Electric Arc Welding Section 8 Unit 25 & 26

Introduction Electric arc welding A group of fusion welding processes that use an electric arc to produce the heat required for melting the metal. Advantages Inexpensive power source Relatively inexpensive equipment Welders use standard domestic current. Portable equipment is available Process is fast and reliable Short learning curve Equipment can be used for multiple functions Electric arc is about 9,000 oF

Introduction-cont. All fusion welding process have thee requirements. Heat Shielding Filler metal The method used to meet these three requirements is the primary difference between arc welding processes.

Arc Welding Requirements Filler Material Process Heat Shielding Stick Electrode SMAW Electric Arc Inert Gas (Flux) Electric Arc Inert Gas (Cylinder) Wire Electrode GMAW In this class you will have the opportunity to use two (2) arc welding processes: SMAW GMAW

Eight Additional Electric Arc Welding Processes FCAW GTAW SAW ESW EGW PAW ASW Flux Core Arc Welding Gas Tungsten Arc Welding Submerged Arc Welding Electroslag Welding Electrogas Welding Plasma Arc Welding Arc Stud Welding

Safe Practices Welders need protection from: Arc’s rays Welding fumes Sparks Contact with hot metal

Arc Welding Power Supplies The current for arc welder can be supplied by line current or by an alternator/generator. The amount of heat is determined by the current flow (amps) The ease of starting and harshness of the arc is determined by the electrical potential (volts). Welding current adjustments can include: Amperage Voltage Polarity High frequency current Wave form

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+ or DC- GTAW Constant Current (CC) ), AC, DC+ or DC-

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. 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.

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 may be 100%, but usually is less. 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 most likely outcome of exceeding a power supply duty cycle?

Five Common Output Currents For Arc Welding 1. AC (Alternating Current) 2. DC (Direct Current) 3. ACHF (Alternating Current-High Frequency) 4. PC (Pulsed Current) 5. Square wave

Arc Welding Electrical Terms To understand how an electric arc welder works, you must understand the following thirteen (13) 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

Electrical Circuit An electrical circuit is a complete path for electricity. Establishing an arc completes an electric circuit .

Alternating Current Alternating current: The type of current where the flow of electrons reverses direction (polarity) at regular intervals. Recommended current for SMAW general purpose electrodes and flat position.

Direct Current Direct current: The type of current where the flow of electrons (polarity) is in one direction. Controlling the polarity allows the welder to influence the location of the heat. When the electrode is positive (+) DCRP or DCEP it will be slightly hotter than the base metal. When the base metal is positive (+), DCSP or DCEN, the base metal will be slightly hotter than the electrode. DC current is required for GMAW It is frequently used for SMAW

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 The greater the amperage flowing through the resistance (air gap)--the greater the heat. The electrode also has resistance. Excessive amperage for the diameter of the electrode (current density) over heats the electrode. Insufficient amperage for the diameter of electrode makes the electrode hard to start. What are the characteristics of an electrode that was used with excessive current density?

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. Higher voltage = easier starting. Starting voltage is called OCV. Voltage is adjustable in dual control SMAW machines. Changing the voltage adjusts a GMAW machine for different metal thickness.

Resistance Def: that 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. The amount of heat produced is a function of the amount of resistance (Ohm’s) and the amount of current (amps). Is the resistance adjustable in the SMAW process?

Ohm’s Law Ohm's law states that, in an electrical circuit, the current passing through a material is directly proportional to the potential difference. Commonly expressed as: 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. The higher the resistance, the less current that will flow for a given voltage. What does this principle mean for SMAW?

Constant Current In the normal operation of a transformer as amperage is increased, the voltage decreases, and vies versa. Electrical arc welding power supplies are modified so that either the voltage or the amperage is relatively constant as the other factor changes. This allows two different types of power supplies: Constant current Constant potential In a constant current power supply, the current (amperage) stays relatively constant when the voltage is changed. GMAW In a constant potential power supply, the voltage stays relatively constant when the amperage is changed. SMAW

Constant Current--cont. Characteristics of constant current power supply. The machine provides a high voltage for striking the arc. Open circuit voltage (OCV) OCV is not adjustable for most machines When the arc is struck the voltage drops to the welding voltage. Arc voltage Arc voltage varies with the arc length. As the welding proceeds the current will not vary much as the arc length changes.

Constant Current-cont. Increasing the voltage from 20 to 25 volts (25%) only decreases the amperage from 113 to 120 Amp (5.8%).

Constant Potential The constant potential power supply is modified to produce a relatively constant voltage as the amperage changes. Characteristic of GMAW power supplies.

Voltage Drop Voltage drop is the reduction in voltage in an electrical circuit between the source and the load. Primary cause is resistance. When an excessive voltage drop exists, the electrical circuit will not perform as designed. Localized resistance (connection) can cause excessive heat. Excessive heat can cause component failure. When extra long welding leads are used, the amperage must be increased to have the same heat at the weld.

Joints, Welds & Positions Electric arc welding uses the same five (5) types of joints and five (5) types of welds and five (5) positions. Five (5) joints: Corner Butt Lap Edge T

Joints, Welds & Positions Five types of welds Surface Groove Fillet Plug Slot

1. Surface Welds Surface welds are welds were a material has been applied to the surface of another material. May or may not be blended with the work piece. Two common applications are for hard surfacing and padding.

2. Groove Welds Groove welds are used to fuse the sides or ends of two pieces of metal. The primary use of groove welds is to complete butt joints.

3. Fillet Welds Fillet welds have a triangular cross section and are used to fuse two faces of metal that are at a 90 degree angle to each other. Lap Joint Outside Corner T Joint

4. Plug Welds Plug welds are used to attach two surfaces together when a complete joint is not required and the design does not allow for any weld bead outside the dimensions of the metal. The holes can be made with a drill bit or punch. The weld is completed by establishing the arc on the bottom plate and then continuing to weld until the hole is full.

5. Slot Welds Slot welds are identical to plug welds except for the shape of the holes. For slot welds, slots are machined or stamped in the upper plate. They are complete the same as plug welds.

Joints, Welds & Positions Arc Welding Positions Flat Horizontal Vertical Up Vertical Down Overhead

Weld Nomenclature Bead Penetration Base metal Reinforcement Joint Angle Bead Root Face Excessive Penetration Root Opening

Weld Nomenclature-cont. Reinforcement Toe Face Throat Leg Toe Root Leg

Weld Nomenclature-cont. In multiple pass welds, each pass has a specific function. A tack weld is used to hold the joint at the desired gap. If it is not used, the heat of the weld will cause the joint to close. Cover Pass Filler Pass Root Pass The root pass is used to fuse the root of the weld. If the root pass does not have adequate penetration, it must be cut or gouged out before the weld is completed. Tack Weld The filler pass is used to fill in the joint. A pattern bead or multiple stringer beads will be used. The cover pass isn’t used for strength. It is used for appearance and to fill in surface voids.

Bead Patterns Pattern beads are used whenever a wider bead is needed. Hardsurfacing Filler pass Cover pass Reduce penetration Common patterns: Circle Crescent Figure 8

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) 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

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

Q u e s t i o n s