Analysis of dynamic characteristics of Zha, industry and technical machine tools Wang Feiyue Department of Technical Engineering, Zhangyekou Vocational and Technical College, Zhangjiakou 075000, Hebei Province, pointed out the main indicators of the dynamic characteristics of machine tools, and analyzed the type of vibration of machine tools through the example of dynamic and static stiffness. Measures to improve the dynamic stiffness of the machine tool are to improve the static stiffness and rigidity of the machine tool, and to improve the vibration characteristics of the vibration mode of the machine tool structure.
With the high-precision high-surface quality and high-production HirXHlljMg, the machine tool is concerned. The machine tool and the tool form a multi-degree-of-freedom system with constant mass distribution elastic coefficient and viscous damping. This system is subjected to various forces. effect. Such as cutting force, the inertia of the moving parts, the friction between the contact surfaces, as well as the gravity and clamping force. Under the action of static force, the static change between the tool and the workpiece is required. This is the static stiffness. It is only enough to study the static stiffness of the machine because the static stiffness of the machine can only reflect its cutting force and workpiece and machine parts. The role of gravity, etc., and the ability of the machine to resist deformation when considering static force. However, the machine tool is an elastic system. Under certain conditions, for example, when the unbalanced shear force of the rotating member changes, an exciting force is generated. vibration. When the amplitude is outside the allowable range, it will lead to deterioration of the processed clothing. Accelerate the wear of the knife, affect the processing viscosity and low the production efficiency. The shoulder can make the machine not work. So it is not enough to study the static stiffness of the machine. It is also necessary to study the dynamic stiffness of the machine. 1 Basic concept Machine dynamics 圮 refers to the vibration of the machine tool system In the state, the characteristics of the excitation frequency vary. The main index has a natural frequency, or the natural angular frequency is approximately equal to the Yin resonance frequency. The relationship is =12 damping coefficient when Siamese stiffness = factory. For example, the factory is the excitation force, the resonance amplitude dynamic stiffness = the cadaver excitation frequency, and the 左 = left 77 is the natural angular frequency.
Dynamic compliance 47 = 1 can be seen from the small indicators of dynamic characteristics. The dynamic stiffness of the system depends on the static stiffness of the system. The inherent mass damping ratio of the system itself is the inherent angular frequency. The dynamic analysis of the machine is mainly to study the ability to resist vibration, including vibration resistance and cutting stability. Resistance to forced vibration, it and the structural rigidity of the machine tool damped the date of receipt of the responsibility of the editor Wang Shizhong, Wang Xinzhi + female, frequency, the vibration required for the position of the vibration force cutting stability is the machine tool against the self-excited vibration of the cutting Nine is usually the limit cutting width at which the self-excited vibration begins to appear at the time of cutting. The greater the limit cutting width, the better the machine's ability to resist self-excited vibration, that is, the higher the cutting stability.
Under normal circumstances, increasing the static stiffness of the machine tool can improve the dynamic stiffness of the machine tool, but sometimes it is not always possible, for example, to perform grooving experiments on two medium-sized ordinary lathes. The static stiffness values ​​of the spindle systems of the two machine tools are respectively For 0 households, 1 and 135, the grooving, the workpiece with no vibration is limited to 1501 and 12, respectively, and the machine with small static stiffness is more resistant to vibration than the machine with large static stiffness. In the experiment of a machine tool. In one case, the workpieces with a diameter of 10, and 5 were cut, and the limit cutting lengths were 10 and 20, respectively. This shows that although the coarse workpiece has a larger static stiffness than the small workpiece, However, the vibration resistance is smaller than this, and it is necessary to use the concept of dynamic characteristics to analyze, in order to get the phenomenon of the decontamination phenomenon, because the static stiffness is high and the grooving resistance is poor. The spindle system of the machine tool has poor bearing quality, low damping capacity, and the spindle box is smaller than the book, so that the natural frequency of the support system such as the box wall and the bearing is lower, which is close to the frequency of the system. In this case, the coarse workpiece is clamped on the chuck. Due to the large mass of the spindle overhanging front end, the inertial force generated during the vibration is also large and the spindle system is easy to self-excitation. This example shows a new machine smell. To meet the requirements of the machine tool 1 performance, it is necessary to study the dynamic characteristics of the machine tool to find ways to improve the dynamic stiffness of the machine tool. Take effective measures to improve the vibration resistance of the machine tool. 2 Types of machine vibrations Machine vibrations are classified according to two conditions. 2.1 Classification according to the cause of vibration 21.1 Vibration type Free vibration The system of the vibrator leaving the balance position 迓 Factory 7, in the absence of external excitation force, the vibration frequency of the vibrating cloud is maintained by the elastic recovery force alone. When the natural frequency is damped, the vibration gradually decays, and finally the vibration that the elastic system is forced to disappear. The frequency is the same as the frequency of the exciting force. When the frequency of the exciting force is close to the natural frequency of the system, resonance will occur.
