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4. Coating tool material

The coating treatment of the tool is one of the important ways to improve the performance of the tool. The emergence of coated tools has made a major breakthrough in cutting performance. Coated tools are coated with one or more layers of refractory compounds with good wear resistance on the tool body with good toughness. It combines the tool substrate with the hard coating, so that the tool performance is greatly improved. Coated tools can improve processing efficiency, improve processing accuracy, extend tool life, and reduce processing costs.

About 80% of the cutting tools used in the new CNC machine tools use coated tools. Coated cutting tools will be an important tool in the field of CNC machining in the future.

(1) Types of coated tools

According to different coating methods, coated tools can be divided into chemical vapor deposition (CVD) coated tools and physical vapor deposition (PVD) coated tools. Coated carbide tools generally use chemical vapor deposition method, the deposition temperature is about 1000 ℃. Coated high-speed steel tools generally use physical vapor deposition method, the deposition temperature is about 500 degrees C;

According to the different substrate materials of coated tools, coated tools can be divided into carbide coated tools, high-speed steel coated tools, and coated tools on ceramics and superhard materials (diamond and cubic boron nitride).

According to the nature of the coating material, coated tools can be divided into two categories, namely, "hard" coated tools and 'soft' coated tools. The main goal of "hard" coated tools is high hardness and wear resistance, and its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal of "soft" coated tools is to pursue a low coefficient of friction, also known as self-lubricating tools. The coefficient of friction with the workpiece material is very low, only about 0.1, which can reduce bonding, reduce friction, and reduce cutting force and cutting temperature.

A nano-coated (Nanoeoating) tool was developed. This coated tool can use a variety of different combinations of coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. Reasonable design of nano-coating can make the tool material has excellent anti-friction and anti-wear function and self-lubricating performance, suitable for high-speed dry cutting.

(2) Characteristics of coated tools

Good mechanical and cutting properties: The coated tool combines the excellent properties of the substrate material and the coating material, which not only maintains the good toughness and high strength of the substrate, but also has the high hardness, high wear resistance and low friction coefficient of the coating. Therefore, the cutting speed of coated tools can be increased by more than 2 times than that of uncoated tools, and a higher feed rate is allowed. The life of the coated tool is also improved.

The versatility of the coating tool is wide, the processing range is significantly expanded, a coating tool can be used instead of several non-coated tools.

The coating thickness: with the increase of the coating thickness of the tool life will increase, but when the coating thickness reaches saturation, the tool life is no longer significantly increased. When the coating is too thick, it is easy to cause peeling; when the coating is too thin, the wear resistance is poor.

④ heavy grinding: coating blade heavy grinding poor, complex coating equipment, high process requirements, long coating time.

The coating material: different coating materials, cutting performance is not the same. Such as: low speed cutting, TiC coating advantage; high speed cutting, TiN is more appropriate.

Application of coated cutting tools

Coated cutting tools have great potential in the field of CNC machining and will be an important tool in the field of CNC machining in the future. Coating technology has been applied to end mills, reamers, drill bits, composite hole machining tools, gear hobs, gear shaper cutters, shaving cutters, forming broaches and various machine-clamped indexable inserts to meet the needs of high-speed cutting of various steel and cast iron, heat-resistant alloys and non-ferrous metals.

5. Carbide tool material

Carbide tools, especially indexable carbide tools, are the leading products of CNC machining tools. Since the 1980 s, the varieties of various integral and indexable carbide tools or inserts have been extended to various cutting tools. In the field of cutting tools, the indexable carbide tools have been expanded from simple turning tools and face milling cutters to various precision, complex and forming tools.

(1) Types of carbide cutting tools

According to the main chemical composition, cemented carbide can be divided into tungsten carbide based cemented carbide and carbon (nitrogen) titanium (TiC(N)) based cemented carbide.

Tungsten carbide-based hard alloys include tungsten cobalt (YG), tungsten cobalt titanium (YT), and rare carbide (YW). They have their own advantages and disadvantages. The main components are tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), etc. The commonly used metal bonding phase is Co.

Carbon (nitrogen) titanium-based hard alloy is a hard alloy with TiC as the main component (some add other carbides or nitrides), and the commonly used metal bonding phase is Mo and Ni.

