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Basic knowledge about Knives tools

Update:27-01-2021
Summary:

Knives are tools used for cutting in mechanical manufac […]

Knives are tools used for cutting in mechanical manufacturing, also known as cutting tools. Cutting tools in a broad sense include both cutting tools and abrasive tools.
Most of the knives are machine-used, but there are also hand-used ones. Since the tools used in mechanical manufacturing are basically used to cut metal materials, the term "tool" is generally understood as a metal cutting tool. Tools used for cutting wood are called woodworking tools.
The development of knives occupies an important position in the history of human progress. As early as the 28th to the 20th century BC, copper tools such as brass cones and red copper cones, drills and knives appeared in China. In the late Warring States period (third century BC), copper knives were made due to the mastery of carburizing technology. The drill bits and saws at that time have some similarities with modern flat drills and saws.
However, the rapid development of knives was accompanied by the development of steam engines and other machines in the late 18th century. In 1783, René of France first produced milling cutters. In 1792, Mozley of England produced taps and dies. The earliest documentary record of the invention of twist drill was in 1822, but it was not produced as a commodity until 1864.
The tools at that time were made of solid high-carbon tool steel, and the allowable cutting speed was about 5 meters per minute. In 1868, the British Musche made alloy tool steel containing tungsten. In 1898, Taylor and White in the United States invented high-speed steel. In 1923, Schroeter of Germany invented cemented carbide.
When using alloy tool steel, the cutting speed of the tool is increased to about 8 m/min. When using high-speed steel, it is increased by more than two times. When using cemented carbide, it is more than two times higher than that of high-speed steel. The surface quality and dimensional accuracy of the workpiece are also greatly improved.
Because high-speed steel and cemented carbide are relatively expensive, the tool has a welding and mechanical clamping structure. Between 1949 and 1950, the United States began to use indexable inserts for turning tools, and soon they were applied to milling cutters and other tools. In 1938, the German Degussa company obtained a patent on ceramic knives. In 1972, General Electric Company produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride blades. These non-metallic tool materials enable the tool to cut at a higher speed. In 1969, the Swedish Sandvik Steel Plant obtained a patent for the production of titanium carbide coated carbide blades by chemical vapor deposition. In 1972, Bangsar and Lagolan in the United States developed a physical vapor deposition method to coat a hard layer of titanium carbide or titanium nitride on the surface of cemented carbide or high-speed steel tools. The surface coating method combines the high strength and toughness of the base material with the high hardness and wear resistance of the surface layer, so that this composite material has better cutting performance.
Tools can be divided into five categories according to the form of the workpiece surface. Tools for processing various external surfaces, including turning tools, planers, milling cutters, external surface broaches and files, etc.; hole processing tools, including drills, reamers, boring cutters, reamers and internal surface broaches, etc.; thread processing Tools, including taps, dies, automatic opening and closing thread cutting heads, thread turning tools and thread milling cutters, etc.; gear processing tools, including hobs, gear shapers, shaving cutters, bevel gear processing tools, etc.; cutting tools, including inserts Tooth circular saw blades, band saws, bow saws, cut-off turning tools and saw blade milling cutters, etc. In addition, there are combined tools.
According to the cutting motion mode and the corresponding blade shape, cutting tools can be divided into three categories. General tools, such as turning tools, planers, milling cutters (not including formed turning tools, formed planers and formed milling cutters), boring cutters, drills, reamers, reamers and saws, etc.; forming tools, the cutting edges of such tools It has the same or nearly the same shape as the cross-section of the workpiece to be processed, such as forming turning tools, forming planers, forming milling cutters, broaches, conical reamers and various thread processing tools, etc.; generative tools are used to process gears by the generative method Tooth surfaces or similar workpieces, such as hobs, gear shapers, gear shaving cutters, bevel gear planers and bevel gear milling cutters.
The structure of various tools consists of a clamping part and a working part. The clamping part and working part of the overall structure tool are made on the cutter body; the working part (the teeth or the blade) of the insert structure cutter is mounted on the cutter body.
The clamping part of the tool has two types: with hole and with shank. The tool with hole is set on the main shaft or spindle of the machine tool according to the * inner hole, and the torsion moment is transmitted by the axial key or the face key, such as cylindrical milling cutter, sleeve face milling cutter, etc.
