Weld 20 Introduction to Gas Metal Arc Welding GMAW

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1 Fall 2009 Weld 20 Introduction to Gas Metal Arc Welding GMAW 1. Introduction a. Syllabus and Grading. b. Weld Sign-Off Sheets. c. Personal Equipment List. d. Clean-up Procedures. Turn off machine & gas valve. Clean metal out of the booths. Scrap metal goes in the scrap metal bins outside. Do not quench metal in the sinks. Put all tools away. Put all of your personal items away. Sweep the booths w/ broom & dust pan. Clean all counter surfaces. e. The shop (Yuba College) is not liable for your personal equipment. f. 1hr clean-up assignment at the end of the semester. g. Shop Safety. 2. Welding Terms a. Fusing; heating two or more metals or nonmetals until they become liquid, then allowing them to join and. b. Fusion Welding; the use of heat and/or pressure to join two or more pieces of material to form one continual piece indistinguishable from one another. Welding always happens above degrees F. c. Adhesion Welding; Brazing & Soldering, does not melt. (Coalescence of metals) d. Electrode; Filler metals designed to have running though them. e. Rod; Filler metals that are to the welding puddle, melts by heat of flame (OAW) or arc (GTAW). 3. Arc Welding a. Welding process which uses an for welding heat. Processes b. SMAW; Shielded Metal Arc Welding Stick welding, arc welding and stick arc Uses a flux covered electrode Flux creates shielding gas to protect. (Oxygen, Nitrogen) Constant power source. c. GMAW; Gas Metal Arc Welding Also referred to as MIG/MAG, Micro-wire or CO² welding MIG Metal Gas; inert or non-reactive gas, Argon, Helium. MAG Metal Active Gas; CO2 1

2 Uses continuous wire as an electrode & shielding gas in place of. Uses Constant power source. Past - less than 1% of filler metal sold. Today - more than % of filler metals sold. Faster travel speeds, smaller wire sizes, less expensive shielding gases, improved welding techniques and higher deposition rates. Welds both ferrous ( ) and non-ferrous metals. Welds a wide range of metal thicknesses. Less smoke so the weld puddle can be clearly seen by the welder. Faster welding speeds and. Decrease in equipment development and cost. Equipment is to use. Easy to learn. d. FCAW; Flux Arc Welding Uses a continuous wire as it s electrode. Can be inner shield or outer shield (needs a shielding gas) Used where very deposition rates are required. Usually used for materials. e. GTAW Gas Arc Welding TIG Tungsten Gas Heliarc Helium was shielding gas. Used where and control of the weld puddle is required. Uses a tungsten electrode and rod for filler metal. 4. Flame Welding a. Welding process which uses a for welding heat. Process b. OAW; Oxy-Acetylene Welding Mixture of Oxygen & Acetylene to create flame as source. Creates gas which shields molten pool from atmosphere. Filler rod added to increase weld. Manual process, used primarily for gauge steel and repair work. 5. Cutting a. Cutting process which uses for metal removal. Processes b. OAC; Oxy-Acetylene Cutting Mixture of Oxygen & Acetylene to create flame as heat source. Burning process; metal brought to (burning temperature), Oxygen under pressure is introduced to accelerate burning process and blow away metal. Torch designed for cutting. 2

3 c. PAC; Plasma Cutting Constricted arc for heat. High velocity jet of gas removes molten metal. High speed cutting of ferrous & metals. Compressed air works for. d. CAC-A; Carbon Arc Cutting - Air Air Carbon Arc Cutting or. Arc created between electrode and base material. Compressed blows away molten puddle. Constant power source used for SMAW. Electrode holder designed for CAC. 6. GMAW a. United States; C.L. Coffin, Bare metal electrodes patented in. History b. Oxyacetylene welding also being used. c. Bare Electrode welding produced inferior welds, arc. d. 1908; SMAW, coated electrodes developed, displaced electrodes. e. Electrodes improved through the. SMAW popular; eliminated interest in the gas shielding process. f. GTAW (TIG) welding was introduced in the and it was the forerunner of the current gas shielded processes. Use of inert gas made quality welds for ferrous and non-ferrous metals. High cost for. Thick materials required. Increase in and Magnesium products. welding process. g. GMAW; patent for GMAW (MIG/MAG). Uses heat of an electric arc produced between a wire electrode and the base metal. Arc is created by passing electricity through an gas Atoms are ionized when they lose an electron creating a charge. The ions flow from + to and to +. Approximately % of the heat is carried by the electron and the rest is carried by the positive ions. The current GMAW process displaced the slower process. Immediately became popular and was used to weld (do not contain iron) metals. MIG was originally used with to weld aluminum. Could also be used to weld mild and low alloy, cost of the inert gas much higher than flux coated electrodes. 3

4 Flux coated electrodes produce. Discovery lead to use of CO² in the MIG process on Mild and lo-alloy steels. Originally, problems with porosity in welds due to low quality CO² and. CO² process became very popular in the with higher quality gases. Limited to flat & horizontal welds, spatter problems, very fasthard to operate manually. Improved (Constant Voltage) lead to; reduced spatter, smaller wire (Micro-wire) and puddle size, more controlled arc length, welding in all positions. Micro-wire used 100% CO² shielding gas, most commonly used gas today on. added to soften arc. More expensive. More than SMAW; higher quality welds, no slag = less clean-up, little to no spatter, higher deposition rates. ; Spray/ Pulse Spray developed, not commercially viable until solid state electronics were developed. 7. GMAW Types 8. GMAW Advantages a. Semiautomatic Machine controls the wire feed. Movement of the welding gun controlled by. Machine controls arc. Most popular method. b. Mechanized Machine controls the arc length, wire feed and joint guidance of the gun (not hand held). Operator controls the. c. Automatic Uses equipment that is not constantly controlled by an operator. Machinery controls the welding parameters, arc length, joint guidance and wire feed. most popular method. d. Manual Cannot be done with this process a. Highly Process Semiautomatic process. Eliminates the starting and stopping when changing or filler metal like GTAW and SMAW. Higher rates. Saves time with no or little clean-up of and spatter. consumable electrode process that can weld most all commercial metals and alloys, ferrous and non ferrous. 4

5 Variables can be set prior to welding and they will remain constant throughout the. A higher percentage of filler metal is in the weldment. One welding package can weld many types of joints changing equipment. operation, no welding breaks as with stick welding. b. Weld Quality Eliminates starting and stopping failure, wire is fed. Low process; alloy steels can be welded with less risk of cold cracking, Low heat input with high current density, Smaller (Heat Affected Zone), less distortion, more penetration on thin materials. No flux on electrode wire to attract. c. Ease of Operation Less ; allows the welding arc to be clearly seen reducing slag inclusions, incomplete fusion, crater cracking, etc. Allows the operator to concentrate on the weld. Ability to weld in any. Some lighter weight power sources can be hand-carried. d. Versatility Multiple metal methods. Short arc (Short Circuit Transfer) used on gauge materials. Globular- no longer used on structural applications Axial Spray; deeper penetration than, can produce smaller fillet welds with relatively the same strength. Wide current ranges. CV machines can also run Flux Cored, easily be changed back and forth. e. Increased operator safety Low voltages used. 9. GMAW a. Equipment is more complex and costly than. Limitations b. Arc requires shielding ; wind and other elements may blow the shielding gasses away from the arc. c. Larger welding. Difficult to reach some areas or tight spots. Visibility of the puddle and weld area affected by the. d. Many parameters to affect welding may be to completely understand. 5

6 e. Increased costs with equipment: welding guns, liners, drive rollers, etc. f. Less than SMAW. 10. Equipment a. Examine your equipment before welding (every time). Look for cables, worn insulation, or any damages to the equipment. Check the lead, a damaged work lead can cause you to become the ground. Check welding lead, worn leads can lead to an arc. b. Typical Equipment Identification 6

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8 11. Basic Welding a. Voltage, Current (amperage) and. Electricity b. Ohms Law; E = IR, I=E/R and R=I/E E = Voltage I = Current R = Resistance c. Voltage; that causes electron flow. (pressure in hose) Determines potential heat. Sets Arc Length in CV machine. Arc length determines how well the puddle or weld pool will (flatten) out. OCV; Open Circuit Voltage, set on front of machine. Can be as high as V. Voltage while no welding is being done. Load Voltage; voltage after arc is established. Drop of volts per 100 amps is acceptable. d. Current (Amperage); amount of electron past specific point in 1 second. (amount of water coming out of hose) Electron flow is to positive (theoretically). GMAW, amperage is set as speed (WFS) Wire speed determines amount of weld build-up. One knob controls both wire speed and. Effected by distance. e. Resistance; to electron flow, measured in Ohms. (diameter of hose) Greatest resistance is. Resistance across arc gap (air) provides for welding and preheats the electrode. Added stick out the resistance in the welding electrode decreasing the voltage to jump the arc gap -cooling the weld puddle. Decreased CTWD lessens the resistance in the welding electrode to jump the arc gap thus heat in the weld puddle. Welding cables must be sized correctly and in good condition to lesson. 8

