JP2014140918A - Cutting vibration inhibition method, arithmetic control device, and machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit chatter vibrations in cutting equipment.SOLUTION: In a method for correcting a processing state when the presence of chatter vibrations is determined by judging vibrations, which are generated during cutting, by using a chatter index, a cutting frequency and its high-order frequency, and a chatter frequency and its high-order frequency are computed from a processing frequency; such a number of revolution of a rotating shaft as to decrease a phase difference between the cutting frequency and the chatter frequency is computed; and a cutting condition is changed on the basis of the result of computation.

Description

  The present invention relates to a method for suppressing vibration generated in cutting, an arithmetic control device having the function, and a machine tool.

  As a background art of the present invention, there is JP-A-2008-290186 (Patent Document 1). In this public relations, abnormal vibration that occurs during cutting, so-called chatter vibration, is detected by a sensor that detects vibration, and rotation that can suppress chatter vibration when vibration in the chatter frequency range exceeds a predetermined threshold value. An arithmetic means for calculating the optimum rotational speed of the shaft is disclosed. In this means, first, a vibration sensor is attached to the rotary shaft housing, and the vibration acceleration obtained from the sensor is subjected to Fourier analysis with an FFT (Fast Fourier Transform) computing device to obtain the maximum acceleration and its frequency (chatter frequency). A method is disclosed in which chatter vibration is generated when the maximum acceleration exceeds a predetermined threshold value set in advance, and the chatter vibration is suppressed by controlling the number of rotations of the rotation shaft.

  Japanese Patent Laying-Open No. 2012-206230 (Patent Document 2) discloses means for detecting chatter vibration by a combination of a current value of a rotary shaft motor and a frequency filter. In this means, first, torque is converted from the current of the motor that drives the rotary shaft based on known torque conversion information. The angular velocity of the rotating shaft is obtained from the encoder provided on the rotating shaft, and a low-pass filter that cuts off the frequency in the rotating speed region is applied to the torque waveform. By making the cutoff frequency of the low-pass filter high, chatter vibration is detected from the torque waveform that has passed through the filter, and chatter vibration can be detected in a shorter time than Fourier analysis using an FFT device that requires data for computation. The technology which is is disclosed.

  In Japanese Patent Laid-Open No. 2012-56051 (Patent Document 3), a displacement sensor is attached to a rotating shaft, and the presence or absence of chatter vibration is identified in a manner of increasing or decreasing the autocorrelation coefficient of a signal obtained from the displacement sensor, and chatter is detected. Means for suppressing vibration are disclosed. If the maximum value of the autocorrelation coefficient waveform over time deviates from the period in which the cutting edge contacts the work material, chatter vibration has occurred. The occurrence can be detected. In addition, the technology that can suppress chatter vibration by increasing or decreasing the rotation speed of the rotary shaft so as to correct the maximum value of the autocorrelation coefficient waveform over time and the deviation of the period in which the cutting edge contacts the work material Is disclosed.

JP 2008-290186 A JP 2012-206230 A JP 2012-56051 A

  In the technique disclosed in Patent Document 1, chatter vibration is evaluated by the amplitude of the waveform at the chatter frequency (spectrum size) by Fourier transform, and is determined to be chatter vibration when the spectrum exceeds a predetermined threshold. This threshold varies depending on the tool used and the machining conditions. Therefore, since a threshold value in accordance with the machining tool and its machining conditions must be obtained in advance through experiments or the like and held as data, there is a first problem that requires enormous time to obtain the threshold value. Further, it shows how to determine the rotational speed of the rotating shaft that suppresses chatter vibration, a phenomenon in which the frequency of chatter vibration is uniquely determined from the spectrum. However, as a result of displaying the spectrum, if the diagram shows a mixture of chatter vibration components and cutting vibration higher-order components, it is not possible to identify which peaks and valleys of the diagram are due to chatter vibration components, and thus suppress chatter vibration. There was a second problem in which the frequency of chatter vibration as a basis could not be specified.

  In the method disclosed in Patent Document 2, chatter vibration is determined from a torque waveform applied with a low-pass filter. In this method, the characteristics of the low-pass filter to be applied need to be changed depending on the tool to be used and the processing conditions, and there is a problem that takes a lot of time to determine the characteristics beforehand through experiments (similar to the first problem) ).

