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what causes bowing in cylyndrical parts between centers on a cnc turning center

Views:0     Author:Site Editor     Publish Time: 2019-10-19      Origin:Site

Axial workpieces with a ratio of length L to diameter d greater than 25 are call elongated axes. The shape of the elongated shaft is not complicated. But, due to its low stiffness.  Also, the turning process will also affect by cutting force, gravity, cutting heat. And other factors.  

Thus, bending deformation and vibration are generat. Defects such as taper, waist drum shape and bamboo shape. This makes it difficult to guarantee machining accuracy. Can't even process. Although the processing of the elongated shaft is difficult. Yet, it has the commonality of processing ordinary workpieces. 

This paper discusses some difficulties and solutions slender shaft turning. Grab the commonality of turning. Combine the personality of the slender shaft.  Solve turning tool rigidity, thermal deformation elongation. And three key technologies for reasonable selection of geometric parameters of turning tool. .The turning of the slender shaft is also easy.

The problems encountered slender shaft turning

1. The workpiece is subject to cutting resistance and generates vibration and bending deformation. Reduce geometric accuracy and surface finish.

2. The heat of cutting absorbed by the workpiece during the cutting process. This can result in a large axial expansion of the workpiece. Increase bending deformation and increase vibration. Even the workpiece squeezed  between the two tips. Caused by the inability to process.

3. The longer the ratio of long neck to neck, the greater the self-gravity. Because the workpiece is at high speed. Thus, the centrifugal force generated is also larger. And the up and down jump will affect the processing quality.

4. The geometric angle of the tool. The amount of cutting and processing methods are not selected. Will increase the cutting force. Deformation and vibration are exacerbate.

5, the workpiece bending and vibration, the turning must use a lower speed and depth of cut. Limits the increase in production efficiency.

6. The workpiece is under the action of radial cutting force. The shape of the workpiece that has been machine by turning is easy to form a small end. And a large middle, and it is easy to produce a "knife" phenomenon.

7, the machine tool is adjust, easy to produce cone error. Improper change of the fixture, easy to cause bending and produce "bamboo", "diamond" and so on.

Second, the solution to the problem

In production practice. To ensure the machining accuracy and surface quality of the elongated shaft. Increase productivity. We have taken the following measures:

1. To compensate for the lack of rigidity of the elongated shaft. In turning, the tool holder should use. To improve the rigidity of the workpiece and reduce deformation.

2, pay attention to the specific operation methods. There are more stringent process requirements and measures. To ensure the rigidity of the entire process system. Allow the workpiece to achieve the necessary geometric accuracy and surface finish.

3. Turn from left to right in the opposite direction. Reduce internal stress and bending deformation. Guarantee straightness and dimensional accuracy. High processing efficiency and adaptability.

4. Reasonable selection of cutting amount. And tool geometry and parameters.

Third, the reverse direction of the knife method to turn the slender shaft

1. Processing geometry accuracy and surface quality requirements are high. Thus, the conventional machining method is to clamp. the workpiece between the main shaft and the tailstock. There is no flexibility at both ends. And the workpiece is under the influence of cutting force and thermal expansion. Produces internal stress and bending deformation. It is not easy to guarantee straightness and dimensional accuracy. The reverse direction method is one way to overcome the above phenomenon. Suitable for medium speed roughing and large cutting low speed finishing. And has a strong adaptability. The accuracy of the machine tool is not high. High processing efficiency and other characteristics.

2. Processing principle: Turning in the opposite direction is to feed from the spindle of the lathe to the tailstock. The workpiece is clamp from the three-claw self-centering chuck from the turning. Make the clamped end a fixed point that cannot be tilted . Now, the longitudinal cutting generated in the cutting tends toward the tailstock along the workpiece axis. The workpiece is tensioned by the axial force. Increased the actual stiffness of the workpiece. There is no bending (bow) deformation. At the same time, when turning the knife in the opposite direction. A larger feed rate is used, which increases the longitudinal cutting force. Reduce radial runout and reduce and drop large vibrations. The surface quality of the machined surface is guaranteed.


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