Cutting force prediction method and system design based on acceleration signal

Abstract

The invention discloses a cutting force prediction method and system design based on an acceleration signal, the system comprises an upper computer, a data acquisition card, an acceleration sensor, a cutter and a workpiece, one of the cutter and the workpiece is fixed on a machine tool, and the other one is fixed on a slide carriage. The slide carriage is driven by the driving system to move in the broaching direction to enable the workpiece and the cutter to move relatively, so that the cutter cuts off metal materials of the workpiece; the acceleration sensor is placed on the slide carriage and measures vibration signals of the slide carriage in the broaching direction. The acceleration sensor is communicated with the data acquisition card, acceleration signals acquired by the acceleration sensor are transmitted to the data acquisition card, and the data acquisition card decodes and amplifies the acquired acceleration signals and then transmits the acceleration signals to the upper computer. According to the cutting force prediction method and system design based on the acceleration signal, the equipment cost is low, the structure is simple and reliable, actual machining cannot be interfered, and whether the broach is abraded or damaged or not can be visually judged according to the reconstructed broaching force.

Description

Technical Field

[0001] The present invention relates to the field of broaching, and particularly to a cutting force prediction method and system design based on acceleration signals. Background Art

[0002] A broach is a forming tool used for broaching. There are multiple rows of cutting teeth on the tool surface, and the sizes and shapes of the cutting teeth in each row increase and change sequentially from the cutting-in end to the cutting-out end. When the broach performs a broaching movement, each cutting tooth cuts off a certain thickness of metal from the workpiece, and finally the required size and shape are obtained. Broaches are commonly used in batch and mass production to machine round holes, spline holes, keyways, planes, and formed surfaces, etc., with high productivity.

[0003] Cutting force is the most direct indicator reflecting tool wear and machining quality. However, the equipment for directly measuring cutting force is costly and will change the dynamic performance of the machine tool, making it difficult to apply in actual production. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that the existing equipment for measuring cutting force is costly and will change the dynamic performance of the machine tool, making it difficult to apply in actual production. The present invention provides a cutting force prediction method and system design based on acceleration signals, which reconstruct the broaching force using an acceleration sensor to indirectly monitor the broaching force of the broaching machine. The equipment cost is low, the structure is simple and reliable, it will not interfere with actual machining, and it can intuitively judge whether the broach is worn or damaged according to the reconstructed broaching force.

[0005] To achieve the above object, the present invention provides a cutting force prediction system, including a host computer, a data acquisition card, an acceleration sensor, a tool, and a workpiece. One of the tool or the workpiece is fixed on the machine tool, and the other is fixed on the cross slide. The cross slide moves along the broaching direction under the drive of the drive system to make the workpiece and the tool move relative to each other, so that the tool cuts off the metal material of the workpiece; the acceleration sensor is placed on the cross slide to measure the vibration signal of the cross slide along the broaching direction; the acceleration sensor communicates with the data acquisition card, and the acceleration signal collected by the acceleration sensor is transmitted to the data acquisition card, and the data acquisition card decodes and amplifies the obtained acceleration signal and then transmits it to the host computer.

[0006] Further, it further includes a pressure sensor, which is installed between the workpiece and the tooling to measure the cutting force received by the workpiece along the cutting direction.

[0007] Further, the tool includes a broach.

[0008] The present invention provides a cutting force prediction method for a cutting force prediction system, including the following steps:

[0009] The broach and the workpiece perform broaching motion at a constant relative speed, and the teeth of the broach generate excitation on the workpiece;

[0010] The pressure sensor measures the broaching force excitation during the broaching motion, and the acceleration sensor measures the vibration response during the broaching process;

[0011] The vibration response and the broaching system transfer function are used to obtain the high-frequency dynamic AC signal of the broaching force;

[0012] The low-frequency bandwidth expansion technology is used to reconstruct the low-frequency static DC signal in the broaching force;

[0013] The waveform of the low-frequency DC signal of the broaching force under the broaching conditions is determined by using the metal cutting area of each row of teeth, the workpiece thickness, the broaching speed, and the tooth pitch of the row of teeth, and the waveform of the low-frequency DC signal of the broaching force is reconstructed; The order of magnitude of the low-frequency DC signal is determined by using the high-frequency AC signal reconstructed by the acceleration sensor and the metal cutting area of the broach row of teeth;

[0014] The high-frequency AC signal and the low-frequency DC signal are fused to reconstruct the broaching force.

