JP2012187691A - Method for selecting tool rotation speed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for selecting tool rotation speed which avoids chattering by allowing the estimation of an accurate natural frequency.SOLUTION: S1 is the measurement of a natural frequency of a main shaft system mounted with a reference tool. S2 is the analysis of the natural frequency of the main shaft system mounted with the reference tool. In S3, a correction value is obtained from a difference of compliance and a frequency of the natural frequency obtained in S1, S2. S4 is the analysis of a natural frequency of the main shaft system mounted with a tool to be used. S5 is the correction of the natural frequency analyzed in S4 by the correction value obtained in S3. In S6, a plurality of recommended speeds of tool shaft rotation in which the chattering does not occur are calculated based on the frequency and the compliance order of the natural frequency.

Description

  The present invention relates to a tool rotation speed selection method for avoiding chatter vibration using a natural frequency of a tool axis when a workpiece is machined using a rotary tool.

  In order to prevent chatter vibration during machining using a rotating tool, the ratio of the natural frequency frequency measured with the reference tool and the natural frequency calculated from the shape and material of the reference tool is corrected. Prior art 1 for setting a tool rotation speed at which chatter vibration does not occur using a frequency of the natural frequency calculated by multiplying the correction coefficient and the natural frequency calculated from the shape of the rotary tool to be used. For example, see Patent Document 1.

JP 2003-340627 A

In the case of a small tool having a small dynamic rigidity and a small mass, the characteristic value of the tool is dominant and the natural frequency is determined. Therefore, even when the natural frequency is calculated by the correction coefficient of the conventional technique 1, the error is small. However, when the dynamic rigidity of the tool alone is large or the mass is large, the natural frequency is determined as a coupled vibration model consisting of a plurality of masses, springs, and damping including the tool and spindle system. Has a natural frequency. In the prior art 1, one natural frequency is calculated from the characteristic value of only the tool. For this reason, when there are a plurality of natural frequencies, it is unclear which natural frequency causes chatter vibrations. Furthermore, the natural frequency cannot be predicted accurately, and an error may occur in the rotational speed that prevents chatter vibration.
The present invention has been made in view of the above circumstances, and provides a tool rotation speed selection method that enables accurate estimation of the natural frequency and avoids chatter vibration even when a large tool is used. With the goal.

A feature of the invention according to claim 1 for solving the above-mentioned problem is a tool rotation speed selection method for avoiding chatter vibration that occurs when a workpiece is machined by mounting a rotating tool on a spindle.
A reference natural frequency analysis step for calculating an analysis reference natural frequency which is an analysis value of the natural frequency of the spindle system to which the reference tool is attached;
A natural frequency actual measurement step for measuring an actual natural frequency that is a natural frequency measured by mounting the reference tool on the spindle;
A correction value calculation step for calculating a correction value that is a difference between the analysis reference natural frequency and the measured natural frequency for a predetermined natural frequency;
A natural frequency analysis step of calculating an analysis natural frequency which is an analysis value of a natural frequency of a spindle system equipped with a tool excluding the reference tool;
A natural frequency correction step of calculating the predicted natural frequency by correcting the analysis natural frequency using the correction value;
A tool rotation speed calculating step of calculating a recommended tool rotation speed using the predicted natural frequency.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the reference natural frequency analysis step / the natural frequency measurement step detects a natural frequency from a peak value of a frequency response of compliance,
The correction value is a set of a frequency correction value that is a difference in frequency of the natural frequency and a compliance correction value that is a difference in compliance.
The predetermined natural frequency is a natural frequency having a compliance exceeding a predetermined threshold.

  A feature of the invention according to claim 3 is that, in the invention according to claim 1 or claim 2, the reference tool includes a plurality of reference tools having different dimensions from the shape pattern.

  According to the invention according to claim 1, analysis of the natural frequency of the main spindle system to which the tool is attached is used by using a correction value that is a difference between the actual value and the analysis value of the main spindle system to which the reference tool is attached. Since the value is corrected, an accurate natural vibration value of the spindle system on which the tool used is mounted can be calculated. Therefore, it is possible to accurately select the recommended tool shaft rotation speed at which chatter vibration does not occur.

