Fine numerical control machining method for multifunctional tool

Abstract

The invention relates to the technical field of numerical control machining, in particular to a multifunctional tool refined numerical control machining method which comprises the steps that whether a current to-be-machined material meets the semi-precision machining requirement or not is determined according to a comprehensive evaluation value or the difference condition is analyzed; determining whether the recess of the curved surface can be overcome by the semi-precision machining or not, and determining whether the semi-precision machining is performed or adjusting the initial semi-finish machining coordinate corresponding correction feed amount of the semi-precision machining or not; calculating a hidden danger index to determine whether hidden danger analysis is started to judge a hidden danger type or not, pre-judging hidden flutter possibly generated to adjust the rotating speed of a main shaft, determining whether the cutter is tipping or has initial wear or not according to an acoustic emission signal, judging whether the reason is cutting resistance change or not, pre-adjusting the rotating speed of the main shaft or adjusting an initial detection period; calculating a comprehensive evaluation value of the machined workpiece, determining whether the machining precision meets the requirement or not, and adjusting the judgment range. According to the method, the problems of cutting chatter, tool abrasion and the like are predicted and analyzed, machining error superposition and accumulation are avoided, and the machining precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of numerical control machining, in particular to a multi-functional tool fine numerical control machining method. BACKGROUND

[0002] In traditional numerical control machining, the machining of multi-surface workpieces usually requires multiple tools to complete step by step, such as boring first and then grooving, which leads to low machining efficiency and increases the complexity and time cost of operation due to frequent tool replacement. In addition, due to the limitation of machine tool linkage performance, transition surface machining is prone to problems such as tool marks and tool chatter, affecting the appearance quality of the workpiece. In view of the above problems, a multi-functional tool and its fine numerical control machining method have emerged as the times require. This technology integrates multiple cutting functions into one tool through the design of a multi-functional tool, reducing the need for tool replacement and machine tool linkage, thereby achieving efficient and uniform machining results.

[0003] Chinese Patent Publication No. CN111045384A discloses a numerical control machining method, machining device and numerical control machine tool; the numerical control machining method comprises: obtaining a first label corresponding to a to-be-machined object; determining a second label corresponding to a tool according to the first label; recommending a tool with the second label according to the second label for machining the to-be-machined object; and machining the to-be-machined object using the recommended tool. The present application classifies the to-be-machined object and the tool by label, and recommends the tool according to label matching. As can be seen, the numerical control machining method, machining device and numerical control machine tool have the following problems: Several machining steps may have machining error accumulation, and there is no prediction and analysis of possible cutting chatter and tool wear problems. The traditional solution can only trigger adjustment through detection after the problem occurs, at which time the workpiece and tool have already been damaged. SUMMARY

[0004] Therefore, the present application provides a multi-functional tool fine numerical control machining method to overcome the problem that several machining steps in the prior art have machining error accumulation, and there is no prediction and analysis of possible cutting chatter and tool wear problems.

[0005] To achieve the above purpose, the present application provides a multi-functional tool fine numerical control machining method, comprising: According to the key size parameters and the actual weight of the to-be-machined material after rough machining, the comprehensive evaluation value of the current to-be-machined material is calculated, and whether the current to-be-machined material meets the semi-precision machining requirement or the difference of the current to-be-machined material is analyzed according to the comprehensive evaluation value; Detecting and identifying a key area of the curved surface of the material to be processed, determining whether the concave of the curved surface of the material to be processed can be overcome by semi-precision processing according to the concave degree of the key area; Determining whether to perform semi-precision processing or adjusting the initial semi-finishing coordinate of semi-precision processing according to whether the material to be processed meets the semi-precision processing requirement and whether the concave of the curved surface can be overcome by semi-precision processing, and correspondingly correcting the feed amount of semi-precision processing; After determining to perform semi-finishing, calculating a hidden danger index according to the detection result of the curved surface to determine whether to start hidden danger analysis and judge the hidden danger type; Prejudging the implicit chatter that may be generated in the semi-precision processing process by adopting a nonlinear frequency avoidance strategy to dynamically adjust the spindle speed, and determining whether the tool is broken or has initial wear according to the acoustic emission signal generated by the tool in the semi-precision processing process; After determining that the tool is broken or has initial wear, determining whether the reason for the tool being broken or having initial wear is the change of cutting resistance according to the acoustic emission signal, and nonlinearly pre-adjusting the spindle speed or adjusting the initial detection period according to the change of cutting resistance; After performing semi-precision processing and precision processing on the material to be processed in order to obtain a processed workpiece, calculating a comprehensive evaluation value of the processed workpiece to determine whether the processing precision meets the requirement, and correspondingly adjusting the judgment range of the analysis of the difference of the current material to be processed.