9 12. Primary Power a. Supplied from power. Input b. United States; Wall Voltages, 110, 200 (208), 230, 460 (480), and 575 volts. c. hz (hertz, cycle per second) Europe 50 hz. d. 1-phase or 3-phase. 3-phase; smoother arc characteristics, more electrically. CV machines require a very smooth method of delivering voltage and amperage. Internal components have to be added for single phase machines to smooth out the electrical output. Autoline- type power supply can operate on either. e. Current from the wall is not suitable for welding. High Voltage Amperage. 13. GMAW a. Primary purpose; provide the energy to maintain the welding. Power b. Current and voltages may be to adapt for different welding Supplies situations. c. Single phase vs. three phase newer machines detect the primary power and adjusts. manual link machines require the user to set up the machine for the primary power. d. 3-phase has four wires, usually. Ground green Common white Hot black Hot red e. Single phase; drop a leg (usually the red wire), wire in for single phase. f. Both phases have a hot, ground and common, the 3-phase has an extra hot leg. 9

10 14. Power Supply Types a. Generator; driven generator to produce welding electricity. Engine driven generators are popular for welding in the field where electricity is available. Generally CC power supplies require another machine to perform GMAW. Can produce auxiliary power for machine. A style voltage sensing wire feeder can also be used. Noisy, require more maintenance, more expensive and require fuel or an electric motor to run. b. Transformer Rectifier; uses static (nonmoving parts) to the primary power into usable electricity for welding. Most popular machines in industry. Being replaced by. Transformer converts High Voltage/ Amperage primary power to Low Voltage/ Amperage current. changes AC to DC current. Solid State (semiconductors) controls provide the volt amp curve vs. a non solid state device. c. Inverter Machines Components 1. Rectifier: 60 Hz AC to 60 Hz. High Voltage, Low Amperage. 2. Filter: Smoothes DC current. 3. Integrated Circuit: Changes DC current to high frequency. Lincoln; (IBGT) Insulated Gate Bipolar Transistor Miller; (SCR) Silicon Controlled Rectifier Hobart; (TCR) Time Ratio Control 4. Transformer: High frequency, high voltage/low amperage AC to high frequency, low voltage/ amperage AC. 5. Rectifier: High frequency AC to rippled. 6. Choke: Smoothes DC high frequency rippled current Require much less electricity to operate. cooling fans. Less noise. 10

11 response time. Controlled Volt/Amp curve. Utilizes switches to turn on or off the flow of electricity. Higher switching and control frequency produces stable arc characteristic, more efficiency and greater performance Multipurpose models; can accommodate or welding operations. Inverters are becoming more inexpensive, more available to welding shops. More portable; smaller size/weight. Smaller windings more expensive. More sensitive to cable length. 15. Constant a. Constant Voltage Machine; maintains a constant which Voltage establishes arc length. -vs- b. GMAW usually uses a CV power source. CC can be used w/voltage- Constant sensing wire feeder. Delivers a spray or globular transfer only. Current c. CV also referred to as Constant (CP) machines. CV adjusts voltage on the, CC machines adjusts the amperage (current) on the front. CV machines that have a built in wire feeder have a second knob to adjust wire feed speed to adjust the. Systems w/separate wire feeder will adjust the wire feed & amperage on the wire feeder. 11

12 16. Current a. Two types; Alternating current (AC) & Current (DC) Polarity b. DC; two kinds, Direct Current Electrode (DCEP) Direct Current Electrode (DCEN) c. AC; heat distribution is relatively. Electron flow - 50% Positive / 50% Negative. d. DCEP; Electrons flow from negative work piece to electrode. Formerly called Polarity. % of heat located in the electrode % in work piece. Forceful, digging arc. Deeper penetration than and AC Used for most GMAW operations. e. DCEN; Electrons flow from negative electrode to work piece. Formerly called Polarity. % of heat located in the electrode % in work piec Less forceful arc. More shallow penetration than and AC. Polarity Electrode Base Metal DCEP 70% 30 % DCEN 30 % 70 % AC 50 % 50% 17. Machine a. Duty Cycle; the number of minutes (out of minutes) which the Selection power supply can be operated at a specified amperage. Ex. 200 amps = amps. % duty cycles are standard for CC machines; welder has to stop and change electrodes, chip slag, wire brush the weld bead, etc. Modern power supplies, most industrial GMAW power supplies will have a % duty cycle In general, duty cycle is inversely proportional to the current; as current goes up, duty cycle goes. Pick a machine that has a duty cycle that will operate where you will spend % of your time. b. Polarity; AC, DCEP, DCEN AC; SMAW, GTAW (alumimum). DCEP; GMAW, SMAW, FCAW-gs, DCEN; GTAW (mild steel & stainless), FCAW-ss. c. Brand Customer service, warranty, ease of use, etc Consumable costs may be different, and availability may vary depending on the supply house, and popularity of the brand. Off brands may be cheaper initially, but can cost more in the long run. 12

13 d. Processes; process power source may be better deal. 18. Voltage a. Different types depending on make and model. Controls b. Voltage control Voltage is adjusted on the front of the welding machine. Setting the voltage sets the arc. Voltage must be balanced with wire speed ( ). c. Tap and plug selector. have a fine voltage adjustment and increase or decrease by a selected voltage. High range (20-32V) and a low range (12-20V) the welder would then select tap 1-6 which adjust the machine by 1 1/3V increments tap 1= 12V and tap 6= 20V in the low range and tap 1=20V and tap 6=32V in the high range setting d. Selection Switch; Rotating knob to select voltage, represented by a or letter. i.e. 1-7 or A-G. e. Infinite control knob. tune settings. f. Auto-Set; Millermatic 140 Adjust to wire diameter, sets amperage. Adjust to material thickness, sets. Millermatic 212 Millermatic

14 19. Wire Speed a. GMAW; Wire speed set on front of or on wire feeder. Controls b. Wire speed also helps determine metal transfer. Short Circuit Transfer; wire speed to high for low voltage, metal touches base metal and shorts out. Globular and Axial Spray Transfer; wire speed slow enough and voltage high enough to create constant arc. c. WFS (Wire Feed Speed) is given in (ipm) IPM is dependant on thickness and type of metal to be joined, diameter of wire, mode of transfer, weld joint type, etc. d. Material Thickness / Amps/ IPM Conversion constants for wire size and wire feed speed. metal requires 1 amp per every 1000th of an inch 1/8 =0.125 which requires 125 amps wire = 2 times every amp i.e. 1/8 = X 2= wire speed of wire =1.6 times every amp i.e.1/8 = 125 X 1.6= wire feed of wire = 1 times every amp i.e. 1/8 = 125 X 1 = wire feed of 125 These are good starting points and may be changed according to power source being used. e. Metal Thickness / Amperage 14

15 f. General Wire Size, Amperage, and Wire Feed Speed Settings 20. Welding a. Delivers filler metal, shielding gas, to weld area. Guns b. Types; Air Cooled and Water Cooled. c. Conventional; wire feeder wire through liner and gun. Curved to straight neck, different lengths. d. Push/Pull; drive rolls in gun, wire feeder pushes wire, gun wire. Used for soft & cored wires (aluminum, flux core). e. Spool Gun; contains spool of wire, wire feeder as one unit. Uses low motor to drive the wire. f. FCAW-ss; no nozzle, process does use shielding gas. have a straightening curve back to straighten the wire to ensure contact with the contact tip. 21. Gun Parts a. Nozzle; directs shielding gases to the welding area. Slip on nozzles can be loose and short against the. Spatter build up on the nozzle, use MIG pliers to clean, do not against the table. b. Bernard system, nozzle screws on, secures the. Contact tip does screw on. Eliminate cross threading and wear patterns. Made to specific lengths. Nozzle number ends in 00,end is with the contact tip. Number ends in 18,1/8th to the contact tip. Short circuit transfer; Flush w/tip - Brass Axial spray or pulsed spray; recessed tip - copper c. Insulator to keep the nozzle from becoming charged during welding operation and shorting to the base metal. d. Contact tip, delivers current to the wire as the wire makes. Tips are manufacturer specific; never a contact tip into the diffuser, use proper contact tip is being per manufacturer recommendations. Designed for the wire being used. Too small an orifice, causes wire feed to be difficult or stop. Too large an orifice, wire may not make constant contact with the contact tip leading to an arc. Insure contact tip is firmly attached; not able to move, may short against the nozzle or create arc. 15

