1. Shielded Metal Arc Welding
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Shielded Metal Arc Welding

2. 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)
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3. SMAW
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4. SMAW Advantages Not used for welding softer metals
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
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5. 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
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6. 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
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7. SMAW Operating Principle
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8. AC Welding Machine Most common type found in homes, farms, etc.
Good for farm repairs, light jobs.
Low cost
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9. DC Welding Machine Often generator type machines
Diesel or gasoline engine driven
Portable
Expensive
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10. AC/DC Welding Machine Can weld in AC or DC polarity
Less expensive than DC machine
Quieter than DC machine
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11. 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
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12. Welding Power Sources Output slope
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
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13. Type of Output Slope Constant current Referred to as variable voltage
Two basic types
Constant current
Referred to as variable voltage
Constant voltage
Referred to as constant potential
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14. Output Slope Also called volt-ampere characteristic or curve
Relationship between output voltage and output current (amperage) of machine as current increased or decreased
Also called volt-ampere characteristic or curve
Largely determines how much welding current will change for given change in load voltage
Permits welding machine to control welding heat and maintain stable arc
Indicates type and amount of electric current designed to produce
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15. Typical Output Slopes
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16. Four Types of Power Source
Engine-driven generators
Powered by gas or diesel combustion engine
Can be found with a.c. or d.c. electric motor
No longer being manufactured and rarely found
Transformer-rectifiers
Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage
Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current
May be either d.c. or a.c.-d.c. machines
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17. Four Types of Power Source
A.C. transformers
Used to step down a.c. line power voltage to a.c. welding voltage
Inverters
Increases frequency of incoming primary power
Constant current, constant voltage, or both
Produce a.c. or d.c. welding current
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18. Constant Current Welding Machines
Used for shielded metal arc welding
Current remains fairly constant regardless of changes in arc length
Called drooping voltage, variable voltage, or droopers
Load voltage decreases as welding current increases
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19. Constant Current Output Slope
Constant current welding machines
Steep output slope
Available in both d.c. and a.c. welding current
Steeper the slope, the smaller current change
Enables welder to control welding current in specific range by changing length of arc
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20. Constant Current Output Slope
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21. Open Circuit and Arc Voltage
Open circuit voltage runs between volts
Drops to arc voltage when arc struck
Arc voltages
Range: 36 volts (long arc) to 18 volts (short arc)
Determined by arc length held by welder and type of electrode used
Arc lengthened, arc voltage increases and current decreases
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22. Open Circuit and Arc Voltage
Open circuit voltage on constant current machines higher than on most constant voltage machines
Arc voltage depends on physical arc length at point of welding and controlled by welder
Shielded metal arc welding
Arc voltage much lower than open circuit voltage
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23. Polarity Switch
Electrode negative and electrode positive used in d.c. welding
DCEN (d.c. electrode negative)
Electrode connected to negative terminal of power source and work connected to positive terminal
DCEP (d.c. electrode positive)
Electrode connected to positive terminal of power source and work connected to negative terminal
Switch changes to either electrode positive or electrode negative
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24. Volt-Ampere Meters Can indicate polarity as well as current
Sometimes serve dual purpose
Can indicate polarity as well as current
Others, individual meters for volts and amperes
Some, single meter that indicates both volts and amperes
Button engaged to get individual readings
Would need second person for monitoring
Increased demand for additional devices so meters have been discontinued by some manufacturers
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25. Current Controls Quantity of current
Amperage
Quantity of current
Determines amount of heat produced at weld
Voltage
Measure of force of current
Determines ability to strike an arc and maintain its consistency
Two types of dual control generators
Tapped-step current control
Continuously variable current control
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26. Dual Continuous Control
Coarse adjustment dial continuously adjusts current
Fine dial adjusts both current (amperage) and open circuit voltage
Operator adjusts output slope for given current setting by manipulating both coarse and fine adjustment dials together
Wheel or knob on both amperage and voltage setting devices gives welder continuous control of both
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27. Power Supply Ratings The National Electrical manufacturers Association
Standards set
The National Electrical manufacturers Association
Occupational Safety and Health Administration
Provide guidelines for manufacture and performance of power sources
Rated by
Current output
Open circuit voltage
Duty cycle
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28. Current Output 200 amperes or less for light or medium work
Rated on basis of current output in amperes
Amperage range
200 amperes or less for light or medium work
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29. Open Circuit Voltage 80 volts for a.c. or a.c.-d.c. machines
Maximum allowable used for manual welding
80 volts for a.c. or a.c.-d.c. machines
100 volts for d.c. machines
Very smooth output (less than 2% ripple)
Automatic machine welding
Some constant current machines rated up to 125
Constant voltage types normally rated from 15 to 50
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30. Duty Cycle
Percentage of any given 10-minute period that machine can operate at rated current without overheating or breaking down
Rating of 100% means machine can be used at rated amperage on continuous basis
Required by continuous, automatic machine welding
Rating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damage
Satisfactory for heavy SMAW
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31. Efficiency Indicated in percent Motor generator welding machines: 50%
Relationship of secondary power output to primary power input
Indicated in percent
Determined by losses through machine when actually welding at rated current and voltage
Average efficiencies
Motor generator welding machines: 50%
Transformer-rectifier: 70%
Inverter: 85%
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32. Power Factor Primary power used divided by amount total drawn
Measure of how effectively welding machine makes use of a.c. primary line power
Primary power used divided by amount total drawn
Expressed in percent
Three-phase d.c. transformer-rectifiers: 75%
Single-phase a.c. power units: 55%
Welding machines can be purchased with power factor correction
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33. Power Cable
Conductors of ample capacity and adequately insulated for voltage transmit power
Necessary to ground frame of welding machine
Portable cable with extra conductor fastened to machine frame on one end and solid ground on other
Important cable adequately insulated with tough abrasion-resisting insulation
Stand up under rough usage in welding shops
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34. Electrode and Work Cable
Required to complete electric circuit between welding machine and work
Electrode cable (welding cable) attached to electrode holder
Work cable attached to work
Rubber-covered multistrand copper cable generally used
Must have high flexibility
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35. Cable Core Construction
Woven of thousands of very fine copper wire
Greater the number of strands the more flexible
Components
Wires stranded for extra flexibility
Paper wrapping around wires allows conductor to slip within robber covering when bent
Extra strength from open-braided reinforcement of extra cotton cords
Special composition and curing of heavy rubber covering
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36. Work Cable Usually same cable used Amperage of welding machine
Not necessary to have flexibility of electrode cable
Usually same cable used
Important considerations
Amperage of welding machine
Distance from work
Larger cable
Greater the amperage and greater the distance
Resistance increases as diameter of cable decreases
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37. Cable Lugs Soldered or fastened mechanically
Required on both electrode cable and work cable
Soldered or fastened mechanically
Connections MUST be tight and secure
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38. Work Clamps Copper hook, heavy metal weight, C-clamp
Variety of structures to be welded; many types of clamps may be used
Copper hook, heavy metal weight, C-clamp
Specialized work clamps
Lenco dba NLC. Inc.
Lenco dba NLC. Inc.
Spring loaded
C-clamp
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39. Metal Electrode Holders
Device used for holding electrode mechanically
Conveys electric current from welding cable to electrode
Insulated handle protects hand from heat
Jaws of holder grip electrode at any angle
Made of metal with high electrical conductivity and ability to withstand high temperatures
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40. Metal Electrode Holders
Jaws can be replaced with new ones
Should be light in weight, well-balanced and have comfortable grip
Size of holder must be in line with size of welding machine
Fully insulated so stays cool even with high duty cycles
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41. Spring Type Electrode Holder
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42. Short-stub Electrode Holder
Cable connections
Special extruded copper-alloy body
High welding current conductance
One-ton pressure contact
Lifeguard insulation
Entirely insulated
Bernard Welding Equipment Co.
Holds electrodes burned to very short stub.
Twist-type locking device permits electrode- gripping power in excess of 2,000 pounds.
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43. Knowledge is the key to success
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