A fusing system for an additive manufacturing machine, comprising: a first carriage carrying a layering device, a heating lamp, and a fusing lamp, the first carriage movable back and forth over a work area along a line of motion in a first direction and in a second direction opposite the first direction; a second carriage carrying an agent dispenser, the second carriage movable back and forth over the work area along the line of motion in the first direction and in the second direction; characterized in that the fusing system further comprises a controller operatively connected to the first carriage, the heating lamp, the fusing lamp, the second carriage and the agent dispenser configured to cause the fusing system to: while moving the first carriage over the work area in the first direction in a first pass, layer build material over an object structure to form a layer of build material; while moving the first carriage and the second carriage over the work area in the second direction in a second pass, irradiate build material in the layer with the heating lamp and then dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser; while moving the second carriage and the first carriage over the work area in the first direction in a third pass, dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser and then irradiate build material in the layer with the fusing lamp; and while moving the first carriage back over the work area in the second direction in a fourth pass, irradiate build material in the layer with the fusing lamp. a first carriage carrying a layering device, a heating lamp, and a fusing lamp, the first carriage movable back and forth over a work area along a line of motion in a first direction and in a second direction opposite the first direction; a second carriage carrying an agent dispenser, the second carriage movable back and forth over the work area along the line of motion in the first direction and in the second direction; characterized in that the fusing system further comprises a controller operatively connected to the first carriage, the heating lamp, the fusing lamp, the second carriage and the agent dispenser configured to cause the fusing system to: while moving the first carriage over the work area in the first direction in a first pass, layer build material over an object structure to form a layer of build material; while moving the first carriage and the second carriage over the work area in the second direction in a second pass, irradiate build material in the layer with the heating lamp and then dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser; while moving the second carriage and the first carriage over the work area in the first direction in a third pass, dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser and then irradiate build material in the layer with the fusing lamp; and while moving the first carriage back over the work area in the second direction in a fourth pass, irradiate build material in the layer with the fusing lamp. while moving the first carriage over the work area in the first direction in a first pass, layer build material over an object structure to form a layer of build material; while moving the first carriage and the second carriage over the work area in the second direction in a second pass, irradiate build material in the layer with the heating lamp and then dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser; while moving the second carriage and the first carriage over the work area in the first direction in a third pass, dispense a fusing agent and/or a detailing agent on to build material in the layer with the agent dispenser and then irradiate build material in the layer with the fusing lamp; and while moving the first carriage back over the work area in the second direction in a fourth pass, irradiate build material in the layer with the fusing lamp.