Shank tools usually have rectangular, cylindrical and tapered shanks. Turning tools, planers, etc. are generally rectangular shanks; tapered shanks * taper to withstand axial thrust and transmit torque by friction; cylindrical shanks are generally suitable for smaller twist drills, end mills and other tools. The friction force generated transmits the torsion moment. The shank of many shank tools is made of low-alloy steel, while the working part is made of high-speed steel butt-welded two parts.
The working part of the tool is the part that generates and processes chips, including the cutting edge, the structure that breaks or rolls the chips, the space for chip removal or storage, and the passage of cutting fluid. The working part of some tools is the cutting part, such as turning tools, planers, boring cutters and milling cutters, etc.; the working part of some tools includes cutting parts and calibration parts, such as drills, reamers, reamers, and inner surface drawing. Knife and tap etc. The function of the cutting part is to remove chips with the cutting edge, and the function of the calibration part is to polish the machined surface and guide the tool.
The structure of the working part of the cutter has three types: integral type, welding type and mechanical clamping type. The overall structure is to make a cutting edge on the cutter body; the welding structure is to braze the blade to the steel cutter body; there are two mechanical clamping structures, one is to clamp the blade on the cutter body, the other is It clamps the brazed cutter head on the cutter body. Cemented carbide tools are generally made of welded structure or mechanical clamping structure; porcelain tools are all made of mechanical clamping structure.
The geometric parameters of the cutting part of the tool have a great influence on the cutting efficiency and the processing quality. Increasing the rake angle can reduce the plastic deformation when the rake face squeezes the cutting layer, reduce the frictional resistance of the chip flowing through the front, thereby reducing the cutting force and cutting heat. However, increasing the rake angle will reduce the strength of the cutting edge and reduce the heat dissipation volume of the cutter head.
When choosing the angle of the tool, it is necessary to consider the influence of many factors, such as workpiece material, tool material, processing properties (rough and finishing), etc., which must be selected reasonably according to the specific situation. Generally speaking, the tool angle refers to the marking angle used for manufacturing and measurement. In actual work, due to the different installation positions of the tool and the change of the cutting motion direction, the actual working angle and the marked angle are different, but the difference is usually very small. . The material used to make the tool must have high high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertness, good manufacturability (cutting, forging, heat treatment, etc.), and not easy to deform.
Generally, when the material hardness is high, the wear resistance is also high; when the bending strength is high, the impact toughness is also high. But the higher the material hardness, the lower its bending strength and impact toughness. Due to its high bending strength, impact toughness, and good machinability, high-speed steel is still the most widely used tool material in modern times, followed by cemented carbide.
Polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and hard cast iron, etc.; polycrystalline diamond is suitable for cutting non-ferrous metals, alloys, plastics and glass steel, etc.; carbon tool steel and alloy tool steel are only used now For files, dies, taps and other tools.
Cemented carbide indexable inserts have now been coated with titanium carbide, titanium nitride, aluminum oxide hard layer or composite hard layer by chemical vapor deposition. The developing physical vapor deposition method can be used not only for cemented carbide tools, but also for high-speed steel tools, such as drills, hobs, taps and milling cutters. The hard coating acts as a barrier to hinder chemical diffusion and heat conduction, slowing down the wear rate of the tool during cutting, and the life of the coated blade is approximately 1 to 3 times longer than that of the uncoated blade.
Due to the parts that work under high temperature, high pressure, high speed, and corrosive fluid medium, more and more difficult-to-machine materials are used, and the automation level of cutting processing and the requirements for machining accuracy are getting higher and higher. In order to adapt to this situation, the development direction of the tool will be the development and application of new tool materials; the further development of the vapor deposition coating technology of the tool, the deposition of a higher hardness coating on the high toughness and high strength substrate, and a better solution The contradiction between the hardness and strength of the tool material; further develop the structure of the indexable tool; improve the manufacturing accuracy of the tool, reduce the difference in product quality, and optimize the use of the tool. 

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