1.The requirements of Cnc Turning for tools
In Cnc Turning, most of the tools are the same as those for normal machining, but the requirements for Cnc Turning are higher. The specific contents are as follows.
In order to ensure the quality of processing and improve productivity should have high reliability and durability, in order to adapt to the rough machining of large depth of cut and fast feed requirements should be good stiffness and high strength; should have good chip removal performance so that the normal operation of the machine; easy to install and adjust, as well as the use of high-quality tool materials.
2.Classification of Cnc Turning Tools
From the tool structure, there are integral type, such as vertical milling cutter; inlay type; special type, etc.
From the tool material, there are high-speed steel tools, carbide tools, diamond tools, etc.
3.Cnc Turning material selection
Tool materials used for Cnc Turning are divided into high-speed steel, carbide, coated alloy, ceramic, cubic boron nitride and diamond, etc. Cutting metal tool materials, generally have hardness, strength, red hardness thermal conductivity and other indicators of the requirements. Among them, hardness and strength are important indicators. The ideal tool is of course both hardness and strength. Therefore, carbide and coated carbide tools are the most used in the actual machining.
Therefore, the requirements of the machined surface quality, surface accuracy, the size of the cutting load and the presence of shock and vibration of the machined material during the cutting process are the main basis for the selection of Cnc Turning tools.
High-speed steel tools. Containing more tungsten, chromium, and other alloying elements of high alloy steel tools called high-speed steel. There are general-purpose high-speed steel and high-performance high-speed steel. General purpose HSS. Its hardness is between 62 ~ 69HRC, with a certain degree of wear resistance and high strength and toughness, cutting speed is generally not higher than 45 ~ 60m / min, not suitable for high-speed cutting.
High-performance high-speed steel. It is based on high-speed steel, by increasing the content of carbon, vanadium and heat resistance, higher wear resistance of steel. High-performance high-speed steel has a good red hardness, in 620 ~ 660 ℃ can still maintain the hardness of 60HRC, its durability is 2 ~ 3.5 times the general high-speed steel. High-performance high-speed steel is mostly used for processing high-temperature alloys, titanium alloys and other difficult-to-machine materials. But its comprehensive performance can not be compared with general-purpose high-speed steel.
Was the mainstream of cutting tools of high-speed steel, with the increasingly widespread application of CNC machine tools, because of its low cutting efficiency, has been gradually replaced by carbide tools. In cutting certain difficult-to-machine materials as well as in the manufacture of complex tools, high-speed steel with its comprehensive performance in strength, toughness, red hardness and process still has a wider range of applications.
Cemented carbide tools and coated carbide tools
Cemented carbide tools are powder metallurgical products made of carbide with high hardness and melting point with C0, mo, ni as binder. Its hardness can reach 77~81HRC, can withstand 810~1100℃ high temperature, and the permitted cutting speed is 4~11 times of HSS. But its impact toughness
and flexural strength are not as high speed steel. In recent years, new tools have emerged that can be used in turning, milling, drilling, reaming, boring and other applications, and are suitable for a wider range of workpiece materials.
Coated carbide tool is a material obtained by coating a thin layer of refractory metal compound with high thickness and wear resistance on a carbide substrate with good toughness by chemical vapor deposition or physical vapor deposition method. It makes it not only have the toughness and strength of the base material, but also have high wear resistance.
Other material tools
(1) Ceramic knives. There are silicon nitride ceramic knives and alumina ceramic knives , alumina ceramic knives are also divided into single-component alumina ceramic knives, composite alumina ceramic knives and enhanced alumina ceramic knives. Because of its higher hardness, good red hardness, so adapt and processing of cast iron, steel and non-ferrous metals and non-metallic materials.
(2) Super hard tool materials. Including diamond and cubic boron nitride, their high cutting performance, high, very small surface roughness value adapted to engage in a high hardness of the material processing.
- CNC turning tool selection
CNC turning tools are also divided into pointed turning tools, arc turning tools and shaped turning tools, which are divided according to the different shapes of turning tool tips; CNC turning processing is widely used in the machine clamping indexable turning tools. Its tool body does not need to re-clamp the tool to save time and improve efficiency; machine tool has been standardized, stable size, high accuracy of the production of the tool bar tool groove; tool edge does not need to re-sharpen, convenient to use the coated tool, so that the tool life is extended and other advantages. The selection of the machine tool is mainly considered in the following aspects
(1) The main factors affecting the machine tool are machine tool type, tool holder form and clamping method, workpiece clamping
(2) The clamping method of the insert is divided into rigid clamping, thread clamping, lever clamping, wedge clamping.
(3) The choice of insert shape mainly considers the surface shape of the workpiece to be machined, cutting method and the number of times the insert is indexed and other factors. The strength of the insert determines the size of the tip angle. Machine rigidity, power allows the conditions, large margin roughing should be selected large tip angle inserts and vice versa, choose a small. There are two kinds of positive and negative inserts. Due to the internal contour of small machine tool system rigidity should be selected positive. For external processing metal cutting rate should be selected negative type. The choice of the main angle of the turning tool.
① The front angle mainly affects the chip deformation and the size of the cutting force and tool durability and processing surface quality. The increase of the front angle will promote chip deformation and friction reduction, so the cutting force is small, less cutting heat, high surface quality. However, too large a front angle, will make the tool strength to reduce heat dissipation volume to reduce its durability. Carbide turning tool cutting steel front angle of 8 ° ~ 22 ° cutting gray cast iron to 4 ° ~ 16 ° cutting high-strength steel to -4 °.
② The role of the rear angle is to reduce the friction between the main rear tool face and the elastic recovery layer of the transition tool face, so that tool wear is reduced. Small back angle, will make the main back tool surface and the workpiece surface friction between the tool wear increased workpiece cold hardness increased resulting in poor machining surface quality. An increase in the back angle reduces the friction and also reduces the radius of the blunt edge, which is beneficial in the case of small cutting thicknesses but makes the strength of the cutting edge and heat dissipation worse. For roughing and load-bearing tools, the back angle of the cutting edge should be small enough to take 3º~8º for finishing and 6º~14° for machining.
③ main deflection angle can affect the tool life and cutting force size commonly used 45º, 60º, 75°, 90°, etc. ④Reducing the friction between the sub-cutting edge and the machined surface is the main role of the sub-deflection angle. Smaller sub-deflection angle can improve tool strength and improve heat dissipation conditions, reduce the residual area height is generally selected 4º ~ 16 °. Finish machining to take small rough machining to take large.
In summary, the choice of CNC turning tools should consider the processing requirements of the workpiece to be machined machining process cutting materials and other factors in order to make the correct