Method and system for precision machining of taper thread of drill rod based on combined turning and milling

Abstract

The present application belongs to the technical field of precision machining, and particularly relates to a drill rod taper thread precision machining method and system based on turning and milling combination, to solve the technical problem that the traditional control strategy is prone to instability and forms machining defects on the thread surface. The machining method comprises: S1, calculating the basic spiral feed amount through a gradual disappearance function; S2, calculating the instantaneous instability index in real time to obtain the cumulative instability index; S3, synchronously adjusting the feed amount and the spindle speed according to the cumulative instability index; S4, using the synthetic feed amount and the instantaneous spindle speed to control the machine tool to complete the finishing machining. The present application suppresses the vibration in the finishing stage, avoids the generation of machining defects, obtains the taper thread with clear profile and excellent surface quality, and improves the connection reliability and service life of the drill rod product.

Description

Technical Field

[0001] This invention belongs to the technical field of precision machining, specifically relating to a precision machining method and system for taper threads on a chisel based on milling and turning. Background Technology

[0002] Drill rods are components used in mining, geological exploration, and geotechnical engineering to transmit impact energy and torque. The tapered thread at their end serves to connect and transmit loads. In mill-turn machining of tapered threads, the thread termination stage is a crucial factor determining machining quality. After completing the helical cut, the tool needs to withdraw from the workpiece surface, forming a complete and clearly defined thread tail. Traditional control methods typically employ a constant helical feed rate throughout the thread machining process, or, at the termination stage, reduce the feed rate according to a preset fixed program, such as linearly or stepwise, to instruct the tool to withdraw.

[0003] However, the control method based on the preset trajectory does not consider the changes in the cutting state during the final stage: as the cutting allowance of the tool gradually decreases and it leaves the workpiece, the cutting force changes, and the stiffness and damping characteristics also change accordingly. This can easily induce regenerative chatter instability at the weak points of the cutting process. The abrupt change causes the tool to produce slight vibrations or path deviations, forming machining defects on the thread surface. This affects the thread's fit accuracy, sealing performance, and connection strength, failing to meet the precision machining requirements of high-performance drill rods. Summary of the Invention

[0004] This invention provides a precision machining method and system for taper threads of drill rods based on milling and turning, in order to solve the technical problem that traditional control strategies are prone to instability and thus form machining defects on the thread surface.

[0005] In a first aspect, the present invention provides a method for precision machining of taper threads on a chisel based on milling and turning, comprising the following steps:

[0006] S1, obtain the taper, pitch and total number of threads to be processed of the drill rod, and set the finishing processing area as the helical path of the last 1.0-1.5 threads; after entering the finishing processing area, calculate the basic helical feed amount based on the remaining length of the tool on the helical path through the fading function. The value of the fading function converges to zero as the remaining length decreases to zero.

[0007] S2, calculate the instantaneous instability index in real time according to the current cutting state; within the preset tool rotation angle window, integrate or weighted average the instantaneous instability index to obtain the cumulative instability index;

[0008] S3, Synchronously adjust the feed rate and spindle speed according to the cumulative instability index: When adjusting the feed rate, determine the modulation function that changes periodically with the tool rotation phase angle. The amplitude of the modulation function in one cutting cycle is proportional to the cumulative instability index. Use the modulation function to modulate the basic helical feed rate to obtain the modulated feed rate; When adjusting the spindle speed, adjust the preset spindle speed according to the cumulative instability index to obtain the instantaneous spindle speed.

[0009] S4. If the instantaneous instability index exceeds the preset instability threshold, the synthetic feed rate is set to the preset minimum safe feed rate; otherwise, the synthetic feed rate is set to the modulated feed rate; the machine tool is controlled to complete the finishing process using the synthetic feed rate and the instantaneous spindle speed.

[0010] Furthermore, the basic helical feed rate is calculated using the implicit function, including:

[0011] The fading function is a cubic polynomial function, and the basic spiral feed rate is... ,in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. This is the total length of the finishing processing area.

[0012] Furthermore, the instantaneous instability index is calculated in real time, including:

[0013] Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder;

[0014] The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz.

[0015] The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

[0016] Furthermore, within a preset tool rotation angle window, the instantaneous instability index is integrated or weighted averaged to obtain a cumulative instability index, including:

[0017] The tool rotation angle window is set to the tool's rotation cycle over the past 360°.

