A molten metal behavior on the underside of a workpiece in the gas cutting process was observed by a high-speed camera to clarify the effects of preheating gas and cutting speed on the behavior. Moreover, the molten metal behavior was modeled using a particle method. As a result, the molten metal behavior and the dross detachability were different for each preheating gas when the cutting speed was set to be 150 mm/min. From computational results, it was clarified that the molten metal showed different behavior because the cutting groove shape was different for each heat source. When hydrogen gas was used as the preheating gas, the molten metal indicated similar behavior regardless of increase of the cutting speed. However, it became hard to remove the dross from the underside of the workpiece. In addition, computational results showed that the average oxidation ratio of the dross surface which was jointed to the underside of the workpiece was different for each cutting condition. From these tendencies of the oxidation ratio and dross detachability, it was suggested that the oxidation ratio of the dross surface was one of factors to determine the dross detachability.