  According to the second aspect of the invention, it is possible to determine the ranking of the possibility of chatter vibration occurrence for a plurality of natural frequencies using the compliance value of the natural frequencies. For this reason, the recommended tool axis rotation speed can be selected in the order of the high possibility of chatter vibration.

  According to the invention of claim 3, by providing a plurality of reference tools having different shape patterns and dimensions, it is possible to use the correction value of the reference tool having characteristics close to that of the tool used, and a more accurate characteristic of the tool used. Vibration value can be calculated. Therefore, the recommended tool axis rotation speed at which chatter vibration does not occur can be selected more accurately.

It is a figure which shows the measuring method of the natural frequency of the tool and spindle system of this embodiment. It is a figure which shows the frequency response of the compliance of the type | system | group equipped with the reference | standard tool. It is process drawing which shows the process of the recommended tool rotational speed selection method. It is a figure which shows the concept of the calculation of a correction value. It is the figure which showed the concept which selects the peak pair of the type | system | group equipped with the reference | standard tool and the type | system | group equipped with the use tool. It is the figure which showed the concept which correct | amends the natural frequency of the system | strain with which the tool used was mounted | worn using a correction value. It is a figure which shows the pattern of a reference | standard tool.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing an outline of a main shaft 1 on which a tool 2 is mounted and a concept of measuring a natural frequency by an impulse response test using a natural frequency measuring device 3.
The main shaft 1 includes a spindle 11 that holds the tool 2 and a housing 16 that rotatably supports the spindle 11 via bearings 12 and 13. A motor rotor 14 is fixed to the central portion of the spindle 11 in the axial direction, and a motor stator 15 is fixed to the housing 16.

In the impulse response test, the tool 2 with the sensor 32 fixed is struck with a hammer 31 while the spindle 11 is stationary, and a signal output at that time is calculated with a natural frequency calculator 33 and measured.
FIG. 2 is a diagram showing the frequency response of compliance of the spindle / tool system, with the horizontal axis representing frequency and the vertical axis representing compliance. The natural frequency is a position where the compliance shows peaks such as a, b, c, and d in FIG.

Regenerative chatter vibration is generated when periodic fluctuations in chip thickness occur around the natural frequency and fluctuations in cutting force increase. For this reason, it is known that this can be prevented by making the working period of the cutting edge of the tool coincide with the natural frequency to eliminate the fluctuation of the chip thickness. Therefore, assuming that the natural frequency is f (Hz), the number of tool blades is e, an integer of 1 or more is n, and the tool rotation speed is N (min ⁻¹ ), N = (f · 60) / (e.n). It is known that chatter vibration does not occur when machining at the tool rotation speed calculated in (1).

When viewed as a vibration model, the spindle system is composed of the mass of the tool 2, the spindle 11, and the motor rotor 14, the spring of the tool 2, the spindle 11, the bearing 12, and the bearing 13. For this reason, there are a plurality of natural frequencies as a vibration system in which a plurality of masses and springs are coupled. It is known that the frequency and compliance of this natural frequency can be obtained analytically by determining the mass, spring and damping coefficient and performing modal calculation.
Chatter vibration of a system with multiple natural frequencies is likely to occur at a natural frequency with large compliance, but it is not necessarily determined in order, and is one of the higher natural frequencies of compliance. Often occurs.

A recommended tool rotation speed selection method for avoiding chatter vibration will be described with reference to the process diagram of FIG.
First, an impulse response test is performed with the reference tool 2 mounted on the spindle 11, and a compliance frequency response diagram as shown by a solid line in FIG. 2 is measured (S1). In parallel, a system in which the reference tool 2 is mounted on the spindle 11 is analyzed, and a compliance frequency response diagram as shown by a broken line in FIG. 2 is calculated (S2). Determine the corresponding peak of the measured and analyzed values of the system with the reference tool. Specifically, in FIG. 2, the peak value corresponding to the peak in the same order in descending frequency (or ascending order) from the peak pair a to the peak pair a corresponding to the measured compliance value and the maximum value of the analysis value. Let b, c, d. The target peaks are four peaks that are actually measured values that are larger than a predetermined threshold value. (S3).

