Wear mechanism of ceramic tool in cutting

In the cutting process of ceramic tools, there are always two friction pairs, that is, the friction pair between the rake face and the chip and the friction pair between the rake face and the workpiece. Among them, the former affects the wear of the front tool surface, while the latter affects the wear of the back tool surface and the quality of the machined surface. The wear of the front and back tool surfaces both affect the tool life. Ceramic tools are mainly used for high-speed cutting. The cutting temperature is often as high as 800~1000 ℃ (even higher), and the cutting pressure is also very high. Therefore, the wear of ceramic tools is the result of the combined action of mechanical wear and chemical wear, and its wear mechanisms mainly include abrasive wear, adhesive wear, chemical reaction, diffusion wear, oxidation wear, etc. The existing research shows that the wear of ceramic tools is closely related to the cutting conditions. When different ceramic tool materials process different workpiece materials under different cutting conditions, the dominant wear mechanism may be different. When cutting at low speeds, the wear mechanism often manifests as abrasive wear due to the lower cutting temperature; In high-speed cutting, adhesive wear, chemical reaction, oxidation wear, and diffusion wear caused by high temperature are the main causes.

The wear mechanism of Al2O3 based ceramic tool in continuous cutting steel parts is mainly abrasive wear with micro chipping edge and adhesive wear, while in cutting cast iron it is mainly abrasive wear. Wayne and Brandt et al. concluded that abrasive wear and adhesive wear are the main wear mechanisms of ceramic tools under low speed cutting conditions through their research on machining Inconel 718 materials with Al2O3/SiCw ceramic tools; Under the condition of high-speed cutting, adhesive wear, chemical reaction wear and diffusion wear are the main wear mechanisms of ceramic tools. Due to the high high-temperature strength, large plastic deformation, severe work hardening, and high cutting force and temperature of Inconel718 material. When the cutting temperature is less than 900 ℃, the front face of the tool is mainly subject to adhesive wear; When the temperature reaches 1200 ℃, Ni begins to diffuse towards the center of the tool. Due to the diffusion of Ni, on the one hand, the surface hardness of the tool material decreases and its performance decreases; On the other hand, it increases the affinity between the tool and the workpiece, leading to increased adhesive wear.

When machining Inconel 718 with Al2O3/SiCw ceramic tools, Cutting fluid must be used (Cutting fluid containing Chlorinated paraffins is better). Casto et al. concluded that the wear mechanism of the tool is mainly adhesive wear and abrasive wear by studying the processing of AISI1040 material with Al2O3/ZrO2 ceramic tools, while there are serious chemical reactions on the tool surface when Si3N4 ceramic tools are used to process AISI1040 steel. When machining AISI4337 steel with Al2O3/ZrO2 and Al2O3/TiCN ceramic tools, the wear mechanisms of the front and rear tool surfaces are different. Chemical reactions and plastic deformation are the main reasons for the wear of the front blade surface, while the wear mechanism of the rear blade surface is caused by the fracture between ceramic particles, which leads to the detachment of ceramic particles. Brandt found the plastic deformation of the surface layer when cutting Al2O3 based ceramic tools, and believed that this was due to the reaction of Al2O3 with FeO (steel surface oxidation products) or MgO (ceramic additives) to form a spinel structure, or the interaction of Al2O3 with SiO2 and CaO to form a compound with low melting point and low hardness. The author's research shows that Al2O3/TiB2 ceramic tools have good wear resistance when machining high-strength steel and hardened steel. With the increase of TiB2 content, the wear resistance of the tools increases.

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