UNIT IV JOINING PROCESSES WELDING Welding is a

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UNIT IV JOINING PROCESSES

UNIT IV JOINING PROCESSES

WELDING § Welding is a materials joining process which produces coalescence of materials by

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.

Two Categories of Welding Processes § Fusion welding - coalescence is accomplished by melting

Two Categories of Welding Processes § Fusion welding - coalescence is accomplished by melting the two parts to be joined, in some cases adding filler metal to the joint § Examples: arc welding, resistance spot welding, oxyfuel gas welding § Solid state welding - heat and/or pressure are used to achieve coalescence, but no melting of base metals occurs and no filler metal is added § Examples: forge welding, diffusion welding, friction welding

WELDING PROCESSES 1. 2. 3. 4. 5. 6. 7. Arc Welding Resistance Welding Oxyfuel

WELDING PROCESSES 1. 2. 3. 4. 5. 6. 7. Arc Welding Resistance Welding Oxyfuel Gas Welding Other Fusion Welding Processes Solid State Welding Weld Quality Weldability

Classification of welding processes: (i). Arc welding § Carbon arc § Metal inert gas

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

Arc Welding (AW) A fusion welding process in which coalescence of the metals is

Arc Welding (AW) A fusion welding process in which coalescence of the metals is achieved by the heat from an electric arc between an electrode and the work § Electric energy from the arc produces temperatures ~ 10, 000 F (5500 C), hot enough to melt any metal § Most AW processes add filler metal to increase volume and strength of weld joint

Consumable Electrode AW Processes § § § Shielded Metal Arc Welding Gas Metal Arc

Consumable Electrode AW Processes § § § Shielded Metal Arc Welding Gas Metal Arc Welding Flux‑Cored Arc Welding Electrogas Welding Submerged Arc Welding

Non-consumable Electrode Processes § § Gas Tungsten Arc Welding Plasma Arc Welding Carbon Arc

Non-consumable Electrode Processes § § Gas Tungsten Arc Welding Plasma Arc Welding Carbon Arc Welding Stud Welding

What is an Electric Arc? An electric arc is a discharge of electric current

What is an Electric Arc? An electric arc is a discharge of electric current across a gap in a circuit § It is sustained by an ionized column of gas (plasma) through which the current flows § To initiate the arc in AW, electrode is brought into contact with work and then quickly separated from it by a short distance

Arc Welding A pool of molten metal is formed near electrode tip, and as

Arc Welding A pool of molten metal is formed near electrode tip, and as electrode is moved along joint, molten weld pool solidifies in its wake Figure 31. 1 Basic configuration of an arc welding process.

Two Basic Types of AW Electrodes § Consumable – consumed during welding process §

Two Basic Types of AW Electrodes § Consumable – consumed during welding process § Source of filler metal in arc welding § Nonconsumable – not consumed during welding process § Filler metal must be added separately

Consumable Electrodes § Forms of consumable electrodes § Welding rods (a. k. a. sticks)

Consumable Electrodes § Forms of consumable electrodes § Welding rods (a. k. a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently § Weld wire can be continuously fed from spools with long lengths of wire, avoiding frequent interruptions § In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal

Nonconsumable Electrodes § Made of tungsten which resists melting § Gradually depleted during welding

Nonconsumable Electrodes § Made of tungsten which resists melting § Gradually depleted during welding (vaporization is principal mechanism) § Any filler metal must be supplied by a separate wire fed into weld pool

Arc Shielding § At high temperatures in AW, metals are chemically reactive to oxygen,

Arc Shielding § At high temperatures in AW, metals are chemically reactive to oxygen, nitrogen, and hydrogen in air § Mechanical properties of joint can be seriously degraded by these reactions § To protect operation, arc must be shielded from surrounding air in AW processes § Arc shielding is accomplished by: § Shielding gases, e. g. , argon, helium, CO 2 § Flux

Flux A substance that prevents formation of oxides and other contaminants in welding, or