16 Most contact tips screws into the diffuser; made in different lengths. Flush for short circuit transfer- can stick out a maximum 1/8th past the nozzle with adequate gas flow. Recessed for axial spray or pulsed spray. Replace if hole is worn or egg shaped; worn contact tip causes erratic arc, outages, cold lap, improper heating of the filler wire and improper weld characteristics. Generally, replace every lbs of wire. e. Diffuser; carries the current to the contact tip, can the shielding gas to provide better coverage. f. Trigger; turns on/off welding circuit, current flow, gas flow, wire feed. 22. Welding Cable a. Supplies welding wire, shielding gas, current to gun. Never use to drag machine around. b. Liner; carries the wire to the gun. Keep straight as possible, do not kink,. Clean with air every time you change the spool of wire. c. Braided cable delivers the. d. Gas line to deliver the gas. 23. Work a. Completes and is part of the welding. Connection b. Attaches power source to. Incorrectly but commonly called the ground connection. Ground connection grounds the (power supply) and equipment. c. Directs electricity away from the person welding for safety. d. Work Clamp; clamp to work, table, structure. Do not through bearings, moving parts. Insure tight connection; will cause arc/wire feed. 24. Wire Feeders a. Controls supply of to welding gun. 16

17 b. Constant speed; used only with a Constant (CV) power source. Feeder has control cable connected to. Control cable supplies power to the feeder, capable of control with certain power source/feeder combinations. Wire Feed Speed (WFS) set on the feeder; will always be for a given preset value. c. Voltage Sensing; can be used with either Constant Voltage (CV) or Constant Current (CC) direct current (DC) power source. Feeder is powered off of the arc voltage and does not have a. When set to (CV), feeder is similar to a constant feeder. When set to (CC), the wire feed speed depends on the present. Feeder changes wire feed speed as the changes. Voltage sensing feeder does not have the capability of voltage control. 25. Wire Feeder a. Mode Switch (optional); selects type of mode (spot, intermittent, Controls seam). b. Trigger Lock (in switch); allows welder to feed wire continuously keeping trigger depressed. c. Burn Back Control; prevents wire from sticking in the weld puddle when the trigger is released. Control. d. Spot Weld Time (optional); controls and of the spot weld process e. Stitch Weld Time (optional); sets duration of the stitch weld when making a long seam weld or a specific weld. f. Pre-Flow; controls the time gas flows weld begins - purging weld area. g. Purge; allows welder to clear lines with shielding gas or set flow meter/gauge prior to welding without feeding. h. Jog or Inching; moves wire through the line without energizing the wire or. i. Reel Brake Control; stops reel from rotating when welding stops. Generally adjusted with a nut in middle of the. Should be adjusted so reel stops within when welding stops. Wire should never touch metal housing or positive power lug 26. Drive Rolls a. Two wheel & Four wheel systems available. Make sure roll size matches wire. Some rollers have two different sizes on one roller. Stamped size on side of roller will be read on opposite groove. 17

18 Some feeder systems will have one drive roller and one or idler roller. Some feeders will have both rollers w/geared teeth. Both rollers wire. b. Push Type Feeders Two rolls; solid and wires. Four rolls; soft or wires. (FCAW) c. Push/Pull Type Feeders Roller sets in both feeder &. wires or long leads. d. Roller Shapes V - Groove; solid,. V - Knurled; tubular,. U - Grooved; soft wires,. e. Drive Roller Tension Set only enough pressure to feed wire. Over tightening flattens the wire. Causes feed issues, may not make full contact at the contact tip. arc/feed. Stop wire with your hand by bending the wire over while feeding. 27. Feed a. Equipment settings, work clamp, variable settings. Problems b. Bird Nest; tangled wire inside of the. Improper roller pressure. Wrong inlet/outlet tube, liner diameter per wire. Wire/tip fusion or burn back. Do not burn off stick-out on edge of. (Safety issue also) Kinking gun. Negative lead cable lug may cause short inside drive assembly compartment. Keep lug covered w/. c. Slipping: Drive Roll tension set. Reel Brake tension set. Drive roll / wire size. c. Worn liner. Last step, check all other variables and equipment first. d. Tip Contact; worn, damaged,. Wire too tight from heat expansion (Spray Arc). May put in tip. Ex = dia. Crushed wire from excessive pressure, poor tip contact. 28. Shielding a. Critical to quality of the finished weld. Gasses b. Gasses act differently under heat of the arc. Effects current flow across the. Effects transfer of molten. Some gasses won t support some modes. 18

19 29. Shielding a. potential of the gas components. Gas b. Thermal conductivity (affects current density) of the Criteria components. c. Ability of gas to transfer. Most important consideration in selecting a shielding gas. High thermal conductivity levels result in more of thermal energy to the workpiece. Affects the shape of arc and temperature distribution within the weld region. d. Chemical reactivity of the shielding gas with the weld puddle. Inert; Argon, Helium,. Reactive; CO2, Oxygen,. e. Selection includes the following (not limited to). Alloy of wire electrode. Desired mechanical properties of the deposited weld metal. Material thickness and Joint Design. Material Condition;, corrosion, resistant coatings or oil. The mode of metal transfer; Short Arc, Spray, Pulse Spray. Welding position, Fit-up conditions. Desired profile. Desired final weld bead profile Gas Densities a. Shielding gasses have different densities. & Flow Rates b. Lighter or than air. Higher flow rates are required for Helium than and Argon. Often up to. c. Joint configuration, position, stick-out, affect flow rate. Tee joints require gas flow than groove joints. Welding overhead; slightly gas flow with heavier shielding gasses. Longer stick-outs; higher shielding gas flow due to the distance between tip to weld puddle. (Spray Transfer) Excessive gun can cause poor gas coverage. d. Gas flow rate; just high enough to shielding for the weld puddle. 15 Cubic Feet Per Hour (CFH); Short Circuit. 30 CFH; Axial and/or Pulse Spray. e. Excessive flow. Cool puddle too rapidly causing. Turbulence, draw in contamination to weld puddle.. Flow meter. f. Gas drift; maximum air flow for GMAW welding. 19

20 31. Argon a. Inert Gas; does not react with molten puddle. b. Chemical symbol;. c. commonly used inert gas. d. More dense than (can use lower flow rates). e. 100% Argon can weld nickel, copper, aluminum, titanium and alloyed metal. 100% for metals most common. Usually for ferrous metals. f. Largest part in (two part) and (three part) gas mixtures for GMAW. g. Easily ionized; can carry across long arcs. Makes it less sensitive to changes in arc. Ionization energy is ev., Argon easier to ionize than, better arc starting than helium. h. Lower thermal conductivity rate than other inert gases. of helium and hydrogen. i. Gas mixtures with high percentages of. Penetration profile; finger like projection into the base metal, due to the thermal conductivity. j. molten droplet transfer rate. k. Supports axial transfer. l. Provides action associated with DCEP. Important in welding. m. Irregular arc and deposit of metals when welding metal. emit electrons that attract the arc, but are not evenly distributed. Problem solved by adding a small amount of. Generally is sufficient. About is acceptable for stainless steel. Prevents scale of chromium oxide. Carbon dioxide may be substituted for Oxygen, but more than is needed. optimal for ferrous metal. Carbon Dioxide mix for ferrous metal; better bead profile, more stable arc. n. Obtained two ways: Cryogenic;, separate the gases as the liquid warms, fractional distillation Non-cryogenic; separate air with a molecular, a screen with very small holes. 32. Helium a. Product of the natural gas industry. b. Atomic symbol;. c. Inert Gas; does not chemically with molten puddle. c. than air; flow rates about that of argon. Stiffness of gas stream must push atmosphere away from the weld puddle. 20

