2WELDINGDefinition: Material joining process. Two parts connected at their contacting surfaces by suitable heat and pressure.Many welding processes are accomplished by heat alone, some others by heat and pressure, and some with pressure only.In some welding operations a filler material is used.Welding operation usually applied to metals but also used for plastics.22
3Joining ProcessesParts produced by any of the manufacturing processes can be made into larger, more complex bodies via Joining processesCreating a metallurgical bond by adhesion and diffusionJoining by fusion with the use of various heat sourcesBrazing or soldering with a lower-melting metalMechanical fastening
6Sources of Energy for Fusion Welding Chemical reactionsBurning gasesGAS WELDINGHeat from electricityArcARC WELDING SYSTEMSResistance weldingLightLASER
7Three Specific Types of Welding Modules In this Welding, Cutting, and Brazing module, three specific types of welding are covered. These are listed below:Oxygen-fuel gas welding and cuttingArc welding and cuttingResistance weldingIn this Welding, Cutting, and Brazing module, three specific types of welding are covered. These are listed below:Oxygen-fuel gas welding and cuttingArc welding and cuttingResistance welding.
8Resistance Welding Definition: This is a group of fusion welding processes that use heat and pressure to make the coalescence.The heat comes from electrical resistance to current flow at the site of the weld.The processes include:Spot WeldingProjection WeldingSeam WeldingElectric current and mechanical pressureResistance to the flow of current heats the material.Pressure is simultaneously applied to the joint, forming a solidified nugget that attaches the pieces.Note: FP&M only does spot welding.
9Resistance Welding Spot Welding A process typically used in high-volume, rapid welding applications.The pieces to be joined are clamped between two electrodes under force, and an electrical current is sent through them.
10Welding/Cutting Hazards Potential HazardsFires may start by hot materials igniting nearby combustibles.Burns to the operator may occur if unprotected skin comes into contact with the extremely hot work.Magnetic fields could easily destroy/disrupt electronic components, stored data if not careful.
11Welding/Cutting Hazards Potential Hazards Cont.:Metal fumes from vaporizing of the work with the extremely hot arcs may be inhaled into the worker’s lungs.Certain metals and metal oxide fumes, including zinc, cadmium and beryllium, produce serious illnesses when inhaled.Fluxes used with welding to create inert atmospheres at the point of the weld also present inhalation hazards.All welding and cutting must have adequate ventilation to protect the person doing the welding and those working around the welding area.
12Weld Joint Structure Characteristics of a typical fusion-weld zone in oxyfuel-gas and arc welding. Microhardness (HV) profile across a weld bead.A fusion joint is far from homogenous. Degree of inhomogeity increases from pure metals to multiphase alloys.
13Typical weld zone in arc and gas welds The base material adjacent to the melt boundary is exposed to high temperatures, and the properties and structure are changed within the heat-affected zone.Cold worked base material will show recrystallization in HAZ, with coarse grain sizes.In either case, a coarse-grained structure of lower strength exits at the melt boundary.Melt
15Welding DefectsFusion welding defects due wrong heat input, insufficient rate of weld metal deposition, and cooling.Lack of bonding or gas porosity due to surface contaminants, including oxides, oils, etc.Undesirable reactions with surface contaminantsSolidification cracks in the weld.5. Solidification shrinkage coupled with solid shrinkage imposes internal tensile stresses on the structure, may lead to distortion.6. Gases released or formed during welding (eg CO) can lead to porosity which weakens the joint and acts as a stress raiser.
16There are 5 basic joint types in welding Weld jointThere are 5 basic joint types in weldingButt joint: Two materials are in the same plane, joined from the edges.Corner joint:The corners of two materials form a right angle and joined.Lap joint: Two parts overlaps.Tee joint: One part is perpendicular to the other, making a T shape.Edge joint: Edges of the two materials joined.16
18Types of weld Fillet weld: Used in T joints,corner joints, lap joints. Groove weld:Used in butt joints.Plug weld: Used in lap joints.Slot weld: Used in lap joints.Spot weld: Used in lap joints.Seam weld: Used in lap joints.Flange weld:Used in edge joints.Surfacing weld:Not a joining process, it is used to increase the thickness of the plate, or provide a protective coating on the surface.18
20Metal TreatmentPreheating the weld zone – reduces energy input, cooling rates in the weld and HAZ, reduces differential shrinkage, residual stresses, and distortion.Postwelding heat treatment of the entire welded structureStress-relief anneal reduces residual stresses to acceptable level.Normalizing a steel wipes out most undesirable effects of welding.Full heat treatment (quenching and tempering of steels)Peening (hammering or rolling) of weld bead improves the strength of welds.