  In the method disclosed in Patent Document 3, chatter vibration is determined from the waveform of the autocorrelation coefficient with time. However, it is not possible to identify chatter vibration with an amplitude that is harmful to the machining result only by the period shift, and evaluation is performed with some threshold value. Has the disadvantages that need to be done. When trying to prepare this threshold value in advance, there was a problem that required a lot of time because it had to be obtained by experiments or the like depending on the tool and machining conditions (similar to the first problem). In addition, when obtaining the rotation speed of the rotating shaft that suppresses chatter vibration from the phase of the time-varying waveform of the autocorrelation coefficient, there was a problem that there was no confirmation that the waveform specifying the phase was due to chatter vibration (No. 1). Same as the second issue). In Patent Documents 1 and 2, a method of suppressing chatter vibration by changing the number of rotations of the rotating shaft is adopted, but the number of rotations of the rotating shaft is a main factor that determines the cutting speed of the tool. The cutting speed of the tool is a factor governing tool wear, and when a high cutting speed is selected in order to suppress chatter vibration, there is a third problem in which the cutting tool exhibits abnormal wear.

  In summary, there were the following problems.

(1) A problem that takes a long time to determine a threshold value for identifying chatter vibration.
(2) A problem of a phenomenon in which it is difficult to specify a frequency that is a basis for suppressing chatter vibration.
(3) The problem that the cutting tool wears abnormally when an excessively high rotational speed is selected.

  In view of the above, an object of the present invention is to solve at least one or all of the above-described problems (1) to (3) in detecting the occurrence of chatter vibration and obtaining a machining condition for suppressing chatter vibration. That is, it is to provide a technique capable of realizing the following points.

(1) Reduce the cost by shortening the determination of the threshold value for identifying chatter vibration.
(2) Ensure that the basis for suppressing chatter vibration is specified.
(3) Increase the options for chatter vibration suppression to prevent abnormal wear of the tool.

  In order to achieve the above object, in order to cope with the problem of chatter vibration generated in the above-described cutting process, the representative embodiment of the present invention specifies chatter vibration occurrence, obtains its frequency, and makes the tool abnormal. This is a method of suppressing cutting vibration by a method that does not occur, and is characterized by using the following method.

  (1) A process for obtaining vibration generated by machining with a sensor and calculating a cutting frequency and a chatter frequency and the magnitude of both from the vibration data, and (2) quantitatively determining whether or not chatter vibration has occurred from the calculation result. The chatter index to be determined is calculated, and in the state where chatter vibration is occurring, a process of calculating the rotational shaft rotational speed to reduce the phase difference between the cutting frequency and the chatter frequency, and (3) cutting at this rotational speed. A process for suppressing chatter vibration by changing the machining conditions, and (4) determining whether the rotational speed of the rotating shaft after the change corresponds to a cutting speed region that causes an abnormality in the tool. When it is determined that the rotational speed is not appropriate, a process of reducing the cutting depth of the tool until chatter vibration is suppressed is performed.

  More simply, in the present invention, as a result of determining vibration generated during cutting using the chatter index, the machining state determined to have chatter vibration is determined based on the rotational speed of the rotating shaft and the amount of tool cutting (path). By correcting the above, it becomes possible to provide a method, an arithmetic control device, a machine tool, etc. for suppressing cutting vibration.

  In addition, as a result of judging vibration generated during cutting using the chatter index, it is a method for correcting a machining state that is judged to have chatter vibration, which is based on the machining frequency, its cutting frequency, its higher order frequency and chatter frequency. And a high-order frequency thereof, a rotation shaft rotational speed that reduces a phase difference between the cutting frequency and the chatter frequency is calculated, and cutting conditions are changed based on the calculation result. This is a vibration suppression method.

  According to the typical embodiment of the present invention, at least one or all of the following effects corresponding to the above-described conventional problems (1) to (3) are provided.

(1) Reduce the cost by shortening the determination of the threshold value for identifying chatter vibration.
(2) Ensure that the basis for suppressing chatter vibration is specified.
(3) Increase the options for chatter vibration suppression to prevent abnormal wear of the tool.

