Basic knowledge of cutting tools

The cutting tool is used in the machinery manufacturing for cutting processing tools, also known as cutting tools. Generalized cutting tools include both tools and abrasives.
The vast majority of cutters are machine tools, but some are hand tools. The term "tool" is generally understood to mean a metal-cutting tool, since the tools used in machine manufacturing are basically used to cut metal materials. The tools used to cut wood are called woodworking tools.
The development of cutting tools occupies an important position in the history of human progress. As early as 28 BC ~ 20 century ago in China, there have been brass cone and copper cone, drill, knife and other copper cutting tools. In the late Warring States Period (the third century BC), copper cutters were made because of the mastery of carburizing technology. Drills and saws at that time bore some resemblance to modern flat drills and saws.
However, the rapid development of the cutting tool came in the late 18th century, with the development of machinery such as the steam engine. In 1783, Renet of France first made the milling cutter. In 1792, Maudsley of England produced the tap and die. The invention of the twist drill is first documented in 1822, but it was not produced as a commodity until 1864.
At that time, tools were made of monolithic high-carbon tool steels with allowable cutting speeds of about 5 m/min. In 1868, alloy tool steels containing tungsten were made by Muschet in England. In 1898, the United States, Taylor and. White invented high speed steel. In 1923, Germany's Schlueter invented cemented carbide.
In the use of alloy tool steel, the cutting speed of the tool increased to about 8 m/min, the use of high-speed steel, and more than two times, to the use of carbide, and than the use of high-speed steel increased by more than two times, the cutting workpiece surface quality and dimensional accuracy is also greatly improved.
Due to the high price of high speed steel and cemented carbide, the tool appears welding and mechanical clamping structure. In 1949-1950, the United States began to use indexable blades for turning tools and soon after for milling cutters and other tools. In 1938, the German Degusa company obtained the patent on the ceramic cutting tool. In 1972, General Electric Company produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride blades. These non-metallic tool materials allow the tool to be cut at higher speeds. In 1969, Sandvik Steel in Sweden obtained a patent for the production of titanium carbide coated carbide inserts by chemical vapor deposition. In 1972, Bonsa and Laguran in the United States developed a physical vapor deposition process in which hard layers of titanium carbide or titanium nitride were coated on the surface of cemented carbide or HSS tools. The surface coating method combines the high strength and toughness of the base material with the high hardness and wear resistance of the top layer, resulting in better cutting performance of the composite.
Cutters can be divided into five categories according to the form of the workpiece surface. Processing all kinds of surface cutting tools, including turning tool, planer, milling cutter, surface broach and file, etc. Hole processing tools, including drill, reaming drill, boring cutter, reamer and inner surface broach, etc. Thread cutting tools, including tap, die, automatic thread cutting head, thread turning tool and thread milling cutter, etc. Gear processing tools, including hob, gear shaper, gear shaver, bevel gear processing tools; Cutting tools, including inset circular saw blades, band saws, bow saws, cutting lathe cutters and saw blade mills, etc. In addition, there are combination knives.
According to the cutting motion mode and the corresponding blade shape, the cutting tools can be divided into three categories. General cutting tools, such as turning tools, planer tools, milling tools (excluding forming turning tools, forming planer tools and forming milling tools), boring tools, drills, reaming drills, reamers and saws, etc. Forming tool, the cutting edge of this kind of tool has the same or close to the same shape with the section of the workpiece to be processed, such as forming turning tool, forming planer, forming milling cutter, broach, taper reamer and various thread processing tools; The developed tool is used to process the tooth surface of gears or similar workpieces by the developed method, such as hob, gear shaver, gear shaving cutter, bevel gear planer and bevel gear milling cutter head.
The structure of the cutter is composed of a clamping part and a working part. The clamping part and working part of the overall structure of the tool are done on the tool body; The working part of the cutter (tooth or blade) is mounted on the body of the cutter.
The clamping part of the cutter has two types: the hole and the handle. The tool with hole is set on the spindle or mandrel of the machine tool according to the inner hole, with the help of the axial key or end key to transfer the torsional moment, such as cylindrical milling cutter, sleeve type face milling cutter, etc.
