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Assessment of the TWI top face control system for TIG welding


TWI Industrial Member Report Summary 703/2000

G B Melton and R L Jones


In manual welding, the welder adjusts the welding parameters, or his technique, to compensate for variations in component dimensions, joint fit-up, composition and surface condition of the parent material. In mechanised and automated welding, a sensor is required to detect these deviations and implement the necessary changes in welding parameters in real time in order to maintain satisfactory welding conditions. Many attempts have been made to find a method of sensing penetration so that it can be adequately controlled. The earlier systems measured the radiation emitted, or size of the penetration, from the back of the weld. However, these systems require access to the back of the joint, which is not practical in many applications.

TWI has developed a top face control system for TIG welding based on the use of an infrared camera. The infrared camera allows simultaneous viewing and thermal imaging of the weld pool and surrounding area to be achieved using a single sensor. Viewing is used to estimate the weld pool dimensions whilst thermal imaging can be used to determine the temperature profile of the surrounding area.

This report assesses the demonstration top face control system. It includes a description of the underlying principles involved, its operation and verification of its control functions.


The objectives of this report are to review the infrared top face control systems and to assess its ability to:

  • Control bead width
  • Control penetration
  • Track the seam
  • Detect variations in joint gap
  • Compensate for cast to cast variations

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