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The development history and application of CNC tools in the machinery manufacturing industry

Posted by: Alan Xia 2021-10-21 Comments Off on The development history and application of CNC tools in the machinery manufacturing industry

CNC tools are tools used for cutting in mechanical manufacturing, also known as cutting tools. In a broad sense, cutting tools include both cutting tools and abrasive tools; at the same time, “CNC cutting tools” include not only cutting blades, but also accessories such as tool holders and tool holders! The development of CNC cutting tools occupies an important position in the history of human progress. As early as the 28th to the 20th century BC, copper knives 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 CNC tools was in the late 18th century, accompanied by the development of steam engines and other machines. In 1783, René of France first produced milling cutters. In 1792, Mozley of England produced taps and dies. The earliest documentary record about 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 m/min. In 1868, the British Musche made alloy tool steel containing tungsten. In 1898, Taylor and the United States. White invented high-speed steel. In 1923, Schroeter of Germany invented cemented carbide.

When alloy tool steel is used, the cutting speed of CNC tools is increased to about 8 m/min. When high-speed steel is used, it is increased by more than two times. When cemented carbide is used, the cutting speed is more than twice that of high-speed steel. The surface quality and dimensional accuracy of the resulting workpieces are also greatly improved.

As high-speed steel and cemented carbide are relatively expensive, CNC cutting tools appear welding and mechanical clamping structures. Between 1949 and 1950, the United States began to use indexable inserts for turning tools, and soon it was applied to milling cutters and other CNC tools. In 1938, the German Degussa company obtained a patent on ceramic CNC cutting tools. In 1972, General Electric Company of the United States produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride blades. These non-metallic tool materials allow the tool to cut at higher speeds.

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.

CNC tools can be divided into five categories according to the form of the workpiece surface. CNC tools for processing various external surfaces, including turning tools, planers, milling cutters, external surface broaches and files, etc.; hole processing tools, including drills, reaming drills, alloy tool 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, gear shaving cutters, bevel gear processing tools, etc.; cutting tools , Including toothed circular saw blades, band saws, bow saws, cut-off turning tools and saw blade milling cutters, etc. In addition, there are combined CNC tools.

According to the cutting motion mode and the corresponding blade shape, CNC tools can be divided into three categories. General CNC tools, such as turning tools, planers, milling cutters (excluding formed turning tools, formed planers and formed milling cutters), boring cutters, drills, alloy tool reamers, reamers and saws, etc.; forming CNC tools, this The cutting edge of similar tools has the same or close to the same shape as the section of the workpiece to be processed, such as forming turning tools, forming planing cutters, forming milling cutters, broaching cutters, conical reamers and various thread processing tools. To process gear tooth surfaces or similar workpieces, such as hobs, gear shaping cutters, gear shaving cutters, bevel gear planers, and bevel gear milling cutters.

The structure of various CNC tools consists of a clamping part and a working part. The clamping part and working part of the integral structure CNC tool are made on the cutter body; the working part (the tooth or the blade) of the insert structure cutter is inlaid on the cutter body.

The clamping part of the CNC tool has two types: with hole and with shank. Numerically controlled tools with holes rely on the inner hole to be set on the main shaft or mandrel of the machine tool, and the torsional moment is transmitted by the axial key or the face key, such as cylindrical milling cutters, sleeve face milling cutters, etc.

There are usually three types of shank CNC tools: rectangular shank, cylindrical shank and tapered shank. Turning tools, planers, etc. are generally rectangular shanks; tapered shanks rely on taper to bear axial thrust and transmit torque with the help of friction; cylindrical shanks are generally suitable for small twist drills, end mills and other CNC tools. The resulting friction force transmits the torsional moment. Many shank CNC tools have shanks made of low-alloy steel, and the working part is made of high-speed steel butt-welded two parts.

The working part of the CNC tool is the part that generates and processes the chips, including the cutting edge, the structure for breaking or rolling up 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 CNC tools includes cutting parts and calibration parts, such as drills, reamers, reamers, and inner surfaces Broaches and taps, 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 cut surface and guide the tool.

The structure of the working part of the CNC tool has three types: integral type, welding type and mechanical clamping type. The overall structure is to make the 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 CNC 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 CNC tool, it is necessary to consider the influence of many factors, such as the workpiece material, the material of the CNC tool, and the processing properties (rough and fine machining), etc., which must be selected reasonably according to the specific situation. Generally speaking, the angle of the tool 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 CNC 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 currently only used For files, dies, taps and other tools.

Cemented carbide indexable inserts are now coated with titanium carbide, titanium nitride, aluminum oxide hard layer or composite hard layer by chemical vapor deposition. The physical vapor deposition method under development 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 thermal conduction, which slows 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 CNC tool, reduce the difference in product quality, and optimize the use of the tool. #p#分页头#e#

CNC tool materials are roughly divided into the following categories: high-speed steel, cemented carbide, cermet, ceramic, polycrystalline cubic boron nitride and polycrystalline diamond.

Ceramics are mainly mentioned here. Ceramics are used for cutting tools earlier than cemented carbide, but due to their brittleness, the development is very slow. But since the 1970s, there has been relatively rapid development. There are two main series of ceramic tool materials, namely alumina series and silicon nitride series. As a numerical control tool, ceramics have the advantages of low cost, high hardness, and good high temperature resistance, and have good prospects.

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