JP6888375B2 - Vibration analysis system and processing machine - Google Patents

Description

The present invention relates to a vibration analysis system that can obtain the vibration characteristics of a cutting processing system (machining system) that can generate chatter vibration, and a processing machine that can perform cutting while suppressing chatter vibration by utilizing the vibration characteristics.

During cutting, large vibrations (so-called "chatter vibrations") may occur between the cutting tool (particularly the cutting edge) and the work material. Chatter vibration causes deterioration of dimensional accuracy and surface roughness of the machined surface, deterioration of productivity and yield, damage to cutting tools, malfunction of the processing machine, and the like. Therefore, it is required not to generate chatter vibration during processing.

Chatter vibration is divided into multiple types depending on the cause of its occurrence, and vibration countermeasures differ for each type. As described in detail in Non-Patent Document 1, chatter vibration is roughly classified into self-excited chatter vibration (type) and forced chatter vibration (type). Self-oscillation vibration is caused by the presence of a closed loop in the machining process that feeds back and expands the vibration. Forced chatter vibration is caused by the expansion of some forced vibration cause (for example, fluctuation of cutting force due to intermittent cutting such as milling, vibration inside machine tool, etc.) through a transmission system (vibration characteristic) of a machine tool or the like. Occurs.

Self-excited chatter vibrations include regenerative chatter vibrations and mode-coupling chatter vibrations. The regenerative chatter vibration is generated by the vibration generated during cutting one rotation before (one blade before with a multi-blade tool), which remains as the undulations of the machined surface and is regenerated as the fluctuation of the depth of cut during the current cutting. Further, the mode coupling type chatter vibration occurs in a coupled manner when the vibration modes in the two directions have similar resonance frequencies.

As a measure to suppress chatter vibration, the depth of cut is often reduced or the spindle speed is changed. However, for example, reducing the cutting amount (cutting thickness) reduces the fluctuation of the cutting force, but does not affect the closed loop in which vibration is generated. Therefore, even if the forced chatter vibration is suppressed by reducing the depth of cut, the self-excited chatter vibration is not suppressed. Therefore, Patent Document 1 has made a proposal to suppress chatter vibration according to the type of chatter vibration.

Japanese Unexamined Patent Publication No. 2010-105160

Eiji Company Moto: Mechanism and suppression of chatter vibration in cutting, Daido Steel Co., Ltd. Electric Steelmaking, 82, 2 (2011), pp143-155.

Patent Document 1 classifies chatter vibration types based on the chatter vibration frequency detected by a vibration sensor (accelerometer, displacement sensor, sound sensor, etc.), and according to the type, the rotation speed of the cutting tool (spindle rotation). Number) is changed to the number of revolutions that can reduce chatter vibration.

However, Patent Document 1 merely suppresses chatter vibration after the fact when chatter vibration occurs, and if it does not suppress chatter vibration in advance, processing conditions and the like in which chatter vibration is likely to occur are set in advance. It's not something to predict.

The present invention has been made in view of such circumstances, and it is required to obtain vibration characteristics effective for predicting processing conditions and the like that may cause chatter vibration in a processing system for processing a work material by a processing machine. It is an object of the present invention to provide a vibration analysis system capable of performing cutting and a processing machine capable of cutting within a range in which chatter vibration is suppressed by utilizing the vibration characteristics.

As a result of diligent research to solve this problem, the present inventor frequency-analyzes the vibration detected during actual machining, obtains the vibration characteristic when the vibration is forced chatter vibration, and based on this vibration characteristic, The idea was to specify or predict in advance the resonance frequency of the processing system and the range in which chatter vibration is likely to occur. By embodying and developing this idea, the present invention described below was completed.

《Vibration analysis system》
(1) The vibration analysis system of the present invention is a vibration analysis system that analyzes the vibration characteristics of a machining system in which the cutting force applied from a cutting tool to a work material periodically fluctuates. An analysis means for frequency-analyzing the vibration detected during actual machining with a cutting tool under certain set conditions to obtain a transmission function of the vibration with respect to the cutting force in the frequency region, and an analysis means obtained from the analysis means. of transfer function storage means for peak frequencies of the vibration is the transfer function in the setting conditions when substantially matches the natural number times the fundamental frequency of the fluctuation of the cutting force is stored as the vibration characteristics of the setting conditions provided with a door.

