Method for controlling feed axes in a machine tool and a machine tool that performs machining using the method for controlling feed axes

Abstract

Method for controlling feed axes in a machine tool, wherein the machine tool processes a workpiece (10) by rotating a tool (7), the tool (7) contains a plurality of rows having a plurality of cutting edges (7a) arranged in an axial direction on concentric circles, and the method is characterized by having steps of: a calculation of an increase or decrease in machining allowances of a workpiece (10) currently being machined by respective cutting edges (7a), based on previously measured out-of-roundness values ​​of the cutting edges (7a); a calculation of control amounts, whereby maximum values ​​of the machining allowances in the respective cutting grooves are averaged; and a superimposition of a control of a minor procedure of the feed axes in an opposite direction of a machining operation based on the control amounts while a machining operation is being performed.

Description

[0001] The present invention relates to a method for controlling infeed axes in a machine tool to suppress chatter vibration and tool chipping by controlling the infeed axes in consideration of runout amounts at cutting edges of the tool during machining by the machine tool, particularly during heavy-duty cutting of a difficult-to-cut material such as a titanium alloy. The present invention also relates to a machine tool that performs cutting using the method for controlling infeed axes.

[0002] When machining difficult-to-cut materials by milling, a tool to which removable so-called "one-way" or "insert" cutting edges are attached is used to reduce machining costs. In this tool, the heights of the attached cutting edges are not uniform due to the effect of machining accuracy on a support surface for attaching the cutting edges of the tool itself and on the cutting edges themselves, and therefore, runout amounts (relative assembly errors between respective cutting edges) are generated. In a case of cutting edges with a large amount of runout, tool chipping occurs and tool life is reduced. Accordingly, the present inventors have provided the invention in the Japanese Patent Application Laid-Open No. 2013-240837.In JP 2013-240837 A, an amplitude and a phase are determined based on respective positions of cutting edges and previously measured runout amounts, and infeed axes are moved in an opposite direction to a machining progress direction synchronously with a main spindle to cancel the runout amounts, so that a single-cutting-edge infeed amount close to an originally designed value is generated from each cutting edge.

[0003] In the machining method of JP 2013-240837 A, when machining is performed using the tool having a plurality of cutting edges (a plurality of cutting edge rows) in a groove, the amount of operation of the feed axes in the opposite direction of machining is determined to an average value of the runout amount measured in a cutting groove in respective cutting edge rows, since the runout amount varies in respective cutting edges. However, it is difficult to achieve a sufficient tool life if the runout amount does not become minimum at the average value. As a countermeasure to the above, it is considered that there is a calculation method of control amounts, for example, using a solve function of a spreadsheet application, so that actual machining allowances for respective cutting edges are averaged.However, since the value in this method converges by repeatedly performing a calculation to obtain the maximum solution, it is necessary to execute the method several times, it consumes time and a calculation formula becomes complicated.

[0004] In view of the above, it is an object of the present invention to provide a method for controlling feed axes in a machine tool and a machine tool capable of providing a control amount in which maximum values ​​of the actual machining allowances are averaged by a simple calculation, and capable of increasing the life of the tool.

[0005] The object is achieved by a method for controlling feed axes in a machine tool having the features of patent claim 1 and by a machine tool having the features of patent claim 3. Advantageous further developments are contained in the dependent claims.

[0006] According to a first aspect of the present invention, a method for controlling infeed axes in a machine tool is provided, wherein the machine tool machines a workpiece by rotating a tool including a plurality of rows having a plurality of cutting edges arranged on concentric circles in the axial direction. The method includes steps of calculating an increase or decrease in machining allowances of a workpiece to be currently machined by respective cutting edges based on previously measured runout amounts of the cutting edges, calculating control amounts by averaging maximum values ​​of the machining allowances in respective cutting grooves, and superimposing control of infeed axes moved slightly in an opposite direction to machining based on the control amounts while machining is being performed.

[0007] In the above structure, according to a second aspect of the present invention, a control amount R i calculated by the following procedures.