There are usually three kinds of cutter with handle: rectangular handle, cylindrical handle and tapered handle. Turning tool, planer, etc., generally rectangular handle; Taper handle bearing axial thrust, and transfer torque with the help of friction force; The cylindrical shank is generally suitable for small twist drill, end milling cutters and other tools, with the help of the friction generated during clamping to transfer the torsional moment. Many tools with handles are made of low alloy steel for the handles, and the working parts are butt-welded with high speed steel.
The working part of the tool is to produce and process the chip part, including the blade, the chip broken or rolled up structure, chip discharge or storage space, cutting fluid channels and other structural elements. The working part of some tools is the cutting part, such as turning tool, planer, boring cutter and milling cutter, etc.; The working part of some tools includes the cutting part and the calibration part, such as drill, reamer, inner surface broach and tap. The function of the cutting part is to cut the chip with the blade, and the function of the calibration part is to polish the machined surface that has been cut and guide the tool.
The structure of the tool working part has three kinds: integral type, welding type and mechanical clamping type. The overall structure is made on the cutter body cutting edge; The welding structure is to braze the blade to the steel cutter body; There are two kinds of mechanical clamping structure, one is to clamp the blade on the tool body, the other is to clamp the brazed tool head on the tool body. Carbide cutting tools are generally made of welding structure or mechanical clamping structure; Porcelain cutters are all mechanically clamped.
The geometric parameters of the cutting part of the tool have great influence on the cutting efficiency and machining quality. Increasing the rackangle can reduce the plastic deformation of the rackface when squeezing the cutting layer, reduce the frictional resistance of the chip flowing through the front, and thus reduce the cutting force and cutting heat. However, increasing the rake Angle will reduce the intensity of the cutting edge and reduce the heat dissipation volume of the tool head.
In the choice of the tool Angle, the need to consider the influence of a variety of factors, such as workpiece material, tool material, processing properties (rough, finishing), must be reasonable choice according to the specific situation. Generally speaking, the tool Angle refers to the marking Angle used for manufacturing and measurement in the actual work. Due to the change of the tool installation position and the direction of cutting motion, the actual work Angle and the marking Angle are different, but usually the difference is very small. The material to make the tool must have high temperature hardness and wear resistance, the necessary bending strength, impact toughness and chemical inertia, good technology (cutting, forging and heat treatment, etc.), and not easy to deformation.
Usually when the material hardness is high, the wear resistance is high; When the bending strength is high, the impact toughness is high. However, the higher the hardness of the material, the lower the bending strength and impact toughness. Due to its high bending strength, impact toughness and good machinability, HSS is still the most widely used tool material, followed by cemented carbide.
The polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and hard cast iron. Polycrystalline diamond is suitable for cutting non-ferrous metals, alloys, plastics and FRP, etc. Carbon and alloy tool steels are now used only for tools such as files, dies and taps.
Carbide indexable inserts are now coated with hard layers of titanium carbide, titanium nitride, aluminum oxide or composite hard layers by chemical vapor deposition. Physical vapor deposition is being developed not only for carbide tools, but also for HSS tools such as drill bits, hobs, taps and milling cutters. Hard coating as a barrier to block chemical diffusion and heat conduction, so that the tool in the cutting wear speed slowed down, the life of the coated blade compared with the uncoated about 1 ~ 3 times.
Due to the high temperature, high pressure, high speed, and in the corrosive fluid medium of the parts, its application of difficult to machining materials more and more, the level of automation of cutting and processing precision requirements are more and more high. In order to adapt to this situation, the development direction of cutting tool will be to develop and apply new cutting tool materials; In order to better solve the contradiction between hardness and strength of tool materials, the technology of vapor deposition coating is further developed to deposit coating with higher hardness on the matrix with high toughness and strength. The structure of indexable tool is further developed. Improve the tool manufacturing precision, reduce the difference of product quality, and optimize the use of the tool