Processing technology and high-speed machine tools

Machining technology of high-speed cutting and high-speed machine tools

in modern machining technology, high-speed cutting is being mentioned more and more, and its technology has begun to be used, followed by high-speed machine tools. Then, what is the difference between high-speed cutting and traditional cutting technology? What are the conditions for its realization? What are the benefits of implementing it? How applicable is it? This paper will try to answer these questions, and try to analyze the structure and characteristics of Mikron's machine tool in combination with the actual glass fiber length (i.e. the preservation length of glass fiber) in Rui abs+gf material, which is currently at the leading level in the world, which is always far lower than the length of raw glass fiber. It will be compared with the traditional processing methods and cutting theories still widely used in China at present, so as to promote the application and popularization of high-tech in China

high speed machine tools

shortening the cutting and non cutting time during processing, reducing the processing procedures for complex shapes, difficult to machine materials and high hardness materials, and maximizing their advantages to achieve high precision and high quality products are an important goal for us to improve labor productivity and achieve economic production

some people think that when it comes to high-speed machining, the spindle speed needs tens of thousands of revolutions; As long as the spindle speed reaches tens of thousands of revolutions, high-speed cutting can be achieved, which is actually not comprehensive

with the development of science and technology, modern machine tools have the following conditions, and only with these conditions can high-speed cutting become possible

1. The spindle of electromechanical integration is the so-called motorized spindle. The modern spindle is an organic combination of motor and spindle. Electronic sensors are used to control the temperature. Its own water cooling or oil cooling circulation system makes the spindle "constant temperature" at high speed; In addition, due to the use of new technologies such as oil mist lubrication and mixed ceramic bearings, the spindle can be maintenance free, long life and high precision. Due to the electromechanical integration of the spindle, minus the pulley, gearbox and other intermediate links, the spindle speed can easily reach 0 ~ 42000r/min, or even higher. Moreover, due to the simplification of the structure, the cost is reduced, the accuracy and reliability are improved, and even the cost of the machine tool is reduced. The noise and vibration sources are eliminated, and the heat source of the spindle itself is also eliminated. Mikron adopts the motorized spindle produced by the group's "step-tec" company. This motorized spindle adopts its special and most advanced vector closed-loop control, high dynamic balance spindle structure, oil mist lubricated hybrid ceramic bearing, and a temperature control system that can be adjusted with room temperature to ensure that the temperature of the spindle is constant during all working hours

what is vector closed-loop control? In fact, with the help of D/a conversion, the electric quantity of the AC asynchronous motor is transformed into the DC model. In this way, the advantages of the DC motor can be realized by using the brushless AC motor, that is, at low speed, the full torque is maintained, the power is output in full, and the spindle motor starts and brakes quickly. Taking ucp710 machine tool for cutting 45# steel as an example, the spindle of step-tec is used for milling. The diameter of milling cutter is 63mm, the spindle speed is 1770r/min, and the amount of metal cutting is 540cm/min; When drilling without bottom hole, the drill bit with a diameter of 50mm and a rotating speed of 1350r/min can be drilled at one time, without the common method of drilling a central hole first, then drilling and then expanding the hole

2. Linear rolling guide rail is widely used in machine tools to replace the past sliding guide rail, and its moving speed, friction resistance, dynamic response, and even damping effect have changed qualitatively. A few hundred kilograms or even thousands of kilograms of heavy workbench can be pushed by hand. Its unique double V-shaped structure greatly improves the torsional resistance of the machine tool; At the same time, because the wear is almost zero, the precision life of the guide rail is several times higher than that in the past. In addition, due to the use of digital servo drive motor, its feed and fast-moving speed has increased from the highest 6m/min in the past to 20 ~ 60m/min now. The latest machine tool of Mikron company uses linear motor, and the feed and fast-moving speed can reach 80m/min

3. At present, the most advanced CNC system can control more than 8 axes at the same time, realizing five axes and five linkage, or even six axes and five linkage. With multiple CPUs, the processing time of data blocks does not exceed 0.4ms; At the same time, they are equipped with powerful post-processing software, which has fast calculation speed, strong simulation ability, and has the "forward-looking" function during program operation, so they can intervene and modify at any time. External socket, fast data transmission speed, and even direct connection with Ethernet; Coupled with the full closed-loop measurement system and the use of digital servo drive technology, the linear movement of the machine tool can achieve 1 ~ 2G acceleration and deceleration

4. The structure of machine tool bed is further optimized. Modern machine tools adopt floor type bed, integral cast iron structure, and the spindle column of gantry frame. As far as possible, the linear movement of two or even three axes is realized by the spindle components. Considering that the change of tool weight is very small, in this way, the weight of the fast and linear moving parts of the machine tool is almost constant without the rapid linear movement of the workpiece and even the workbench. Therefore, It is easier to realize the inertia and dynamic balance under the condition of rapid acceleration and deceleration, and reduce the instability caused by dynamic impact, so as to ensure stable and higher machining accuracy and product quality