(2) In the vibration analysis system of the present invention, frequency analysis is performed based on the vibration detected during actual machining, and when the vibration is a forced chatter vibration type, the transfer function of the vibration to the cutting force is transmitted in the machining system. Adopted as vibration characteristics. As a result, it is possible to accurately obtain the vibration characteristics peculiar to the processing system, which cannot be obtained by a static vibration test or the like during non-processing.

By using the vibration characteristics obtained in this way, it is possible to predict the machining area (spindle speed, depth of cut, etc.) where chatter vibration is likely to occur with high accuracy, and to efficiently perform high-quality cutting with a machining machine. It will be possible.

(3) By analyzing the vibration during actual machining as described above, the reason why the vibration characteristics of the machining system that can be effectively used to suppress chatter vibration can be accurately obtained is considered as follows. During actual machining, unlike during non-machining, the contact rigidity and damping characteristics between the cutting tool (especially the cutting edge) and the work material may change due to bending and vibration generated in the cutting tool and work material. .. Therefore, the vibration detected during actual processing includes a lot of information that is not included in the vibration obtained in the vibration test or the like during non-processing. For example, a large-amplitude vibration generated during actual machining may cause the flank of the cutting tool (cutting tool) to come into contact with the machined surface of the work material, resulting in a process damping effect. The influence of such a process damping effect and the like cannot be understood by analyzing the vibration obtained in the vibration test during non-processing, but can be understood only by analyzing the vibration during actual processing as in the present invention.
Further, during actual machining, self-excited chatter vibration may occur due to a factor other than the vibration characteristics of the machining system. However, in the present invention, the case where such self-excited chatter vibration occurs is excluded. Only the forced chatter vibration type vibration caused by the vibration characteristics of the processing system is analyzed substantially.
In this way, according to the vibration analysis system of the present invention, it is considered that it is possible to accurately grasp the vibration characteristics of the processing system during actual processing, which is effective for highly accurate prediction of chatter vibration generated during actual processing. Be done.

By using the vibration characteristics obtained by the vibration analysis system of the present invention, not only the occurrence of forced chatter vibration but also the occurrence of self-excited chatter vibration can be quantitatively predicted, and it is possible to prevent any type of vibration. It is possible to shake. For example, in the case of self-excited chatter vibration, by applying the modal parameters obtained from the vibration characteristics according to the present invention to the established theory, it is suitable for actual machining and the stable region or unstable region of the chatter vibration can be determined with high accuracy. Can be clarified.

Further, in the case of forced chatter vibration generated in response to fluctuations in cutting force, it is possible to select machining conditions that can suppress the vibration. For example, by grasping the vibration displacement and selecting the machining conditions that anticipate it. It is also possible to perform machining with substantially zero machining error from the beginning.

"Processing machine"
The present invention can be grasped not only as a vibration analysis system but also as a processing machine capable of cutting within a range in which chatter vibration is suppressed by utilizing the vibration characteristics obtained by the system. For example, the present invention is a processing machine that applies a cutting force from a cutting tool to a work material to cut the work material, and the cutting tool is based on the vibration characteristics or resonance frequency obtained by the vibration analysis system described above. It may be a processing machine provided with a control device for controlling the depth of cut and / or the spindle rotation speed of the work material.

<< Other >>
(1) The vibration characteristics according to the present invention are not limited to those obtained by analyzing the vibration detected during actual machining under one certain setting condition (also referred to as "machining condition"), but under different setting conditions. It may be obtained by analyzing a plurality of types of vibrations detected during actual processing (integrated vibration characteristics). By using this integrated vibration characteristic, it is possible to specify the resonance frequency and the like of the processing system with higher accuracy. Therefore, in the vibration analysis system of the present invention, for example, the frequency when at least one of the gain and the phase obtained from the integrated vibration characteristic consisting of a plurality of types of vibration characteristics obtained under a plurality of types of setting conditions is within a predetermined range is set. It is preferable to provide a means for specifying the resonance frequency as the resonance frequency of the processing system.

(2) The "-means" referred to in the present specification can be paraphrased as "-step", whereby the vibration analysis system of the present invention can also be used as a vibration analysis method.