[0015] Furthermore, the high-frequency AC signal is reconstructed by using the vibration acceleration data, and the low-frequency DC signal is reconstructed by using the low-frequency bandwidth expansion technology.

[0016] Furthermore, the sampling frequency of the pressure sensor is set to more than 100 times the broaching excitation frequency.

[0017] Furthermore, the signals measured by the pressure sensor and the acceleration sensor are stored in the time domain form.

[0018] Furthermore, the time domain of the vibration acceleration signal is transformed into the frequency domain through the fast Fourier transform, then the double integral of the Fourier series expansion of the vibration acceleration signal is used to obtain the time domain signal of the displacement, and then the fast Fourier transform is used to obtain the displacement frequency domain signal; The displacement is transformed into the broaching force signal through the transfer function of the broaching system. Limited by the low-frequency bandwidth of the vibration sensor, this broaching force signal needs to be high-pass filtered to obtain the accurate high-frequency AC signal of the broaching force.

[0019] Furthermore, the low-frequency DC signal of the reconstructed broaching force is compensated by using the low-frequency bandwidth expansion technology. According to the metal cutting principle, the metal cutting force is proportional to the metal cutting area under the same working conditions.

[0020] Furthermore, the low-frequency DC part F of the broaching force obtained by the low-frequency bandwidth expansion technology DC and the high-frequency AC part F AC Adding them in the time domain can obtain the reconstructed broaching force curve.

[0021] Technical effects

[0022] The present invention provides a cutting force prediction method and system design based on acceleration signals, which reconstructs the broaching force by using an acceleration sensor so as to indirectly monitor the broaching force of a broaching machine. The equipment cost is low, the structure is simple and reliable, and it will not interfere with actual processing. The wear and damage of the broach can be intuitively judged according to the reconstructed broaching force.

[0023] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the drawings to fully understand the purpose, features and effects of the present invention. Description of the Drawings

[0024] Figure 1 is a schematic structural diagram of a cutting force prediction system according to a preferred embodiment of the present invention;

[0025] Figure 2 is a schematic flow diagram of a cutting force prediction method according to a preferred embodiment of the present invention;

[0026] Figure 3 is a time-frequency diagram of the original acceleration signal according to a preferred embodiment of the present invention;

[0027] Figure 4 is a time-frequency diagram of the displacement signal after double integration of the original acceleration signal according to a preferred embodiment of the present invention;

[0028] Figure 5 is a dynamic response curve diagram with Kalman filtering for dynamic compensation of the broaching system noise and measurement noise according to a preferred embodiment of the present invention;

[0029] Figure 6 is a time-frequency diagram of the broaching force signal obtained by the displacement signal through the transfer function according to a preferred embodiment of the present invention;

[0030] Figure 7 is a time-frequency diagram of the high-frequency alternating current component extracted from the time-frequency diagram of the broaching force signal according to a preferred embodiment of the present invention;

[0031] Figure 8 is a diagram of the metal cutting area and the actual broaching force corresponding to each row of teeth according to a preferred embodiment of the present invention;

[0032] Figure 9 is a diagram of the actual broaching force corresponding to the metal cutting area per square millimeter of each row of teeth according to a preferred embodiment of the present invention;

[0033] Figure 10 is a time-frequency domain diagram of the broaching force calculated according to the average metal cutting area per square millimeter according to a preferred embodiment of the present invention;

[0034] Figure 11It is the time-frequency diagram of the low-frequency DC broaching force signal extracted according to the calculated broaching force in a preferred embodiment of the present invention;

[0035] Figure 12 It is the time-frequency domain comparison diagram of the reconstructed broaching force and the measured broaching force in a preferred embodiment of the present invention. Detailed implementation manners

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] In the following description, for the purpose of illustration rather than limitation, specific details such as specific internal programs and technologies are proposed in order to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0038] As Figure 1 As shown, an embodiment of the present invention provides a cutting force prediction system, including a host computer 1, a data acquisition card 2, an acceleration sensor 4, a tool 5 and a workpiece 6. One of the tool 5 or the workpiece 6 is fixed on the machine tool, and the other is fixed on the cross slide. The cross slide moves along the broaching direction under the drive of the drive system to make the workpiece 5 and the tool 6 move relative to each other, so that the tool cuts the metal material of the workpiece; the acceleration sensor is placed on the cross slide to measure the vibration signal of the cross slide along the broaching direction. The acceleration sensor communicates with the data acquisition card 2, and the signal collected by the sensor 4 is transmitted to the data acquisition card 2. The data acquisition card 2 (VSE150) transmits the acquired digital signal to the host computer 1. Specifically, the acceleration sensor 4 (VSA001) communicates with the data acquisition card 2, and the acceleration signal collected by the acceleration sensor is transmitted to the data acquisition card. The data acquisition card decodes and amplifies the acquired acceleration signal and then transmits it to the host computer.