[0006] Further, the process of determining whether the current material to be processed meets the semi-precision processing requirement comprises, When the comprehensive evaluation value is greater than or equal to the first standard value, it is determined that the current material to be processed does not have difference problems and meets the semi-precision processing requirement; When the comprehensive evaluation value is less than the first standard value and greater than or equal to the second standard value, the difference of the current material to be processed is analyzed; When the comprehensive evaluation value is less than the second standard value, it is determined that the current material to be processed has difference problems and does not meet the semi-precision processing requirement.

[0007] Further, the process of analyzing the difference of the current material to be processed comprises, Detecting the curved surface of the material to be processed, dividing a plurality of measurement points into convex points and concave points, extracting the maximum convex point and the maximum concave point to identify the key area of the curved surface of the material to be processed, and the key area includes a convex area and a concave area; When the depth of the maximum concave point in the concave area is less than the semi-precision processing allowance critical value, it is determined that the concave of the curved surface of the material to be processed can be compensated; When the depth of the maximum concave point in the concave area is greater than or equal to the semi-precision processing allowance critical value, it is determined that the concave of the curved surface of the material to be processed cannot be overcome.

[0008] Further, when the current material to be processed has no difference problem and meets the semi-precision processing requirement and the surface concave of the material to be processed can be compensated, semi-precision processing is performed. When the surface concave of the material to be processed cannot be overcome or the difference problem does not meet the semi-precision processing requirement, the current material to be processed is removed by pre-warning. When the surface concave of the material to be processed can be compensated, the tool is moved to the initial semi-precision processing coordinate at which the feature point is located according to the three-dimensional coordinates of the feature point at the initial semi-precision processing coordinate, and the feed amount of semi-precision processing is corrected accordingly.

[0009] Further, the process of calculating the hidden danger index to determine whether to start hidden danger analysis includes calculating the hidden danger index according to the maximum convex point, the maximum concave point and the key area; When the hidden danger index is greater than the critical index, it is determined that there is a hidden danger risk in semi-precision processing for the current material to be processed, and the hidden danger type is determined by hidden danger analysis in the semi-precision processing process. When the hidden danger index is greater than the critical index, it is determined that there is no hidden danger risk in semi-precision processing for the current material to be processed.

[0010] Further, the process of determining the hidden danger type by hidden danger analysis includes collecting high-frequency vibration signals of the tool during semi-precision processing, and extracting feature parameters of the high-frequency vibration signals. The feature parameters include a frequency band energy ratio and a phase correlation. When the frequency band energy ratio is greater than a first parameter value and the phase correlation is greater than a second parameter value, it is determined that there is a chatter precursor, and the spindle speed of the tool is dynamically adjusted.

[0011] Further, the acoustic emission signals generated by the tool during semi-precision processing are obtained, and the number of burst signals and the change trend of signal energy concentration frequency band in a unit time are determined according to an initial detection period. The event count rate is calculated according to the number of burst signals in a unit time, and the energy proportion of normal frequency band and specific frequency band in total energy is calculated. If the ratio of the energy proportion of the specific frequency band in the two current initial detection periods to the energy proportion of the specific frequency band in the historical initial detection period is greater than a reference threshold value, it is determined that the main frequency band has shifted.

[0012] Further, when the growth rate of the event count rate is greater than a critical percentage and the main frequency band has shifted, it is determined that the tool has broken or has initial wear.

[0013] Further, the process of determining the reason for the tool breaking or having initial wear includes calculating the entropy value of the acoustic emission signal. If the entropy value changes by more than a change amplitude within a standard time, it is determined that the cutting resistance has suddenly changed and is about to penetrate the interlayer interface, and the spindle speed is nonlinearly adjusted. When the cutting resistance mutation is determined to exist, the tool chipping or the initial wear is determined to be caused by the cutting resistance change, and the nonlinear pre-adjustment of the spindle speed is performed before the interface penetration; When the cutting resistance mutation is not determined to exist, the tool chipping or the initial wear is determined to be not caused by the cutting resistance change, and the initial detection period is reduced.

[0014] Further, the process of determining whether the machining precision meets the requirement comprises calculating a comprehensive evaluation value of the machined workpiece. When the comprehensive evaluation value of the machined workpiece is less than a first standard value, it is determined that the machining precision of the machined workpiece does not meet the requirement, and the first standard value and the second standard value are increased according to the ratio of the first standard value to the comprehensive evaluation value of the machined workpiece.