Flux A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal § Provides protective atmosphere for welding § Stabilizes arc § Reduces spatter

Various Flux Application Methods § Pouring granular flux onto welding operation § Stick electrode

Various Flux Application Methods § Pouring granular flux onto welding operation § Stick electrode coated with flux material that melts during welding to cover operation § Tubular electrodes in which flux is contained in the core and released as electrode is consumed

Power Source in Arc Welding § Direct current (DC) vs. Alternating current (AC) §

Power Source in Arc Welding § Direct current (DC) vs. Alternating current (AC) § AC machines less expensive to purchase and operate, but generally restricted to ferrous metals § DC equipment can be used on all metals and is generally noted for better arc control

Consumable Electrode AW Processes § § § Shielded Metal Arc Welding Gas Metal Arc

Consumable Electrode AW Processes § § § Shielded Metal Arc Welding Gas Metal Arc Welding Flux‑Cored Arc Welding Electroslag Welding Submerged Arc Welding

Shielded Metal Arc Welding (SMAW) Uses a consumable electrode consisting of a filler metal

Shielded Metal Arc Welding (SMAW) Uses a consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding § Sometimes called "stick welding" § Power supply, connecting cables, and electrode holder available for a few thousand dollars

Shielded Metal Arc Welding Figure 31. 3 Shielded metal arc welding (SMAW).

Shielded Metal Arc Welding Figure 31. 3 Shielded metal arc welding (SMAW).

Shielded Metal Arc Welding Figure 31. 2 Shielded metal arc welding (stick welding) performed

Shielded Metal Arc Welding Figure 31. 2 Shielded metal arc welding (stick welding) performed by a (human) welder (photo courtesy of Hobart Brothers Co. ).

SMAW Applications § Used for steels, stainless steels, cast irons, and certain nonferrous alloys

SMAW Applications § Used for steels, stainless steels, cast irons, and certain nonferrous alloys § Not used or rarely used for aluminum and its alloys, copper alloys, and titanium

Gas Metal Arc Welding (GMAW) Uses a consumable bare metal wire as electrode and

Gas Metal Arc Welding (GMAW) Uses a consumable bare metal wire as electrode and shielding accomplished by flooding arc with a gas § Wire is fed continuously and automatically from a spool through the welding gun § Shielding gases include inert gases such as argon and helium for aluminum welding, and active gases such as CO 2 for steel welding § Bare electrode wire plus shielding gases eliminate slag on weld bead - no need for manual grinding and cleaning of slag

Gas Metal Arc Welding(MIG) Figure 31. 4 Gas metal arc welding (GMAW).

Gas Metal Arc Welding(MIG) Figure 31. 4 Gas metal arc welding (GMAW).

GMAW Advantages over SMAW § Better arc time because of continuous wire electrode §

GMAW Advantages over SMAW § Better arc time because of continuous wire electrode § Sticks must be periodically changed in SMAW § Better use of electrode filler metal than SMAW § End of stick cannot be used in SMAW § Higher deposition rates § Eliminates problem of slag removal § Can be readily automated

Flux‑Cored Arc Welding (FCAW) Adaptation of shielded metal arc welding, to overcome limitations of

Flux‑Cored Arc Welding (FCAW) Adaptation of shielded metal arc welding, to overcome limitations of stick electrodes § Electrode is a continuous consumable tubing (in coils) containing flux and other ingredients (e. g. , alloying elements) in its core § Two versions: § Self‑shielded FCAW - core includes compounds that produce shielding gases § Gas‑shielded FCAW - uses externally applied shielding gases

Flux-Cored Arc Welding Figure 31. 6 Flux‑cored arc welding. Presence or absence of externally

Flux-Cored Arc Welding Figure 31. 6 Flux‑cored arc welding. Presence or absence of externally supplied shielding gas distinguishes the two types: (1) self‑shielded, in which core provides ingredients for shielding, and (2) gas‑shielded, which uses external shielding gases.