It is a schematic diagram which shows the outline of a processing machine and a vibration analysis apparatus. It is a schematic diagram which shows the outline of the processing machine and the vibration analysis apparatus which changed the arrangement of the vibration sensor. It is a flowchart which shows the analysis procedure such as a vibration characteristic. It is explanatory drawing which shows the geometric shape used for the calculation of the cut-out thickness of end mill processing. It is a figure which shows the cutting force data F (t) in the time domain. It is a figure which shows the vibration data V (t) in the time domain. It is a figure which shows the cutting force data F (s) in a frequency domain. It is a figure which shows the vibration data V (s) in a frequency domain. It is a figure which shows the vibration characteristic data G (s) in a frequency domain. It is the figure which superposed each vibration characteristic data G (s) and vibration characteristic based on a vibration test. It is the figure which superposed each phase data θ (s) and the phase based on the vibration test. It is a figure which superposed each vibration characteristic data G (s) and vibration characteristic obtained from a modal parameter. It is the figure which superposed each phase data θ (s) and the phase obtained from the modal parameter. It is a stability limit diagram which concerns on a reproduction chatter vibration.

One or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. The contents described in the present specification may appropriately apply not only to the vibration analysis system (method) of the present invention but also to a processing machine (particularly its control device) using the analysis result. Which embodiment is the best depends on the target, required performance, and the like.

《Processing system》
The machining system (also referred to as “machining system”) according to the present invention comprises a combination of a work material that generates vibration during actual machining and a machining machine including a cutting tool. Even when the same processing machine is used, different work materials and cutting tools generate different vibrations, and the vibration characteristics obtained by the analysis according to the present invention also differ.

The processing system according to the present invention is a case where the cutting force fluctuates periodically with respect to the object of vibration analysis. This variation may be intermittent (discrete) or continuous. Such cases include, for example, milling and end milling in which the cutting edge and the work material are in intermittent contact with each other. In general, even in turning where the cutting edge and the work material are in continuous contact, if the cutting force fluctuates periodically (or if the cutting force fluctuates periodically), it is the target of vibration analysis according to the present invention. Become.

《Vibration analysis》
(1) Vibration detection (detection means)
Vibration usually may be detected or measured as either displacement, velocity or acceleration. Further, the vibration near the machining point (for example, the vibration of the cutting edge or the like) may be directly detected, or the vibration at the portion where the vibration near the machining point is transmitted may be indirectly detected. An appropriate detection means is selected according to the detection position. The detection means may be provided exclusively for the vibration analysis of the present invention, or may be used as the detection means according to the present invention by also using the measurement / detection device provided in the processing machine itself.

(2) Vibration type determination (determination means)
There are various vibrations detected during actual machining, but in the present invention, when it is determined that the detected vibration is a forced chatter vibration type by using the frequency (or period) of the fluctuating cutting force. , Vibration characteristics are required.

Specifically, in determining whether or not it is a forced chatter vibration type, the frequency at which the peak appears is abbreviated to the natural number of the fundamental frequency of the cutting force from the results obtained by frequency analysis of the detected vibration. It depends on whether they match or not. If the detected vibration is a self-excited chatter vibration or a mixture of the self-excited chatter vibration and the forced chatter vibration, a peak appears even at a frequency different from the natural number of the fundamental frequency of the cutting force. Therefore, by the above-mentioned method, it is possible to determine whether or not the detected vibration is a forced chatter vibration type.

Here, the fundamental frequency of the cutting force is a fluctuating frequency of the cutting force, which is the minimum frequency specified by the machining method (particularly the type and form of the cutting tool). For example, in the case of milling, the frequency at which the cutting edge of the cutting tool passes through the machining point is the fundamental frequency referred to in the present invention. In the equation (12) described later, when n = 1, the fundamental frequency also increases in proportion to the set spindle speed Sset and the number of blades N.

Note that the fact that the peak frequency and the natural number multiple of the fundamental frequency are approximately the same means that the match / mismatch is substantially determined in consideration of the effects of detection error and minute noise, in addition to the case where the two are completely matched. Is.

《Use》
The vibration analysis system of the present invention may be a vibration analysis device, a (numerical value) control device of a processing machine, or the like, or may be a program incorporated therein. Further, the vibration analysis system of the present invention automatically performs vibration detection, frequency analysis, determination of vibration type, storage of vibration characteristics, identification / calculation of resonance frequency, etc. and processing conditions in cooperation with a processing machine (particularly a control device). It is preferable that it is done in a targeted manner.

