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Arc Welding Introduction & Fundamentals 8609-B Instructional Materials Service Texas A&M University
Importance of Welding
Serves a variety of purposes across several domains Used regularly on many agricultural operations Used in construction of fences and livestock trailers Used for making quick repairs to many types of agricultural equipment such as combines, hay rakes, and field cultivators Not limited to agricultural uses
Used mostly in industry –Machinery & equipment fabrication –Pipeline and manifold welding –Structural welding –Offshore welding –Ornamental welding Industry is always actively seeking certified weldors to enter the workplace and fill vacancies.
A person cannot become proficient at arc welding without having some basic knowledge of the components that play a part in the fusing of metal. Definition: the process of fusing two or more pieces of metal together through the use of an electric arc welding machine Dates back to the end of the nineteenth century Uses an electric arc, which is struck between an electrode and metal, to create heat
The arc heats the metal to a melting point, and the electrode is removed to break the arc, allowing the metal to freeze or solidify. This flame (arc) of intense heat is generated as the electric current passes through a highly resistant air gap. –Air gap: space between the lower tip of the electrode and the base metal
Ice Demonstration Melt two ice cubes together with a match. When the match is removed, the ice solidifies and freezes. This is the same process that takes place when fusing metals together.
Challenge Find ways to strengthen the welds that are produced –As metals are heated to very high temperatures, they become chemically reactive with gases in the air such as oxygen (O 2 ) and nitrogen (N 2 ). –When these gases come into contact with the molten pool of metal formed during the arc welding process, they destroy the strength properties of welds and the welds become brittle and weak.
Solution All arc-welding processes now provide some form of cover or shield for the molten pool of metal. –Shielded Metal Arc Welding (SMAW): Coated electrode produces a gas that shields the molten pool from O 2 and N 2 in the air –Tungsten Inert Gas Welding (TIG) –Metallic Inert Gas Welding (MIG)
Shielded Metal Arc Welding Process (SMAW)
WELDER: describes a welding machine or a person who welds, but in most cases is used to describe the machine WELDOR: describes a person who actually performs welds
Enables the utilization of new and recycled metal for construction and repair of items Repairs needed quickly on machinery and equipment can be made without delay. Cracks or breaks found on machinery can be repaired before breakdowns occur. Arc welding repairs are more economical than other types of repair processes. Fusing metal is not the only job that an arc welder can perform.
Types of Arc Welding Machines
The five basic types are: –AC (Alternating Current) –DC (Direct Current) –AC/DC (Alternating and Direct Current) –TIG (Tungsten Inert Gas) –MIG (Metallic Inert Gas)
Alternating Current (AC)
Alternating Current: current that alternates or changes direction several times per second Welding machine found in most on-farm agricultural facilities and agricultural science programs Relatively small machine Used for home construction, agricultural repair, and light industry & maintenance work
Most AC welders are usually 180- ampere or 225-ampere units that run best when the power supply is between 220 and 240 volts. –Will produce an arc voltage of 25 Advantages: –Physical size is small –Portability is high –Can handle most agricultural tasks –Arc blow is generally not as great as in DC machines
Percentage of a ten-minute period that a welding machine can be safely operated at a given output Example: –A 225-ampere AC welder will typically have a duty cycle of 20% if operating at 200 amp. –A duty cycle of 20% means the machine can be safely operated for 2 minutes out of a 10 minute period of time when set on 200 amp. Rule of thumb: –As amperage increases, duty cycle decreases –As amperage decreases, duty cycle increases
Direct Current (DC)
Most often used for large industry and heavy equipment Adopted primarily because of its portability Runs off current that flows steadily and constantly in one direction Powered by a motor (usually electric or gas)
Created out of necessity –American forces needed to weld in order to make repairs on war machinery and equipment during WWI in Europe. –AC welders did not work because Europe used electric current on a different cycle. –DC welders solved the problem. Advantages: –Increased portability –Increased output
Direction in which the current flows across an arc Will differ according to the type of welding machine that is used DC welders can produce straight & reverse polarity. Straight: electrode is negative and the work is positive (mild steel) Reverse: electrode is positive and the work is negative (cast iron, thin materials, and aluminum)
