CNC Tool Materials and Selection Guide

Advanced processing equipment and high-performance CNC tooling to give full play to its due performance, and achieve good economic benefits. With the rapid development of tool materials, a variety of new tool materials, its physical, mechanical properties and cutting performance have been greatly improved, the scope of application is also expanding. Today we will learn about the tool materials and how to choose the tool.

I. Tool materials should have basic properties

The choice of tool material has a great impact on tool life, processing efficiency, processing quality and processing costs. Tool cutting to withstand high pressure, high temperature, friction, impact and vibration and other effects. Therefore, the tool material should have some of the following basic properties.

(1) Hardness and wear resistance. 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 the wear resistance.

(2) strength and toughness. Tool material should have high strength and toughness, in order to withstand the cutting force, impact and vibration, to prevent the tool brittle fracture and collapse of the blade.

(3) heat resistance. Tool materials should have good heat resistance, can withstand high cutting temperature, with good oxidation resistance.

(4) process performance and economy. Tool materials should have good forging performance, heat treatment performance, welding performance; grinding performance, but also to pursue high performance price ratio.

Properties and characteristics of layer tool materials and tool applications

Coating of tools is one of the most important ways to improve tool performance. The emergence of coated tools, so that the cutting tool performance has a major breakthrough. Coating tool is in the tougher body, coated with one or more layers of good abrasion resistance refractory compounds, which will combine the tool matrix and hard coating, thereby greatly improving the performance of the tool. Coating tooling can improve machining efficiency, improve machining accuracy, extend tool life, reduce processing costs.

New CNC machine tools used in cutting tools about 80% of the use of coating tool. Coating tool will be the future of CNC machining in the field of the most important varieties of cutting tools.

(1) types of coated tools

According to different coating methods, coating 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, deposition temperature of about 1000 ℃. Coated high-speed steel tools are generally used physical vapor deposition method, deposition temperature of 500 ℃ or so.

According to the different coating tool matrix material, coating tool can be divided into carbide coated tools, high-speed steel coated tools, and in ceramic and super-hard materials (diamond and cubic boron nitride) on the coating tool, etc..

According to the nature of the coating material, the coating tool can be divided into two categories, namely "hard" coated tools and 'soft' coated tools. "Hard" coating tool pursuit of the main goal is high hardness and wear resistance, its main advantage is high hardness, good wear resistance, typically TiC and TiN coating. "Soft" coated tools in pursuit of the goal is a low coefficient of friction, also known as self-lubricating tool, it and the workpiece material friction coefficient is very low, only about 0.1, can reduce the bonding, reduce friction, reduce the cutting force and cutting temperature.

Recently, nano-coated tools have been developed. This type of coating tool can use different combinations of various coating materials (e.g. metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. Rationally designed nano-coating can make the tool material has excellent friction reduction and anti-wear function and self-lubricating performance, suitable for high-speed dry cutting.

(2) Characteristics of coated tools

The performance characteristics of the coating tool are as follows.

① good mechanical and cutting performance: coated tool will be the base material and coating material of the excellent performance of the combination, not only to maintain the base of good toughness and high strength, but also has the high hardness of the coating, high wear resistance and low friction coefficient. As a result, the cutting speed of coated tools can be increased by more than two times compared to uncoated tools and allows for a higher feed rate. The life of the coated tool is also increased.

One type of coated tool can be used instead of several types of uncoated tools.

③ Coating thickness: With the increase of coating thickness will also increase tool life, but when the coating thickness reaches saturation, tool life will no longer increase significantly. When the coating is too thick, it is easy to cause peeling; when the coating is too thin, it has poor wear resistance.

④ Re-grinding property: poor regrinding property of coated blade, complex coating equipment, high process requirements and long coating time.

⑤ Coating material: different cutting tools with different coating materials will have different cutting performance. Such as: low speed cutting, TiC coating has the advantage; high speed cutting, TiN is more suitable.

(3) Application of coating tool

Coating tools in the field of CNC machining has great potential, will be the future of CNC machining in the field of the most important tool varieties. Coating technology has been applied to end milling cutters, reamers, drills, composite hole processing tools, gear hobs, gear shaping cutters, shaving cutters, shaping broaches and a variety of machine folder indexable inserts to meet the needs of high-speed machining of a variety of steel and cast iron, heat-resistant alloys and non-ferrous metals and other materials.

Types, properties, characteristics and applications of carbide cutting tool materials

Carbide cutting tools, especially indexable carbide cutting tools, is the leading product of CNC machining tools, since the 1980s, a variety of integral and indexable carbide cutting tools or insert varieties have been extended to a variety of cutting tool areas, which can be indexable carbide cutting tools by a simple turning tools, face milling cutters to expand to a variety of precision, complex, forming the field of cutting tools.

