Discussion on NC programming and practical experie

2022-09-23
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Discussion on NC programming and practical experience of high-speed machining

these attractive products have produced a large number of frying speed machining, as one of the high-efficiency processing means, has been widely used in the current manufacturing industry. After high-speed machining entered the practical stage at the end of last century, it immediately received a response in the domestic manufacturing industry. At the initial stage, our engineering and technical personnel were very unfamiliar with such processing equipment and programming means, so they encountered many problems in practical application. Up to now, such processing means are far from being familiar and mastered by the majority of engineering and technical personnel, which can be seen from the current media and the reflection on the forum. Here are some problems and skills in high-speed machining. 1 Temperature control of extruder host: some discussion, I hope to bring you some inspiration and help

high speed machining includes two meanings: one is high spindle speed. Generally, the spindle speed is at least 12000 rpm, and at present, it is up to 60000 RPM (Mikron can provide such equipment). The second is high-speed feed. The feed speed is generally a few meters or even tens of meters per minute. Due to the great difference between the normal working state of machine tools and cutting tools and ordinary machining, the old ideas can no longer be used when writing NC machining programs and technological processes

in the process of high-speed machining, due to the large feed speed, the inertia of the machine tool spindle (or workbench and other moving parts) becomes an element that cannot be ignored, which should be fully considered in the process of machine tool design and control system selection. As a successful product facing the market, this kind of equipment must have made many improvements in this aspect in the design and manufacturing process. But don't think that the inertia problem has been completely solved. In the process of use, users should always consider this factor, otherwise improper use will not only shorten the service life of the existing high-speed processing equipment, but also affect the quality of your products. How to improve the design and manufacturing process of machine tools is not discussed here, but we are concerned about the precautions in the use process

in order to avoid the influence of machine tool inertia in the process of high-speed machining, theoretically, as long as we try to reduce the change of feed direction in the process of machining, but it is really impossible to achieve in practice. Changing the feed direction is inevitable and often used. At this time, we should try to change the direction when the tool is empty, not when the tool is in the cutting state; Or reduce the feed speed before changing the feed direction; This poses a problem for us to write machining programs. At this time, we can choose the appropriate CAM software to complete the programming work

for example, in the example in Figure 2, we choose the spiral method for milling, and its effect is much better than the traditional milling method in Figure 1

try to change the feed direction when the tool is not in the cutting state. For example, the following two examples:

Figure 3: use arc export (import) to change the cutting direction when the tool is in a non cutting state

Figure 4: change the cutting direction when the tool is completely exported

when machining special shapes such as cavities, because the tool cannot be exported, when programming, try to use arc transition in the corner part, so as to make the steering as smooth as possible, If the feed speed can be properly reduced at the corner, the effect will be better

in high-speed machining, we also need to pay attention to the control of cutting depth. There are two levels to pay attention to, one is the axial cutting depth of the tool, and the other is the radial cutting depth of the tool. The control of cutting depth plays a key role in whether a beautiful part can be machined and the service life of the tool can be prolonged. At present, most users are used to using high-speed machining when finishing. In fact, using high-speed cutting when rough machining can eliminate machining allowance faster, and it should also be popularized; Generally, in the rough machining process, the most commonly used machining method is to use axial small cutting depth and multiple layered cutting to remove the machining allowance; In the process of finishing, high-speed cutting with small allowance can get good surface processing quality, which is mainly aimed at the finishing in the process of mold manufacturing. We can't absolutely copy it. For example, when finishing long edge strips, we should consider the influence of machining deformation. If we choose the finishing method with small allowance at this time, the influence of edge strip deformation will be increased. At this time, we usually use the method of large allowance layered cutting to reduce the influence of the middle deformation of the edge strip. That is to say, more allowance should be reserved during rough machining, rather than less allowance for finish machining; (generally, when machining such slender edge strips, it is not easy to machine the middle part of the edge strips without deformation when the width to depth ratio reaches 1:5. If high-speed machining is adopted, it is easy to reach 1:10) as shown in the following figure:

Figure 5 example of large allowance layered cutting finish machining edge strips in high-speed machining

the selection of tools in high-speed machining is very important, At present, almost all tool suppliers can provide tools suitable for high-speed machining. The selection of tools mainly includes the following two aspects: one is the dynamic balance state of the tool under high-speed rotation, and the other is the effective cutting time of the tool (i.e. tool life). In order to ensure that the tool can rotate stably around the axis under the condition of high-speed rotation, two methods are adopted at present: one is to use the tool with dynamic balance device, and the tool sleeve is equipped with mechanical blocks or adopts fluid dynamic balance design; The other is to use the integral tool, which integrates the tool sleeve and the tool body. In fact, the purpose is to ensure that the installation clearance between the tool body and the tool sleeve is reduced during the installation process. The integral tool is the most ideal. However, as the tool sleeve and the tool body are integrated, once the tool quantity M2 is liquidated, the tool body will be scrapped, and the tool sleeve will be scrapped together, so the cost is high. Using the method of thermal expansion and cold contraction to clamp the tool can also get a good effect, that is, the tool sleeve is heated by the heating device and then installed into the tool body, and the tool can be tightened after cooling. In the process of high-speed machining, the wear of cutting tools is much larger than that in the low-speed state, so the service life of cutting tools is also a reason that affects the wide application of high-speed machining. When using high-speed machining, we should find a balance point between reducing costs and improving efficiency according to the actual situation of the factory, so as to truly reflect the value of high-speed machining

whether to choose high-speed machining or not should not blindly follow the trend. In fact, it is not suitable for all industries to adopt this kind of machining method. High speed machining can certainly improve processing efficiency, but because the cost of equipment and cutting tools also increases correspondingly, it is particularly important to find a balance point between improving efficiency and reducing cost. High speed machining can not only improve machining efficiency, but also overcome some technological problems encountered in low-speed machining. For example, the deformation of parts in the process of processing is a headache in engineering application. Using ordinary processing methods often can not get ideal results. At this time, we can consider using high-speed processing to solve it. First of all, 90% of the cutting heat generated in the process of high-speed cutting is taken away by chips rather than transmitted to the workpiece, which can greatly reduce the thermal deformation of the workpiece due to the transfer of cutting heat into the workpiece. Secondly, in the above example, we can see that after all, a query vocabulary for matching is formed. In the process of machining long edge strips, if the method of small cutting depth and layered machining is adopted, the influence of radial cutting force on the workpiece can be reduced, so as to reduce the deformation of the workpiece. In addition, high-speed machining has a recognized advantage, that is, the surface quality after machining is very good. If high-speed machining is used to meet some process requirements, the cost factor is not so important. In short, whether to adopt high-speed machining or not, the proportion of high-speed machining should be determined according to the situation of the factory itself

high efficiency machining means at present, in addition to high-speed machining, strong cutting with large cutting depth is also an effective means. Before the high-speed machining was not practical, people have done a lot of research and discussion in this area. At present, high-speed small deep cutting is more popular, but large deep cutting and strong cutting have not been forgotten. Maybe one day it will be paid attention to again, because different industry characteristics and processing content have different goals

this paper describes some characteristics of high-speed machining and some precautions in the programming process, and puts forward some solutions to the problems encountered in the practice process. The above views are for reference only, welcome to discuss! The programming method mentioned in this paper is provided by the new generation of NC programming software Edgecam. (end)

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