[0018] The arithmetic mean of all instantaneous instability indices collected and calculated within the rotation period is used as the cumulative instability index.

[0019] Furthermore, the modulation function is used to modulate the basic spiral feed amount to obtain the modulated feed amount, including:

[0020] The modulation function is set to a sine function. ,in, The real-time rotation phase angle of the tool; A is the amplitude, and amplitude A is related to the cumulative instability index. The relevant dimensionless values, through The calculation yielded, where The preset dimensionless feed modulation gain, It is the acceleration due to gravity;

[0021] The modulation feed amount ,in, This is the basic spiral feed rate.

[0022] Furthermore, the preset spindle speed is adjusted according to the cumulative instability index to obtain the instantaneous spindle speed, including:

[0023] Set the preset spindle speed When the cumulative instability index When the speed exceeds a preset stability threshold, the spindle speed is reduced using a linear function, resulting in an instantaneous spindle speed. ,in, This is the preset dimensionless speed adjustment coefficient. This is the acceleration due to gravity.

[0024] Furthermore, if the instantaneous instability index exceeds the preset instability threshold, the synthesized feed rate is set to the preset minimum safe feed rate, including:

[0025] When the instantaneous instability index exceeds the instability threshold, the synthetic feed rate is set to 0.02 mm / rev.

[0026] Secondly, the present invention provides a precision machining system for taper threads of chisels based on milling and turning, comprising the following modules:

[0027] The precision machining system for taper threads on chisels based on milling and turning includes the following modules:

[0028] The convergence module obtains the taper, pitch, and total number of threads to be processed of the drill rod, and sets the finishing processing area as the helical path of the last 1.0-1.5 threads; after entering the finishing processing area, based on the remaining length of the tool on the helical path, the basic helical feed is calculated by the fading function, and the value of the fading function converges to zero as the remaining length decreases to zero;

[0029] The calculation module calculates the instantaneous instability index in real time based on the current cutting state; within a preset tool rotation angle window, it integrates or performs a weighted average on the instantaneous instability index to obtain the cumulative instability index.

[0030] The adjustment module synchronously adjusts the feed rate and spindle speed according to the cumulative instability index: When adjusting the feed rate, a modulation function that periodically changes with the tool rotation phase angle is determined. The amplitude of the modulation function within one cutting cycle is proportional to the cumulative instability index. The basic helical feed rate is modulated using the modulation function to obtain the modulated feed rate; when adjusting the spindle speed, the preset spindle speed is adjusted according to the cumulative instability index to obtain the instantaneous spindle speed.

[0031] If the instantaneous instability index exceeds the preset instability threshold, the finishing module sets the synthetic feed rate to the preset minimum safe feed rate; otherwise, it sets the synthetic feed rate to the modulated feed rate. The finishing module uses the synthetic feed rate and the instantaneous spindle speed to control the machine tool to complete the finishing process.

[0032] Furthermore, the basic helical feed rate is calculated using the implicit function, including:

[0033] The fading function is a cubic polynomial function, and the basic spiral feed rate is... ,in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. This is the total length of the finishing processing area.

[0034] Furthermore, the instantaneous instability index is calculated in real time, including:

[0035] Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder;

[0036] The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz.

[0037] The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

[0038] The beneficial effects are as follows: This invention improves the machining quality of taper threads on drill rods by utilizing a composite control strategy based on cutting state feedback during the thread finishing stage. By employing an implicit function to plan the basic helical feed rate, it smoothly converges to zero with the remaining path length, ensuring the inherent smoothness of the path when the tool exits the workpiece. Through real-time calculation of instantaneous instability indices and obtaining cumulative instability indices within the tool rotation angle window, it is possible to detect weak vibration trends during the finishing process and simultaneously adjust the feed rate and spindle speed in a coordinated manner based on these trends. The periodic modulation applied to the feed rate can offset and suppress the accumulation of regenerative chatter; simultaneously, the fine-tuning of the spindle speed optimizes the cutting conditions, bringing the machining process away from the unstable chatter zone. This invention suppresses vibration during the finishing stage, avoids machining defects, and yields taper threads with clear contours and excellent surface quality, improving the connection reliability and service life of drill rod products. Attached Figure Description

[0039] Figure 1 A flowchart of a precision machining method for taper threads on a chisel based on milling and turning;

[0040] Figure 2 A schematic diagram of the basic spiral feed rate attenuation method;

[0041] Figure 3 This is a schematic diagram of the original vibration signal collected.

