Method and system for suppressing chatter vibrations of machine tools

Abstract

To enable changing of a cutting condition by generating a stability limit diagram without identifying a chattering vibration frequency.SOLUTION: After machining on an initial cutting condition (S1), a machined surface pattern of the side surface of a workpiece machined by an end mill is acquired by a camera (S2 and S6), vibration displacement and / or a vibration frequency of a tool system are calculated from the acquired machined surface pattern (S3 and S7), a transmission function is defined from the vibration displacement and the vibration frequency which have been acquired (S8-S10), a stability limit diagram is generated on the basis of the identified transmission function (S11), and a main spindle rotation speed and / or a cutting amount are changed on the basis of the generated stability limit diagram (S12).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a method for suppressing chatter vibration in end milling in a machine tool and a system for suppressing chatter vibration.

Background Art

[0002] In end milling, chatter vibration occurs when the dynamic characteristics of the machine tool, tool, and workpiece and the cutting process satisfy certain conditions. The dynamic characteristics of the machine tool, tool, and workpiece are measured by a hammering test that requires expensive measuring instruments and specialized knowledge to obtain the transfer function. It is known that a stability limit diagram can be created from the transfer function measured by the hammering test, and chatter vibration can be suppressed by changing the spindle rotation speed. On the other hand, Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 propose identifying the chatter vibration frequency from the machining surface pattern of chatter vibration and repeatedly changing the spindle rotation speed to suppress chatter vibration without measuring the transfer function by a hammering test.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

[0005] However, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2, generate chatter vibrations, which damage the tool. Furthermore, while the chatter vibration frequency can be identified from the machining surface pattern, the modal parameters necessary for creating a stability limit diagram, such as "mass m, spring constant k, and damping coefficient c," cannot be identified. Therefore, to suppress chatter vibrations, it is necessary to repeatedly identify the chatter vibration frequency from the machining surface pattern and change the spindle rotation speed.

[0006] Therefore, the present disclosure aims to provide a method and system for suppressing chatter vibration in a machine tool that allows for the creation of a stability limit diagram without identifying the chatter vibration frequency and for changing cutting conditions. [Means for solving the problem]

[0007] To achieve the above objective, the first configuration of this disclosure is a method for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step is performed, which involves changing the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram. death, The vibration information is vibration displacement and / or vibration frequency. In the vibration information acquisition step, the vibration displacement is calculated based on the magnitude of the width of the machined surface pattern generated each time the cutting edge, which is positioned in the rotational direction of the cutting tool, rotates. characterized by doing so. In order to achieve the above objective, Another aspect of the first configuration is A method for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step which changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Execute, The vibration information is vibration displacement and / or vibration frequency. In the vibration information acquisition step, the vibration frequency is calculated based on a cycle in which the width of the machined surface pattern generated by the blade arranged in the rotational direction of the cutting tool varies every rotation. In order to achieve the above objective, Another aspect of the first configuration is A method for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step which changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Execute, The vibration information is vibration displacement and / or vibration frequency. In the transfer function identification step, compliance values corresponding to the respective vibration frequencies obtained by machining at a plurality of spindle rotational speeds are calculated from the ratio of the respective vibration displacements and cutting forces obtained by machining at a plurality of spindle rotational speeds, and the transfer function is identified based on the relationship between the vibration frequency and the compliance value. Another aspect of the first configuration is that in the stability limit diagram creation step, for the transfer function, curve fitting is performed to identify modal parameters, the stability limit diagram is created based on the identified modal parameters, and the spindle rotational speed and / or the depth of cut are changed. To achieve the above objective, the second configuration of this disclosure is a system for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A processing surface pattern acquisition means for acquiring the processing surface pattern of the processed side surface, A vibration information acquisition means for calculating tool system vibration information from the acquired machined surface pattern, A transfer function identification means for identifying the transfer function from the acquired vibration information, A means for creating a stability limit diagram that creates a stability limit diagram based on the identified transfer function, The system includes cutting condition changing means for changing the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram. 、 The vibration information is vibration displacement and / or vibration frequency. The vibration information acquisition means calculates the vibration displacement based on the magnitude of the width of the machined surface pattern generated each time the blade, which is positioned in the rotational direction of the cutting tool, rotates. It is characterized by the following. [Effects of the Invention]

