Machining condition setting method and machine tool

Abstract

To suppress chatter vibrations while cutting.SOLUTION: A machining condition setting method setting a machining condition for cutting has: a measuring step which measures a cutting force added to a workpiece from a cutting tool and vibrations at a plurality of measurement points of the workpiece while applying first trial machining to the workpiece with the cutting tool; a vibration estimation step which uses a measurement result of vibrations during the first trial machining at the plurality of measurement points to estimate vibrations of the workpiece at the cutting point; a frequency analysis step which performs a frequency analysis of the measurement result of the cutting force during the first trial machining and vibrations estimation result; a machining condition selection map creating step which uses a result of frequency analysis of the cutting force and a frequency analysis result of vibrations to create a machining condition selection map showing a relation between the cutting position on the workpiece when applying major machining to the workpiece with the cutting tool and prediction values of the machining condition and the vibration amplitude; and a setting step which uses the machining condition selection map to set the machining condition during the major machining so that the vibration amplitude is predetermined value or smaller.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a machining condition setting method and a machine tool. [Background technology]

[0002] Patent Document 1 discloses a device for assisting in the design of a jig that is installed to suppress chatter vibrations of a workpiece to be cut. This device predicts the machining accuracy of the workpiece using CAE (Computer Aided Engineering) analysis results, and if it predicts that the desired machining accuracy will not be obtained, the device prompts the user to change the design data of the jig, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-118973 Summary of the Invention [Problem to be solved by the invention]

[0004] If chatter vibration occurs during cutting, machining accuracy will decrease. Therefore, there is a need to suppress chatter vibration during cutting. In Patent Document 1, chatter vibration during cutting is suppressed by changing the design of a jig. However, there are cases where it is difficult to change the design of the jig, or where installing the jig itself is difficult. Therefore, there is a need for a technology to suppress chatter vibration without changing the design of the jig. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to a first aspect of the present disclosure, there is provided a machining condition setting method for setting machining conditions for cutting, the machining condition setting method comprising: a measurement step of measuring a cutting force applied to a workpiece from a cutting tool and vibrations at a plurality of measurement points on the workpiece while performing a first trial machining on the workpiece with the cutting tool; a vibration estimation step of estimating vibrations of the workpiece at a cutting position using the vibration measurement results at the plurality of measurement points during the first trial machining; a frequency analysis step of performing frequency analysis on the measurement results of the cutting force during the first trial machining and the estimated vibration results; a machining condition selection map creation step of creating a machining condition selection map representing the relationship between the cutting position on the workpiece, machining conditions, and predicted values ​​of vibration amplitude when performing a main machining on the workpiece with the cutting tool, using the machining condition selection map; and a setting step of setting the machining conditions for the main machining using the machining condition selection map so that the vibration amplitude is equal to or less than a predetermined value. According to this method for setting machining conditions, machining conditions are set using a machining condition selection map that shows the relationship between the cutting position, machining conditions, and predicted vibration amplitude values. Therefore, practical machining conditions suitable for suppressing chatter vibration can be set without trial and error. Therefore, even when it is difficult to install a jig or change the jig design, chatter vibration can be suppressed by adjusting the machining conditions. (2) In the machining condition setting method of the above embodiment, prior to the machining condition selection map creation step, it may be determined whether or not the maximum value of compliance of the workpiece at the cutting position, calculated using the frequency analysis result of the cutting force and the frequency analysis result of the vibration, exceeds a predetermined threshold value, and if it is determined that the maximum value of compliance of the workpiece does not exceed the threshold value, the machining condition selection map creation step may be executed. According to the machining condition setting method of this aspect, machining conditions can be set while ensuring the rigidity of the workpiece, thereby effectively suppressing chatter vibrations. (3) In the above-described machining condition setting method, if it is determined that the maximum compliance value of the workpiece exceeds the threshold value, a determination result as to whether or not measures to improve the rigidity of the workpiece can be implemented is obtained, and if the determination result that the measures can be implemented is obtained, the measures are implemented and then the process returns to the measurement step, and if the determination result that the measures cannot be implemented is obtained, the machining condition selection map creation step is executed. According to this embodiment of the machining condition setting method, machining conditions can be set in a state where the lack of rigidity of the workpiece is eliminated as much as possible, thereby effectively suppressing chatter vibrations. (4) In the machining condition setting method of the above embodiment, a second test machining is performed on the workpiece using the cutting tool in accordance with the machining conditions set using the machining condition selection map, a determination result is obtained as to whether forced chatter vibration of the workpiece has occurred during the second test machining, and if a determination result is obtained that forced chatter vibration of the workpiece has occurred during the second test machining, a countermeasure plan for suppressing the occurrence of forced chatter vibration may be implemented. According to the machining condition setting method of this aspect, by implementing a countermeasure plan for suppressing the occurrence of forced chatter vibration prior to the actual machining, it is possible to suppress the occurrence of forced chatter vibration during the actual machining. (5) In the machining condition setting method of the above aspect, a second test machining is performed on the workpiece using the cutting tool in accordance with the machining conditions set using the machining condition selection map, and a determination result is obtained as to whether self-excited chatter vibration of the workpiece has occurred during the second test machining. If a determination result is obtained that self-excited chatter vibration of the workpiece has occurred during the second test machining, a countermeasure plan for suppressing the occurrence of self-excited chatter vibration may be implemented. According to the machining condition setting method of this aspect, by implementing a countermeasure plan for suppressing the occurrence of self-excited chatter vibration prior to the actual machining, it is possible to suppress the occurrence of self-excited chatter vibration during the actual machining. (6) In the machining condition setting method of the above embodiment, the machining condition is the feed rate per tooth of a cutting tool, and in the setting step, the machining condition for the main machining may be set by selecting one of a first condition under which the feed rate per tooth is kept constant and a second condition under which the feed rate per tooth is changed during machining so that the machining time is shorter than that under the first condition. According to this embodiment of the machining condition setting method, it is possible to satisfy a predetermined machining accuracy by selecting the first condition, and to further shorten the machining time by selecting the second condition. The machining conditions to be set may be the feed rate per tooth of the cutting tool TL, the rotational speed of the cutting tool TL, and the depth of cut in the axial direction (Z-axis in FIG. 1) or radial direction (Y-axis in FIG. 1) of the cutting tool TL. (7) According to a second aspect of the present disclosure, there is provided a machine tool that performs cutting on a workpiece using a cutting tool. The machine tool includes a machining condition setting unit that sets machining conditions for the cutting. The machining condition setting unit measures a cutting force applied to the workpiece from the cutting tool and vibrations at multiple measurement points on the workpiece while performing a first trial machining on the workpiece using the cutting tool, estimates vibration of the workpiece at a cutting position using the vibration measurement results at the multiple measurement points during the first trial machining, performs frequency analysis on the measurement results of the cutting force during the first trial machining and the estimated vibration results, creates a machining condition selection map that represents the relationship between cutting positions on the workpiece, machining conditions, and predicted values ​​of vibration amplitude when performing a main machining on the workpiece using the cutting tool, and sets the machining conditions for the main machining using the machining condition selection map so that the vibration amplitude is equal to or less than a predetermined value. According to this type of machine tool, the machining condition setting unit sets the machining conditions using a machining condition selection map that shows the relationship between the cutting position, machining conditions, and predicted vibration amplitude values. This allows the operator to set practical machining conditions suitable for suppressing chatter vibration without trial and error. Therefore, even when it is difficult to install a jig or change the jig design, chatter vibration can be suppressed by adjusting the machining conditions. The present disclosure can be realized in various forms other than a machining condition setting method and a machine tool, such as a machining condition setting device, a machining condition selection map creation method, a machining condition selection map creation device, etc. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing a schematic configuration of a machine tool. [Figure 2] FIG. 10 is a side view showing an example of the layout of the support members. [Figure 3] FIG. 10 is a rear view showing an example of the layout of the support members. [Figure 4] 10 is a first flowchart showing the contents of a processing condition setting process. [Figure 5] 10 is a second flowchart showing the contents of the processing condition setting process. [Figure 6] FIG. 10 is an explanatory diagram showing an example of a compliance map. [Figure 7] FIG. 4 is an explanatory diagram showing an example of a processing condition selection map. [Figure 8] FIG. 10 is an explanatory diagram showing the surface roughness of the processed surface after main processing. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. First embodiment: FIG. 1 is a perspective view showing a schematic configuration of a machine tool 11 in a first embodiment. In this embodiment, the machine tool 11 is configured as a vertical machining center. The machine tool 11 has three coordinate axes, X, Y, and Z, which are perpendicular to each other. In this embodiment, the X axis is a coordinate axis along the left-right direction of the machine tool 11, the Y axis is a coordinate axis along the front-rear direction of the machine tool 11, and the Z axis is a coordinate axis along the up-down direction of the machine tool 11.