(1) Types of Cemented Carbide Cutting Tools

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

Tungsten carbide tungsten carbide includes tungsten cobalt (YG), tungsten cobalt titanium (YT), added rare carbides (YW) three categories, they have their own advantages and disadvantages, the main components of tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), the common metal bonding phase is Co.

Titanium carbide (nitrogen) carbide is a titanium carbide with TiC as the main component (some add other carbides or nitrides), the common metal bonding phases are Mo and Ni.

ISO (International Organization for Standardization) classifies cutting tungsten carbide into three categories.

K class, including Kl0-K40, equivalent to China's YG class (the main component of WC.TiC.Co).

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

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

Each grade is indicated by a number between 01 and 50 for a series of alloys ranging from high hardness to maximum toughness.

(2) The performance characteristics of the carbide tool

The performance characteristics of carbide tools are as follows.

①High hardness: Cemented carbide cutting tools are made by the high hardness and melting point of carbide (called hard phase) and metal binder (called adhesive phase) by powder metallurgy methods, the hardness of 89 ~ 93HRA, much higher than high-speed steel, at 5400C, the hardness is still up to 82 ~ 87HRA, and high-speed steel at room temperature hardness (83 ~ 86HRA) the same. The hardness value of the carbide varies with the nature, quantity, particle size and content of the metallic bonding phase, and generally decreases with the increase of the content of the bonding metallic phase. In the adhesive phase content is the same, YT alloy hardness is higher than the YG alloy, add TaC (NbC) alloy has a high temperature hardness.

② bending strength and toughness: the commonly used cemented carbide bending strength in the range of 900 ~ 1500MPa. The higher the content of the metallic adhesive phase, the higher the flexural strength. When the adhesive content is the same, the strength of the YG class (WC-Co) alloy is higher than the YT class (WC-TiC-Co) alloy, and with the increase in TiC content, the strength decreases. Cemented carbide is a brittle material, its impact toughness at room temperature is only 1/30 ~ 1/8 of high-speed steel.

(3) Commonly used cemented carbide tooling applications

YG-type alloys are mainly used for machining cast iron, non-ferrous and non-metallic materials. Fine grain carbide (such as YG3X, YG6X) in the same amount of cobalt content than the medium grain hardness and wear resistance is higher, suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloys, titanium alloys, hard bronze and wear-resistant insulation materials.

The outstanding advantages of YT class carbide are high hardness, good heat resistance, high temperature hardness and compressive strength than YG class, good oxidation resistance. YT class alloys are suitable for processing plastic materials such as steel, but should not be processed titanium alloy, silicon aluminum alloy.

YW class alloys both YG, YT class alloys performance, comprehensive performance, it can be used for processing steel, but also can be used for processing cast iron and non-ferrous metals. If the content of cobalt is increased appropriately, the strength of these alloys can be very high, and can be used for roughing and intermittent cutting of various difficult-to-process materials.

Types and characteristics of high-speed steel tools and applications

High Speed Steel (HSS) is a kind of high-alloy tool steel with more W, Mo, Cr, V and other alloy elements. HSS tools have excellent overall performance in strength, toughness and process, and still occupy a major position in complex cutting tools, especially in the manufacture of hole processing tools, milling cutters, threaded tools, broaches, gear cutting tools and other complex cutting edge shape. HSS tools are easy to grind a sharp cutting edge.

According to different applications, HSS can be divided into general-purpose HSS and high-performance HSS.

(1)General-purpose high-speed steel cutter

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

① Tungsten steel: general-purpose high-speed steel tungsten steel typical grade for W18Cr4V, (referred to as W18), with better overall performance, high temperature hardness of 48.5HRC at 6000 ℃, can be used to manufacture a variety of complex tools. It has the advantages of good grindability and small decarburization sensitivity, but due to higher carbide content, more uneven distribution, larger particles, strength and toughness is not high.

Tungsten molybdenum steel: is a part of the tungsten steel with molybdenum instead of a high-speed steel obtained. The typical tungsten-molybdenum steel grade is W6Mo5Cr4V2, (referred to as M2). m2 carbide particles are small and uniform, strength, toughness and high-temperature plasticity are better than W18Cr4V. Another tungsten-molybdenum steel for the W9Mo3Cr4V (referred to as W9), which is slightly more thermally stable than M2 steel, bending strength and toughness than W6M05Cr4V2 good, with good machinability.

(2) High-performance high-speed steel tools

High-performance high-speed steel refers to the general-purpose high-speed steel composition and then add some carbon content, vanadium content and add Co, Al and other alloying elements of the new steel, so that it can improve its heat resistance and wear resistance. The main categories are as follows.