As an example of the vibration analysis system of the present invention, the vibration obtained during actual machining with a milling machine was analyzed, and the vibration characteristics during actual machining in the machining system (machining system) were clarified. Further, the resonance frequency of the processing system was specified based on the vibration characteristics. Furthermore, the stability limit of the regenerative chatter vibration was clarified using the modal parameters calculated based on the vibration characteristics. The present invention will be described in detail below with reference to such specific examples.

<< Overview of processing machine and vibration analyzer >>
As a processing machine, a milling machine 1 (simply referred to as “processing machine 1”) as shown in FIG. 1 was prepared. The milling machine 1 fixes a spindle 2 whose drive source is a motor, a cutting tool 3 (cutting tool) attached to the tip of a shank fitted in a holder of the spindle 2, and a work 4 (work material). It is provided with a numerical control (NC) device 10 that controls the feed amount of the bed and the rotation speed of the spindle 2 (spindle rotation speed).

The vibration analysis device 7 (vibration analysis system) that detects and analyzes the vibration generated when the work 4 is processed by the processing machine 1 is a vibration sensor 5 or a vibration sensor 5 that directly detects the vibration (displacement) near the processing point. It is processed by the vibration sensor 6 (detecting means) that indirectly detects the vibration (displacement) of the fixed portion of the spindle 2, the arithmetic device 9 (analyzing means) that arithmetically processes the input signals from those sensors, and the arithmetic apparatus 9. It includes a storage device 8 (storage means) for storing the data, and an input device 11 (input means) for inputting information such as initial values, set values, and parameters required for arithmetic processing of the arithmetic device 9.

The vibration sensor 5 and the vibration sensor 6 may be both, but may be only one. The vibration sensor 5 is preferable because it can be realized by a laser measuring instrument, an electric capacity sensor, or the like, and the vibration displacement generated in the cutting tool 3 near the machining point can be directly measured. The vibration sensor 6 can be realized by using a strain gauge, an acceleration sensor, or the like, and is preferable in that the vibration displacement occurring in the cutting tool 3 near the machining point can be indirectly and easily measured. Although the details will be described later, even when the vibration sensor 6 is used, the vibration displacement occurring in the vicinity of the machining point can be known by using the correction coefficient (see equation (4)).

As shown in FIG. 2, the vibration sensor 5 or the vibration sensor 6 may detect the vibration displacement on the work 4 side. In this case, the vibration sensor 5 directly measures the vibration displacement occurring in the work 4 near the machining point, and the vibration sensor 6 directly measures the vibration displacement occurring in the work 4 near the machining point via a bed or the like. It will be measured indirectly.

Each vibration sensor may be capable of detecting or measuring velocity and acceleration in addition to displacement. Further, although at least one vibration sensor is required, a plurality of vibration sensors may be arranged in different directions to detect or measure vibration information (displacement, velocity, acceleration, etc.) in the plurality of directions. Further, the vibration sensor may be separately provided as a part of the vibration analysis device 7, or may also be used as a sensor or a measuring device included in the processing machine 1. For example, it is conceivable to substitute a power meter or the like provided on the spindle motor of the processing machine 1 as a vibration sensor. Hereinafter, as shown in FIG. 1, a case where the displacement generated in the cutting tool 3 is directly measured by the vibration sensor 5 will be described.

The storage device 8 may be a volatile memory or the like that performs temporary storage, or a fixed storage device or a non-volatile memory or the like that performs long-term (semi-permanent) storage. However, it is preferable that each vibration characteristic obtained by the vibration analysis and the analysis result based on the vibration characteristic are stored in the storage device 8 for a long period of time as a database.

<< Analysis of vibration characteristics, etc. >>
The vibration characteristics and the like when the work 4 was actually machined by the processing machine 1 were analyzed according to the processing flow as shown in FIG. Hereinafter, each step of the processing flow will be described.

In step S1, various parameters required for the analysis process by the arithmetic unit 9 are input from the input device 11 (input step). The parameters include, for example, variables related to the tool shape (tool diameter, number of blades, torsion angle, pitch angle, etc.), variables related to machining conditions (spindle rotation speed, feed amount, axial depth of cut, radial depth of cut, etc.), Specific cutting resistance, etc.

In step S2, the range (lower limit value and upper limit value) of the spindle rotation speed at the time of actual machining is similarly input from the input device 11 and set.

