WELDING Welding is a materials joining process which

WELDING • Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material. • Welding is used for making permanent joints. • It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.

TYPES • Plastic Welding or Pressure Welding The piece of metal to be joined are heated to a plastic state and forced together by external pressure (Ex) Resistance welding • Fusion Welding or Non-Pressure Welding The material at the joint is heated to a molten state and allowed to solidify (Ex) Gas welding, Arc welding

Classification of welding processes: (i). Arc welding • Carbon arc • Metal inert gas • Tungsten inert gas • Plasma arc • Submerged arc • Electro-slag (ii). Gas Welding • • • Oxy-acetylene Air-acetylene Oxy-hydrogen (iii). Resistance Welding • Butt • Spot • Seam • Projection • Percussion (iv)Thermit Welding (v)Solid State Welding Friction Ultrasonic Diffusion Explosive (vi)Newer Welding Electron-beam Laser (vii)Related Process Oxy-acetylene cutting Arc cutting Hard facing Brazing Soldering

Arc welding • Equipments: • A welding generator (D. C. ) or Transformer (A. C. ) • Two cables- one for work and one for electrode • Electrode holder • Electrode • Protective shield • Gloves • Wire brush • Chipping hammer • Goggles

Arc Welding Equipments

Metal arc welding

Arc Welding Uses an electric arc to coalesce metals Arc welding is the most common method of welding metals Electricity travels from electrode to base metal to ground

Carbon Arc Welding

Arc welding Advantages • Most efficient way to join metals • Lowest-cost joining method • Affords lighter weight through better utilization of materials • Joins all commercial metals • Provides design flexibility Limitations • Manually applied, therefore high labor cost. • Need high energy causing danger • Not convenient for disassembly. • Defects are hard to detect at joints.

Comparison of A. C. and D. C. arc welding Alternating Current (from Transformer) More efficiency Power consumption less Cost of equipment is less Higher voltage – hence not safe Not suitable for welding non ferrous metals Not preferred for welding thin sections Any terminal can be connected to the work or electrode

Comparison of A. C. and D. C. arc welding Direct Current (from Generator) Less efficiency Power consumption more Cost of equipment is more Low voltage – safer operation suitable for both ferrous non ferrous metals preferred for welding thin sections Positive terminal connected to the work Negative terminal connected to the electrode

GAS WELDING • Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch • The temperature generated during the process is 33000 c • When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld • Fluxes are added to the welded metal to remove oxides • Common fluxes used are made of sodium, potassium. Lithium and borax. • Flux can be applied as paste, powder, liquid. solid coating or gas.

GAS WELDING EQUIPMENT. . . 1. Gas Cylinders Pressure Oxygen – 125 kg/cm 2 Acetylene – 16 kg/cm 2 2. Regulators Working pressure of oxygen 1 kg/cm 2 Working pressure of acetylene 0. 15 kg/cm 2 Working pressure varies depends upon the thickness of the pieces welded. 3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve work

Oxy-Acetylene welding

TYPES OF FLAMES… • Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000 c) • Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000 c) • Used for welding steels, aluminium, copper and cast iron • If more oxygen is added, the cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame • Has the highest temperature about 34000 c • Used for welding brass and brazing operation

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.

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.

GAS CUTTING • Ferrous metal is heated in to red hot condition and a jet of pure oxygen is projected onto the surface, which rapidly oxidizes • Oxides having lower melting point than the metal, melt and are blown away by the force of the jet, to make a cut • Fast and efficient method of cutting steel to a high degree of accuracy • Torch is different from welding • Cutting torch has preheat orifice and one central orifice for oxygen jet • PIERCING and GOUGING are two important operations • Piercing, used to cut a hole at the centre of the plate or away from the edge of the plate • Gouging, to cut a groove into the steel surface

GAS CUTTING… Automatic Gas Cutting Manual Gas Cutting

Weld joints

Brazing and Soldering • Brazing It is a low temperature joining process. It is performed at temperatures above 840º F and it generally affords strengths comparable to those of the metal which it joins. It is low temperature in that it is done below the melting point of the base metal. It is achieved by diffusion without fusion (melting) of the base Brazing can be classified as Torch brazing Dip brazing Furnace brazing Induction brazing

