2. 11 - 2
Objectives
1. List the percentage of usage of SMAW in
the industry.
2. Name the components that make up the
schematic representation of the shielded
metal arc.
3. Know the maximum arc temperature of
an SMAW electrode.
4. List the four constant current welding
machines.
3. 11 - 3
Objectives
5. List the common type and uses of
constant current welding machines.
6. Name the power supply ratings.
7. Name the characteristics of the four basic
types of welding machines.
8. Choose the correct cable size based on
the application.
9. List the welder’s safety equipment.
6. 11 - 6
Process Capability
• Shielded metal arc welding one of most used
of various electric arc welding processes
42%
34%
13%
9% 2%
SMAW
GMAW/FCAW
GTAW
SAW
Others
7. 11 - 7
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
9. 11 - 9
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
11. 11 - 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
12. 11 - 12
Welding Power Sources
• 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
13. 11 - 13
Type of Output Slope
• Two basic types
– Constant current
• Referred to as variable voltage
– Constant voltage
• Referred to as constant potential
15. 11 - 15
Output Slope
• Indicates type and amount of electric current
designed to produce
• Each arc welding process has characteristic
output slope
– SMAW and GTAW require steep output slope from
constant current welding machine
– GMAW and FCAW require relatively flat output
slope from constant voltage power source
– Submerged arc welding adaptable to either slop
17. 11 - 17
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
18. 11 - 18
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
19. 11 - 19
Power Sources
• Important to select right power source for each
job
• Table 11-1 "Common types and uses of arc
welding machines" should be studied
• Study of job indicates whether a.c. or d.c.
– Shielded metal arc welding and gas tungsten arc
welding must use constant current machine
– Gas metal arc prefers constant voltage machine
20. 11 - 20
Constant Current
Welding Machines
• Used for shielded metal arc welding and gas
tungsten 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
21. 11 - 21
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
23. 11 - 23
Open Circuit Voltage
• Voltage generated by welding machine when
no welding being done
– Machine running idle
• Arc voltage
– Voltage generated between electrode and work
during welding
• Load voltage
– Voltage at output terminals of welding machine
when arc is going
– Combination of arc voltage plus voltage drop in
welding circuit
24. 11 - 24
Open Circuit and Arc Voltage
• Open circuit voltage runs between 50-100 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
25. 11 - 25
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
– Gas Tungsten arc welding
• Arc voltage much lower than open circuit
voltage
26. 11 - 26
Motor Generator Welding
Machines
• Usually supply only direct current
– Can be made to supply a.c.
• Most constant current type
• Used chiefly for shielded metal arc welding
and gas tungsten arc welding
34. 11 - 34
Motor Generator Desirable
Characteristics
• Have forceful penetrating arc
• Versatile
– Can be used to weld all metals that are weldable by
arc process
• Flexible
– With proper electrode, can be used in all positions
• Durable and have long machine life
36. 11 - 36
Sizes
• Determined on basis of amperage
• Range
– 100-ampere rated for home
– 1,500 ampere rated for use with automatic
submerged arc welding equipment
• Manual welding machine idle sometimes
• Automatic power supply units 100% duty cycle
– Should not be used at or beyond max over extended
period
37. 11 - 37
Maintenance
• Contacts of starter switch and control rheostat
should be inspected, cleaned frequently and
replaced when necessary
• Brushes need frequent inspection for wear
– Check commutator for wear or burning
• Rewound and turned on lathe
• Main bearings on shaft inspected and greased
at each 6-month period
– Clean old grease out of bearing housings
38. 11 - 38
Start and Stop Buttons
• Purpose of starting and stopping the motor
• Start button black
• Stop button red
• Important buttons be engaged firmly
39. 11 - 39
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
40. 11 - 40
Volt-Ampere Meters
• 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
41. 11 - 41
Current Controls
• 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
42. 11 - 42
Dual Tapped-Current Control
• Coarse adjustment dial selects current range
– Called steps or taps
– Impossible to secure current value between two
steps by setting dial between them
• Fine adjustment dial trims current between steps
– Whether set high or low depends on type and
size of electrode, thickness of metal, soft or digging
arc required, arc starting, restricting characteristics,
and Position of welding
43. 11 - 43
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
45. 11 - 45
Remote Control
• Welding machines may be installed in remote
part of plant
• Welder may adjust current without leaving job
• Timesaving on work
– Welder does not have to leave fabrication to
readjust current
46. 11 - 46
Air Filters
• Wear in arc welding machines costly
– Cost of replacement parts and labor
– Loss of production due to nonuse of machine
• Bearing wear critical
– May be reduced through use of air filter fitted on
suction end of motor generator machine
• Filter cleaned regularly
– High pressure air, commercial solvent or steam
48. 11 - 48
Transformer-Rectifier Machines
• Have two basic parts
– Transformer for producing and regulating
alternating current that enters machine
– rectifier that converts a.c. to d.c.
