SAW Electrical Systems & Wiring 3 ā Questions and Answers
Question 1: Voltage drop in the welding cable between the power source and the work clamp causes:
- Increased arc voltage at the weld
- Reduced arc voltage at the weld and potential loss of penetration (Correct answer)
- Higher wire feed speed
- Increased flux consumption
Correct answer: Reduced arc voltage at the weld and potential loss of penetration
Resistance in long or undersized cables causes voltage drop, reducing the actual arc voltage available at the weld joint.
Question 2: In SAW, the contact-tip-to-work distance (CTWD) affects the electrical circuit primarily by:
- Changing the flux layer depth
- Altering the electrode extension resistance and thereby the effective heat input (Correct answer)
- Modifying the open-circuit voltage
- Controlling the travel speed
Correct answer: Altering the electrode extension resistance and thereby the effective heat input
Longer CTWD increases electrode extension resistance (IĀ²R heating), reducing amperage and altering deposition characteristics.
Question 3: Which power source characteristic is best suited for SAW with a constant voltage (CV) system?
- Drooping (CC) volt-ampere curve
- Flat (CV) volt-ampere curve (Correct answer)
- Rising volt-ampere curve
- Pulsed DC output
Correct answer: Flat (CV) volt-ampere curve
A flat CV characteristic maintains relatively constant voltage regardless of current changes, providing stable arc length control with a constant-speed wire feeder.
Question 4: What is 'arc blow' in the context of SAW electrical systems?
- Excessive flux being expelled by the arc
- Deflection of the arc caused by magnetic fields in the workpiece or circuit (Correct answer)
- A sudden increase in arc voltage
- Wire burnback into the contact tip
Correct answer: Deflection of the arc caused by magnetic fields in the workpiece or circuit
Arc blow is the deflection of the welding arc from its intended path due to asymmetric magnetic fields, common with DC welding on ferromagnetic materials.
Question 5: A SAW welder notices porosity increasing as cable length between the power source and work increases. The most likely electrical cause is:
- Increased travel speed from voltage drop
- Voltage drop causing reduced arc energy, leading to poor flux melting and gas entrapment (Correct answer)
- Increased wire feed speed
- Short circuit at the contact tip
Correct answer: Voltage drop causing reduced arc energy, leading to poor flux melting and gas entrapment
Voltage drop over long cables reduces arc energy, which can prevent complete flux melting and allow gases to become trapped in the weld.
Question 6: For SAW, the AWS D1.1 code requires that welding cables be sized to:
- Carry the maximum rated current without exceeding safe temperature limits (Correct answer)
- Minimize inductance in the circuit
- Maximize voltage drop to stabilize the arc
- Be no longer than 10 feet from source to work
Correct answer: Carry the maximum rated current without exceeding safe temperature limits
Welding cables must be sized to carry the maximum expected current without overheating, ensuring safe operation and minimal voltage drop.
Question 7: What electrical hazard is specifically associated with the open-circuit voltage (OCV) of SAW power sources?
- It can cause arc blow in the workpiece
- It presents an electric shock risk to the operator when the arc is not established (Correct answer)
- It causes excessive wire burn-off rates
- It melts the contact tip if left on too long
Correct answer: It presents an electric shock risk to the operator when the arc is not established
OCV (typically 60ā100V) is present at the electrode whenever the power source is energized but no arc is established, posing an electric shock risk.
SAW Electrical Systems & Wiring 3
Voltage drop in the welding cable between the power source and the work clamp causes: