Why would a welder insert the end of the filler rod into the weld pool when stopping a weld?

Inserting the end of the filler rod into the weld pool when stopping a weld serves a crucial purpose in preventing crater cracks. When a welder brings the arc to a stop, the cooling process of the weld pool begins, and if the molten metal solidifies too quickly or unevenly, it can lead to shrinkage cracks at the end of the bead—these are known as crater cracks. By inserting the filler rod into the weld pool, the welder helps to add additional metal, which allows for a more controlled cooling of the weld pool and ensures that the joint is filled adequately, mitigating the risk of cracking and ensuring the integrity of the final weld. This technique is particularly vital in high-quality welds where structural integrity is paramount.