[0015] Compared with the prior art, the beneficial effects of the present application are that the rough machining material has different degrees of difference due to different batches or machining fluctuations in rough machining. The present method solves the difference between the rough machining material and the requirement through semi-precision machining before precision machining, avoids the influence of the difference of the machining material on the machining precision or the abnormal wear of the tool chipping, improves the machining precision and reduces the error generated in subsequent precision machining. The present method can also analyze and judge the difference degree and the type of existing problems through semi-precision machining. The present method determines whether the difference of the rough machining material has a difference problem by generating a comprehensive evaluation value of the machining material through laser ranging combined with weight detection. The difference problem of the machining material is divided into three types: the difference is very small and can be ignored, the difference is large and exceeds the reserved range and cannot be modified, or the difference needs to be further analyzed and the parameters of semi-precision machining are adjusted according to the difference. When the difference problem needs to be further analyzed, the surface of the machining material is detected, the specific situation of the deviation of the surface is judged according to the three-dimensional coordinates of the measuring points of the surface of the machining material, and whether the deviation type is uneven. Whether the concave area of the surface can be overcome by semi-precision machining is determined, which avoids the machining of the machining material with defects that cannot be overcome, increases the yield of the machined workpiece and the machining efficiency, and adjusts the initial semi-precision machining coordinates of the tool movement and the correction of the semi-precision machining feed amount, which avoids the under-cutting of the insufficient area or the excessive wear of the tool.

[0016] Further, the sudden increase in cutting force in the excessive allowance area may cause tool deflection, resulting in surface vibration on the machined surface, and the insufficient allowance area may cause air cutting, resulting in micro-chipping of the cutting edge. The method predicts the risk of potential problems in semi-precision machining according to the surface inspection results. When it is determined that there is a risk of potential problems in semi-precision machining of the current material to be machined according to the hidden trouble index, it is predicted whether there is hidden chatter or the degree of wear according to the acoustic emission signal in the machining process, so as to determine whether the evaluation criteria of the above comprehensive evaluation value or the parameter setting of the feed rate of semi-precision machining is reasonable, thereby increasing the accuracy of numerical control machining.

[0017] Further, cutting chatter is a self-excited vibration caused by dynamic coupling of the tool-workpiece-machine system in numerical control machining. When there is a certain degree of difference between the machined material after rough machining and the expected value in the present application, the material properties change, the natural frequency of the cutting process changes, and when the system natural frequency coincides, resonance occurs. In addition, the rough machined surface (such as vibration marks and scales) and the three-dimensional difference of the material to be machined may exacerbate tool vibration or cause cutting force fluctuation, which is easy to trigger chatter. The method extracts the characteristic parameters of high-frequency vibration signals, predicts the precursors of chatter in semi-precision machining according to the frequency band energy ratio and phase correlation, and dynamically adjusts the spindle speed of the tool before the emergence of chatter, thereby avoiding the problem that in the traditional technology, the adjustment can only be triggered by detecting the vibration amplitude after the occurrence of chatter, at which time the workpiece surface has been damaged, and the linear proportional adjustment (such as reducing the speed by a fixed percentage) cannot accurately avoid the sensitive frequency band of the system. The method establishes a hidden chatter prediction mechanism and dynamically adjusts the spindle speed using a nonlinear frequency avoidance strategy, thereby improving the adaptability to cutting chatter in numerical control machining and reducing the machining risk.

[0018] Further, characteristic acoustic emission signals are generated during tool wear, and the physical sources include micro-chipping of the cutting edge, intensified friction, and material tearing. The method detects the characteristic spectrum of the acoustic emission signal generated during tool machining, evaluates the wear state of the tool in real time during semi-precision machining through the event count rate and main frequency band migration, and determines whether the tool is chipped or has initial wear. Based on the principle that the cutting resistance of different layers will cause the hole axis to deviate when machining laminated materials or materials with layered hardness, the method further determines the reason for tool chipping or initial wear according to the degree of energy distribution disorder of the acoustic emission signal in a specific frequency band when the tool is chipped or has initial wear. Whether it is caused by cutting resistance mutation is determined according to the wavelet packet energy entropy of the acoustic emission signal in a specific frequency band. The material fingerprint feature of the acoustic emission signal is used to identify the interface transition in advance, the spindle speed is nonlinearly adjusted according to the entropy amplitude before the interface is penetrated, "preventive" regulation is achieved, and the accuracy of detecting the tool wear state is increased by returning to the initial detection period when there is no cutting resistance mutation, that is, the wear reason is not the conversion of laminated materials.

