Joining and Cutting Processes Fusion Welding Processes Fusion

Joining and Cutting Processes

Fusion Welding Processes • Fusion Welding involves heating two materials above their melting temperatures (electrically or chemically). • Filler (rods) metals are added to the weld area during the welding of a joint (supply additional material to weld zone). Engr 241 -R 1 1

Processes Oxyfuel Gas Arc Consumed Electrode Non-Consumed Electrode Resistance Solid State Other – “High Energy” Engr 241 -R 1 2

Oxyfuel Gas Welding • Process that uses a fuel gas combined with oxygen to produce a flame • Typically used for structural sheet-metal fabrication, automotive bodies, and various repair tasks • Most common fuels used - acetylene (oxyacetylene). • Manual operation, portable & flexible. Low equipment cost. Engr 241 -R 1 3

Torch • allows for controlling and mixing gases

Oxygen and fuel gas cylinders

Cylinder Safety • • • Caps on when moving Secure to truck or wall Keep upright (Acetylene) (1/7 Rule) Hand over regulator when opening Read labels – don’t rely on colors Dangers of compressed oxygen Engr 241 -R 1 6

Oxyfuel Gas Welding- Flame Types • Neutral Flame: 1: 1 ratio (oxygen vs. fuel). • Oxidizing Flame: greater oxygen supply (not for steels). • Reducing (Carburizing) Flame: lower oxygen supply (lower temperature)brazing. Engr 241 -R 1 7

• Neutral - the oxygen and fuel gases combine • oxygen burns up the carbon and the hydrogen in the fuel gas then releases only heat and harmless gases • flame temp is 5589 deg F.

Oxyfuel Gas Welding- Flux • Retard oxidation of surfaces of the parts being welded • Dissolves/Removes oxides or other substances • Stronger joints Engr 241 -R 1 9

Arc Welding Processes (Consumable Electrode) • Developed in the mid-1800 s • Heat obtained through electrical energy Engr 241 -R 1 10

Shielded Metal Arc Welding (SMAW) • Stick welding • 50% of all large-scale industrial welding operations- portable process. • Electric arc generated between tip of coated electrode and the workpiece. • Electrode coating produces a shielding gas to protect from oxygen. Engr 241 -R 1 11

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Electric arc between flux covered electrode and base metal 11/6/2020

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SMAW (Cont. ) • (DCEN) electrode negative • Workpiece positive, electrode negative. • Sheet metals - shallow penetration, gap joints. • (DCEP) electrode positive • Electrode positive, workpiece negative. • Deeper penetration. • (AC) Alternating current Engr 241 -R 1 15

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SMAW (Cont. ) • Thick sections, large electrodes at max current. • Manual, portable, and flexible. ACDC machines, low cost equipment Engr 241 -R 1 17

Submerged Arc Welding • Weld arc is shielded by a granular flux. • Flux is fed to weld zone by gravity. • Flux covers molten metal which prevents spatter, sparks, UV radiation, or fumes. • Flux is recovered. • 4 -10 times productivity of SMAW, automatic, horizontal, low skill, Engr 241 -R 1 18

Submerged Arc

Underwater SMAW • use well insulated electrode holder and special water proof covered electrodes • because of rapid cooling - use stringer beads not weaving • short arc length and DCEN • poor visibility - use #4 or #8 lens • communication system • normally have 80% of the tensile strength and 50 of the ductility of normal welds

Gas Metal Arc Welding (GMAW) • Formerly MIG (Metal Inert Gas). • Argon, helium, carbon dioxide, or mix (Shield the arc to prevent oxidation). • Wire fed automatically through nozzle into arc. Engr 241 -R 1 21

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GMAW (Cont. ) • Rapid, economical, twice SMAW productivity. • Most production done today • Can be automated (robots), low skill, DC, medium cost equipment. Engr 241 -R 1 23

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Flux Cored Arc Welding (FCAW) • Same as GMAW but electrode is tubular and filled with flux. • Automatic feeding of wire (like GMAW). • Uses no external gas source • Fast growing • Thin to thick sections. • Can be automated (robotics), DC, medium cost. Engr 241 -R 1 26

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Electrogas Welding • For welding butt joint edges vertically in one pass. • Metal deposited between two pieces joined – space enclosed by copper shoes sliding upward with weld • Also around pipe • 1/2” to 3” thickness. • Usually automated, High equipment cost. • For welding bridges, pipes, tanks, ships Engr 241 -R 1 29

Electrogas - use shielding gas - flux cored wire fed in joint • arc maintained between electrode and weld

