“…Therefore, from the previous mentioned studies we can conclude there are several factors preventing or reducing pore formation in WAAM process. These factors are slower cooling rate [98], low process pulse frequency [98], higher interpass temperature [99,100], clean and high-quality wire [86,101,105], CMT technique [109] or CMT with advanced mode and pulsing current [101,110], lower total energy input per unit volume [89], avoid using alloy composition with great difference in solubility between liquid and solid metal such as aluminum alloys [102,103], vibrating workpiece [104], CMT mode combined with interlayer rolling [90], lower flow rate of shielding gas [87], equilibrium melt pool sounding pressure [25], equiaxed fine grain structure [106,107], smaller weld pool or weld bead size [91,108], stable or smooth arc [86], eliminate the existence of hydrogen around the weld pool as much as it is possible [92], and reducing the distance between the nozzle and workpiece during WAAM process [111].…”