Choosing CNC Machine Tooling: Expert Advice

I. Material of Cutters and Their Selection

1. Basic Properties Required for Cutter Materials:

1. High Hardness

2. Sufficient Strength and Toughness

3. High Wear Resistance and Heat Resistance

4. Good Thermal Conductivity

5. Good Workability and Economy

6. Resistance to Adhesion

7. Chemical Stability

2. Types and Selection of Cutting Tool Materials

(1) High-Speed Steel (HSS)

High-Speed Steel is a tool steel that contains a large number of alloying elements such as tungsten (W), molybdenum (MO), chromium (Cr), and vanadium (V). It has excellent mechanical properties and good workability, capable of withstanding high cutting forces and impacts.

① Ordinary High-Speed Steel

The most commonly used ordinary high-speed steel in the world is W6Mo5Cr4V2 (M2 molybdenum series) and W18Cr4V (W18 tungsten series) steel, with a carbon content of 0.7%~0.9%, hardness 63~66HRC, not suitable for high-speed cutting and hard material cutting.

② High-Performance High-Speed Steel

This refers to ordinary high-speed steel alloyed with elements like cobalt (Co), aluminum (Al) etc., enhancing its heat resistance and wear resistance, with high thermal stability. For example, W12Mo3Cr4V3Co5Si, W6Mo5Cr4V2Al, W10Mo4Cr4V3Al, with hardness reaching 67~69HRC, can be used to manufacture export drills, reamers, milling cutters, etc.

③ Powder Metallurgy High-Speed Steel

This can avoid carbide segregation produced in molten steel. Its strength and toughness are significantly improved compared to molten steel. It can be used for machining super high-strength steel, stainless steel, titanium alloys, and other difficult-to-machine materials. It is used to manufacture large broaches and gear cutting tools, especially when the cutting tools are under impact load.

(2) Cemented Carbide

1) Ordinary Cemented Carbide

① Tungsten-Cobalt (YG)

WC+Co, with good strength but relatively poor hardness and wear resistance, is used for machining brittle materials, non-ferrous metals, and non-metallic materials. Commonly used grades: YG3, YG6, YG8, YG6X. The numbers represent the percentage content of cobalt (Co). The more cobalt, the better the toughness, suitable for rough machining; less cobalt is used for precision machining.

② Tungsten Titanium Cobalt Types (YT)

TiC+WC+Co types (YT): Common grades include YT5, YT14, YT15, YT30, etc. This type of hard alloy significantly improves hardness, wear resistance, and heat resistance. However, it has poor toughness and resistance to impact vibration, mainly used for processing steel materials and not suitable for processing brittle materials. High TiC content and low Co content provide good wear resistance, suitable for fine machining; low TiC content and high Co content offer good impact resistance, suitable for rough machining.

2) New Type of Hard Alloy

① Tungsten Titanium Tantalum (Niobium) Cobalt Types (YW)

By adding TaC or NbC, the high-temperature hardness, strength, and wear resistance are improved. It is used for processing difficult-to-cut materials and intermittent cutting. Common grades are: YW1, YW2.

② Titanium Carbide Based Types (YN)

TiC+Ni+Mo, high hardness, strong anti-adhesion, resistance to crescent pit wear and strong anti-oxidation ability. Used for continuous fine machining of alloy steel, tool steel, and quenched steel. Grades: YN05, YN10.

(3) New Type of Cutting Tool Material

① Coated Tools

Tool materials obtained by coating a thin layer of high wear-resistant refractory metal compound on the base material of the tool. Common coating materials: TiN, TiC, Al2O3.

② Ceramic Cutting Tool Materials (Ceramics)

a. Al2O3-based Ceramic Tools

The main component is Al2O3, which has higher hardness, heat resistance, and abrasion resistance than hard alloys, and does not stick to the tool. It is brittle and prone to chipping, mainly used for cutting tool steel and quenched steel of 45-55HRC.

b. Si3N4-based Ceramic Tools

The main component is Si3N4. It has higher strength, toughness, fatigue strength, and cutting stability than Al2O3-based ceramic tools. It is primarily used for end milling and cutting blanks with an oxide skin. It can also be used for fine and semi-fine machining of cast iron and hardened steel.

c. Sialon Ceramics

A new material formed by adding Al2O3 and others to Si3N4. It is the strongest material in ceramics to date, with excellent chemical stability and oxidation resistance.

③ Superhard Cutting Tool Materials

The general term for diamond and cubic boron nitride, used for ultra-precision machining and hard and brittle material processing.

a. Polycrystalline Diamond (PCD)

It has high hardness and good wear resistance. However, it has poor heat resistance, low strength, and high brittleness. It has a strong affinity with iron, used for high-speed precision turning, boring non-ferrous metals and their alloys, and non-metal materials. It is not suitable for processing black metals.

b. Cubic Boron Nitride (CBN)

Its hardness and wear resistance are second only to diamond, but it has good thermal stability. It is mainly used for processing difficult-to-machine materials such as high hardness (64-70HRC) quenched steel, chill cast iron, and high-temperature alloys.

II. Types and Characteristics of CNC Machine Tool Cutters

1. CNC Machine Tool Cutter System

(1) Tool Handle

①7:24 Taper Tool Handle

7:24 Taper Shank Features:

• Cannot self-lock, tool change is relatively convenient
• Compared to straight shanks, it has higher centering accuracy and rigidity
• The shank must be fitted with a pull stud to be fixed in the spindle taper hole
• The shank and pull stud are standardized
• The selection of the shank should correspond to the spindle hole of the machine tool
• Shank models: JT, BT, ST.

② HSK Shank (Shank taper is 1:10)

Features of the HSK Tool Holder:

• High positional accuracy. Its radial and axial repeat positioning accuracy is generally within 2μm and can maintain high precision for a long period.
• High static and dynamic rigidity. It uses taper and end face positioning at the same time (over-positioning).
• Suitable for high-speed machining.
• Lightweight, small size, and compact structure.
• Easy to clean and remove dirt.

(2) TSG82 Boring and Milling Tool System

① Integral Structure

When chosen, it must be configured as per the diagram shown.

The code and significance of the TSG82 tool system

② Modular Structure (TMG10/TMG21)

III. Indexable Inserts and their Codes

1. Advantages of Indexable Tools

① High Tool Lifespan

② High Production Efficiency

③ Promotes the Adoption of New Technologies and Processes

Components of Indexable Turning Tool

1. Tool Shank;
2. Tool Pad;
3. Tool Insert;
4. Clamping Element.

2. The coding and marking method for indexable inserts

The coding method for indexable inserts, according to ISO1832-1985, is composed of a 10-character string.

IV. Selection of CNC Tooling

(1) Factors to Consider When Choosing a Cutting Tool

① Type of material being machined

② Condition of the material being machined

③ Type of cutting process

④ Geometric shape of the workpiece being machined

(2) Considerations in Selecting a Boring (Internal Hole) Tool

① Choose as large a tool rod diameter as possible, close to the bore diameter.

② Choose as short a tool arm as possible.

③ Select a main lead angle (entrance angle Kr) close to 90°, greater than 75°.

The relationship between the shape of the tool and the shape of the workpiece

(3) Considerations when selecting CNC milling cutters

① When milling a flat surface on a CNC machine tool, indexable carbide milling cutters should be used.

② High-speed steel end mills are mostly used for machining bosses and grooves, and it’s best not to use them for machining raw surfaces, as raw surfaces have a hardened layer and contain embedded grit, which will accelerate the tool’s wear.

The relationship between the shape of the workpiece and the shape of the tool during milling operations.