The question is too general. There is no fixed way to collect fire. Every time the fire is collected, it depends on the situation, but it is generally collected from the periphery to the middle. When dropping the hammer, we should pay attention to the cooperation between the technique and the pad iron, and also look at the deformation degree and direction of the sheet metal parts. Generally speaking, fire collection can not be summarized in just a few words, and the essence of fire collection can only be mastered by combining rich practical experience. Many sheet metal workers can't collect fire perfectly after working for many years. I hope Lou.