[0039] In this embodiment, a pressure sensor 3 (F33F-N105-200KN) is further included. The pressure sensor is installed between the workpiece and the tooling to measure the cutting force received by the workpiece along the cutting direction.

[0040] The tool in this embodiment is set as a broach.

[0041] As Figure 2 As shown, another preferred embodiment of the present invention provides a cutting force prediction method and system design based on acceleration signals, including the following steps:

[0042] Step 100, the broach and the workpiece perform a broaching motion at a constant relative speed, and its cutting teeth generate excitation on the workpiece;

[0043] Step 200, a pressure sensor measures the broaching force excitation during the broaching motion, and an acceleration sensor measures the vibration response during the broaching process; wherein, the sampling frequency of the pressure sensor is set to be more than 100 times the broaching excitation frequency.

[0044] Step 300, use the low-frequency bandwidth expansion technology to reconstruct the low-frequency static DC signal in the broaching force; specifically, use the vibration acceleration data to reconstruct the high-frequency AC signal, and use the low-frequency bandwidth expansion technology to reconstruct the low-frequency DC signal.

[0045] Step 400, determine the waveform of the low-frequency DC signal of the broaching force under the broaching conditions by using the metal cutting area, tooth pitch, broaching speed, and workpiece thickness of each row of cutting teeth, and reconstruct the waveform of the low-frequency DC signal of the broaching force; use the high-frequency AC signal reconstructed by the acceleration sensor and the metal cutting area of the row of teeth to determine the order of magnitude of the low-frequency DC signal;

[0046] Step 500, fuse the high-frequency AC signal and the low-frequency DC signal to reconstruct the broaching force.

[0047] The following will use a specific embodiment to illustrate a method for predicting cutting force provided by the present invention.

[0048] Step 100, the broach and the workpiece perform a broaching motion at a constant relative speed, and its cutting teeth generate excitation on the workpiece;

[0049] Step 200, as Figure 1 shown, the pressure sensor 3 is placed between the workpiece 6 and the fixed end of the machine tool to measure the cutting force on the workpiece along the broaching direction. The measured signal is directly stored in the time domain, and the sampling frequency is 1094 Hz. A pressure sensor measures the broaching force excitation during the broaching motion, and an acceleration sensor measures the vibration response during the broaching process; wherein, the sampling frequency of the pressure sensor is set to be more than 100 times the broaching excitation frequency.

[0050] Specifically, as Figure 1 shown, the acceleration sensor 4 is installed on the two side slides of the broaching machine to mainly measure the acceleration signal in the broaching direction ( Figure 1 X direction). The acceleration sensor transmits the collected acceleration signal to the data acquisition card 2, which is amplified by the data acquisition card and then transmitted to the upper computer 1. At this time, the vibration response during the broaching process is obtained, and the time-frequency domain signal of the vibration acceleration signal is as Figure 3As shown. When the broach's row of teeth cuts the workpiece, the broach generates an excitation on the workpiece, and there will be an obvious excitation amplitude in the acceleration time domain. The position of the time domain excitation is related to the tooth pitch of the broach. In the acceleration frequency domain, there will be obvious equally spaced multiple-frequency harmonics, and the fundamental frequency value of the multiple frequencies is equal to the excitation frequency of the broach on the workpiece. Obvious vibration mode cluster harmonics can be seen in the acceleration frequency domain. The mode value is approximately equal to 27 Hz.

[0051] Step 300, use the low-frequency bandwidth expansion technology to reconstruct the low-frequency static DC signal in the broaching force; specifically, use the vibration acceleration data to reconstruct the high-frequency AC signal and use the low-frequency bandwidth expansion technology to reconstruct the low-frequency DC signal.

[0052] For Figure 3 The vibration acceleration signal time domain represented ( Figure 3 (a) After performing a fast Fourier transform, the frequency domain is obtained ( Figure 3 (b), and the following relationship exists when they are expanded

[0053]

[0054] where the fundamental frequency

[0055]

[0056] T is the intercepted duration of the vibration acceleration signal.