21 d. Requires voltage to ionize. Produces a much arc. e. Makes welding thicker magnesium and easier. f. Commonly added to gas mix for and aluminum. g. Up to helium can be added to argon. power of arc without affecting the desirable attributes of axial spray. helium; transfer process becomes progressively more globular. h. Broad but penetrating bead profile. i. Helium/Argon blend, reduces of base metal in corrosion resistant applications. j. Helium/argon blend; commonly used for aluminum greater than thick. Ionization energy of ev. k. Higher thermal conductivity; provide broader penetration pattern, depth of penetration. 33. Reactive a. Carbon Dioxide, Nitrogen, Oxygen, and Hydrogen. Shielding Gasses 34. Carbon a. Inert at room temperature, reactive at temperature. Dioxide b. 100% carbon dioxide was most commonly used gas for welding steel. Replaced by / blend. c. Advantages: weld speed. Generally penetration. Greater properties. Costs than inert gases. d. Disadvantages: Less steady poor weld bead appearance. More weld (kept to a minimum by maintaining a very short, uniform arc length) Reactive; in the presence of the arc plasma and molten weld puddle. Limited to Short Arc and Globular Transfer modes. e. Carbon dioxide molecule breaks apart ( ) at the DCEP (DC+) side of the arc. Reforms (recombination) at the DC- side of the arc. Ionization energy is ev. f. energy levels exist during recombination. Create deep, broad penetration profile - characteristic of carbon dioxide. g. Carbon Dioxide breaks down into Carbon Monoxide &. Oxygen combines with the silicon, manganese and iron to form. Glass on the finished weld bead; know as. 21

22 levels of carbon dioxide; increases the amount of silicon oxides on surface of weld. levels increase the level of alloy (silicon and manganese) retained in the weld. Must use filler metal w/ high amounts of. h. Carbon - increase the yield and ultimate strength of a finished weld. i. Flow rate not to exceed CFH. Meter Icing; may need manifold system. 35. Nitrogen a. Not inert but relatively to the molten weld pool. b. Atomic symbol is. c. Added to the arc s heat and temperature. d.100% nitrogen is used to weld and copper alloys. 36. Oxygen a. Reactive; mixed in small amounts with other gasses. b. Atomic symbol is O. c. Ionization potential of O 2 is ev. d. Mixed in small amounts ( %) with argon. Provides good and excellent weld bead appearance. e. Larger amounts form in the weld puddle. f. Deoxidizers added filler metal ( ). Compensate for the oxidizing effects of oxygen. Form oxides which to the surface while you are welding. 37. Hydrogen a. Reactive; mixed in small amounts with other gasses. b. Mixed in small amounts ( %) with argon. Welding and nickel alloys. c. High thermal conductivity. Produces a puddle. Promotes improved. Permits travel speeds. 38. Argon Gas a. Oxygen, Carbon Dioxide, Helium and Nitrogen; blended with argon to Blends change its welding characteristics. b. Reactive Oxidizers; Oxygen and Carbon Dioxide. Stabilize the arc, promote a favorable metal transfer, and reduce. Results in an improved pattern. Undercutting is or eliminated. c. Non Reactive Gases Helium or Nitrogen Increases heat. Promotes penetration. 22

23 d. Amount of mix gas required to produce desirable effects are small sometimes as little as %. Most blend a maximum of1-5%. % Carbon Dioxide Less than % Carbon Dioxide may not give the desired results. Most common Carbon Dioxide blend is 25% e. Oxidizing shielding gas. Filler metal must contain to prevent porosity. f. Oxygen in shielding gas can cause some loss of agents. Chromium, Vanadium, Aluminum, Titanium, Manganese, Silicon. 39. Argon/ Helium a. Welding nickel and. Blends b. Spray or pulsed spray. c. Helium; Improves puddle fluidity, bead. Faster travel speeds. d. Helium on Aluminum; Reduces finger-like projection found with pure. Reduces pores in welds made with Aluminum/Magnesium fillers & series base alloys. e. Argon; Provides excellent starting. Promotes on aluminum. f. 75% Argon- 25% Helium Improve penetration profile for aluminum, nickel applications. Puddle is more fluid than % argon. Use for Spray Arc on aluminum. g. 75% Helium -25% Argon thermal conductivity. Increase puddle fluidity. penetration profile. Excellent penetration. Use for Spray Arc on aluminum. 23

24 40. Argon/ CO2 a. Argon is more expensive than. Blends b. Argon/CO2 blends; Pulse spray on stainless if the CO2 level does not exceed %. Spray transfer and pulsed spray transfer requires the CO2 levels below %. CO2 levels = heat input & chance of burn through. Short Circuit Transfer requires minimum level of % CO2. c. 75% Argon - 25% CO2. Higher price; Commonly called. Most commonly used by home hobbyist and fabricators. Advantages for Carbon Steel; Lower levels of spatter, more arc = improved weld bead appearance. More narrower but penetration than 100%CO2. Limited to short circuit and transfer. d. 80% argon 20% CO2. Reduces. Enhance weld bead appearance on steel applications. e. 82%Argon 18% CO2. Effective limit for with CO2. Popular European blend. Broad arc; good penetration profile. Good for short arc and (surface tension transfer) applications. f. 85% Argon - 15% CO2. Higher price, Most commonly used by fabricators. Combination of lower spatter levels, excellent penetration for heavier plate & steels with heavier. Increased sidewall fusion. Improved toe. heat for welding parts = less risk of burn through in short circuit transfer. Used for short circuit, globular, pulse and transfer. g. 90% Argon 10% CO2. price. Most commonly used by fabricators. Combination of lower spatter levels, good penetration, used for variety of steel plate applications. Broader penetration; reduces the depth of the penetration exhibited by argon + oxygen blends. Used for short circuit, globular, pulse and transfer. (Yuba College Spray & Pulse Spray) h. 95% Argon 5 % CO2. Pulsed spray w/ wire. % CO2 improves puddle fluidity. Better for heavier fabrication than % CO2 blends. 24

25 i. 98%Argon 2% CO2 Axial and Pulsed Spray. Higher energy in axial transfer puddle fluidity. 41. Argon/Oxygen Blends a. Argon/Oxygen -vs- Argon/CO2. Attain axial spray at currents. droplet sizes. Weld puddle is more. Higher travel speeds on metals. b. 99% Argon - 1% O 2 Used for applications. Oxygen is arc stabilizer; enhances fine droplet transfer, maintains puddle fluidity. Stainless Steel welds appear, oxidizing effect on the weld pool. c. 98% Argon - 2% O 2 Axial or pulsed spray with stainless steel and carbon steel electrodes. Success in sheet metal applications. Excellent puddle fluidity, travel speeds. Stainless deposits appear gray. Used when superior mechanical properties are required from alloy carbon steel electrodes. d. 95%Argon - 5% O 2 General purpose axial and pulse spray transfer on sections of carbon steels Base metal usually required free of contaminations, lower level of. 25

26 42. Ternary a. part Shielding gas. Gas Blends b. Used on carbon & stainless steel, some restricted cases nickel. c. Short Circuit; 40% Helium added to Argon/CO2. penetration profile. Greater thermal conductivity on carbon and. Increases sidewall fusion reducing the tendency for fusion. d. Short Circuit - Stainless Steels; three part mix is common. 55% - 90% Helium added to Argon w/ % CO2. Reduces spatter, improves puddle fluidity, providing bead shape. e. 90% Helium - 7.5%Argon 2.5% CO2. Most popular blend, short circuit on. Higher thermal conductivity; flat bead shape, excellent. Adapted to pulse spray but limited to stainless or nickel base material greater than thick. High travel speeds on stainless. d. 55% Helium 42.5% Argon 2.5% CO2. popular than above, but features a cooler arc for pulsed spray Lends itself to short circuit arc transfer on and nickel alloys. helium lends itself to axial spray transfer. 26

27 e. 38% Helium 65%Argon 7% CO2. Short circuit arc transfer on and low alloy steel applications. Used on for open root welding. High thermal conductivity; penetration profile, reduces tendency to cold lap. f. 90%Argon - 8% CO2 2% oxygen Short circuiting, pulsed spray and axial spray modes on carbon steel applications. High inert gas content spatter. 43. Filler Materials a. Bare or Copper Clad solid continuous wire electrode. Copper acts as a. Protects electrode from moisture/. Aids in conductivity. b. AWS Classifications (American Welding Society) A5.7 Copper and Copper alloys A5.9 Stainless steels A5.10 Aluminum and aluminum alloys A5.14 Nickel and nickel alloys A5.16 Titanium and titanium alloys A5.18 Carbon steels A Magnesium alloys A5.24 Zirconium and Zirconium alloys A5.28 Low alloy steels c. Wire Rolls, Spools, Reels. Standard hole sizes ( ). 4, 8, 12, 14 spools. (12 most common size) 12, 14, 16 coils (mount on reels) Drum size barrels. d. Cast & Helix Cast; of one circular form of wire as it lies flat and loose. Helix; how high one end of wire is above other end when lying flat. Cast & Helix; insures contact between wire electrode and. Larger cast; wire feed. Helix kept small; if not - wire will, causing unstable arc. 44. Electrode a. Many electrode types to match service requirements. Identification b. ER 70S-X E Electrode. R Rod. (can be used with other welding processes) lb Tensile strength. S Solid Wire. X Class or Characteristics. (s-3, s-4, s-6) 27

