In general, when a lathe is used for machining, a so-called "vibrating knife" may occur in the following cases:
(1) Forming turning using a forming blade.
(2) External turning of the slender round bar.
(3) External turning of thin meat round rods.
(4) Turning of box-shaped parts (such as sheet metal welded structural parts).
(5) Cutting of super-hard materials.
(6) The bearing has been damaged and continues to cut.
When the vibrating knife occurs, the vibration of the tool, the workpiece and the lathe often causes harsh noise inside the factory, and the amplitude of the amplitude is several tens of micrometers (μm) or more, and sometimes it is more than 100 micrometers. This vibrating knife not only causes the clamping of the tool or the workpiece to become loose, but also causes a bad physical and mental impact on the operator due to its noisy noise, and the machining accuracy cannot meet the requirements of the customer, so the tool machine manufacturers do not The war and the ruthlessness of the vibrating knives are regarded as a big challenge.
This article briefly describes the classification and removal methods of the "vibration knife", and illustrates the problem of the elimination and prevention of the vibration knife in a practical case. Through the actual measurement of the instrument, the original vibration can be improved by more than ten times by partial modification design.
First, the basic method
The chattering theory analysis of the machine tool is quite difficult in the research of the machine tool. The source of the tool is quite related to the processing material, mechanical design and cutting conditions [2, 3]. Explain the entire cutting system, in which the "cutting process" involves the hardness of the material (workpiece), the size of the feed, etc., while the "machine structure" part involves the structural strength design of each machine tool, such as the spindle bearing, head Features such as body, cutter design and tool clamping.
Since the theory has a lot of mathematical equations [4], this part is not introduced in depth here. It only divides the vibration knife phenomenon that often occurs in general customers into the following two categories:
(1) Forced Vibration (Forced Vibration)
This is the forced vibration caused by intermittent cutting or the vibration caused by the turning of the rotating parts. Generally, common noise such as bearing damage or poor gear meshing and poor workpiece clamping, spindle This phenomenon is such a phenomenon that the swing is too large. Among such problems, intermittent turning is a processing technology problem, and most of the parts are derived from the assembly technology of the machine tool and the quality control of its key components, and also related to the machine structure design concept. It is characterized by the fact that the characteristics of the vibration are directly related to the magnitude of the number of revolutions.
(2) Self-excited Uibration
This is because the periodic work of the irregularities caused by the periodic unevenness of the cycle and the repeated effects of the regenerative effect are generally called "resonance", and the main cause comes from the machine tool. The natural frequency of the structure is excited or caused by the excitation of the workpiece clamping system being too low. Since the natural frequency of the structure changes only with the change of clamping or fixing mode, when the vibration knife occurs, changing the cutting conditions (such as changing the rotation speed) tends to improve the cutting vibration, but in some occasions where the cutting speed cannot be changed (such as For tapping or cutting of certain materials, it is often only possible to solve such problems by changing the clamping method or even changing the tool or tool fixing method.
Second, the countermeasures to suppress the vibration knife
According to the vibration knife principle obtained from the research, there are some more specific and practical methods applied to the processing site:
(1) Try to choose all the conditions with small cutting impedance, that is, the most appropriate tool feed rate and cutting speed (or spindle speed).
(2) Adjust the cutting speed to avoid resonance.
(3) Reducing the working weight of the part causing the vibration, the smaller the inertia, the better.
(4) Fix or clamp the place with the largest vibration, such as the center frame, work holder, etc.
(5) Improve the rigidity of the processing system, for example, using a tool holder with a high modulus of elasticity or using a special shock force added to a Dynamic Damper to absorb the impact energy.
(6) Working hard from the direction of the blade and the work rotation (the work will lower the tool while also increasing the stability of the tool).
(7) Change the shape and advance angle of the tool. For example, the smaller the nose radius (Nose Radius), the better, to reduce the cutting resistance. The Sick Rake Angle must take a positive value to make the cutting direction closer to vertical. The Back Rake Augle is preferably positive, but the chipping ability is relatively poor. Therefore, the slotting knife is generally used to make the inclination angle negative, but still has a positive cutting effect.
(8) The lead angle (Lead Augle) is as small as possible, preferably zero.
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A UV accelerated aging test chamber is a specialized piece of equipment used to simulate the effects of long-term exposure to ultraviolet (UV) radiation on various materials and products. It is commonly used in industries such as automotive, aerospace, cosmetics, and electronics to evaluate the durability and performance of materials under accelerated aging conditions.
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