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. Advantages of electric arc compared to gas welding?
Common Electric Arc Welding Processes • SMAW • GMAW • FCAW • GTAW What do these acronyms stand for?
Additional Arc Welding Processes • SAW • ESW • EGW • PAW • ASW Submerged Arc Welding Electroslag Welding Electrogas Welding Plasma Arc Welding Arc Stud Welding
Arc Welding Requirements How do these arc welding processes meet the three requirements of arc welding? Filler Material Shielding Heat SMAW GMAW FCAW GTAW
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. • Electrical Circuit • Direct current (DC) • Alternating current (AC) • Ampere • Volt • Resistance • Ohms Law • Constant potential • Constant current • Voltage drop • Open circuit voltage • Arc voltage • Polarity • Watt
Terms 1 - Electrical Circuit • An electrical circuit is a complete path for electricity. • Establishing an arc completes an electric circuit . Why is this important for arc welding?
Terms2 - Direct Current • Direct current: A type of current where the flow of electrons is in one direction. • In arc welding the direction of flow is called the polarity. • Recommended for out of position welding and low hydrogen electrodes. • How does changing the polarity change the application of the heat?
Terms3 - 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.
Terms4 - 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. • An air gap is a high resistance Knowing these facts, how do you change the amount of heat at the weld? What are the characteristics of an electrode that was used with excessive current density? What is the effect when the electrode was used with insufficient current?
Terms5 - Voltage • Voltage is the measure of electromotive force (Emf). • Emf is measured in units of volts • The voltage at the electrode for SMAW determines the ease of starting and the harshness of the arc. • Voltage is adjustable on dual control machines. If an arc welder has dual controls, what will the two controls adjust.? Why does the electricity jump across the air gap?
Terms6 - 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. What determines the amount of heat that an electric current will produce? Is the resistance adjustable in the SMAW process? Is the resistance adjustable in the GMAW process?
Terms7 - Ohm’s Law • Commonly expressed as: • Voltage is equal to amps x resistance • For arc welding rearranged as: • Amperage is the voltage divided by the resistance. How does Ohm’s law apply to arc welding?
Terms7 - 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. • The higher the resistance, the less current that will flow for a given voltage. What should you do to keep you resistance high when arc welding? 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.
TermsConstant 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 limit this effect.
Terms8 - Constant Potential A constant potential power supply is designed to produce a relatively constant voltage over a range of amperage changes. Primarily used for GMAW FCAW
Terms8 - Constant Potential—cont. The voltage has only a small change for a large change in amperage. What does this mean for GMAW and FCAW?
Terms9 - 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
Terms9 - 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?
Terms10 - 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. • Are there any circumstances where excessive voltage drop can be a problem when stick welding? Yes Explain!
Terms11 - 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?
Terms12 - 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?
Terms13 - 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?
Terms14 - 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?
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?
Safe Practices • Arc welders need protection from: • Arc’s rays • Welding fumes • Sparks • Contact with hot metal What BMP are used for each hazard?
Twelve (12) Considerations When Selecting An Arc Welding Power Supply • Maximum Amperage • Duty cycle • Amperage range • Amperage adjustment mechanism • Input power requirements • Initial cost and operating cost • Size and portability • Future needs for a power supply • Available skills • Safety • Manufacturer's support • Open circuit voltage
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. What determines the best amperage for a weld?
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?
Joints, Welds & Positions Electric arc welding uses the same five (5) types of joints and five (5) types of welds and five (5) positions discussed in fusion welding. Name the five (5) types of joints. Name the five (5) types of welds. Name the five (5) welding positions.
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.
Common Defects and Causes Description Cause(s) Excessive heat Excessive speed. The depth of the weld is less than specifications. 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
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. • Moisture • Rust • Dirt • Accelerated cooling Small voids throughout the weld material.
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