5. The development of cutting tool materials and technology is also an important factor for the realization of high-speed cutting. In high-speed cutting, the cutting force is no longer an important factor, and large cutting torque is not required, so the tool handle is no longer a traditional conical handle, but a short round handle, that is, HSK handle, which does not need to pull nails. The spindle locking device fully considers the influence of centrifugal force. The important thing is to need dynamic balance, that is to add a dynamic balance ring. After the tool is installed, it is balanced by the dynamic balance instrument. The cutting tool itself adopts full body cemented carbide cutter, or coated with CBN, tic, etc. on the cemented carbide, or artificial diamond, i.e. PCD, etc., so that the cutting tool can withstand a cutting linear speed of up to 300 ~ 500m/min

6. When cutting, oil mist is used to lubricate the processing area instead of traditional cooling and lubricating fluid

high speed cutting

as the name suggests, high speed cutting, first of all, is high speed, that is, high spindle speed, such as 12000r/min, 18000r/min, 30000r/min, 40000 R/min, and even higher speed is still under test; On the other hand, there should be a larger feed rate, such as 30000mm/min, 40000mm/min, or even 60000mm/min; Then there is fast movement, fast tool change, the acceleration time of the spindle from static to its required speed after tool change, and so on. Only when the above standards are met can it be called high speed

secondly, it is necessary to select appropriate and reasonable parameters for different processing objects, different hardness, different tensile testing machines, materials suitable for chemical consumption enterprises, and different shapes, instead of blindly pursuing high-speed and high-speed, especially for cavity processing, the shape is complex and the tool diameter is small, because the motion path of the tool is not a simple straight line motion, but a curve, and even a right angle turning, The rationality of the process parameters is particularly important, because if you want to maintain the same feed speed for right angle cutting, it may cause the sudden fracture of the tool during the bending movement due to the huge inertia of the moving parts of the machine tool, and the variable-speed movement will cause the instantaneous change of the cutting thickness due to the acceleration and deceleration, which will lead to the change of the cutting tool and the cutting lines on the surface of the workpiece, thereby reducing the processing quality. Therefore, For different machining objects, programmers need to choose a reasonable tool path and optimize cutting parameters; On the other hand, choose the appropriate cutting speed according to the needs. Only in this way can we really give full play to the advantages of high-speed cutting

using high-speed cutting, we can achieve the following goals:

(1) due to the small cutting depth and thickness, the cutting amount of each edge of the tool is very small, so the force on the spindle and guide rail of the machine tool is small, the precision life of the machine tool is long, and the tool life is also extended

(2) although the cutting depth and thickness are small, because the spindle speed is high and the feed speed is fast, the metal removal amount per unit time is increased, and the processing efficiency is also improved

(3) rough machining, semi precision machining and precision machining can be integrated during machining, all of which are completed on one machine tool, reducing the number of machine tools and avoiding accuracy errors due to multiple clamping

(4) it can process high hardness and difficult to process materials (up to about 62Hrc), and it can drill holes below 1mm

(5) the most important thing is that the processing time is short and the economic performance is good

application of high-speed cutting

at present, high-speed cutting is no longer a technology in the laboratory. It is more applied to the following aspects. (1) Non ferrous metals, such as aluminum, aluminum alloys, especially thin-wall processing of aluminum. At present, the formed surface with thickness of 0.1mm and height of tens of millimeters can be cut

(2) graphite processing. Graphite electrodes are widely used in mold cavity manufacturing due to EDM. However, graphite is very brittle, so high-speed cutting must be used to better shape processing

(3) processing of molds, especially hardened molds. Since hardened materials can be purchased directly from suppliers, the mold can be cut out directly by using high-speed cutting, which not only saves the previous processes of machining → electrical machining; Save man hours. At present, high-speed cutting can achieve high surface quality (RA ≤ 0.4um), so the grinding and polishing processes behind EDM are omitted; On the contrary, the compressive stress state of the machined surface formed in cutting will also improve the wear resistance of the surface of the die workpiece (according to statistics, the service life of the die can be increased by 3 ~ 5 times). In this way, it is possible that the forging die and casting die can be machined only by milling

(4) hard and difficult to cut materials, such as heat-resistant stainless steel

applicability of high-speed cutting

as a new technology, the advantages of high-speed machining are obvious. It has brought a revolutionary change to the traditional metal cutting theory. So, is it universal? Obviously not. At present, even in Switzerland, Germany, Japan and the United States, which have advanced metal cutting machine tools, the research on this new technology is still in the process of continuous exploration and research. In fact, people have little experience in high-speed cutting, and there are still many problems to be solved: for example, the dynamic and thermal characteristics of high-speed machine tools; Tool material, geometric angle and durability, interface technology between machine tool and tool (tool dynamic balance, torque transmission), selection of cooling and lubricating fluid, post-processing of cad/cam program, optimization of tool path in high-speed machining, etc. So far, the machine tool with a spindle speed of 42000r/min of Mikron company in Switzerland is really used in actual processing in China. Nanjing University of Aeronautics and Astronautics purchased the machine tool with a spindle speed of 18000r/min of Mikron, Shanghai Jiaotong University and Dalian University of technology also bought the machine tool with a spindle speed of 18000r/min. Shandong University of technology, Xi'an Jiaotong University and Beijing University of technology will purchase high-speed machine tools for corresponding research. It should be said that in China, high-speed cutting has not officially entered the university classroom. If some professors and tutors are still blank in their minds, how can they teach students and develop corresponding technologies? Not to mention the situation of domestic machine tool manufacturers