21-07-2012, 03:19 PM
Shielded Metal Arc Welding Principles
Arc Welding Principles.ppt (Size: 4.45 MB / Downloads: 40)
Objectives
List the percentage of usage of SMAW in the industry.
Name the components that make up the schematic representation of the shielded metal arc.
Know the maximum arc temperature of an SMAW electrode.
List the four constant current welding machines.
List the common type and uses of constant current welding machines.
Name the power supply ratings.
Name the characteristics of the four basic types of welding machines.
Choose the correct cable size based on the application.
List the welder’s safety equipment.
Shielded Metal Arc Welding(SMAW)
Manual arc welding
Heat for welding generated by electric arc established between flux-covered consumable metal rod (electrode) and work
Called stick electrode welding
Combustion and decomposition of electrode creases gaseous shield
Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contamination
Additional shielding provided by covering of molten slag (flux)
SMAW Advantages
Equipment less complex, more portable and less costly
Can be done indoors or outdoors, in any location and any position
Electrodes available to match properties and strength of most base metals
Not used for welding softer metals
Not as efficient in deposition
SMAW Operating Principles
Sets up electric circuit
Includes welding machine, work, electric cables, electrode holder and electrodes, and a work clamp
Heat of electric arc brings work to be welded and consumable electrode to molten state
Heat intense: as high at 9,000ºF at center
Welding Process
Electric arc started by striking work with electrode
Heat of arc melts electrode and surface of base metal
Tiny globules of molten metal form on tip of electrode and transferred by arc into molten pool on work surface
After weld started, arc moved along work.
Welding Power Sources
Each type of power source has fundamental electrical differences that best suit particular processes
Welding machine
Must meet changing arc load and environmental conditions instantly
Must deliver exact amount of electric current precisely at right time to welding arc
Available in wide variety of types and sizes
Also known as power supplies and welding machines
Two classifications
Output slope
Whether constant current or constant voltage
Power source type
Transformer
Transformer-rectifier
Inverter
Generator