[0042] Figure 4 This is a schematic diagram of the filtered frequency domain spectrum. Detailed Implementation

[0043] An embodiment of the precision machining method for taper threads of drill rods based on milling and turning provided by this invention:

[0044] like Figure 1 As shown, the precision machining method for taper threads on a chisel based on milling and turning includes the following steps:

[0045] S1. Obtain the taper, pitch, and total number of turns of the thread to be processed on the drill rod, and set the finishing processing area as the helical path of the last 1.0-1.5 turns of the thread; after entering the finishing processing area, calculate the basic helical feed amount based on the remaining length of the tool on the helical path through the fading function. The value of the fading function converges to zero as the remaining length decreases to zero.

[0046] Specifically, the tapered angle of the tapered thread is extracted from a pre-programmed machining program or a 3D model file of the workpiece read by the CNC system. Pitch The system can handle various design parameters, such as the total number of thread turns to be processed. For example, if a drill rod has 20 thread turns, the finishing processing area is set as the helical path from turn 18.5 to turn 20. The CNC system calculates the starting and ending coordinates of the finishing processing area based on the parameters and plans the three-dimensional helical trajectory that the tool center should follow.

[0047] Record the total length of the spiral path in the finishing machining area when the tool enters the starting point of the finishing machining area. During the machining process, the current position of the tool is monitored in real time, and the remaining length of the tool from the end point of the path is calculated. Basic screw feed rate The calculation is performed using a smooth function, such as a half-cosine function: ,in This is the stable cutting feed rate before entering the finishing machining area. This function ensures that the feed rate starts from... The smooth decay to zero avoids the problem of excessively large velocity gradients at the end caused by linear decreases, such as... Figure 2 As shown.

[0048] To achieve a smooth decay of the feed rate as the tool leaves the workpiece and avoid chatter marks or surface defects at the end of machining, in an optional embodiment, the base helical feed rate is calculated using a fading function, including:

[0049] The fading function is a cubic polynomial function, and the basic spiral feed rate is... ,in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. This is the total length of the finishing processing area.

[0050] Specifically, when the tool enters the preset finishing zone, record the initial feed rate and the total length of the spiral in the finishing zone. For example, the initial feed rate... The total length of the finishing processing area is 0.1 mm / rad. It is 5mm.

[0051] As the tool moves along the radial endpoint of the helical path, the remaining length of the helical path is updated in real time. The basic screw feed rate is recalculated based on the cubic polynomial function. Assuming the tool has traveled 2mm, the remaining length is... The length is 3mm, and the basic helical feed rate is 0.0216mm / rad. As the tool is about to leave the workpiece, the remaining length... When reduced to 0.5 mm, the basic helical feed rate drops sharply to 0.0001 mm / rad. Compared to linear decay, cubic decay allows for a rapid and smooth feed rate reduction at the end of the machining path, thereby suppressing shock and vibration upon exiting the cut.

[0052] S2, calculate the instantaneous instability index in real time according to the current cutting state; within the preset tool rotation angle window, integrate or weighted average the instantaneous instability index to obtain the cumulative instability index.

[0053] Specifically, a high-frequency accelerometer or force gauge is installed on the tool holder or workpiece fixture to collect vibration signals or cutting force signals in real time during the cutting process, such as... Figure 3 As shown, the control system acquires signals at a sampling frequency of 10kHz, filters out low-frequency components generated by spindle rotation and feed motion using a high-pass digital filter, retaining only the high-frequency components related to chatter. Within a short time window (e.g., 1ms), the root mean square (RMS) value of the filtered signal is calculated. The RMS value serves as an instantaneous instability index representing the current vibration intensity of the cutting system. .

[0054] One revolution of the tool is defined as an evaluation window, and the real-time rotation angle of the tool is acquired via a spindle encoder. Starting from an arbitrary angle, all instantaneous instability indices within one rotation cycle are continuously acquired and calculated. All within one rotation cycle The cumulative instability index, which reflects the overall vibration level within a cutting cycle, is obtained by summing and averaging the values, or by integrating over time and dividing by the cycle duration. This calculation process continues within the finishing machining area, updating once per tool rotation cycle. value.

[0055] In an optional embodiment, the instantaneous instability index is calculated in real time, including:

[0056] Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder;

[0057] The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz.