Electroslag Welding (ESW) Uses a continuous consumable electrode, either flux‑cored wire or bare with

Electroslag Welding (ESW) Uses a continuous consumable electrode, either flux‑cored wire or bare with externally supplied shielding gases, and molding shoes to contain molten metal § When flux‑cored electrode wire is used and no external gases are supplied, then special case of self‑shielded FCAW § When a bare electrode wire used with shielding gases from external source, then special case of GMAW

Electroslag Welding Figure 31. 7 Electrogas welding using flux‑cored electrode wire: (a) front view

Electroslag Welding Figure 31. 7 Electrogas welding using flux‑cored electrode wire: (a) front view with molding shoe removed for clarity, and (b) side view showing molding shoes on both sides.

Submerged Arc Welding (SAW) Uses a continuous, consumable bare wire electrode, with arc shielding

Submerged Arc Welding (SAW) Uses a continuous, consumable bare wire electrode, with arc shielding provided by a cover of granular flux § Electrode wire is fed automatically from a coil § Flux introduced into joint slightly ahead of arc by gravity from a hopper § Completely submerges operation, preventing sparks, spatter, and radiation

Submerged Arc Welding Figure 31. 8 Submerged arc welding.

Submerged Arc Welding Figure 31. 8 Submerged arc welding.

SAW Applications and Products § Steel fabrication of structural shapes (e. g. , I‑beams)

SAW Applications and Products § Steel fabrication of structural shapes (e. g. , I‑beams) § Seams for large diameter pipes, tanks, and pressure vessels § Welded components for heavy machinery § Most steels (except hi C steel) § Not good for nonferrous metals

Non-consumable Electrode Processes § § Gas Tungsten Arc Welding Plasma Arc Welding Carbon Arc

Non-consumable Electrode Processes § § Gas Tungsten Arc Welding Plasma Arc Welding Carbon Arc Welding Stud Welding

Gas Tungsten Arc Welding (GTAW) Uses a non-consumable tungsten electrode and an inert gas

Gas Tungsten Arc Welding (GTAW) Uses a non-consumable tungsten electrode and an inert gas for arc shielding § Melting point of tungsten = 3410 C (6170 F) § A. k. a. Tungsten Inert Gas (TIG) welding § In Europe, called "WIG welding" § Used with or without a filler metal § When filler metal used, it is added to weld pool from separate rod or wire § Applications: aluminum and stainless steel most common

Gas Tungsten Arc Welding Figure 31. 9 Gas tungsten arc welding.

Gas Tungsten Arc Welding Figure 31. 9 Gas tungsten arc welding.

Advantages / Disadvantages of GTAW Advantages: § High quality welds for suitable applications §

Advantages / Disadvantages of GTAW Advantages: § High quality welds for suitable applications § No spatter because no filler metal through arc § Little or no post-weld cleaning because no flux Disadvantages: § Generally slower and more costly than consumable electrode AW processes

Plasma Arc Welding (PAW) Special form of GTAW in which a constricted plasma arc

Plasma Arc Welding (PAW) Special form of GTAW in which a constricted plasma arc is directed at weld area § Tungsten electrode is contained in a nozzle that focuses a high velocity stream of inert gas (argon) into arc region to form a high velocity, intensely hot plasma arc stream § Temperatures in PAW reach 28, 000 C (50, 000 F), due to constriction of arc, producing a plasma jet of small diameter and very high energy density

Plasma Arc Welding Figure 31. 10 Plasma arc welding (PAW).

Plasma Arc Welding Figure 31. 10 Plasma arc welding (PAW).

Advantages / Disadvantages of PAW Advantages: § Good arc stability § § Better penetration

Advantages / Disadvantages of PAW Advantages: § Good arc stability § § Better penetration control than other AW High travel speeds Excellent weld quality Can be used to weld almost any metals Disadvantages: § High equipment cost § Larger torch size than other AW § Tends to restrict access in some joints

Classification of welding processes: (i). Arc welding § Carbon arc § Metal inert gas

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

GAS WELDING § Sound weld is obtained by selecting proper size of flame, filler

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.

