Method and apparatus for controlling root pass weld penetration in open butt joints

A method of controlling weldpool penetration during root pass welding in an open butt joint defined in a workpiece to be welded by a welding torch with a welding wire being continuously fed from the welding torch to said joint to form a weldpool penetrating the joint, said workpiece and said welding torch being movable relative to one another, said method comprising the steps of:

• (a) positioning visual sensing means ahead of said welding torch and in alignment with said joint for frontly viewing the weldpool at an angle of about 10.degree. to about 20.degree. relative to a line tangent to said workpiece at said weldpool to thereby provide a full image of said weldpool defining a weldpool contour line, said sensing means and said welding torch being disposed on a common side relative to said workpiece;
• and
• (b) processing said weldpool image through computer means including image processing means operatively coupled to control means, said image processing means analysing said weldpool contour line to derive therefrom weldpool penetration depth and comparing said weldpool penetration depth with a predetermined value, to thereby provide an information signal representative of weldpool penetration error which is fed to said control means, said control means issuing control signals in response to said information signal for controlling welding parameters such as to provide a root pass weld having a predetermined penetration.