[0057] For Figure 3 The vibration acceleration signal The double integral of the Fourier series expansion can obtain Figure 4 The time domain signal x(t) of the displacement ( Figure 4 (a). After performing a fast Fourier transform on x(t), the displacement frequency domain signal x(jkw) is obtained ( Figure 4 (b) is represented. The calculation method of x(t) is as follows

[0058]

[0059] The displacement is transformed into the broaching force signal through the transfer function Φ of the broaching system k Figure 5 are the amplitude-frequency response curve and phase-frequency response curve of the system transfer function. The broaching force frequency domain can be calculated by the following formula:

[0060]

[0061] ( Figure 6 (b) After performing an inverse Fourier transform, the time domain of the broaching force is obtained ( Figure 6 ​(a), The broaching force in the time domain can be expanded in the form of the following Fourier series:

[0062]

[0063] All are the amplitude coefficients related to the series expansion, w is the fundamental frequency, and k is the series number

[0064] Limited by the measurement of the low-frequency bandwidth of the acceleration sensor, Figure 6 The low-frequency DC signal of the reconstructed broaching force signal is inaccurate. Therefore, only the high-frequency AC signal is extracted in this embodiment. The cut-off frequency is the first-order multiple frequency. Figure 6 The high-frequency AC signal F in AC (t) is extracted, and its time-frequency diagram is as shown in Figure 7 . F AC can be calculated by the following formula:

[0065]

[0066] k f is the serial number of the first broaching excitation frequency, expressed as:

[0067]

[0068] Here, is the floor function symbol, f is the broaching excitation frequency, and T is the sampling duration of the collected signal.

[0069] Step 400, determine the waveform of the low-frequency DC signal of the broaching force under this broaching condition by using the metal cutting area, tooth pitch, workpiece thickness, and broaching speed of each row of teeth, and reconstruct the low-frequency DC signal of the broaching force; determine the order of magnitude of the low-frequency DC signal by using the high-frequency AC signal reconstructed by the acceleration sensor and the metal cutting area of the broach teeth.

[0070] The low-frequency DC signal of the reconstructed broaching force is compensated by using the low-frequency bandwidth expansion technology. According to the metal cutting principle, the metal cutting force is proportional to the metal cutting area under the same working conditions. Figure 8 (a) shows the statistical result of the total cutting area of each row of 49 spline broach teeth, denoted by C area (n), where n represents the serial number of the broach teeth row. The high-frequency AC part of the broaching force in formula (3) is the result of the alternating stress excitation generated by the broach teeth on the workpiece. Therefore, 49 rows of broach teeth generate 49 high-frequency AC waveforms. Statistically Figure 7 (a)F AC The difference between the wave peaks and wave valleys can be obtained, and the statistical result F of the excitation force caused by 49 rows of broach teeth as shown in Figure 8 (b) can be obtained. Where n represents the serial number of the broach teeth row. A1

[0071] According to C area (n)( Figure 8 (a)) and (F 0C (n) Figure 8 (b)), the broaching force required for each row of 49 broach teeth to remove one unit square millimeter of metal, that is, the cutting force density (this coefficient could only be measured through broaching experiments or inaccurately estimated based on the metal orthogonal cutting model before), and its statistical results are as Figure 9 shown. The calculation method of the cutting force density of the broach teeth numbered n is as follows:

[0072] K(n) = F AC (n) / C area (n) (8) According to K(n), the broaching force required to remove one unit square millimeter of metal on average for 49 rows of broach teeth under this working condition (average cutting force density) can be calculated. The calculation method is as follows:

[0073]

[0074] Among them, N is the total number of rows of broach teeth.

[0075] By the broaching force required to remove each unit square millimeter, the workpiece length, the tooth pitch of the broach teeth, and the broaching speed, the broaching force time-domain curve F(t) can be calculated, and the calculated time-frequency domain information is as Figure 10 shown. The series expansion of F(t) can be expressed as:

[0076]

[0077] a0, a k , b k are all amplitude coefficients related to the series expansion, w is the fundamental frequency, and k is the series number.

[0078] Considering that the high-frequency AC component of the graph F(t) is a numerical calculation value and cannot reflect tool wear and machining quality. Therefore, only the low-frequency DC curve F DC is extracted, and the extracted time-frequency signal is as Figure 11 shown. F DC is obtained by the following formula:

[0079]

[0080] Step 500, fuse the high-frequency AC signal and the low-frequency DC signal to reconstruct the broaching force.

