Joining Processes and Equipment

Joining Processes

and Equipment

ME305 Manufacturing Techniques Course Material, Adnan Menderes University

(Source: Serope Kalpakjian, Steven Schmid-Manufacturing, Engineering and Technology, 6e)

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Joining Processes

Joining processes fall into three major categories;

• Welding,• Fusion Welding,

• Solid-state Welding,

• Brazing and Soldering.

• Adhesive Bonding,

• Mechanical Fastening

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Joining Processes

• Fusion Welding is defined as the melting together and coalescing of materials by means of heat, usually supplied by chemical or electrical means; filler metals may or may not be used.

• Fusion welding is composed of

• Consumable- and non-consumable electrode arc welding and

• High-energy-beam welding processes.

• The Welded joint undergoes important metallurgical and physical changes, which, in turn, have a major effect on the properties and performance of the welded component or structure.

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Joining Processes

• In solid-state welding, joining takes place without fusion; consequently, there is no liquid (molten) phase in the joint.

• The basic processes in this category are

Diffusion bonding,

Cold welding,

Ultrasonic welding,

Friction welding,

Resistance welding, and

Explosion welding.

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Joining Processes

• Brazing uses filler metals and involves lower temperatures than welding.

• Soldering uses similar filler metals (solders) and involves even lower temperatures.

• Adhesive bonding has unique applications that require strength, sealing, thermal and electrical insulating, vibration damping, and resistance to corrosion between dissimilar metals.

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Joining Processes

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Joining Processes

Examples of joints that can be made through the various joining processes.

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Fusion-Welding Processes

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Fusion Welding

•Fusion welding is a generic term for welding processes that rely upon melting to join materials of similar compositions and melting points. – Wikipedia

• These processes include the oxyfuel-gas, arc, and high-energy-beam (laser-beam and electron-beam) welding processes, which haveimportant and unique applications in modern manufacturing.

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Fusion Welding

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Fusion Welding: Oxyfuel Gas Welding

• Oxyfuel-gas welding (OFW) is a general term used to describe any welding process that uses a fuel gas combined with oxygen to produce a flame.

• The most common gas-welding process uses acetylene; the process is known as oxyacetylene-gas welding (OAW) and is typically used for structural metal fabrication and repair work.

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Three basic types of oxyacetylene flames used in oxyfuel–gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; and (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 process. 13


•Versatility: OFW can be used with most ferrous and nonferrous metals for almost any workpiece thickness.•Deep groove joints are made in multiple

passes. Cleaning the surface of each weld bead prior to depositing a second layer is important.•The equipment for oxyfuel-gas welding

consists basically of a welding torchconnected by hoses to high-pressure gas cylinders and equipped with pressure gages and regulators. 14


2𝐶𝑂 + 𝐻2 + 1,5𝑂2 → 2𝐶𝑂2 + 𝐻2𝑂 + 𝑯𝑬𝑨𝑻

𝐶2𝐻2 +𝑂2 → 2𝐶𝑂 + 𝐻2 +𝑯𝑬𝑨𝑻

The primary combustion process, which occurs in the inner core of the flame;

The secondary combustion process is;

*** The temperatures developed in the flame can reach 3300°C.15


• The low equipment cost is an attractive feature of oxyfuel-gas welding.

• Although it can be mechanized, this operation is essentially manual and, hence,slow.

• However, it has the advantages of being portable, versatile, and economical for simple and low-quantity work.

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(a) General view,

(b) cross-section of a torch used in oxyacetylene welding. • The 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.

(c) Oxygen regulators usually are painted green and acetylene regulators red.

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Fusion Welding: Pressure-Gas Welding

The welding of two components starts with the heating of the interface by means of a torch using (typically) an oxyacetylene-gas mixture. After the interface begins to melt, the torch is withdrawn.

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Fusion Welding: Pressure-Gas Welding

A force is applied to press the two components togetherand is maintained until the interface solidifies. Note the

formation of a flash due to the upsetting of the joined ends of the two components. 19

Fusion Welding: Arc-Welding Processes

Nonconsumable Electrode

•The heat required is obtained fromelectrical energy.

•An AC or a DC power supply produces an arc between the tip of the electrode and the workpiece to be welded.