[0008] According to this disclosure, chatter vibration can be suppressed by identifying the transfer function from the machined surface pattern of side milling with an end mill, creating a stability limit diagram based on the transfer function, and changing the spindle rotation speed and / or depth of cut, without the need for hammering tests which require expensive measuring instruments and specialized knowledge. In this disclosure, there is no need to repeatedly identify the chatter vibration frequency from the machined surface pattern and change the spindle rotation speed, so no damage is caused to the tool. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of a chatter vibration suppression system for machining centers. [Figure 2] (A) is an explanatory diagram showing the machined surface pattern of side milling using an end mill, and (B) is an explanatory diagram of an end mill. [Figure 3] This graph shows a method for identifying modal parameters such as "mass m, spring constant k, and damping coefficient c". [Figure 4]This is an explanatory diagram of the stability limit diagram created from the identified modal parameters. [Figure 5] This is a flowchart of a method for suppressing chatter vibrations. [Figure 6] This is an explanatory diagram showing a method for acquiring the pattern of a machined surface using a laser displacement meter. [Figure 7] This is an explanatory diagram showing a method for acquiring the pattern of a machined surface using a contact-type displacement sensor. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with reference to the drawings. Figure 1 is a schematic diagram showing an example of a chatter vibration suppression system S according to the second configuration in a machining center 1, which is an example of a machine tool. Here, the configuration for side machining using an end mill 9 is shown. In the machining center 1, the workpiece 4 is fixed via a jig to a table 3 that moves on the bed 2. The machining center 1 has a saddle 6 and a spindle head 7 that move on a column 5 fixed on the bed 2. The end mill 9 is held on the spindle 7a of the spindle head 7 via a holder 8. The machining center 1 performs cutting by the relative movement of the workpiece 4 and the end mill 9 according to commands from the control device 12. The machining center 1 is equipped with a camera 10 and an analysis device 11. The camera 10 captures the machining surface pattern of the workpiece 4 by the end mill 9. The camera 10 is an example of the machining surface pattern acquisition means of this disclosure. The analysis device 11 includes a machined surface pattern analysis means 13, a transfer function calculation means 14, a stability limit diagram creation means 15, and a recommended cutting condition calculation means 16.

[0011] The machining surface pattern analysis means 13 analyzes the machining surface pattern acquired from the camera 10 and calculates vibration displacement and / or vibration frequency, which are vibration information of the tool system. The machining surface pattern analysis means 13 is an example of the vibration information acquisition means of this disclosure. The transfer function calculation means 14 identifies the transfer function from the vibration information obtained from the machined surface pattern analysis means 13. The transfer function calculation means 14 is an example of the transfer function identification means of this disclosure. The stability limit diagram creation means 15 creates or estimates a stability limit diagram based on the transfer function obtained from the transfer function calculation means 14. The stability limit diagram creation means 15 is an example of the stability limit diagram creation means of this disclosure. The recommended cutting condition calculation means 16 calculates the optimal spindle rotation speed and / or depth of cut based on the stability limit diagram obtained from the stability limit diagram creation means 15. The control device 12 changes the spindle rotation speed and / or depth of cut based on the recommended cutting conditions obtained from the recommended cutting conditions calculation means 16. The recommended cutting conditions calculation means 16 and the control device 12 are examples of cutting condition changing means of this disclosure.