[0009] The machine tool 11 includes a bed 20, a saddle 30, a table 40, a column 50, a spindle device 60, a cutting force sensor 70, three vibration sensors 80A to 80C, and a control device 100.

[0010] The saddle 30 is supported by the bed 20. The saddle 30 moves along the Y-axis while being guided by the bed 20. The table 40 is supported by the saddle 30. The table 40 moves along the X-axis while being guided by the saddle 30. A workpiece WK is fixed to the table 40. In this embodiment, the lower end of the workpiece WK is clamped by a clamp 45 fixed to the table 40, thereby fixing the workpiece WK to the table 40. The column 50 is fixed to the bed 20. The spindle unit 60 is supported by the column 50. The spindle unit 60 moves along the Z-axis while being guided by the column 50.

[0011] The spindle device 60 includes a spindle 65, a spindle motor 67, and a rotation angle sensor 69. A cutting tool TL for cutting a workpiece WK is attached to the spindle 65. The spindle motor 67 rotates the spindle 65 and the cutting tool TL about a rotation axis parallel to the Z axis. The spindle motor 67 may be, for example, a servo motor. The cutting tool TL has a generally cylindrical shape centered on a central axis and has at least one cutting edge on its side surface. In this embodiment, the cutting tool TL is an end mill having two cutting edges equally spaced circumferentially around the central axis. Note that in other embodiments, the number of cutting edges on the cutting tool TL may be one or three or more. The cutting tool TL may be a milling tool other than an end mill, such as a flat milling cutter. The rotation angle sensor 69 detects the rotation angle of the spindle 65, in other words, the rotation angle of the cutting tool TL. Information relating to the rotation angle detected by the rotation angle sensor 69 is transmitted to the control device 100. The rotation angle sensor 69 may be, for example, a rotary encoder.

