AWS Certified Welding Inspector — FundamentalsWelding ProcessesHard
A CWI is inspecting a Resistance Spot Welding (RSW) operation on two sheets of 0.040-inch (1.0 mm) galvanized steel. The inspector notes that many of the spot welds are exhibiting excessive expulsion (spitting) and a shallow, irregular nugget. What is the most likely cause of these defects?
- AToo low electrode force.
- BInsufficient hold time.
- CExcessive weld current.
- DInsufficient squeeze time.
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive weld current.
Excessive expulsion and shallow, irregular nuggets in RSW are classic indicators of too much weld current. High current causes the material to heat up too rapidly, leading to explosive expulsion of molten metal, often before a proper nugget can form. This issue is often exacerbated with galvanized steel due to the lower melting point of the zinc coating.
Why the other options are wrong
- A. Too low electrode force would cause poor contact resistance, potentially leading to overheating at the contact surfaces but not typically the *primary* cause of excessive expulsion and irregular nuggets as directly as excessive current.
- B. Insufficient hold time would result in the nugget collapsing under pressure after solidification, leading to insufficient strength, not necessarily excessive expulsion.
- D. Insufficient squeeze time would primarily cause poor fit-up and potentially arc initiation issues, not typically excessive expulsion and irregular nuggets.
RSW Expulsion Control
Expulsion (spitting) in Resistance Spot Welding is the forceful ejection of molten metal, often indicating improper weld parameters, primarily excessive current.
- Reduces weld strength and quality.
- Caused by overheating and pressure.
- Galvanized steel is more prone.
Memory trick: Too much current, too much pop, weld strength will drop.