A method for automatically feeding a drill spindle current adaptive counter sinking

Abstract

The application discloses an automatic feeding drill spindle current adaptive counterbore method, and specifically comprises the following steps: according to the counterbore hole to be machined and the cutter size parameters, the machining parameters of the drill counterbore process are determined, and the machining parameters are written into a control program. The control program first executes a hole making process, and after the drilling is completed, a spindle current adaptive counterbore identification program is started. A filtering technology combining software and hardware is adopted to filter out high-frequency noise signals and low-frequency vibration signals in real time. In the counterbore process, the spindle current signals of N points are extracted in real time, and the real-time spindle current gradients of the N points are calculated. According to the functional relationship between the spindle current gradient of the counterbore starting stage and the real-time spindle current gradient of the counterbore stable stage, the intersection point of the two functions is determined, and then the starting point of the counterbore is identified. Then, the counterbore endpoint is updated according to the preset counterbore depth, and the accurate control of the counterbore depth is realized. Compared with the traditional counterbore method which depends on the proficiency of workers, the application realizes the accurate control of the counterbore depth by monitoring the spindle current in real time and identifying the counterbore starting point, significantly improves the hole diameter consistency and the reliability of the counterbore quality, and solves the problem of accurately controlling the counterbore depth.

Description

Technical Field

[0001] This invention relates to the field of hole-making technology in the assembly process of aerospace components and aircraft, and in particular to an automatic feed drill spindle current adaptive countersinking method. Background Technology

[0002] With the rapid development of the aviation industry, aerospace materials such as CFRP, titanium alloys, and aluminum alloys are increasingly widely used in aircraft laminated structures. These laminated structures fully utilize the advantages of various materials, improving the structural strength of the aircraft, reducing weight, and lowering energy consumption. These laminated structures are typically connected using bolts or countersunk rivets, which requires countersunk machining of the connecting holes.

[0003] The error in countersunk depth largely depends on the operator's skill level. Too shallow a countersunk depth will cause fasteners to protrude from the workpiece surface, reducing the contact area between the connector and the skin, thus lowering the connection strength; while too deep a countersunk depth will reduce the structural thickness at the connection, similarly affecting connection strength. To ensure that countersunk rivets or bolts are flush with the workpiece surface after installation, the countersunk depth must be strictly controlled within a certain range. Precisely controlling the countersunk depth is a challenge in the aerospace assembly field.

[0004] When machining aerospace materials such as CFRP, titanium alloys, and aluminum alloys, traditional automatic feed drills typically rely on spindle limiters for axial accuracy control. As described in the literature "Research on High-Precision Semi-Automatic Countersinking Technology for Large-Diameter Titanium Alloys," the relative position of the tool and workpiece is not fixed during automatic feed drilling due to the inconsistent distance between the drill template and the workpiece, making it difficult to control the countersinking depth. Furthermore, the drill tip undergoes micro-deformation due to heat and its own rigidity during the drilling and countersinking process, further complicating the control of the countersinking depth.

[0005] To address the challenge of precisely controlling the depth of countersinking, the author's previous invention patent CN202210728909.3 proposed a control system and method for an automatic feed drill used in aerospace assembly. This method describes an electronically controlled approach for controlling the axial position of the spindle. This electronically controlled approach can accurately calculate the distance between the drill template and the workpiece by setting the zero-point position of the drill tip and monitoring the relative position. Building upon this, this patent proposes an adaptive countersinking method for the automatic feed drill spindle current, utilizing real-time spindle current monitoring, filtering, and feature extraction techniques during the automatic feed drill's countersinking process. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide an automatic feed drill spindle current adaptive countersinking method to solve the problem of how to accurately control the countersinking depth in the aerospace assembly field.

[0007] Technical solution: To achieve the above objectives, the present invention provides an automatic feed drill spindle current adaptive countersinking method, comprising the following steps:

[0008] Step S1: Determine the machining parameters for the drilling and countersinking process based on the countersink hole and tool size parameters, and write them into the control system (CN114995257A An automatic feed drilling control system and control method for aerospace assembly).