[0019] Further, the method generates a comprehensive evaluation value of the processed workpiece according to the laser ranging combined with the weight detection after obtaining the processed workpiece, judges whether the processing precision meets the requirements, and the reason that the processing precision does not meet the standards may be that the judgment standard range set when detecting the workpiece vibration, tool wear or difference of the material to be processed fails to cover the precision requirement, the judgment standard range formed by increasing the first standard value and the second standard value improves the strictness of the judgment standard of the material to be processed, reduces the difference of the material to be processed in semi-precision processing, increases the processing precision of the processed workpiece prepared, and improves the fine degree of numerical control processing and the adaptability to the quality problems of different batches of materials to be processed. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a flowchart of the fine numerical control processing method of the multifunctional tool in the embodiment of the application. Figure 2 It is a machining diagram of semi-precision machining of chamfering in the multifunctional machining method in the embodiment of the application. Figure 3 It is a machining diagram of semi-precision machining and precision machining in the embodiment of the application. Figure 4 It is a flowchart of determining whether the current material to be processed meets the semi-precision machining requirement according to the comprehensive evaluation value in the embodiment of the application. In the figure: 1-tool head, 2-material to be processed, 3-processed workpiece. DETAILED DESCRIPTION

[0021] In order to make the purpose and advantages of the application more clear and obvious, the application is further described below in combination with the embodiments; it should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the protection scope of the application.

[0022] The preferred embodiments of the application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the application, and are not used to limit the protection scope of the application.

[0023] It should be noted that in the description of the application, the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the direction or positional relationship of the terms based on the direction or positional relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0024] Moreover, it needs to be explained that in the description of the present application, unless explicitly defined and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] Please refer to Figures 1-4 as shown, Figure 1 is a flowchart of the fine numerical control machining method of the multifunctional cutter in the embodiment of the present application; Figure 2 is a machining diagram of semi-precision machining of chamfering in the multifunctional machining method in the embodiment of the present application; Figure 3 is a machining diagram of semi-precision machining and precision machining in the embodiment of the present application; Figure 4 is a flowchart of determining whether the current material to be machined meets the semi-precision machining requirement according to the comprehensive evaluation value in the embodiment of the present application.

[0026] The drawings of the present embodiment are used to explain the semi-precision machining and precision machining of chamfering in the multifunctional machining method, but not to limit the shape of the cutter, the material to be machined and the machining workpiece formed by machining.

[0027] In the present embodiment, the material to be machined is fixed at the fixed point of the numerical control machine tool, and the machining workpiece 3 is obtained after rough machining, semi-precision machining and precision machining of the material to be machined.

[0028] As shown in the figure, semi-precision machining needs to move the cutter head 1 to the machining side of the rough machined material to be machined according to the set initial semi-precision machining coordinates.

[0029] The present application provides a fine numerical control machining method of multifunctional cutter, comprising: Step S1, calculating the comprehensive evaluation value of the current material to be machined according to the key size parameters and actual weight of the rough machined material to be machined, and determining whether the current material to be machined meets the semi-precision machining requirement or analyzing the difference of the current material to be machined according to the comprehensive evaluation value; Step S2, detecting and identifying the key area of the curved surface of the material to be machined, and determining whether the curved surface depression of the material to be machined can be overcome by semi-precision machining according to the depression degree of the key area; Step S3, determining whether to perform semi-precision machining or adjusting the initial semi-precision machining coordinates of semi-precision machining according to whether the material to be machined meets the semi-precision machining requirement and whether the curved surface depression can be overcome by semi-precision machining, and correcting the feed amount of semi-precision machining accordingly; Step S4, after determining to carry out semi-finishing, calculating hidden danger index according to the surface detection result to determine whether to start hidden danger analysis to determine hidden danger type; Step S5, predicting the hidden chatter that may be generated in the semi-precision machining process, adopting a nonlinear frequency avoidance strategy to dynamically adjust the spindle speed, and determining whether the tool is broken or has initial wear according to the acoustic emission signal generated by the tool in the semi-precision machining process; Step S6, after determining that the tool is broken or has initial wear, judging whether the reason for the tool being broken or having initial wear is the change of cutting resistance according to the acoustic emission signal, and nonlinearly pre-adjusting the spindle speed or adjusting the initial detection period according to the change of cutting resistance; Step S7, calculating the comprehensive evaluation value of the machined workpiece after sequentially performing semi-precision machining and precision machining on the material to be machined, determining whether the machining precision meets the requirements, and adjusting the judgment range corresponding to the analysis of the difference of the current material to be machined.

