JP2018181059A - Method of controlling feed shaft of machine tool, and machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an infinitesimal displacement superposition control with a tool having a large stage number of a cutting edge and a larger torsion angle thereof by optimizing a control start angle and a control amount.SOLUTION: The present invention is directed to a machine tool for processing a work piece 10 by rotating a tool 7 mounted with a plurality of stages of cutting edges provided on a concentric circle in a shaft direction and for superposing infinitesimal displacement control of a feed shaft in a process reverse direction on the basis of a swing amount of the cutting edge pre-measured relative to the feed shaft under processing. An arithmetic apparatus 12 calculates an increased or decreased amount of a processing margin actually processed by each of the cutting edges, divides a one circle amount of the tool 7 by a predetermined control number (larger than one), calculates a maximum value of the increased or decrease amount of the processing margin of the cutting edge fixed in the divided control range for each of the control ranges, calculates a control amount and a control position which can average it for each of the control ranges, and superposes the infinitesimal displacement control on the basis of the control amount and the control position.SELECTED DRAWING: Figure 1

Description

  The present invention suppresses the generation of chatter vibration and tool chipping by controlling the feed axis in consideration of the amount of deflection of the cutting edge of the tool, particularly in heavy cutting of difficult-to-cut materials such as titanium alloys during machining of machine tools. And a machine tool that performs cutting using the control method.

  When machining difficult-to-cut materials by milling, a type of tool with a detachable cutting edge called throwaway or insert is used to reduce machining cost, but the cutting edge mounting surface of the tool body or cutting edge itself Due to the influence of the processing accuracy of (4), the mounted blade has a swing amount (a relative attachment error between the blades). Since this value is not small, there has been a problem that tool chipping occurs from a cutting edge having a large amount of runout and tool life is shortened. As a countermeasure, in Patent Document 1, a processing method is provided in which the amount of blade deflection of the tool is measured in advance, and the influence is suppressed by controlling the feed shaft by the amount of blade deflection in the direction opposite to the processing advancing direction. .

Patent No. 5908342 JP, 2016-83728, A

In the processing method of Patent Document 1, processing is performed by superimposing minute displacement control of the feed shaft for each cutting edge row of cutting edges. At this time, for the calculation of the control amount and the control timing, an optimum value is calculated by averaging the maximum values of the actual machining allowances in the respective blade rows, using the method described in Patent Document 2 above. In this method, since the calculation of each optimum value is performed for each blade row of the cutting edge, when the number of stages of the cutting edge mounted on the same blade row is small, the mounting position of the cutting blade in the same blade row (tool rotation angle Difference is small, and control is sufficiently effective in all cutting edges.
However, when the number of steps of the cutting edge is large, the phase difference of each cutting edge attachment position in the same cutting edge row is large due to the tool twist angle, and a cutting edge largely deviates from the control position is generated. I could not.

  Therefore, the present invention provides a feed axis control method and machine tool capable of performing micro displacement superposition control by optimizing the control start angle and the control amount even in a tool having a large number of cutting edges and a twist angle. Purpose.

In order to achieve the above object, the invention according to claim 1 is a machine that processes a workpiece by rotating a tool in which a plurality of steps of cutting edges disposed on a plurality of concentric circles are axially mounted. A control method of a feed shaft which superimposes control of minutely displacing the feed shaft in the reverse direction of processing based on the deflection amount of the cutting edge measured in advance with respect to the feed shaft being processed in a machine.
A machining allowance calculation step of calculating an increase or decrease of a machining allowance that each of the cutting blades actually machine;
One round of the tool is divided by a predetermined number of controls (except once), and the maximum value of the machining allowance of the cutting edge attached within the divided control range is divided for each control range A control amount calculating step of calculating a control amount and a control position which are calculated and averaged for each control range;
And performing a superimposing step of superposing the control of the minute displacement based on the control amount and the control position.
The invention according to claim 2 is characterized in that, in the configuration according to claim 1, the control amount is the maximum value of the machining allowance within the control range at a predetermined number of control times, in each of the control ranges. It is characterized in that the average of the maximum values of the increase and decrease of the machining allowance is subtracted and the control amount in the previous control number of the control number is added.
The invention according to claim 3 is characterized in that, in the configuration according to claim 1 or 2, the control position is an average of attachment positions of the cutting edges within the control range.
In order to achieve the above object, the invention according to claim 4 processes a workpiece by rotating a tool in which a plurality of steps of cutting edges disposed on a plurality of concentric circles are axially mounted. A machine tool that superimposes control to slightly displace the feed shaft in the reverse direction of processing based on the deflection amount of the cutting edge measured in advance with respect to the feed shaft being processed,
A machining allowance calculation unit that calculates an increase or decrease in a machining allowance that each of the cutting blades is actually machined;
One round of the tool is divided by a predetermined number of controls (except once), and the maximum value of the machining allowance of the cutting edge attached within the divided control range is divided for each control range Control amount calculating means for calculating a control amount and a control position which are calculated and averaged for each control range;
And D. superimposing means for superimposing the control of the minute displacement based on the control amount and the control position.
The invention according to claim 5 is the configuration according to claim 4, wherein the control amount calculation means determines the control amount from the maximum value of the increase or decrease of the machining allowance within the control range at a predetermined number of control times. It calculates by adding the said control amount in the said control frequency of the control frequency | count of the said control frequency by subtracting the average of the maximum value of the increase / decrease in the said processing allowance in each said each control range.
The invention according to claim 6 is characterized in that, in the configuration according to claim 4 or 5, the control amount calculating means sets the control position as an average of attachment positions of the cutting edges within the control range. I assume.

