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In the previous article, we introduced the application background and significance of gradient chamfering.
In this article, we introduce the manufacturing method of gradient chamfering. In order to ensure the progressive relationship with the previous article, we still use the chapter number of the previous article.
The focus of this issue 3. Gradual chamfering PCBN tool preparation
3.1 Approximate grinding path planning
The grinding surface of the traditional fixed-parameter chamfering structure tool is composed of a rotating surface and an inclined surface with a fixed inclination value. It can be ground and formed by setting the inclination angle of the grinding wheel and the grinding enveloping wedge angle. The grinding principle is shown in Figure 6. shown.
Compared with the chamfered structure with fixed parameters, the curvature of the grinding surface of the gradient chamfered structure changes greatly, which requires high grinding precision and is difficult to form.
Combining the face grinding method and the idea of reduction, this paper discretizes the gradient chamfering structure and divides it into multiple grindings. Each time the inclination angle and the enveloping wedge angle of the grinding wheel are changed to approximate the gradient chamfering structure.
However, while the grinding surface of the gradient parameter chamfering area is being formed, the sweeping action of the grinding wheel on the boundary of the adjacent fixed parameter chamfering area will introduce a small range of overcut areas, so that the fixed parameter chamfering area will be reduced, as shown in Fig. 7a.
Here, by reducing the inclination angle of the grinding wheel for the initial grinding, the initial removal amount of the material in the chamfering interface area of the constant parameters and gradual parameters is appropriately reduced. In addition, a tool path is added in the overcut area and the fixed-parameter chamfering area. The grinding inclination angle is the initial chamfering angle, and the grinding trajectory is the same as the initial tool path, so as to remove the residual area introduced by the adjustment of the initial grinding wheel inclination angle. In this way, the influence of the overcut of the grinding wheel is eliminated, and the result is shown in Fig. 7b.
The approximation grinding trajectory planning scheme is shown in Figure 8. Gradual chamfering can be formed in the cutting edge area of the tool tip through n times of grinding, and each grinding trajectory can be divided into two straight lines and a circular arc.
Assuming that the angle variation range of the gradient chamfering structure is (γA, γB), the inclination angle of the grinding wheel is γi, and the enveloping wedge angle is εi, then when the mth (m<n) grinding is performed, the inclination angle of the grinding wheel is:
In the formula, γ1 is the inclination angle of the first grinding wheel, and γ1<γA. The envelope wedge angle is
The starting and ending angles of the grinding track of the arc segment are:
At this time, two linear grinding trajectories are formed by sweeping along a straight line with an inclination angle of 90°+Φ1 and Φ2-90° respectively.
In the nth grinding, the inclination angle of the grinding wheel is γn (γn=γA), the enveloping wedge angle is 0, and the grinding trajectory is the same as the first time.
3.2 Grinding simulation optimization
In the grinding simulation process, the entire grinding surface of the tool is first decomposed into several grinding segments. When grinding each segment, the grinding wheel sweeps along the grinding trajectory to form a corresponding overlapping area with the tool entity, and the corresponding area is compared. The material removal of each grinding section can be achieved by subtracting Boolean operations, so that the entire tool can be ground through a series of approximation segment grinding.
Taking an 80° diamond blade as an example, the chamfering width is 0.15 mm, and the chamfering angle varies from 15° to 30°. The grinding simulation process and results are shown in Figure 9.
During the processing, the number of grinding has a great influence on the processing efficiency and grinding accuracy. The following four different grinding times, 4 times, 6 times, 8 times and 10 times, are selected for simulation, and the gradient chamfering obtained by grinding simulation The tool is shown in Figure 10.
The extracted tool edge line data points are fitted and drawn into a space curve, and compared with the theoretical edge line, the results are shown in Figure 11.
It can be seen from Figure 10 and Figure 11 that the fitting effect of 4 times of grinding deviates greatly from the theoretical edge line; while the fitting effect of 6 times, 8 times and 10 times of grinding is relatively good.
In order to further analyze the deviation of the gradient chamfered structure formed by different grinding methods from the theoretical value, the simulation results are further analyzed in the follow-up.
As shown in Figure 12, take an average of 5 points on the arc curve of the tool nose on the left side of the tool center line, and connect them with the center 0, and use these 5 lines as the benchmark to make a section perpendicular to the rake face, which are I, II, III, IV, V.
Extract the contour of the chamfered part on the section and compare it with the theoretical section, as shown in Figure 13.
The measured angle values are shown in Table 1 (the angle of the theoretical model at this section is in brackets).
According to Figure 13 and Table 1, it can be seen that with the increase of grinding times, the grinding error of each section gradually decreases, and when the grinding times reach 8 or more, the grinding error gradually approaches; under the condition of the same grinding times, Compared with the grinding errors of sections III and IV, the error of section II is relatively the largest.
3.3 Tool grinding
Gradual chamfering PCBN tool grinding adopts Coborn's five-axis grinding machine RG9, the grinding wheel spindle power is 2.2kW, and the maximum rotation speed is 4000r/min. Among them, the X-axis positioning error and repeatability positioning error are ±1 μm, and the A-axis and C-axis angle errors are ±0.05°.
The tool blank is a PCBN blade DCC500 with a Vickers hardness of 36.4±0.48 GPa and a particle size of 1.5 μm. The grinding wheel adopts the disc-shaped diamond grinding wheel 6A2 with ceramic as the binder, the diameter is 150mm, and the speed is 2000r/min. The tool grinding and sample tool are shown in Figure 14.
During the grinding process, the blank blades are divided into 3 groups, and the corresponding grinding times are 6, 8 and 10 times respectively. Each group grinds 4 cutting tools, a total of 12 pieces, and the group number is convenient for subsequent grinding accuracy detection.