Welding Parameters and Procedure Selection
This domain tests how current, voltage, travel speed and heat input interact, and how a WPS controls them. Exam questions often ask which variable to change or how to calculate heat input.
Core rules
- Current controls penetration and deposition. Too low causes lack of fusion; too high causes burn-through, undercut and spatter.
- Voltage controls arc length and bead shape. Too high gives a wide, flat bead and spatter; too low gives a narrow, high bead and stubbing.
- Travel speed controls bead width and heat input. Fast travel can cause lack of fusion; slow travel can cause excess reinforcement and distortion.
- Heat input in kJ/mm is Q = (V × I × 60) / (travel speed in mm/min × 1000).
Worked example
A weld runs at 25 V, 200 A and 150 mm/min. Q = (25 × 200 × 60) / (150 × 1000) = 2.0 kJ/mm. If travel speed rises to 300 mm/min, Q falls to 1.0 kJ/mm. The reasoning is that faster travel puts less heat into each millimetre of weld.
Traps that cost marks
- Using travel speed in mm/s without converting.
- Changing current without checking voltage and travel speed.
- Assuming higher heat input always improves quality; it can reduce toughness and increase distortion.
- Ignoring the WPS range for each variable.