• Third important part is ventilating fan
– Keeps rectifier from overheating
• Design improves arc stability and makes it easy
to hold short arc which is soft and steady
• No major rotating parts so consume little power
49. 11 - 49
A.C.-D.C. Transformer-Rectifier
Welding Machines
• Permit welder to select either a.c. or d.c. and
electrode negative or electrode positive
• Switch
– Permits welder to use only transformer part of
machine for a.c. welding
– Flipping switch then output current directed
through rectifier which converts it to d.c. welding
• High frequency arc-starting devices,
water/gas flow controls, balance controls
for a.c. operation, remote control often built
into machine
52. 11 - 52
Advantages of a.c. Power
Sources
• Reduces tendency to arc blow
• Can use larger electrodes
– Resulting in faster speeds on heavy materials
• Lower cost
• Decreased power consumption
• High overall electrical efficiency
• Noiseless operation
• Reduced maintenance
54. 11 - 54
Cost Comparisons:
Arc Power Sources
• Three main areas
– Cost of purchasing equipment (nearly equal)
– Operating efficiency
• Motor generator machine: 52-65%
• Transformer-rectifiers: 64-72%
• Inverters: 85%
– Maintenance
• Motor generator machine: replacing parts, lubrication
• Transformer-rectifiers and inverters have no moving parts
See Table 11-2
for more comparisons
56. 11 - 56
Power Supply Ratings
• 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
– Efficiency of output
– Power factor
57. 11 - 57
Current Output
• Rated on basis of current output in amperes
• Amperage range
– 200 amperes or less for light or medium work
– Over 2,000 amperes for submerged arc welding
58. 11 - 58
Open Circuit Voltage
• 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
59. 11 - 59
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 and GTAW
60. 11 - 60
Efficiency
• 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%
61. 11 - 61
Power Factor
• 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
62. 11 - 62
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
65. 11 - 65
Work Cable
• 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
See Table 11-3 to help
choose the right size of
welding cable
70. 11 - 70
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
74. 11 - 74
Other Electric Arc processes
• Generates heat for several major welding
processes
– Gas tungsten arc welding (GTAW)
– Gas metal arc welding (GMAW)
• Arc cutting utilizes much of same equipment as
arc welding
75. 11 - 75
Carbon Arc Welding
• Welding heat comes from arc formed between
base metal and carbon electrode or arc formed
between two carbon electrodes
– With or without addition of filler rod
• Carbon electrodes available: 1/4, 5/16, 3/8 inch
• Alternating current: 30-125 amperes
• Metal electrode holders not suitable
– Carbon electrode hotter than metal electrode
77. 11 - 77
Atomic-Hydrogen Arc Welding
• Process in which electric arc surrounded by
atmosphere of hydrogen
– Gas shields molten metal from oxidation and
contamination from the air
– Transfers heat from electrode to work
– Arc formed between two electrodes
• Temperature produced by arc: 7,500ºF
• Current supplied by a.c. welding transformer
• Hydrogen supplied in cylinders
79. 11 - 79
Atomic-Hydrogen Arc Welding
• Metal of same analysis as being welded can be
deposited
• Welds may be heat treated
– Unusually smooth, ductile, nonporous and free
from impurities
– Surface free from scale
• May weld hard-to-weld metals
• Advantages: increased production, low
operating cost, and low maintenance cost
83. 11 - 83
Head Shield Lens
• Sizes: 2 x 4.5 or 4.5 x 5.25
• Colored to screen out ultraviolet, infrared rays,
and most of visible rays
• Variety of shades of color
– Density depends on brilliance of arc
– Varies with size of electrode and volume of current
• Side exposed to weld pool protected by clear
polycarbonate plastic cover lens
– Protect costly filter lens from molten metal spatter
and breakage (replaced when pitted and clouded)
89. 11 - 89
Further Protection
• Ear Protection
– Full ear muffs that cover entire ear or ear plugs
– Dangers
• Noise
• Hot weld spatter or slag entering ear canal
• Flume Protection
– Always use proper ventilation to keep head out of
fume plume