Plasma arc heating for ceramic assisted cutting technology

Plasma arc heating cutting uses arc discharge to excite high-energy ions, which impact the surface of the workpiece and generate high temperatures locally at the impact point, changing its cutting properties during material cutting. Due to the high ion energy, its heating speed and temperature range can be comparable to laser heating.

The use of plasma heating assisted cutting of metal materials has significantly reduced cutting force and tool wear, improved cutting speed and surface roughness, and achieved significant results. The theory is relatively mature. Hot pressed high-speed steel has greatly improved its performance due to the elimination of network brittle structures, and has been widely used in processing molds. However, due to its high hardness, its conventional workability is poor and the processing cost is high. The use of plasma heating assisted cutting has greatly improved its workability.

Plasma heating assisted cutting of engineering ceramics has been tested on various materials, such as alumina, zirconia, and silicon oxide. The machinability performance of materials can be divided into three types:

(1) As the temperature increases, the cutting force first decreases, then increases, and then decreases. When the cutting force of the material decreases for the second time, it undergoes a transition from brittleness to plasticity. For example, silicon nitride has a transition temperature of 1050 ℃.

(2) The cutting force increases with the increase of temperature until the temperature and cutting force cause material fracture, and the cutting properties do not change, such as aluminum oxide.

(3) The cutting force continuously decreases with the increase of temperature, and at a certain temperature, the cutting ability of the material changes, and the roughness of the machined surface is improved, such as zirconia.

Plasma heating poses certain difficulties for ceramic materials because ceramic workpieces are not conductive and cannot directly serve as cathodes. If non transfer arc heating is used, the heat flux density is insufficient. The non-metallic hard and brittle materials have strong thermal sensitivity, and the plasma arc will produce certain Thermal shock effect, making it difficult to guarantee the processing quality; When plasma arc heating assisted cutting, the hot spot must be at a certain distance from the tool, and the heating effect is difficult to control. Tian Xinli of the Armoured reconnaissance Engineering College and others tried to draw out the plasma arc with the maximum current of 100A by the auxiliary electrode method, and then heat the alumina ceramic coating with the inertia flame pocket at the exit, which can realize the turning of the ceramic coating, but for structural ceramics, the density of the plasma heat source needs to be greatly increased. In early 2006, Tian Xinli, Lu Fang, and others attempted to use a self-developed new type of water medium plasma arc equipment for arc heating assisted cutting of silicon nitride ceramic materials. The experiment found that using plasma arc assisted heating cutting can reduce cutting force and cutting heat during the cutting process, and this method has certain feasibility.

The volume of the plasma generator is relatively large, and its heating point needs to be at a certain distance from the cutting point; The generation of plasma relies on the discharge of the electrode, so there is erosion of the electrode during operation; Plasma emits harmful gases during operation, and protection should be taken during use; Plasma heating has no special requirements for the absorption rate of the working surface and the transmittance of the material, which is a major advantage compared to laser heating; In addition, plasma heating devices are much cheaper than lasers.

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