Have the ability to produce both types of current from AC current input Equipped with a rectifier Rectifier: –An electrical device that changes alternating current to direct current –Most common are silicon diodes which is placed near the output center of the machine –Not necessary to run at all times
Transformer/rectifier: –Found in some types of welders –Combination of a transformer and a rectifier –Transformer: device that is used to convert high voltage-low amperage inputs to the form of low voltage-high amperage needed for arc welding –Plays a critical dual role in newer AC/DC welders operating on AC current
Advantages: –Most efficient machine for general purpose welding; used in many manufacturing plants –Noise level is lower during operation than other types of machines –Allows the individual to select the type of arc and current that will be best for the job –Practical for any operation in which many different types of tasks will be performed –Generally inexpensive as compared to DC machines
Consist of an electric power unit, a pressure reducing regulator, torch or electrode holder, tungsten electrode, nozzle, gas passages, torch cable, welding cable, water and gas hoses, and gas supply unit Commonly used in metal fabrication and repair shops on jobs that require skillful metal joining Also used when welding aluminum and stainless steel
Two gases used: –Argon (Ar 18 ): heavier than air & tends to blanket the weld zone very well –Helium (He 2 ): much lighter than air & has a high rate of travel speed that enables it to cover the weld zone very quickly –Are supplied by a high-pressure cylinder system –Serve as protection for the Tungsten and weld zone to prevent weakening of the welds due to atmospheric contamination –Measured and purchased by the ft 3
Uses a non-consumable Tungsten electrode which does not become part of the weld TIG welding heats the torch tip to high levels. –Cooling mechanisms required on machines with a capacity of 200 amps or more –Cooling mechanism can be either air coolers or water coolers Can also be referred to as GTAW (Gas Tungsten Arc Welding) or Heliarc TM welding
Advantages: –Welds are free of corrosive residue. –Weld is usually stronger and has less corrosion than other forms of welding. –Weld is free of fumes, sparks, and slag. Post weld cleaning is eliminated. –Stresses are reduced due to heat concentration in a small area, so there is little distortion near the weld. –There is no spatter in this process.
Metallic Inert Gas One of the easiest methods of welding to put into practice Made up of a welding machine, wire drive, wire wheel, gas supply, contractor, gun, hoses, current cable (wire), and a control unit for the wire drive, current & gas flow Often referred to as “wire feed” welders “wire feed” name comes from the basic process that occurs in MIG welding
A continuous wire electrode is fed from a spool through a flexible conduit into a welding gun. The wire electrode exits the gun through a copper tube called a contact tip (tube) into an electric arc produced by an external power source. The wire fed through the tip and into the arc melts and comes into contact with base metals thereby producing a weld.
Molten pool is protected by Carbon Dioxide (CO 2 ), Argon (Ar 18 ), Helium (He 2 ), or different combinations of the three Shielding gases supplied by a nearby high-pressure cylinder or manifold system Also possible for a flux located in the core of the wire electrode to produce some shielding gas as it melts during welding It is necessary to set the speed at which the wire electrode will be fed through the machine prior to welding.
Speed will vary and is dependent on the type of metal being welded After the initial wire speed has been set, welding is started and stopped by squeezing a trigger on the gun. Only job weldor must do is position the gun properly and cross the weld joint at the proper speeds Trigger activation takes the place of the “manual striking of the arc”
It is possible to set up the machine to weld automatically. –Welding is completed with limited labor. –The only labor required from humans is the initial setup and programming of the equipment. –Robotic equipment then performs the necessary welds to complete the work. –Largely practiced in industry Very good for welding stainless steel, aluminum, and carbon steel Very thin metals can easily be welded Can also be used to weld heavy metal
Advantages: –Used in industry as an automatic welder –Similar to the TIG process, however, there is a slag cover on the weld when using a flux-cored wire –May be operated by hand
Other Welding Processes
Laser welding Submerged arc welding Electro-slag welding MIG welders are becoming more widely used Most commonly used type of arc welding process today is still the use of a coated electrode that serves as a shield for the weld. –Known as “stick welding” –Process by which most entry-level weldors learn the technique
Selecting a Welder and Welding Equipment
Guidelines to follow: –Select a welder that is made by a respected and reliable manufacturer. –Purchase a welder only from a respected and reliable dealer. –Compare price and guarantees on different types of welding machines. –Take notice that the dealer provides prompt service and information when needed.