[0012] Figure 2 is an explanatory diagram showing a method for calculating vibration displacement and vibration frequency from the machined surface pattern of a workpiece 4 machined on the side by an end mill 9. As shown in Figure 2(A), the machined surface pattern 21 is generated when the end mill 9 is excited by the cutting force and vibrates slightly while cutting. Therefore, the machined surface pattern 22 for one tooth feed (the machined surface pattern generated by the blades arranged in the rotational direction for each rotation) 22 does not have a uniform width but fluctuates. The machined surface pattern 22 for one tooth feed is machined from bottom to top in Figure 2(A) due to the helix angle 28 of the end mill 9 shown in Figure 2(B). At the minimum width 23, the end mill 9 moves away from the machined surface due to vibration, and at the maximum width 24, the end mill 9 moves closer to the machined surface due to vibration. The depth (ymin, ymax) at the minimum width (wmin) 23 and maximum width (wmax) 24 can be calculated using the following formula (1). Here, D is the tool diameter.

[0013]

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[0014] The vibration displacement (x) is the difference in depth and can be calculated using the following equation (2).

[0015]

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[0016] Cutting speed from downward to upward (V c(up) )27 is the cutting speed in the circumferential direction (V c From )26 and the twist angle (β)28, it can be calculated using the following equation (3).

[0017]

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[0018] Furthermore, the vibration frequency f can be calculated using the following equation (4) from the cutting speed 27 from the downward to the upward direction and the length (L) 25 over which the width of the machined surface pattern 22 changes.

[0019]

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[0020] Figure 3 is an explanatory diagram of the method for identifying the modal parameters "mass m, spring constant k, and damping coefficient c". The vibration displacement and vibration frequency are calculated from the machined surface pattern obtained by changing the spindle rotation speed, and the ratio of the vibration displacement to the cutting force obtained from the cutting force simulation is defined as compliance. The graph 31 of the transfer function is plotted with compliance on the vertical axis and vibration frequency on the horizontal axis. Note that the cutting force may be measured directly without performing a cutting force simulation, or it may be obtained by referring to a pre-created database. The transfer function is estimated by performing curve fitting 33 on the plotted points 32 using a Gaussian function (equation (5) below). Note that a curve fitting method other than the Gaussian function may be used.

[0021]

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[0022] From a Gaussian function, compliance (Gmax), natural frequency (f0), and damping rate (ξ) can be calculated using the following equations (6) to (8).

[0023]

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[0024] Furthermore, the modal parameters, namely mass (m), spring constant (k), and damping coefficient (c), can be calculated using the following equations (9) to (11).

[0025]

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[0026] Figure 4 shows the creation of a stability limit diagram based on the transfer function, and the modification of the spindle rotation speed and depth of cut. The method for creating the stability limit diagram based on the transfer function is the method described in Non-Patent Document 3. The procedure is described below. (1) Chatter vibration frequency ω in the region where the real part of the transfer function identified from the machined surface pattern is negative. c Let's assume that. (2) From the following equation (12), the stability limit a lim Calculate K. f is the specific cutting resistance, and G is the real part of the transfer function.

[0027]

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[0028] (3) The rotational speed n is calculated for each wavenumber k=0,1,2·· using the following equation (13).

[0029]

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[0030] Solving equation (13) for T, we obtain the following equation (14), where T is the rotation period and n is the spindle rotation speed.

[0031]

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[0032] (4) Repeat steps (1) through (3) by changing ω near the resonant frequency. Then, by changing the spindle rotation speed to the recommended cutting conditions 43, which have a higher stable limit depth of cut than the initial cutting conditions 42 initially set in the machining program, stable machining becomes possible even when the depth of cut is changed to a larger amount than the initial cutting conditions 42, based on the stability limit diagram 41 in Figure 4. The range of change in the depth of cut is greater than or equal to the depth of cut of the initial cutting conditions 42 and less than or equal to the stable limit depth of cut of the stability limit diagram 41.