It is a figure showing the whole machine tool outline composition of the present invention. It is a figure which shows the hardware constitutions of the arithmetic and control apparatus for controlling a machine tool. It is a figure which shows the hardware constitutions of the arithmetic / control apparatus which simplified the component. It is a figure explaining chatter vibration, and is an example in which a tool is processing a workpiece. It is a figure explaining chatter vibration, and is an example of a cutting force waveform in which chatter vibration does not occur. It is the example of the cutting force waveform which chatter vibration has generate | occur | produced in the figure explaining chatter vibration. It is a figure explaining the calculation method of a chatter index | exponent, and is the example of a diagram which FFT-processed the cutting force waveform in which chatter vibration has not generate | occur | produced. It is a figure explaining the calculation method of a chatter index | exponent, and is the example of a diagram which FFT-processed the cutting force waveform in which chatter vibration has generate | occur | produced. It is an example of the cutting force waveform which chatter vibration has generate | occur | produced. It is explanatory drawing of the calculation method of the rotating shaft rotational speed which shows an example of phase difference (alpha) of a cutting force component and chatter vibration component, and suppress chatter vibration. It is the example of a diagram explaining the unstable area | region where chatter vibration generate | occur | produces, and the stable area | region which chatter vibration does not generate | occur | produce. It is explanatory drawing which shows the example of a tool movement direction which reduces the amount of cuts in order to suppress chatter vibration in the example of a processing form. It is a figure which shows the flow of the chatter vibration determination and chatter vibration suppression processing in the arithmetic and control unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an outline of the configuration of the entire main part of a machine tool to which the present invention is applied. In FIG. 1, 1 is the whole machine tool, 2 is a tool rotation spindle, 3 is an NC (Numerical Control) device, 4 is a table, 5 is a communication I / F (Inter Face), 6 is an arithmetic / control device, T Is a cutting tool and W is a workpiece.

  The machine tool 1 performs cutting of the workpiece W by controlling the relative position with the workpiece W mounted on the table 4 by the NC device 3 while the tool rotation spindle 2 rotates the tool T. FIG. 1 shows an example of a machine tool of orthogonal three-axis control in which the tool rotation main spindle 2 and the workpiece W move in three directions X, Y, and Z indicated by arrows. It may be a multi-axis control machine tool that performs a turning operation or controls and processes four or more axes on which the table 4 rotates. Moreover, although the machine tool 1 of the form in which the tool T rotates was illustrated in FIG. 1, the machine tool of the form in which the workpiece W rotates may be used.

  The machine tool 1 incorporates a sensor (not shown) that detects vibration during cutting. As the sensor type, a sensor capable of converting vibration into a signal such as a force sensor, an acceleration sensor, a displacement sensor, and a sound sensor is incorporated. As a basic configuration, vibration information can be obtained by incorporating any one type of sensor, but two or more types of sensors may be incorporated in order to improve the reliability of the determination. A typical example of the position where the sensor is incorporated is the table 4 or the tool rotation spindle 2. The sound sensor can be installed outside the machine tool 1 to collect sound during processing. With respect to the detection direction of the sensor, in order to detect vibrations in all directions of the cutting tool T, the X, Y, and Z directions can be detected except for the sound sensor. In a machine tool having a configuration in which the moving direction of the cutting tool T is limited, the number of sensors may be reduced.

  With the configuration as described above, vibration generated when the cutting tool T cuts the workpiece W is detected by a sensor, and a signal is sent to the calculation / control device 6 via the communication I / F 5. In the arithmetic / control device 6, when a signal related to the vibration that has been sent is processed and a determination result that requires a change related to the machining condition is obtained, a control command for changing the machining condition of the machine tool is sent via the communication I / F5. And sent to the NC device 3. In response to this control command, the NC device 3 changes the machining conditions scheduled for the machine tool 1 and performs subsequent machining.

  Although FIG. 1 shows an example in which the communication I / F 5 and the calculation / control device 6 are arranged outside the machine tool 1, the communication I / F 5 and the calculation / control device 6 are the NC device 3 of the machine tool 1. May be incorporated in the entire control device (not shown).

  An outline of the configuration of the calculation / control apparatus 6 will be described with reference to FIG.

  2, 601 is a CPU (Central Processing Unit), 602 is a ROM (Read Only Memory), 603 is a RAM (Random Access Memory), 604 is a magnetic disk drive, 605 is an optical disk drive, 606 is an optical disk, 607 is a display, 608 is a mouse, 609 is a keyboard, 610 is a printer, 611 is a program, and 612 is data.