In step S3, the actual machining of the work 4 is started by the processing machine 1, and the vibration generated at that time is detected and measured by the vibration sensor 5. The initial value of the set rotation speed Sset of the spindle was set to the lower limit value of the spindle rotation speed set in step S2.

In step S4, the set rotation speed Sset at the time of processing, the cutting force data F (t) in the time domain when processing with the set rotation speed Sset, and the vibration data V (t) obtained via the vibration sensor 5 are obtained. Store in the storage device 8. The details of the cutting force calculation method will be described later.

In step S5, the cutting force data F (t) and the vibration data V (t) obtained in step S4 are frequency-analyzed (fast Fourier transform / FFT processing) by the arithmetic unit 9. As a result, the cutting force data F (t) and the vibration data V (t) in the time domain become the cutting force data F (s) and the vibration data V (s) in the frequency domain, respectively.

From these, the vibration characteristic data G (s) corresponding to the transfer function can be obtained as shown in the equation (1). If the vibration data based on the displacement is frequency-analyzed and then the processing based on the equation (2) or the equation (3) is performed, the vibration data indicating the velocity and the acceleration can be obtained. When the vibration data is displacement, velocity or acceleration, the vibration characteristic data is compliance, mobility or acceleration, respectively. Either one may be used, but in this example, the vibration data based on the displacement was used as it was for the analysis.

In step S6, the type of vibration (chatter vibration) generated in the processing system of the processing machine 1 and the work 4 is determined based on the vibration data V (s) obtained in step 5. When the vibration is forced chatter vibration, the vibration characteristic data G (s) is stored in the storage device 8 in accordance with the set rotation speed Sset at that time in step 7.

Whether or not the vibration is forced chatter depends on whether the peak frequency of the vibration data V (s) matches the natural frequency of the fluctuating fundamental frequency of the cutting force (the cutting edge passing frequency of the cutting tool 3). When the two are substantially the same, it is determined that the type of vibration generated in the processing system is forced chatter vibration.

The forced chatter vibration that occurs in the case of this embodiment is caused by the cutting tools 3 (cutting edges) that are arranged at regular intervals and intermittently cut the work 4, so that the work 4 has a periodic cutting force. Is applied, and the cutting force can be generated as a vibrating force. Therefore, using the set rotation speed Sset (rpm) and the cutting edge number N of the cutting tool 3, the basic frequency of the cutting force is obtained as the cutting edge passing frequency (N · Sset / 60), which is a natural number multiple (n). The frequency fcut of = 1, 2, 3 ...) Can be obtained by the equation (12).

When the peak frequency of the vibration characteristic data G (s) does not match the fcut, it is considered that unexpected vibrations such as self-excited chatter vibrations occur in addition to the forced chatter vibrations, or at least they are mixed. The vibration characteristic data G (s) at this time is not stored in the storage device 8, and the set rotation speed Sset of the spindle is changed in step S11. In step S12, if the set rotation speed Sset is within the upper limit value of the spindle rotation speed set in advance, the processes after step S3 are repeated under conditions different from the previous time (spindle rotation speed).

In step S8, it is determined whether the phase data θ (s) of the vibration characteristic data G (s) stored in step S7 is within a predetermined threshold range at each frequency fcut. Specifically, when the vibration data V (s) is based on the displacement, if there is a frequency fcut in which the phase data θ (s) is within a predetermined range near −90 °, the frequency fcut is set to the resonance frequency fn (or). It is determined that the frequency is in the vicinity) and stored.

If the vibration data V (s) is based on velocity or acceleration, the frequency fcut when the phase data θ (s) is near 0 ° or 90 ° is set to the resonance frequency fn (or its vicinity). Frequency).

In step S9, it is determined whether the gain of the vibration characteristic data G (s) related to the forced chatter vibration is larger than a predetermined threshold value at each frequency fcut. If there is a frequency fcut whose gain is within a predetermined range (exceeding the threshold value), the frequency fcut is determined to be the resonance frequency fn (or a frequency in the vicinity thereof) and stored.

It should be noted that only one of step S8 and step S9 can determine whether a certain frequency fcut is a resonance frequency fn or a frequency in the vicinity thereof. However, the resonance frequency fn that affects machining can be more accurately specified by judging by both the phase and the gain.