Oxyacetylene Welding (OAW) The oxyacetylene welding process uses a combination of oxygen and acetylene

Oxyacetylene Welding (OAW) The oxyacetylene welding process uses a combination of oxygen and acetylene gas to provide a high temperature flame.

Oxyacetylene Welding (OAW) § OAW is a manual process in which the welder must

Oxyacetylene Welding (OAW) § OAW is a manual process in which the welder must personally control the torch movement and filler rod application. § The term oxyfuel gas welding outfit refers to all the equipment needed to weld. § Cylinders contain oxygen and acetylene gas at extremely high pressure.

GAS WELDING EQUIPMENT. . . 1. Gas Cylinders Pressure Oxygen – 125 kg/cm 2

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 welded. 3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve work pieces

Typical Oxyacetylene Welding (OAW) Station

Typical Oxyacetylene Welding (OAW) Station

Oxyacetylene Welding

Oxyacetylene Welding

Oxyfuel Gas Welding (OFW) Group of fusion welding operations that burn various fuels mixed

Oxyfuel Gas Welding (OFW) Group of fusion welding operations that burn various fuels mixed with oxygen § OFW employs several types of gases, which is the primary distinction among the members of this group § Oxyfuel gas is also used in flame cutting torches to cut and separate metal plates and other parts § Most important OFW process is oxyacetylene welding

Oxyacetylene Welding (OAW) Fusion welding performed by a high temperature flame from combustion of

Oxyacetylene Welding (OAW) Fusion welding performed by a high temperature flame from combustion of acetylene and oxygen § Flame is directed by a welding torch § Filler metal is sometimes added § Composition must be similar to base metal § Filler rod often coated with flux to clean surfaces and prevent oxidation

Alternative Gases for OFW § § § Methylacetylene‑Propadiene (MAPP) Hydrogen Propylene Propane Natural Gas

Alternative Gases for OFW § § § Methylacetylene‑Propadiene (MAPP) Hydrogen Propylene Propane Natural Gas

Acetylene (C 2 H 2) § Most popular fuel among OFW group because it

Acetylene (C 2 H 2) § Most popular fuel among OFW group because it is capable of higher temperatures than any other § Up to 3480 C (6300 F) § Two stage reaction of acetylene and oxygen: § First stage reaction (inner cone of flame) C 2 H 2 + O 2 2 CO + H 2 + heat § Second stage reaction (outer envelope) 2 CO + H 2 + 1. 5 O 2 2 CO 2 + H 2 O + heat

Flame Types § There are three distinct types of oxyacetylene flames, usually termed: §

Flame Types § There are three distinct types of oxyacetylene flames, usually termed: § Neutral § Carburizing (or “excess acetylene”) § Oxidizing (or “excess oxygen” ) § The type of flame produced depends upon the ratio of oxygen to acetylene in the gas mixture which leaves the torch tip.

Carburizing Flame § Oxygen is turned on, flame immediately changes into a long white

Carburizing Flame § 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) § The flame is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. § Used on steel, it will cause an increase in the carbon content of the weld metal.

Pure Acetylene and Carburizing Flame profiles

Pure Acetylene and Carburizing Flame profiles

Carburizing Flame

Carburizing Flame

Neutral Flame § Addition of little more oxygen give a bright whitish cone surrounded

Neutral Flame § 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) § The neutral flame is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. It’s termed ”neutral” because it will usually have no chemical effect on the metal being welded. § It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal. § Used for welding steels, aluminum, copper and cast iron

Neutral Flame Profile

Neutral Flame Profile

Oxidizing Flame § If more oxygen is added, the cone becomes darker and more

Oxidizing Flame § 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 § The oxidizing flame results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or ”burn” some of the metal being welded. § Used for welding brass and brazing operation

Oxidizing Flame Profile

Oxidizing Flame Profile

GAS CUTTING § Ferrous metal is heated in to red hot condition and a

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

GAS CUTTING… Automatic Gas Cutting Manual Gas Cutting

Classification of welding processes: (i). Arc welding § Carbon arc § Metal inert gas