[0012] The cutting force sensor 70 is provided on the spindle 65. The cutting force sensor 70 detects the cutting force applied to the workpiece WK from the cutting tool TL. Information related to the cutting force detected by the cutting force sensor 70 is transmitted to the control device 100. The cutting force sensor 70 may be, for example, a cutting dynamometer.

[0013] Three vibration sensors 80A to 80C are installed on the workpiece WK. Each of the vibration sensors 80A to 80C detects a physical quantity representing the vibration state of the workpiece WK. Information related to the physical quantity representing the vibration state detected by each of the vibration sensors 80A to 80C is transmitted to the control device 100. The physical quantities representing the vibration state include acceleration, velocity, and displacement. In this embodiment, each of the vibration sensors 80A to 80C is an acceleration sensor that detects the acceleration of the workpiece WK. In the following description, the points on the workpiece WK where the vibration sensors 80A to 80C are installed may be referred to as measurement points MP1 to MP3. Note that the number of vibration sensors 80A to 80C may be the minimum number required to estimate the vibration of the workpiece WK at the cutting position during cutting. In other embodiments, each of the vibration sensors 80A to 80C may be a displacement sensor that detects the displacement of the workpiece WK or a velocity sensor that detects the velocity of the workpiece WK instead of an acceleration sensor. In addition, in this embodiment, contact type vibration sensors are used as the vibration sensors 80A to 80C, but in other embodiments, non-contact type vibration sensors may be used.

[0014] The control device 100 is configured as a computer including a CPU 101, a memory 102, an input / output interface 103, and an internal bus 104. The CPU 101 executes a computer program stored in the memory 102 to function as an NC control unit 110 and a machining condition setting unit 120.

[0015] The NC control unit 110 controls each motor of the machine tool 11, such as the spindle motor 67, in accordance with predetermined machining conditions, thereby bringing the rotating cutting tool TL into contact with the workpiece WK and performing cutting on the workpiece WK. In the following description, cutting to manufacture a product is referred to as main machining, and cutting performed prior to main machining is referred to as trial machining.

[0016] The machining condition setting unit 120 sets machining conditions for cutting. The machining conditions include the rotation speed of the cutting tool TL, the feed rate per blade of the cutting tool TL, and the radial and axial cutting depths of the cutting tool TL into the workpiece WK. The machining condition setting unit 120 sets the machining conditions used in this machining by executing a machining condition setting process described later.

[0017] An input device 105 and a display device 106 are connected to the control device 100. The input device 105 is configured with, for example, a plurality of operation buttons. The display device 106 is configured with, for example, a liquid crystal display. The input device 105 and the display device 106 may be integrated as a touch panel.

[0018] FIG. 2 is a side view showing an example of the layout of the support members 48. FIG. 3 is a rear view showing an example of the layout of the support members 48. As shown in FIG. 2, in addition to the clamps 45 for fixing the workpiece WK to the table 40, support members 48 may be used to suppress chatter vibration of the workpiece WK during cutting. In this embodiment, the support members 48 are formed in a rod shape with a circular cross section. One end of the support member 48 contacts a portion of the workpiece WK other than the portion clamped by the clamps 45, and the other end of the support member 48 is fixed to the table 40 via a fixing member 49. As shown in FIG. 3, the workpiece WK is supported by, for example, one support member 48. The surface of the workpiece WK opposite to the surface supported by the support member 48 is cut by a cutting tool TL. Vibration sensors 80A to 80C are installed on the surface of the workpiece WK supported by the support member 48. In other embodiments, the support member 48 may be formed in a plate, block, or spherical shape instead of a rod shape. The number of support members 48 is not limited to one, and may be two or more. If the rigidity of the workpiece WK is sufficiently high, the support member 48 may not be provided.

[0019] 4 and 5 are flowcharts showing the contents of the machining condition setting process. FIG. 6 is an explanatory diagram showing an example of a compliance map created in the machining condition setting process. FIG. 7 is an explanatory diagram showing an example of a machining condition selection map created in the machining condition setting process. The machining condition setting process shown in FIGS. 4 and 5 is executed by the machining condition setting unit 120 to set the machining conditions for the actual machining. The machining condition setting process is started, for example, by pressing a start button provided on the input device 105 prior to the actual machining. The method executed in the machining condition setting process may be called the machining condition setting method.

[0020] First, in step S110 of FIG. 4, the machining condition setting unit 120 causes the NC control unit 110 to perform trial machining, measures the cutting force applied to the workpiece WK from the cutting tool TL at each time during the trial machining using the cutting force sensor 70, and measures the acceleration occurring at each measurement point MP1-MP3 on the workpiece WK at each time during the trial machining using the vibration sensors 80A-80C. In this embodiment, the NC control unit 110 performs trial machining on the workpiece WK from the machining start point SP to the machining end point EP along a machining path that passes behind the measurement points MP1-MP3 where the vibration sensors 80A-80C are installed, as shown in FIG. 3. The trial machining performed in step S110 may be referred to as the first trial machining. Step S110 may be referred to as the measurement process.

