The present invention relates to an additive manufacturing system and its methods. The system includes a material conveyor, an energy source, and a micro-forging device. The material conveyor is configured to convey material. The energy source is configured to direct an energy beam toward the material, the energy beam fuses at least a portion of the material to form a solidified portion. The micro-forging device is movable along with the material conveyor for forging the solidified portion, wherein the micro-forging device comprises a first forging hammer and a second forging hammer, the first forging hammer is configured to impact the solidified portion to generate a first deformation, and the second forging hammer is configured to impact the solidified portion to generate a second deformation greater than the first deformation.