This paper reports the possibility of detecting bead deflection defects during electron beam welding (EBW) using in-process monitoring by ultrasonics. Experiments were conducted using a 6 kW (150 kV) high vacuum type welding machine and a 5 MHz ultrasonic transducer. All welding was performed at a 30 mm penetration depth in the flat position on SM41 steel plates. A coupling method of the ultrasonic transducer to the plate at a high temperature in the vacuum chamber was investigated. A 1 mm gap was maintained by using 0-rings between the transducer and the steel plate surface and silicon oil was pumped into the gap for coupling and cooling.
The following points were concluded from the study.
(1) It is possible to monitor the bead deflection during EBW by detecting the time difference between the ultrasonic echo from the weld metal and that from the groove face.
(2) The detected voltage of the bead deflection is proportional to the measured bead deflection and the accuracy of detection is within ±10%.
(3) A bead deflection defect as small as 0.6 mm can be detected.
(4) The maximum echo height from the weld metal is obtained using the following conditions:
(a) the measurement depth equals the maximum depth of penetration,
(b) the measurement distance is 15 mm behind the weld cavity.
(5) The echoes from the weld metal are those arising from the root defects which occur at the bottom of the weld zone.
