When using ceramic tools to process difficult-to-machine materials such as ordinary steel, cast iron, hardened steel, high manganese steel, nickel-based superalloys, powder metallurgy sintered parts, glass fiber reinforced plastics, and various engineering plastics, the tool life can be several times higher than that of cemented carbide tools.
Ceramic tools have a slight affinity with metal materials such as steel, with low friction coefficient, strong anti-adhesion, and anti-diffusion capabilities. They are not easy to stick to the tool and generate built-up edges during cutting, and the machined surface quality is good.
Most of the modern ceramic tool materials are composite ceramics, and different toughening and strengthening mechanisms are used to design the microstructure. Among them, alumina (Al2O3)-based and silicon nitride (Si3N4)-based ceramic tool materials are the most widely used.
This paper mainly introduces Al2O3/SiCw whisker toughened ceramics.
Add 20% to 30% SiCw whiskers to the Al2O3 ceramic matrix (single crystals with a diameter of fewer than 0.6 μm and a length of 10 to 80 μm, with a certain fiber structure, a tensile strength of 7 GPa, and a tensile elastic modulus of more than 700 GPa ), the Al2O3/SiCw whisker toughened ceramics.
Can be effectively used for interrupted cutting and rough turning, milling, and reaming operations. Suitable for machining nickel-based alloys, high-hardness cast iron, and hardened steel. Siew whiskers act like steel bars in reinforced concrete and can become obstacles to block or change the development of cracks, which greatly improves their toughness.
Due to the high brittleness and low strength of ceramic tool materials, the rake angle of the tool is usually 0° to -10°, and the clearance angle is 5° to 12°.
In order to improve the strength of the cutting edge, a negative chamfer must be ground on the cutting edge. The width of the chamfer can be taken as b =0.1～0.8 mm, and the rake angle of the chamfer is -10°～-20°; the tooltip needs to be rounded properly, and the rounding radius r = 0.2 ~ 1.0mm.
However, the larger the tool nose rounding radius and the negative chamfer, the greater the cutting force and the greater the chance of chattering.
Therefore, when the rigidity of the machine tool-fixture-tool-workpiece system is insufficient, especially when processing slender workpieces, it is not appropriate to use an excessively large tool nose radius and negative chamfering.
Using lower cutting speeds increases tool life. Cutting speed, turning ordinary steel and cast iron, generally Vc = 200 ~ 600 m/min; machining high hardness steel with a hardness of 65HRC, Vc = 60 ~ 200 m/min; milling steel and cast iron Vc = 200 ~ 500 m/min; milling Heat-resistant alloy Vc=100～250 m/min, feed rate 0.05～0.08 mm/z.