  Signals are sent from the external sensor 7 and the communication I / F 5 to the arithmetic / control device 6, and the CPU 601 loads data from the magnetic disk drive 604, the optical disk 606, and the ROM 602 to the RAM 603 and executes program processing. Is realized. Even in a calculation result that requires sending of a control command, creation of a control command to be sent is realized by executing program processing in the same manner as described above. The communication I / F device 5 may be configured to have a function of connecting to a communication network (LAN) 8 and perform processing for data communication with other devices. A mouse 608 and a keyboard 609 are used by a user to input data and instructions. The display 607 and the printer 610 display / print out various data and user interface information on the screen / paper based on the processing. The user interface information includes, for example, signal data of the sensor 7, processing result information, command input / output, and the like.

  The example of FIG. 2 includes a display 607, a mouse 608, a keyboard 609, and a printer 610, and a program 611 and data necessary for calculation are stored on a magnetic disk. Machine tools used for production often have few opportunities to change programs 611 and data 612 used for computation and control. In such a machine tool, the calculation / control device 6 attached to the outside of the machine tool 1 is obstructed by the operation of the machine tool. In that case, as shown in FIG. 3, it is possible to simplify the arithmetic / control device and store it in the accommodating portion of the control device of the machine tool 1.

  FIG. 3 shows a simplified configuration example of the calculation / control apparatus of FIG. The symbols used are the same as in FIG. A program 611 and data 612 necessary for calculation and control are stored in a ROM and used. The display 607, mouse 608, keyboard 609, and printer 610 in FIG. 2 are omitted. A user interface or the like can be substituted by using an input / output device or a display device provided in the NC device 3.

  Here, chatter vibration will be briefly described with reference to FIG.

  FIG. 4A shows an example in which the cutting tool forms a groove in the workpiece, and Table 1 shows an example of the processing conditions. 4 (b) and 4 (c) are examples showing the change over time of the cutting force obtained by the processing of FIG. 4 (a). In FIG. 4, T is a rotary cutting tool and an end mill, W is a workpiece, and an example is carbon steel for machine structure.

In FIG. 4A, the end mill T rotates in the direction of the arrow n and advances in the direction of the arrow f to process a groove having a depth ap in the carbon steel for mechanical structure W1. As shown in Table 1, as an example, the processing conditions are as follows: tool diameter (D) is 40 mm, number of blades (NT) is 2, blade speed (N) is 3120 min ⁻¹ , 1 blade feed (fz) is 0.07 mm / It is a blade.

  FIG. 4B is a result of measuring the time change of the cutting force generated in the direction of arrow Y when the depth ap is 0.4 mm in the processing of FIG. Since the number of blades is 2 and 3120 revolutions per minute, the cutting cycle is 0.0096 seconds (= 60 / (3120 × 2)). The measurement in FIG. 4B is performed at the beginning of machining, and chatter vibration does not occur. Therefore, the measurement waveform G1 is a waveform in which peaks and valleys generated at every cutting cycle are smoothly connected. FIG. 4C shows the result of measuring the time change of the cutting force generated in the direction of the arrow Y after the time has elapsed in the machining of FIG. 4B. In the measurement waveform G2, peaks and valleys with a short cycle are superimposed on peaks and valleys with a cutting cycle.

  In FIG. 4C, chatter vibration is generated, and a waveform having a period extremely shorter than the cutting period is a chatter vibration waveform. In other words, chatter vibration is a vibration generated by a vibration having a period (high frequency) extremely shorter than the cutting period during the cutting process. When the amplitude is large, the surface roughness of the machined surface is increased, or damage to the cutting tool is caused. Therefore, short-period vibration that has reached an amplitude level that is harmful to cutting is called chatter vibration. It is customary. Performing the cutting process without generating the chatter vibration is important in designing the process conditions of the cutting process.

  Next, a chatter index calculation method will be described with reference to FIG.

