What is arc blow and how can it affect weld quality?

• A. A mechanical misalignment of the torch causing straight welds.
• B. A type of arc that penetrates too deeply.
• C. A purely thermal phenomenon that reduces electrode consumption.
• D. Arc blow occurs when the current path is affected by magnetism causing an erratic arc; can cause inconsistent penetration and waviness; mitigated by proper grounding and electrode manipulation.

Answer: (D)

Arc blow is the wandering of the welding arc caused by magnetic forces around the current path. When magnetism from the workpiece, lead, and grounding setup interacts with the DC or AC current, it creates a sideways pull on the arc, making it drift off course. That wandering concentrates heat unevenly and changes the depth and location of fusion, leading to inconsistent penetration and a wavy bead or other weld quality defects. Proper grounding helps establish a stable return path and reduces stray magnetic fields, while deliberate electrode manipulation and control of the travel angle can steer the arc back toward the joint and keep heat input more even. This phenomenon isn’t about a simple mechanical torch misalignment, nor is it just a deeper or shallower penetration by itself, and it isn’t solely a thermal effect; it’s the magnetic influence on the arc path that drives the quality issues.