Current self-adaptive dimpling method for automatic feeding drill spindle

Abstract

The invention discloses a current self-adaptive dimple method for a main shaft of an automatic feeding drill, which specifically comprises the following steps of: determining machining parameters of a drilling and dimple process according to a dimple hole to be machined and a cutter size parameter, and writing the machining parameters into a control program; the control program firstly executes the hole making process, and after drilling is completed, the main shaft current self-adaption dimple recognition program is started. A filtering technology combining software and hardware is adopted, and high-frequency noise signals and low-frequency vibration signals are filtered out in real time. In the dimpling process, spindle current signals of N points are extracted in real time, and the real-time spindle current gradients of the N points are calculated; and determining an intersection point of two functions according to a functional relationship between the main shaft current gradient of the dimple initial stage and the real-time main shaft current gradient of the dimple stable stage, and further identifying the dimple initial point. And then, the dimple end point is updated according to the preset dimple depth, and accurate control over the dimple depth is achieved. Compared with a traditional dimple method depending on the operation proficiency of workers, the method has the advantages that accurate control over the dimple depth is achieved by monitoring the current of the main shaft in real time and recognizing the dimple start, the aperture consistency and the reliability of the dimple quality are remarkably improved, and the problem of accurate control over the dimple depth is solved.

Description

Technical Field

[0001] The invention relates to the technical field of hole making in the process of assembling aerospace components and aircraft, and in particular to an automatic feed drill spindle current adaptive countersinking method. Background Art

[0002] With the rapid development of the aviation industry, CFRP, titanium alloy, aluminum alloy and other aviation materials are increasingly used in aircraft laminated structures. This type of laminated structure gives full play to the advantages of various materials, improves the structural strength of the aircraft, reduces weight and reduces energy consumption. This type of laminated structure is usually connected by bolts or countersunk rivets, which requires countersinking of the connection holes.

[0003] The error of countersink depth depends largely on the worker's proficiency. If the depth is too shallow, the fastener will protrude from the workpiece surface, reducing the contact area between the fastener and the skin and reducing the connection strength; while if the depth is too large, the structural thickness of the connection will be reduced, which will also affect the connection strength. To ensure that the countersunk rivet or bolt is flush with the workpiece surface after installation, the depth of the countersink must be strictly controlled within a certain range. How to accurately control the depth of the countersink is a difficult problem in the field of aviation assembly.

[0004] When processing aviation materials such as CFRP, titanium alloy, and aluminum alloy, traditional automatic feed drills usually rely on spindle limiters for axial precision control. As described in the document "Research on Semi-automatic Countersinking Technology for Large-aperture High-precision Titanium Alloys", due to the inconsistent distance between the drill template and the workpiece, the relative position of the tool and the workpiece is not fixed during automatic feed drilling countersinking, making it difficult to control the countersinking depth. In addition, during the countersinking process, the drill tip will also be slightly deformed due to the influence of heat and its own rigidity, which makes the countersinking depth even more difficult to control.

[0005] In order to solve the problem of accurately controlling the depth of countersinking, the author's previous invention patent CN202210728909.3 proposed an automatic feed drill control system and control method for aviation assembly. This method explains that the axial position control of the spindle can rely on an electric control method. This electric control method can accurately calculate the distance between the drill template and the workpiece by setting the working zero position of the drill tip and monitoring the relative position. On this basis, this patent uses real-time spindle current monitoring, filtering and feature extraction technology of the automatic feed drill countersinking process to propose an automatic feed drill spindle current adaptive countersinking method. Summary of the invention

[0006] Purpose of the invention: The purpose of the present 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 field of aviation assembly.

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

[0008] Step S1: Determine the processing parameters of the countersinking process according to the countersinking hole to be processed and the tool size parameters, and write them into the control system (CN114995257A A control system and control method for automatic feed drill for aviation assembly).

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

[0010] Step S3: Using 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 current signal of the spindle as I S (t). Set the sliding window to N, extract N data each time, and use the following linear regression formula to calculate the slope of N data, marked 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 processing time recorded by the software.

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

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

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

[0017] Step S8: updating the countersinking end point according to the preset countersinking depth, thereby achieving precise control of the countersinking depth.

[0018] Furthermore, the spindle current signal filtering method described in step S3 may use not only an IIR filter but also a filter such as FFT.