  According to the present invention, even for a tool with a large number of cutting edges and a large twist angle, processing is performed by correcting the amount of blade deflection with the feed shaft, and determined for each control range obtained by dividing the machining allowance maximum value in micro displacement superposition control. The control amount that averages this is obtained by a simple calculation. Thereby, the influence of the amount of runout can be suitably suppressed and processed, and the life extension of the tool can be achieved.

It is a block diagram of a machine tool. It is a longitudinal cross-sectional view of a tool. It is a measurement result of the amount of runouts of each cutting edge at the time of processing using six steps of cutting edges by four rows of blades, and a calculation result of an increase or decrease in actual processing cost. Calculated value of micro displacement superposition control amount in case of processing with 6 rows of cutting edges with 4 rows of blades obtained by the conventional method, and increase / decrease in actual processing allowance when controlled based on the calculated value And the calculated value of. Calculated value of micro displacement superposition control amount in case of processing with 6 rows of cutting edges with 4 rows of blades obtained by the method of the present invention, and increase or decrease in actual processing cost when controlled based on the calculated value The calculated value of the minutes is shown (the number of times of superimposition control which enters during one rotation of the main spindle is six).

Hereinafter, embodiments of the present invention will be described based on the drawings.
FIG. 1 is a block diagram showing an example of a machine tool that implements a feed axis control method according to the present invention. In the figure, 1 is a bed, 2 is a column, and the spindle head 3 can be controlled to move in the X-axis direction and Z-axis direction by the X-axis control unit 4 and the Z-axis control unit 5 on the front of the column 2 It is provided. A tool 7 is mounted on a spindle 6 provided downward at the lower part of the spindle head 3.
On the other hand, a table 9 which can be controlled to move in the Y-axis direction by the Y-axis control unit 8 is provided on the bed 1 so that the workpiece 10 can be fixed on the table 9.

  The control system of the machine tool includes a spindle rotation control device 11 that controls the rotation speed of the spindle 6, an arithmetic device 12 that calculates control amounts and control positions of feed axes (each control unit 4, 5, 8), and feed axes And a storage device (not shown). The shake amount of the cutting edge of the tool 7 described later can be input to the calculation device 12 by the external input device 14.

In the machine tool configured as described above, the arithmetic unit 12 calculates an increase or decrease in the machining allowance actually machined by each cutting edge of the tool 7 (machining allowance calculation step). Calculate the control amount and control position that divide the number of times of control (except once) and average the maximum value of the machining allowance of the cutting edge attached within the divided control range for each control range (Control amount Calculation step) The calculated control amount is converted in each axis direction and superimposed on the axis feed amount of NC program command by each axis control device (superimposition step). That is, the computing device 12 has functions as a machining allowance calculation unit, a control amount calculation unit, and a superposition unit.
Then, the numerical control device 13 carries out machining by adding control of causing the feed axes to be slightly displaced in the reverse direction based on the axial feed amount on which the control amount is superimposed by the arithmetic device 12. For example, in the case of processing in the X-Y plane, the control amount calculated in the processing advancing direction is distributed in the X-axis and Y-axis directions to control the feed axis in the processing reverse direction.

In order to perform this control, it is necessary to measure in advance each position of the tool cutting edge and its deflection amount, and to calculate the optimum control amount and the control position (tool rotation angle).
As an example of the tool used at this time, the tool 7 having the number of blade rows Z = 4 and the number of blade steps N = 6 will be mentioned. The tool 7 has four cutting edges 7a, 7a, ... arranged concentrically at 90 ° intervals (circled numbers 1 to 4 in Fig. 2 (1)) as shown in Fig. 2 (1) As the same blade stage (Fig. 2 (2) 7b), six stages are provided in the axial direction. However, the cutting edges 7a of the same blade row in the axial direction are arranged so as to be gradually shifted forward in the rotational direction from the tip of the tool 7 (FIG. 2 (2) 7c).

