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Friction heat caused by the motion of one surface against another enables plastic deformation and atomic diffusion at the interface.

Used by the automotive industry for decades in the manufacture of a range of components.

The weld is formed across the entire cross-sectional area of the interface in a single shot process.

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• Dissimilar metals can be joined• No fusion zone• Can be used under water • Very high reproducibility - an essential requirement for a mass

production industry• Excellent weld quality, with none of the porosity that can arise in

fusion welding • environmentally friendly, because no fumes or spatter are generated,

and there is no arc glare or reflected laser beams with which to contend

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•Welding produced by explosively forcing one plate (or component) against the one to which it is to be joined at an approximate angle of incidence, known as the impact angle.•Methods:1.Inclined gap method2. Parallel gap methodIn parallel gap method, detonation velocity should be equal to or less than the speed of sound in the metal being welded.

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Explosive Detonation velocity, m/s

RDX (Cyclotrimethylene trinitramine, C3H6N6O6 8100

PETN (Pentaerythritol tetranitrate, C5H8N12O4) 8190

TNT (Trinitrotoluene, C7H5N3O6) 6600

Tetryl (Trinitrophenylmethylinitramine, C7H5O8N5) 7800

Lead azide (N6Pb) 5010

Detasheet 7020

Ammonium nitrate (NH4NO3) 2655

Explosives

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• Cladding plates• Joining of pipes and tubes• Major areas of the use of this method are heat exchanger

tube sheets and pressure vessels• Tube Plugging• Remote joining in hazardous environments• Joining of dissimilar metals - Aluminium to steel,

Titanium alloys to Cr – Ni steel, Cu to stainless steel, Tungsten to Steel, etc.

• Attaching cooling fins• Other applications are in chemical process vessels, ship

building industry, cryogenic industry, etc.7

1. Can bond many dissimilar, normally unweldable metals.2. Minimum fixturing/jigs.3. Simplicity of the process.4. Extremely large surfaces can be bonded.5. Wide range of thicknesses can be explosively clad

together.6. No effect on parent properties.7. Small quantity of explosive used.

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1. The metals must have high enough impact resistance, and ductility.

2. Noise and blast can require operator protection, vacuum chambers, buried in sand/water.

3. The use of explosives in industrial areas will be restricted by the noise and ground vibrations caused by the explosion.

4. The geometries welded must be simple – flat, cylindrical, conical.

5. Area should be cleaned and sound grounded for explosion.

6. Licences are necessary to hold and use explosives.

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Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic vibrations are locally applied to workpieces under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.•Empirical relation for a ultrasonic welding:

E=k(HT)3/2

Where, E = Electrical energyk = Constant for given welding systemH = Vickers hardnessT = Thickness of the work piece

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Ultrasonic welding control

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Advantages:

•Energy efficiency

•High productivity with low costs and ease of automated assembly line production

Disadvantages:

The maximum component length that can be welded by a single horn is approximately 250 mm. This is due to limitations in the power output capability of a single transducer, the inability of the horns to transmit very high power, and amplitude control difficulties.

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Electron beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed under vacuum conditions to prevent dissipation of the electron beam.

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• Advantage: Very deep penetration can be achieved. For example, joining of 200 mm aluminium plates requires 600 passes when conventional gas metal arc process requires over 100 passes even using specially developed narrow-grove process. By using the EB process, the same plate can be welded in only 2 passes.

• Disadvantage: Dealing with the vacuum needed for the process

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Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding.

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• The laser beam can be transmitted through air rather than requiring a vacuum

• The process is easily automated with robotic machinery

• x-rays are not generated

• LBW results in higher quality welds

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• The LaserStar® Workstation is an Nd:YAG laser. The host material is a cylindrical crystal of yttrium- aluminum -garnet (Y3Al5O12), YAG doped by weight with neodymium (Nd3+) ions. Laser emission takes place at 1.064 μm (infrared).

LASER POWER• Joules: The “hot light” energy output is measured

in joules. This industry term by definition is “ the capacity for doing work”. Hot light energy output is determined by the amount of voltage and pulse-length selected by the operator

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• Electrofusion is a method of joining MDPE, HDPE and other plastic pipes using special fittings that have built-in electric heating elements which are used to weld the joint together.

• The pipes to be joined are cleaned, inserted into the elusion ectroffitting (with a temporary clamp if required) and a voltage (typically 40V) is applied for a fixed time depending on the fitting in use. The built in heater coils then melt the inside of the fitting and the outside of the pipe wall, which weld together producing a very strong homogeneous joint. The assembly is then left to cool for a specified time. 19

Plasma arc welding is an arc welding process wherein coalescence is produced by the heat obtained from a constricted arc setup between a tungsten/alloy tungsten electrode and the water-cooled (constricting) nozzle (non-transferred arc) or between a tungsten/alloy tungsten electrode and the job (transferred arc). The process employs two inert gases, one forms the arc plasma and the second shields the arc plasma. Filler metal may or may not be added.

At least two separate (and possibly three) flows of gas are used in PAW:Plasma gas – flows through the orifice and becomes ionized.Shielding gas – flows through the outer nozzle and shields the molten weld from the atmosphereBack-purge and trailing gas – required for certain materials and applications.

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Plasma arc welding is an advancement over the GTAW process. PAW can be used to join all metals that are weldable with GTAW. Difficult-to-weld in metals by PAW include bronze, cast iron, lead and magnesium. Several basic PAW process variations are possible by varying the current, plasma gas flow rate, and the orifice diameter, including:Micro-plasma (< 15 Amperes)Melt-in mode (15–100 Amperes)Keyhole mode (>100 Amperes)Plasma arc welding has a greater energy concentration as compared to GTAW.PAW requires relatively expensive and complex equipment as compared to GTAW.Welding procedures tend to be more complex and less tolerant to variations in fit-up, etc.Operator skill required is slightly greater than for GTAW.Orifice replacement is necessary.

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