Spot welding ultrasonic testing

What is a Spotweld?


  • Electrical Resistance Welding
  • Cast nugget holds together two or more sheets of a rolled material

Spotweld Sizes are Determined By

  • Tips of the welding tool
  • Welding time
  • Current

Three Classically Accepted Methods

  • Four Point Resistivity – Requires a well trained hand and does not work well with all metals
  • Tear Test / Destructive Testing – Turns a finished product into scrap.? Classification can be user biased.
  • Ultrasonic Testing – Quickly learned, easy classification, non-destructive, theory does not change for different metal types

How does UT of Spotwelds Work?

  • Cast nugget formed within material
  • Columnar transmission of ultrasound into weld nugget
  • Transducer crystal is sized to match weld nugget
  • Two types of transducer delay line: Plastic Delay Tip and Captive Water Column

What is Ultrasonic Testing?

  • Sound vibrations higher than audible range
  • Technique uses high frequency sound waves and their reflected echoes
  • We use 10-25 MHz for Spotweld Testing

Several classifiable failure conditions

  • Unweld Condition – Twice as many echoes appear on display and there is a long ring-down time.
  • Undersized Nugget – Caused by a low current condition.? Intermittent echoes will appear and there will be a short ring-down time.
  • Stick Weld – Caused by insufficient contact time.? Echoes will appear with proper spacing but long ring-down time.
  • Burnt Weld Nugget – This results from a long contact time.? Very few echoes will appear due to extremely fast ring-down time.
  • Thin Weld Nugget – May result from excess pressure on weld nugget during weld process.? Echoes will have proper ring-down time with reduced spacing.

Good Weld

Transducer on a Good Weld




Unweld Condition

Transducer on an Unweld Condition




Undersized Weld

Transducer on an Undersized Weld




Stick Weld

Transducer on a Stick Weld




DIO 1000 – example of using