28 c. Additives Deoxidizers and Scavengers- Silicon, Manganese, Aluminum. 45. Wire Care a. Packaging foil wrapped,. b. Use in a timely manner once opened. c. Protect from atmosphere/. 46. Choosing a. Parent material; electrode should match mechanical and chemical Wire properties of parent ( ) material. b. Deposition requirement. Smaller wire - wire speed for comparable depositions of larger diameter wires. Diameter;.035 and., most common production wire sizes. c. Tensile strength. d. Brand; inexpensive not always better. e. Shielding Gas. f. Condition of to be welded. (rust, millscale, dirt) 47. Steel a. Many electrode types, brand names available. Electrode b. All must conform to standards. Wires c. Wire diameters; 0.024, weld 24 gauge to heavy plate. d. ER70S-2 Once preferred electrode for GTAW. (replaced by S-3 & ) Deoxidized; (triple deoxidized wire) Silicon, Manganese & Aluminum, Zirconium, Titanium. Welds all grades of & some low alloy steels. Excellent w/75% A -25% CO2 shielding gas. Used w/ A-O2 mixtures & % CO2. Weld rusty, dirty steel. spatter. Yield Strength & Ultimate Tensile Strength than carbon steels. Fast Freeze; sticky, does not well at toes. Produces Islands. priced than other wires. e. ER70S-3 Most popular GMAW electrode. deoxidizer than S-2. Welds most carbon steels, problems w/ steel. (Rimmed steels differ from killed steels in that the amount of deoxidizing agent added is less. Killed steels are totally deoxidized, whereas rimmed steels are only partially deoxidized. Rimmed steels also have smooth attractive surfaces on sheet products after processing. Most steels with carbon contents lower then 0.15% are rimmed. Used for sheet steel.) Harsh arc w/75%a 25%CO2 compared to S-2; spatter. 28

29 Better puddle fluidity than, flatter weld bead. Silicon Island removal than S-2. priced. f. ER70S-4 More deoxidizer than. Flatter & bead profile than S-2 & S-3 electrodes. Was used in work. Better results on and Rimmed steels. (*Deoxidation or "killing" is a process by which a strong deoxidizing element is added to the steel to react with the remaining oxygen in the bath to prevent any further reaction between carbon and oxygen. Completely deoxidized steels are known as killed steels. Produce steels with carbon contents greater then 0.25%. All forging grades of steel. Structural steels with carbon content between 0.15 to 0.25%) Short Circuit or Transfer. More spatter than electrodes. g. ER70S-6 High amount of Silicon/Manganese. Better for rust/ on steel. No deoxidizer; puddle more fluid. Popular electrode; (Yuba College) expensive but more versatile. Used for Spray/Pulse Spray & Short Circuit transfer. Good results w/short circuit & %CO Modes of a. Short Circuit. Metal b. Globular. Transfer c. Axial Spray. d. Pulse Spray. e. Surface Tension Transfer STT (Lincoln) Regulated Metal Deposit RMD (Miller). Controlled Short Circuit w/ heat input. Used for root pass on. 29

30 f. Profile of Transfer; each type has specific. 49. Short Circuit a. (GMAW-s) Transfer b. Also called, Short Arc, Dip-matic, Micro-wire, and Fine Wire. Terms all mean same process. c. Most common process of GMAW: sound w/ correct parameters. Sounds like. Use; thin metal (up to ), thick metal - require preparation. Capable of welding combination; thick and thin material. Root Pass; pipe applications. d. Uses lowest welding current & in GMAW Between volts. amps; 24 gauge material up to 1/8 (3/16 single pass open root butt weld). Produces low heat input. Small (Heat Affected Zone) Reduces distortion and. e. High operator appeal, ease of use. All positions; less fluid puddle than other metal transfer methods. Gap filling,. f. High electrode efficiencies, approximately or more. 30

31 g. Fine spatter; some of base metal after welding. spatter is result of improper settings. h. Wide range of electrode diameters., 0.030, and i. Wide range of shielding gases. Most common; % Carbon Dioxide, ferrous metals. Shielding gas type; less effect on (unlike Spray). j. Poor welding parameters/procedure control. Limited to thick material. Lead to incomplete fusion; cold laps,, common problems. Excessive spatter; leading to labor costs, higher inefficiencies Gas Drift; controlled work environment, lead to weld defects,. 50. GMAW-s a. Current, Voltage, Wire Time Line (Lincoln Electric GMAW Welding Guide) A.) The solid or metal-cored electrode makes physical contact with the molten puddle. The arc voltage approaches zero, and the current level increases. The rate of rise to the peak current is affected by the amount of applied inductance. B.) This point demonstrates the effect of electromagnetic forces that are applied uniformly around the electrode. The application of this force necks or pinches the electrode. The voltage very slowly begins to climb through the period before detachment, and the current continues to climb to a peak value. 31

32 C.) This is the point where the molten droplet is forced from the tip of the electrode. The current reaches its maximum peak at this point. Jet forces are applied to the molten puddle and their action prevents the molten puddle from rebounding and reattaching itself to the electrode. D.) This is the tail-out region of the short-circuit waveform, and it is during this down ward excursion toward the background current when the molten droplet reforms. E.) The electrode at this point is, once again, making contact with the molten puddle, preparing for the transfer of another droplet. The frequency of this varies between 20 and 200 times per second. The frequency of the short-circuit events is influenced by the amount of inductance and the type of shielding gas. Additions of argon increase the frequency of short-circuits and it reduces the size of the molten droplet. 51. Pinch a. Electrode tip touches the metal or molten weld puddle. Referred to as Force time. (Picture A) b. Arc and resistance removed. (Picture B) Increase of magnetic force; provides the force to the molten droplet from end of electrode. Filler metal transferred to weld puddle only during period when electrode is in with work. One droplet transferred each cycle. No filler metal is transferred across the. c. Without arc resistance; amperage rapidly, current flows freely to weld puddle. Resistance higher at end & arc puddle. Higher temperature = higher to current flow. d. High current flow & high resistance causes rapid of electrode tip. 32

33 e. Current flow increases, electrode, explodes into a vapor when it touches base metal, establishing an arc. Called, Arc On. (Picture C) Explosion causes, needs to be controlled. Controlled with Slope and Inductance settings. f. Arc gap reformed; voltage increases, current. (Picture D) g. Decrease in current, not sufficient to melt the electrode tip as fast as it is being fed into the. h. Arc gap rapidly decreases until electrode tip the weld puddle. (Picture E) i. Cycle begins again. j. System properly set; short circuit rate between 20 and shorts per second. An average welding condition, however, 90 and shorts per second. Wire diameter; smaller wire diameter = wire feed speed, more short circuits per second. Slope & Inductance; effects number and of shorts per second. 52. Slope a. Slant (ratio) of the Volt-Amp curve; Flat to. b. Controls of current available during short circuit or Arc Off time and/or time of current. Flatter Curve ( slope); Spray Arc, short circuit only at start of bead. Thick Aluminum. Average Curve; Short Circuit, Aluminum. Steeper Curve ( slope); Short Circuit - Stainless Steel, thin Aluminum. Slope not as important for ; controls short circuit only. c. Flat Curve; current available when shorted = quick response time. More violent pinch effect, more short circuits per second, shorter time. Easier starting. (Spray Arc) More spatter. Less wet out, stiff puddle, bead profile. 33

34 d. Steeper Curve; response time. Less violent pinch effect, less short circuits per second, Arc On time. Softer Arc. Better, more fluid puddle, flatter bead profile. (Stainless Steel) Harder bead. Too steep; not enough current to ignite and maintain arc. High, ropey bead, wire may pile up on. e. Fixed Slope; most common, preset from factory, usually slope needed for all types of GMAW. f. Slope Reactor Control; change & # of short circuits per second. (response time) Physically change (turns) on coil windings; 8 turns - average. May have adjustable range; on front of machine. (ex: 0 turns, Flat Slope, high current 14 turns, Steep Slope, low current) Two slope range; Range (high current) & Steep Range low current). g. Moving Coil Slope Control; changes relationship between machines primary and secondary coils. crank control. Amount of changes response time. 34