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

Solid-State Welding Processes

Solid-State Welding Processes

SOLID STATE WELDING PROCESSES Forge Welding Cold Welding Roll Welding Resistance Welding Hot pressure

SOLID STATE WELDING PROCESSES Forge Welding Cold Welding Roll Welding Resistance Welding Hot pressure Welding Diffusion Welding Explosion Welding Friction Welding Ultrasonic Welding

Resistance Welding Developed in the early 1900’s A process in which the heat required

Resistance Welding Developed in the early 1900’s A process in which the heat required for welding is produced by means of electrical resistance across the two components RW does not requiring the following: ◦ Consumable electrodes ◦ Shield gases ◦ Flux

Resistance Spot Welding RSW uses the tips of two opposing solid cylindrical electrodes Pressure

Resistance Spot Welding RSW uses the tips of two opposing solid cylindrical electrodes Pressure is applied to the lap joint until the current is turned off in order to obtain a strong weld Fig: (a) Sequence in the resistance spot welding

Resistance Spot Welding Surfaces should be clean Accurate control of and timing of electric

Resistance Spot Welding Surfaces should be clean Accurate control of and timing of electric current and of pressure are essential in resistance welding Fig: b)Cross-section of a spot weld, showing the weld nugget and the indentation of the electrode on the sheet surfaces. This is one of the most commonly used process in sheet -metal fabrication and in automotive-body assembly

Resistance Seam Welding RSEM is modification of spot welding wherein the electrodes are replaced

Resistance Seam Welding RSEM is modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers The electrically conducting rollers produce a spot weld RSEM can produce a continuous seam & joint that is liquid and gas tight Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b) Overlapping spots in a seam weld. (c) Roll spot weld (d) Resistancewelded gasoline tank

Resistance Projection Welding RPW is developed by introducing high electrical resistance at a joint

Resistance Projection Welding RPW is developed by introducing high electrical resistance at a joint by embossing one or more projections on the surface to be welded Weld nuggets are similar to spot welding Fig: a) Resistance projection Welding b)A welded bracket c) & d) Projection welding of nuts r threaded hosses and stack

Resistance Projection Welding The electrodes exert pressure to compress the projections Nuts and bolts

Resistance Projection Welding The electrodes exert pressure to compress the projections Nuts and bolts can be welded to sheet and plate by this process Metal baskets, oven grills, and shopping carts can be made by RPW

Resistance Projection Welding

Resistance Projection Welding

FLASH(BUTT) WELDING In flash welding the two pieces of metal to be joined are

FLASH(BUTT) WELDING In flash welding the two pieces of metal to be joined are clamped in dies which conduct the electric current to the work the ends of the two metal pieces moved together until an arc established

Flash Welding Heat is generated from the arc as the ends as the two

Flash Welding Heat is generated from the arc as the ends as the two members contacts An axial force is applied at a controlled rate Weld is formed in plastic deformation Fig : (a)Flash-welding process for end-to –end welding of solid rods or tubular parts (b) & (c) Typical parts made by flash welding (d)Design Guidelines for flash welding

PERCUSSION WELDING (PEW) Percussion welding is a process in which heat is produced from

PERCUSSION WELDING (PEW) Percussion welding is a process in which heat is produced from an arc that is generated by the rapid discharge of electrical energy between the workpieces and followed immediately by an impacting force which weld the pieces together.

Stud Welding Small part or a threaded rod or hanger serves as a electrode

Stud Welding Small part or a threaded rod or hanger serves as a electrode Also called as Stud arc welding Prevent oxidation to concentrate the heat generation Portable stud-welding is also available Fig: The sequence of operation in stud welding, which is used for welding bars threaded rods and various fasteners onto metal plates

Classification of welding processes: (i). Arc welding § Carbon arc § Metal inert gas

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). Brazing (v). Soldering (vi). Adhesive Bonding (vii). Edge preparation (viii). Types of Welded Joint (ix). Welding Defects

Brazing and Soldering

Brazing and Soldering

Introduction § Soldering and brazing provide permanent joint to bond metal pieces. § Soldering

Introduction § Soldering and brazing provide permanent joint to bond metal pieces. § Soldering and brazing process lie some where in between fusion welding and solid state welding.