Electro-slag Welding • Similar to EGW. • Weld begins at part bottom, molten slag extinguishes arc. • Heat then produced continuously by elect. Resist. of molten slag • Very thick sections - 2” to 36”. • High cost of equipment. Engr 241 -R 1 31

Vertical joint - arc started between electrode & bottom

Electrodes • Strength of deposited metal. • Type of coating. • Size (1/16 to 5/16 in diameter). Engr 241 -R 1 33

Electrode Classifications • E 6011 -A 1 • E - arc welding electrode • 60 – 60, 000 psi min. tensile strength • 1 – next to last digit – position • 11 – last two digits together, type of covering and current to be used • A 1 – alloying elements Engr 241 -R 1 34

Electrode Coatings • Clay like material. • Silica binders and powdered materials (Oxides, carbonates, fluorides, metal alloys, cellulose) Engr 241 -R 1 35

Electrode Coatings (Cont. ) 1. Stabilize the arc. 2. Generate a gas shield. 3. Control rate at which the electrode melts. 4. Act as a flux to protect weld (from oxidation). 5. Add alloying elements to joint ie. Protect from becoming brittle). Engr 241 -R 1 36

Arc Welding (Non. Consumable Electrode) • Gas Tungsten-Arc Welding (GTAW) • Plasma Arc Welding (PAW) Engr 241 -R 1 37

Gas Tungsten-Arc Welding (GTAW) • Formerly TIG (Tungsten Inert Gas). • Shielding gas is supplied from an external source. Argon or helium (high cost). • Filler metal is supplied from filler wire. • Tungsten electrode is not consumed. Engr 241 -R 1 38

GTAW-NCE (Cont. ) • Good for thin parts, high quality welds. Used for welding aluminum, magnesium, titanium, and refractory metals. • all positions, AC-DC, medium distortion, portable equipment, medium cost of equipment. Engr 241 -R 1 40

Plasma Arc Welding • Argon and helium. • Arc is hot ionized gas (60, 000 degrees °F). • Transferred- workpiece is part of circuit. • Non-transferred- Arc between tungsten electrode and nozzle. • High energy, deep penetration, stable arc, less thermal distortion, high speed, > ¼” thick material, high skill, medium cost of equipment. Engr 241 -R 1 41

Separate shielding gas protects the welding or cutting process

Resistance Welding Processes • • • Spot Seam Projection Stud Flash Engr 241 -R 1 43

1. ) Resistance Spot Welding • Uses pressure and resistivity of parts to form nugget. • Must be clean but not oxide free • Used for sheet metal parts Engr 241 -R 1 44

Spot - most common

Two pieces fused with small nugget

2. ) Resistance Seam Welding • Like spot welding but with rollers. • Continuous or “roll spot welding”. Engr 241 -R 1 47

two wheeled electrodes travel over metal - current passes through them

can produce intermittent seam of overlapping spots for leak proofing

Seam welding I-Beams

3. ) Resistance Projection Welding • High elect resistance developed at joint by embossing projections on surfaces to be welded Engr 241 -R 1 51

form projections with dies

current passes through two pieces and is concentrated at bumps

4. ) Resistance Stud welding • Similar to flash welding • Threaded rod or hanger welded to flat plate Engr 241 -R 1 54

Stud • no drilling or punching holes in structure

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5. ) Resistance Flash welding • Also Called “Upset Welding” • Heat generated from arc as ends of two bars or sheets begin to make contact and develop an electrical resistance at the joint • After heating occurs and metal softens, an axial force is applied. Engr 241 -R 1 57

generally used to weld the butt ends of two pieces

parts are held in two clamps with ends together

high current passed between them • high resistance causes small arcs to occur between uneven surfaces

adv: fast and no pre cleaning of surfaces

Solid State Welding • Processes in which joining takes place without fusion of the workpiece, thus no liquid (molten) phase is present in the joint. • Clean surfaces in atomic contact under pressure and maybe heat (increases diffusion) form bonds and produce a strong joint. Engr 241 -R 1 62

Solid State Welding • Cold Welding • Ultrasonic Welding • Friction Welding • Explosion Welding Engr 241 -R 1 63

1. ) Cold Welding • Surfaces degrease, wire brush, or wiped to remove oxide smudge. • Roll bonding or hot roll bonding (cladding). • Processes takes advantage of materials solubility (soft, ductile materials) Engr 241 -R 1 64

Tool can be hand, pneumatic, or hydraulic • dies must be designed to impose proper pressure for different metals

