On Turning the Vibration and Control

[Abstract] In the vibration machining has forced vibration and self-excited vibration, and machine tools, fixtures, tool and work process system consisting of the dynamic characteristics. Turning a detailed analysis of the main types of vibration and the resulting reasons, the vibration of the hazards, and from the tools, fixtures, cutting technology and other aspects of the measures to reduce or eliminate vibration.

[Keywords:] turning low-frequency vibration; high frequency vibration; elimination measures

[Abstract] In the machine process creation of vibration all have is forced a vibration and from arouse vibration, and tool machine, tongs, knife and work piece the dynamic state characteristic of craft system for constitute relevant.Detailed analysis the car pare to process medium vibration of main type and creation of reason, vibration of endanger, and from the knife, tongs, sliced to pare craft's etc. to put forward to let up or cancellation vibration of measure.

[Keywords:] The car pare low frequency vibration; High frequency vibration; Cancellation measure

Preface
In turning the vibration generated in the process, not only interfere with the normal cutting process, seriously affecting the surface quality of machined parts, machine tools and tool life will be shortened. The resulting noise and may even affect the morale operator on the normal carry out the work to bring a certain negative impact, and to reduce vibration, often had to reduce the amount of feed processing, which reduces productivity. I work through continued observation of this phenomenon, analysis, practice, review, and achieved Some effects are a few comments for our discussion.

1. In general, the classification of vibration in the vibration machining has forced vibration and self-excited vibration, and machine tools, fixtures, tool and work process system consisting of the dynamic characteristics. In the elimination of rotating machine components ( such as motors, parts, rotating shafts, etc.) and transmission (such as pulleys, bearings, hydraulic system pressure pulse, etc.) of the vibration, the vibration of the main turning process is not changing with the turning speed of self-excited vibration, is turning process bending vibration in the workpiece system (its frequency is close to the natural frequency of the workpiece low frequency vibration) and the Tool of the deformation of the bending vibration (the vibration frequency is close to the natural frequency of the turning tools high frequency vibration.)
2. Vibration Analysis of low frequency low frequency vibration, usually relatively low noise, vibration is more intense, leaving the surface of the vibration in the processing of traces of deep and wide. Usually in the low-frequency vibration system and the workpiece vibration cutting tool system are They sometimes becoming much, sometimes approaching, resulting in equal and opposite role and reaction. In the vibration process, when the workpiece when the tool becoming far, far from the cutting force F trend in the same direction with the piece displacement, the work is done positive, the system receives the input energy E (+), when the tool approaches the workpiece, the cutting force F tends to shift in the opposite direction and the workpiece, the work done is negative, the system energy consumption E (-), in the turning process , due to various factors can cause cyclical changes of cutting force, and to increasingly distant F> F approach, E (+)> E (-), that is, in each vibration cycle, the cutting force on the workpiece ( or tool) of the positive work done is always greater than its parts (or tool) of the negative work done, so that the workpiece (or tool) to obtain additional generating self-excited vibration of energy.

In the turning process, the impact of cutting force changes periodically, and to exit F> F cut people's situation the following factors:
2.1 Cutting and friction produced by relative motion of the tool. Ductile steel in the processing of the radial cutting force F when started with the increase of cutting speed, since the beginning of a pace, with the cutting speed increases. According to the principle known cutting , depends on the radial cutting force Fv cutting tool relative movement with friction, that is, cutting and tool rake face friction. friction with the friction velocity increases with the decrease of the feature, that is, negative friction characteristics. In mechanical systems, with negative friction characteristics of the system easier to stimulate the cutting vibration.

2.2 Regeneration cutting jobs due to rotation and vibration of the previous traces of the changes caused by periodic cutting thickness, thus affecting the cycle of cutting force. Generally speaking, after the turn (after time) cutting chatter relative to the previous turn ( last) the total cutting chatter is not synchronized, they will always be a phase difference ��, in a vibration cycle, the vibration pattern curves Yn = Ycos��t, Y n (t) in phase behind the last of the Yn -1 (t) is 0 <�� <�� the situation can be seen in the half cycle of vibration in the cutting thickness is greater than the average person's half-cycle of vibration, the average cutting thickness, cutting force so when the vibration made out of power greater than the vibration of people doing negative work when the cutting force, the system will have the energy input, vibration is likely to be maintained. So Yn Yn-1 lead over �� of the case, and lag time of just the opposite.

2.3 vibration, the tip trajectory of relative motion is a shape and position are not very stable, closed the approximate ellipse. This situation is turning thread or with a wide blade knife (blade width less than the pitch) turning the outer side thread circle is easy to produce, then a turn after a turn before the cutting and not cutting surface overlap. due to elliptical orbit with phase change, which led to periodic changes in the cutting surface, and ultimately lead to periodic changes in cutting force.