FIG. 5A shows a result obtained by processing FFT of FIG. 4B, which is a cutting force waveform of machining in which chatter vibration is not generated. In the region of G3, the spectrum has a significant peak at a cutting frequency (104 Hz) corresponding to the cutting cycle, and no significant peak occurs at a frequency higher than the cutting frequency. On the other hand, FIG.5 (b) is the result of having processed FIG.4 (c) which is the cutting force waveform of the process in which chatter vibration has generate | occur | produced by FFT. In the G4 region, there is a waveform in which there is a significant peak at the cutting frequency (104 Hz), and a significant peak is also generated in the G5 region in the higher frequency band. The remarkable peak generated in the region of G5 represents the spectrum of the chatter vibration component. The inventor of the present application has found a phenomenon in which the vibration amplitude of a cutting tool that increases due to chatter vibration is proportional to the ratio of the maximum value of the cutting force component and the maximum value of the chatter vibration component. Therefore, a chatter index CVI (Chatter Vibratin Index) is defined as the following formula 1 as a judgment index of chatter vibration.

CVI = fb / fa (Equation 1)

If a threshold value is set for this CVI, it is possible to determine whether chatter vibration has occurred or not with a constant. Furthermore, since normalization is performed with the cutting force component fa, it is possible to determine whether chatter vibration has occurred with the same threshold even when the cutting condition is changed. Conventionally, it has been necessary to collect and accumulate data for determining the occurrence of chatter vibration according to tools and cutting conditions through extensive experiments. However, this chatter index (CVI) is not necessary, and the determination of the occurrence of chatter vibration can be greatly simplified.

  Next, a first method for suppressing chatter vibration after it is determined that chatter vibration has occurred based on the chatter index (CVI) described above will be described with reference to FIG.

  FIG. 6A is an example in which chatter vibration is generated with a cutting force waveform obtained by the same processing method as in FIG. FIG. 4 (a) shows an example of grooving performed using the full width of the tool, but FIG. 6 (a) shows a so-called shoulder cutting in which the side surface of the workpiece is cut by the radius of the tool. It is the waveform of the cutting force obtained by (1).

FIG. 6B shows the result of performing FFT processing on this cutting force waveform, extracting only the chatter vibration component excluding the cutting force component, and separating it into the cutting force component and the chatter vibration component. The cutting force component shows a result in which a plurality of peaks occur at a frequency that is an integral multiple of the cutting frequency. On the other hand, in the chatter vibration component, there is a maximum peak at 620 Hz, and a peak is generated at 120 Hz. The peak frequency of the cutting force component closest to the frequency indicating the maximum peak of the chatter vibration component is searched, and the difference between the two is α. In the case of this example, the peak of the cutting force component near 620 Hz is 635 Hz. In order to eliminate this frequency difference α (to zero), the number of rotations of the tool per minute is changed according to the following formula 2.

ΔN = α × 60 / NT (Formula 2)

In Equation 2, ΔN is the number of rotations that increases or decreases from the current tool rotation number. The right side α is the frequency difference, and NT is the number of cutting edges of the tool.

In the example of FIG. 6B, the higher order frequency of the cutting force component is 15 Hz higher than the chatter vibration frequency. The number of teeth NT is 2 (two-blade tool). Therefore, from Equation 2, ΔN is 450 (ΔN = 15 × 60/2), and the tool rotational speed may be reduced by 450 min ⁻¹ . Since the difference between the cutting force component of the frequency and the chatter vibration component is eliminated by the reduction of the tool rotation speed, vibration that is not synchronized with the frequency of the cutting force disappears and chatter vibration can be suppressed. Contrary to the above example, when the cutting force component adjacent to the chatter frequency is smaller, ΔN may be obtained according to Equation 2 and increased by the number of rotations. If the frequency of the cutting force component adjacent to the chatter frequency does not appear as a clear peak as a result of the FFT process, the primary frequency of the cutting force component is multiplied by an integer, and the frequency of chatter vibration is the highest. A close frequency may be set as a high-order frequency of the cutting force for obtaining α.

  In the chatter vibration suppressing means described above, the rotational speed of the cutting tool is changed. However, increasing the speed of the tool may result in a choice that the cutting speed falls within the abnormal wear area of the tool. In order to prevent this selection, when α is obtained by the above equation 2, if the tool rotational speed is forcibly decelerated using a frequency that is first order smaller than the higher order frequency of the optimum cutting force component, Becomes extremely low rotation and significantly impedes machining efficiency. As described above, in a situation where it is determined that changing the tool rotation speed to suppress chatter vibration causes a new problem, it is possible to select to suppress chatter vibration by reducing the cutting depth of the tool.

  This selection will be described with reference to FIG.