[0030] Detect the key size parameters of the material to be machined after rough machining through a laser ranging system, and measure the actual weight of the material to be machined through a weight detection system; Specifically, a cross laser scanning array is used to obtain the three-dimensional coordinates of a plurality of feature points on the surface of the material to be machined, and the maximum deviation ΔL in the length direction, the thickness direction fluctuation δT, and the flatness error F are calculated. The three-dimensional coordinates are composed of measurement values in the length direction, the thickness direction, and the height direction; The maximum deviation ΔL in the length direction is (the maximum measured value in the length direction - the theoretical length value) / 2, the thickness direction fluctuation δT is the standard deviation of the three-dimensional coordinates of a plurality of feature points in the thickness direction, and the flatness error F is the sum of the difference between the maximum measurement value and the minimum measurement value in a plurality of planes of the material to be machined.

[0031] The comprehensive evaluation value P = (size stability factor S × 0.6) + (weight matching factor W × 0.4), The weight matching factor W = e^(-2.5×|Kw -1|), where Kw is the ratio of the actual weight to the theoretical weight; The size stability factor S = 1-[(ΔL / L0) / 0.05+(δT / T0) / 0.03+F / 0.1] / 3, where L0 is the nominal length and T0 is the nominal thickness; The nominal length, the nominal thickness, and the theoretical weight are preset standard values required by the material to be machined after rough machining to meet the semi-precision machining requirements.

[0032] When the comprehensive evaluation value is greater than or equal to the first standard value, it is determined that there is no difference problem in the current material to be machined, which meets the semi-precision machining requirements. when the comprehensive evaluation value is less than the first standard value and greater than or equal to the second standard value, it is determined that the difference of the current material to be processed needs to be further analyzed; when the comprehensive evaluation value is less than the second standard value, it is determined that the current material to be processed has a difference problem that does not meet the semi-precision machining requirement; The first standard value is 0.85, and the second standard value is 0.60.

[0033] The process of further analyzing the difference includes: The cross laser scanning array is used to detect the curved surface of the material to be processed, and the deviation distance of the three-dimensional coordinates of each measurement point from the theoretical coordinates is obtained, and the measurement points are divided into convex points and concave points according to the deviation distance; The maximum convex point and the maximum concave point are extracted, and the key area of the curved surface of the material to be processed is identified, and the key area includes a convex area and a concave area; When the depth of the maximum concave point in the concave area is less than the semi-precision machining allowance critical value, it is determined that the concave area of the curved surface of the material to be processed can be compensated; When the depth of the maximum concave point in the concave area is greater than or equal to the semi-precision machining allowance critical value, it is determined that the concave area of the curved surface of the material to be processed cannot be overcome; The semi-precision machining allowance critical value is equal to 0.7 times the semi-precision machining allowance, and the semi-precision machining allowance is a preset value.

[0034] When the difference problem meets the semi-precision machining requirement and the concave area of the curved surface of the material to be processed can be compensated, semi-precision machining is performed; When the concave area of the curved surface of the material to be processed cannot be overcome or the difference problem does not meet the semi-precision machining requirement, the current material to be processed is removed.

[0035] When the concave area of the curved surface of the material to be processed can be compensated, the three-dimensional coordinates of the feature points located at the initial semi-precision machining coordinates are adjusted to move the tool to the initial semi-precision machining coordinates of the start of semi-precision machining, and the feed amount of semi-precision machining is corrected accordingly; Specifically, when the absolute value of any measurement value in the length direction, the thickness direction and the height direction of the three-dimensional coordinates is greater than the theoretical value of the length direction, the thickness direction and the height direction corresponding to the initial semi-precision machining coordinates, the theoretical value corresponding to the initial semi-precision machining coordinates is increased according to the any measurement value; at the same time, the feed amount of semi-precision machining in the corresponding direction is increased according to the difference between the any measurement value and the corresponding theoretical value.