•The arc generates temperatures of about

30,000°C (in both consumable and nonconsumable processes).

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Nonconsumable Electrode•The electrode is typically a tungsten

electrode.•Because of the high temperatures involved,

an externally supplied shielding gas is necessary to prevent oxidation of the weld zone.•The selection of current levels depends on

such factors as the type of electrode, metals to be welded, and depth and width of the weld zone.

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•Typically, direct current is used, and its polarity (the direction of current flow) is important.

• In straight polarity, (or direct-current electrode negative, DCEN), the workpiece is positive (anode), and the electrode is negative (cathode). DCEN generallyproduces welds that are narrow and deep.

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• In reverse polarity (or direct-current electrode positive DCEP), the workpiece is negative and the electrode is positive. Weld penetration is less, and the weld zone is shallower and wider. Hence, DCEP is preferred for sheet metals and for joints with very wide gaps.

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(a) DCEN current with straight polarity; (b) DCEPcurrent with reverse polarity; and (c) AC current.

In the AC current method, the arc pulsates rapidly. This method is suitable for welding thick sections and for using large-diameter electrodes at maximumcurrents.

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Gas Tungsten-arc Welding (GTAW)

-Gaz Örtülü Ark Kaynağı-

•Formerly known as TIG (for “tungsten inert gas”) welding, the filler metal is supplied from a filler wire.

•Because the tungsten electrode is not consumed in this operation, a constant and stable arc gap is maintained at a constant current level.

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Fusion Welding: Arc-Welding ProcessesNonconsumable Electrode

Gas Tungsten-arc Welding (GTAW)•Welding with GTAW may be done without

filler metals-for example, in the welding of close-fit joints.• Since not being consumed during the

process, tungsten electrode contamination by the molten metal can be a significant problem, particularly in critical applications, because it can cause discontinuities in the weld.

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Gas Tungsten-arc Welding (GTAW)•The GTAW process is used for a wide

variety of applications and metals, particularly aluminum, magnesium, titanium, and the refractory metals. • It is especially suitable for thin metals. •The cost of the inert gas makes this process

more expensive than SMAW (ShieldedMetal-Arc Welding) but provides welds of very high quality and surface finish.

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Plasma Arc Welding (PAW)•A plasma is an ionized hot gas composed of

nearly equal numbers of electrons and ions.•A concentrated plasma arc is produced and

directed towards the weld area. The arc isstable and reaches temperatures as high as 33,000°C.•The plasma arc is concentrated by forcing it

through a relatively small orifice.30


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Plasma Arc Welding (PAW)

• In the transferred-arc method, the workpiece being welded is part of the electrical circuit. The arc transfers from the electrode to the workpiece hence the term transferred.

• In the nontransferred method, the arc occurs between the electrode and the nozzle, and the heat is carried to the workpiece by the plasmagas. This thermal-transfer mechanism is similar to that for an oxyfuel flame.

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Two types of plasma-arc welding processes: (a) transferred and (b) nontransferred; deep and narrow welds can be made

by these processes at high welding speeds.33


Plasma Arc Welding (PAW)

Compared with other arc-welding processes,

• Plasma-arc welding has better arc stability,

• Less thermal distortion, and

• Higher energy concentration, permittingdeeper and narrower welds.

• In addition, higher welding speeds, from 120 to1000 mm/min, can be achieved.

• A variety of metals can be welded with part thicknesses generally less than 6 mm.

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Consumable Electrode

Shielded Metal-arc Welding (SMAW)

•One of the oldest, simplest, and most versatile joining processes.

•About 50% of all industrial and maintenance welding currently isperformed by this process.

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Shielded Metal-arc Welding• The electric arc is generated by touching the tip of a coated

electrode against the workpiece and withdrawing it quickly to a distance sufficient to maintain the arc.

• The heat generated melts a portion of the electrode tip, its coating, and the base metal in the immediate arc area.

• The electrode coating deoxidizes the weld area and provides a shielding gas to protect it from oxygen in the environment.36


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Shielded Metal-arc Welding

•For sheet-metal welding, DC is preferred because of the steady arc it produces.

•Power requirements generally are less than 10 kW.

