Types and Performance Comparison of CNC Cutting Tool Materials Used in CNC Machine Tools

Types and Performance Comparison of Cutting Tool Materials Used in CNC Machine Tools

Currently, the cutting tool materials used in CNC machine tools mainly include high-speed steel, cemented carbide, ceramics, cubic boron nitride (CBN), and polycrystalline diamond (PCD).

(1) High-Speed Steel:

High-speed steel is a high-alloy tool steel that contains a significant amount of tungsten, molybdenum, chromium, vanadium, and other alloying elements. It exhibits high thermal stability, strength, toughness, a certain level of hardness, and wear resistance. It can maintain high hardness even at temperatures up to 600°C. Depending on the application, high-speed steel can be classified into general-purpose high-speed steel and high-performance high-speed steel.

General-purpose high-speed steel is widely used for manufacturing various complex cutting tools and can cut structural steels and cast iron materials with hardness below 250-280 HBS. Typical grades include W18Cr4V (also known as W18), W14Cr4VMnXt, W6M05Cr4v2 (also known as M2), and W9Mo3Cr4V (also known as W9). High-performance high-speed steels include high-carbon high-speed steel, high-vanadium high-speed steel, cobalt high-speed steel, and super-hard high-speed steel. These high-performance grades have a tool life approximately 1.5 to 3 times longer than general-purpose high-speed steel tools and are suitable for machining difficult-to-cut materials, such as super-high-strength materials. Typical grades include W2Mo9Cr4Vo8 (M42), which is the most widely used cobalt-containing super-hard high-speed steel, offering excellent overall performance, and W6Mo5Cr4V2AI and W10Mo4Cr4V3AI (5F-6), two aluminum-containing super-hard high-speed steels known for their excellent cutting performance.

(2) Cemented Carbide:

Cemented carbide is produced by sintering hard refractory metal carbides like tungsten carbide (WC), tungsten-titanium carbide (WC-TiC), tungsten-tantalum carbide (WC-TiC-TaC), with a metal binder like cobalt (Co) or nickel (Ni).

According to the ISO standard, cemented carbide used for cutting tools is classified into three classes based on hardness, flexural strength, and other parameters: Class P (equivalent to YT class in China), Class K (equivalent to YG class in China), and Class M (equivalent to YW class in China). These classes are further divided with numbers like 01, 05, 10, 20, 30, 40, 50, etc., where smaller numbers indicate higher hardness but lower toughness, and larger numbers indicate higher toughness but lower hardness.

Coated cemented carbide tools have a wear-resistant layer of hard refractory metal compounds, such as TiC, YiN, YiCN, TiB2, ZrO2, and Al2O3, deposited on a tough cemented carbide or high-speed steel substrate. Coating thickness typically ranges from 0.005 to 0.015mm.

There are two main methods of coating cemented carbide tools: Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD). CVD involves depositing various compounds on the tool surface through chemical reactions at temperatures around 1000°C. PVD involves spraying metal and gas ions on the tool surface at temperatures below 550°C.

Coated cemented carbide tools have excellent hardness, oxidation resistance, anti-adhesion properties, and low friction coefficients, resulting in high wear resistance and the ability to reduce cutting forces and temperatures. This allows for higher cutting speeds and feeds, significantly improving production efficiency.

(3) Ceramic Cutting Tool Materials:

There are many varieties of ceramic cutting tool materials, broadly categorized into the following three types based on their main constituents:

1. Alumina-based ceramics: These ceramics have high hardness and wear resistance, but they are brittle with low flexural strength and poor resistance to thermal shocks. They are commonly used for high-speed precision machining of cast iron and quenched steels.
2. Silicon Nitride-based ceramics: These ceramics have improved flexural strength and fracture toughness compared to alumina-based ceramics, and they also exhibit good resistance to thermal shocks. They perform well in processing hardened steel, chilled cast iron, graphite products, and fiberglass-reinforced materials.
3. Composite Silicon Nitride and Alumina (Si3N4+Al2O3) ceramics: This material offers excellent high-temperature resistance, thermal shock resistance, and mechanical impact resistance, making it an ideal tool for machining cast iron materials. It allows for large feed rates and high cutting speeds, significantly improving productivity.

(4) Cubic Boron Nitride (CBN):

CBN is a new synthetic material created using ultra-high pressure and high-temperature techniques, and its structure is similar to that of diamond. CBN's hardness is slightly lower than diamond but its thermal hardness is significantly higher, and it has a lower affinity with iron elements, making it less prone to chip adherence during machining.

(5) Polycrystalline Diamond (PCD):

PCD tools are made from artificial diamond particles, combined with CO, hard metal containing cobalt, NiCr, Si-SiC, and ceramic binders, sintered and formed at high temperatures (around 1200°C). They have found wide application in various fields.

In general, among the mentioned cutting tool materials, diamond has the highest hardness and wear resistance, followed by CBN, ceramics, cemented carbide, and high-speed steel in decreasing order. Regarding toughness, high-speed steel has the highest toughness, followed by cemented carbide, ceramics, CBN, and diamond. Coated cutting tool materials exhibit excellent practical performance and are an important means to achieve a combination of high hardness and toughness in cutting tools. Among them, cemented carbide is currently the most widely used cutting tool material in CNC machine tools due to its overall advantages in terms of economics, adaptability, versatility, and processability when compared to ceramics, CBN, and PCD.

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