When milling complex workpieces on a milling machining center, the use of CNC end mills should pay attention to the following issues:
1. Clamping of end mills
Most of the end mills used in machining centers adopt the spring clamp set clamping method, and they are in a cantilever state during use. During the milling process, sometimes the end mill may gradually protrude from the tool holder, or even fall completely, causing the workpiece to be scrapped. The reason is generally between the inner hole of the tool holder and the outer diameter of the end mill holder. There is an oil film, resulting in insufficient clamping force. End mills are usually coated with anti-rust oil when they leave the factory. If non-water-soluble cutting oil is used during cutting, a misty oil film will also be attached to the inner hole of the tool holder. When there is an oil film on both the tool holder and the tool holder, the tool holder It is difficult to clamp the tool holder firmly, and the end mill is easy to loosen and fall during processing. Therefore, before the end mill is clamped, the shank of the end mill and the inner hole of the tool holder should be cleaned with cleaning fluid, and then clamped after drying.
When the diameter of the end mill is large, even if the tool holder and the tool holder are clean, a tool drop accident may still occur. At this time, the tool holder with flattened notch and the corresponding side locking method should be selected.
Another problem that may occur after the end mill is clamped is that the end mill breaks at the tool holder port during processing. The reason is generally because the tool holder has been used for too long and the tool holder port has worn out into a cone.
2. Vibration of the end mill
Due to the tiny gap between the end mill and the tool holder, the tool may vibrate during the machining process. Vibration will cause uneven cutting of the circumferential edge of the end mill, and the cutting and spreading amount will be larger than the original value, which will affect the machining accuracy and tool life. But when the processed groove width is too small, the tool can also be purposefully vibrated, and the required groove width can be obtained by increasing the cutting and expanding amount. In this case, the maximum amplitude of the end mill should be limited to less than 0.02mm , Otherwise stable cutting cannot be performed. In normal processing, the vibration of the end mill is as small as possible.
When tool vibration occurs, you should consider reducing the cutting speed and feed rate. If both have been reduced by 40% and there is still greater vibration, you should consider reducing the amount of tooling.
If the processing system resonates, it may be caused by factors such as excessive cutting speed, low feed rate, insufficient tool system rigidity, insufficient workpiece clamping force, workpiece shape or workpiece clamping method, etc. At this time, adjustments should be taken to cut Measures such as increasing the rigidity of the tool system and increasing the feed rate.
3. End cutting of end mills
In the numerical control milling of the cavity of a workpiece such as a mold, when the cut point is a concave part or a deep cavity, the extension of the end mill needs to be lengthened. If a long-edged end mill is used, due to the large deflection of the tool, it is easy to produce vibration and cause the tool to break. Therefore, in the machining process, if only the cutting edge near the end of the tool is required to participate in the cutting, it is best to choose a short-edged long-shank end mill with a longer total tool length. When using a large-diameter end mill on a horizontal cnc machine tool to process a workpiece, the deformation caused by the weight of the tool is relatively large, and more attention should be paid to the problems that are prone to edge cutting. In the case of a long-edged end mill must be used, the cutting speed and feed rate must be greatly reduced.
4. Selection of cutting parameters
The choice of cutting speed mainly depends on the material of the workpiece to be processed; the choice of feed speed mainly depends on the material of the workpiece to be processed and the diameter of the end mill. The tool samples of some foreign tool manufacturers are attached with a tool cutting parameter selection table for reference. However, the selection of cutting parameters is also affected by many factors such as the machine tool, the tool system, the shape of the workpiece to be processed, and the clamping method. The cutting speed and feed rate should be adjusted appropriately according to the actual situation.
When the tool life is the priority factor, the cutting speed and feed speed can be appropriately reduced; when the chip leaving the edge condition is not good, the cutting speed can be appropriately increased.
5. Selection of cutting method
Climbing milling helps prevent damage to the cutting edge and can increase tool life. But there are two points to pay attention to: ① If you use ordinary machine tools, you should try to eliminate the gap of the feed mechanism; ② When the surface of the workpiece is left with the oxide film or other hardened layers formed by the casting and forging process, it is advisable to use up-cut milling.
6. The use of cemented carbide end mills
The application range and application requirements of high-speed steel end mills are relatively wide. Even if the cutting conditions are slightly improperly selected, there will be no major problems. Although cemented carbide end mills have good wear resistance during high-speed cutting, their use range is not as wide as that of high-speed steel end mills, and the cutting conditions must strictly meet the requirements of the use of the tool.
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