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Joining Processes: Welding

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Jared Cammon

on 5 May 2016

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Transcript of Joining Processes: Welding

Joining Processes: Welding
Electric Arc Welding
One of the most common methods of joining metals
Used often for steel structural fabrication and construction

Solid State Welding Processes
Solid State Welding Processes
Definition of Fusion Welding
Joining process in which two materials are heated to their fusion temperature, joined and then allowed to cool.

Filler material (of same composition as the parent metal) may be added to fill the weld during the process.
Types of Weld Joints
Electric Arc Welding Basic Process...
Converts the flow of electric current into heat that is then used to heat materials to their fusion temperatures.
There are many kinds of electric arc welding processes...
Shielded Metal Arc Welding
Current flows from the power supply through the
copper wire cables to the electrode holder
A wire electrode (welding rod) is clamped within the electrode holder
The coating on the welding rod serves several very important functions...
Serves as fluxing - cleaning/flowing agent
Serves as arc stabilization
Turns into a gas which shields the weld zone from atmospheric oxygen and nitrogen
The wire core of the welding rod acts as the filler metal in the joint between the materials being welded.
As the operator touches the rod to the work current flows across the junction and an arc is created
Heat develops at the workpiece and in the electrode which causes the filler rod to melt.
Gas Metal Arc Welding or Metal Inert Gas (MIG)
Similar to SMAW but with some improvements...
MIG machines come with a constant voltage power supply, a wire feed unit and a shield gas cylinder with pressure and flow regulators
wire is continually fed
Shield gas flows from the shield gas cylinder around the wire and through the welding gun...thereby displacing air from the weld zone
Gas Tungsten Arc Welding (GTAW) or
(TIG) Tungsten Inert Gas
Similar to MIG except that a non consumable tungsten electrode is used.
Filler material is fed externally into the welded joint during welding
TIG is useful for welding applications
where detail is required and can produce
superior quality welds.
Submerged Arc Welding
The welding process takes buried under a fluxing agent that is deposited in the joint ahead of the electrode
What does the flux do?
Acts as a shielding agent for the molten metal (like a gas)
Helps to cleanse impurities from the molten metal
Slows down the cooling rate of the weld
Prevents spatter
Results in a very good quality weld
Limited to flat or horizontal positions due to flux
Used for automatic welding of pipes and structural items like I-Beams
Plasma Arc Welding
Heat is created by ionizing a plasma gas by an electric arc
The plasma arc can deliver temperatures of more than 40,000 deg F to the weld zone
The plasma arc permits high quality welds with minimal effect on the surrounding welding area

Fusion Welding Processes
Two pieces of metal are joined together by applying enough heat to melt and fuse the metals together
Solid State Welding Processes
Joining occurs without fusion. Instead of relying
on heat to melt and fuse, pressure and movement is used to bond the materials. Heat is often generated, but not enough to melt and fuse.
Ultrasonic Welding
Two materials are pressed together
The materials are vibrated against each other
Frequencies of 10,000 to 75,000 times a sec
Friction creates rise in temperature but only up to 1/3 the melting temperature
Can be used with metallic and non-metallic materials
Often used to join plastics and in the automotive industry

Friction Welding
Heat needed for welding is created by friction at the interface of the two pieces being joined
The heat created by friction and the pressure created when the two pieces are forced together cause a strong bond to form
Spot Welding
The tips of two electrodes touch a lap joint of two sheet metals
The heat needed for welding is produced by running electrical current through the electrodes
The resistance created as the electricity passes through the metals generates heat...enough to reach welding temperatures.
Pressure is applied to complete the weld until the current is turned off
Currents from 3000 to 40,000 Amps
Widely used for fabrication of sheet metal parts
Friction Inertia Welding
A flywheel is allowed to freely spin
allowing one workpiece to spin while
the other remains stationary. As
they are forced together
Friction Stir Welding
A "probe" is forced into the joint and rubs on the surfaces
of the two metals to be joined.
The probe forces mixing of the materials.
Temperatures are 450 to 500 deg.
Linear Friction Welding
Similar to inertia except the workpieces are subjected to a linear reciprocating motion.
This makes it allowable to use parts that are not circular in cross section
(Also called stick welding)
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