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

High-vanadium high-speed steel. Typical grades, such as, W12Cr4V4Mo, (referred to as EV4), with V increased to 3% a 5%, good abrasion resistance, suitable for cutting tool wear on great materials, such as fibers, hard rubber, plastic, etc., can also be used for processing stainless steel, high-strength steel and high-temperature alloys and other materials.

③ Cobalt high-speed steel. Typical grade, such as W2Mo9Cr4VCo8, (M42 for short), has high hardness, and 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-process materials, M42 has good grinding properties, and is suitable for making precision and complex cutting tools, but should not be used in impact cutting conditions.

Aluminum high-speed steel. Typical grade, such as W6Mo5Cr4V2Al, (501 for short), has a high temperature hardness of 54HRC at 6000C, and its cutting performance is equivalent to M42. It is suitable for making milling cutters, drills, reamers, gear tools, broaches, etc. It is used for processing alloy steel, stainless steel, high strength steel and high temperature alloys and other materials.

⑤ Nitrogen super-hard high-speed steel. Typical grades, such as, W12M03Cr4V3N, referred to as (V3N), is a nitrogen-containing super-hard high-speed steel, hardness, strength, toughness and M42 is comparable, can be used as a substitute for cobalt high-speed steel, for low-speed cutting of difficult-to-process materials and low-speed high-precision machining.

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

According to different manufacturing process, HSS can be divided into melting HSS and powder metallurgy HSS.

①Melting high-speed steel: ordinary high-speed steel and high-performance high-speed steel are made by melting method. They have been smelted, cast ingots and plated rolling process to make tools. Melting HSS is prone to serious problems of carbide segregation, hard and brittle carbide in the HSS uneven distribution, and coarse grain (up to dozens of microns), on the HSS tool wear resistance, toughness and cutting performance adversely affected.

Powder metallurgy high-speed steel (PM HSS): Powder metallurgy high-speed steel (PMHSS) is a high-frequency induction furnace melting the liquid steel, high-pressure argon or pure nitrogen to make it atomized, and then quench to get small uniform crystalline tissue (HSS powder), and then the resulting powder at high temperature, high pressure pressed into a billet, or first made of billet and then forged, rolled into the shape of the tool. Compared with the molten HSS, PMHSS has the advantage of: carbide grain size and uniformity, strength and toughness, wear resistance relative to molten HSS are improved a lot. In the field of complex CNC tooling PMHSS tooling will be further developed and occupy an important position. Typical grades, such as F15, FR71, GFl, GF2, GF3, PT1, PVN, etc., can be used to manufacture large size, heavy load, impact of large tools, but also can be used to manufacture precision tools.

three. The principle of selection of CNC tool materials

Currently widely used CNC tool materials are mainly diamond tools, cubic boron nitride tools, ceramic tools, coated tools, carbide tools and high-speed steel tools. The total number of tool materials brand, its performance varies greatly. The following table is a variety of tool materials, the main performance indicators.

CNC machining tool materials must be processed according to the nature of the workpiece and processing to choose. The selection of tool material should be reasonably matched with the processing object, cutting tool material and processing object matching, mainly refers to the mechanical properties of the two, physical properties and chemical properties to match, in order to obtain the longest tool life and maximum cutting productivity. 1.

1 cutting tool material and the mechanical properties of the processing object match

Cutting tool and machining object mechanical properties matching problem is mainly refers to the tool and the workpiece material strength, toughness and hardness of mechanical properties parameters to match. Have different mechanical properties of the tool material suitable for machining the workpiece material is different.

① tool material hardness order: diamond tool> cubic boron nitride tool> ceramic tool> carbide> high-speed steel.

② The order of bending strength of tool material is: HSS > Carbide > Ceramic > Diamond and CBN.

③ The order of toughness of the tool material is: HSS > Carbide > Cubic Boron Nitride, Diamond and Ceramic tools.

High hardness workpiece materials must be machined 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 60 HRC. The higher the hardness of the tool material, the better its wear resistance. Such as, when the amount of cobalt in cemented carbide increases, its strength and toughness increases, the hardness decreases, suitable for roughing; reduce the amount of cobalt, its hardness and wear resistance increases, suitable for finishing.

Cutting tools with excellent high-temperature mechanical properties are particularly suitable for high-speed cutting. Ceramic cutting tool excellent high temperature properties to enable it to a high speed cutting, allowing the cutting speed can be increased by 2 to 10 times the carbide.

2 cutting tool materials and processing object physical properties match

Tools with different physical properties, such as HSS tools with high thermal conductivity and low melting point, ceramic tools with high melting point and low thermal expansion, and diamond tools with high thermal conductivity and low thermal expansion, are suitable for different workpiece materials. When machining workpieces with poor thermal conductivity, the following should be used.