[0009] Step S2: The control system first executes the hole-making process, and after drilling is completed, it starts the spindle current adaptive countersinking identification program.

[0010] Step S3: Use a filter to filter out high-frequency noise signals and low-frequency vibration signals in real time.

[0011] Step S4: During the countersinking process, mark the real-time spindle current signal as I. S (t). Set the sliding window to N, extract N data points at a time, and calculate the slope of the N data points using the following linear regression formula, denoted as k. IS (t);

[0012]

[0013] Among them, I S (t) is the real-time current signal of the spindle, and t is the real-time machining time recorded by the software.

[0014] Step S5: Calculate the current gradient in the initial stage of the countersinking based on historical data, and label it as k. INI (t).

[0015] Step S6: Based on k IS (t) and k INI (t) Establish a function model and find the intersection point of the function model, which is marked as P. Point P is the starting point of the countersink.

[0016] Step S7: Slide the window and update N data points, then the spindle current gradient k IS (t) is updated accordingly, and point P is also updated accordingly.

[0017] Step S8: Update the countersink endpoint according to the preset countersink depth, thereby achieving precise control of the countersink depth.

[0018] Furthermore, the spindle current signal filtering method described in step S3 can employ not only IIR filters but also filters such as FFT.

[0019] Furthermore, the slope calculation method described in step S4 can be implemented not only by the sliding window method, but also by the Kalman filter optimal estimation method or the numerical differentiation method.

[0020] Furthermore, the process of adaptively adjusting the initial position of the countersink includes real-time monitoring of spindle current changes and dynamic feedback to the control system to achieve real-time control of the countersink depth.

[0021] Furthermore, the starting point of the countersinking is the intersection of the real-time window function and the initial countersinking function model during the countersinking process. As the countersinking depth increases, the countersinking process becomes more stable. Therefore, the accuracy of the algorithm in identifying the starting point of the countersinking gradually improves as the countersinking process progresses.

[0022] Furthermore, since the spindle adopts a precise position control mode, when the system identifies the starting point of the countersink, it can determine the ending point of the countersink according to the preset countersink depth, thereby achieving precise control of the countersink depth.

[0023] Furthermore, the automatic feed drill spindle current adaptive countersinking method can adapt to different types of materials. These materials include aerospace materials such as aluminum alloys, titanium alloys, and CFRP, as well as other materials.

[0024] Furthermore, the automatic feed drill spindle current adaptive countersinking method described above can adapt to different drilling processes. These drilling processes include not only traditional drilling but also various other drilling techniques such as spiral milling, ultrasonic vibration drilling, and low-frequency vibration drilling, demonstrating broad application prospects and flexibility.

[0025] Furthermore, by analyzing the current signal during the machining process, the cutting status of the tool during the countersinking process can also be determined in real time, such as overload and tool wear.

[0026] Furthermore, the automatic feed drill spindle current adaptive countersinking method proposed in this paper is innovative in that it can achieve intelligent decision-making by adding sensing devices such as force sensors and acoustic emission sensors, and by learning from historical data, so as to further improve the stability and accuracy of the drilling and countersinking process.

[0027] The beneficial effects and innovative points of this invention are as follows:

[0028] 1. Signal processing technology: This method uses advanced hardware and software filtering technology to process the spindle current signal collected at the motor end, and completes real-time feature extraction and display of the spindle current on the host computer.

[0029] 2. Current Adaptive Mechanism: This method is based on real-time acquisition of spindle current signal, which can automatically find the starting point of the countersink and then update the end point of the countersink through the preset countersink depth. This adaptive mechanism can control the countersink depth more accurately than the traditional method.

[0030] 3. Multi-process compatibility: This method is applicable to a variety of drilling processes, including traditional drilling, spiral milling, ultrasonic vibration drilling, and low-frequency vibration drilling.