In step S10, the frequency fcut indicating the phase and gain within the predetermined range in steps S8 and S9 is stored in the storage device 8 as the resonance frequency fn (resonance frequency specifying means). When the phase or gain is out of the predetermined range in step S8 or step S9, the resonance frequency fn (frequency fcut) is not stored.

In step S11, in order to more accurately identify the resonance frequency fn, the set rotation speed Sset is changed to the upper limit value side, and steps S3 to S11 are repeated. At this time, the increase (width) of the set rotation speed Sset may be constant, but if the increase of the set rotation speed Sset is reduced in the vicinity where the phase or gain of the vibration characteristic data G (s) fluctuates greatly, the resonance frequency The fn can be specified more accurately and efficiently. Then, in step S12, when the set rotation speed Sset reaches the upper limit value, the analysis of the vibration characteristics is completed.

《Vibration data》
As shown in equation (4), the vibration data V _{6 (s)} detected from the vibration sensor 6 provided on not the position at node vibration mode, frequency correction factor P _{56 (s)} (gain and phase) By multiplying in the region, the vibration data V ₅ (s) at the position of the vibration sensor 5 can be indirectly obtained. Even if the converted vibration data V ₅ (s) is used, the vibration characteristic data G (s) can be obtained in the same manner.

The correction coefficient P ₅₆ (s) is determined by, for example, performing a vibration analysis using the finite element method (FEM), a vibration test using an impulse hammer or a vibration element, and the position of the vibration sensor 5 and the vibration sensor 6. It can be obtained by clarifying the vibration mode between the position and the position.

《Cutting force data》
An example of calculating the cutting force data F (t) used in step S4 will be described below. The cutting force data F (t) can be calculated from a cutting component proportional to the cutting thickness h (t) and an edge force component (intercept component) generated at zero cutting thickness. Specifically, the cutting force data F (t) is expressed by the equation (5) using the specific cutting resistance Kc and the edge force Ke.

In the case of two-dimensional cutting with a straight cutting edge, the cutting force has two components, the main component force (component parallel to the cutting direction) Fp (t) and the back component force (component perpendicular to the cutting direction) Ff (t). The corresponding specific cutting resistances Kcp and Kcf and edge force Kep and Kef are also two components.

In the case of milling in which the cutting thickness h (t) changes, the cutting force can be calculated by integrating the cutting forces ΔFt, ΔFr, and ΔFa of the minute elements in contact with the work (work material) (References). : Let's learn in practice "Basic knowledge of cutting and chatter vibration" Japan Society of Mechanical Engineers 2012 Production Processing Basic Course Workshop Material Text).

In the case of end mill machining, consider a rotating coordinate system with respect to the rotation angle φ (t) with respect to the end mill (tool). The circumferential cutting force Ft (φ), radial cutting force Fr (φ), and rotary axial cutting force Fa (φ) of the end mill are the axial depth of cut a and the cutting of the work (work material) at the axial coordinate z. Using the thickness h (φ, z) and the specific cutting resistance Kt, Kr, Ka, it can be expressed as the equations (6) to (8).

The cut-out thickness h (φ, z) can be obtained from the geometric shape shown in FIG. 4 by using each parameter input by the input device 11. By integrating this in the z-axis direction (rotation axis direction), the cutting area of the entire end mill can be obtained. Assuming that the xy plane is a plane perpendicular to the rotation axis, the cutting force in the fixed coordinate system is as shown in the equations (9) to (11).

In addition to milling and end milling in which intermittent cutting is performed, cutting force can be similarly calculated according to the cutting thickness in turning processing, which is continuous cutting. Further, the cutting force data F (t) may be an actually measured value in addition to the calculated value. For example, the cutting force data F (t) may be obtained based on the measured value of the motor power or the like of the processing machine 1 or the measured value of the power meter or the like attached to the work 4. At this time, it is also possible to determine whether or not the cutting force data F (s) for which frequency analysis has been performed is forced chatter vibration, depending on whether or not the cutting force data F (s) matches the peak frequency of the vibration data V (s) in step S6.

By the way, when the cutting force is a calculated value instead of a measured value, if the cutting force data F (t) is calculated in consideration of the cutting thickness generated by the vibration displacement, more accurate vibration characteristic data G (s) is calculated. Becomes possible.