First, the deflection amount of each cutting edge 7 a of the tool 7 is measured and input to the arithmetic device 12 in advance via the external input device 14. Arithmetic unit 12 calculates the control amount at the rotation angle using a predetermined calculation formula.
In the conventional small displacement superposition control, in order to calculate the optimum value of the control amount and the control timing for each cutting edge row, when the number of steps is large, as shown in FIG. 2 (2) 7c, the tool twist angle As a result, the difference between the positions of the cutting edges in the same blade row is large, and a cutting edge largely deviates from the control position is generated, which makes it difficult to obtain a sufficient effect.
Therefore, according to the present invention, even for a tool having a large number of stages and twist angles of the cutting edge to be mounted, in order to optimize the control start angle and the control amount, one round of the tool is divided by the number of controls and installed within the divided range. The optimum value of the control amount and the control position is calculated for each of the determined cutting edges.

The calculation of this control amount is as follows.
Here, the number of the blade row is suffixed i (1 ≦ i Z Z, Z: number of blade rows), the number of the blade step is suffixed j (1 j j N N, N: number of blade steps), each cut measured Let the deflection amount of the blade be C _{i, J} (μm), and the position of each blade (tool rotation angle) be P _{i, J} (°).
First, the increase or decrease _{Di, J} of the actual machining allowance at each cutting edge can be calculated by the following equation 1.

  That is, the magnitude of the swing amount of each cutting edge is not the actual machining allowance at each cutting edge, but the difference (increase or decrease) in the deflection amount is the difference between the actual machining allowances. The larger the difference is, the faster the chipping progresses and the tool life becomes shorter.

Therefore, in order to average this value, feed axis control of the control amount R _k is superimposed at control position Q _k (tool rotation angle) L times during one rotation of the spindle. The cutting edges used to calculate the optimal control amount and control position of the predetermined k-th (k = 1, 2 ·· L) superposition control are divided into control ranges shown in FIG. 2 (1) 7d.
For example, in the tool shown in FIG. 2 (1), in the case of L = 6, the control range is divided into six by i to vi.
Here, the range of the attachment position (tool rotation angle) P _{i, J} of the cutting edge used for the number of times of control k is Equation 2 below.

At this time, the number of times L of micro displacement superposition control which enters during one rotation of the spindle is set to a maximum value that can ensure the operation from the spindle rotational speed to be machined and the control cycle of the numerical controller.
Then, assuming that Di _{, j, k} is an increase or decrease in the actual machining allowance of each cutting edge within the control range in the predetermined k-th superposition control, the control amount R _k is obtained by the following equation 3.
R _k = (maximum value of real machining allowance increase / decrease _{Di, j, k} within the kth control range)
− (Average of maximum values of increases and decreases in actual machining allowance Di _{, j, k} at all control times (k = 1, 2 ·· L))
+ (K-1st control amount R _k-1 )
(However, in the case of k = 1, R ₁ = 0.)

In this calculation formula, it is meant that the maximum value of the increase / decrease in the actual cutting allowance of the cutting edge in the kth control does not become smaller than the average value of the maximum values of the increase / decrease in the actual cutting allowance calculated in each control frequency. There is.
Similarly, with regard to the mounting position of the cutting edge, assuming that the mounting position of each cutting edge within the control range in the predetermined k-th superposition control is P _{i, j, k} , the control position Q _k is P _{i, j, k} Obtained as an average of
Here, the phase relationship between each position of the cutting edge 7 a and the main body of the tool 7 is grasped by, for example, an encoder connected to the main shaft 6. The spindle rotation control device 11 can obtain phase information of the cutting edge 7a based on the output of the encoder.

FIG. 3 shows the measured values of the amount of runout and the calculated values of the increase and decrease of the actual machining allowance when it is assumed that a tool having 4 rows of blades per stage and 6 stages of cutting edges is used. It is. In this case, the cutting edge with the largest actual machining allowance is 20 μm in the third row of the second row (thick frame portion).
FIG. 4 shows the calculated values of the control amount calculated for each conventional blade row based on the deflection amount of the cutting edge and the increase / decrease of the actual machining cost in the same tool as FIG. 3. In this case, the control amount can not be optimized, and the maximum value of the increase or decrease in the machining allowance is 20 μm (thick frame portion), and does not change from no control.