•The process has the advantages of being relatively simple, versatile, and requiring a smaller variety of electrodes.

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•The SMAW process commonly is used ingeneral construction, shipbuilding, pipelines, and maintenance work.

• SMAW is best suited for workpiece thicknesses of 3 to 19 mm, although this range can be extended easily by skilled operators using multiple-pass techniques.

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• The multiple-pass approach requires that the slag be removed after each weld bead.

•Both labor costs and material costs are high.

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Fusion Welding: Arc-Welding ProcessesConsumable Electrode

Submerged-arc Welding• The weld arc is shielded by a granular flux consisting of lime, silica,

manganese oxide, calcium fluoride, and other compounds.

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Consumable Electrode Submerged-arc Welding

• The thick layer of flux completely covers the molten metal. It prevents spatter and sparks and suppresses the intense ultraviolet radiation and fumes characteristic of the SMAW process. The flux also acts as a thermal insulator by promoting deep penetration of heat into the workpiece. 42


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Consumable Electrode Submerged-arc Welding

• The unfused flux can be recovered, treated, and reused.

• SAW is automated and is used to weld a variety of carbon and alloy steel and stainless-steel sheets orplates at speeds as high as 5 m/min.

• The quality of the weld is very high with goodtoughness, ductility, and uniformity of properties. The SAW process provides very high welding productivity, depositing 4 to 10 times the amount of weld metal perhour as the SMAW process.

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Consumable Electrode Submerged-arc Welding• Because the flux is gravity fed, the process is limited to welds in a flat or

horizontal position having a backup piece. Circular welds can be made on pipes and cylinders-provided that they are rotated during welding.

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Gas Metal-arc Welding

•Formerly called metal inert-gas (MIG) welding, the weld area is shielded by an effectively inert atmosphere of argon, helium, carbon dioxide, or various other gas mixtures.

•The consumable bare wire is fed automatically through a nozzle into the weld arc by a wire-feed drive motor.

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Gas Metal-arc Welding• The temperatures

generated in GMAW are relatively low;

• Thus the method is suitable only for sheets and sections of less than 6 mm; otherwise incompletefusion may occur.

• Pulsed-arc systems are used for thin ferrous and nonferrous metals.

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GMAW vs GTAW – also helpful to take a look…

51https://www.youtube.com/watch?v=Iju5tHB2UCc

https://www.youtube.com/watch?v=Iju5tHB2UCc



• The GMAW process is used extensively in the metal-fabrication industry.

• Because of the relatively simple nature of the process, the training of operators is easy. The process is versatile, rapid, and economical, and welding productivity is double that of the SMAW process.

• The GMAW process can be automated easily and lends itself readily to robotics and to flexible manufacturing systems.

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Electroslag Welding

•The arc is started between the electrode tipand the bottom of the part to be welded.

•Flux is added, which then melts by the heatof the arc.

•After the molten slag reaches the tip of the electrode, the arc is extinguished. Heat is produced continuously by the electrical resistance of the molten slag.

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Electroslag Welding

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Electroslag Welding

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Electroslag Welding•Capable of welding plates with thicknesses

ranging from 50 mm to more than 900 mm, and welding is done in one pass.•The travel speed of the weld is in the range

from 12 to 36 mm/min. •Weld quality is good. This process is used

for large structural-steel sections, such as heavy machinery, bridges, oil rigs, ships, and nuclear-reactor vessels.

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Electrodes for Arc-welding•Electrodes for consumable arc-welding

processes are classified according to thefollowing properties:

Strength of the deposited weld metal

Current (AC or DC)

Type of coating.

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Fusion Welding: Arc-Welding Processes• Electrodes are

identified by numbers and letters or by color code if the numbers and letters are too small to imprint.

• Typical coated-electrodedimensions are in the range from 150 to 460 mm in length and 1.5 to 8 mm indiameter.

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Electrode Coatings

•Electrodes are coated with claylike materials that include silicate binders and powdered materials, such as oxides, carbonates, fluorides, metal alloys, cotton cellulose, and wood flour.