[0019] Furthermore, the slope calculation method described in step S4 may not only adopt a sliding window method, but also a Kalman filter optimal estimation method or a numerical differentiation method.

[0020] Furthermore, the process of adaptively adjusting the initial position of the countersink includes real-time monitoring of the spindle current change and dynamically feeding back to the control system to achieve real-time control of the countersink depth.

[0021] Furthermore, the countersink starting point is the intersection of the real-time window function and the initial countersink 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 countersinking starting point will gradually increase with the countersinking process.

[0022] Furthermore, since the spindle adopts a precise position control mode, when the system identifies the starting point of the countersinking, the end point of the countersinking can be determined according to the preset countersinking depth, thereby achieving precise control of the countersinking depth.

[0023] Furthermore, the automatic feed drill spindle current adaptive countersinking method can adapt to different types of materials, including aviation materials such as aluminum alloy, titanium alloy, CFRP and other materials.

[0024] Furthermore, the automatic feed drill spindle current adaptive countersinking method can adapt to different drilling processes. The drilling process includes not only traditional drilling, but also spiral milling, ultrasonic vibration drilling, low-frequency vibration drilling and other drilling technologies, which has broad application prospects and flexibility.

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

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

[0027] Beneficial effects and innovations of the present invention:

[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 the real-time feature extraction and display of the spindle current on the host computer.

[0029] 2. Current adaptive mechanism: This method is based on the real-time collected spindle current signal, which can automatically find the starting point of the countersinking, and then update the countersinking end point by the preset countersinking depth. Compared with the traditional method, this adaptive mechanism can control the countersinking depth more accurately.

[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 aviation materials such as aluminum alloy, titanium alloy and CFRP, but also to other materials such as steel and copper, showing its diversified scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of the current adaptive countersinking algorithm provided by the present invention;

[0033] Figure 2 A graph of spindle current signals collected during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure provided in Example 1 of the present invention; Figure 3 An identification diagram of the countersink starting point during the integrated drilling and countersinking process of the TC4 / TC4 laminated structure provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0035] Embodiment 1: Spindle current self-adaptation method when processing TC4 / TC4 stacked structure.

[0036] like Figure 1 The figure shows a flow chart of the current adaptive countersinking method provided by the present invention, which is divided into eight steps, which have been specifically described in the content of the invention and will not be repeated here.

[0037] In this embodiment, the drilling diameter of the tool is 6mm, the countersink diameter is 12mm, and according to the basic information of the tool, it can be known that 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 processing, the processing parameters are set according to the material to be processed. The drilling parameters used for the TC4 / TC4 stacked structure are n s =600rpm, f=0.03mm / r; countersinking parameters are set to n s =300rpm, f=0.02mm / r. And start MQL cooling mode.

[0038] Start the drilling and countersinking program, and the control system captures the spindle current signal and real-time spindle position of the machining process in real time and reports it to the host computer for real-time display. Determine the vibration frequency f of the spindle during countersinking osc The spindle speed n of this embodiment 1 is 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] In order to filter out low-frequency vibration signals, an IIR filter is built into the control system software, and the f low=8Hz Butterworth filter for low pass filtering. Butterworth filter can provide a very flat gain response in the passband without obvious fluctuations, which enables this software filtering method to maintain the integrity of the signal in the channel, improve the accuracy of the identification of the countersink starting point, and facilitate the subsequent calculation of the countersink gradient.

[0040] like Figure 2 As shown, the spindle current signal diagram collected during the integrated drilling and countersinking process of the TC4 / TC4 stacked structure is provided for the present invention. Figure 2 The information shown in the figure shows that the countersinking process of the TC4 / TC4 stacking structure can be specifically 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 stacking; Stage 3 represents the no-load stage, which is because the thickness of the TC4 / TC4 stacking structure is only 6mm, and the distance from the drill tip to the countersinking starting point is 21.65mm; Stage 4 is the countersinking stage. Figure 2 As shown in the figure, the countersink starting point and the countersink end point can be clearly observed in the spindle current curve. Stage 5 is the drilling stage. Stages 1 and 3 are no-load stages, at which the tool surface still has slight friction with the material and the drill sleeve, so there will be a small spindle current.

[0041] Figure 3 This is an identification diagram of the countersink starting point during the integrated drilling and countersinking process of the TC4 / TC4 laminated structure provided by the present invention. Figure 3 As shown in Figure 4, stage 4 (countersinking stage) can be divided into stage 4a and stage 4b. Stage 4a represents the initial stage of countersinking, and stage 4b ​​represents the stable stage of countersinking. The spindle current slope of stage 4a is marked as k IS1 , the main shaft current slope of phase 4b is marked as k IS2 . Figure 3 It can be clearly seen that there is an intersection between the function curve of stage 4a and the function curve of stage 4b, which is the starting point P of the countersinking.

[0042] In order to search for the countersink starting point, this embodiment provides a sliding window method, according to the formula The vibration period of Example 1 is determined to be 80ms, and the sampling period of the spindle current is once every 2ms. Assuming that each sliding window is two vibration periods, N is set to 40. Therefore, the slope gradient of the countersinking stage can be expressed by the following formula:

[0043]

[0044] It should be noted here that the spindle current slope k in stage 4a is IS1 Can be learned from historical data.

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

[0046]

[0047] In the function equation group, the countersink starting point is the equivalent point of the function equation group. Therefore, the countersink starting point can be determined by solving the function equation group, and then the countersink end point can be determined by the preset countersink depth (the countersink depth provided in this embodiment is 3mm). As the countersink depth increases, the countersink process becomes more stable; therefore, the accuracy of the algorithm in identifying the countersink starting point will gradually increase as the countersink process proceeds.

[0048] The automatic feed drill spindle current adaptive countersinking method monitors the spindle current in real time, uses fast software and hardware combined filtering and signal processing methods to filter out high-frequency noise and low-frequency vibration signals, and then calculates the spindle current gradient in the countersinking stage through the spindle current characteristics, and then searches for the countersinking starting point according to the spindle current gradient in the countersinking stage, and updates the countersinking end point according to the preset countersinking depth. This method solves the problem of accurately controlling the countersinking depth through signal processing and feature extraction technology and current adaptive mechanism. This method can adapt to the processing requirements of different materials and different drilling processes, and has broad application prospects.

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

Claims

1. An automatic feed drill spindle current adaptive countersinking method, characterized in that: The following steps are involved: Step S1: Determine the processing parameters of the countersinking process according to the countersinking hole to be processed and the tool size parameters, and write them into the automatic feed drill control system for aviation assembly; Step S2: The control system first executes the hole making process, and after the drilling is completed, starts the spindle current adaptive countersink recognition program; Step S3: Using 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 current signal of the spindle as I S (t); Set the sliding window to N, extract N data each time, and use the linear regression formula to calculate the slope of N data, marked as k IS (t); Step S5: Calculate the current gradient at the initial stage of countersinking based on historical data and mark it as k INI (t); Step S6: According to k IS (t) and k INI (t) Establishing a function model and finding the intersection of the function model, marked as P, where point P is the starting point of the countersink; Step S7: Slide the window and update N data. Then the spindle current gradient k IS (t) is updated accordingly, and point P is also updated accordingly; Step S8: updating the countersinking end point according to the preset countersinking depth, thereby achieving precise control of the countersinking depth.

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

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

4. The method for adaptive countersinking of an automatic feed drill spindle current 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 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 processing time recorded by the software.

5. The method for adaptive countersinking of an automatic feed drill spindle current 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 achieve real-time search of the countersinking starting point, and then the countersinking end point is updated by presetting the countersinking depth to achieve real-time control of the countersinking depth.

6. The method for adaptive countersinking of an automatic feed drill spindle current according to claim 1, characterized in that: In step S6, according to k IS (t) and k INI (t) The established function model is as follows: Among them, k IS1 is the slope of N data at the initial stage of countersinking, k IS2 is the slope of N data in the stable stage of countersinking, t is the real-time processing time recorded by the software; I s4a (t) is the spindle current value at the initial stage of countersinking, I s4b (t) is the spindle current value at the stable stage of countersinking; The countersinking starting point is the intersection of the real-time window function and the initial countersinking function model during the countersinking process.

7. The method for adaptive countersinking of an automatic feed drill spindle current according to claim 1, characterized in that: The materials applicable to the method include, but are not limited to, aluminum alloys, titanium alloys, CFRP, aviation materials, and metal materials such as steel and copper.

8. The method for adaptive countersinking of an automatic feed drill spindle current according to claim 1, characterized in that: The drilling processes adapted by the method include but are not limited to conventional drilling, spiral milling, ultrasonic vibration drilling and low-frequency vibration drilling.

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