Self-excited vibration has no external excitation force, and the energy of vibrating vibration is not like the input of free vibration. It is like the forced vibration. The energy that is like self-excited vibration is not like forced vibration. Sexual input energy, but 41 continuous effects on the system, the vibration generated on this non-periodic machine is mostly forced vibration and self-excited vibration 2.1.2 vibration source to analyze the vibration source, the most important The imbalance of the rotating body is four. The vibration source inside the machine tool is roughly caused by the centrifugal force generated by the + 肀 肀 以下 以下 以下 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些 这些
The inertial impact caused by the reciprocating mechanism and the rocking mechanism, such as the reciprocating motion of the gear shaping cutter of the gear shaping machine, the forced vibration caused by the change of the transmission force, such as the joint of the tape and the uniform smell of the tape, the gear pitch and Tooth shape error and tooth profile deformation, gears on the high-speed shaft, etc. 4 Forced vibration caused by uneven hydraulic drive 5 Vibration of the cutting process. For example, in the milling process, due to the intermittent cutting of each tooth of the milling cutter and the change of the cutting area, the method of eliminating the vibration of the edge is mainly used in the vibration source with less salt and forced vibration, and the vibration isolation measures are adopted to reasonably improve the dynamic rigidity of the machine tool. . The frequency of the forced vibration is far from the internal frequency of the system. The self-excited vibration on the machine tool is a kind of relative vibration between the wide tool and the workpiece. It is generated during the cutting process and the exciting force is obtained from the cutting process. That is, the larger the amount of cutting energy is obtained from the machine tool transmission. The greater the cutting force. The more intense the vibration, the more the self-excited vibration condition is eliminated, and the main vibration mode of the machine tool and the weak link causing the main vibration mode are found. To meet the dynamic stiffness of the machine tool or to take measures such as vibration damping device. 12 According to the characteristics of machine vibration, the amplitude of each point along the length direction and the height direction of the machine tool when the whole machine shakes the vibration form on the bearing foundation. According to the linear distribution, the whole machine is shaken. The most important influence of the dynamic stiffness is the rigidity of the machine support part and the foundation and the relative vibration between the joint surfaces of the damping parts. The machine tool is composed of many components according to the requirements, and the joint parts between these parts It is called a joint. Regarding the joint surface contact member, linear vibration or shaking is generated at the joint surface with respect to the other member. For the movable joint surface, the natural frequency is low, but the damping is large; for the fixed joint surface, the overall vibration of the machine tool component such as the machine bed 1 secondary vibration of the main shaft and column, torsional vibration of the transmission system, etc. The frequency is higher than the first two vibration modes. 3 Measures to improve the dynamic stiffness of the machine tool structure 3.1 Improve the static stiffness and natural frequency of the machine tool components. The shape and diameter of the broken blood to have a higher stiffness and natural frequency at the same mass. By increasing the size of the section wheel gallery without increasing the wall thickness, the bending and torsional rigidity of the hollow section is increased; the main torsion member should be circular in shape; the members subjected to eccentric load and torsional moment should be closed as much as possible. If the shape is required for the chip removal, such as helium gas cooling, etc., the sweat hole must be made. If it is not completely closed, the hole should be opened near the geometric center of the support wall or cross the center line, the hole width or The aperture is preferably not more than 0.25 times the wall thickness, so that the rigidity reduction caused by the opening is not large, and the bending rigidity can be restored to the extent that the bending is not opened by the capping.
