TWI Industrial Member Report Summary 550/1996
C N Ribton
Real-time seam tracking, using backscattered electrons to detect the joint position, has been developed at TWI over the past 10 years. This report describes the latest improvements made to the signal processing components of the tracker which have enabled more consistent operation at up to 30kW beam power.
Real-time seam tracking is a technique where electron beam-to-joint misalignment is corrected as the weld is being made. This requires the control unit to measure the position of the joint line in relation to the beam position and to output a corrective drive to an axis. Application areas include components which thermally distort during welding and those which are shaped such that programming the joint path would be excessively time- consuming. Many of these applications have been at beam powers in the range of 6-30kW ( ie medium power) where weld shrinkage can give rise to distortion at joint lines close to the weld, or where components are massive such that jigging cannot restrain thermal expansion.
The joint line position is detected by scanning the electron beam across the workpiece surface just ahead of the weld pool. The electrons backscattered from the surface are collected and after analysis the signal indicates a pulse as the beam passes over the joint line. The pulse is enhanced by preparing the joint line with a groove or notch feature. This signal is then examined by an analysis system which carries out a corrective movement of the beam to the joint line. This may be by mechanical movement of the gun or workpiece, or by magnetic deflection of the beam.
- To examine and advance the range of application of the seam tracking device.
- To develop the equipment further for improved reliability, particularly at beam powers up to 30kW.