JP2016161971A - Method for controlling feed shaft of machine tool and machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To elongate the service life of a tool by optimizing a control start angle when cutting a side face.SOLUTION: In S1, each position and deflection amount of cutting edges of a tool is measured and input, and a control amount of each blade line at a rotation angle is calculated with the use of a predetermined formula. In S2, the amount of depth of cut (ae) in a radial direction and a tool radius are input. In S3, a preset formula is used for calculating the amount of angle correction θfor correcting a control position. In S4, the amount of angle correction θcalculated in S3 is added to a control position of each cutting edge. In S5, on the basis of a feed shaft command value obtained by correcting a control position, each feed shaft (control unit) is controlled and then processing is executed.SELECTED DRAWING: Figure 2

Description

  The present invention controls chatter vibration and tool chipping by controlling the feed shaft in consideration of the amount of tool edge runout during machining of machine tools, especially heavy cutting of difficult-to-cut materials such as titanium alloys. The present invention relates to a feed shaft control method performed for suppression, and a machine tool that performs cutting using the control method.

  When machining difficult-to-cut materials by milling, a tool for attaching a detachable cutting blade called a throwaway or insert is used to reduce machining costs. In this tool, the height of the mounted cutting edge does not become uniform due to the mounting seating surface of the cutting edge of the tool body and the processing accuracy of the cutting edge itself. Relative mounting error) occurs. In the case of a cutting edge with a large amount of runout, there is a problem that tool chipping occurs and the tool life is shortened. Therefore, in the case of Patent Document 1, the present applicant sets the amplitude and phase based on each position of the cutting edge and the pre-measured shake amount, and synchronizes with the main shaft so as to cancel the shake amount. There is provided an invention in which tool chipping is suppressed by making a slight displacement in the direction opposite to the machining progress direction to bring the one-blade feed amount of each cutting edge closer to the original command value.

JP 2013-240837 A

In the machining method of Patent Document 1, since only the amount of deflection is controlled in the direction opposite to the machining progress direction, a sufficient effect is exhibited in groove cutting.
However, in side cutting, the starting angle of cutting changes depending on the amount of cutting in the tool radial direction (hereinafter referred to as “ae”) to the workpiece, and the cutting force is not uniform, so that a sufficient tool life can be obtained. could not.

  Therefore, the present invention has an object to provide a feed axis control method and a machine tool in a machine tool that can achieve a long tool life by optimizing the control start angle even when performing side cutting. It is.

In order to achieve the above object, according to the first aspect of the present invention, a workpiece is machined by rotating a tool having at least one stage of cutting blades arranged on a concentric circle in the axial direction. In a machine tool, a feed shaft control method that superimposes a control for minutely displacing the feed shaft in the machining reverse direction based on the amount of deflection of the cutting edge measured in advance with respect to the feed shaft being processed,
When calculating the angle correction amount for correcting the control start angle based on the cutting depth in the radial direction of the tool, correcting the start angle from the calculated angle correction amount, and performing side machining with the tool Is characterized by superimposing the control of the minute displacement based on the corrected start angle.
According to a second aspect of the present invention, in the configuration of the first aspect, the angle correction amount θ _C is calculated by the following calculation formula.
When ae <R: θ _C = sin ⁻¹ {1- (ae / R)}
When ae ≧ R: θ _C = 0
ae: Radial depth of cut (mm), R: Tool radius (mm)
In order to achieve the above object, according to a third aspect of the present invention, a workpiece is machined by rotating a tool formed by mounting at least one stage of cutting blades arranged on a concentric circle in the axial direction. In addition, a machine tool that superimposes a control for finely displacing the feed shaft in the machining reverse direction based on the amount of deflection of the cutting edge measured in advance with respect to the feed shaft being processed,
An angle correction amount calculating means for calculating an angle correction amount for correcting a start angle of the control based on a cutting amount in the radial direction of the tool, and the start angle from the angle correction amount calculated by the angle correction amount calculating means. A starting angle correcting means for correcting; and a control means for superimposing the control of the minute displacement based on the starting angle corrected by the starting angle correcting means when performing side machining with the tool. To do.
According to a fourth aspect of the present invention, in the configuration of the third aspect, the angle correction amount calculation means calculates the angle correction amount θ _C by the following calculation formula.
When ae <R: θ _C = sin ⁻¹ {1- (ae / R)}
When ae ≧ R: θ _C = 0
ae: Radial depth of cut (mm), R: Tool radius (mm)

  According to the present invention, when calculating the angle correction amount for correcting the control start angle based on the cutting amount in the radial direction of the tool, correcting the start angle from the calculated angle correction amount, and performing side machining with the tool Is superimposed on the control of minute displacement based on the corrected start angle. Therefore, even when performing side cutting, the control start angle can be optimized to extend the tool life.