[0058] The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

[0059] Specifically, the piezoelectric accelerometer collects the vibration signal of the mechanical vibration and converts it into a continuous voltage signal. The control system digitally samples the voltage signal at a sampling frequency of 20kHz to form the original vibration data stream. For example, 200 discrete vibration data points are collected within a 10ms time period.

[0060] The filter removes all signals with frequencies below 500Hz, such as low-frequency vibrations caused by the machine tool's own structure, and also removes all signals with frequencies above 8kHz, such as high-frequency electrical noise. After processing, only signals in the 500 to 8kHz range are retained, which is precisely the frequency range where cutting chatter most commonly occurs. A Fast Fourier Transform is performed on the filtered data within 10ms to convert the time-domain signal into a frequency-domain spectrum, such as... Figure 4 As shown. Identify the frequency point with the highest amplitude in the frequency domain spectrum. For example, if a peak with an amplitude of 1.5g appears at 3200Hz, then 1.5g is the instantaneous instability index at the current moment.

[0061] To obtain an index that more stably reflects the overall cutting state than the instantaneous value, in an optional embodiment, the instantaneous instability index is integrated or weighted averaged within a preset tool rotation angle window to obtain a cumulative instability index, including:

[0062] The tool rotation angle window is set to the tool's rotation cycle over the past 360°.

[0063] The arithmetic mean of all instantaneous instability indices collected and calculated within the rotation period is used as the cumulative instability index.

[0064] Specifically, a time window is defined, the length of which is equal to the time required for the tool to complete one 360° rotation. For example, if the spindle speed is 6000 revolutions per minute, then each revolution takes 10ms, and this time window is 10ms.

[0065] Since the instantaneous instability index is calculated every 10 ms, in the example of 6000 revolutions per minute, a new instantaneous instability index is generated exactly within each 360° rotation cycle. If the rotation speed is reduced to 3000 revolutions per minute, it takes 20 ms per revolution, and two instantaneous instability indices are calculated within each 360° rotation cycle. Assuming the two instantaneous instability indices obtained within 20 ms are 1.2g and 1.4g, the arithmetic mean of the two instantaneous instability indices is used to calculate the cumulative instability index as 1.3g. The averaging process smooths out the random jumps of individual instantaneous instability indices, providing a reliable assessment of the flutter level.

[0066] S3, Synchronously adjust the feed rate and spindle speed according to the cumulative instability index: When adjusting the feed rate, determine the modulation function that changes periodically with the tool rotation phase angle. The amplitude of the modulation function in one cutting cycle is proportional to the cumulative instability index. Modulate the basic helical feed rate using the modulation function to obtain the modulated feed rate; When adjusting the spindle speed, adjust the preset spindle speed according to the cumulative instability index to obtain the instantaneous spindle speed.

[0067] Specifically, a sinusoidal modulation function is defined. ,in, For the real-time rotation phase angle of the tool, This is a preset phase compensation angle used to compensate for delay. Amplitude A and cumulative instability index. Proportional, that is ,in, This is a preset control gain coefficient. The larger the value, the more intense the vibration, and the larger the amplitude A. The sinusoidal modulation function... The modulated feed rate is obtained by superimposing it onto the basic screw feed rate. This adjustment causes the feed rate to fluctuate actively and in a small, vibration-trend-related manner with each revolution of the tool, suppressing the formation of regenerative chatter.

[0068] Based on cumulative instability index The preset spindle speed is finely adjusted through a control law. For example, when Adjustments are initiated when the instantaneous spindle speed exceeds a relatively low attention threshold. Among them, speed adjustment amount and The value is related, for example G is the speed regulation gain. This is the stability threshold. When instability increases, the spindle speed will decrease or increase slightly, changing the phase relationship between the cutting frequency and the natural frequency, thereby taking the cutting process away from the unstable chatter zone.

[0069] To suppress vibration by varying the feed rate per revolution of the tool, in an optional embodiment, the base helical feed rate is modulated using the modulation function to obtain a modulated feed rate, including:

[0070] The modulation function is set to a sine function. ,in, The real-time rotation phase angle of the tool; A is the amplitude, and amplitude A is related to the cumulative instability index. The relevant dimensionless values, through The calculation yielded, where The preset dimensionless feed modulation gain, It is the acceleration due to gravity;

[0071] The modulation feed amount ,in, This is the basic spiral feed rate.