2. ) Ultrasonic Welding • Sonotrode oscillates 10 -75 k. Hz • Contact causes plastic deformation. • Temperature is 1/3 to 1/2 of melting temperature (except in plastics). • Suited for metallic dissimilar metals and non-metallic materials (thin parts). • Can use roll transducer for seams. Engr 241 -R 1 66

UT spot welds

UT seam welds with lateral drive rollers

3. ) Friction welding • One component rotates at high speed while other is stationary. Pressure contact causes heating. Part must be stopped fast to avoid shearing weld. • Wide variety of materials, good joint strength • Solid bars up to 3” & tubes up to 10”. • Surface speed 3000 ft/min. • Automated, low skill, high machine cost. Engr 241 -R 1 69

Friction welding

4. )Explosion Welding • Pressure generated by detonating a layer of explosive placed over one of the components. • Causes wavy interface and cold pressure welding by plastic deformation. • Good bond strength. • Clad dissimilar metals. Engr 241 -R 1 71

“Other” High Energy Welding Processes • involves concentrating a lot of energy on a small spot • produces deep narrow welds • two processes include: • Electron beam • LASER beam Engr 241 -R 1 73

Electron beam welding (EBW) • Electrons-focused, Vacuum required. • High quality welds, very expensive equipment Engr 241 -R 1 74

Laser Beam Welding (LBW) • Focused laser • Good quality, little distortion, good strength, ductile, non-porous. • Automated, • high equipment cost. Engr 241 -R 1 76

Cutting Engr 241 -R 1 78

Oxyfuel Gas Cutting • Cuts mostly by oxidation • For ferrous metals • Rough surface, high distortion, can cut underwater. Engr 241 -R 1 79

Cutting

Alignment of torch tip orifices with the kerf • one orifice should proceed and one should follow the cut

Plasma Arc Cutting (PAC) • Highest temperatures • Rapid cutting, good surface, narrow kerf, popular with Robotics/Flexible automation Engr 241 -R 1 82

protects the welding or cutting process

Transferred vs. Non Transferred Arc

Lasers & Electron Beam Cutting • Accurate • Wide variety of material • Good surface, narrow kerf. Engr 241 -R 1 85

Brazing, Soldering, Adhesive Bonding, and Mechanical Fastening Processes Engr 241 -R 1 86

Brazing • Characteristics • filler metal is placed at or between the faying surfaces to be joined. • temperature is raised to melt the filler metal but not the work piece. • Above 840 deg F. • surface should be cleaned. • Flux • prevents oxidation. • removes films from work piece surfaces. Engr 241 -R 1 87

Soldering Characteristics • solder fills joint by capillary action. • use of soldering irons, torches, ovens. • lower temperature than brazing. (below 840) • Copper, Silver and Gold are easy to solder while • Aluminum and stainless steels are not. Engr 241 -R 1 88

Flux • Inorganic acids or salts • Zinc ammonium chloride solutioncleaning. • Remove afterward to avoid corrosion. • Non-corrosive resin based fluxes • Electrical application. Engr 241 -R 1 89

Adhesive Classifications • Chemically reactive • Pressure sensitive • Hot Melt • Evaporative or diffusion • Film and tape • Delayed tack • Electrically and thermally conductive Engr 241 -R 1 90

Adhesives Advantages • Interface gives strength, sealing, insulation, electrochemical corrosion from dissimilar metals, reduces vibration and noise. • Distributes load, gives structural integrity (no holes), improved appearance. • Good for thin, fragile, and porous parts. • Limited distortion because of low temperature. Engr 241 -R 1 91

Adhesives Limitations • • Service temperatures. Possibly long bonding time. Great care in surface preparation. Difficulty in testing bonded joints nondestructively. • Limited reliability of adhesively bonded structures during service life. Engr 241 -R 1 92

Mechanical Fastening Characteristics • Ease of manufacture. • Ease of assembly and transportation. • Ease of disassembly, maintenance, replacement or repair. • Ease on creating designs for movable joints (hinges, sliding mechanisms, adjustable components, fixtures). • Lower over all cost of manufacture of the product. Engr 241 -R 1 93

Mechanical Fastening Methods • • Threaded fastener. Rivets. Metal stitching or stapling. Seaming. Crimping. Snap-in fasteners. Shrink & Press fit. Engr 241 -R 1 94

Thermoplastic Joining • External heat sources • Hot air, gasses, elect resist, lasers • Internal heat sources • Ultrasonic, Friction Engr 241 -R 1 95

Thermoset Welding • Threaded or molded inserts • Mechanical fasteners (self tapping screws) • Solvent bonding Engr 241 -R 1 96