Analysis On Underwater Flux-cored Wire Arc Cutting Process Based On High-speed Photography

The flux-cored arc cutting method is a high efficiency,security,and low cost cutting method,have a good prospect in the construction and maintenance of offshore and ship maintence industry.The cutting process of this method is difficult to observe because the cutting wire usually extends into the workpiece,and the bubbles and turbidity produced by the cutting wire reaction will affect the fluctuation of water light.For these reasons,the cutting mechanism is not clear.This thesis aims to clarify the mechanism of the underwater flux-cored arc cutting method by using high-speed camera system,and analyze its cutting procedure in water.To observe the cutting area condition by using high-speed camera,a narrow Q235 workpiece was processed,and the narrow workpiece could be completely removed in the cutting process that the light could be passed through the cutting area.To overcome the fluctuation of water caused by bubbles during underwater cutting process,two high temperature glasses were added on both sides of the narrow workpiece to form a sandwich structure.The height of the glass was higher than that of the workpiece to prevent the bubbles and cutting turbidity from affecting the clarity of the underwater light path.Light could be entered the camera through the sandwich structure.With the help of the sandwich structure,the“arc sensor and high speed photography” synchronous acquisition system was established to obtain the cutting current,arc voltage,and cutting process images to analyze its cutting process.The results showed that the observation system obtained clear images of the cutting area,the arc inducing mode was contact type,and the droplet transfer was mainly fine droplet transfer.The cutting process was mainly divided into two stages.In the first stage,the cutting wire extended into the workpiece and cut a hole from top to bottom.The arc force was not as strong as the plasma arc cutting force,and the workpiece cannot be cut through directly.The flux-cored wire moved down with the movement of the molten pool under the arc digging action.In the second stage,there were two cases for the cutting wire.In the first case,the tip of the cutting wire moved far from the cutting edge of the workpiece,and the arc would be extinguished.The arc would be re-ignited until the cutting wire re-contacted with the front cutting edge of workpiece.In the second case,the arc was ignition in the side of the cutting wire,and the arc in the tip cutting wire would be extinguished under the principle of minimum voltage.Both cases could realize the switching of the arc area,which realized the continuous cutting process.The arc ignition area was related to the shape of the cutting edge.The bottom of the workpiece was easy to form slag hanging or bridging if the arc extinguished in the bottom of workpiece during the switching of the arc area.In order to further study the underwater cutting mechanism,the cutting current and arc voltage on the cutting process were studied.The research revealed that when the current was increased,the depth of cutting wire into the workpiece was increased,and the arc extinguished time in the whole cutting process was increased.When the arc voltage was low,the position of the cutting wire tip changed with the cutting process,and the arc length was short.When at a large arc voltage,the cutting wire tip was mainly on the upper side of the workpiece,with a large arc length and a wide cutting range.In this thesis,the research on the process of underwater flux-cored wire cutting is helpful for higher efficiency cutting and automation.