[0036] Specifically, the rough machining of the to-be-machined material has different degrees of difference due to machining fluctuations of different batches or rough machining. The method solves the difference between the rough machining material and the need before precision machining through semi-precision machining, avoids the influence of the difference of the to-be-machined material on the machining precision or causes the abnormal wear of the tool, improves the machining precision and reduces the error generated by subsequent fine machining, and can also analyze and judge the difference degree and the type of existing problems through semi-fine machining. The method determines whether the difference of the rough machining of the to-be-machined material has a difference problem by generating a comprehensive evaluation value of the to-be-machined material through laser ranging combined with weight detection. The difference problem type of the to-be-machined material is divided into a difference that is very small and can be ignored, a difference that is too large to be modified beyond the reserved range, or a difference that needs to be further analyzed and adjusted according to the difference of the parameters of semi-fine machining. When the difference problem needs to be further analyzed, the surface of the to-be-machined material is detected, the specific situation of the deviation of the surface is judged according to the three-dimensional coordinates of the measurement points of the surface of the to-be-machined material, and whether the deviation type is uneven. Whether the concave area of the surface can be overcome by semi-precision machining is determined, which avoids the machining of the to-be-machined material with defects that cannot be overcome, increases the yield of the machined workpiece and the machining efficiency, and adjusts the tool to move to the initial semi-fine machining coordinates of the start of semi-precision machining and the feed amount of the correction of semi-precision machining, avoiding air cutting in the area with insufficient allowance or excessive allowance of the tool.

[0037] After determining to perform semi-fine machining, calculating a hidden danger index H according to the surface inspection result to determine whether to start hidden danger analysis and judge the type of hidden danger; The hidden danger index H = 0.35 x (hm / δ) + 0.30 x (dm / δ) + 0.35 x Ac; In the formula, hm is the protruding depth of the maximum convex point, dm is the recess depth of the maximum concave point, δ is the semi-precision machining allowance, and Ac is the area ratio of the key area to the surface. When the hidden danger index is greater than the critical index, it is judged that there is a hidden danger risk for the semi-precision machining of the current to-be-machined material, and the hidden danger type is determined in the hidden danger analysis during semi-precision machining. When the hidden danger index is greater than the critical index, it is judged that there is no hidden danger risk for the semi-precision machining of the current to-be-machined material. The critical index is 0.6.

[0038] Specifically, the excessive cutting force in the excessive allowance area may cause tool deflection, resulting in surface vibration on the machined surface, and the insufficient allowance area may cause air cutting, resulting in micro-chipping of the cutting edge. The method predicts the risk of potential problems in semi-precision machining according to the curved surface inspection results. When it is determined that there is a risk of potential problems in semi-precision machining of the current material to be machined according to the potential problem index, it is predicted whether there is hidden chatter in the machining potential problem according to the semi-finishing machining condition or the wear degree according to the acoustic emission signal, so as to determine whether the evaluation criterion of the above comprehensive evaluation value or the parameter setting of the feed rate of semi-precision machining is reasonable, thereby increasing the accuracy of numerical control machining.

[0039] The process of starting the hidden danger analysis to determine the hidden danger type includes: In the semi-precision machining process, an acceleration sensor is used to collect high-frequency vibration signals of the tool, and characteristic parameters of the high-frequency vibration signals are extracted and calculated. In implementation, a MEMS acceleration sensor with a bandwidth of 50 kHz installed at the handle end of the multifunctional tool is used for sampling detection with a sampling frequency of 100 kHz, and the detection frequency band is in the high-frequency range of 5-25 kHz.

[0040] Specifically, the characteristic parameters include a frequency band energy ratio RE and a phase correlation γ 2 (f); The frequency band energy ratio RE is the energy proportion of each frequency band, and the phase correlation is γ 2 (f) is the coherence function of the tool vibration signal and the cutting force signal, and f is the frequency. It can be understood that the implementer can calculate γ 2 (f) according to the cross-power spectrum of the vibration signal (x) and the cutting force signal (y) and the respective self-power spectrum, which is not described herein again.

[0041] In the semi-precision machining process, when RE is greater than a first parameter value and γ 2 (f) is greater than a second parameter value, it is determined that there is a prelude to chatter, and the spindle speed of the tool is dynamically adjusted. The adjusted spindle speed = the spindle speed before adjustment x (1 ± k / (2m+1)); In the formula, k is the ratio of the current speed to the system natural frequency, and m is the iteration number. In implementation, the value range of k is 0.8-1.2, and the implementer can set the iteration number m according to the requirement, so as to ensure that the adjusted speed is not at the 1 / 3, 1 / 5, etc. Fractional frequency point. The first parameter value is 0.35, and the second parameter value is 0.6.