2.4 out tool in cutting the workpiece and the metal hardening encountered by different degrees, so that the cutting force in the change. In addition, the vibration of the tool during the cyclical changes in the actual geometry will lead to periodic changes of cutting force.

3. Damper measures from the above analysis, the occurrence of chatter system is not only related with the cutting process, but also the structure and stiffness of process systems for vibration characteristics, special propose appropriate measures to eliminate vibration.

3.1 In the low-frequency vibration, mainly due to the vibration caused Y cutting force direction changes, we have to increasingly distant F> F approach, the vibration produced. Therefore, in addition to increasing the system along the Y direction of the stiffness and damping, but try to reduce the cutting force Fy and any stop along the Y direction of the workpiece and the tool relative displacement factor can usually weaken or eliminate vibration. mainly the following types of measures can be taken:

Links to Research Papers Download http://www.hi138.com (1) turning, generally when v = 30 ~ 70m/min speed range, prone to vibration, so choose the turning speed of the cutting force should be avoided there With the rate of decline in the speed zone, in the high or low range for cutting, very easy to produce vibration.

(2) should be wide and thin as possible to avoid cutting the chip, or vulnerable to vibration. In the circumstances permit (such as the machine has sufficient rigidity, sufficient electrical power requirements of the surface roughness lower reference value, etc.) , and increase the feed rate and depth of cut also helps to reduce vibration suppression.

(3) increasing the rake angle �� appropriate to decrease the Fy force, thus weakening the vibration. But in the context of the higher cutting speed, rake angle on the vibration will be weakened, so the high speed machining with negative rake angle, will not produce strong vibration. usually double front damper blade, use Figure 1 to control the front f the width of the contact length of the cutting tool and can significantly reduce the cutting force to suppress vibration. low speed ��1> 0, high speed ��0 < 0, ��1 and ��2 difference between the 15 ��

(4) When the cutting depth and feed rate is constant, with the main angle K�� increases, cutting force Fy reduced. Therefore, an appropriate tool edge angle increases, you can eliminate or reduce the vibration. (5) Cutting Tools After the angle is too large or too sharp knife, cutting tool when the artificial parts, prone to vibration. When the horn is reduced to 2 �� ~ 3 ��, the vibration significantly reduced. in the back until it has a negative cutter chamfering, as shown in Figure 2 shows, about 0.1-0.3mm negative chamfer, can reduce the radial cutting forces and vibration suppression.

(6) cutting tool system if there is a negative stiffness, the easy to "eating people" workpiece vibration. Therefore, as far as possible to avoid the turret turning system produced negative stiffness on the vibration.

3.2 workpiece system and tool system stiffness is not the main reason for low frequency vibration, can be taken the following measures to eliminate or reduce the vibration:
(1) or four claws with claw clamp the workpiece as the workpiece and the spindle rotation center rotation center of the coaxial error minimum, to avoid cutting the workpiece is tilted or uneven cutting caused intermittent cutting force generated by the cyclical changes vibration.

(2) processing time with a slender shaft with the knife, the center frame can increase the stability of the cutting process.

(3) when turning instead to adopt a flexible top dead center, the top edge to avoid excessive force causing the size of the workpiece is bent or not achieve the top of the workpiece supporting the role of swing, and note that not too long overhang tailstock sleeve.

(4) Regular inspection of extension units and large carriage, a small knife between the dovetail rail and the extension units of the exposure, adjust the clearance section helical inserts to prevent movement when crawling tool holder. In addition, you can scrape it with a Research association surface enhancement methods to improve the coupling stiffness of the vibration of structural systems.

(5) reasonable arrangements for the direction of the main cutting force, such as cutting off and reverse the workpiece, the cutting force direction and the direction of maximum stiffness line system will improve system stability.

3.3 high frequency vibration frequency is high, shrill noise generated in the processing of the surface traces of fine and dense, the vibration is vibration of the tool itself, and the workpiece and machine components are very stable. The main cause is As the larger flank wear, the friction between tool and workpiece behind the decline in performance caused by high frequency vibration to eliminate or reduce the measures are: (1) reduce the turning tool overhang length.

(2) Strengthening Tool and the arbor of the bending stiffness.

(3) the timely replacement of a large tool flank wear.

(4) installed the tool, should ensure that the workpiece holder and the center of rotation perpendicular to the force when tightened evenly to avoid bending Arbor receive the uneven and vibration.

(5) the use of damping devices.

4. Conclusion for turning through a series of different vibration generated in the process, the reasons for the analysis of vibration response after the measures taken can significantly reduce the vibration during turning, improved surface quality and productivity, to extend the tool life.

References
[1] Chen Yu. Sewing technicians, skills [M]. Beijing: China Labor and Social Security Publishing House. 2003.

[2] Pender shade. Cut technology and skills training [M]. Beijing: China Labor and Social Security Publishing House, 2001.

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