[0021] In step S115, the machining condition setting unit 120 estimates the vibration between the machining start point SP and the machining end point EP at each time during trial machining using the acceleration measurement results at each measurement point MP1 to MP3. In this embodiment, the machining condition setting unit 120 estimates the acceleration between the machining start point SP and the measurement point MP1 closest to the machining start point SP by linear extrapolation using the acceleration of the measurement point MP1 closest to the machining start point SP and the acceleration of the measurement point MP2 second closest to the machining start point. The machining condition setting unit 120 estimates the acceleration between adjacent measurement points by linear interpolation using the accelerations of two adjacent measurement points. The machining condition setting unit 120 estimates the acceleration between the machining end point EP and the measurement point MP3 closest to the machining end point EP by linear extrapolation using the acceleration of the measurement point MP3 closest to the machining end point EP and the acceleration of the measurement point MP2 second closest to the machining end point EP. In other embodiments, the machining condition setting unit 120 may estimate the vibration between the machining start point SP and the machining end point EP by, for example, the Lagrangian method or the spline method, instead of linear interpolation or linear extrapolation. Step S115 may also be referred to as a vibration estimation step.

[0022] In step S120, the machining condition setting unit 120 performs frequency analysis on the cutting force measurement results and the acceleration estimation results. In this embodiment, the machining condition setting unit 120 extracts the results for one cutting edge from each of the cutting force measurement results and acceleration estimation results, and then converts each result for one cutting edge expressed in the time domain into each result for one cutting edge expressed in the frequency domain by performing a fast Fourier transform on the result for one cutting edge expressed in the time domain. The result for one cutting edge refers to the measurement or estimation result of the period from when the cutting tool TL blade cuts into the workpiece WK to when the cutting tool TL blade next cuts into the workpiece WK. The time from when the cutting tool TL blade comes into contact with the workpiece WK to when the cutting tool TL blade next comes into contact with the workpiece WK is sometimes referred to as the cutting edge passage period. When a cutting tool TL with multiple equally spaced blades is used, the cutting edge passage period can be calculated, for example, by dividing the rotation period of the cutting tool TL measured using the rotation angle sensor 69 by the number of blades on the cutting tool TL. Prior to the fast Fourier transform, the machining condition setting unit 120 may add a predetermined number of zero data to the end of each result for one tooth so that the number of data for each result for one tooth is a power of two, and then perform the fast Fourier transform. Zero data is data that indicates that the cutting force value or acceleration value is zero. By adding zero data to each result for one tooth, the frequency resolution of each result after the fast Fourier transform can be improved. Note that step S120 is sometimes referred to as the frequency analysis process.

[0023] In step S125, the machining condition setting unit 120 uses the results of the frequency analysis of the cutting force and the results of the frequency analysis of the displacement to create a compliance map that represents the distribution of the relationship between the frequency at the cutting position on the workpiece WK and the level of compliance of the workpiece WK. FIG. 6 shows an example of a compliance map. In FIG. 6, the horizontal axis represents the cutting position on the workpiece WK, the vertical axis represents the frequency, and the shade of color represents the level of compliance of the workpiece WK. In FIG. 6, the lighter the color, the higher the compliance. Since compliance is the reciprocal of stiffness, the higher the compliance, the lower the stiffness. The machining condition setting unit 120 calculates the compliance at each cutting position and each frequency and aggregates the compliance calculation results to create the compliance map. In this embodiment, the machining condition setting unit 120 calculates the acceleration as (2π × frequency) 2 The displacement is calculated by dividing by the cutting force, and the compliance is calculated by dividing the displacement by the cutting force. Note that step S125 may be referred to as a compliance map creation step.

[0024] In step S130, the processing condition setting unit 120 determines whether the maximum value of compliance in the compliance map exceeds a predetermined threshold value. In this embodiment, the predetermined threshold value is 1.0×10 -6 m / N.

[0025] If it is determined in step S130 that the maximum compliance value in the compliance map exceeds the predetermined threshold, the machining condition setting unit 120 acquires in step S140 a determination result as to whether or not it is possible to implement a workpiece rigidity improvement measure to improve the rigidity of the workpiece WK. In this embodiment, the machining condition setting unit 120 causes the display device 106 to display a determination request as to whether or not it is possible to implement a workpiece rigidity improvement measure, thereby prompting the operator to input the determination result as to whether or not it is possible to implement the workpiece rigidity improvement measure. In this embodiment, the workpiece rigidity improvement measure may include installing a support member 48 that supports a portion of the workpiece WK where rigidity is insufficient or the periphery of the portion where rigidity is insufficient. The operator inputs the determination result into the input device 105, and the machining condition setting unit 120 acquires the determination result input to the input device 105.

[0026] If a determination result is obtained in step S140 that measures to improve the rigidity of the workpiece can be taken, the machining condition setting unit 120 causes the compliance map to be displayed on the display device 106 in step S145. The operator refers to the compliance map displayed on the display device 106 and takes measures to improve the rigidity of the workpiece, and after the measures to improve the rigidity of the workpiece are completed, the machining condition setting unit 120 starts the machining condition setting process again from step S110.

[0027] If it is determined in step S130 that the maximum value of compliance in the compliance map does not exceed the predetermined threshold, the machining condition setting unit 120 proceeds to step S150 in Fig. 5. Even if it is determined in step S140 that measures to improve the rigidity of the workpiece are not possible, the machining condition setting unit 120 also proceeds to step S150. In other words, if the desired rigidity of the workpiece WK can be ensured or if the rigidity has been increased as much as possible, the machining condition setting unit 120 proceeds to step S150.