  FIG. 7A is a stability limit diagram, which is an unstable region in which chatter vibration is generated under a machining condition having a larger cut amount than the curve G6 called a lobe, and chatter vibration is generated under a condition in which the cut is smaller than the curve G6. This is a stable region where no occurrence occurs. A curve G6 is a curve obtained by calculation from the processing conditions shown in Table 1. Chatter vibration occurs in P1 where the cutting amount is 0.4 mm under the processing conditions shown in Table 1, but no chatter vibration occurs in the stable region when the cutting amount is 0.25 mm. Further, there is an unconditional stability limit in which chatter vibration does not occur at any tool rotation speed in a region where the cutting depth is smaller. Thus, chatter vibration can be suppressed by reducing the amount of cut.

  FIG. 7B is a diagram showing a state in which the end mill T is machining the workpiece W, and the symbols used are the same as those in FIG. When processing under the condition of P1 in FIG. 7A while monitoring the chatter index (CVI), occurrence of chatter vibration is detected. Following this detection, the feed of the tool T is controlled in the direction of f1 so as to reduce the cutting amount ap while monitoring the chatter index (CVI). When the chatter index (CVI) stops detecting chatter vibration, the feed direction of the tool T is changed to f2 so that the cutting amount ap becomes steady. If the cut amount ap is reduced, the chatter vibration can be suppressed as shown in FIG.

  In order to obtain the lobe G6 in FIG. 7A, data such as the rigidity of the tool T and the specific cutting resistance of the workpiece W are required, and the lobe G6 changes depending on the wear of the tool. Therefore, it is not realistic to obtain the lobe G6 in real time during processing to obtain a condition for suppressing chatter vibration. However, since it is clear from the form of the lobe G6 that chatter vibration can be suppressed by reducing the cut amount ap, the method of reducing the cut amount ap while monitoring the chatter index (CVI) reliably suppresses chatter vibration. It is an effective means that can be done.

  However, since reducing the cutting amount ap results in a reduction in machining efficiency, it is a means that is adopted when it is determined that the means for suppressing chatter vibration by changing the tool rotation speed will cause a failure. is there. Since the time required for evaluation of the chatter index (CVI) is extremely short (in one example, 0.1 second or less), chatter vibration can be quickly suppressed even when means for reducing the cutting depth ap is adopted.

  In order to change the cutting amount ap, it is necessary to change the program of the NC device that controls the tool path created in advance. Furthermore, in order to process into a predetermined shape after changing the cutting amount ap, it is necessary to recreate the NC program after changing the cutting amount ap and send it to the NC device. This function can be dealt with by providing the program 611 of the calculation / control apparatus 6 shown in FIG. 2 with a tool path calculation function.