Reasonably arranging the ribs and ribs of the members to improve their rigidity and the inherent frequency of the ribs can increase the rigidity of the support members because the ribs can transfer the local load of the outer wall of the support member to the other wall plates to balance them. The ground transmits the load, and the shape is changed by the factory. Therefore, the deformation of the outer wall can be prevented. The wall of the supporting raft is strengthened as a whole, and the deformed longitudinal rib can be reduced when subjected to the torque. The role of the plate is to improve the bending stiffness; the role of the transverse ribs is to improve the torsional stiffness and the diagonal ribs to improve the bending and torsional stiffness. The longitudinal ribs should be arranged in a curved plane, which can significantly increase the moment of inertia, thereby increasing the bending stiffness. The difference between the ribs and the ribs is that they do not connect the entire wall, but only have a limited height, which has the rigidity of the reinforced panels. effect. Judging must make the ribs in the curved plane of the slab. In order to effectively reduce the bending deformation of the wall plate, the support member of the machine tool is subjected to the vertical direction of the ribs and the bending plane. The rib arrangement is not suitable to be arranged in a single direction, but should be arranged in a crosswise manner, so as to significantly enhance the rigidity of the wall plate to improve the components or components. The stiffness at the joint with the mantle increases the local stiffness of the joint at the screw, which improves the stiffness of the entire structure and appropriately selects the size of the screw and the arrangement of the screws to increase the contact stiffness. From the perspective of bending stiffness, the screws should be more concentrated in the stretched 1 side; considering the bending strength, the screws should be evenly arranged in the 锾 to increase the thickness of the flange to increase the moment of inertia. However, due to the snail addition, the extension 1 deformation is increased, but the contact stiffness is reduced, so the flange thickness should not be too large. 3.2 Improving the damping characteristics of the machine tool structure. The damping is improved by the friction damping between the joint surfaces and the internal friction damping of the material. The characteristic measures are as follows: the principle of using the frictional damping between the joint surfaces to increase the damping between the joint surfaces is that the frictional surface of the joint surface has a large pressure, and the movement can be slightly moved during the vibration. Although the static stiffness is lowered, the stiffness is increased due to damping and addition. The welding method of 1 is that the two welded parts have flat facets which are mutually adhered to each other. Although the surface is not welded, but it is close to the welding stress, it can move relative to the vibration, thereby increasing the damping of the structure by using the core and The damping material such as concrete fills the cavity in the support of the machine tool, and uses the relative friction to absorb the vibration energy when vibrating. The core of the support member remains in the casting, and the damping of the bed of the mud core can be removed. Significantly increased strength.
Damping coating on the surface of the support member For the bending vibration member, the surface of the sprayed layer has a high internal damping and a viscous material with a good elastic modulus, such as a cement damping agent made of leaching, a polymer and a paint. Putty, etc., the coating thickness is large, the damping is larger, and the wall thickness is 3 times.
The meter uses a constrained damping band or a damping sandwich structure. 2, when the beam 1 is vibrating, the mountain is constrained by the body of the constrained zone, and the damping layer 2 sandwiched in the middle produces alternating shear deformation and consumes energy, thus producing a high damping when shear deformation occurs. Come. E.g. Make it with. 1. The angle of the 2+ is 1/2; the direction of vibration of the former is perpendicular to 1; the direction, that is, the vibration displacement does not affect the change of the cutting thickness, that is, does not cause the change of the cutting force; the vibration direction of the latter is perpendicular to the direction of the cutting force, that is, cutting The force does not arouse the vibration of the mode. In these two cases, the direction coefficient is supplied, so the system has high vibration resistance, and it is not easy to cause self-excited vibration. For example, under the condition of forced vibration, the influence of the vibration of the former is small, and the vibration will cause the vibration to stay on the machine. When designing the structure, the vibration direction of the vibration mode with poor dynamic stiffness should be as close as possible or close to the two stages of the current situation. The dynamic characteristics of the machine tool and the method for determining the dynamic stiffness of the machine tool are mainly made by the actual machine tool or model. The excitation experiment uses a sinusoidal signal random signal pulse signal and a non-periodic signal, according to different input signal methods, using no distinction. The measurement method, through experiments, finds the weak link affecting the dynamic stiffness, proposes improvement measures to improve the structural design, or install an effective vibration damping device, so as to improve the vibration direction of the vibration mode of the machine tool to change the vibration mode of the machine tool 3.3. The cutting force and the direction perpendicular to the cutting surface are generally not the cutting force, the vibration direction of the vibration mode, and the direction of the cutting force perpendicular to the cutting surface is only related to the cutting condition. To consider, the vibration direction of the machine tool vibration mode is variable, 1 Chen 7 ç‘ž. Yes, the cutting machine 6 is provided with juice. 1. Too Mt. Hawthorn Science, 2 Yellow Crane Ting. Metal cutting machine design. Beijing Machinery Industry Publishing 3 Zhu Mengzhou, Zhang Dequan. Metal cutting machine tool experiment. Beijing mechanics turned down the 27th page to identify the types of clay minerals, the test results are stable, the repeatability is good, the error is small, can be effectively used to guide the production, the strong and weak in the kaolinite montmorillonite Very weak 1 Kunming Institute of Technology. Modeling materials 41. Kunming Yunnan People's Publishing House, IW3.2029.
2 He Peizhi. Foundry Material Chemistry 1 Beijing Mechanical Industry Press, 1981.5444.
3 Xu Minglin. Casting Technology 1 Jinan Shandong People's Publishing House, l97hTI0.
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