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
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.
Transducer on a Good Weld
Transducer on an Unweld Condition
Transducer on an Undersized Weld
Transducer on a Stick Weld
DIO 1000 – example of using