<< Analysis example >>
Using the processing machine 1 and the vibration analysis device 7 described above, the vibration generated during the actual processing of the work 4 was detected, and the vibration characteristics in the processing system were specifically obtained. Vibration data was obtained by measuring displacement in one direction. The cutting force was obtained from the specific cutting resistance.

The parameters (tool shape, variables related to machining conditions, specific cutting resistance) input in step S1 and the upper and lower limit values of the spindle speed (set rotation speed Sset) input in step S2 are as follows. The cutting edge of the tool is sharp enough and the edge force component can be ignored, so it was set to zero.
・ Tool shape: Tool diameter: 20 mm, number of blades: 1, blade angle: 0 °
・ Machining conditions: Single blade feed amount: 0.15 mm,
Axial depth of cut: 2 mm, radial depth of cut: 0.15 mm
-Specific cutting resistance: Circumferential direction: 3029 MPa, radial direction: 2040 MPa
・ Spindle speed: Lower limit: 3900 rpm, Upper limit: 6850 rpm,

The cutting force data F (t) and the vibration data V (t) in the time domain when the set rotation speed Sset is set to a certain value (3900 rpm) are shown in FIGS. 5 and 6, respectively. Further, the cutting force data F (s) and the vibration data V (s) in the frequency domain obtained by frequency analysis of them are shown in FIGS. 7 and 8, respectively. Further, the vibration characteristic data G (s) obtained from them and the equation (1) is shown in FIG.

When the set rotation speed Sset = 3900 rpm, the number of blades N = 1, so the frequency fcut = 65 n (n = 1, 2, 3 ...) Hz according to the equation (12). In the vibration data V (s) shown in FIG. 8, a peak appears every 65 n (n = 1, 2, 3 ...) Hz. Therefore, it can be determined that the vibration in this processing system is forced chatter vibration. Further, from the vibration characteristic data G (s), the gain of the fifth harmonic component is maximized, and it is predicted that the resonance frequency fn may exist at or near the frequency fcut = 325 Hz (5 × 65 Hz). ..

The set rotation speed Sset is sequentially increased over the entire range of 3900 to 6850 rpm, and the vibration characteristic data G (s) is obtained in the same manner. FIG. 10 shows a superposition of the vibration characteristic data G (s) obtained in this manner (integrated vibration characteristic data G (s)). Further, FIG. 11 shows a superposed phase data θ (s) obtained from each vibration characteristic data G (s) (integrated phase data θ (s)).

From FIGS. 10 and 11, the frequency at which the gain is maximized or the frequency whose phase is closest to −90 ° is 345 Hz. From this result, it was specified that the resonance frequency fn = 345 Hz in this processing system.

Apart from the vibration analysis described above, the vibration characteristic G (s) * in the unprocessed state (the state where the cutting edge is not in contact with the work) was obtained by a vibration test using an impulse hammer. In addition, the phase θ (s) * was also obtained from this vibration characteristic G (s) *. These are shown in FIGS. 10 and 11 by superimposing them with broken lines, respectively.

Comparing the case where the vibration analysis was performed and the case where the vibration test was performed, the difference between the two became large near the resonance frequency where the vibration displacement was likely to occur. From this, it was found that the vibration generated in the machining system can be grasped more accurately by using the vibration characteristics analyzed based on the vibration data during actual machining.

<< Calculation of vibration characteristics based on modal parameters >>
(1) Modal parameters (resonance frequency, damping ratio, vibration mode or mass, damping coefficient, spring constant) can be calculated from the vibration characteristic data G (s) (Hitohiko Yasuda: Basics of Vibration Engineering, Corona).

The continuous vibration characteristic G (s) ** calculated based on the modal parameter when the resonance frequency (fn) is set to 345 Hz described above, and the phase θ (s) calculated from the vibration characteristic G (s) **. ** and the above-mentioned discrete vibration characteristic data G (s) and phase data θ (s) are shown superimposed on FIGS. 12 and 13, respectively. It was confirmed that the consistency was high at least in the vicinity of the resonance frequency, which is important for vibration countermeasures.

(2) Based on this result, using the modal parameters calculated from the vibration characteristic data G (s), the stability limit line related to the regenerated chatter vibration (a type of self-excited chatter vibration) that is likely to be regarded as a problem at the actual processing site. The figure was calculated (see: Non-Patent Document 1). The stability limit diagram thus obtained and the stability limit diagram calculated based on the vibration test without processing as in the conventional case are shown in FIG. 14 in an overlapping manner.