21Oxyacetylene Gas Welding Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene. (d) The principle of the oxyfuel-gas welding operation.
22Oxyacetylene TorchThe acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted.Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red.
24Oxygen-fuel gas welding & Cutting The elements of Oxygen-fuel gas welding and cutting:General RequirementsCylindersService Pipe SystemsPipe System Protection
25Oxygen-fuel gas welding and cutting General RequirementsFocuses on using Acetylene SafelyFlammableUnstableCannot be adjusted above 15 psiSafe Work PracticesBlow out cylinder valveTurn on cylinder valve first and then adjust the regulator pressure screw.Never stand in front or behind a regulator when opening the cylinder valveOpen cylinder valve slowlyThe pressure adjusting screw:Turning clockwise allows the gas allows to flow.Turning counterclockwise reduces or stop the gas flow.I. Speaker’s Notes:Acetylene is extremely dangerous because of its flammability range.Oxyacetylene torch cutting is very common throughout the industry as it has a wide flammable range.Acetylene is extremely unstable.Acetylene is generated in the cylinder from a reaction of acetone and calcium silicate.Relief valves for generating chamber shall be set to open at a pressure not in excess of 15 psi.Using acetylene at pressures in excess of 15 psig pressure (or about 30 psia pressure) is a hazardous practice.II. Speaker’s Notes:This slide lists basic rules to follow when welding with oxyacetylene.Before connecting to the regulator, always blow out the cylinder valve.Release the regulator by adjusting the screw before opening the cylinder valve.Always stand to the side of the regulator while opening the cylinder in case of accidental pressure release.Open the valve cautiously and slowly.Never use acetylene at pressures above 15 pounds per square inch.
26Oxygen-fuel gas welding and cutting General Requirements Cont.:Safe Work PracticesPurge oxygen and acetylene passagesLight the acetyleneNever use oil or greaseDo not use oxygen as a substitute for airKeep your work area cleanI. Speaker’s Notes:Before lighting the torch, remember to purge acetylene and oxygen passages.Before opening the oxygen on the torch, light the acetylene.Never use oil or grease on regulators, tips, or any part that may come into contact with oxygen.Do not use oxygen as a substitute for air.Always keep your work area free of items that could ignite.
27Oxygen-fuel gas welding and cutting CylindersCylinder approval and markingmarked for the purpose of identifying the gas content, with either the chemical or trade name of the gasStorage of cylindersStorage area must be well ventilatedCylinders must be at least 20 feet from combustiblesValves must be closedValve protection must be in placeInside storage must be limited to 2,000 cubic feet.Cylinders must be stored in upright positionOxygen must be at least 20 feet from fuel gas or 5 feet with a 1/2 hour fire barrierSeparate oxygen from fuel gas
28Oxygen-fuel gas welding and cutting Cylinders Cont.:Operating ProceduresOperation must emphasize the absence of oily or greasy substances. Follow these rules of operation:Cylinders, cylinder valves, couplings, regulators, hose, and apparatus shall be kept free from oily or greasy substances.Oxygen cylinders or apparatus shall not be handled with oily hands or gloves.A jet of oxygen must never be permitted to strike an oily surface, greasy clothes, or enter a fuel oil or other storage tank.
29Oxygen-fuel gas welding and cutting Service Pipe SystemsThere are special requirements for service pipe systems when using oxygen or acetylene.OxygenAcetylene or Acetylene CompoundsSpeaker’s Notes:Oxygen: When oxygen is supplied to a service piping system from a low pressure oxygen manifold without an intervening pressure regulating device, the piping system shall have a minimum design pressure of 250 psig.A pressure regulating device shall be used at each station outlet when the connected equipment is for use at pressures less than 250 psig. Acetylene or Acetylene Compounds: Piping for acetylene or acetylenic compounds shall be steel or wrought iron.
30Oxygen-fuel gas welding and cutting Pipe System ProtectionThe entire service pipe system must be protected against build-up of excessive pressure and leaks. This protection is accomplished with:Protective equipmentRegulatorsProper hose and hose connections.
