What Is a Special Tool?
Special tools are tools with specific materials and performance characteristics compared to commercially available general cutting tools.
They are used to process parts with complex shapes and dimensions that are difficult to achieve with general-purpose tools. These tools are specially designed with materials and shapes suitable for specific applications and environmental conditions, aiming to provide high efficiency and precision. Each tool possesses characteristics suitable for specific materials and applications, offering high wear resistance, heat resistance, durability, and precision. Therefore, special tools are crucial for achieving high-quality processing tailored to specific workpieces or conditions.
Uses of Special Tools
Here are examples of general applications for special tools:
- Machining of hard metals such as stainless steel, hard aluminum alloys, and superhard alloys.
- Processing non-metallic hard materials like ceramics, glass, and gemstones.
- Grinding and drilling of other hard materials.
- Ultra-precision processing and high-speed cutting.
- CNC turning and milling operations.
- Manufacturing precise optical components and semiconductor devices.
- Shaping and drilling of metal parts.
- Processing complex shapes and grooves.
- Metal cutting at high temperatures.
- Common metal processing, especially cutting, drilling, and milling of common steel.
- Manufacturing of machine parts and tools.
- Reducing tool replacement frequency in automated lines for labor savings.
Special tools find applications in various industries, including aerospace, automotive manufacturing, medical device production, gemstone processing, and precision machinery manufacturing.
Principles of Special Tools
The principle of cutting tools is based on the idea that when a hard material comes into contact with a softer material and force is applied to move either material, the surface of the softer material peels off. Therefore, the principle of cutting tools involves using a material harder than the material being cut.
In recent years, as the hardness of materials to be cut has increased, the materials used for tools have also become harder. With the diversification of cutting purposes and materials, there are various types of cutting tools. Some of the main materials include cemented carbide, high-speed tool steel (HSS), diamond, polycrystalline diamond (PCD), cubic boron nitride (CBN), ceramics, and cermet. Considering the size, shape, and purpose of the tool, there is an extremely diverse range of types.
The manufacturing methods of special tools vary depending on the type, application, and design of the tool. Generally, materials such as cemented carbide and tool steel are selected for their hardness and shape. Depending on the size, tools can be manufactured as solid (the entire tool is made of high-hardness material) or with only the cutting edge made of high-hardness material. Additionally, advanced materials like diamond and CBN may be attached or coated through methods such as spattering, chemical vapor deposition (CVD), or physical vapor deposition (PVD).
It is important to note that diamond tools experience minimal wear during cutting. This allows diamond tools to maintain high performance over an extended period. Even in situations where other materials would wear out quickly, diamond tools effectively continue cutting materials. They also have excellent thermal conductivity, rapidly transferring heat from the tool’s edge to cool the cutting surface. This characteristic prevents the accumulation of heat during material processing, extending the tool’s lifespan.
However, due to the nature of diamond being a cluster of carbon atoms, it is unsuitable for cutting steel materials. When cutting steel materials, carbon atoms are absorbed by the steel as the cutting edge temperature rises, leading to edge wear or damage. Furthermore, diamond tools enable highly precise cutting and grinding, providing a high-quality finish. This is particularly crucial for applications requiring precise workpieces and high-precision dimensions.
Types of Special Tools
Below are the main types of special tools.
These special cutting tools with unique materials operate based on different principles according to each material’s characteristics, providing high efficiency and durability. Understanding the principles of cutting tools and selecting and using them appropriately are key to achieving high-quality and high-efficiency machining operations. There are various shapes, such as drills, reamers, end mills, fly cutters, side cutters, metal saws, countersinks, T-slot cutters, trepanning tools, recessing tools, boring tools, taps, dies, hobs, broaches, punches, and bits, based on one or a combination of the materials listed below.
1. Cemented Carbide Cutting Tools
Cemented carbide refers to an alloy composed of hard metal carbides and iron-based metals. A typical composition of cemented carbide is made by mixing powder of rare metals called tungsten carbide (WC) and cobalt (Co), sintering them at around 1,400°C.
It has characteristics such as higher hardness, elastic modulus, compressive strength, thermal conductivity, and specific gravity, as well as a lower coefficient of thermal expansion compared to tool steels like high-speed tool steel (HSS). Due to these characteristics, cemented carbide tools have a longer lifespan, maintaining sharpness without frequent replacements. The cutting edge is less prone to wear, providing stable performance even at high temperatures. Cemented carbide has become a common tool material, replacing the previously mainstream high-speed tool steel (HSS).
2. Diamond Cutting Tools
Diamond cutting tools, made from extremely hard natural or synthetic diamonds, have diamond particles or sintered diamond bodies attached to the cutting edges. They are used for cutting hard materials such as cemented carbide. Diamonds are highly resistant to wear and have high thermal conductivity, making them suitable for working at high temperatures. They are used for cutting, grinding, and drilling hard materials like aluminum, ceramics, glass, gemstones, and others.
3. Ceramic Cutting Tools
Ceramic materials can withstand high temperatures and have high hardness, making them suitable for cutting operations at elevated temperatures. Ceramic cutting tools provide thermally stable performance. Although ceramics are brittle and can chip during cutting, recent improvements have addressed these issues. They are primarily used for metal cutting at high temperatures (dry or semi-dry processing), processing superhard materials, and ultra-precision machining.
4. Steel Cutting Tools
Steel cutting tools, typically made from high-speed tool steel (HSS), enhance hardness and wear resistance through alloying or heat treatment. The cutting tools made from steel generally follow the normal principles of metal cutting but leverage the specific characteristics of certain types of steel. HSS tools, with higher impact strength and fracture toughness compared to cemented carbide, can outperform carbide tools in specific machining operations when coated.
These are some of the common types of special cutting tools, each optimized for different applications and materials. The selection of cutting tools is based on the material being processed, the machining process, desired precision, and working conditions. Special cutting tools with unique materials are designed to meet the specific needs of machining, possessing characteristics such as high wear resistance, heat resistance, and hardness.