Advanced Welding Processes: Technologies and Process Control

Monitoring and control of welding processes 215
Before penetration; highfrequency
wave
oscillation of pool
Photo sensor
On penetration;
characteristic low
frequency develops
10.19 Principle of front face penetration control system.
and penetration to predict the onset of full penetration. Although the system
appears to be feasible, complex image analysis facilities are required and
mathematical models capable of accurately predicting the pool profile/
penetration relationships are required.
Radiographic control. Radiographic monitoring has been used for analysis
of process performance in the slag-shielded processes such as SAW and
ESW. The availability of high-quality real-time radiography and imageprocessing
techniques has led to the development of an on-line penetration
and quality-control system. [260] The x-ray source is placed above the plate
being welded and the image intensifier and camera are positioned below the
workpiece. A computer control system is used to analyse the image and this
provides appropriate corrections to the control system to ensure consistent
penetration is maintained.
This approach is obviously complex and costly and is only likely to be
used in special applications where no alternative technique is available and
the overall cost is justified by quality constraints.
Quality control
The seam tracking, arc length and penetration control systems described
above are intended to compensate for relatively small variations in joint