint design Small indentions in the surface of the weld Excessive gas in the weld zone. Small voids throughout the weld material. Accelerated cooling Moisture Rust Dirt 35
    36. 36. Common Defects and Causes--cont. Description Cause(s) Usually visible cracks on the surface or through the weld Accelerated cooling Constrained joint Small weld volume Cracks in the transition zone between the weld and base metal Induced hydrogen Incompatible electrode or wire Accelerated cooling Misshapen and/or uneven ripples Inconstant speed Incorrect manipulation Incorrect welder settings 36