It is a block diagram of a machine tool. It is a flowchart of a feed axis control method. It is a cross-sectional view of a tool. It is explanatory drawing of the side surface process by a milling tool. This is a control amount (control position and cutting blade runout amount) when machining using one cutting edge with 4 blades. This is the angle correction amount calculated from the cutting depth in the radial direction and the tool radius. This is a control amount (control position and control amount) to which an angle correction amount is added. It is a measurement result of the cutting force in a normal case. It is a measurement result of the cutting force in the conventional control without angle correction. It is a measurement result of cutting force in this control in consideration of side cutting.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an example of a machine tool that implements a feed shaft control method according to the present invention. In the figure, 1 is a bed, 2 is a column, and a spindle head 3 is provided on the front surface of the column 2 so that movement can be controlled in the X-axis direction and Z-axis direction by an X-axis control unit 4 and a Z-axis control unit 5 Thus, a tool 7 is mounted on a main shaft 6 provided downward at the lower portion of the main shaft head 3. On the other hand, a table 9 that can be controlled to move in the Y-axis direction by the Y-axis control unit 8 is provided on the bed 1, and 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 angle correction amount calculation means that calculates a control amount of the feed shaft (each control unit 4, 5, 8), and a start angle correction. And a numerical control device 13 as a control means for controlling the feed axis, and a storage device (not shown). The arithmetic device 12 includes a tool 7 described later by an external input device 14. The amount of runout of the cutting edge, radial cutting depth ae, tool radius, etc. can be input.

In the machine tool configured as described above, machining is performed based on the flowchart of FIG. As shown in FIG. 3, the tool 7 is provided with three concentric steps provided with four cutting edges 7a, 7a,... At intervals of 90.degree. The cutting edges 7a in each row of directions (the circle numbers shown in FIG. 3) are attached with gradually shifting from the tip of the tool 7 to the front side in the rotational direction. In each row circle numbers 1 to 4, three cutting edges 7a, 7a are arranged in the twist direction.
First, in S1, each position of the cutting edge 7a of the tool 7 and the amount of deflection thereof are measured and input to the arithmetic device 12 via the external input device 14, and the arithmetic device 12 rotates using a predetermined calculation formula. The control amount and control position of each blade row at an angle are calculated. This calculation of the control amount is performed as follows, for example.

First, the number suffix of the blade row is i (1 ≦ i ≦ Z, Z: number of blades)
The step number suffix of the cutting edge 7a in each blade row is j (1 ≦ j ≦ N, N: the number of cutting blade steps used for actual machining in the blade row).
C _{i, j} (μm)
Then, the increase or decrease D _{i, j} of the actual machining allowance at each cutting edge can be calculated by the following equation (1).
D _{i, j} = C _{i, j} −C _{i−1, j} (1)
However, if i-1 is zero, it is replaced with Z.
That is, the magnitude of the deflection amount of each cutting edge 7a is not the actual machining allowance in each cutting edge 7a, but the difference (increase / decrease) in the deflection amount of each cutting edge 7a is the difference in actual machining allowance. This value is calculated because the cutting edge 7a having a larger difference advances the chipping earlier and shortens the tool life.

Then, calculated by Equation (2) below a control quantity Q _i in each blade array.
As Q ₁ = 0,
Q _i = _{(D i, 1} from _{D i,} the maximum value of up to _j) - {value obtained by dividing the sum by the number of blades Z of the respective blade row i _(the maximum value from _{D i, 1} to _{D i, j)} } + Q _i-1 (2)
Note that this calculation formula means that the actual machining allowance maximum value in the blade row is not smaller than the average value of the maximum values calculated in each blade row.

  The control position (starting angle) is, for example, only the cutting edge 7a actually used for machining from the position (rotation angle from the reference position (α in FIG. 3)) where the deflection amount at each stage in the blade row is measured. Use the average rotation angle. You may make it grasp | ascertain the phase relationship between each position of the cutting edge 7a and the main body of the tool 7 with the encoder connected to the main axis | shaft 6, for example. Based on the output of this encoder, the spindle rotation control device 11 can obtain the phase information of the cutting edge 7a.

However, in the side cutting in the milling process, as shown in FIG. 4, since the starting position of cutting varies depending on the cutting depth ae in the radial direction, it is necessary to perform control at the starting position. In FIG. 4, the arrow A indicates the machining progress direction, and the arrow B indicates the tool rotation direction.
Therefore, in S2, the cutting depth ae (mm) and the tool radius R (mm) in the radial direction are input in advance via the external input device 14, and the arithmetic unit 12 uses the calculation formula set in advance in S3. Then, an angle correction amount θ _C for correcting the control position is calculated. This angle correction amount θ _C is calculated by the following calculation formula.
θ _C = sin ⁻¹ {1- (ae / R)}
However, this calculation is performed only when ae <R, and when ae ≧ R, the angle correction amount θ _C is not calculated (θ _C = 0) and the angle correction is not performed. This is because the cutting force is maximized in the processing progress direction.