Brazing

Advantages & Disadvantages Advantages Dissimilar metals which canot be welded can be joined by brazing Very thin metals can be joined Metals with different thickness can be joined easily In brazing thermal stresses are not produced in the work piece. Hence there is no distortion • Using this process, carbides tips are brazed on the steel tool holders • • Disadvantages • Brazed joints have lesser strength compared to welding • Joint preparation cost is more • Can be used for thin sheet metal sections

Soldering • It is a low temperature joining process. It is performed at temperatures below 840ºF for joining. • Soldering is used for, • Sealing, as in automotive radiators or tin cans • Electrical Connections • Joining thermally sensitive components • Joining dissimilar metals

Fusion Welding Processes Consumable Electrode SMAW – Shielded Metal Arc Welding GMAW – Gas Metal Arc Welding SAW – Submerged Arc Welding Non-Consumable Electrode GTAW – Gas Tungsten Arc Welding PAW – Plasma Arc Welding High Energy Beam Electron Beam Welding Laser Beam Welding Processes

SMAW – Shielded Metal Arc Welding Processes • Consumable electrode • Flux coated rod • Flux produces protective gas around weld pool • Slag keeps oxygen off weld bead during cooling • General purpose welding—widely used • Thicknesses 1/8” – 3/4” • Portable Power. . . Current I (50 - 300 amps) Voltage V (15 - 45 volts) Power = VI 10 k. W

Electric Arc Welding -- Polarity Welding Processes SMAW - DC Polarity Straight Polarity Reverse Polarity (–) (+) Shallow penetration (thin metal) AC - Gives pulsing arc - used for welding thick sections (+) (–) Deeper weld penetration

GMAW – Gas Metal Arc Welding (MIG) Welding Processes • DC reverse polarity - hottest arc • AC - unstable arc Gas Metal Arc Welding (GMAW) Torch • MIG - Metal Inert Gas • Consumable wire electrode • Shielding provided by gas • Double productivity of SMAW • Easily automated Groover, M. , Fundamentals of Modern Manufacturing, , p. 734, 1996

SAW – Submerged Arc Welding Processes • 300 – 2000 amps (440 V) • Consumable wire electrode • Shielding provided by flux granules Gas Metal Arc Welding (GMAW) Torch • Low UV radiation & fumes • Flux acts as thermal insulator • Automated process (limited to flats) • High speed & quality (4 – 10 x SMAW) • Suitable for thick plates http: //www. twi. co. uk

GTAW – Gas Tungsten Arc Welding (TIG) Welding Processes Current I (200 A DC) (500 A AC) Power 8 -20 k. W • a. k. a. TIG - Tungsten Inert Gas • Non-consumable electrode • With or without filler metal • Shield gas usually argon • Used for thin sections of Al, Mg, Ti. • Most expensive, highest quality

Laser Welding Processes • Laser beam produced by a CO 2 or YAG Laser • High penetration, high-speed process • Concentrated heat = low distortion • Laser can be shaped/focused & pulsed on/off • Typically automated & high speed (up to 250 fpm) • Workpieces up to 1” thick Typical laser welding applications : • Catheters & Other Medical Devices • Small Parts and Components • Fine Wires • Jewelry • Small Sensors • Thin Sheet Materials Down To 0. 001" Thick

Solid State Welding Processes Friction Welding Diffusion Welding Ultrasonic Welding Resistance Welding Processes

Friction Welding (Inertia Welding) • One part rotated, one stationary • Stationary part forced against rotating part • Friction converts kinetic energy to thermal energy • Metal at interface melts and is joined • When sufficiently hot, rotation is stopped & axial force increased Welding Processes

Resistance Welding is the coordinated application of electric current and mechanical pressure in the proper magnitudes and for a precise period of time to create a coalescent bond between two base metals. • Heat provided by resistance to electrical current (Q=I 2 Rt) • Typical 0. 5 – 10 V but up to 100, 000 amps! • Force applied by pneumatic cylinder • Often fully or partially automated - Spot welding - Seam welding Welding Processes

Resistance Welding is the coordinated application of electric current and mechanical pressure in the proper magnitudes and for a precise period of time to create a coalescent bond between two base metals. • Heat provided by resistance to electrical current (Q=I 2 Rt) • Typical 0. 5 – 10 V but up to 100, 000 amps! • Force applied by pneumatic cylinder • Often fully or partially automated - Spot welding - Seam welding Welding Processes