[0042] Specifically, the cutting chatter is a self-excited vibration caused by dynamic coupling of the tool-workpiece-machine tool system in numerical control machining, in the present application, when there is a certain difference between the rough machining material and the expected rough machining material, the material properties change, the natural frequency of the cutting process changes, and when the natural frequency of the system coincides, resonance occurs, and the rough machined surface (such as vibration marks and scales) and the three-dimensional difference of the material to be machined may exacerbate tool vibration or cause cutting force fluctuations, which may easily trigger chatter; the method extracts the characteristic parameters of the high-frequency vibration signal, predicts the precursors of chatter in semi-precision machining according to the frequency band energy ratio and phase correlation, and dynamically adjusts the spindle speed of the tool before the emergence of chatter, avoiding the problem that in the traditional technology, the adjustment can only be triggered by detecting the vibration amplitude after the occurrence of chatter, at this time the workpiece surface has been damaged, and the linear proportional adjustment (such as reducing the speed by a fixed percentage) cannot accurately avoid the sensitive frequency band of the system, an implicit chatter prediction mechanism is established, and a nonlinear frequency avoidance strategy is used to dynamically adjust the spindle speed, improving the adaptability to cutting chatter in numerical control machining and reducing the hidden danger of machining.

[0043] Using a wideband sensor to obtain the acoustic emission signal generated by the tool during semi-precision machining, determining the number of burst signals in a unit time and the change trend of the signal energy concentration frequency band; Specifically, according to the acoustic emission signal, an FFT spectrum is generated according to an initial detection period, and an event count rate is calculated according to the number of burst signals in a unit time, the event count rate = number of burst signals ÷ unit time; In implementation, the signal amplitude increases from 10% to 90% in <5us, and the signal meeting the pulse width range of 50-500us is identified as a burst signal; According to the change trend of the signal energy concentration frequency band, the main frequency band shift is judged, the signal energy of the normal frequency band and the characteristic frequency band is detected, and the energy proportion of the normal frequency band and the specific frequency band in the total energy is calculated; If the energy proportion ratio of the specific frequency band of the two current initial detection periods to the energy proportion of the specific frequency band of the historical initial detection period is greater than the reference threshold, it is judged that the main frequency band shift occurs; In implementation, the normal frequency band is 150-250kHz frequency band, and the characteristic frequency band is 300-400kHz frequency band.

[0044] According to the initial detection period, the event count rate is detected, and the growth rate of the event count rate is calculated, when the growth rate of the event count rate is greater than a critical percentage and the main frequency band shift occurs, it is judged that the tool collapses or there is initial wear; Wherein, the critical percentage is 15%, the reference threshold is 1.8, and the historical initial detection period is the first initial detection period.

[0045] After determining the tool chipping or the existence of initial wear, the cause of tool chipping or the existence of initial wear is judged according to the acoustic emission signal; The wavelet packet energy entropy of the acoustic emission signal in the 80-120 kHz wave band is analyzed in real time, and the wavelet packet energy entropy reflects the energy distribution disorder degree of the signal in a specific frequency band; The acoustic emission signal is preprocessed for noise reduction, wavelet packet decomposition is performed to obtain a plurality of sub-bands, the sub-bands corresponding to 80-120 kHz are located, and the wavelet packet coefficients of the corresponding sub-bands are obtained to calculate the energy distribution; In implementation, the basis function is selected as Daubechies 4 (db4) wavelet when wavelet packet decomposition is performed, the wavelet packet is decomposed into 5 layers of a plurality of nodes, the node coefficients Wi (i=1, 2, 3) of the first three nodes of the fifth layer are obtained; The sub-band energy Ei of any sub-band is Ei=Wi^2, the total energy Et of the 80-120 kHz wave band is Et=E1+E1+E3, the energy proportion pi of each node is pi=Ei / Et, the entropy value is -Σ(pi × log2pi), and the value range of the entropy value is 0-1.589; A time series entropy H is calculated every 2 ms, and the entropy amplitude ΔE is |H(t)-H(t-Δt)| / Δt, where H(t) is the time series entropy at time t, and Δt is the change value 20 ms.

[0046] If the entropy value changes more than the change amplitude within the standard time, it is determined that the cutting resistance suddenly changes and is about to penetrate the interlayer interface, and the spindle speed is nonlinearly adjusted; When it is determined that the cutting resistance suddenly changes, the cause of tool chipping or the existence of initial wear is determined to be the change of cutting resistance, and the spindle speed is nonlinearly pre-adjusted before the interface penetration; When it is determined that the cutting resistance does not suddenly change, the cause of tool chipping or the existence of initial wear is determined to be other than the change of cutting resistance, and the initial detection period is reduced; Specifically, 200 ms before the interface penetration, the spindle speed is nonlinearly adjusted as n=n0×(1+e^(-kΔE)).

[0047] The standard time is 0.5 s, and the change amplitude is 40%.