[0028] In step S150, the machining condition setting unit 120 creates a machining condition selection map that represents the relationship between each cutting position on the workpiece WK and the magnitude of the predicted value of the vibration amplitude of the workpiece WK, and displays the map on the display device 106. The machining condition selection map is used to select machining conditions such as the rotational speed of the cutting tool TL, the feed rate per tooth of the cutting tool TL, and the cutting depth of the cutting tool TL into the workpiece WK according to the operator's objectives, such as improving machining efficiency and machining accuracy. FIG. 7 shows an example of the machining condition selection map. In FIG. 7, the horizontal axis represents the cutting position on the workpiece WK, the vertical axis represents the feed rate per tooth, and the shade of color represents the magnitude of the predicted value of the vibration amplitude. In FIG. 7, the darker the color, the larger the predicted value of the vibration amplitude. In this embodiment, in step S150, the machining condition setting unit 120 first identifies modal parameters such as the mass M, the damping coefficient C, and the spring constant K based on the vibration mode at the cutting position. The machining condition setting unit 120, for example, creates a graph showing the relationship between frequency and compliance for each cutting position and identifies the frequency at which the compliance peak exceeds a predetermined threshold. Multiple frequencies may be identified. A transfer function that fits the peak shape for each identified frequency can be derived using curve fitting to identify modal parameters such as the mass M, damping coefficient C, and spring constant K of each vibration mode. Next, the machining condition setting unit 120 calculates a predicted value of vibration amplitude during machining based on the modal parameters for each cutting position and arbitrarily set machining condition parameters. The machining condition setting unit 120 can calculate the predicted value of vibration amplitude during machining, for example, by following the method for determining vibration amplitude during machining as shown in Takaaki Hashimoto, Daisuke Kono, Masataka Furusawa, and Atsushi Matsubara, "Effect of Anisotropy of Dynamic Characteristics of Cutting Systems on Vibration Stability," Journal of the Japan Society for Precision Engineering, Vol. 87, No. 2, 2021, pp. 238-244. The machining condition setting unit 120 then creates a machining condition selection map showing the distribution of predicted vibration amplitude values ​​for each cutting position. FIG. 7 shows an example of a machining condition selection map when it is determined in step S140 that measures to improve the rigidity of the workpiece are not possible.In this embodiment, the machining condition parameters, such as the outer diameter, number of teeth, helix angle, rotational speed, radial and axial depths of cut of the cutting tool TL, component force ratio (ratio of normal resistance to tangential resistance acting on the cutting tool TL), and specific cutting resistance of the workpiece WK, can be set to arbitrary values, and the feed rate per tooth of the cutting tool TL can be determined so that the magnitude of the predicted value of vibration amplitude is equal to or less than a predetermined value. In addition, the machining condition setting unit 120 may determine other machining conditions, such as the radial or axial depth of cut of the cutting tool TL, so that the magnitude of the predicted value of vibration amplitude is equal to or less than a predetermined value. Note that step S150 may also be referred to as a machining condition selection map creation process.

[0029] In step S155, the machining condition setting unit 120 displays a screen on the display device 106 for selecting either a first condition F1, which prioritizes high machining accuracy over short machining time, or a second condition F2, which prioritizes short machining time over high machining accuracy, and allows the operator to select one of the first condition F1 and the second condition F2. The machining condition setting unit 120 generates the first condition and the second condition using a machining condition selection map. In the first condition F1, the feed rate per tooth is kept constant so that the predicted value of the vibration amplitude is equal to or less than a predetermined value at all cutting positions from the machining start point SP to the machining end point EP. In the second condition F2, the feed rate per tooth is changed between the machining start point SP and the machining end point EP so that the predicted value of the vibration amplitude is equal to or less than a predetermined value at all cutting positions from the machining start point SP to the machining end point EP and the machining time is shorter than that under the first condition. Note that step S155 is sometimes referred to as the setting process.

[0030] In step S160, the machining condition setting unit 120 causes the NC control unit 110 to execute the second trial machining using the machining conditions selected in step S155.

[0031] In step S170, the machining condition setting unit 120 acquires the determination result as to whether forced chatter vibration has occurred in the workpiece WK during the second test machining. In this embodiment, the machining condition setting unit 120 causes the display device 106 to display a determination request as to whether forced chatter vibration has occurred in the workpiece WK during the second test machining, thereby prompting the operator to input the determination result as to whether forced chatter vibration has occurred in the workpiece WK during the second test machining. The operator inputs the determination result as to whether forced chatter vibration has occurred into the input device 105, and the machining condition setting unit 120 acquires the determination result as to whether forced chatter vibration has occurred that has been input into the input device 105.

[0032] If a determination result indicating that forced chatter vibration has occurred in the workpiece WK during the second test machining is acquired in step S170, the machining condition setting unit 120 waits in step S175 until the forced chatter vibration countermeasures are completed while displaying a forced chatter vibration countermeasure plan KT pre-stored in the memory 102 on the display device 106. The forced chatter vibration countermeasure plan KT includes, for example, a plan to reduce the feed rate per tooth or a plan to reduce the depth of cut in at least one of the radial and axial directions. The operator refers to the forced chatter vibration countermeasure plan KT displayed on the display device 106 and executes the forced chatter vibration countermeasures. After the forced chatter vibration countermeasures are completed, the operator inputs into the input device 105 that the forced chatter vibration countermeasures have been completed. When the input device 105 receives information indicating that the forced chatter vibration countermeasures have been completed, the machining condition setting unit 120 restarts the machining condition setting process from step S150. If a determination result is acquired in step S170 that forced chatter vibration did not occur during the second test machining, the machining condition setting unit 120 advances the process to step S180.