On the other hand, FIG. 5 shows the calculated values of the control amount obtained by the method of the present invention based on the shake amount and the calculated values of the shake amount when controlled based on the calculated value in the same tool as FIG. The calculated values of the increase and decrease of the actual machining cost are shown. In this case, the cutting edge having the largest relative increase or decrease in the machining allowance is 13 μm at the sixth stage, where the mounting position is 163 ° (thick frame portion).
The reason why the control amount R ₁ is not 0 in FIG. 5 is because the control amount is 0 or more in an actual machine tool. However, since the control amount only needs to have the same relative difference in each control range, addition is not essential, and the value of R _k obtained by the above calculation may be left as it is.

  As described above, according to the machine tool that executes the feed axis control method of the above embodiment, the machining cost is increased or decreased by the increase or decrease in the actual machining cost obtained based on the measurement results of the deflection amount and the mounting position of each cutting edge. When calculating the control amount at which the maximum value of the increase or decrease averages, one tool rotation is divided by the number of controls, and the control amount and control position are calculated for each cutting edge attached within the divided control range It is like that. As a result, even with the tool 7 having a large number of cutting edges and a large twist angle, the tool runout amount in each axial direction corresponding to the tool position (rotation angle) is corrected on the feed shaft side during machining by simple calculation. Thus, a controlled variable is obtained in which the maximum value of the actual machining allowance is averaged. Therefore, the influence of the tool runout amount can be suppressed suitably, and it can process, and lifetime improvement of the tool 7 can be achieved.

The number of cutting edges in the tool, the number of cutting edges in one cutting edge, and the number of controls are not limited to those described above, but can be increased or decreased appropriately (however, one control is excluded for the purpose of the invention).
A machine tool is also capable of processing by rotating a tool formed by mounting a plurality of steps of cutting edges disposed concentrically in a plurality of stages in the axial direction and performing feed axis control, such as a complex processing machine or a machining center, etc. There is no particular limitation on the model.

  1 bed 2 column 3 spindle head 4 X axis control unit 5 Z axis control unit 6 spindle 7 tool 7a cutting edge 7b Blade stage 7c Blade row 7d Control range 8 Y-axis control unit 9 Table 10 Workpiece 11 Spindle rotation control device 12 Arithmetic unit 13 · · Numerical control device, · · · External input device.

Claims (6)

In a machine tool for processing a workpiece by rotating a tool formed by mounting a plurality of steps of cutting edges arranged concentrically in a plurality of steps in the axial direction, the cutting edge measured in advance with respect to a feed shaft during processing And a control method of a feed shaft on which control for slightly displacing the feed shaft in the processing reverse direction based on the amount of deflection of
A machining allowance calculation step of calculating an increase or decrease of a machining allowance that each of the cutting blades actually machine;
One round of the tool is divided by a predetermined number of controls (except once), and the maximum value of the machining allowance of the cutting edge attached within the divided control range is divided for each control range A control amount calculating step of calculating a control amount and a control position which are calculated and averaged for each control range;
Superimposing step of superposing control of the minute displacement based on the control amount and the control position;
A control method of a feed axis in a machine tool, characterized in that   The control amount is obtained by subtracting the average of the maximum value of the increase and decrease of the machining allowance in each of the control ranges from the maximum value of the increase and decrease of the machining allowance within the control range at a predetermined number of control times. The control method of a feed axis in a machine tool according to claim 1, wherein the control amount in the previous control number of the control number is added to the control number.   The control method of a feed axis in a machine tool according to claim 1 or 2, wherein the control position is an average of attachment positions of the cutting edges within the control range. A tool formed by mounting a plurality of steps of a plurality of cutting edges arranged concentrically in the axial direction is rotated to process a workpiece, and the deflection of the cutting edge measured in advance with respect to a feed axis during processing A machine tool that superimposes control to slightly displace the feed shaft in the processing reverse direction based on an amount,
A machining allowance calculation unit that calculates an increase or decrease in a machining allowance that each of the cutting blades is actually machined;
One round of the tool is divided by a predetermined number of controls (except once), and the maximum value of the machining allowance of the cutting edge attached within the divided control range is divided for each control range Control amount calculating means for calculating a control amount and a control position which are calculated and averaged for each control range;
A machine tool comprising: superimposing means for superimposing control of the minute displacement based on the control amount and the control position.   The control amount calculation means determines the control amount as the maximum value of the increase and decrease of the machining allowance in each of the control ranges from the maximum value of the increase and decrease of the machining allowance within the control range at a predetermined number of control times. The machine tool according to claim 4, wherein the machine tool is calculated by subtracting an average and adding the control amount at the previous control number of the control number.   The machine tool according to claim 4 or 5, wherein the control amount calculating means sets the control position as an average of attachment positions of the cutting edges within the control range.

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