31Oxygen-fuel gas welding and cutting Pipe System Protection Cont.:Protective equipment is divided into the two categories listed here:Pressure Relief DevicesThe pressure relief device should discharge upwards to a safe location.Pressure relief valves are required in fuel-gas piping systems to prevent excessive pressure build up within the system.Speaker’s Notes:Pressure Relief Devices: Relief valves will vent automatically at preset pressures or may be manually operated to relieve pressure in the system.
32Oxygen-fuel gas welding and cutting Pipe System Protection Cont.:Approved protective equipment shall be installed in fuel-gas piping to prevent:Backflow of oxygen into the fuel-gas supply systemPassage of a flash back into the fuel-gas supply systemExcessive back pressure of oxygen in the fuel-gas supply system.Speaker’s Notes:The three function: The protective equipment in fuel-gas piping systems shall be located either at the main supply line, at the head of each branch line, or at each location where fuel-gas is withdrawn
35Arc Welding and Cutting Definition:A fusion process wherein the coalescence of the metals is achieved from the heat of an electric arc formed between an electrode and the work.ApplicationInstallationOperation & Maintenancet
36Arc Welding & Cutting Application Installation Applies to a large and varied group of processes that use an electric arc as the source of heat to melt and join metals.InstallationArc welding requires proper installation of equipment.A critical part of installation is ensuring that proper grounding is completed.
37Arc Welding & Cutting Operation & Maintenance All connections to the machine shall be checked to make certain that they are properly made.The work lead shall be firmly attached to the work.Magnetic work clamps shall be free from adherent metal particles of spatter on contact surfaces.Coiled welding cable shall be spread out before use to avoid serious overheating and damage to insulation.
38Arc Welding & Cutting Operation and Maintenance Cont.: During welding operations, cables with splices within 10 feet (3m) of the holder shall not be used.Welders should not coil or loop welding electrode cable around parts of their body.Cables with damaged insulation or exposed bare conductors shall be replaced.Joining lengths of work and electrode cables shall be done by the use of connecting means specifically intended for that purpose.The connecting means shall have insulation adequate for the service conditions.
39Methods of Arc Welding Three Types of Welding Methods: Tungsten Inert Gas Welding (TIG)Gas Metal Arc Welding (MIG)Shielded Metal Arc Welding (SMAW)/ Stick Welding
40Electric Arc Welding Heat input Direct Current Electrode Negative (DCEN): Deeper weld.Direct Current Electrode Positive (DCEP): Shallower and WiderHeat is produced from electric arc between workpiece and electrode material for melting the workpiece material.AC and DC are usedAn Inert gas shields both electrodesMost heat energy is due to electron flow to metalHeat inputH- heat input, E, Voltage, I, Current, and v the velocity of the arc travels along the weld line
41Electric Arc Welding - Classification - The ElectrodeConsumable: melts and serves as a filling materialNon-consumable: does not melt, parent metal is used, or a separate filler rodCoated or UncoatedCoatingProvides a gaseous shield to prevent oxidationLowers the voltage needed to establish the arcMay provide slag-blanket to protect the jointAdd alloying elements to enhance the properties of the joint.
43Non-Consumable-Electrode Welding: Gas Tungsten-Arc Welding (GTAW) Nonconsumable gas tungsten Inert gas welding (TIG)Weld zone is protected by inert gasDC with straight polarity is used with steel, cast iron, and stainlessAC with Al, Mg alloys where ac helps in stripping the oxideBoth hand and automatic operations are possibleThe process demands considerable skill but produces very high-quality welds on almost any materialNo weld spatter or slag formation
44Consumable Electrode Arc Welding Processes Shielded metal arc weldingSubmerged arc weldingGas metal arc welding
45Consumable Electrode Arc Welding Shielded-Metal Arc Welding Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.
46Consumable-Electrode Welding: Gas Metal-Arc Welding (GMAW) - MIG Consumable gas metal-arc welding (MIG)Consumable electrode is metal which melts to become part of the weld seam.Weld zone is protected by a gas or a fluxNo slag is formedSeveral layers could be build with little or no intermediate cleaningIt is suitable for most metalsWire electrode can be supplied in long, coiled lengths which allow uninterrupted welds in any welding position.