Then, in S4, the arithmetic unit 12 adds the angle correction amount theta _C calculated in step S3 to the position of the control at each cutting edge. Therefore, in S5, the numerical controller 13 controls each feed axis (control unit) based on the feed axis command value in which the control position is corrected, and performs machining. For example, in the case of machining on the XY plane, the control amount calculated with respect to the machining progress direction is distributed in the X-axis and Y-axis directions to control the feed axis in the machining reverse direction. The processes in S4 and S5 are repeated until the processing is finished in S6.
By this control, a minute forced vibration is superimposed on the feed operation, but this forced vibration has a frequency equal to the vibration of the tool 7, so that the amount of vibration of the tool 7 within one rotation of the spindle 6 is suppressed. Thus, the vibration can be superimposed on the feed shaft, and the influence of the tool runout amount can be canceled. As a result, the maximum cutting force acting on the cutting edge 7a can be reduced and the occurrence rate of tool chipping can be reduced. In addition, reduction of the maximum cutting force leads to suppression of chatter vibration.

Specific examples will be described below.
FIG. 5 shows the measured values of the amount of run-out of each cutting edge when it is assumed that the number of cutting edges is 4 and a tool having one cutting edge is used.
6 shows the angle correction amount θ _C calculated from the cutting depth ae and the tool radius in the tool of FIG. 5, and FIG. 7 is controlled by adding the angle correction amount θ _C to the measured value of FIG. Is a control amount obtained by correcting the position of.
As described above, since the tool runout amount in each axis direction is corrected on the feed shaft side at an appropriately controlled position during side cutting, the influence of the tool runout amount can be suppressed, and the tool life is improved. .

In order to confirm the effect of this control, titanium alloy processing was carried out with an insert type milling tool having a diameter of 50 mm. When cutting speed V _C : 45 m / min, feed rate per tooth f _Z : 0.1 mm / tooth, axial cutting depth ap: 8 mm, radial cutting depth ae: 15 mm, cutting conditions such as side cutting, FIG. 8 is normal FIG. 9 shows the cutting force measurement result in the conventional control without angle correction, and FIG. 10 shows the cutting force measurement result in the main control considering the side cutting.
As is apparent from FIG. 10, when the angle correction is performed, the cutting force becomes uniform, so that the tool life is improved.

Thus, according to the feed shaft control method and machine tool of the above embodiment, the angle correction amount θ _C for correcting the control start angle is calculated based on the cutting depth ae in the radial direction of the tool, and the calculated angle correction When the start angle is corrected from the amount θ _C and the side surface machining is performed by the tool 7, the control start angle can be set even when the side cutting is performed by superimposing the fine displacement control based on the corrected start angle. The tool life can be extended by optimization.

Note that the number of cutting edges in a tool and the number of cutting edges in one stage are not limited to the above-described form, and can be appropriately increased or decreased. Moreover, in the said form, although the control direction is a process progress direction, the direction which considered the angle correction amount (theta) _C in the process progress direction is also possible.
As long as a machine tool performs machining by rotating a tool with at least one stage of cutting blades arranged on concentric circles in the axial direction and controlling the feed axis, a multi-task machine, machining center, etc. The model is not particularly limited.

  1 .... bed, 2 .... column, 3 .... head spindle, 4 .... X axis control unit, 5 .... Z axis control unit, 6 .... spindle, 7 .... tool, 7a ..., cutting edge, 8 .... -Y-axis control unit, 9-Table, 10-Workpiece, 11-Spindle rotation control device, 12-Arithmetic device, 13-Numerical control device, 14-External input device

Claims (4)

In a machine tool for processing a workpiece by rotating a tool in which a plurality of cutting blade steps arranged on concentric circles are mounted in the axial direction, the cutting edge measured in advance with respect to the feed shaft being processed A feed shaft control method that superimposes a control for finely displacing the feed shaft in the machining reverse direction based on the amount of blade deflection,
When calculating the angle correction amount for correcting the control start angle based on the cutting depth in the radial direction of the tool, correcting the start angle from the calculated angle correction amount, and performing side machining with the tool Is a method for controlling a feed axis in a machine tool, wherein the control of the minute displacement is superimposed on the basis of the corrected start angle. 2. The feed axis control method for a machine tool according to claim 1, wherein the angle correction amount [theta] _C is calculated by the following formula.
When ae <R: θ _C = sin ⁻¹ {1- (ae / R)}
When ae ≧ R: θ _C = 0
ae: Radial depth of cut (mm), R: Tool radius (mm) The work piece is machined by rotating a tool formed by mounting at least one stage of cutting edges arranged concentrically in the axial direction, and the cutting edge measured in advance with respect to the feed shaft being machined is processed. A machine tool that superimposes a control for minutely displacing the feed shaft in the machining reverse direction based on a deflection amount,
An angle correction amount calculating means for calculating an angle correction amount for correcting a start angle of the control based on a cutting amount in the radial direction of the tool, and the start angle from the angle correction amount calculated by the angle correction amount calculating means. A starting angle correcting means for correcting; and a control means for superimposing the control of the minute displacement based on the starting angle corrected by the starting angle correcting means when performing side machining with the tool. Machine tool to do. The machine tool according to claim 3, wherein the angle correction amount calculating means calculates the angle correction amount θ _C by the following calculation formula.
When ae <R: θ _C = sin ⁻¹ {1- (ae / R)}
When ae ≧ R: θ _C = 0
ae: Radial depth of cut (mm), R: Tool radius (mm)

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