35 h. Resistance Slope Control; changes only of Volt/Amp curve, doesn t change # of short circuits ( ). Has two positive terminals; added to one terminal, causes more slope (Steep Range - low current) or less slope (Flat Range - high current). i. Machines may have separate Slope and control. Inverters; Slope - computer controlled, operator controls inductance. j. Voltage - Slope Relationship. Generally set for good starts, soft-smooth arc, spatter. Increasing slope changes volt/amp relationship, more needed to maintain set amperage. 35

36 k. Wire Diameter Slope. Larger diameter wire volt/amp curve. Dependant on of current, power supply. Larger diameter wire requires voltage, slope. 53. Inductance a. Controls of current rise in the short circuit. Control (not slope - volt/amp curve) b. Only effects transfer process. c. Also labeled as Arc Force,. Controls the pinch force or pinch. Controls the amount of Arc On - Arc Off. Controls of machine, number of shorts per second. d. Increased inductance; response time of peak current flow. Increases Arc On time. 36

37 number of shorts per second. Increases droplet size, more transferred through each droplet. Optimizes toe wetting, flattens bead profile, penetration. Less forceful short; spatter, smoother bead appearance. Helps flatten & wet-out bead in out of position welds, welds. e. Excessive Inductance; slower response time. arc starting, wire stubbing. into contact tube. f. Decreased Inductance; response time of peak current flow. shorts per second. Decreases size, amount of energy in droplet.( ) Harsher, arc; increased spatter, more bead profile, less penetration. Help control arc for material, out of position welding. g. General rule; increase current and inductance w/increase in. h. Power sources have either variable or inductance. i. Fixed; manufacture has determined the (average) inductance setting for machine. Most modern machines built this way. k. Variable; High/Low negative terminal lugs or Infinite Control Knob. High setting; inductance, short circuit - stainless steel, spray arc. Low setting; inductance, short circuit mild steel, aluminum. l. Measured in Henries. 54. Electrode Extension a. Electrical Sick-Out (ESO) or. Term used generally for process. b. Contact to Work Distance ( ) Term used more for or Mechanized process. c. Un-melted portion of the electrode sticking out from the. d. Consult typical operating procedure by manufacturer. 37

38 e. Welding starts; use angle cutters or suitable tool to cut the wire to the proper. Do not burn wire off onto the table, work clamp or project. Leave sharp wires; can lead to, added clean up costs, destroy tip. 55. Stick Out a. Amount of stick out can be used to control puddle w/out adjusting Affect settings. b. Long stick-out; increases resistance, current & shorts per second. puddle. Good for filling gaps, poor fit up,. c. Short stick-out; decreases resistance, current & shorts per second. Arc, less erratic arc w/100% CO2. arc starts. More fluid puddle, flattens bead profile, bead profile. 56. Buried Arc a. Process used in high speed welding of thin materials. Transfer b. Wire tip driven molten surface of puddle. c. Work done w/ ; Large droplets & high spatter. d. Also done w/ ; advantages of inert gas. e. Forceful but smaller arcs create droplets. f. Spatter in arc cavity; less clean-up, reduces labor costs. 38

39 57. Globular a. Rare use; than other transfer methods. Transfer b. Characteristics; large droplets & arc. Good penetration, high deposition rates, high quality welds. spatter, rough bead appearance, flat position only. c. Occurs at approximately V. Generally between 22 and 24.5 V. Globular transfer occurs even at higher volt/amp levels. Mistakenly thought to be transfer. d. Most common shielding gas; CO2. Low cost for shielding gas. Can be used with other gases at operating ranges. e. Not suitable for out of position welding; large droplet size and dependence of to transfer filler metal. f. Electrode wire touches base metal only at start of weld. Metal transferred across. g. Droplet forms on the of the electrode wire. Grows in size until larger than of electrode. Droplet detaches; transfers across the arc due to the force of. h. Unstable Arc. Arc moves to part of the droplet to the weld puddle. (electric current will take the shortest path to ground) Arc waves around on the end of the. Droplets or follow arc to base metal. i. Creates spatter; offsets savings from shielding gas. Spatter is wasted metal. Less process. Added costs j. Used in combination with Process. Pulse drops to background current; creates droplet. 58. Axial Spray a. High deposition rates; used in manufacturing and Transfer welding. b. Suited for welding material in flat and horizontal positions only. Highly arc w/highly fluid puddle, excellent weld fusion. Up to thick plate in single pass. Flat position; tight fit-up. Horizontal; T & Lap Joint - welds. or more efficient; very little spatter. With correct parameters, produces characteristic or buzzing sound. c. Three Requirements; or argon rich shielding gas. Argon easily ionized, inert. Power settings above current; depends on material being welded and diameter of wire. DCEP ; Direct Current - Electrode. d. Argon or argon mix shielding gases. 39

40 95-98% and 5-2% O2; Oxygen produces a more penetration profile. Argon/CO2; 10% - 18%, produce a more penetration profile. Higher flow rates needed; CFH. Argon is more. Higher level of welding. e. Higher power settings; produce high levels of heat and UV light. Generally uses larger ( ) diameter electrode; increases deposition rates, more current needed for larger electrode. Voltage; starts at volts or more. Amperage; amps or more. Used darker shade lens; 11 min., shade. Avoid getting your face too close to the arc; can shatter the filter lens. Wear heavy protection, on glove. Can cause high levels of distortion, Melt-through on materials. Weld puddle difficult to control slight out of position. f. Filler metal transfers across arc; said to be all of the time - once arc is established. High voltage overcomes the wire feed speed; maintains an. Electrode short circuits at beginning of weld. End of the electrode tapers down to a. Small droplets are formed and electromagnetically off at the tapered point of the electrode tip. Droplets than the diameter of the electrode, detach much more rapidly than in globular transfer. Arc Force; propels very fine droplet s axially the arc to base metal. Arc more directional than globular transfer; achieves bead appearance, less post weld cleanup no spatter. High current densities produces metal deposition rates, vary from less than one hundred times per second to several hundred times a second. g. Clean materials for best results; free of oil, dirt, rust,. h. Slope & Inductance settings beneficial for welding only; Machines w/slope and inductance control; Set slope slightly, some added inductance level. Too little slope/inductance; current rises too quickly burn backs or explodes wire at start. Too much; current rises too slowly wire at start.. Machines w/inductance control only; slightly inductance than short arc. 40

41 *Composite Steel; two metallically joined steel components having different chemical compositions. 59. Pulse Spray a. (GMAW-P) Highly versatile, high production process; more controlled Transfer than Axial Spray Transfer. Capable of travel speeds up to or greater than. Capable of continuous welding, spot welding or welding. 41

42 b. Power output is pulsed between (high) current and (low) current. Pulse creates average current than spray arc mode. Allows for all position welding of thin to thick materials. Lower heat input leads to less distortion,. Virtually no. Less smoke. Excellent bead appearance, not prone to lack of defects. Limits the tendency for. c. Peak current; high current. Set above to spray transfer transition current. Creates one or more small from electrode end. 42

43 Metal is detached and transferred across no short circuit. Amplitude; current level of the power at the peak or maximum level, expressed as. d. Background current; low current. Sustains/stabilizes. Does not cause drops to form - no transfer. Allows puddle to slightly. Time spent below transition current is about seconds. Controls overall into puddle. e. Frequency; measured in pulses per. Controls number of times occurs per second. Increases in proportion to. Increased frequency; arc narrows, average current increases, droplets become. Decreased frequency; arc and weld bead becomes. f. Peak Current Time; amount of time the peak amperage is allowed to. (width of pulse event) Expressed in. Time needed for a globule to form; about 0.1 second Increased peak time; increased droplet size, average current,. g. Frequency and Amplitude of the pulses control the energy level of he arc, rate at which the wire. Allows welding on sheet metal or reduce metals deposition rates to allow welding in. 60. Pulse Spray a. (Lincoln Electric) Event. 43

44 (1) Front Flank Ramp-up Rate: The ramp-up rate determines how rapidly the current will increase from the background current to the peak current. The ramp-up rate assists in the formation of the molten droplet at the end of the electrode. The rate is measured in terms of amps/millisecond. The rate of rise can reach 1000 amps/millisecond. As the slope of the ramp-up rate increases, the stiffness of the arc also increases. A fast ramp-up rate is associated with arc stiffness and louder arc noise. Decreasing the rate of rise contributes to a softer sounding arc. (2) Overshoot: Overshoot describes the condition where the front flank increases to a predetermined level beyond the level of the peak current. It is expressed in units of percent. Increasing overshoot is associated with a more rigid arc that is less prone to deflection. Overshoot adds to the pinch current and it increases the electromagnetic pinch force applied to the molten droplet. (3) Peak Current Peak current is the nominal current for the high energy pulse. It is adjusted to a level that is set consistently above the globular to spray transition current. Peak current is expressed in units of ampere. During the time when the peak current is delivered, the molten droplet detaches from the electrode. An increase in peak current increases the average welding current and the weld penetration. (4) Peak Current Time Peak current time describes the length of time that the current is at its peak. It is associated with droplet size. Peak time is expressed in terms of milliseconds. As the peak time increases, the droplets decrease in size. As the peak time decreases, the droplet size increases. The traditional expectation is that a single molten droplet is transferred with each pulse peak. The effective time at peak can range from less than 1 millisecond to 3 or more milliseconds. An increase in peak time increases average current, and it also increases weld penetration. 44