[0072] Specifically, based on the cumulative instability index Calculate the amplitude A of the sinusoidal modulation function. Assume the current... 2.0g, preset feed modulation gain If the value is 0.05, then the amplitude A is calculated as A = 0.05 × (2.0 g / g) = 0.1. The amplitude A determines the degree of drastic change in the feed rate; the higher the instability, the larger the amplitude.

[0073] Real-time tracking of tool rotation phase angle And a periodic modulation factor is generated using a sine function. For example, when the tool rotates to a 90° phase angle, =1, modulation factor =0.1. When the tool rotates to a phase angle of 270°, =-1, modulation factor =-0.1. Apply the modulation factor to the base screw feed rate. Assuming =0.1mm / rad, at a phase angle of 90°, the modulated feed rate =0.11mm / rad; at a phase angle of 270°, it is 0.09mm / rad. The feed rate fluctuates sinusoidally every revolution, thereby disrupting the regeneration cycle of chatter and achieving a vibration reduction effect.

[0074] To find a more stable cutting zone by fine-tuning the spindle speed when chatter occurs, in one optional embodiment, the instantaneous spindle speed is obtained by adjusting a preset spindle speed according to a cumulative instability index, including:

[0075] Set the preset spindle speed When the cumulative instability index When the speed exceeds a preset stability threshold, the spindle speed is reduced using a linear function, resulting in an instantaneous spindle speed. ,in, This is the preset dimensionless speed adjustment coefficient. This is the acceleration due to gravity.

[0076] Specifically, a preset spindle speed is set. ,For example The speed is set to 10,000 revolutions per minute, with a preset stability threshold, such as 1.2g. Simultaneously, a preset speed adjustment coefficient is set. Set to 0.1, and stipulate that the maximum speed reduction shall not exceed 8%, that is, the minimum speed is 0.92 times the preset speed.

[0077] During the processing, the cumulative instability index is monitored in real time. Assuming Once the pressure rises to 2.2g, exceeding the 1.2g threshold, the speed adjustment program is activated. An adjustment factor is calculated using the following formula: Substituting the data, we get 0.78. The calculated adjustment factor of 0.78 is compared with the preset minimum factor of 0.92, and the larger value, 0.92, is taken. Instantaneous spindle speed. The speed is set to 9200 rpm. This adjustment method can reduce the speed when chatter intensifies, avoiding unstable speed ranges, while preventing excessive speed drop that could affect processing efficiency.

[0078] S4. If the instantaneous instability index exceeds the preset instability threshold, the synthetic feed rate is set to the preset minimum safe feed rate; otherwise, the synthetic feed rate is set to the modulated feed rate; the machine tool is controlled to complete the finishing process using the synthetic feed rate and the instantaneous spindle speed.

[0079] Specifically, an instability threshold representing severe flutter is preset. And a low minimum safe feed rate For example, minimum safe feed rate It is 1% of the nominal feed rate. The instantaneous instability index is calculated in real time during each sampling period. and Compare. If > This indicates that a violent, uncontrolled vibration is about to occur or has already occurred. In this case, abandon the modulated feed rate and switch to the synthetic feed rate. Set as This slows down the speed and protects the tool and workpiece. Conversely, if... Always lower Then it will operate normally, and the synthesis feed rate will be adjusted accordingly. Equal to the modulation feed amount calculated above .

[0080] The control system will calculate the synthetic feed rate in real time. and instantaneous spindle speed As instructions, these are sent to the CNC core of the machine tool within each control cycle. The interpolation module of the CNC core then... The speed commands of each feed axis, such as the Z-axis and C-axis, on the helical path are calculated in real time, and the movement of each axis motor and the spindle motor is controlled by the servo driver. This achieves closed-loop control of the tool's motion posture and cutting state in the finishing stage until the tool completely exits the workpiece, completing the entire finishing process.

[0081] In an optional embodiment, if the instantaneous instability index exceeds a preset instability threshold, the synthetic feed rate is set to a preset minimum safe feed rate, including:

[0082] When the instantaneous instability index exceeds the instability threshold, the synthetic feed rate is set to 0.02 mm / rev.

[0083] Specifically, in the control system, a high vibration threshold, or instability threshold, is preset at 3.5g. This value represents a severe chatter state that could cause permanent damage to the tool, spindle, or workpiece. Simultaneously, a minimum safe feed rate, such as 0.02mm / rad, is preset, which is a low feed rate that generates almost no cutting force.

