The development of modern manufacturing technology and the widespread use of CNC machining equipment have greatly promoted the advancement of cutting technology. With the need for numerical control and automation in the production and processing process, the emergence of super heat-resistant alloys, titanium alloys and carbon fiber-containing composite materials, etc., have more stringent requirements for the quality of metal cutting tools, high reliability, high precision, long life, and fast speed. Indexing replacement, good chip breaking, etc., the thermal hardness of the tool and tool wear problems have become the key to the cutting process.
Common tool wear patterns
In cutting, the tool wear that usually occurs includes the following three forms:
The first type is worn due to mechanical action, such as chipping or abrasive wear;
The second type of wear due to cutting heat, such as adhesion, diffusion, etc.;
The third type is a fracture, thermal fatigue, and thermal cracking caused by the softening and melting of the cutting edge caused by chemical factors.
1) Causes of mechanical wear
When cutting difficult-to-machine materials, tool wear occurs in a short period of time. This is due to the fact that there are many factors that promote tool wear in the processed material. Most difficult-to-machine materials have the characteristics of low thermal conductivity. As a result of this effect, the bonding strength of the binder in the tool material will decrease at high temperatures, thereby accelerating tool wear.
2) Wear caused by cutting heat
When cutting materials with high hardness and high toughness, the temperature of the cutting edge is very high, and similar tool wear will also occur when cutting difficult-to-machine materials. Especially when machining workpiece materials that generate short chips, craters wear near the cutting edge, and tool breakage often occurs in a short time.
3) Wear caused by chemical factors
The components in the difficult-to-machine materials and some components in the tool materials react undercutting high-temperature conditions, and the components appear, fall off, or generate other compounds, which will accelerate the formation of chipping and other tool wear phenomena.
Performance requirements of cutting tools
1) Wear resistance
The metal cutting tool materials used today are different, from high-speed steel with the lowest cutting speed and worst wear resistance to polycrystalline diamond tools with the best high-speed performance.
2) Impact resistance
Has relatively good impact toughness, in addition, high-speed cutting tools must have extremely high thermal hardness and chemical stability.
3) Service life
The use of coating materials with good heat resistance and high hardness and multi-layer coating technology enables the coated carbide tools to have a large cutting range and long life.
Commonly used tool materials
1) Alloy tool steel
It has high thermal hardness but a low price. It is often used to manufacture low-speed tools with complex shapes, such as reamers, taps and dies.
2) High-speed tool steel
Its high-temperature hardness and wear resistance are better than alloy tool steel. Because of its good heat treatment performance, high strength and good sharpening properties, it is widely used in the manufacture of forming turning tools, milling cutters, drills and broaches and other machine tools.
3) Cemented carbide
It is an alloy made of tungsten carbide, titanium carbide and cobalt by powder metallurgy. Usually, the cemented carbide insert is fixed on the tool body for use. At present, cemented carbide has become one of the main tool materials.