[0031] 4. Wide range of material applicability: This method is not only applicable to aerospace materials such as aluminum alloys, titanium alloys and CFRP, but also to other materials such as steel and copper, demonstrating its diverse range of applications. Attached Figure Description

[0032] Figure 1 The flowchart of the current adaptive countersinking algorithm provided by this invention;

[0033] Figure 2 This is a diagram of the spindle current signal collected during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure provided in Embodiment 1 of the present invention; Figure 3 An identification diagram of the starting point of the countersink during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure provided in Embodiment 1 of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0035] Example 1: Adaptive method for spindle current when machining TC4 / TC4 stacked structures.

[0036] like Figure 1 The diagram shown is a flowchart of the current-adaptive countersinking method provided by this invention. It consists of eight steps, which have been described in detail in the invention description and will not be repeated here.

[0037] In this embodiment, the drilling diameter of the tool is 6mm, the countersink diameter is 12mm, and based on the tool's basic information, the drill tip height is 1.73mm, the effective countersink depth is 3mm, and the distance from the drill tip to the countersink starting point is 21.65mm. Before machining, the machining parameters are set according to the material to be machined. The drilling parameters used for the TC4 / TC4 stacked structure are n. s =600rpm, f=0.03mm / r; countersinking parameters set to n s =300rpm, f=0.02mm / r. And MQL cooling mode is activated.

[0038] The drilling and countersinking program is started, and the control system captures the spindle current signal and spindle position in real time during the machining process and reports them to the host computer for real-time display. According to the formula... Determine the vibration frequency f during the spindle countersinking process osc The spindle speed n in this embodiment 1 s The speed is 300 rpm, and the frequency-to-speed ratio ω is 2.5 osc / r. Therefore, the vibration frequency is 12.5 Hz.

[0039] To filter out low-frequency vibration signals, an IIR filter is built into the control system software, and with f lowA Butterworth filter with a frequency of 8Hz is used for low-pass filtering. The Butterworth filter provides a very flat gain response within the passband with no obvious fluctuations. This allows this software filtering method to maintain signal integrity within the channel, improve the accuracy of countersink initiation point identification, and facilitate subsequent countersink gradient calculation.

[0040] like Figure 2 The image shown is a diagram of the spindle current signal collected during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure provided by this invention. According to... Figure 2 The information shown indicates that the drilling and countersinking process of the TC4 / TC4 stacked structure can be further divided into five stages. Stage 1 represents the no-load stage between the drill tip and the drill template; Stage 2 represents the drilling stage of the TC4 / TC4 stack; Stage 3 represents the no-load stage, because the thickness of the TC4 / TC4 stacked structure is only 6mm, while the distance from the drill tip to the starting point of the countersink is 21.65mm; Stage 4 is the countersinking stage. Figure 2 As shown, the starting and ending points of the countersink can be clearly observed in the spindle current curve. Stage 5 is the drilling stage. Stages 1 and 3 are the no-load stages, during which the tool surface still experiences slight friction with the material and drill bushing, resulting in a small spindle current.

[0041] Figure 3 This is an identification diagram of the starting point of the countersink during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure provided by this invention. (Example:) Figure 3 As shown, stage 4 (counterfeiting stage) can be further subdivided into stage 4a and stage 4b. Stage 4a represents the initial stage of counterfeiting, and stage 4b ​​represents the stable stage of counterfeiting. The principal shaft current slope in stage 4a is denoted as k. IS1 The principal shaft current slope in stage 4b ​​is denoted as k. IS2 . Figure 3 It can be clearly seen that the function curve of stage 4a and the function curve of stage 4b ​​intersect at a point, which is the starting point P of the countersink.

[0042] To search for the starting point of the countersink, this embodiment provides a sliding window method, based on the formula... The vibration period in Example 1 was determined to be 80 ms, and the sampling period for the spindle current was 2 ms. Assuming each sliding window represents two vibration periods, N was set to 40. Therefore, the slope gradient during the countersinking stage can be expressed by the following formula:

[0043]

[0044] It is important to note here that the principal shaft current slope k in stage 4a... IS1 It can learn from historical data.