[0084] During the cutting process, the transient instability index is monitored at a high frequency, such as every 10ms. Assuming that under normal machining conditions, the transient instability index fluctuates between 0.5g and 1.5g, the synthesized feed rate might be around 0.1mm / rad. If, due to material inhomogeneity or other unforeseen circumstances, the transient instability index suddenly spikes to 3.6g, exceeding the 3.5g instability threshold, an emergency response will be immediately triggered. All other feed rate calculations, including the base feed rate and modulated feed rate, will be ignored, and the machine tool's synthesized feed rate command will be modified to the preset minimum safe feed rate of 0.02mm / rad. This reduces the cutting load, prevents tool breakage or workpiece scrap, and buys time for operator intervention or recovery.

[0085] An embodiment of the precision machining system for taper threads of chisels based on milling and turning provided by this invention:

[0086] The precision machining system for taper threads on chisels based on milling and turning includes the following modules:

[0087] The convergence module obtains the taper, pitch, and total number of threads to be processed of the drill rod, and sets the finishing processing area as the helical path of the last 1.0-1.5 threads; after entering the finishing processing area, based on the remaining length of the tool on the helical path, the basic helical feed is calculated by the fading function, and the value of the fading function converges to zero as the remaining length decreases to zero;

[0088] The calculation module calculates the instantaneous instability index in real time based on the current cutting state; within a preset tool rotation angle window, it integrates or performs a weighted average on the instantaneous instability index to obtain the cumulative instability index.

[0089] The adjustment module synchronously adjusts the feed rate and spindle speed according to the cumulative instability index: When adjusting the feed rate, a modulation function that periodically changes with the tool rotation phase angle is determined. The amplitude of the modulation function within one cutting cycle is proportional to the cumulative instability index. The basic helical feed rate is modulated using the modulation function to obtain the modulated feed rate; when adjusting the spindle speed, the preset spindle speed is adjusted according to the cumulative instability index to obtain the instantaneous spindle speed.

[0090] If the instantaneous instability index exceeds the preset instability threshold, the finishing module sets the synthetic feed rate to the preset minimum safe feed rate; otherwise, it sets the synthetic feed rate to the modulated feed rate. The finishing module uses the synthetic feed rate and the instantaneous spindle speed to control the machine tool to complete the finishing process.

[0091] In an optional embodiment, the basic helical feed rate is calculated using a fade-out function, including:

[0092] The fading function is a cubic polynomial function, and the basic spiral feed rate is... ,in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. This is the total length of the finishing processing area.

[0093] In an optional embodiment, the instantaneous instability index is calculated in real time, including:

[0094] Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder;

[0095] The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz.

[0096] The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

[0097] In addition, in the description of this specification, "multiple" means at least two, such as two, three or more, etc., unless otherwise expressly and specifically defined.

Claims

1. A method for precision machining of taper threads on a chisel based on milling and turning, characterized in that, Includes the following steps: S1, obtain the taper, pitch and total number of threads to be machined of the drill rod, and set the finishing processing area as the helical path of the last 1.0-1.5 threads; after entering the finishing processing area, calculate the basic helical feed amount based on the remaining length of the tool on the helical path through the fading function, including: the fading function is a cubic polynomial function; Basic screw feed , in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. This is the total length of the finishing processing area; The value of the fading function converges to zero as the remaining length decreases to zero. S2, calculate the instantaneous instability index in real time according to the current cutting state; within the preset tool rotation angle window, integrate or weighted average the instantaneous instability index to obtain the cumulative instability index. S3, Synchronously adjust the feed rate and spindle speed according to the cumulative instability index: When adjusting the feed rate, determine the modulation function that periodically changes with the tool rotation phase angle. The amplitude of the modulation function within one cutting cycle is proportional to the cumulative instability index. Use the modulation function to modulate the basic helical feed rate to obtain the modulated feed rate, including: Set the modulation function to a sine function ,in, The real-time rotational phase angle of the tool; A is the amplitude, and amplitude A is related to the cumulative instability index. The relevant dimensionless values, through The calculation yielded, where The preset dimensionless feed modulation gain, It is the acceleration due to gravity; Modulated feed rate ; When adjusting the spindle speed, the preset spindle speed is adjusted according to the cumulative instability index to obtain the instantaneous spindle speed, including: Set the preset spindle speed When the cumulative instability index When the spindle speed exceeds the preset stability threshold, the spindle speed is reduced using a linear function. Instantaneous spindle speed ,in, This is the preset dimensionless speed adjustment coefficient; S4. If the instantaneous instability index exceeds the preset instability threshold, the composite feed rate is set to the preset minimum safe feed rate; otherwise, the composite feed rate is set to the modulated feed rate. The composite feed rate and instantaneous spindle speed are used to control the machine tool to complete the finishing process.

