Application skills of end mills in the processing of pipe fitting joints

In the processing of pipe fitting joints, the application skills of end mills are mainly reflected in tool clamping, vibration control, optimization of cutting parameters, and selection of processing strategies, etc. The following is a specific analysis:

Tool clamping

Most end mills used in machining centers are clamped by spring clamps and are in a cantilever state when in use. During the milling process, there may sometimes be a phenomenon where the end mill gradually extends out of the tool holder or even completely falls off, resulting in the scrapping of the workpiece. The reason for this is generally that there is an oil film between the inner hole of the tool holder and the outer diameter of the end mill shank, causing 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 mist-like oil film will adhere to the inner hole of the tool holder. When there is an oil film on both the tool holder and the tool holder, it is difficult for the tool holder to firmly hold the tool holder, and the end mill is prone to loosening and falling during processing. Therefore, before clamping the end mill, the shank part of the end mill and the inner hole of the tool holder should be thoroughly cleaned with cleaning solution, dried and then clamped. When the diameter of the end mill is relatively large, even if the tool holder and the tool holder are very clean, a tool drop accident may still occur. At this time, a tool holder with a 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 clamping port during processing. The reason is usually that the clamping port has been used for too long and worn into a conical shape. At this time, a new clamping should be replaced.

Vibration control

Due to the tiny gap between the end mill and the tool holder, the tool may vibrate during the machining process. Vibration will cause the cutting depth of the circumferential edge of the end mill to be uneven, and the cutting allowance will increase compared to the original value, affecting the machining accuracy and the service life of the tool. However, when the width of the machined groove is too small, the tool can be purposefully vibrated to obtain the required groove width by increasing the cutting expansion. But in this case, the maximum amplitude of the end mill should be limited to less than 0.02mm; otherwise, stable cutting cannot be carried out. The smaller the vibration of the neutral milling cutter during normal processing, the better. When tool vibration occurs, it is necessary to consider reducing the cutting speed and feed rate. If significant vibration still exists after both have been reduced by 40%, the depth of cut should be reduced. If resonance occurs in the processing system, the reasons may be excessive cutting speed, insufficient feed rate, insufficient rigidity of the tool system, insufficient workpiece clamping force, as well as factors such as the shape of the workpiece or the clamping method of the workpiece. At this time, measures such as adjusting the cutting parameters, increasing the rigidity of the tool system, and raising the feed rate should be taken.

Cutting parameter optimization

The selection of cutting speed mainly depends on the material of the workpiece being processed. The selection of feed rate mainly depends on the material of the workpiece to be processed and the diameter of the end mill. Some foreign tool manufacturers’ tool samples are accompanied by tool cutting parameter selection tables, which can be used for reference. However, the selection of cutting parameters is also influenced by multiple factors such as the machine tool, tool system, shape of the workpiece to be processed, and clamping method. The cutting speed and feed rate should be appropriately adjusted according to the actual situation. When tool life is given priority, the cutting speed and feed rate can be appropriately reduced. When the chip’s removal from the cutting edge is not good, the cutting speed can be appropriately increased.

Selection of processing strategy

In the CNC milling of the cavities of workpieces such as molds, when the cutting point is a concave part or a deep cavity, the extension of the end mill needs to be increased. If long-edge end mills are used, due to the large deflection of the tool, vibration is likely to occur and the tool may break. Therefore, during the processing, if only the cutting edge near the end of the tool participates in the cutting, it is best to choose a short-edge long-shank end mill with a longer total tool length.