–Observe that the dealer has personal protective equipment, electrodes, and operating information readily available. –Check the duty cycle of weldors to ensure that it matches the requirements of the job. –Check that the equipment is properly installed and if a used weldor is purchased, check to ensure it has been properly maintained. –Check that all necessary components such as ground and work cables are present.
Additional welding equipment: –Safety glasses with side shields –Welding helmet with dark lens –Face shield –Goggles –Hard hat –Anvil –Power grinder –Leather welding gloves –Chipping hammer & Wire brush –C-clamps & pliers –Welding screen –Welding table
A core wire that can be left bare or covered with flux Flux: –Fusible material that covers the electrode that is meant to produce a shielding gas during the welding process –Prevents the formation of oxides, nitrides, and other undesirable inclusions during welding –Floats out the impurities in the air and then settles on top of the weld in the form of slag –Slag is beneficial in most welding processes because it holds heat and keeps the weld from cooling too quickly, thus preventing the weld from becoming weak.
It is important to consider the type of base metal and welding current when selecting the proper electrode. Electrode selection depends on: –Metal type –Metal thickness –Welding position Several tools available to aid in the selection of electrodes
Types of Electrodes Coated Electrode: –Covered with flux that is coded for its properties –Core wire should possess the same properties as that of the base metal that is begin welded –Very common type Carbon Electrode: –Melts slowly while supplying a stable arc –Used for special purpose welding
Bare Electrode: –Not as widely used –Smoke free –Makes weld visible at all times during the welding process –Requires a tremendous amount of heat be produced (10,000 o F) as it passes across the arc –Extremely sensitive to voltage change and electrode angle
American Welding Society (AWS) has provided a means of electrode classification to allow for wide spread standardization and application. The AWS system was first set up in 1942. Electrodes are identified by the manufacturer’s trade name, and/or a combination of letters and numbers from the AWS classification system. In order to receive a classification from the AWS, a manufacturer must meet and maintain strict standards.
These standards call for electrodes that comply with a set of minimum chemical and physical specifications. Numbers used for classification represent four different factors: –1 st two digits: minimum tensile strength of the weld metal –3 rd digit: welding positions in which the electrode should be used 1=all welding positions, 2=only flat & horizontal positions, 3=only flat position –4 th digit: type of welding current that is to be used and the type of flux covering
Example: –E6010 –E: Electrode –60: tensile strength of the electrode metal (60,000 pounds/in 2 ) –1: electrode can be used in all welding positions –0: a DC and electrode positive current –E7024 –E: Electrode –70: tensile strength of electrode metal –2: electrode can be used for flat and horizontal positions –4: a DC and electrode positive or negative current
Determined by the diameter of the bare end of a rod Diameter of electrode should not exceed the thickness of the metal being welded
Specifications for electrodes are as follows: (For example E6013) Standard Size Diameter of Core Wire # of Electrodes per pound Standard Length Amperage Range Setting 1/16 inch5318”20-40 3/32 inch3612”30-80 1/8 inch1714”70-120 5/32 inch1114”12-170 3/16 inch814”140-240
Be familiar with the many types of electrodes and their designed uses in order to maximize the efficiency of the welding process. Electrodes can be damaged if they are not stored properly. Store electrodes in sealed containers until they are ready to be used. Extreme changes in temperatures and moisture in the air can damage or ruin electrodes.
Electrode #Electrode Use E6010Used for all-purpose welding and with mild steel. Allows for deep penetration and rapid solidification. Utilizes DC+ current. E6011Used for all-purpose welding and with mild steel. Allows for deep penetration and rapid solidification. Utilizes DC and AC current. E6012Used on mild steel. Allows for deep penetration and rapid solidification. Utilizes DC or AC current. E6013Used with mild steel. Good general-purpose electrode. Allows for medium penetration, medium slag, and a quiet arc. Utilizes DC or AC current. E7018Used with high carbon steel. More difficult to weld. Utilizes DC+ or AC current. E7028Used with high carbon steel. More difficult to weld. Can only weld in the flat and horizontal positions. Utilizes DC+ or AC current.