47Consumable Electrode Arc Welding Gas - Gas Metal-arc Welding Process- (a) Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding. (b) Basic equipment used in gas metal-arc welding operations.
48Other Welding Processes High Energy Beam Welding Electron Beam welding (EBW)Heat is produced by high velocity electron gun in a narrow beamNo filler materialHigh rate of heating results in greater depth and heat-affected zone is very smallSuitable for welding refractory materials like: molybdenum and zirconiumRequires a vacuum (limitation)x-ray will be generated around the welding gun which may be cancerous
49High Energy Beam Welding LASER Beam welding (LBW)Uses a focused high power monochromatic light beam as a source of heat to the metalBeam can be directed to the welding spot with a lensDepth of welding similar to electron beam weldingVacuum is not necessary (advantage)Workpiece usually needs protection by a gasProcess is suitable for automationWelding speeds can be upto 7 m/min
64Brazing Definition: Torch Brazing A process which a filler metal is placed at or between the faying surfaces, the temperature is raised high enough to melt the filler metal but not the base metal.The molten metal fills the spaces by capillary attraction.Torch BrazingOxy-fuel torch with a carburizing flameFirst heat the joint then add the filler metal
65Safe Work Practices Electric & Gas Welding Safety Check: Ensure electrical cord, electrode holder and cables are free from defectsNo cable splices within 10 feet of electrode holder.Ensure welding unit is properly grounded. This helps to avoid over heating.All defective equipment shall be repaired or replaced before using.
66Safe Work Practices Electric & Gas Welding Cont.: Safety Check: Remove all jewelry – rings, watches, bracelets, etc…Ensure PPE e.g.. welding hood, gloves, rubber boots or safety shoes, apron are available and in good condition.Ensure fire extinguisher is charged and available.Ensure adequate ventilation and lighting is in place.Set Voltage Regulator to Manufacture’s specifications.Avoid electrical shock DON’T wrap cables around any body part.Ensure fittings are tight.
67Safe Work Practices Electric & Gas Welding Cont.: Safety Check: Inspect hoses for cuts and frayed areas.Set gauges to desired PSI.Ensure that sufficient PPE is made available.Locate welding screens to protect employee’s – DON’T block your exit.Ensure that adequate ventilation and lighting are in place.
68Fire Protection & Prevention Cont.: Welding areas should meet the following requirements:Floors swept & cleared of combustibles 35 ft. radius of work area.Flammable and combustible liquids kept 35 ft. radius of work area.At least one fire extinguisher – on siteProtective dividers to contain sparks and slagWelding curtainsNon-combustible wallsFire resistant tarps & blanketsUW-Eau ClaireFacilities Planning & Management
69Proper Ventilation for Welding Proper ventilation can be obtained either naturally or mechanically.Natural Ventilation is considered sufficient for welding and brazing operations if the present work area meets these requirements:Space of more than 10,000 square feet is provided per welderA ceiling height of more than 16 feet.Mechanical ventilation options generally fall into two basic categories.Low vacuum system which takes large volumes of air at low velocities.High vacuum system that are captured and extracted fumes as near to the work as possible.Speaker’s Notes:Local exhaust Ventilation have enough velocity to draw away the contaminants.Natural Ventilation: Welding is not done in a confined space, and Welding space does not contain partitions, balconies or structured barriers that obstruct cross ventilationMechanical Ventilation: These systems consist of hoods positioned at a distance from the work area.
70Fire Protection & Prevention Fire hazards must be removed, orGuards installed, orWelding/cutting must NOT take placeHot work permit should be used outside designated areas to ensure that all fire hazards are controlledUse of fire watch1/2 hour after operation ceases
71Proper Ventilation for Welding Ensure protection from fumes and gases by one or a combination of the following:Good general ventilation.Use of a booth.Local exhaust ventilation on the hand piece.Air supply to the helmet.
72Welding Operators Protection Welding involves specialized personal protection that must be worn every time you perform welding operations. The following is a list of basic PPE:Fire-resistant glovesApronsSafety shoesHelmetUltraviolet radiation filter plate (arc welding)Goggles with filter lensesU
73Welding, Cutting and Brazing SummaryMajor hazards include:FireBurnsShockToxic ExposureFollow proper procedures to prevent firesUse appropriate engineering controlsWear appropriate PPE