Plasma Arc Cutting: Scientists Decode Gas Flow Dynamics

Plasma Arc Cutting (PAC) is a thermal cutting technology widely used in manufacturing applications such as shipbuilding, aerospace, manufacturing, abolition of nuclear power plants, construction and automotive industries. This process involves high-speed ejection of plasma or ionized gases, and then melts and removes parts of unwanted material from the electrically conductive workpiece, such as metals.

Plasma jets are usually generated in two steps. It compresses the gas through a small nozzle hole and generates an electric arc through the power source. Surprisingly, the introduced arc ionizes the gas coming out of the nozzle, which creates a very hot plasma. This allows plasma jets to slice different metals and alloys easily, quickly, and accurately.

The quality of workpieces cut using PAC depends on a variety of factors. The type of plasma gas and its pressure, the shape and size of the nozzle hole, current and voltage, cutting speed, and distance between the plasma torch and workpiece. Most of these factors are well understood in the context of PACs, but the effect of gas flow dynamics on cut quality is clearly unknown. This is primarily due to challenges in visualizing flow dynamics.

To fill this knowledge gap, a team of researchers led by Dr. Upendra Tuladhar, currently based in HD Hyundai Maipo after completing his Ph.D. Research under Professor Sekyoung Ahn of the Faculty of Mechanical Engineering at Busan National University, in collaboration with the Korean Institute of Machinery and Materials to visualize and understand the gas flow dynamics of PACs. Their findings were published in Journal International Communications in Heat and Muss Transfering.

Dr. Tuladhar explains the motivations behind their research. “Our goal was to assess the gas flow behavior within the kerf or grooves of various geometry derived from actual PAC workpieces. The shape of the skin cutting front surface is different in cutting speed. , and as a result, it adversely affects reduction performance in order to better understand the mechanisms behind this observation.

In this study, the researchers proposed an innovative computational fluid dynamics simulation model to investigate the effects of curved cutting fronts on PAC flow behavior. Additionally, they performed Schlen imaging of the gas flow. In this specification, fluid flow is photographed by imagining the deflection of a ray refracted by a moving fluid, allowing for visualization of normal, unobservable changes in the refractive index of the fluid. Finally, the team compared the results of Schlieren imaging with the gas flow patterns predicted by the simulation.

They found that pre-cutting curvature results in an oblique shock wave structure, resulting in a significantly lower flow velocity. In particular, the weak impact structures present on the curved cutting front gradually reduced the speed. Furthermore, it was possible to achieve the critical flow velocity of kerf with a very curved cutting front. This speed cannot be exceeded to allow the workpiece to penetrate vertically.

Furthermore, the researchers examined numerical results by noting that the shear stress lines matched the layer patterns of the kerf wall.

“The improved PAC can be used to cut thick metal components of nuclear reactors, such as pressure vessels, steam generators and other larger structures. This leads to safer and more efficient dismantling of nuclear facilities, and It can reduce the risk of radiation exposure. It can also reduce the financial burden on government and taxpayers on workers and surrounding communities. Structure,” concludes Dr. Tuladhar.