[0008] When an index for a number of the cutting groove is “i” (1≤i≤Z, Z: the number of cutting edges), an index for a number of the row of cutting edges in each cutting groove is “j” (1≤j≤N, N: the number of cutting edge rows used in the cutting groove in the current machining), and the measured runout amount of each cutting edge C i, j (µm), an increase or decrease D i, j the current machining allowance at each cutting edge can be calculated by the following formula (1). Di,j=Ci,j−Ci−1,j (if i-1 is 0(zero), it is replaced by Z)

[0009] Next, when R1=0, the control amount R i calculated by the following formula (2), Ri=(maximum value from Di,1 to Di,j)−{value obtained by dividing the total sum of (the maximum values ​​from Di,1 to Di,j) in each cutting groove "i" by the number of cutting edges Z}+Ri−1

[0010] According to a third aspect of the present invention, there is provided a machine tool that machines a workpiece by rotating a tool including a plurality of rows, each of which has a plurality of cutting edges arranged on concentric circles in the axial direction. The machine tool includes a control value calculation unit for calculating an increase or decrease in machining allowances of a workpiece to be currently machined by respective cutting edges based on previously measured runout amounts of the cutting edges, and for calculating a control amount by averaging the maximum values ​​of the machining allowances in respective cutting grooves, and a control unit for superimposing control of infeed axes moved slightly in an opposite direction to machining based on the control amounts while machining is being performed.

[0011] In the structure according to a fourth aspect of the present invention, a control amount R i calculated by the following procedures.

[0012] When an index for a number of the cutting grooves is “i” (1≤i≤Z, Z: the number of cutting edges), an index for a row number of the cutting edges in each cutting groove is “j” (1≤j≤N, N: the number of rows of cutting edges used in a current machining in the cutting groove), and the measured runout amount of each cutting edge C i, j (µm), an increase or decrease D i, j the current machining allowance at each cutting edge can be calculated by the following formula (1). Di,j=Ci,j−Ci−1,j (if i-1 is 0(zero), it is replaced by Z)

[0013] Next, when R1=0, the control amount R i calculated by the following formula (2), Ri=(maximum value from Di,1 to Di,j)−{value obtained by dividing the total sum of (the maximum values ​​from Di,1 to Di,j) in each cutting groove "i" by the number of cutting edges Z}+Ri−1

[0014] According to the present invention, the tool runout amounts in the respective axial directions according to the tool position (rotation angle) on the feed axis side during machining are corrected by a simple calculation rather than a complicated calculation method that consumes time. Therefore, the control amounts are obtained by averaging the maximum values ​​of the current machining allowances. Accordingly, machining can be performed while suppressing the effect of the tool runout amount, thus increasing the tool life. Fig. 1 is a structural view showing an example of a machine tool. Fig. 2 is a flowchart of a method for controlling infeed axes. Fig. 3 is a view of a horizontal cross section of a tool, Fig. 4 shows measurement results of runout amounts of respective cutting edges and calculation results of an increase or decrease of actual allowances when machining is performed using cutting edges in four grooves with three rows per groove. Fig. 5 shows measurement results of runout amounts of respective cutting edges and calculation results of an increase or decrease of actual allowances when machining is performed using cutting edges in four grooves with three rows per groove, and calculation results obtained when average values ​​of runout amounts of a tool are used as control amounts. Fig. 6 shows measurement results of runout amounts of respective cutting edges and calculation results of an increase or decrease of actual allowances when machining is performed using cutting edges in four grooves with three rows per groove, and calculation results of control amounts in which the maximum values ​​of actual allowances are averaged.

[0015] Hereinafter, an embodiment of the present invention will be explained with reference to the drawings.

[0016] Fig. 1 is a structural view showing an example of a machine tool that implements a feed-axis control method according to the present invention. In the drawing, 1 denotes a bed, and 2 denotes a column. A spindle head 3 is provided in front of the column 2 to be controlled by an X-axis control unit 4 and a Z-axis control unit 5 in an X-axis direction and a Z-axis direction. A tool 7 is attached to a main spindle 6 provided below the spindle head 3 so as to face downward. A table 9, which can be controlled by a Y-axis control unit 8 to move in a Y-axis direction, is provided above the bed 1, and a workpiece 10 can be fixed on the table 9.

[0017] A control system of the machine tool includes a main spindle rotation control unit 11 that controls a rotational speed of the main spindle 6, an arithmetic unit 12 that calculates control amounts of infeed axes (respective control units 4, 5, and 8), a numerical value control unit 13 that controls the infeed axes, and a storage unit (not shown). Runout amounts at cutting edges of the tool 7, described later, can be input to the arithmetic unit 12 through an external input unit 14.

[0018] In the machine tool having the above configuration, machining is performed based on a flow chart of Fig. 2. As in Fig. As shown in Figure 3, the tool 7 is formed by providing three rows, each of which has four cutting edges 7a, 7a..., which are provided at intervals of 90° on concentric circles in the axial direction at predetermined intervals. The cutting edges 7a in each groove (of Fig. 3) are arranged in the axial direction such that the cutting edges 7a are successively offset from a tip end of the tool 7 at the front in the rotation direction, that is, three cutting edges 7a, 7a ... are arranged in respective grooves of the circled numbers 1 to 4 in a spiral direction.

