1. Arc Welding – Part II
AG 221 – Metals and Welding

2. Controlling distortion (Volume changes of expansion followed by contraction during cooling)
Do not overweld.
Avoid continuous welds.
Consider chain intermittent
Or staggered intermittent
Use fewer beads (passes).
Backstep Weld
Use Wedging

3. Welding Machines Types
AC Transformer
DC Generator
DC Rectifier
AC-DC (Transformer-Rectifier)
Welders may be adjusted by levers, cranks, wheels or plug-in arrangements
DC welders may be
Straight polarity (electrode negative)
Reverse polarity (electrode positive)

4. AC (Alternating Current) Welder
Single phase transformer
Least expensive – initial cost
Lightest and smallest (not portable)
180, 200, 300, 400, 500, 750 and 1000 amp output
Maximum current is 25% more than rated output)
Forceful arc – little sticking problem

5. AC (Alternating Current) Welder
For using low hydrogen electrodes (higher carbon steels) like E7018
No arc blow
Fast welding – large electrodes, high amp
Little maintenance required
Economical in operation
Use only AC electrodes
Doesn’t work well in thin metal welding

6. AC Welder Parts Primary Circuit Secondary Circuit
Input lead cable (240 Volts AC grounded cable)
Power source outlet to primary coils of welder
Secondary Circuit
Secondary coils to electrode holder and ground clamp
25-85 volts usually
0-250 amps usually

7. Transformer Two types of winding materials Step down type
Copper – best
Aluminum – loses power with heat
Step down type
Primary coils
Many windings
Small wire
Great magnetic field

8. Transformer Secondary coils few windings Large wire
Current established by induction
Volts and amps are inversely related (more amps = less volts)
Volts directly related to number of windings

9. DC (Direct Current) Welders
Range amps
amps - light shielded arc welding
200, 300, 400 amps – industrial welding
600 amp – submerged arc welding and carbon arc cutting

10. DC Generator May be driven by Single or 3 phase motor Gasoline engines
PTO

11. Characteristics of DC Welders
Have a forceful arc
Not affected by changes in power (line voltage drop)
Reserve power is available
Variable use – weld all metals and alloys
Requires maintenance
Subject to blow
Voltage and amperage are readily adjusted
Polarity may be adjusted
Expensive

12. DC Rectifier AC power use – DC welder advantages and disadvantages
Quiet operation
Welds well at low currents
Soft arc
Arc blow

13. AC-DC Transformer-rectifier
AC transformer or DC rectifier operation straight polarity or reversed polarity
Require little maintenance
Weld well at low currents
Versatile – weld all metals and alloy’s
Expensive
Subject to arc blow on DC
3 phase- smoother arc
Single phase less expensive
Uses AC power

14. Definitions
Duty Cycle – measure of a welder’s ability to perform at its “amp-volt” rating under practical welding conditions
it indicates the percentage of working time and idling time for which the machine is safely designed
60% duty cycle means 36 minutes working per hour at rated load (.60*60 minutes = 36 minutes)
Welder Efficiency – power consumed (output) related to power used (input) in welding
(Efficiency = output/input )