Calculate the correction value of the system with the reference tool. FIG. 4 shows a specific example of the peak b. When the frequency obtained by analyzing the peak b is Mfk _b and the actually measured frequency is Mf _b , the frequency correction value Δf _b is Δf _b = Mf _b −Mfk _b . When the compliance by analysis of the peak b is MCk _b and the compliance by measurement is MC _b , the compliance correction value ΔC _b is ΔC _b = MC _b −MCk _b . Similarly, frequency correction values Δf _{a to} Δf _d and compliance correction values ΔC _{a to} ΔC _d are calculated for each corresponding peak pair (S4). An analysis of the state in which the tool used is mounted on the spindle is performed, and a frequency response diagram is calculated (S5). The corresponding peak of the analysis value of the system with the reference tool and the analysis value of the system with the tool used is determined. Specifically, as shown in FIG. 5, the peak a of the analysis value of the system with the reference tool determined in S3 is made to correspond to the maximum peak of the analysis value of the system with the tool used, and the frequency from peak pair a Peaks in the same order in descending order (or ascending order) are set as corresponding peak pairs b, c, d (S6). Calculate the frequency of natural frequency and the predicted value of compliance of the system with the tool used. Specifically, as shown in FIG. 6, frequency correction values Δf _{a to} Δf _d corresponding to the frequency and compliance values of the peak values a, b, c, d in the analysis of the system in which the tool used is mounted, respectively. Then, the compliance correction values ΔC _{a to} ΔC _d are added to calculate the predicted frequency values fha to fhd and predicted compliance values Cha to Chd (S7). Determination of recommended order and recommended tool axis rotation speed. The recommended order is the order of the predicted compliance value. The first recommended tool axis rotation speed N _{1 in the} ranking is N ₁ = (fha · 60) / (en). Here, e is the number of blades of the tool, and n is an integer of 1 or more. (S8). The recommended tool axis rotation speed and its recommended order are output (S9).

  As described above, according to the present invention, chatter vibration is reduced from the frequency of the predicted natural frequency obtained by correcting the analysis value of the tool used, using the correction value obtained from the difference between the analysis value of the reference tool and the actual measurement value. Since the recommended tool axis rotation speed that does not occur is calculated, an accurate recommended tool axis rotation speed can be set without performing actual measurement. In addition, since multiple recommended tool axis rotation speeds are output along with the recommended order based on the compliance order of multiple natural frequencies, the recommended tool does not generate chatter vibrations reliably even for spindle systems with multiple natural frequencies. The shaft rotation speed can be calculated.

  In the above description, the example using the correction value of one reference tool has been described. However, as shown in FIG. 7, a plurality of reference tools are prepared, and the shape of the tool used is positioned between the two reference tools. When doing, you may correct | amend using the average value of the correction value of two reference tools.

1: Spindle system 2: Tool 3: Natural frequency measuring device 11: Spindle 12, 13: Bearing 14: Motor rotor 15: Stator 16: Housing 31: Hammer 32: Sensor 33: Natural frequency calculation device

Claims (3)

A tool rotation speed selection method for avoiding chatter vibration that occurs when machining a workpiece with a rotating tool mounted on the spindle,
A reference natural frequency analysis step for calculating an analysis reference natural frequency which is an analysis value of the natural frequency of the spindle system to which the reference tool is attached;
A natural frequency actual measurement step for measuring an actual natural frequency that is a natural frequency measured by mounting the reference tool on the spindle;
A correction value calculation step for calculating a correction value that is a difference between the analysis reference natural frequency and the measured natural frequency for a predetermined natural frequency;
A natural frequency analysis step of calculating an analysis natural frequency which is an analysis value of a natural frequency of a spindle system equipped with a tool excluding the reference tool;
A natural frequency correction step of calculating the predicted natural frequency by correcting the analysis natural frequency using the correction value;
A tool rotation speed selection method comprising: calculating a recommended tool rotation speed using the predicted natural frequency; and a tool rotation speed calculation step. The reference natural frequency analysis step / the natural frequency measurement step detects the natural frequency from the peak value of the frequency response of the compliance,
The correction value is a set of a frequency correction value that is a difference in frequency of the natural frequency and a compliance correction value that is a difference in compliance.
The tool rotation speed selection method according to claim 1, wherein the predetermined natural frequency is a natural frequency having a compliance exceeding a predetermined threshold.   The tool rotation speed selection method according to claim 1 or 2, comprising a plurality of reference tools having different dimensions from the shape pattern as the reference tool.

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