45 (5) Tail-out Tail-out is associated with current decay from the peak to the background current. It generally follows an exponential path to the background current. The increase in tail-out time increases the average current and marginally increases penetration. Tail-out time is increased to provide an increase in droplet fluidity. This results in improved toe wetting, a softer arc sound, and increased puddle fluidity. (6) Tail-out Speed Tail-out speed defines the rate at which the waveform moves from the peak current to either the step-off current or the background current. Manipulation of this portion of the waveform increases or decreases the exponential fall to the background current. (7) Step-off Current Step-off current defines the current level at the portion of the waveform where tail-out ends. It can add to, or take away from, the area under the waveform. It is associated with stabilizing the arc with stainless or nickel alloy filler metals. (8) Background Current Background current refers to the lower nominal current of the output. The unit of measure for the background current is ampere. Increases in background current will increase penetration. (9) Pulse Frequency Pulse frequency is responsible for how often the pulse cycle occurs in one second. As the frequency increases, the arc nar rows, the average current increases, and the molten droplets become smaller. As the frequency decreases, the weld bead and the arc become wider. Frequency is generally proportional to the wire feed speed. 45

46 61. Pulse Spray a. Machines can be run in Pulse or. Equipment b. Line Frequency Pulse Power Source; generation. Conventional power source w/pulse. Pulse only in frequencies that were a multiple of power source frequency. ( pulse/sec.) Superimposed higher pulsing current with amplitude greater than the transition current necessary for. Interval between short, large droplet formation (globular transfer). c. Pulsed Wire Feed; called. Switches wire feed motor and. Actually a pulsed Short Circuit Transfer. Pulse on and pulse off is adjustable; heat input into the weld. Wire advances in ; no advance pulse off, puddle freezes slightly. May be part of GMAW-Spot Welding control, optional or built in. Used for gauge & thinner materials w/out burn through, bridging gaps. Great for Auto-body work. d. Inverter Power Source: controls wave and of pulse. Pulse welding current at set intervals. High control of current, quick response time. e. Synergic System. Wire feed and power supply adjusted with knob. Usually Inverter power source. Power source adjusts/adapts all variables to change in. Manufacturer programs most common settings and combinations. Additional programming possible; or manufacturer. Can be programmed for wire size, wire type and shielding gas, materials. 62. Pulse Spray Consumables a. Electrode Wire; same as for. b. Larger wire sizes can be used. Electrode diameters from. Solid Core and Metal Core wire,. Wide range of metals and metal alloys. Great for larger size wires through conventional gun. c. Shielding Gas; requires minimum % Argon rich shielding gas. d. Steel & Stainless Steel; Argon/O2 or. Argon alone has poor wet-out, undercut & poor bead contour. e. Common gas for Steel; 98% Ar/5% O2 (Spray Arc also) 90% Ar/10% CO2. (Bead profile, ) 46

47 f. Common gas for Stainless Steel; 99%Ar/ 1%O2 98%Ar/ 2%O2(decreased corrosion resistance over %O2) 90%Ar/8%CO2/2%O2. ( ) g. Common gas for Aluminum; 100%. Helium/Argon blends; 75% 25% blends, ( thick). 63. Pulse Spray a. Power sources and equipment is more than conventional Disadvantages systems. b. Shielding gases are more expensive. c. Higher arc energy and light require greater. Harder on gun equipment. d. Takes greater skill levels by the weldor. 64. STT & a. Surface Tension Transfer (Lincoln), Regulated Metal Deposit RMD (Miller) computer controlled Short Arc process. Transfer b. Use: & Pipe; root pass with solid wire. c. High Speed Technology. d. Neither Constant Current (CC) nor (CV). e. Modified Short Arc, Voltage and Changes Based Upon the Needs of the Arc. f. Precise Amperage Control During the Entire Weld Cycle. g. Electrode Current is Based on the Instantaneous Heat Requirements of the. h. Limits current and pinch effect, less turbulent puddle and less spatter. % efficiency i. Low Voltage; 16V To V. j. Two Amperage Levels; Peak Current (0A To A). Background Current (0A To A). 47

48 k. STT Waveform. (Lincoln Electric) 48

49 A. The molten tip of the electrode makes physical contact with the molten pool at the background current level. B. The background current is reduced to a lower level to prevent the occurrence of a premature molten droplet detachment. C. The current then ramps up quickly to a point where the pinch force associated with the rise in current (electromagnetic force) starts to neck down the molten column of the electrode. The power source at this point begins to monitor the changes in voltage over time as it relates to the necking of the molten droplet. The molten metal is still in contact with the molten weld pool. Via the sensing lead, the power source references the observed voltage, and continuously compares the new voltage value to the previous voltage value. D. At the point where the molten metal is about to disconnect from the end of the electrode, the power source reduces the current to a lower than back ground current level. At this point in the waveform, surface tension forces collapse and the molten droplet transfers to the weld pool. This controlled detachment of the molten droplet is free of spatter. E. The power source then rises to the peak current level where a new droplet begins to form. Anode jet forces depress the molten weld puddle to prevent it from reattaching to the electrode. On its descent to the background current, the tail-out current provides the molten droplet with additional energy. The added energy increases puddle fluidity, and the result is improved wetting at the toes of the weld. F. A plasma boost is applied which provides the energy to re-establish the arc length, provide a new molten droplet, and force the molten puddle away from the molten droplet. The length of time is nominally 1 ms for carbon steel electrodes and 2 ms for both stainless and nickel alloyed filler metals. G. The tail-out region is employed in applications where the energy added to the molten droplet provides faster travel speeds and improved finished weld wetting action at the toes. In most pipe root applications, this value is kept to a minimum. l. Peak Current Control; responsible for establishing the. Provides sufficient energy to preheat the work piece, insures good. Set too high; molten droplets will become too. Molten droplet formed should times electrode diameter. m. Background Current; responsible for providing weld into the base material. Responsible for heat input into weld. Controls level of weld penetration, effects of molten droplet. n. Tail-out Current; adds energy to the molten droplet, increases droplet. Applies added energy without effecting droplet. Increasing tail-out current increases puddle fluidity, faster travel speeds, improves weld wetting. 49

50 p. Wire Electrode Size. Typically larger diameters, and larger. q. Shielding Gases. 100% CO2. 75% Ar / 25%. r. Advantages. Controlled Heat Input. Minimal. Minimal. All Positions. Low Cost Gas. Good. Handles Poor Fit Up. s. Limitations. of equipment. Limited to a Modified Short Circuit Mode. 50

51 WELD JOINTS & TYPES 1. Weld Terms a. Weld puddle; molten metal created by the arc or flame while welding. b. Weld bead; metal deposited by consuming the electrode or rod and depositing it combined with the base metal. c. Reinforcement; two types. Face reinforcement; amount of weld bead above the surface of base metal after welding. Usually limited to 1/8. Root reinforcement; amount weld metal excess in the root of the joint. Usually limited to 1/16. d. Weld puddle; Molten metal created by the arc or flame while welding. e. Weld bead; Metal deposited by consuming the electrode or rod and depositing it combined with the base metal. f. Partial Joint Penetration (PJP). Used when maximum joint strength is not necessary. Cost less. g. Complete Joint Penetration (CJP). Used when maximum joint strength is necessary. 2. Weld a. Numbered for Position, Lettered for Type. Positions b. Flat; 1 position, (1G- Groove or 1F Fillet). c. Horizontal; 2 position, (2G or 2F). d. Vertical; 3 position, (3G or 3F). e. Overhead; 4 position, (4G or 4F). f. 5G & 6G; Pipe position, rolled or fixed. Plate Pipe 51