The stability limit line indicates an unstable region in which chatter vibration is likely to occur in the upper region, and a stable region in which chatter vibration is unlikely to occur in the lower region. As is clear from FIG. 14, it can be seen that the calculation result based on the modal parameters according to this embodiment has a wider stable region than the calculation result based on the vibration test. In the former case calculated based on the vibration characteristics during machining, the result was obtained by considering the process damping effect that occurs only during actual machining, as opposed to the latter case calculated based on the vibration characteristics during non-machining. It is considered that the stable region in the stability limit diagram has expanded.

By using the vibration characteristics obtained by analyzing the vibration during actual machining in this way, it is possible to predict the range that can be machined by suppressing the occurrence of chatter vibration with higher accuracy, and set the machining conditions, etc. than before. Can be performed appropriately, and high-quality cutting can be efficiently produced.

<< Supplement >>
(1) By using the vibration characteristics according to the present invention, it is possible to estimate the occurrence of forced chatter vibration. For example, as can be seen from the equation (1), the vibration data V (s) in the frequency domain can be obtained by multiplying the vibration characteristic data G (s) by the cutting force data F (s). If the vibration data V (s) is inversely transformed (inverse FFT processing), the vibration data V (t) in the time domain can be obtained. This makes it possible to easily determine the vibration displacement and the like that may occur during actual machining.

(2) When determining the vibration characteristics by the vibration analysis system of the present invention, it is suitable when a cutting force (periodic cutting force) having a fluctuating component is generated as in milling and end milling, but it is suitable for turning. Is also applicable. In the turning process, the cutting force is generally substantially constant, but if a periodic cutting force is intentionally generated by, for example, making a notch in the work material, the turning process is performed by the above-mentioned method. The vibration characteristics of the system can be obtained.

Further, in obtaining the vibration characteristics by the vibration analysis system of the present invention, it can be applied not only when the cutting force fluctuates intermittently but also when the cutting force fluctuates due to changes in the machining conditions. The cutting force at that time can also be calculated by the method described above.

(3) The prediction of forced chatter vibration or self-excited chatter vibration using the vibration characteristics according to the present invention can be applied to milling, turning, etc. regardless of the periodicity of the cutting force. (Self-excited chatter vibration can occur even in turning where the cutting force is constant.)

(4) The vibration analysis system of the present invention is intended to elucidate the vibration characteristics of the processing system, and is incorporated into the processing machine or its control device to operate the processing machine in a stable region where chatter vibration can be suppressed. It may be a control system. For example, the vibration generated during the machining of the work material may be measured at any time (real-time measurement), and the machining conditions capable of suppressing chatter vibration may be updated at any time based on the vibration characteristics obtained each time. As a result, even if the shape of the tool edge changes due to wear or the like and the vibration characteristics change due to the process damping effect, stable machining can be performed with chatter vibration suppressed for a long period of time. ..

1 Processing machine 2 Main shaft 3 Cutting tool (cutting tool)
4 Work (work material)
5 Vibration sensor 7 Vibration analysis device 8 Storage device 9 Arithmetic logic unit

Claims (3)

A vibration analysis system that analyzes the vibration characteristics of a machining system in which the cutting force applied to the work material from a cutting tool fluctuates periodically.
An analysis means for frequency-analyzing the vibration detected when the work material is actually machined with the cutting tool under a certain set condition to obtain a transfer function for the cutting force of the vibration in the frequency domain.
Among the transfer functions obtained from the analysis means, the transfer function in the setting conditions when the peak frequency of the vibration is substantially equal to a natural number multiple of the fundamental frequency in accordance with variations in cutting force, vibration in the setting conditions A storage means to memorize as a characteristic and
Vibration analysis system equipped with. Resonance frequency specification in which the frequency when at least one of the gain and the phase obtained from the integrated vibration characteristic consisting of a plurality of types of vibration characteristics obtained under a plurality of types of setting conditions is within a predetermined range is set as the resonance frequency of the processing system. The vibration analysis system according to claim 1, further comprising means. A processing machine that applies cutting force from a cutting tool to a work material to cut the work material.
A processing machine including a control device for controlling the depth of cut and / or the spindle speed of a work material by a cutting tool based on the vibration characteristics or resonance frequency obtained by the vibration analysis system according to claim 1 or 2.

Images