ISO (International Organization for Standardization) divides cemented carbide for cutting into three categories:

Class K, including Kl0 ~ K40, is equivalent to China's YG class (the main component is WC.Co).

P class, including P01 ~ P50, is equivalent to China's YT class (the main component is WC.TiC.Co).

M class, including M10 ~ M40, is equivalent to China's YW class (the main component is WC-TiC-TaC(NbC)-Co).

Each grade is represented by a series of alloys with numbers between 01 and 50 from high hardness to greater toughness.

The performance characteristics of carbide cutting tools

① high hardness: cemented carbide cutting tool is made by high hardness and melting point of carbide (called hard phase) and metal binder (called bonding phase) by powder metallurgy method, its hardness of 89 ~ 93HRA, far higher than high speed steel, at 5400C, the hardness can still reach 82 ~ 87HRA, and high speed steel at room temperature hardness (83 ~ 86HRA) the same. The hardness value of cemented carbide varies with the nature, quantity, particle size of carbide and the content of metal bonding phase, and generally decreases with the increase of the content of metal bonding phase. When the content of the bonding phase is the same, the hardness of YT alloy is higher than that of YG alloy, and the alloy with TaC(NbC) has higher high temperature hardness.

Bending strength and toughness: The bending strength of commonly used cemented carbide is in the range of 900 ~ 1500MPa. The higher the content of the metallic binder phase, the higher the flexural strength. When the binder content is the same, the strength of YG (WC-Co) alloy is higher than that of YT (WC-TiC-Co) alloy, and the strength decreases with the increase of TiC content. Cemented carbide is a brittle material, and its impact toughness at room temperature is only 1/30~1/8 of high-speed steel.

Application of Common Cemented Carbide Cutting Tools

YG alloys are mainly used for processing cast iron, non-ferrous metals and non-metallic materials. Fine grain cemented carbide (such as YG3X, YG6X) has higher hardness and wear resistance than medium grain at the same cobalt content. It is suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloy, titanium alloy, hard bronze and wear-resistant insulating materials.

The outstanding advantages of YT cemented carbide are high hardness, good heat resistance, high temperature hardness and compressive strength than YG, good oxidation resistance. Therefore, when the tool is required to have higher heat resistance and wear resistance, the brand with higher TiC content should be selected. YT alloy is suitable for processing plastic materials such as steel, but it is not suitable for processing titanium alloy, silicon aluminum alloy.

YW alloy has the performance of YG, YT alloy, good comprehensive performance, it can be used for processing steel, but also can be used for processing cast iron and non-ferrous metals. If the cobalt content is appropriately increased, the strength of this kind of alloy can be very high, and it can be used for roughing and intermittent cutting of various difficult-to-machine materials.

6. High speed steel cutter

High Speed Steel (HSS) is a kind of high alloy tool steel with more W, Mo, Cr, V and other alloying elements. High-speed steel tools in the strength, toughness and technology and other aspects of excellent comprehensive performance, in the complex tool, especially in the manufacture of hole machining tools, milling cutters, thread tools, broach, cutting tools and other complex blade tool, high-speed steel still occupy the main position. High-speed steel tools are easy to grind out sharp cutting edges.

According to different purposes, high-speed steel can be divided into general-purpose high-speed steel and high-performance high-speed steel.

⑴ General-purpose high-speed steel cutter

General purpose high speed steel. Generally can be divided into two types of tungsten steel, tungsten and molybdenum steel. This kind of high speed steel containing (C) is 0.7~0.9%. According to the different tungsten content in steel, it can be divided into tungsten steel containing 12% or 18% W, tungsten molybdenum steel containing 6% or 8% W, and molybdenum steel containing 2% or no W. General-purpose high-speed steel has a certain hardness (63-66HRC) and wear resistance, high strength and toughness, good plasticity and processing technology, so it is widely used in the manufacture of various complex tools.

① Tungsten steel: The typical grade of general-purpose high-speed steel tungsten steel is W18Cr4V (W18 for short), which has good comprehensive performance and high temperature hardness of 48.5HRC at 6000C, which can be used to manufacture various complex tools. It has the advantages of good grindability and low decarburization sensitivity, but due to the high carbide content, uneven distribution, large particles, low strength and toughness.