[0033] Figure 5 is a flowchart showing an example of a chatter vibration suppression method related to the first configuration implemented in the chatter vibration suppression system S. First, in step (hereinafter referred to as "S") 1, the control device 12 performs machining with the initial cutting conditions 42. In S2, the machined surface pattern 21 is photographed by the camera 10 (machined surface pattern acquisition step). In S3, the machining surface pattern analysis means 13 calculates the vibration displacement and vibration frequency of the tool system from the image of the machining surface pattern 21 acquired in S2. In S4, the machined surface pattern analysis means 13 calculates the range of variation in the spindle rotation speed from the vibration frequency (S3, S4: vibration information acquisition step). In S5, the control device 12 changes the spindle rotation speed based on the variation range and performs machining again. In S6, the machined surface pattern 21 is photographed by the camera 10 (machined surface pattern acquisition step).

[0034] In S7, the machining surface pattern analysis means 13 calculates the vibration displacement and vibration frequency of the tool system from the image of the machining surface pattern 21 acquired in S6 (vibration information acquisition step). In S8, the transfer function calculation means 14 calculates compliance by dividing the vibration displacement by the cutting force obtained from the cutting force simulation. In S9, the transfer function calculation means 14 plots the data with compliance on the vertical axis and vibration frequency on the horizontal axis, and estimates the transfer function by curve fitting (S8, S9: transfer function identification step). In S10, the stability limit diagram creation means 15 identifies the modal parameters "mass m, spring constant k, and damping coefficient c" from the estimated transfer function. In S11, the stability limit diagram creation means 15 creates a stability limit diagram 41 based on the modal parameters (S10, S11: Stability limit diagram creation step). In S12, the recommended cutting condition calculation means 16 calculates the optimal spindle rotation speed and depth of cut from the stability limit diagram 41 (cutting condition change step).

[0035] In the chatter vibration suppression system S of the above configuration, the machined surface pattern 21 on the side of the workpiece 4, which has been machined with an end mill 9 (an example of a cutting tool), is acquired by a camera 10 (S2, S6). From the acquired machined surface pattern 21, the vibration displacement and vibration frequency (an example of vibration information) of the tool system are calculated (S3, S7). The transfer function is identified from the acquired vibration displacement and vibration frequency (S8~S10). A stability limit diagram 41 is created based on the identified transfer function (S11). Based on the created stability limit diagram 41, the spindle rotation speed and depth of cut are changed (S12). With this configuration, chatter vibration can be suppressed by identifying the transfer function from the machined surface pattern 21 of the side milling with the end mill 9, creating a stability limit diagram 41 based on the transfer function, and changing the spindle rotation speed and depth of cut, without the need for hammering tests which require expensive measuring instruments and specialized knowledge. In this configuration, there is no need to repeatedly identify the chatter vibration frequency from the machined surface pattern 21 and change the spindle rotation speed, so no damage is caused to the tool.

[0036] In the above configuration, the process involves taking photos of the processed surface pattern and acquiring vibration information twice, but this can be done three or more times. In the above configuration, the vibration displacement and vibration frequency of the tool system are acquired as vibration information, but it is also possible to acquire only one of either the vibration displacement or the vibration frequency. In the above configuration, the spindle speed and depth of cut are changed as recommended cutting conditions, but either the spindle speed or the depth of cut may be changed. In the above configuration, the processing surface pattern is acquired by a camera, but the means for acquiring the processing surface pattern is not limited to a camera. For example, as shown in Figure 6, the processing surface pattern 21 may be acquired by a laser-type displacement meter 101, or as shown in Figure 7, by a contact-type displacement meter 102. The machine tool does not have to be a machining center. The chatter vibration suppression system may be configured as described above, with the control device and analysis device provided separately, or the analysis device may be integrated into the control device. Furthermore, the analysis device may be installed externally, separate from the machine tool. In this case, chatter vibration suppression can be achieved for each machine tool by performing analysis on multiple machine tools with a single analysis device and providing recommended cutting conditions to each individual control device. [Explanation of symbols]

