When the high-flow jet cooling system is used in ultra-high-speed cutting, a large amount of hot chips will be generated per unit time, which must be quickly removed from the table to prevent the high-speed cutting from being performed normally and to avoid thermal deformation of the machine tool, the tool and the workpiece. High-speed machining features High-speed machining not only greatly shortens machining time, improves machining efficiency, reduces machining costs, but also enables surface machining quality and machining accuracy of parts to reach higher levels. High-speed machining has the following main features:
(1) Reduction of workpiece thermal deformation In high-speed machining, since the chips are cut off in a very short time, most of the cutting heat is carried away by the chips, so the workpiece temperature is not high, and the possibility of heat deformation is reduced, and Surface defects such as thermal stress and hot cracks can be avoided.
(2) Conducive to ensuring the size and shape accuracy of the part In high-speed machining, the unit cutting force is reduced due to the softening of the material of the cutting layer, thereby reducing the deformation of the part processing, which is particularly advantageous for processing thin-walled parts with poor rigidity.
(3) Good surface quality can be obtained. High-speed machining can reduce the depth of the surface hardened layer, reduce the residual stress of the surface layer and the thermal damage of the surface layer microstructure, thereby reducing the mechanical, physical and chemical properties of the surface layer material of the part. The possibility of change, the intrinsic quality of the machined surface, and the usability of the part.
(4) Reduction of process system vibration In ultra-high-speed machining, the spindle speed is high and the excitation frequency is far from the natural frequency of the machine tool, thus reducing the vibration of the process system and improving the processing quality.
(5) Significantly improve the material removal rate while increasing the cutting speed while increasing the feed rate, thereby significantly increasing the material removal rate. For example, in ultra-high-speed milling, when the cutting thickness is kept constant (feed per tooth and depth of cut), the feed rate can be increased by 5 to 10 times compared to conventional milling, resulting in a high material removal rate.
High-speed milling has been widely used in the automotive industry, aerospace industry and mold manufacturing, processing light metal alloys such as aluminum and magnesium, steel and cast iron. For example, automotive engine block, cylinder head, reducer housing, aircraft aluminum alloy thin-walled parts, hardened die steel and nickel-based alloys, titanium alloys and other difficult materials. The strategy to increase the material removal rate has been turned from strong and slow to fast and light, and the machine has been switched from a strong type (increasing the mechanical characteristic parameter) to a high speed type (increasing the speed characteristic parameter).
High-speed machining requirements for tools (1) When the tool material is cut at high speed, as the cutting speed increases, the cutting force decreases, and the cutting temperature rises very high. After reaching a certain value, the rise gradually slows down. The main cause of tool damage is mechanical friction, bonding, chemical wear, chipping, crushing and plastic deformation under the action of cutting force and cutting temperature. Therefore, the most important requirement for high-speed cutting tool materials is high temperature. Mechanical properties, thermophysical properties, anti-blocking properties, chemical stability (oxidation, diffusivity, solubility, etc.) and thermal shock resistance as well as resistance to coating cracking.
High-speed and ultra-high-speed machining is based on this important premise. The tool material requires high hardness, good wear resistance, heat resistance (thermo-hardness), and good toughness and impact resistance. In the past 30 years, the breakthroughs in tool materials have made this problem well solved: 1 With the application of reinforced ceramic tools and coating technology, the hardness of the tool has been greatly improved, and the tool has high hardness. Blade and high toughness matrix. 2 Polycrystalline Cubic Boron Nitride Blade (PCBN), with a hardness of 3 500 ~ 4 500 HV, has become the tool of choice for high-speed cutting hardened steel. 3 Polycrystalline diamond (PCD) blades, also obtained by polycrystalline method, have hardness of 6 000 ~ 10 000 HV. They have been used in turning tools, milling cutters, drill bits, etc., and have entered the field of high-speed cutting non-ferrous metals, sometimes used in cutting. Steel materials.
Tool materials for high speed machining must be selected based on the material of the workpiece and the nature of the process. In general, ceramics, cermets and PCBN tools are suitable for high-speed machining of steel materials; tool materials such as PVD and CVD are suitable for high-speed machining of non-ferrous metals such as aluminum, magnesium and copper.
(2) The structure of the cutter adopts the indexable insert and the integral cutter made of high-quality and low-cost cemented carbide, cermet and coating materials, and overcomes the centrifugal force with the integrated balance device and the corresponding structure to make the high stress generated by the cutter.
Cutting edge shape: The shape of the cutting edge of the tool also has a great influence on the machining quality. For example, when the cutting edge of the diamond tool has a proper crystallizing direction, the tool life and the roughness of the machined surface can be greatly improved. The cutting edge of the tool is developing in the direction of high rigidity, composite, multi-blade and surface superfinishing. With the practical use of new tool materials and superabrasives and the advancement of machine tools, the high parameterization of machining is endless. At present and in the future, high speed will still have obvious advantages.
High-speed cutting machine requirements for machine tools High-speed cutting machines are one of the necessary conditions for high-speed cutting. The main requirements for high speed cutting on machine tools are as follows:
(1) It is necessary to have a variable speed range of the main shaft component that is adapted to the ultra-high speed operation, which is completely realized by the variable frequency speed control AC main shaft motor, and the motor and the machine tool main shaft are combined into one to form a so-called electric main shaft. The electric spindle is an ideal structure for a high-speed spindle unit because of its compact structure, light weight, low inertia, good response characteristics, and vibration and noise.
The core of the high speed spindle unit is a high speed precision bearing. The bearings that can be used for high-speed spindles include air bearings, hydrostatic bearings, dynamic pressure bearings, rolling bearings and magnetic bearings. At present, two new types of bearings suitable for ultra-high speed operation, ceramic rolling bearings and magnetic bearings, have been successfully developed and widely used in high-speed spindles.
The ceramic bearing made of ball of silicon chloride ceramic material has the advantages of high speed, high rigidity, low temperature rise and long life, and is a widely used and economical high speed bearing. At present, hybrid ceramic ball bearings (silicon chloride balls and steel rails) are mainly used on the spindle of high-speed machine tools, and the raceway can be coated or other surface treatment.
The magnetic floating bearing is a new type of intelligent bearing that uses electromagnetic force to suspend the spindle without mechanical contact. It has high speed performance, high precision, easy real-time diagnosis and online control. It is an ideal supporting component for high-speed machining machine spindles and has been used by many countries. High speed machining on the machine.
(2) There must be a quick response CNC servo system and feed components. High-speed machine tools are precision CNC machine tools. In the case of ultra-high-speed cutting, in order to keep the feed rate per blade constant, the feed speed must be greatly increased as the spindle speed increases. At present, the feed rate of the high-speed machining center and the NC milling machine table has reached 20 ~ 30m / min, the fast idle speed is up to 40 ~ 60m / min, the acceleration is 25m / s2, so the dynamic characteristics of the feed parts are very High requirements.
(3) During the ultra-high-speed cutting, the large-flow jet cooling system will generate a large amount of hot chips per unit time, which must be quickly removed from the workbench to avoid hindering the high-speed cutting and avoiding the heat of machine tools, tools and workpieces. Deformation.
(4) There must be a “three-rigid†(static stiffness, dynamic stiffness, thermal stiffness) machine support components such as polymer concrete, the so-called “artificial granite†Or the column, its damping characteristics are 7 ~ 10 times higher than cast iron, and the density is only 1/3 of cast iron.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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