2 tungsten and molybdenum steel: refers to a part of tungsten in tungsten steel with molybdenum instead of a high-speed steel. The typical grade of tungsten molybdenum steel is W6Mo5Cr4V2 (M2 for short). The carbide particles of M2 are fine and uniform, and the strength, toughness and high temperature plasticity are better than W18Cr4V. Another kind of tungsten molybdenum steel is W9Mo3Cr4V steel (W9 for short), its thermal stability is slightly higher than M2 steel, bending strength and toughness are better than W6M05Cr4V2 steel, and it has good processability.

(2) High-performance high-speed steel cutting tools

High-performance high-speed steel refers to a new steel that adds some carbon content, vanadium content and Co, Al and other alloying elements to the general-purpose high-speed steel composition, which can improve its heat resistance and wear resistance. There are mainly the following categories:

① High carbon high speed steel. High-carbon high-speed steel (such as 95 W18Cr4V), room temperature and high temperature hardness, suitable for manufacturing and processing of ordinary steel and cast iron, high wear resistance requirements of drill bits, reamers, taps and milling cutters, etc. or processing of harder materials, should not withstand large impact.

② high vanadium high speed steel. Typical brands, such as W12Cr4V4Mo,(EV4 for short), contain V up to 3%-5%, have good wear resistance, and are suitable for cutting materials with great tool wear, such as fiber, hard rubber, plastic, etc., and can also be used for processing stainless steel, high-strength steel, high-temperature alloy and other materials.

Cobalt high speed steel. It is a cobalt-containing superhard high-speed steel, a typical brand, such as W2Mo9Cr4VCo8 (M42), with high hardness, its hardness can reach 69-70HRC, which is suitable for processing high-strength heat-resistant steel, high-temperature alloy, titanium alloy and other difficult-to-machine materials. M42 has good grindability and is suitable for making precision and complex tools, but it is not suitable for working under impact cutting conditions.

④ Aluminum high speed steel. It is an aluminum-containing superhard high-speed steel with typical brands, such as W6Mo5Cr4V2Al (501 for short), and its high-temperature hardness at 6000C also reaches 54HRC, and its cutting performance is equivalent to M42. It is suitable for manufacturing milling cutters, drill bits, reamers, gear cutters, broaches, etc. and is used for processing alloy steel, stainless steel, high-strength steel, high-temperature alloy and other materials.

⑤ nitrogen superhard high speed steel. Typical grades, such as W12M03Cr4V3N, referred to as (V3N), are nitrogen-containing superhard high-speed steel, hardness, strength, toughness and M42, can be used as a substitute for cobalt-containing high-speed steel, used for low-speed cutting of difficult-to-process materials and low-speed high-finish processing.

(3) Melting high speed steel and powder metallurgy high speed steel

According to different manufacturing processes, high-speed steel can be divided into smelting high-speed steel and powder metallurgy high-speed steel.

① smelting high-speed steel: ordinary high-speed steel and high-performance high-speed steel are manufactured by smelting method. They are made into cutting tools through smelting, ingot casting and plating rolling. The serious problem of melting high-speed steel is carbide segregation, hard and brittle carbides are not evenly distributed in high-speed steel, and the grains are coarse (up to tens of microns), which has a negative impact on the wear resistance, toughness and cutting performance of high-speed steel tools.

② Powder metallurgy high speed steel (PM HSS): Powder metallurgy high speed steel (PM HSS) is a molten steel melted in a high-frequency induction furnace, atomized with high-pressure argon or pure nitrogen, and then quenched to obtain a fine and uniform crystal structure (high-speed steel powder), and then the obtained powder is pressed into a blank at high temperature and high pressure, or the blank is first made into a blank and then forged and rolled into a tool shape. Compared with high-speed steel manufactured by melting method, PM HSS has the advantages that the carbide grains are fine and uniform, and the strength, toughness and wear resistance are improved a lot compared with melting high-speed steel. In the field of complex NC tool PM HSS tool will be further development and occupy an important position. Typical grades, such as F15, FR71, GF1, GF2, GF3, PT1, PVN, etc., can be used to manufacture large size, bear heavy load, large impact tools, can also be used to manufacture precision tools.