[0081] The low-frequency DC part F DC ( Figure 11 (a)) and the high-frequency AC part F AC ( Figure 7(a)) Adding them in the time domain gives Figure 12 The reconstructed broaching force curve f(t) in (a)

[0082] f(t) = FDC AC (12)

[0083] Such as Figure 12 As shown, the broaching force f(t) predicted by the technology of accurately predicting cutting force in the machining field based on the low-frequency bandwidth expansion of the acceleration sensor coincides highly with the broaching force measured by the pressure sensor (3) in the time domain ( Figure 12 a) and the frequency domain ( Figure 12 b). This shows that a cutting force prediction method and system design based on acceleration signals have extremely high accuracy in the field of cutting force prediction.

[0084] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A prediction cutting force system based on acceleration signals, characterized in that It includes a host computer, a data acquisition card, an acceleration sensor, a cutting tool and a workpiece. One of the cutting tool or the workpiece is fixed on the machine tool, and the other is fixed on the cross slide. The cross slide moves along the broaching direction under the drive of the drive system to make the workpiece and the cutting tool move relative to each other, so that the cutting tool removes the metal material of the workpiece. The acceleration sensor is placed on the cross slide to measure the vibration signal of the cross slide along the broaching direction. The acceleration sensor communicates with the data acquisition card, and the acceleration signal collected by the acceleration sensor is transmitted to the data acquisition card. The data acquisition card decodes and amplifies the acquired acceleration signal and then transmits it to the host computer.

2. The predictive cutting force system based on acceleration signals according to claim 1, wherein It further includes a pressure sensor. The pressure sensor is installed between the workpiece and the tooling to measure the cutting force exerted on the workpiece along the cutting direction.

3. The prediction cutting force system according to claim 1, wherein The cutting tool includes a broach.

4. A cutting force prediction method based on an acceleration signal as described in any one of claims 1-3, characterized in that, It includes the following steps: The broach and the workpiece perform a broaching motion at a constant relative speed, and its cutting teeth generate excitation on the workpiece. The pressure sensor measures the broaching force excitation during the broaching motion, and the acceleration sensor measures the vibration response during the broaching process. Use the vibration response and the broaching system transfer function to obtain the high-frequency dynamic AC signal of the broaching force. Use the low-frequency bandwidth expansion technology to reconstruct the low-frequency static DC signal in the broaching force. Determine the waveform of the low-frequency DC signal of the broaching force under this broaching condition by using the metal cutting area of each row of cutting teeth, the workpiece thickness, the broaching speed, and the pitch between rows of teeth, and reconstruct the low-frequency DC signal of the broaching force. Use the high-frequency AC signal reconstructed by the acceleration sensor and the metal cutting area of the broach row teeth to determine the order of magnitude of the low-frequency DC signal. Fuse the high-frequency AC signal and the low-frequency DC signal to reconstruct the broaching force.

5. The cutting force prediction method based on acceleration signals according to claim 4, characterized in that Reconstruct the high-frequency AC signal by using the vibration acceleration data, and reconstruct the low-frequency DC signal by using the low-frequency bandwidth expansion technology.

6. The method for predicting cutting force according to claim 5, characterized in that, The sampling frequency of the pressure sensor is set to be more than 100 times the broaching excitation frequency.

7. The cutting force prediction method based on acceleration signals according to claim 5, characterized in that The signals measured by the pressure sensor and the acceleration sensor are stored in the time domain.

8. The cutting force prediction method based on acceleration signals according to claim 7, characterized in that, The time domain of the vibration acceleration signal is subjected to a fast Fourier transform to obtain the frequency domain. Then, the double integral of the Fourier series expansion of the vibration acceleration signal is performed to obtain the time domain signal of the displacement. After that, a fast Fourier transform is performed again to obtain the displacement frequency domain signal. The displacement is transformed into a broaching force signal through the transfer function of the broaching system. Limited by the low-frequency bandwidth of the vibration sensor, the broaching force signal is subjected to a high-pass filter to obtain an accurate high-frequency AC signal of the broaching force.

9. The cutting force prediction method based on acceleration signals according to claim 4, wherein, The low-frequency DC signal of the reconstructed broaching force is compensated by using the low-frequency bandwidth expansion technology. According to the metal cutting principle, the metal cutting force under the same working conditions is proportional to the metal cutting area.

10. The cutting force prediction method based on acceleration signals according to claim 5, characterized in that The low-frequency DC part F of the broaching force obtained by low-frequency bandwidth extension technology DC and high frequency AC part F AC The reconstructed broaching force curve can be obtained by adding in the time domain.

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