52 3. Weld Types a. Fillet; triangular shaped cross section that joins materials at approximately 90º angles. b. Groove; weld made in groove between work pieces. c. Back; weld made on the face of the primary weld. d. Plug & Slot; join two overlapping pieces by welding holes or slots. e. Surfacing; applied to surface in order to strengthen surfaces or increase. f. Stud; joins metal to work piece. g. Spot & Seam; circular or continuous welds made overlapping members. h. Projection; similar to spot & seam welds uses heat obtained from to current flow. 4. (5) Joint Types a. Butt; two work pieces set approximately and placed edge to edge. b. Tee; two pieces positioned at approximately to each other. c. Lap; two overlapping pieces on planes. One of the strongest joints, despite the lower unit strength of the filler metal. d. Corner; two pieces positioned at right angles in the shape of an. e. Edge; edges of two or more or near parallel pieces are joined. 52

53 5. Weld and Joint Types 53

54 6. Fillet Weld a. Triangular shaped weld between two pieces of metal at an angle. Used for Lap, Tee, or Joints. Most commonly used joint. Preferred over joints easier to prepare and less expensive to complete. Used when load stresses are relatively low and effective throat is less than. Sized by length or actual and/or effective throat. Strength gained from Effective Throat. Root, Root fusion, effective throat are measured from intersection of riser and base piece fusion. Term penetration is not used for fillet welds, replaced by. Under-fill and undercut are common problems along the of the upper part of the weld. b. Fillet weld types; Tee, Lap, and (specialized application). c. Fillet bead shape; ; leg & size are same dimension. Less stress created at toe, less reinforcement more tendency for cracking from shrinkage. ; leg & size are same dimension; least shrink cracking, easier to prevent undercutting at toes, excessive reinforcement must be avoided more stress at toes, distortion, HAZ, cost. 54

55 ; size & leg two different dimensions, measured by largest inscribe triangle, least stress at toe best fatigue resistance, greatest tendency for cracking from shrinkage. d. Ideal fillet weld. e. General rule for Fillet size; leg size equal to material being welded. Depth of fusion allows for reduction of leg size to thickness of thinnest material. f. Unequal leg Fillets; thickness of thinnest piece. Over welding creates joint, less efficient. 55

56 7. Groove Weld a. Made between two pieces of metal that form a groove. b. Groove Weld Terms. ROOT OPENING: The separation between the members to be joined at the root of the joint. ROOT FACE: Groove face adjacent to the root of the joint. GROOVE FACE: The surface of a member included in the groove. BEVEL ANGLE: The angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member. GROOVE ANGLE: The total included angle of the groove between parts to be joined by a groove weld. SIZE OF WELD: The joint penetration (depth of bevel plus the root penetration when specified). The size of a groove weld and its effective throat are one and the same. PLATE THICKNESS: Thickness of plate welded. c. Groove Angle: Correct bead shape and penetration. Deep, narrow beads tend to lack penetration and tend to crack. Groove angle typically Angle reduces with in plate thickness. Angle increases with in root opening. Excess bevel creates more cost,, HAZ. 56

57 d. Groove Bead Terms: e. Material Thickness & Size/Strength of Weld. Material thickness, weld size same dimension for. Material Thickness, Penetration & Weld size different for. 57

58 8. Weld Pass a. Single pass welds utilized on base metal. b. Multiple pass welds used to create specific size welds that cannot be attained with a pass. Generally used for material. Always start on bottom of previous pass; creates a shelf for the passes above. Electrode very important; direct the arc, use the force of the arc to counteract gravity. c. Generally, fewer passes are preferred to multiple passes. HAZ, efficiency. d. Generally, smaller beads preferred over larger bead. HAZ, efficiency. f. Bead depth should never exceed bead width. Leads to weld defects; cracking, cold shuts, inclusions. 9. Butt Joints a. Square: One of the most frequently used weld joints. Intended for materials thick or less. Closed type used for or less. Open type use root opening. Require joint penetration for optimum strength. Relatively strong at static tension but not recommended for use subjected to fatigue or especially at low temperatures. Minimal to no edge preparation weld joint. b. Single Bevel: Generally welded from one side only. Generally used on materials thick or less. Material 1/8 to 3/16 thick use, featheredge bevel with bottom edges placed together. Material over 1/4 thick use 1/16 to 1/8 root face on bottom edge with 1/8 root opening. Use. More costly than square butt. c. Double Bevel: Alternate weld sides to minimize. 58

59 d. Single V: Used for material 3/8 to 3/4 thick. 60º bevel angle larger angle increases distortion/ contraction and cost more to fill. 3/32 to 1/8 root face applied to lower on both bevels w/ 1/16 to 1/8 root opening. Use backing strip to prevent excessive. joint to prep and fill. Relatively strong at static tension but not recommended for use subjected to or. e. Double V: Used for material over 3/4 thick. Suitable for load conditions. Penetration should be on both sides for maximum strength. 3/32 to 1/8 applied on both bevels w/ 1/16 to 1/8 root opening. weld sides to minimize distortion. More costly to prepare than single V butt joint but less filler needed, offset cost. f. Single U: Used on materials thick. Used for work requiring quality welds. Meets all ordinary load requirements. fill material needed than single and double V joint. Generally distortion than single and double V joint. CAC A (Carbon Arc Cutting Air or Air Arc gouging) useful to prep edge. g. Double U: Used for heavy material - thick or larger. Used for work requiring high quality welds. Meets all ordinary load requirements. Penetration should be complete on both sides for maximum strength. 3/32 to 1/8 root face applied on both bevels w/ 1/16 to 1/8 root opening. Alternate weld sides to minimize distortion. 59

60 h. Single J: Used for heavy material - 3/4 thick or larger. Typical radius w/ slope angle. Recommended for normal loading in some pressure vessels. Total cost of welding is than V or U joints. fill material needed than single and double V joint. More difficult to get (root) penetration. Small often used before multi-pass welds. i. Double J: Alternate weld sides to minimize distortion. 10. T- Joints a. Square: Relatively joint unless welded on both sides Can be made on thicknesses of metal. Used where joint experiences longitudinal shear. Requires the use of a weld. May require space on thick materials. Weld leg should equal the thickness of material. Weld leg should equal the thickness of the thinner material when joining thickness material. b. Single Bevel: Welded from one side only. Generally used on materials thick or less. Withstand more load than square fillet. More costly than square - T. c. Double Bevel: Must be welded from sides. Used were heavy loads are applied from both longitudinal and directions. Alternate weld sides to minimize. d. Single J: Used for heavy material - thick or larger. Used where joint is exposed to severe loads. Typical 1/2 radius w/ º slope angle. Used when welding is limited to one side. Less fill material needed than single and double V joint. More difficult to get full ( ) penetration. Small often used before multi-pass welds. 60

61 e. Double J: Alternate weld sides to minimize distortion. Used for heavy material thick or larger. Welded from both sides. Used where joint is exposed to loads. 11. Lap Joints a. Single Fillet: Requires the use of a fillet weld. Easy to weld. Strength depends on the size of fillet weld. Welds up to ½ thick can be welded in fillet if load is not too severe. Generally, overlap pieces at least the thickness of thinnest piece. b. Double Fillet: Welded from two sides. One of the most widely used joints in welding. Withstand load than single fillet lap. Strength is comparable to. Generally overlap pieces at least 3X the thickness of thinnest piece. 12. Corner Joints a. Butt: Flush; Square flush corner joints are designed for welding sheet metal and lighter. Limited penetration. Supports moderate loads. Half-Open; Better for thicknesses over gauge. Use where impact or fatigue are not too severe. Has tendency to burn through the edge. Full-Open; Permits welding on both sides. Can carry heavy loads. metal thicknesses can be welded. b. Bevel, V, U, & J Groove; Used for thick materials. See weld type page. 13. Edge/Flange Joints a. Square, Single & Double Bevel: Used for materials thick or less. Sustain light loads. Flange joints have one member that is bent. 61

62 14. Weld Joint Selection a. Forces placed on joint. Tension, Compression, Bending, Torsion, Shear. Compression Tension Bending Torsion Shear b. How the load is applied to the weld joint. Static, cyclic, impact or variable. c. Where the load is applied in proximity to the joint. d. of the load across the joint. e. The direction the load is applied to the joint. f. of preparing the metal for the joint. g. Weld joints must be selected for strength. h. Safety and requirements. 15. Stress vs Strain a. Stress; Load units per. Measured in. (pounds per square inch). Pressure acting on weld or metal. One or more loads may be applied. b. Strain; Resulting of the applied stress. Weldment has twisting or bending stress applied, extent to which weldment twists or bends is measure of strain. c. Stress and strain go hand in hand. If you stress you knees, the resulting pain and damage would be the strain. 62

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