In modern mechanical manufacturing, metal cutting processes are the most widely used methods, accounting for over 50% of the total workload in mechanical manufacturing. Whether it’s a conventional lathe, an advanced CNC machine, or a machining center, high-performance cutting tools are indispensable. This article will delve into the geometric angles, cutting elements, common tool types, and materials of metal cutting tools to help you better understand and choose the right tools.
Cutting Movements and Cutting Parameters
In cutting processes, the relative movement between the tool and the workpiece determines the cutting effect. The main cutting movements include:
- Primary Movement: Responsible for the majority of the cutting work.
- Feed Movement: The tool moves along the workpiece to complete the cutting process.
These movements combine to form composite cutting movements, sometimes requiring auxiliary movements to adjust and support the cutting process.
Cutting parameters are crucial in determining machining efficiency and quality, including:
- Cutting Speed: The instantaneous speed of the cutting edge relative to the workpiece, measured in m/s or m/min.
- Feed Rate: The displacement of the tool in the feed direction, measured in mm/r.
- Depth of Cut: The vertical distance between the machined surface and the surface to be machined, measured in mm.
Geometric Parameters of Cutting Tools
The geometric parameters of the tool determine the stability and effect of the cutting process. Different cutting forms and tool designs affect cutting efficiency and quality. Tools can be classified according to the type of surface being machined, such as external surface machining tools, hole machining tools, thread machining tools, gear machining tools, and cutting tools.
Composition of Cutting Tools
Tools usually consist of two parts: the tool head and the tool body:
- Tool Head: Responsible for the actual cutting work, requiring the selection of appropriate materials and reasonable geometric shapes.
- Tool Body: Supports the tool head and provides clamping and positioning functions.
The cutting part of the tool, which participates in the actual work, mainly consists of the rake face, main flank face, secondary flank face, main cutting edge, secondary cutting edge, and tool tip.
Application of Basic Cutting Theory
Machinability of Workpiece Materials refers to the ease with which a workpiece material can be machined under certain cutting conditions. Evaluation indicators include tool durability and surface quality of the machined surface.
| Workpiece Material Classification | Machining Grade | Representative Materials | Relative Machinability |
|---|---|---|---|
| Very Difficult-to-Cut Materials | 8 | Cast Iron Nickel-Based Superalloys | < 0.15 |
| Difficult-to-Cut Materials | 7 | 1Cr18Ni9Ti, Tempered 50CrV | 0.15～0.5 |
| Fairly Difficult-to-Cut Materials | 6 | Tempered 45Cr, Tempered 65Mn | 0.5～0.65 |
| Slightly Difficult-to-Cut Materials | 5 | Tempered 2Cr13, 85 Steel | 0.65～1.0 |
| Common Materials | 4 | 45 Steel, Gray Cast Iron, Structural Steel | 1.0～1.6 |
| Easy-to-Cut Materials | 3 | Annealed 15Cr, Free Cutting Steel | 2.5～3.0 |
| Very Easy-to-Cut Materials | 1 | 5-5-5 Copper-Lead Alloy, Aluminum-Magnesium Alloy | > 3.0 |
Selection of Cutting Fluids: Proper cutting fluid can effectively reduce cutting force, lower cutting temperature, extend tool life, and improve the quality of the machined surface. The main functions of cutting fluids include cooling, lubrication, chip removal, and rust prevention.
Tool Materials
Common Tool Materials include tool steels (such as carbon tool steel, alloy tool steel, high-speed steel), cemented carbide, ceramics, cubic boron nitride, and diamond. High-speed steel and cemented carbide are the most commonly used in production.
| Category | Grade | Normal Temperature Hardness (HRC) | Bending Strength (GPa) | Impact Toughness (MJ·m-2) | High-Temperature Hardness at 600°C (HRC) |
|---|---|---|---|---|---|
| General High-Speed Steel | W18Cr4V | 63～66 | 3～3.4 | 0.18～0.32 | 48.5 |
| High-Performance High-Speed Steel | W6Mo5Cr4V2 | 63～66 | 3.5～4 | 0.3～0.4 | 47～48 |
Cemented Carbide is made by sintering high-hardness metal carbide powder and a binder at high temperatures. It is mainly classified into tungsten-cobalt, tungsten-titanium-cobalt, rare metal carbide, and titanium carbide-based types.
Common Types of Cutting Tools
Turning Tools are one of the most basic cutting tools, including external turning tools, grooving tools, threading tools, and internal turning tools. They can be categorized by structure into solid turning tools, welded turning tools, welded assembly turning tools, clamp turning tools, and indexable turning tools.
Forming Turning Tools are designed according to the contour of the part to be machined, used for machining the internal and external forming surfaces of rotating parts. They are characterized by high machining accuracy, high efficiency, long tool life, and simple sharpening.
Hole Machining Tools include twist drills, reamers, countersinks, boring tools, and reamers, used for various hole machining needs. Twist drills are the most widely used, reamers improve hole quality, and countersinks process hole end faces.
Milling Cutters are widely used multi-tooth tools for machining various planes, shoulders, grooves, cuts, and formed surfaces.
Grinding Tools are abrasive tools used for grinding processes, including grinding wheels, belts, and stones. Grinding wheels consist of abrasive materials, bonding agents, grinding wheel hardness, and structure.
CNC Tools and Their Tool Systems
CNC tools require high performance and long life, ensuring reliable chip breaking, rolling, and chip removal, and quick blade replacement. CNC tools include turning tools, milling tools, drilling tools, and boring tools. The automatic tool change system coordinates with mechanical hands, tool magazines, and the machine spindle to achieve continuous tool changes between operations.
Automatic Tool Change System
The automatic tool change system (ATC) is a crucial component of machining centers, enabling continuous tool changes between operations to ensure the technological concentration characteristic of machining centers. It is typically composed of a tool magazine and a mechanical hand.