A system for realizing the chatter vibration suppression function described above with reference to FIGS. 1 to 7 will be described with reference to the flowchart of FIG. 8 and FIG.
(S1) First, in S1, based on the data 612 of the calculation / control device 6, the tool used by the program 611, the tool trajectory, and the tool machining conditions are set. Here, the data 611 includes information such as the shape of the work material before processing, the shape of the work material (product) after processing, and the shape of the tool 1 used for processing. The program also includes a function for setting a tool to be used, a tool trajectory, and a tool machining condition based on the data 611. The tool to be used, the tool trajectory, and the tool machining conditions may be set manually by using the input function of the calculation / control device 6 or the NC device 3. In S <b> 1, a program for driving the NC device 3 is created and sent to the NC device 3.
(S2) In S2, the frequency being processed is measured. As described with reference to FIG. 1, the measurement means is a sensor that can convert vibrations such as a force sensor, an acceleration sensor, a displacement sensor, and a sound sensor into signals. The vibration during processing is converted into a signal by any one of these sensors or a plurality of sensors and sent to the arithmetic / control device via the communication I / F 5.
(S3) In S3, the program 611 performs frequency conversion on the signal sent in S2. As an example, as described above, the power spectrum is obtained by FFT.
(S4) In S4, the program 611 separates the cutting frequency and the chatter vibration frequency to obtain the magnitude of the cutting vibration and the magnitude of the chatter vibration.
(S5) In S5, the above-described chatter index (CVI) is obtained using FIG. 5 and Equation 1 (S6). It is determined whether chatter vibration is occurring. If it is determined that there is no chatter vibration, steps S2 to S5 are repeatedly executed to continue monitoring the machining state. If it is determined that chatter vibration has occurred, the process proceeds to S7 and S8.
(S7) In S7, the program 611 calculates the cutting frequency. From the primary cutting frequency, a high-order frequency until the chatter vibration frequency is exceeded is calculated. If a clear peak is obtained up to the chatter vibration frequency by FFT processing, the value of the peak is obtained. In the case of a signal in which a clear peak cannot be obtained up to the chatter vibration frequency by FFT processing, the primary cutting frequency is multiplied by an integer and substituted.
(S8) In S8, the program 611 calculates the chatter vibration frequency. In the FFT processing, the peak frequency that appears in the high frequency band is determined from the cutting frequency.
(S9) In S9, the phase difference α described with reference to FIG. 6 is obtained from the result obtained by the program 611 in S7 and S8.
(S10) In S10, the program 611 calculates the increase / decrease rotational speed ΔN of the tool according to Equation 2. This ΔN is added to or subtracted from the tool rotational speed at that time to calculate the corrected tool rotational speed.
(S11) In S11, it is determined whether or not the tool rotation speed obtained in S10 gives the cutting speed causing abnormal wear stored in the data 612 to the tool. If it is evaluated that the corrected tool rotational speed is appropriate, the corrected rotational speed is sent to the NC device 3 via the communication I / F 5 to change the tool rotational speed. If it is evaluated that the corrected tool rotational speed is inappropriate, the process proceeds to S12 without changing the tool rotational speed.
(S12) In S12, the program 611 gives a command to reduce the cutting amount to the NC device 3 via the communication I / F 5. This command is continued until it is determined that there is no chatter vibration in S1 to S5 monitoring the machining state. When chatter vibration is suppressed, the cutting amount reduction command is stopped, the program 611 calculates a subsequent tool path based on the reduced cutting amount, and sends the path program to the NC device 3 via the communication I / F 5.

  In addition, even if it has a structure that does not have the functions of S11 and S12 and sends the corrected tool rotation speed obtained in S10 to the machining condition setting means in S1, it can function to suppress chatter vibration.

DESCRIPTION OF SYMBOLS 1 Machine tool 2 Tool rotating shaft 3 NC apparatus 4 Table 5 Communication interface 6 Arithmetic / control apparatus 601 CPU
602 ROM
603 RAM
604 Magnetic disk drive 605 Optical disk drive 606 Optical disk 607 Display 608 Mouse 609 Keyboard 610 Printer 611 Program 612 Data 7 Sensor 8 LAN
T Cutting tool W Work piece

Claims (5)

  As a result of judging the vibration generated during cutting using the chatter index, it is a method for correcting the machining state that is judged to have chatter vibration, which is based on the machining frequency, its cutting frequency, its higher order frequency, and its chatter frequency. Cutting vibration suppression characterized by calculating a high-order frequency, calculating a rotational shaft rotational speed that reduces a phase difference between the cutting frequency and the chatter frequency, and changing the cutting processing condition based on the calculation result Method.   2. The cutting according to claim 1, wherein whether or not the calculated number of rotations of the rotating shaft is appropriate is determined, and if the determination result is negative, the cutting amount of the tool is reduced until chatter vibration is suppressed. Vibration suppression method.   An arithmetic and control device for cutting conditions, comprising: machining condition setting means; machining vibration and frequency measurement means; means for calculating a chatter index from a signal measured by the machining vibration and frequency measurement means; and the chatter index. Means for determining the presence or absence of chatter vibration, and in the state where chatter vibration is occurring, calculating a cutting frequency and chatter vibration frequency, calculating a phase difference between the cutting frequency and chatter vibration frequency, and Means for correcting the tool rotational speed so as to reduce the phase difference.   A means for storing the characteristics of the tool and the clothing material; a means for storing a material to be processed and a processing shape; a means for determining whether the corrected tool rotational speed is appropriate; 4. The cutting according to claim 3, further comprising means for reducing the amount of cutting of the tool until chatter vibration is suppressed, and calculating and controlling the path of the tool after changing the amount of cutting. Processing condition calculation control device.   5. The cutting condition calculated by the cutting condition calculation control device according to claim 3 or 4 is received by the NC device by the communication interface device, and the machining state can be controlled by the cutting condition and the tool path. Machine Tools.

Images