Selecting the Correct Electrode
Pay attention to the following factors when choosing electrodes. –Identification of base metal –Welding current available –Thickness and shape of the base metal –Joint design –Welding position –Job specifications and service conditions –Deposition rate in relation to production efficiency –Environmental job conditions –Electrode storage
If safeguards are ignored, it is possible to be exposed to such dangers as fumes and gases, overexposure to arc radiation, fire and electric shock. General safety rules that should be adhered to at all times during arc welding: –Wear personal protective equipment (PPE) that allows for freedom of movement but will provide adequate cover against sparks and weld spatters. –Wear heavy flame-resistant leather gloves. –Flame-resistant welding aprons, suits, and caps are recommended. –Weld only in well-ventilated areas.
–Protect eyes against “welder’s flash” caused by harmful UV radiation. –Wear a welding helmet at all times. –Wear earplugs to prevent hearing loss. –Be certain that the welder is properly grounded. –Do not stand on wet surfaces while welding. –Use electrode holders that are properly insulated.
–Protect welding cables from hot objects and sharp edges. –Yell “COVER” prior to striking an arc in order to alert bystanders. –Use pliers or tongs when handling hot metal. –Avoid welding on containers that have held combustible materials. –Properly dispose of used electrodes.
Miscellaneous Safety Rules
When welding: –Do not lay the electrode holder on the welding table. –Do not stand on the grounded metal. –Keep the work area free of clutter to avoid falling accidents. –Keep tools and equipment in a safe and proper place to prevent accidents. –Do not hold the electrode holder between the knees or under the arm.
–If the electrode sticks and cannot be twisted free, cut off the machine; allow the electrode to cool and break it loose with pliers. –Do not cool the electrode holder in water. –Always wear eye protection. –If foreign particles get into your eyes, avoid rubbing them.
Arc Welding Fundamentals
Body Position: –It is impossible to get in a totally comfortable position on most welding jobs, but the weldor should find a position that allows him/her to be as relaxed and braced as possible. Correct Electrode Size: –Consider type, position, and preparation of the joint, deposition efficiency, and requirements pertaining to weld quality when choosing an electrode.
Correct Amperage Setting: –If the current is too high, the electrode melts too fast and the molten pool is large & irregular. –If the current is too low, there is not enough heat to melt the base metal and the molten pool will be too small, pile up & look irregular. Correct Electrode Angle: –When making a flat weld, the correct angle is 15 o from 90 o in the direction of travel. –The electrode should be held perpendicular to the base metal.
Correct Arc Length: –If the arc is too long, metal melts off the electrode in large pools that wobble from side to side as the arc wavers, resulting in a wide, spattered, and irregular bead with poor fusion between the original metal and the deposited metal. –If the arc is too short, there is not enough heat to melt the base metal properly and the electrode will stick to the work, resulting in a high uneven bead with irregular ripples, poor fusion, and slag and gas holes. –Correct arc length is equal to the diameter of the bare end of the the electrode.
Correct Electrode Type: –Depends upon type of base metal to be welded and type of current available Correct Travel Speed: –Too fast: puddle does not last long enough and impurities and gases are locked in; bead will be narrow and ripples pointed –Too slow: metal will pile up, bead will be high and wide, and ripple will be straight
Preparation of the Work
Prior to beginning the welding process, take the time to prepare the metal. Use a grinder, a metal saw, or a torch for preparation. Will result in stronger, more attractive welds than if metal is left unprepared.
A welder needs preventive maintenance. Basic recommendations: –Flush or ventilate the system with clean compressed air. –Clean the outside of the machine. –Inspect accessories such as the electrode holder, cables, or wire feeders. –Inspect all dials, knobs,or switches for damage. –Grease bearings periodically. –For portable machines: check oil daily, fill fuel tank, and clean the air filter.
Acknowledgements Kirk Edney, Curriculum Specialist, Instructional Materials Service, edited and reviewed this PowerPoint presentation. Kristie Weller, Undergraduate Technician, Instructional Materials Service, organized and developed the information used in this PowerPoint presentation.
All Rights Reserved Reproduction or redistribution of all, or part, of this presentation without written permission is prohibited. Instructional Materials Service Texas A&M University 2588 TAMUS College Station, Texas 77843-2588 http://www-ims.tamu.edu 2007