Types of Vibration in Boring Process and Its Treatment
1、 Type of oscillation in boring process
1. Forced oscillation
It is an oscillation caused by the effect of external periodic disturbance force. Such as intermittent cutting, uneven rotation of the rotary table when machining large holes, and uneven transmission organization of the machine tool.
2. Self-excited oscillation
It is an undamped oscillation based on the natural frequency of the machine tool part thing system The reason why it can remain undamped is that the oscillation process itself can affect the periodic change of the external force, which in turn makes the system make up the most periodically, and then maintains the existence of the oscillation, such as the zigzag oscillation and torsional oscillation of the file rod in file cutting.
2、 Methods of Reducing Oscillation in Boring Process
1. Reasonable selection of cutting parameters
In boring, the cutting parameters have a great influence on the onset of oscillation. Choosing the cutting parameters reasonably is usually one of the useful methods to prevent the onset of oscillation. Therefore, in order to prevent the onset of vibration, it is often necessary to choose a lower cutting parameter For example, when the hole diameter is large, the imbalance of the key cutter head often leads to forced oscillation, which forces the cutting speed not to be high. At this moment, boring with a lower cutting speed is more stable. For the selection of cutting depth and feed rate, cutting depth and feed rate are usually selected The method of increasing the number of knife passes can greatly reduce the occurrence of oscillation. This has an important meaning for the fine key hole.
2. Reasonable selection of several parameters for grinding and impacting cutter head
According to the raw materials and processing quality requirements of parts, W cutter head suitable for several parameters is selected and ground The main deflection angle and rake angle of the tool have a great influence on the oscillation strength. Because the smaller the main deflection angle is, the wider the chip section will be, and the chip will become wide and thin, which is easy to oscillate. On the contrary, the larger the main deflection angle of the tool is, the smaller the cutting resistance Py is, and the oscillation is not easy to occur. Generally, the main deflection angle is 90 '-- 45. The scale is more suitable Under any cutting olive, decreasing the rake angle of the tool will promote the oscillation intensity, so it is suitable to increase the rake angle to reduce the body and force, and then weaken the oscillation The size of the most suitable front angle should be selected according to the rigidity of the system. The worse the rigidity of the system, the larger the front angle should be. When the back angle of the cutter increases and the grinding is too sharp, the cutter edge in boring is easy to gnaw into the machined surface of the part, which is called the cutter image. This will seriously improve the roughness of the machined surface In practice, the sharpened blade is ground with an oilstone to make it properly passivated or ground to a negative back angle of 5-10 degrees, which can play a role in vibration elimination Therefore, in the case of rough wok and fine file (semi fine key), properly reducing the back angle can weaken the oscillation, while in the case of fine boring, due to the small back angle, the rear side conflict will lead to the intensification of the oscillation, so properly increasing the back angle can also weaken the oscillation intensity.
3. Try to improve the rigidity of boring machine and accessories
Adding the rigidity of the boring machine system and the rigidity of the accessories has a direct impact on weakening or eliminating the vibration. The method is to eliminate the excessive clearance in each part of the boring machine Adjust them to the cooperation precision and clearance allowed by the machine tool. The cooperation gap of assistive devices shall be minimized under the condition of ensuring functions The diameter of boring bar shall be selected with larger diameter and shorter length. When using the long boring bar, some additional supporting equipment or guiding equipment should be selected as far as possible to reduce the vibration in the mirror cutting process. Secondly, when the auxiliary tools are connected with the spindle taper hole, it is better not to use the reducing sleeve, but to use the direct insertion connection
4. Selection of damping equipment knife bar
In practice production, some box parts have small diameter holes and are far away from the external box wall of the box due to the connection in layout. At this time, they must be processed with slender boring bars. Even if the angle is picked up to the minimum cutting depth, the vibration will still occur. In this case, it is necessary to select some boring bars with vibration elimination equipment for processing. Figure 3-9 shows the structural diagram of the vibration and impact reduction cutter bar
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