Welding and Cutting Processes Flashcards
6 cards from real Millwright Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Welding and Cutting Processes flashcards as text
What is the primary purpose of a shielding gas in GMAW (MIG) welding?
Answer: To protect the molten weld pool from atmospheric contamination (oxygen, nitrogen, hydrogen)
The shielding gas creates an inert or reactive atmosphere around the molten weld pool, preventing oxygen, nitrogen, and hydrogen from the atmosphere from causing porosity, embrittlement, and other defects.
When making an oxy-fuel cut on carbon steel, what causes the actual cutting action?
Answer: A high-pressure oxygen stream rapidly oxidizes (burns) the preheated steel, and the force of the oxygen blows the molten oxide away
In oxy-fuel cutting, the preheat flames bring the steel to its ignition temperature (about 870 degrees C), then a stream of pure oxygen rapidly oxidizes (burns) the steel. The oxygen jet's force blows the molten iron oxide out of the kerf.
What is the main advantage of plasma cutting over oxy-fuel cutting?
Answer: Plasma cuts faster, works on any electrically conductive metal, and produces a narrower kerf with less heat distortion
Plasma cutting is significantly faster (up to 5x on thin material), cuts any conductive metal (stainless, aluminum, copper, not just carbon steel), and its concentrated arc produces a narrower kerf with a smaller heat-affected zone.
What does preheat accomplish before welding on thick or high-carbon steel?
Answer: It slows the cooling rate to prevent hydrogen cracking, reduces residual stress, and allows hydrogen to diffuse out of the weld zone
Preheating raises the base metal temperature to slow post-weld cooling rates, which reduces the risk of hydrogen-induced cracking in the heat-affected zone, lowers residual stresses, and allows trapped hydrogen to escape.
What is undercut in welding, and what causes it?
Answer: A groove melted into the base metal at the weld toe that is not filled by weld metal, caused by excessive current, speed, or improper technique
Undercut is a groove or channel melted into the base metal adjacent to the weld toe (or root) that was not filled with weld metal, creating a stress concentration that weakens the joint and can initiate fatigue cracking.
Why must acetylene gas never be used at pressures exceeding 15 PSI (103 kPa)?
Answer: Acetylene becomes unstable and can spontaneously decompose explosively above 15 PSI gauge pressure
Acetylene is chemically unstable, and at pressures above 15 PSI (103 kPa) gauge, it can spontaneously decompose in a self-accelerating exothermic reaction (explosion) even without a spark or flame present.