[0033] In step S180, the machining condition setting unit 120 acquires the determination result as to whether or not self-excited chatter vibration has occurred in the workpiece WK during the second test machining. In this embodiment, the machining condition setting unit 120 causes the display device 106 to display a determination request as to whether or not self-excited chatter vibration has occurred in the workpiece WK during the second test machining, thereby prompting the operator to input the determination result as to whether or not self-excited chatter vibration has occurred in the workpiece WK during the second test machining. The operator inputs the determination result as to whether or not self-excited chatter vibration has occurred into the input device 105, and the machining condition setting unit 120 acquires the determination result as to whether or not self-excited chatter vibration has occurred, which has been input to the input device 105.

[0034] If a determination result is acquired in step S180 that self-excited chatter vibration has occurred in the workpiece WK during the second test machining, the machining condition setting unit 120 waits in step S185 until the self-excited chatter vibration countermeasures are completed while displaying a self-excited chatter vibration countermeasure plan JT pre-stored in the memory 102 on the display device 106. The self-excited chatter vibration countermeasure plan JT includes, for example, a plan to change the spindle rotation speed or a plan to reduce the depth of cut in at least one of the radial and axial directions. The operator refers to the self-excited chatter vibration countermeasure plan JT displayed on the display device 106 and implements the self-excited chatter vibration countermeasures. After the self-excited chatter vibration countermeasures are completed, the operator inputs into the input device 105 information that the self-excited chatter vibration countermeasures have been completed. When the input device 105 receives information that the self-excited chatter vibration countermeasures have been completed, the machining condition setting unit 120 restarts the machining condition setting process from step S150. Note that implementing measures to suppress the occurrence of either forced chatter vibration or self-excited chatter vibration may result in the occurrence of the other type of chatter vibration. In this embodiment, if measures to suppress forced chatter vibration are implemented in step S175, the machining condition setting process is repeated from step S150, making it possible to confirm that both forced chatter vibration and self-excited chatter vibration are not occurring. Also, if measures to suppress self-excited chatter vibration are implemented in step S185, the machining condition setting process is repeated from step S150, making it possible to confirm that both forced chatter vibration and self-excited chatter vibration are not occurring.

[0035] If a determination result is acquired in step S180 that self-excited chatter vibration did not occur during the second test machining, or if a determination result is acquired that either forced chatter vibration or self-excited chatter vibration occurred during the second test machining and neither chatter vibration occurred in the second test machining executed again after taking measures against the chatter vibration, the machining condition setting unit 120 ends the machining condition setting process. Thereafter, the main machining is executed according to the machining conditions set in step S155 of the machining condition setting process. Note that the vibration sensors 80A-80C may be detached from the workpiece WK during the main machining.

[0036] FIG. 8 is an explanatory diagram showing the surface roughness of the machined surface after this machining. In FIG. 8, the horizontal axis represents the cutting position, and the vertical axis represents the surface roughness of the machined surface of the workpiece WK. FIG. 8 shows the surface roughness when machined under the first condition F1, which has a small feed rate per tooth, the surface roughness when machined under the second condition F2, which has a variable feed rate per tooth, and the surface roughness when machined under the third condition F3, which has a large feed rate per tooth. The third condition F3 is shown as a comparative example. The feed rate under the third condition F3 is the same as the maximum feed rate under the second condition F2 and is kept constant from the machining start point SP to the machining end point EP. If the surface roughness of the machined surface is equal to or less than the threshold value S shown by the dashed line in FIG. 8, the workpiece WK is determined to be non-defective. If the surface roughness exceeds the threshold value S, the workpiece WK is determined to be defective. When machined under the first condition F1 or the second condition F2, the surface roughness is equal to or less than the threshold value S in all sections. When processed under the third condition F3, there is a section where the surface roughness exceeds the threshold value.

[0037] In the machine tool 11 of the present embodiment described above, the machining condition setting unit 120 sets machining conditions in the machining condition setting process using a machining condition selection map that represents the relationship between the cutting conditions at the cutting position and the predicted value of vibration amplitude. This allows the operator to set practical machining conditions suitable for suppressing chatter vibration without trial and error. Therefore, even if it is difficult to install or change the support member 48, chatter vibration can be suppressed by adjusting the machining conditions.

[0038] In this embodiment, the machining condition setting unit 120 sets, as the machining condition for the actual machining, one of the first condition, under which the feed rate per blade is kept constant, and the second condition, under which the feed rate per blade is changed during machining so that the machining time is shorter than that under the first condition, selected by the operator. Therefore, when the first condition is selected, machining accuracy can be improved, and when the second condition is selected, machining time can be shortened.

[0039] In this embodiment, prior to creating the machining condition selection map, the machining condition setting unit 120 determines whether the maximum compliance value of the workpiece WK, calculated using the results of frequency analysis of the cutting force and the results of frequency analysis of the vibration, exceeds a predetermined threshold. If it determines that the maximum compliance value of the workpiece WK does not exceed the predetermined threshold, the machining condition selection map is created. Therefore, machining conditions can be set while the rigidity of the workpiece WK is ensured. Furthermore, if the machining condition setting unit 120 determines that the maximum compliance value of the workpiece WK exceeds the predetermined threshold, it obtains a determination result as to whether workpiece rigidity improvement measures can be implemented. If the determination result indicates that workpiece rigidity improvement measures can be implemented, the workpiece rigidity improvement measures are implemented, and the process returns to the measurement process. If the determination result indicates that workpiece rigidity improvement measures cannot be implemented, the machining condition selection map is created without changing the current settings. Therefore, machining conditions can be set while resolving the insufficient rigidity of the workpiece WK as much as possible. Therefore, chatter vibration can be effectively suppressed.