§ In case of brazing joining of metal pieces is done with the help

§ In case of brazing joining of metal pieces is done with the help of filler metal. § Filler metal is melted and distributed by capillary action between the faying surfaces of the metallic parts being joined.

Brazing § In this case only filler metal melts, there is no melting of

Brazing § In this case only filler metal melts, there is no melting of workpiece metal. § The melting point of filler metal should be more than 450 o. C.

Brazing Process § The filler metal is drawn through the joint to create this

Brazing Process § The filler metal is drawn through the joint to create this bond is capillary action. In a brazing operation, you apply heat broadly to the base metals. The filler metal is then brought into contact with the heated parts. It is melted instantly by the heat in the base metals and drawn by capillary action completely through the joint.

Brazing Methods § Torch brazing - flux is applied to the part surfaces and

Brazing Methods § Torch brazing - flux is applied to the part surfaces and a torch is used to focus flame against the work at the joint. A reducing flame is used to prevent the oxidation. § Furnace brazing - used to heat the workpieces to be joined by brazing operation. The component parts and brazing metal are loaded into a furnace, heated to brazing temperature, and then cooled and removed.

Brazing Methods § Dip brazing - assembled parts are typically dipped in a heated

Brazing Methods § Dip brazing - assembled parts are typically dipped in a heated chemical bath which serve as both fluxing agent and heat source to melt pre-applied filler material. § Induction brazing – a process that uses electrical resistance of workpiece and high frequency current induced into the same as a source of heat generation. The parts are preloaded with filler metal and placed in a high frequency AC field.

Soldering § Soldering is very much similar to brazing. § The major difference lies

Soldering § Soldering is very much similar to brazing. § The major difference lies with the filler metal, the filler metal used in case of soldering should have the melting temperature lower than 450 o. C.

Soldering § Soldering is normally done by melting the solder with a soldering iron

Soldering § Soldering is normally done by melting the solder with a soldering iron and applying it to the two metals that are going to be joined together. § The filler metal used in the process is called solder, which distributes between the closely fitted surfaces.

Soldering Methods § Iron soldering - The oldest and simplest soldering method and is

Soldering Methods § Iron soldering - The oldest and simplest soldering method and is still widely used today. Soldering irons have copper tips which easily stores and transfers heat to the joint. § Wave soldering -A specific method used in the fabrication of electronic components and printed circuit boards (PCB). In this method, continually circulating fountains or waves of solder are lifted into contact with the joints.

Filler Metals § Brazing : Aluminum-silicon , Copper- phosphorus, Magnesium, Silver, Nickel alloys. §

Filler Metals § Brazing : Aluminum-silicon , Copper- phosphorus, Magnesium, Silver, Nickel alloys. § Soldering : combinations of tin-lead, tinsilver-lead, tin-zinc, silver-copper-zinc and zinc-aluminum alloys.

Advantages of Brazing & Soldering § Joining dissimilar metals and -metals. § Low temperature

Advantages of Brazing & Soldering § Joining dissimilar metals and -metals. § Low temperature compared to welding. § less thermal distortion. § Less chance of damage § Speed of joining. § Less manual skills. non

Disadvantages of Brazing & Soldering § Low strength § damaged under high temperature condition

Disadvantages of Brazing & Soldering § Low strength § damaged under high temperature condition

Summary Brazing and soldering are process that have many great advantages that are often

Summary Brazing and soldering are process that have many great advantages that are often overlooked. They are an excellent process for portable applications and the versatility makes them great choices for many jobs. Their ability to join may different materials with a limited variety of fluxes and filler metals reduces the need for a large inventory of materials.