Diffusion Welding Processes • Parts forced together at high temperature (< 0. 5 Tm absolute) and pressure • Heated in furnace or by resistance heating • Atoms diffuse across interface • After sufficient time the interface disappears • Good for dissimilar metals • Bond can be weakened by surface impurities Kalpakjian, S. , Manufacturing Engineering & Technology, p. 889, 1992

Soldering & Brazing Metal Joining Processes Soldering & Brazing • Only filler metal is melted, not base metal • Lower temperatures than welding • Filler metal distributed by capillary action • Metallurgical bond formed between filler & base metals • Strength of joint typically – stronger than filler metal itself – weaker than base metal – gap at joint important (0. 001 – 0. 010”) • Pros & Cons – Can join dissimilar metals – Less heat - can join thinner sections (relative to welding) – Excessive heat during service can weaken joint

Soldering Metal Joining Processes Soldering Solder = Filler metal • Alloys of Tin (silver, bismuth, lead) • Melt point typically below 840 F Flux used to clean joint & prevent oxidation • separate or in core of wire (rosin-core) Tinning = pre-coating with thin layer of solder Applications: • Printed Circuit Board (PCB) manufacture • Pipe joining (copper pipe) • Jewelry manufacture • Typically non-load bearing Easy to solder: copper, silver, gold Difficult to solder: aluminum, stainless steels (can pre-plate difficult to solder metals to aid process)

PCB Soldering Manual PCB Soldering Metal Joining Processes PTH - Pin-Through-Hole connectors • Soldering Iron & Solder Wire • Heating lead & placing solder • Heat for 2 -3 sec. & place wire opposite iron • Trim excess lead

PCB Reflow Soldering Automated Reflow Soldering Metal Joining Processes SMT = Surface Mount Technology • Solder/Flux paste mixture applied to PCB using screen print or similar transfer method • Solder Paste serves the following functions: – supply solder material to the soldering spot, – hold the components in place prior to soldering, – clean the solder lands and component leads – prevent further oxidation of the solder lands. Printed solder paste on a printed circuit board (PCB) • PCB assembly then heated in “Reflow” oven to melt solder and secure connection

Brazing Metal Joining Processes Brazing Use of low melt point filler metal to fill thin gap between mating surfaces to be joined utilizing capillary action • Filler metals include Al, Mg & Cu alloys (melt point typically above 840 F) • Flux also used • Types of brazing classified by heating method: – Torch, Furnace, Resistance Applications: • Automotive - joining tubes • Pipe/Tubing joining (HVAC) • Electrical equipment - joining wires • Jewelry Making • Joint can possess significant strength

Brazing Metal Joining Processes Brazing Use of low melt point filler metal to fill thin gap between mating surfaces to be joined utilizing capillary action • Filler metals include Al, Mg & Cu alloys (melt point typically above 840 F) • Flux also used • Types of brazing classified by heating method: – Torch, Furnace, Resistance Applications: • Automotive - joining tubes • Pipe/Tubing joining (HVAC) • Electrical equipment - joining wires • Jewelry Making • Joint can possess significant strength

Brazing Metal Joining Processes Brazing Figuring length of lap for flat joints. X = Length of lap T = Tensile strength of weakest member W = Thickness of weakest member C = Joint integrity factor of. 8 L = Shear strength of brazed filler metal Let’s see how this formula works, using an example. Problem: What length of lap do you need to join. 050" annealed Monel sheet to a metal of equal or greater strength? Solution: C =. 8 T = 70, 000 psi (annealed Monel sheet) W =. 050" L = 25, 000 psi (Typical shear strength for silver brazing filler metals) X = (70, 000 x. 050) /(. 8 x 25, 000) =. 18" lap length

Soldering & Brazing Metal Joining Processes Brazing Figuring length of lap for tubular joints. X = Length of lap area W = Wall thickness of weakest member D = Diameter of lap area T = Tensile strength of weakest member C = Joint integrity factor of. 8 L = Shear strength of brazed filler metal Again, an example will serve to illustrate the use of this formula. Problem: What length of lap do you need to join 3/4" O. D. copper tubing (wall thickness. 064") to 3/4" I. D. steel tubing? Solution: W =. 064" D =. 750" C=. 8 T = 33, 000 psi (annealed copper) L = 25, 000 psi (a typical value) X = (. 064 x (. 75 –. 064) x 33, 000)/(. 8 x. 75 x 25, 000) X =. 097" (length of lap)