Influence Of Radial Groove On Vibration Characteristics Of Circular Saw Blade

In the sawing process, there are serious problems of vibration and noise of the saw blade. It is one of the effective ways to control the vibration and noise of the saw blade to cut the appropriate groove on the saw blade. In order to provide mathematical basis for the design of slotted saw blade and the re correction of saw blade with radial root crack, this paper regards radial slot and radial crack as the same thing, and analyzes their influence on the vibration characteristics of saw blade by finite element method.

Vibration characteristics of general saw blade

For comparison, first analyze and understand the vibration mode of general saw blade. Taking a metal hot cutting circular saw blade as the analysis object, its basic parameters are: outer diameter 2A = 1.0m, thickness h = 0.006m, clamp diameter ratio (ratio of outer diameter of chuck to outer diameter of saw blade) f = 0.5, Young's modulus of elasticity e = 2.058 × 1011n / m2, Poisson's ratio v = 0.3, density r = 7.8 × 103kg/m3。 According to the axial symmetry of the saw blade, only half of the saw blade can be taken to establish the finite element model. It is divided into 90 quadrilateral plate elements and 114 nodes (5 equal parts in radial direction and 18 equal parts in circumferential direction) and calculated by sap6. At the end of the calculation, the output file of sap6 is processed twice with the special post-processing program, and the vibration mode of the saw blade is identified (M is the number of pitch circles, n is the number of pitch diameters), and the grid diagram and various vibration mode diagrams are made.

In order to investigate the influence of unit differentiation density on the calculation results, the unit differentiation of half saw blade is encrypted into 180 units, 222 nodes (radial 5 equal parts, circumferential 36 equal parts), 360 units, 407 nodes (radial 10 equal parts, circumferential 36 equal parts) and re calculated. The calculation results of the natural frequency of the saw blade with various element densities are compared with the accurate solutions. It can be seen that the calculation results of the lower order natural frequencies are basically the same and very accurate under the three element discrimination densities. Generally, it is only interested in the lower order modes, such as 0-pitch circle and 0-6-pitch diameter modes, so it is enough to take the element differentiation density of 90.

Vibration characteristics of saw blade with radial groove

Let the parameters of the saw blade be the same as before. Cut 1-3 edge radial grooves with the width not exceeding 1 mm uniformly distributed along the circumference on the saw blade. These grooves together also represent radial root fatigue cracks. The general saw blade is divided into 180 units and 216 nodes. The unit division of slotting saw blade is carried out by reference, and the slotting is replaced by blank units. Change the groove length, check the vibration mode of the saw blade under various conditions and make various vibration mode diagrams.

The vibration mode is identified by a special post-processing program. It should be pointed out here that when there are radial grooves, the pitch line of the vibration mode of the saw blade is not necessarily the exact diameter, which depends on the distribution mode of the grooves. However, for convenience, the pitch line is still approximately described by the pitch diameter.

The number and dispersion of slots determine which modal frequencies can be separated. With the increase of the groove length, the frequency of each order decreases slowly. When the ratio of the groove length to the radius of the saw blade does not exceed 0.2, the frequency decreases by no more than 10%. When the slot length is constant, with the increase of the number of slots, the general trend of frequency change is slowly decreasing (very few exceptions). When there is a radial groove, the pitch radius of the blade vibration mode and the relative orientation of the blade are fixed, which can prevent the formation of the stationary wave at the critical speed.

3. Conclusion

When the saw blade is slotted, some overlapped modal frequencies are separated, so the energy of the slotted saw blade is more dispersed when it is stimulated by pulse. The vibration mode of a saw blade with radial grooves depends on the number and distribution of grooves. The pitch radius and the relative orientation of the saw blade are fixed, while the pitch diameter orientation of a general saw blade is arbitrary.

When the number and distribution of radial grooves remain unchanged, the natural frequencies of each order decrease with the increase of groove length. However, when the ratio of groove length to saw blade radius does not exceed 0.2, the decrease of frequency is small, so there is no need to worry about the weakening of bending stiffness of saw blade caused by short groove.

When the slot length is constant, with the increase of the number of slots, the general trend of the frequency change of each order is slowly decreasing.

When the ratio of radial root fatigue crack length to saw blade radius does not exceed 0.2, the crack will not lead to the decline of dynamic performance of the saw blade. After the stress concentration is eliminated by drilling holes at the crack tip and proper dynamic balance is made, the saw blade can continue to be used.