The development of modern manufacturing technology and the extensive use of CNC machining equipment have greatly promoted the advancement of cutting technology. With the need for numerical control and automation of production and processing, the appearance of superalloys, titanium alloys and composite materials containing carbon fibers is more demanding on the quality of metal cutting tools, high reliability, high precision, long life and fast. The replacement of the index, the good chip breaking, etc., the hot hardness of the tool and the problem of tool wear become the key to the cutting process.
1. Common tool wear patterns
In the cutting process, the tool wear that usually occurs includes the following three forms:
The first type is wear due to mechanical action, such as chipping or abrasive wear;
The second type of wear due to the heat of cutting, such as bonding, diffusion, etc.;
The third type is due to chemical factors such as softening of the cutting edge, breakage caused by melting, thermal fatigue, thermal cracking, and the like.
(1) Causes of mechanical wear
When cutting difficult-to-machine materials, tool wear occurs in a short period of time due to the presence of more tool wear in the material being machined. Most difficult-to-machine materials have the characteristics of low thermal conductivity. As a result of this effect, the bond strength of the binder in the tool material is lowered at high temperatures, thereby accelerating tool wear.
(2) Wear caused by cutting heat
The cutting edge temperature is high when cutting high hardness and high toughness materials, and there is also a similar tool wear when cutting difficult materials. In particular, when machining a workpiece material that produces short chips, crater wear occurs near the cutting edge, and tool breakage often occurs in a short period of time.
(3) Wear caused by chemical factors
The components in the difficult-to-machine materials and some of the tool materials react under high-temperature cutting conditions, appear to be analyzed, detached, or form other compounds, which accelerates the formation of tool wear such as chipping.
2. The performance requirements of cutting tools
(1) Wear resistance
The metal cutting tools used today vary in material, from high-speed steel with the lowest cutting speed and the lowest wear resistance to the most high-quality poly crystalline diamond tools.
(2) Impact resistance
It has good impact toughness and high-speed cutting tools with extremely high thermos-hardness and chemical stability.
(3) Service life
The use of a coating material with high heat resistance and high hardness and a multi-layer coating technology make the coated carbide tool have a large cutting range and a long service life.
3. Commonly used tool materials
(1) alloy tool steel
It has high heat hardness but is inexpensive, and is often used to make low-speed tools with complex shapes such as reamer, tap and die.
(2) High speed tool steel
Its high temperature hardness and wear resistance are better than alloy tool steel. Due to its good heat treatment performance, high strength and good sharpness, it is widely used in the manufacture of various machine tools such as forming turning tools, milling cutters, drill bits and broaches.
(3) Cemented carbide
It is an alloy made by powder metallurgy of materials such as tungsten carbide, titanium carbide and cobalt. Carbide inserts are usually used on the body of the tool. Currently, cemented carbide has become one of the main tool materials.
In order to prevent the tool from wearing too fast, special cutting fluid should be selected, which has the following advantages:
(1) Improve process precision The special cutting fluid contains vulcanized extreme pressure anti-wear additive components, which can effectively protect the tool and improve the process precision.
(2) In accordance with the process requirements, special cutting fluids have passed rigorous tests in terms of viscosity, flash point, pour point and thermal conductivity to meet various cutting process requirements.
(3) Good environmental performance Special cutting fluid has good stability compared with rapeseed oil, mechanical oil and reclaimed oil, and will not cause harm to equipment, human body and environment.