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Fusion Welding: Arc-Welding ProcessesElectrode Coatings• The coating, which is brittle and takes part in

complex interactions during welding, has the following basic functions: Stabilize the arc. Generate gases to act as a shield against the

surrounding atmosphere; Control the rate at which the electrode melts. Act as a flux to protect the weld against the

formation of oxides, nitrides, and other inclusions.

Add alloying elements to the weld zone to enhance the properties of the joint.

Provide proper utilization of generated heat.60

Fusion Welding: A Quick Recap

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Fusion Welding: A Quick Recap

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Some interesting pages to visit;

http://weldinghelmethq.com/which-welding-process-to-choose-mig-vs-tig/

http://www.wikihow.com/Weld-Stainless-Steel

http://weldingweb.com/showthread.php?18331-stainless-steel-welding-with-MIG-or-TIG

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http://weldinghelmethq.com/which-welding-process-to-choose-mig-vs-tig/

http://www.wikihow.com/Weld-Stainless-Steel

http://weldingweb.com/showthread.php?18331-stainless-steel-welding-with-MIG-or-TIG

RW covers a number of processes in which the heat required for welding is produced by means of electrical resistance across the two components to be joined.

These processes have major advantages, such as not requiring consumable electrodes, shielding gases, or flux.

Resistance Welding

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Resistance Welding

The total resistance is the sum of the following properties:

a. Resistances of the electrodes;b. Electrode-workpiece contact

resistance;c. Resistances of the individual parts to be

welded;d. Contact resistance between the two

workpieces to be joined (fayingsurfaces).

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Resistance Welding

Sequence of events in resistance spot welding (a).Cross section of a spot weld, showing the weld nugget and the indentation of the electrode on the sheet surfaces (b).

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Resistance Welding

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Resistance Seam Welding

(a) Seam-welding process in which rotating rolls act as electrodes; (b) overlapping spots in a seam weld; (c) roll spot welds; and (d) mash seam welding.

• RSEW is a modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers.

• With a high enough frequency or slow enough traverse speed, these spot welds actually overlap into a continuous seam and produce a joint that is liquid tight and gastight.

• The RSEW process is used to make the longitudinal (side) seam of cans (for household products) mufflers, gasoline tanks, and other containers.

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High-Freq. Resistance Welding

• HFRW is similar to seam welding, except that high-frequency current (up to 450 kHz) is employed.

• A typical application is theproduction of butt-welded tubing or piping where the current is conducted throughtwo sliding contacts to the edges of roll-formed tubes.

• The heated edges then are pressed together by passing the tube through a pair of squeeze rolls.

• Any flash formed is then trimmed off.

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High-Freq. Resistance Welding

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The Weld Joint, Quality and Testing

Three distinct zones can be identified in a typical weld joint:

• Base metal,

• Heat-affected zone,

• Weld metal.

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Solidification of Weld Metal

•The solidification process is similar to that in casting and begins with the formation of columnar (dendritic) grains.•Because metals are much

better heat conductors than the surrounding air, the grains lie parallel to the plane of the two components being welded.

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Solidification of Weld Metal(a) A deep weld and (b) a shallow weld; (c) weld bead on a cold-rolled nickel strip produced by a laser beam. (d) Microhardness (HV) profile across a weld bead.

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Heat-Affected Zone• The heat-affected zone (HAZ) is within the base

metal itself. It has a microstructure different from that of the base metal prior to welding.

• The heat applied during welding recrystallizes the elongated grains of the cold worked base metal. On the one hand, grains that are away from the weld

metal will recrystallize into fine, equiaxed grains. On the other hand, grains close to the weld metal have

been subjected to elevated temperatures for a longer time. Consequently, the grains will grow in size (grain growth), and this region will be softer and have lower strength. Such a joint will be weakest at its HAZ.

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Weld Quality: Major DiscontinuitiesPorosity in welds may be caused by, • Gases released during melting of the weld area

and trapped during solidification,• Chemical reactions during welding,• Contaminants.

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Weld Quality: Major Discontinuities

Slag Inclusions are compounds such as oxides, fluxes, and electrode coating materials that are trapped in the weld zone. *If shielding gases are not effective during welding, contamination from the environment also may contribute to such inclusions.