[0040] Furthermore, in this embodiment, when it is determined that forced chatter vibration has occurred during the second trial machining, the machining condition setting unit 120 causes the display device 106 to display a forced chatter vibration countermeasure plan KT pre-stored in the memory 102. Therefore, by implementing the forced chatter vibration countermeasure plan KT, forced chatter vibration in the main machining can be suppressed. Furthermore, even an operator with a low level of skill can easily implement forced chatter vibration countermeasures by referring to the forced chatter vibration countermeasure plan KT that has been prepared in advance.

[0041] Furthermore, in this embodiment, when it is determined that self-excited chatter vibration has occurred during the second trial machining, the machining condition setting unit 120 causes the display device 106 to display a self-excited chatter vibration countermeasure plan JT stored in advance in the memory 102. Therefore, by implementing the self-excited chatter vibration countermeasure plan JT, it is possible to suppress self-excited chatter vibration in the main machining. Furthermore, even an operator with a low level of skill can easily implement countermeasures against self-excited chatter vibration by referring to the self-excited chatter vibration countermeasure plan JT prepared in advance.

[0042] B. Other Embodiments: (B1) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 creates a machining condition selection map that represents the relationship between the cutting position on the workpiece WK, the feed rate per tooth, and the predicted value of the vibration amplitude of the workpiece WK. In contrast to this, the machining condition setting unit 120 may create, for example, a machining condition selection map that represents the relationship between the cutting position on the workpiece WK, the rotational speed of the cutting tool TL, and the predicted value of the vibration amplitude of the workpiece WK, or may create a machining condition selection map that represents the relationship between the cutting position on the workpiece WK, the depth of cut in the Z-axis direction, and the predicted value of the vibration amplitude of the workpiece WK, or may create a machining condition selection map that represents the relationship between the cutting position on the workpiece WK, the depth of cut in the radial direction of the cutting tool TL, and the predicted value of the vibration amplitude of the workpiece WK.

[0043] (B2) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 displays on the display device 106 a first condition under which the feed rate per tooth is kept constant and a second condition under which the feed rate per tooth is changed during machining so that the machining time is shorter than under the first condition, has the operator select one of the first condition or the second condition, and sets the one selected by the operator as the machining condition. Alternatively, the machining condition setting unit 120 may set one of the first condition or the second condition as the machining condition without having the operator select either the first condition or the second condition.

[0044] (B3) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 determines whether the maximum value of compliance of the workpiece WK calculated using the results of frequency analysis of the cutting force and the results of frequency analysis of the vibration exceeds a predetermined threshold value before creating the machining condition selection map, and creates the machining condition selection map if it determines that the maximum value of compliance of the workpiece WK does not exceed the predetermined threshold value. In contrast, the machining condition setting unit 120 may create the machining condition selection map without determining whether the maximum value of compliance of the workpiece WK exceeds the predetermined threshold value.

[0045] (B4) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 acquires a determination result as to whether forced chatter vibration occurred during the second test machining, and if the determination result that forced chatter vibration occurred during the second test machining is acquired, causes the display device 106 to display a forced chatter vibration countermeasure plan KT. Furthermore, the machining condition setting unit 120 acquires a determination result as to whether self-excited chatter vibration occurred during the second test machining, and if the determination result that self-excited chatter vibration occurred during the second test machining is acquired, causes the display device 106 to display a self-excited chatter vibration countermeasure plan JT. In contrast, the machining condition setting unit 120 does not need to acquire at least one of the determination results as to whether forced chatter vibration occurred during the second test machining and the determination result as to whether self-excited chatter vibration occurred during the second test machining. Furthermore, the forced chatter vibration countermeasure plan KT and the self-excited chatter vibration countermeasure plan JT do not need to be prepared in advance. In this case, when the machining condition setting unit 120 obtains a determination result that forced chatter vibration or self-excited chatter vibration has occurred in the second trial machining, it causes the determination result to be displayed on the display device 106, and the worker may take measures to counter the forced chatter vibration or the self-excited chatter vibration based on, for example, his or her own know-how.

[0046] (B5) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 may determine whether or not it is possible to implement measures to improve the rigidity of the workpiece. For example, the machine tool 11 may be provided with a camera that captures images of the workpiece WK and the table 40, and the machining condition setting unit 120 may determine whether or not it is possible to implement measures to improve the rigidity of the workpiece by analyzing images acquired by the camera. In this case, the determination of whether or not it is possible to implement measures to improve the rigidity of the workpiece can be automated, thereby reducing the burden on the operator.

[0047] (B6) In the machine tool 11 of the above-described embodiment, the machining condition setting unit 120 may determine whether forced chatter vibration or self-excited chatter vibration has occurred during the second test machining. For example, the machine tool 11 may be provided with a camera that captures an image of the machined surface or a probe that measures the surface roughness of the machined surface, and the machining condition setting unit 120 may analyze an image acquired using the camera or determine whether forced chatter vibration or self-excited chatter vibration has occurred during the second test machining based on the results of measuring the surface roughness using the probe.