Diffternt types of Welding Joints

Diffternt types of Welding Joints

Basic Types of Joints & Terms

Basic Types of Joints & Terms

Types of joints

Types of joints

Position of the weld symbols on the drawings

Position of the weld symbols on the drawings

Five Basic Welded Joints 1. Butt Joint 2. Corner Joint 3. T – Joint

Five Basic Welded Joints 1. Butt Joint 2. Corner Joint 3. T – Joint 4. Lap Joint 5. Edge Joint

Butt Joint Butt joint- a joint between two members aligned approximately in the same

Butt Joint Butt joint- a joint between two members aligned approximately in the same plane

Different Edge Shapes and Symbols for some Butt. Joints

Different Edge Shapes and Symbols for some Butt. Joints

Corner Joint Corner joint - a joint between two members located at right angles

Corner Joint Corner joint - a joint between two members located at right angles to each other

Some Different Edge Shapes and Symbols for Corner Joints

Some Different Edge Shapes and Symbols for Corner Joints

T-Joint T- joint - a joint between two members located approximately at right angles

T-Joint T- joint - a joint between two members located approximately at right angles to each other in the form of a T

Some Different Edge Shapes and Symbols for T-Joint

Some Different Edge Shapes and Symbols for T-Joint

Lap Joint- a joint between two overlapping members

Lap Joint- a joint between two overlapping members

Some Different Edge Shapes and Symbols for Lap Joints

Some Different Edge Shapes and Symbols for Lap Joints

Edge Joint Edge joint- a joint between the edges of two or more parallel

Edge Joint Edge joint- a joint between the edges of two or more parallel or nearly parallel members

Some Different Edge Shapes and Symbols for Edge Joints

Some Different Edge Shapes and Symbols for Edge Joints

Weld Quality Concerned with obtaining an acceptable weld joint that is strong and absent

Weld Quality Concerned with obtaining an acceptable weld joint that is strong and absent of defects, and the methods of inspecting and testing the joint to assure its quality Topics: • Residual stresses and distortion • Welding defects • Inspection and testing methods

Weld Quality Rapid heating and cooling in localized regions during FW result in thermal

Weld Quality Rapid heating and cooling in localized regions during FW result in thermal expansion and contraction that cause residual stresses These stresses, in turn, cause distortion and warpage Situation in welding is complicated because: • Heating is very localized • Melting of base metals in these regions • Location of heating and melting is in motion (at least in AW)

Weld Quality Rapid heating and cooling in localized regions during FW result in thermal

Weld Quality Rapid heating and cooling in localized regions during FW result in thermal expansion and contraction that cause residual stresses These stresses, in turn, cause distortion and warpage Situation in welding is complicated because: • Heating is very localized • Melting of base metals in these regions • Location of heating and melting is in motion (at least in AW)

Welding Defects

Welding Defects

Adhesive Bonding • Joining process in which a filler material is used to hold

Adhesive Bonding • Joining process in which a filler material is used to hold two (or more) closely-spaced parts together by surface attachment • Used in a wide range of bonding and sealing applications for joining similar and dissimilar materials such as metals, plastics, ceramics, wood, paper, and cardboard • Considered a growth area because of opportunities for increased applications

Adhesive Bonding -Terminology • Adhesive= filler usually a polymer material, nonmetallic, • Adherends= parts

Adhesive Bonding -Terminology • Adhesive= filler usually a polymer material, nonmetallic, • Adherends= parts being joined • Structural adhesives–of greatest interest in engineering, capable of forming strong, permanent joints between strong, rigid adherends

Adhesive Bonding -Joint Strength Depends on strength of: Adhesive Attachment between adhesive and adherends

Adhesive Bonding -Joint Strength Depends on strength of: Adhesive Attachment between adhesive and adherends Attachment mechanisms: Chemical bonding –adhesive and adherend form primary bond on curing Physical interactions -secondary bonding forces between surface atoms Mechanical interlocking -roughness of adherend causes adhesive to become entangled in surface asperities