2. The precision machining method for taper threads of drill rods based on milling and turning as described in claim 1, characterized in that, Real-time calculation of instantaneous instability indices, including: Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder; The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz. The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

3. The precision machining method for taper threads of drill rods based on milling and turning as described in claim 2, characterized in that, Within a preset tool rotation angle window, the instantaneous instability index is integrated or weighted averaged to obtain the cumulative instability index, including: The tool rotation angle window is set to the tool's rotation cycle over the past 360°. The arithmetic mean of all instantaneous instability indices collected and calculated within the rotation period is used as the cumulative instability index.

4. The precision machining method for taper threads of a drill rod based on milling and turning as described in any one of claims 1-3, characterized in that, If the instantaneous instability index exceeds the preset instability threshold, the synthesized feed rate will be set to the preset minimum safe feed rate, including: When the instantaneous instability index exceeds the instability threshold, the synthetic feed rate is set to 0.02 mm / rev.

5. A precision machining system for taper threads of drill rods based on milling and turning, characterized in that, Includes the following modules: The convergence module obtains the taper, pitch, and total number of threads to be machined on the drill rod, and sets the finishing machining area as the helical path of the last 1.0-1.5 threads. After entering the finishing machining area, based on the remaining length of the tool on the helical path, it calculates the basic helical feed rate using a fading function, including: The fading function is a cubic polynomial function, and the basic spiral feed rate is... ,in This is the initial feed rate when entering the finishing processing area. This represents the remaining length of the spiral path. The total length of the finishing processing area; the value of the fading function converges to zero as the remaining length decreases to zero; The calculation module calculates the instantaneous instability index in real time based on the current cutting state; within a preset tool rotation angle window, it integrates or performs a weighted average on the instantaneous instability index to obtain the cumulative instability index. The adjustment module synchronously adjusts the feed rate and spindle speed based on the cumulative instability index. When adjusting the feed rate, a modulation function that periodically changes with the tool rotation phase angle is determined. The amplitude of the modulation function within one cutting cycle is proportional to the cumulative instability index. The modulation function is used to modulate the basic helical feed rate to obtain the modulated feed rate, including: The modulation function is set to a sine function. ,in, The real-time rotation phase angle of the tool; A is the amplitude, and amplitude A is related to the cumulative instability index. The relevant dimensionless values, through The calculation yielded, where The preset dimensionless feed modulation gain, It is the acceleration due to gravity; The modulation feed amount ,in, The basic spiral feed rate; When adjusting the spindle speed, the preset spindle speed is adjusted according to the cumulative instability index to obtain the instantaneous spindle speed, including: Set the preset spindle speed When the cumulative instability index When the speed exceeds a preset stability threshold, the spindle speed is reduced using a linear function, resulting in an instantaneous spindle speed. ,in, This is the preset dimensionless speed adjustment coefficient. It is the acceleration due to gravity; If the instantaneous instability index exceeds the preset instability threshold, the finishing module sets the synthetic feed rate to the preset minimum safe feed rate; otherwise, it sets the synthetic feed rate to the modulated feed rate. The finishing module uses the synthetic feed rate and the instantaneous spindle speed to control the machine tool to complete the finishing process.

6. The precision machining system for taper threads of drill rods based on milling and turning as described in claim 5, characterized in that, Real-time calculation of instantaneous instability indices, including: Vibration signals during the cutting process are collected by a piezoelectric accelerometer mounted on the tool holder; The signal output from the piezoelectric accelerometer is sampled at a sampling frequency of 20kHz and bandpass filtered to remove signals with frequencies below 500Hz and above 8kHz. The filtered signal is subjected to a Fast Fourier Transform every 10ms to extract the amplitude at the characteristic frequency of the cutting chatter, and the amplitude is used as the instantaneous instability index.

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