[0048] (B7) In the above-described embodiment, the machine tool 11 is a vertical machining center. However, the machine tool 11 does not have to be a vertical machining center. The machine tool 11 may be, for example, a horizontal machining center or an NC milling machine.

[0049] (B8) In the above-described embodiment, the machining condition setting unit 120 is provided in the control device 100 of the machine tool 11. In contrast, the machining condition setting unit 120 may be provided on a computer connected to the control device 100 by wired or wireless communication, for example. In this case, the computer provided with the machining condition setting unit 120 may be referred to as a machining condition setting device.

[0050] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0051] 11...machine tool, 20...bed, 30...saddle, 40...table, 45...clamp, 48...support member, 49...fixing member, 50...column, 60...spindle device, 65...spindle, 67...spindle motor, 69...rotation angle sensor, 70...cutting force sensor, 80A to 80C...vibration sensor, 100...control device, 101...CPU, 102...memory, 103...input / output interface, 104...internal bus, 105...input device, 106...display device, 110...NC control unit, 120...machining condition setting unit, EP...machining end point, MP1 to MP3...measurement point, SP...machining start point, TL...cutting tool, WK...workpiece

Claims

1. A machining condition setting method for setting machining conditions for cutting, comprising: a measuring step of measuring a cutting force applied to the workpiece by the cutting tool and vibrations at a plurality of measurement points on the workpiece while performing a first trial machining on the workpiece with the cutting tool; a vibration estimation step of estimating vibration of the workpiece at a cutting position using measurement results of vibration during the first test machining at the plurality of measurement points; a frequency analysis step of performing frequency analysis on the measurement result of the cutting force during the first trial machining and the estimation result of the vibration; a machining condition selection map creation step of creating a machining condition selection map using the results of the frequency analysis of the cutting force and the frequency analysis of the vibration, the machining condition map representing the relationship between the cutting position on the workpiece, the machining conditions, and the predicted value of the vibration amplitude when the workpiece is subjected to main machining by the cutting tool; a setting step of setting the machining conditions during the main machining using the machining condition selection map so that the vibration amplitude is equal to or less than a predetermined value; and The machining condition is a feed rate per cutting edge of a cutting tool, A machining condition setting method in which, in the setting process, the machining conditions for the main machining are set by selecting one of a first condition in which the feed amount per blade is kept constant and a second condition in which the feed amount per blade is changed during machining so that the machining time is shorter than under the first condition.

2. 2. The machining condition setting method according to claim 1, a machining condition setting method, prior to the machining condition selection map creation step, determining whether or not a maximum value of compliance of the workpiece at the cutting position, calculated using the frequency analysis result of the cutting force and the frequency analysis result of the vibration, exceeds a predetermined threshold value, and executing the machining condition selection map creation step when it is determined that the maximum value of compliance of the workpiece does not exceed the threshold value.

3. 3. The machining condition setting method according to claim 2, When it is determined that the maximum value of compliance of the workpiece exceeds the threshold value, a determination result is obtained as to whether or not measures to improve the rigidity of the workpiece can be implemented; and If a determination result is obtained that the countermeasure can be implemented, the countermeasure is implemented, and then the process returns to the measurement step. When a determination result indicating that the countermeasure cannot be implemented is obtained, the machining condition selection map creating step is executed.

4. 2. The machining condition setting method according to claim 1, performing second trial machining on the workpiece using the cutting tool in accordance with the machining conditions set using the machining condition selection map; Obtaining a determination result as to whether forced chatter vibration of the workpiece occurred during the second test machining; A machining condition setting method, wherein when a determination result is obtained that forced chatter vibration of the workpiece has occurred during the second test machining, a countermeasure plan for suppressing the occurrence of forced chatter vibration is implemented.

5. 2. The machining condition setting method according to claim 1, performing second trial machining on the workpiece using the cutting tool in accordance with the machining conditions set using the machining condition selection map; Obtaining a determination result as to whether or not self-excited chatter vibration of the workpiece occurs during the second test machining; A machining condition setting method, wherein if a determination result is obtained that self-excited chatter vibration of the workpiece has occurred during the second test machining, a countermeasure plan is implemented to suppress the occurrence of self-excited chatter vibration.

6. A machine tool that performs cutting processing on a workpiece using a cutting tool, a machining condition setting unit for setting machining conditions for the cutting process, The processing condition setting unit measuring a cutting force applied to the workpiece from the cutting tool and vibrations at a plurality of measurement points on the workpiece while performing a first trial machining on the workpiece with the cutting tool; Using the vibration measurement results of the first trial machining at the plurality of measurement points, vibration of the workpiece at a cutting position is estimated; performing a frequency analysis on the measurement result of the cutting force and the estimation result of the vibration during the first trial machining; using the results of the frequency analysis of the cutting force and the results of the frequency analysis of the vibration, creating a machining condition selection map that shows the relationship between cutting positions on the workpiece, machining conditions, and predicted values ​​of vibration amplitude when performing actual machining on the workpiece with a cutting tool; Using the processing condition selection map, the processing conditions during the main processing are set so that the vibration amplitude is equal to or less than a predetermined value; The machining condition is a feed rate per cutting edge of a cutting tool, the machining condition setting unit sets one of a first condition under which the feed amount per tooth is kept constant and a second condition under which the feed amount per tooth is changed during machining so that the machining time is shorter than that under the first condition as the machining condition for the main machining. Machine tools.

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