[0019] First, in S1, runout amounts at respective cutting edges 7a of the tool 7 are measured and input in advance to the arithmetic unit 12 via the external input unit 14. The arithmetic unit 12 calculates the control amounts of respective cutting grooves at a rotation angle in S2 using a predetermined calculation formula. The calculation of the control amount is performed in the following manner.

[0020] First, if an index for a number of the cutting groove is “i” (1≤i≤Z, Z: the number of cutting edges), an index for a row number of the cutting edges 7a in each cutting groove is “j” (1≤j≤N, N: the number of rows of cutting edges used in the cutting groove in the current machining), and the measured runout amount of each cutting edge C i, j (µm), an increase or decrease D i, jat the current machining allowance at each cutting edge can be calculated by the following formula (1). Di,j=Ci,j−Ci−1,j

[0021] However, if i-1=0 (zero), it is replaced by Z.

[0022] This means that the amount of runout at each cutting edge 7a does not correspond to the actual machining allowance at each cutting edge 7a, and the difference in the amount of runout at each cutting edge 7a (increase or decrease) corresponds to the difference in the actual machining allowances. The greater the difference at the cutting edges 7a, the faster the chipping progresses and the shorter the service life, so the values ​​are calculated.

[0023] Then a control amount R i in each cutting groove is calculated by the following formula (2).

[0024] If R1=0, Ri=(maximum value from Di,1 to Di,j)−{value obtained by dividing the total sum of (the maximum values ​​from Di,1 to Di,j) in each cutting groove "i" by the number of cutting edges Z}+Ri−1

[0025] The calculation formula states that the maximum value of the current allowance in the cutting groove is not less than an average of the maximum values ​​calculated in the respective cutting grooves.

[0026] As a control position (tool rotation angle), an average value of a rotation angle (α in Fig. 3) from a position (reference position) where the runout amounts in respective rows of cutting grooves of only the cutting edges 7a used for the current machining are measured, for example, at rotation angles. A phase relationship between each position of the cutting edge 7a and the body of the tool 7 can be detected by an encoder connected to the main spindle 6. The main spindle rotation control unit 11 obtains the phase information of the cutting edge 7a based on the encoder output.

[0027] If the control amount R iin each cutting groove, the arithmetic unit 12 in S3 converts the control amount calculated in S2 into an amount in each axis direction and subtracts the value from a feed-axis application value in an NC program stored in the storage unit. Then, the numerical value control unit 13 in S4 executes machining by controlling respective feed axes (control units) based on the subtracted feed-axis instruction values. For example, when machining in an XY plane, the control amount calculated with respect to the machining feed direction is distributed to the X-axis and Y-axis directions, and the feed axes are controlled in the opposite direction of machining. The processing in S3 and S4 is repeated until machining ends in S5.

[0028] Due to the above control, a tiny forced vibration is superimposed on the infeed operation. Since the forced vibration has a frequency equal to the runout of the tool 7, which can cancel out the effect of the runout amount in the tool, the vibration can be superimposed on the infeed axes to suppress the runout amount of the tool 7 upon rotation of the main spindle 6. As a result, the maximum cutting force acting on the cutting edges 7a is reduced, thereby reducing the degree of occurrence of tool chipping. This also leads to the suppression of chatter vibration by reducing the maximum cutting force.

[0029] Fig. Figure 4 shows the measured values ​​of the runout amount of the respective cutting edges and the calculated values ​​of the increases or decreases in the actual machining allowances, assuming that a tool with cutting edges in four grooves with three rows per groove is used. In this case, the cutting edge with the relatively largest machining allowance, which is 30 µm, is in the first row of the third groove (a section surrounded by thick lines).

[0030] Fig. Figure 5 shows the calculated values ​​obtained when the average runout amounts of cutting edges in each row measured in a cutting groove is selected as a control amount, the calculated values ​​of the runout amounts of cutting edges obtained when controlling based on the calculated values, and the calculated values ​​of the increases or decreases of the actual machining allowances. In this case, the cutting edge with the relatively largest machining allowance, which is 12.3 µm, is one in the first row of the third groove (a section surrounded by thick lines).

[0031] On the other hand, Fig.6 control amounts calculated using the above calculation formula, calculated values ​​of cutting edge runout amounts obtained when controlling based on the control amounts, and calculated values ​​of any increase or decrease in the current machining allowances. In this case, the cutting edges with the relatively largest machining allowance are increased to four places (more averaged), the allowance of which is 6.3 µm (sections surrounded by thick lines), meaning the effect of runout amounts is almost eliminated. The result is almost the same as the result of the analysis using the solve function of the spreadsheet application.