Slag inclusions can be prevented by the following practices:• Cleaning the weld-bead surface before the next layer is

deposited.• Providing sufficient shielding gas.• Redesigning the joint to permit sufficient space for proper

manipulation of molten weld metal. 89



Incomplete Fusion produces poor weld beads. A better weld can be obtained by,

•Raising the temperature of the base metal or

•Cleaning the weld area before welding.

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Incomplete Penetration occurs when the depth of the welded joint is insufficient. Penetration can be improved by the following practices:Increasing the heat input,Reducing the travel speed during the

welding,Ensuring that the surfaces to be

joined fit each other properly.91



Weld Profile

• Underfilling results when the joint is not filled with the proper amount of weld.

• Undercutting results from the melting away of the base metal and the consequent generation of a groove. If it is deep or sharp, an undercut can act as a stress raiser.

• Overlap is a surface discontinuity usually caused by poor welding practice or by the selection of improper materials.

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Weld Profile is important for,

• its effects on the strength,

• the appearance of the weld and

•because it can indicate incomplete fusionor the presence of slag inclusions in multiple-layer welds.

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Weld Profile

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Cracks generally result from a combination of the following factors:• Temperature gradients that cause thermal

stresses in the weld zone.• Variations in the composition of the weld zone

that cause different rates of contraction during cooling.

• Fracturing of grain boundaries, caused by the segregation of such elements as sulfur to the grain boundaries.

• Inability of the weld metal to contract during cooling.

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Weld Quality: Different types of Cracks

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Weld Quality: Some Examples

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Weld Quality: Some Examples

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Residual Stresses: Due to localized heating and cooling during welding, the expansion and contraction of the weld area causes residual stresses in the workpiece.

Residual stresses can lead to the following defects:• Distortion, warping, and buckling of the welded

parts,• Stress-corrosion cracking,• Reduced fatigue life of the welded structure.

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Weld Quality: Major DiscontinuitiesResidual StressesBefore welding, the structure is stress free.

As weld bead solidifies, both the weld bead and the surrounding material cool to room temperature.

As these materials cool, they tend to contract, but are constrained bythe bulk of the weldment.

The result is that the weldment and residual stresses develop.

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Residual Stresses: Stress RelievingThe problems caused by residual stresses (such as distortion, buckling, and cracking) can be reduced by preheating the base metal or the parts to be welded. Preheating reduces distortion by reducing

the cooling rate and the level of thermal stresses developed (by lowering the elastic modulus).

This technique also reduces shrinkage and possible cracking of the joint.

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Joint Design and Process Selection

Design Guidelines:•Product design should minimize the

number of welds because, unless automated, welding can be costly.•Weld location should be selected so as to

avoid excessive stresses or stress concentrations in the welded structure.•Weld location should be selected so as not

to interfere with any subsequent processingof the joined components,

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•Components should fit properly prior to welding. The method used to prepareedges, such as sawing, machining, or shearing, also can affect weld quality.•The need for edge preparation should

be avoided or minimized.•Weld-bead size should be as small as

possible, while maintaining the strength of the joint, to conserve weldmetal and for better appearance.

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Welding Process Selection:The selection of a weld joint and an appropriate welding process involve the following topics;• Joint design, thickness and size of the

components, and number of joints required.•The methods used in manufacturing,•The components to be joined,•Types of materials involved, which may be

metallic or nonmetallic,•Location, accessibility, and ease of joining.106


Welding Process Selection:•App and service requirements, such as type

of loading, any stresses generated, etc.

•Costs involved in edge preparation, joining, and post-processing (machining, grinding, and finishing operations).

•Costs of equipment, materials, labor and skills required.

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Joining Process Selection: Frankly, no single joining process has a high rating in all categories:• Arc welding, bolts, and riveting have high strength and

reliability, but generally are not suitable for joining small parts.

• Resistance welding has strength and applications for both small and large parts. However, it is not easy to inspect visually for reliability, and resistance welding has lower tolerances and reliability than other processes.

• Fasteners are useful for large parts and can be easy to inspect visually, but they are costly and do not have much design variability.

• Adhesive bonding has high design variability. However, it has relatively low strength and is difficult to visually inspect for joint integrity.

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Thanks andbest of luck!

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Joining Processes and Equipment