[0045] By determining the principal shaft current slope k in stage 4aIS1 and the real-time updated spindle current slope k of the 4b stage IS2 Establish a system of functional equations. The system of functional equations in Case 1 can be expressed as follows:

[0046]

[0047] In the system of functional equations, the starting point of the countersink is the equivalent point of the system of equations. Therefore, by solving the system of functional equations, the starting point of the countersink can be determined, and then the ending point of the countersink can be determined by a preset countersink depth (the countersink depth provided in this embodiment is 3mm). As the countersink depth increases, the countersinking process becomes more stable; therefore, the accuracy of the algorithm in identifying the starting point of the countersink gradually improves as the countersinking process progresses.

[0048] An adaptive countersinking method for automatic feed drills, utilizing spindle current, monitors the spindle current in real time. It employs a combination of rapid hardware and software filtering and signal processing to remove high-frequency noise and low-frequency vibration signals. Then, it calculates the spindle current gradient during the countersinking stage based on the spindle current characteristics. Subsequently, it searches for the countersinking start point based on this gradient and updates the countersinking end point according to a preset countersinking depth. This method solves the challenge of precisely controlling the countersinking depth through signal processing, feature extraction techniques, and an adaptive current mechanism. This method is adaptable to the processing requirements of different materials and drilling processes, and has broad application prospects.

[0049] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. An automatic feed drill spindle current adaptive countersinking method, characterized in that, Includes the following steps: Step S1: Determine the machining parameters for the drilling and countersinking process based on the countersink hole and tool size parameters, and write them into the automatic feed drill control system for aerospace assembly. Step S2: The control system first executes the hole-making process, and after drilling is completed, it starts the spindle current adaptive countersinking identification program; Step S3: Use a filter to filter out high-frequency noise signals and low-frequency vibration signals in real time; Step S4: During the countersinking process, mark the real-time spindle current signal as I. S (t); Set the sliding window to N, extract N data points each time, and calculate the slope of the N data points using a linear regression formula, denoted as k. IS (t); Step S5: Calculate the current gradient in the initial stage of the countersinking based on historical data, and label it as k. INI (t); Step S6: Based on k IS (t) and k INI (t) Establish a function model and find the intersection point of the function model, which is marked as P. Point P is the starting point of the countersink. Step S7: Slide the window and update N data points, then the spindle current gradient k IS (t) is updated accordingly, and point P is also updated accordingly; Step S8: Update the countersink endpoint according to the preset countersink depth, thereby achieving precise control of the countersink depth.

2. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, The filter described is either an IIR filter or an FFT filter.

3. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, In step S4, the slope calculation method adopts the sliding window method, or the Kalman filter optimal estimation method or the numerical differentiation method.

4. The automatic feed drill spindle current adaptive countersinking method according to claim 3, characterized in that, When the slope is calculated using the sliding window method, the sliding window size is set to N, and the principal spindle current gradient k IS (t) can be expressed as ； Among them, I S (t) is the real-time current signal of the spindle, and t is the real-time machining time recorded by the software.

5. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, In step S8, the spindle current change is monitored in real time and dynamically fed back to the control system to realize the real-time search of the countersink starting point. Then, the countersink ending point is updated by the preset countersink depth to realize the real-time control of the countersink depth.

6. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, In step S6, according to k IS (t) and k INI The function model established by (t) is as follows: ； in, It is the slope of N data points in the initial stage of countersinking. t is the slope of N data points during the stable phase of the countersink, and t is the real-time processing time recorded by the software. This is the spindle current value at the beginning of the countersinking process. This is the spindle current value during the stable phase of the countersink. The starting point of the countersinking is the intersection of the real-time window function and the initial countersinking function model during the countersinking process.

7. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, The materials to which this method is applicable include, but are not limited to, aerospace materials such as aluminum alloys, titanium alloys, and CFRP.

8. The automatic feed drill spindle current adaptive countersinking method according to claim 1, characterized in that, The drilling processes applicable to this method include, but are not limited to, traditional drilling, spiral milling, ultrasonic vibration drilling, and low-frequency vibration drilling.

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