[0032] As described above, when the machine tool implementing the infeed axes control method according to the embodiment is used, the tool runout amounts in respective axis directions according to the tool position (rotation angle) on the infeed axes side during machining are corrected not by a complicated calculation method that consumes time, but by a simple calculation. As a result, the control amounts are obtained by averaging the maximum values ​​of the actual machining allowances. Accordingly, machining can be performed while suppressing the effect of the tool runout amount, which increases the service life of the tool 7.

[0033] The number of rows of cutting edges and the number of cutting edges in a row in the tool are not limited to the above and can be increased or decreased as appropriate. In particular, the types of machine tools are not limited as long as machining is performed by controlling the feed axes while rotating the tool, in which a plurality of rows, each having a plurality of cutting edges, are arranged on concentric circles in the axial direction, and the invention can be applied, for example, to a combined machining device, a machining center, etc.

[0034] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently of one another for the purpose of original disclosure and for the purpose of limiting the claimed invention, regardless of the combination of features in the embodiments and / or the claims. It is explicitly stated that all value ranges or indications of groups of formations, for the purpose of original disclosure and for the purpose of limiting the claimed invention, disclose every possible intermediate value or intermediate formation, in particular as limits of value ranges.

Claims

[1] Method for controlling feed axes in a machine tool, wherein the machine tool machines a workpiece (10) by rotating a tool (7), the tool (7) containing a plurality of rows having a plurality of cutting edges (7a) arranged on concentric circles in an axial direction, and the method is characterized by comprising the steps of: calculating an increase or decrease in machining allowances of a workpiece (10) currently being machined by respective cutting edges (7a) based on previously measured runout amounts of the cutting edges (7a); calculating control amounts, whereby maximum values ​​of the machining allowances in respective cutting grooves are averaged; and superimposing control of a slight movement of the feed axes in an opposite direction of machining based on the control amounts while machining is being performed. [2] Method for controlling feed axes in a machine tool according to claim 1, where a control amount R i is calculated by the following procedures: if an index for a number of the cutting groove is “i”, (1≤i≤Z, Z: the number of cutting edges), an index for a number of a row of the cutting edges (7a) in each cutting groove is “j” (1≤j≤N, N: the number of rows of cutting edges (7a) used in the cutting groove in the current machining), and the measured runout amount of each cutting edge (7a) C i, j (µm), an increase or decrease D i, j the current machining allowance at each cutting edge (7a) can be calculated using the following formula (1): Di,j=Ci,j−Ci−1,j (if i-1 is 0 (zero), it is replaced by Z) next, if R1=0, the control amount R i calculated by the following formula (2), Ri=(maximum value from Di,1 to Di,j)−{value obtained by dividing the total sum of (the maximum values ​​from Di,1 to Di,j) in each cutting groove "i" by the number of cutting edges}+Ri−1 [3] A machine tool which machines a workpiece (10) by rotating a tool (7) which includes a plurality of rows, each of which has a plurality of cutting edges (7a) arranged on concentric circles in the axial direction, the machine tool being characterized by comprising: a control value calculation unit (12) for calculating an increase or decrease in machining allowances of a workpiece (10) currently being machined by respective cutting edges (7a) based on previously measured runout amounts of the cutting edges (7a) and for calculating control amounts, wherein the maximum values ​​of the machining allowances in respective cutting grooves are averaged; and a control unit (13) for superimposing control of a slight movement of feed axes in an opposite direction of machining while machining is being carried out. [4] Machine tool according to claim 3, where a control amount R i is calculated by the following procedures: if an index for a number of the cutting groove is “i” (1≤i≤Z, Z: the number of cutting edges), an index for a number of a row of the cutting edges (7a) in each cutting groove is “j” (1≤j≤N, N: the number of rows of cutting edges (7a) used in the cutting groove in the current machining), and the measured runout amount of each cutting edge (7a) C i, j (µm), an increase or decrease D i, j the current machining allowance at each cutting edge (7a) can be calculated using the following formula (1): Di,j=Ci,j−Ci−1,j (if i-1 is 0(zero), it is replaced by Z) next, if R1=0, the control amount R i calculated by the following formula (2), Ri=(maximum value from Di,1 to Di,j)−{value obtained by dividing the total sum of (the maximum values ​​from Di,1 to Di,j) in each cutting groove "i" by the number of cutting edges Z}+Ri−1

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