[0037] 1. Machining center, 2. Bed, 3. Table, 4. Workpiece, 5. Column, 6. Saddle, 7. Spindle head, 7a. Spindle, 8. Holder, 9. End mill, 10. Camera, 11. Analysis device, 12. Control device, 13. Machining surface pattern analysis means, 14. Transfer function calculation means, 15. Stability limit diagram creation means, 16. Recommended cutting condition calculation means, 21. Machining surface pattern for side machining 22. Machined surface pattern at 1 feed rate, 23. Minimum width of machined surface pattern, 24. Maximum width of machined surface pattern, 25. Length over which the width of the machined surface pattern varies, 26. Circumferential cutting speed, 27. Cutting speed from bottom to top, 28. Helix angle, 31. Transfer function graph, 32. Plotted points, 33. Curve fitting, 41. Stability limit diagram, 42. Initial cutting conditions, 43. Recommended cutting conditions.

Claims

1. A method for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step which changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Execute, The vibration information is vibration displacement and / or vibration frequency. A method for suppressing chatter vibration of a machine tool, characterized in that the vibration information acquisition step calculates the vibration displacement based on the magnitude of the width of the machined surface pattern generated each time a cutting blade, which is arranged in the rotational direction of the cutting tool, rotates.

2. A method for suppressing chatter vibration associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step which changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Execute, The vibration information is vibration displacement and / or vibration frequency. A method for suppressing chatter vibration in a machine tool, characterized in that the vibration information acquisition step calculates the vibration frequency based on the period of change in the width of the machined surface pattern generated each time a cutting blade, which is arranged in the rotational direction of the cutting tool, rotates.

3. A method for suppressing chatter vibration associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A process for obtaining the processed surface pattern of the processed side surface, A vibration information acquisition step that calculates vibration information of the tool system from the acquired machined surface pattern, A transfer function identification step in which the transfer function is identified from the acquired vibration information, A stability limit diagram creation step, which involves creating a stability limit diagram based on the identified transfer function, A cutting condition modification step which changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Execute, The vibration information is vibration displacement and / or vibration frequency. A method for suppressing chatter vibration in a machine tool, characterized in that, in the transfer function identification step, compliance values ​​corresponding to each of the vibration frequencies obtained by machining at multiple spindle rotation speeds are calculated from the ratio of each of the vibration displacements and cutting forces obtained by machining at multiple spindle rotation speeds, and the transfer function is identified based on the relationship between the vibration frequency and the compliance value.

4. The method for suppressing chatter vibration of a machine tool according to claim 2, characterized in that, in the transfer function identification step, compliance values ​​corresponding to each of the vibration frequencies obtained by machining at multiple spindle rotation speeds are calculated from the ratio of each of the vibration displacements and cutting forces obtained by machining at multiple spindle rotation speeds, and the transfer function is identified based on the relationship between the vibration frequency and the compliance value.

5. The method for suppressing chatter vibration of a machine tool according to claim 3, characterized in that, in the step of creating the stability limit diagram, modal parameters are identified by curve fitting to the transfer function, the stability limit diagram is created based on the identified modal parameters, and the spindle rotation speed and / or the depth of cut are changed.

6. A system for suppressing chatter vibrations associated with machining in a machine tool that rotates a cutting tool mounted on a spindle to cut the side surface of a workpiece, A processing surface pattern acquisition means for acquiring the processing surface pattern of the processed side surface, A vibration information acquisition means for calculating tool system vibration information from the acquired machined surface pattern, A transfer function identification means for identifying the transfer function from the acquired vibration information, A means for creating a stability limit diagram that creates a stability limit diagram based on the identified transfer function, A cutting condition changing means that changes the spindle rotation speed and / or the depth of cut by the cutting tool based on the created stability limit diagram, Equipped with, The vibration information is vibration displacement and / or vibration frequency. The vibration information acquisition means is characterized by calculating the vibration displacement based on the magnitude of the width of the machined surface pattern generated each time a blade, which is arranged in the rotational direction of the cutting tool, rotates. This is a chatter vibration suppression system for a machine tool.

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