**4. E**ff**ects of Arc Length on Welding Formation**

During the welding process in Tests 1 and 2, spatters and popping noises occurred from time to time. However, if the arc length were a little longer than that in Test 2, such as in Test 3, those spatters and popping noises would disappear. By comparing the high-speed photographs, it was found that the arc lengths were longer in Tests 3–6, and droplets were all in the projected transfer mode presented in Figure 3, meaning that droplets went into the molten pool after detaching from the

wire. However, the arc lengths were shorter in Tests 1 and 2. Not all droplets were in the projected transfer mode, and some short circuits were found. Therefore, in terms of the modes of droplet transfer, the tests in this experiment can be divided into "the partial projected transfer zone" (Tests 1 and 2) and "the projected transfer zone" (Tests 3–6).
