Centreline cracking known as bead shape induced cracking is associated with deep penetrating processes such as SAW and CO₂ shielded FCAW. When a weld bead is of shape where there is more depth than width to the weld cross-section, the solidifying grains growing perpendicular to the steel surface intersect in the middle, but do not get fusion across the joint. To correct for this condition, the individual weld bead must have at least as much as 1:1 to a1.4:1 width-to-depth ratio to remedy this condition. The total weld configuration, which may have many individual weld beads, can have an overall profile that constitutes more depth than width. If multiple passes are used in this situation, and each bead is wider than depth, a crack free weld can be made.

When centreline cracking is occurred due to bead shape, only solution is to change the width-to-depth relationship. This may involve change in joint design. Also it is advisable to reduce the amount of penetration. This can be accomplished by utilizing lower welding amperages and larger diameter electrodes.

Reference: Weld cracking – Lincoln Arc welding foundation

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Thank you,

KP Bhatt

Four different waveforms available with AC polarity welding are advanced square wave, soft square wave, sine wave, and triangular wave. Each wave changes the arc and puddle characteristics as well as the penetration profile.

Advanced square wave. The advanced square wave waveform offers fast transitions between EN and EP for a responsive, dynamic, and focused arc with better directional control. It forms a fast-freezing puddle with deep penetration and fast travel speeds.

Soft square wave. Soft square wave provides a smooth, soft, “buttery” arc with a fluid puddle and good wetting action. The puddle is more fluid than with advanced square wave and more controllable than with sine wave.

Sine wave. The sine wave offers a soft arc with the feel of a conventional power source. It provides good wetting action and actually sounds quieter than other waves. Its fast transition through the zero amperage point also eliminates the need for continuous high frequency.

Triangular wave. The triangular wave offers peak amperage while reducing overall heat input into the weld. This leads to quick puddle formation, low weld distortion, and fast travel speeds. It is especially good for welding thin aluminium.

Reference: Riding the right wave in aluminum welding-www.thefabricators.com

Keep reading, happy welding

Thank you,

KP Bhatt