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CNC machining tool basic knowledge (III)

Release time： 2023-06-15 10:12:48.735

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Selection Principle of 3. NC Tool Material

At present, the widely used CNC tool materials mainly include diamond tools, cubic boron nitride tools, ceramic tools, coated tools, carbide tools and high-speed steel tools. There are many total grades of tool materials, and their performance varies greatly. The following table shows the main performance indicators of various tool materials.

The main performance indicators of various tool materials

The tool material for CNC machining must be selected according to the workpiece and the nature of the machining. The selection of tool materials should be reasonably matched with the processing object, and the matching of cutting tool materials and processing objects mainly refers to the matching of mechanical properties, physical properties and chemical properties of the two.

1. Matching the mechanical properties of the cutting tool material and the machining object

The problem of matching the mechanical properties of the cutting tool and the processing object mainly refers to the matching of the mechanical properties parameters such as the strength, toughness and hardness of the tool and the workpiece material. Tool materials with different mechanical properties are suitable for processing different workpiece materials.

① Tool material hardness sequence: diamond tools> cubic boron nitride tools> ceramic tools> carbide> high speed steel.

The order of the bending strength of the tool material is: high-speed steel> cemented carbide> ceramic tools> diamond and cubic boron nitride tools.

The order of the toughness of the tool material is: high-speed steel> cemented carbide> cubic boron nitride, diamond and ceramic tools.

The workpiece material with high hardness must be processed with a higher hardness tool, and the hardness of the tool material must be higher than the hardness of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better its wear resistance. For example, when the amount of cobalt in cemented carbide increases, its strength and toughness increase, and its hardness decreases, which is suitable for roughing; when the amount of cobalt decreases, its hardness and wear resistance increase, which is suitable for finishing.

Cutting tools with excellent high-temperature mechanical properties are particularly suitable for high-speed machining. The excellent high temperature performance of ceramic tools enables them to cut at a high speed, and the allowable cutting speed can be increased by 2 to 10 times compared with cemented carbide.

2. The cutting tool material matches the physical properties of the processed object

Tools with different physical properties, such as high thermal conductivity and low melting point of high-speed steel tools, high melting point and low thermal expansion of ceramic tools, high thermal conductivity and low thermal expansion of diamond tools, etc., are suitable for the processing of workpiece materials are different. When machining workpieces with poor thermal conductivity, the tool material with good thermal conductivity should be used to make the cutting heat quickly pass out and reduce the cutting temperature. Due to the high thermal conductivity and thermal diffusion rate of diamond, the cutting heat is easy to dissipate and will not produce great thermal deformation, which is particularly important for precision machining tools with high dimensional accuracy.

① Heat-resistant temperature of various tool materials: diamond tools are 700 ~ 8000C, PCBN tools are 13000 ~ 15000C, ceramic tools are 1100 ~ 12000C, TiC(N)-based cemented carbide is 900 ~ 11000C, WC-based ultrafine grain cemented carbide is 800 ~ 9000C, HSS is 600 ~ 7000C.

The thermal conductivity of various tool materials: PCD>PCBN>WC-based cemented carbide> TiC(N)-based cemented carbide> HSS>Si3N4-based ceramics> A1203-based ceramics.

③ The order of thermal expansion coefficient of various tool materials is: HSS>WC-based cemented carbide> TiC(N)> A1203-based ceramics> PCBN>Si3N4-based ceramics> PCD.

④ The order of thermal shock resistance of various tool materials is: HSS>WC-based cemented carbide> Si3N4-based ceramics> PCBN>PCD>TiC(N)-based cemented carbide> A1203-based ceramics.

3. Matching the chemical properties of cutting tool materials and processing objects

The problem of matching the chemical properties of cutting tool materials and processing objects mainly refers to the matching of chemical properties parameters such as chemical affinity, chemical reaction, diffusion and dissolution of tool materials and workpiece materials. Different materials of the tool for the processing of the workpiece material is different.

① The anti-bonding temperature of various tool materials (with steel) is: PCBN> ceramic> cemented carbide> HSS.

The oxidation temperature of various tool materials is: ceramic> PCBN> cemented carbide> diamond> HSS.

The diffusion strength of the tool material (for steel) is: diamond> Si3N4 based ceramics> PCBN>A1203 based ceramics. The diffusion strength (for titanium) is: A1203 based ceramics> PCBN>SiC>Si3N4> diamond.

4. Reasonable choice of CNC tool materials

In general, PCBN, ceramic tools, coated carbide and TiCN-based carbide tools are suitable for CNC machining of ferrous metals such as steel, while PCD tools are suitable for the processing of non-ferrous metal materials such as Al, Mg, Cu and their alloys and non-metallic materials. The following table lists some of the workpiece materials that are suitable for machining with the above tool materials.

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In addition, the round nose cutter has better processing efficiency than ball cutter and end mill, especially in rough machining. Because the bottom of the round nose knife is flat, the horizontal knife spacing of the round nose knife can be used larger than the ball knife. In finishing, it also has the same advantages as the ball knife, so the knife spacing can also be used in larger values. Therefore, the round nose cutter is a very suitable choice for roughing and finishing.

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The choice of tool material has a great influence on tool life, machining efficiency, machining quality and machining cost. Cutting tool to withstand high pressure, high temperature, friction, impact and vibration and other effects. Therefore, the tool material should have the following basic properties: