CNC tools are tools used in machining in machining, also known as cutting tools. The generalized cutting tools include both tools and grinding tools. In addition to the cutting blades, the “CNC tools†also include accessories such as tool holders and holders!
The development of CNC tools plays an important role in the history of human progress. As early as 28 BC to 20 BC, copper knives such as cones, drills, and knives of brass cones and copper had appeared. In the late Warring States period (3rd century BC), copper cutters were made due to the mastery of carburizing technology. The drill bits and saws at the time were somewhat similar to modern flat drills and saws.
However, the rapid development of CNC tools was developed in the late 18th century with the development of machines such as steam engines. In 1783, France's Rene first produced a milling cutter. In 1792, the British Mozley made taps and dies. The earliest literature on the invention of twist drills was recorded in 1822, but it was not produced until 1864.
The tool at that time was made of integral high carbon tool steel with a cutting speed of about 5 m/min. In 1868, the British Mussett made alloy tool steel containing tungsten. In 1898, Taylor and the United States. White invented high speed steel. In 1923, Schletel of Germany invented cemented carbide.
When using alloy tool steel, the cutting speed of the CNC tool is increased to about 8 m/min, and when using high-speed steel, it is more than doubled. When using hard alloy, it is more than twice as high as that of high-speed steel. The surface quality and dimensional accuracy of the workpiece are also greatly improved.
Due to the high price of high speed steel and hard alloy, CNC tools have welded and mechanically clamped structures. Between 1949 and 1950, the United States began to use indexable inserts on turning tools, and soon applied to milling cutters and other CNC tools. In 1938, the German company Degussa obtained a patent on ceramic CNC tools. In 1972, General Electric Company of the United States produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride inserts. These non-metallic tool materials allow the tool to cut at higher speeds.
In 1969, the Swedish Sandvik Steel Plant patented the production of titanium carbide coated carbide inserts by chemical vapor deposition. In 1972, Bangsa and Lagrange in the United States developed physical vapor deposition to coat hard surfaces 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 the 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 machining various external surfaces, including turning tools, planing knives, milling cutters, outer surface broaches and boring tools, etc.; hole machining tools, including drill bits, reaming drills, alloy tool boring tools, 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; gear processing tools, including hobs, gear shaping cutters, shaving cutters, bevel gear machining tools, etc.; cutting tools Including insert circular saw blades, band saws, hacksaws, cutting tools and saw blades, and so on. 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-purpose CNC tools, such as turning tools, planing knives, milling cutters (excluding formed turning tools, forming planers and forming cutters), boring tools, drill bits, alloy tool reaming drills, reamers and saws; forming CNC tools, this The cutting edge of the tool has the same or nearly the same shape as the workpiece to be machined, such as forming turning tools, forming planers, forming cutters, broaches, cone reamers and various threading tools; Forming the tooth surface of a gear or similar workpiece, such as a hob, a pinion cutter, a shaver, a bevel gear planer, and a bevel gear milling cutter.
The structure of various CNC tools consists of a clamping part and a working part. The clamping part and the working part of the integral structure CNC tool are made on the body; the working part (knife or blade) of the insert structure tool is mounted on the body.
The clamping part of the CNC tool has two types of holes and handles. The perforated NC tool is placed on the spindle or mandrel of the machine tool by means of the inner hole, and the torsional moment is transmitted by means of the axial key or the end face key, such as a cylindrical milling cutter, a sleeve face milling cutter and the like.
CNC tools with handles usually have three kinds of rectangular handles, cylindrical handles and tapered handles. Turning tools, planing knives, etc. are generally rectangular shanks; taper shanks are subjected to axial thrust by taper and transmit torque by friction; cylindrical shanks are generally suitable for smaller CNC tools such as twist drills, end mills, etc. The friction generated produces a torsional moment. Many shank NC tool shanks are made of low-alloy steel, while the working part is made of high-speed steel to butt weld the two parts.
The working part of the CNC tool is the part that generates and processes the chip, including the blade edge, the structure that breaks or rolls the chip, the space for chip removal or chip storage, and the passage of the cutting fluid. Some working parts of the tool are cutting parts, such as turning tools, planing tools, boring tools and milling cutters; some working parts of CNC tools include cutting parts and calibration parts, such as drill bits, reaming drills, reamers, and inner surfaces. Broaches and taps, etc. The function of the cutting part is to cut the chips with a cutting edge. The calibration part is used to polish the machined surface and guide the tool.
The working part of the CNC tool has three types: integral, welded and mechanically clamped. The overall structure is to make a cutting edge on the cutter body; the welded structure is to braze the blade to the steel body; the mechanical clamping structure has two kinds, one is to clamp the blade on the cutter body, and the other is to clamp the blade to the cutter body, and the other The brazed bit is clamped to the body. Carbide tools are generally made of welded structures or mechanically clamped structures; ceramic tools are mechanically clamped.
The geometric parameters of the cutting part of the CNC tool have a great influence on the cutting efficiency and the quality of the machining. Increasing the rake angle reduces the plastic deformation of the rake face when the cutting layer is pressed, and reduces the frictional resistance of the chip flowing through the front, thereby reducing the cutting force and the 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 selecting the angle of the CNC tool, it is necessary to consider the influence of various factors, such as workpiece material, CNC tool material, processing property (rough, finishing), etc., which must be reasonably selected according to the specific situation. Generally speaking, the tool angle refers to the angle of labeling for manufacturing and measurement. In actual work, the actual working angle and the angle of the marking are different due to the different mounting positions of the tool and the change of the cutting motion direction, but usually the difference is 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 processability (cutting, forging and heat treatment, etc.) and not easily deformed.
Generally, when the hardness of the material is high, the wear resistance is also high; when the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower the bending strength and impact toughness. Due to its high flexural strength and impact toughness and good machinability, high-speed steel is still the most widely used CNC tool material, followed by hard alloy.
Polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and hard cast iron; polycrystalline diamond is suitable for cutting iron-free metals, and alloys, plastics and glass steel; carbon tool steel and alloy tool steel are now only used Tools such as trowels, dies and taps.
Carbide indexable inserts have now been coated with titanium carbide, titanium nitride, alumina hard or composite hard layers by chemical vapor deposition. The growing 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. As a barrier to chemical diffusion and heat conduction, the hard coating slows the wear of the tool during cutting, and the life of the coated blade is about 1 to 3 times higher than that of the uncoated one.
Due to the high temperature, high pressure, high speed, and parts working in corrosive fluid media, more and more difficult materials are applied, and the automation level of cutting and the processing precision are getting higher and higher. In order to adapt to this situation, the development direction of the tool will be to develop and apply new tool materials; further develop the vapor deposition coating technology of the tool, and deposit a higher hardness coating on the high toughness and high strength substrate to better solve The contradiction between the hardness and strength of the tool material; further develop the structure of the indexable tool; improve the manufacturing precision of the CNC tool, reduce the difference in product quality, and optimize the use of the tool.
CNC tool materials are broadly classified 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 hard alloys, but they develop very slowly due to their brittleness. However, since the 1970s, it has achieved relatively rapid development. There are two main types of ceramic tool materials, namely alumina and silicon nitride. As a numerical control tool, ceramic has the advantages of low cost, high hardness and good high temperature resistance, and has a good prospect.
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