[0048] Specifically, the tool wear process will produce characteristic acoustic emission signals, the physical source includes blade micro exfoliation, friction aggravation and material tearing, the method detects the acoustic emission signals generated during tool processing by characteristic spectrum, evaluates the tool wear state in semi-precision machining process in real time through event counting rate and main frequency band migration, whether the tool is broken or has initial wear; and based on the principle that the cutting resistance mutation of different layers will cause the hole axis to deviate when processing laminated materials or materials with layered hardness, further determines the reason for tool breakage or initial wear according to the energy distribution disorder degree of acoustic emission signals in a specific frequency band when the tool is broken or has initial wear, determines whether it is caused by cutting resistance mutation according to the wavelet packet energy entropy of acoustic emission signals in a specific wave band, uses the material fingerprint characteristics of acoustic emission signals to identify the interface transition in advance, adjusts the spindle speed according to the entropy amplitude nonlinear before the interface penetration, realizes "preventive" regulation and control, and increases the accuracy of detecting tool wear state by recalling the initial detection period when there is no cutting resistance mutation, that is, the wear reason is not the conversion of laminated materials.

[0049] After the semi-precision machining and precision machining of the material to be processed in order, the machining workpiece is obtained, the key size parameter and weight detection are performed on the machining workpiece, and the comprehensive evaluation value of the machining workpiece is calculated; When the comprehensive evaluation value of the machining workpiece is less than the first standard value, it is judged that the machining precision of the machining workpiece does not meet the requirements, and the first standard value and the second standard value are adjusted. Specifically, the first standard value and the second standard value are increased according to the ratio of the first standard value to the comprehensive evaluation value of the machining workpiece.

[0050] Specifically, the method generates the comprehensive evaluation value of the machining workpiece again after obtaining the machining workpiece according to laser ranging combined with weight detection, judges whether the machining precision meets the requirements, and the reason why the machining precision does not meet the standard may be that the workpiece chatter, tool wear or the judgment standard range set when detecting the difference of the material to be processed fails to cover the precision requirement, the judgment standard range formed by increasing the first standard value and the second standard value improves the strictness of the judgment standard of the material to be processed, reduces the difference of the material to be processed in semi-precision machining, increases the machining precision of the machining workpiece prepared, and improves the fine degree of numerical control machining and the adaptability to quality problems of different batches of materials to be processed.

[0051] So far, the technical scheme of the present application has been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to related technical features without departing from the principles of the present application, and the technical scheme after these changes or replacements will fall within the protection scope of the present application.

[0052] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application; for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multifunctional tool fine CNC machining method, characterized in that: include: Calculate a comprehensive evaluation value of the current material to be processed based on key dimensional parameters and actual weight of the material to be processed after rough processing, and determine whether the current material to be processed meets the semi-precision processing requirements or analyze the differences of the current material to be processed based on the comprehensive evaluation value; Detecting the curved surface of the material to be processed and identifying key areas of the curved surface, and determining whether the concavity of the curved surface of the material to be processed can be overcome by semi-precision machining according to the degree of concavity of the key areas; Determine whether to perform semi-precision machining or adjust the initial semi-precision machining coordinates according to whether the material to be machined meets the semi-precision machining requirements and whether the surface concavity can be overcome by semi-precision machining, and correct the feed rate of semi-precision machining accordingly; After determining to carry out semi-finishing, calculate the hidden danger index according to the surface inspection results to determine whether to start hidden danger analysis and determine the hidden danger type; The potential hidden chatter during semi-precision machining is predicted, and a nonlinear frequency avoidance strategy is used to dynamically adjust the spindle speed. The acoustic emission signals generated by the tool during semi-precision machining are used to determine whether the tool is chipping or experiencing initial wear. After determining that the tool is chipping or has initial wear, determine whether the cause of the tool chipping or initial wear is a change in cutting resistance based on the acoustic emission signal, and pre-adjust the spindle speed or adjust the initial detection period based on the nonlinear change in cutting resistance; After semi-precision machining and precision machining are sequentially performed on the material to be machined to obtain a machined workpiece, a comprehensive evaluation value of the machined workpiece is calculated to determine whether the machining precision meets the requirements, and the judgment range of the analysis of the difference of the current material to be machined is adjusted accordingly.

2. The multifunctional tool fine numerical control processing method according to claim 1, characterized in that: The process of determining whether the material to be processed meets the semi-precision machining requirements includes: When the comprehensive evaluation value is greater than or equal to the first standard value, it is determined that the current material to be processed does not have any discrepancy problem and meets the semi-precision processing requirements; When the comprehensive evaluation value is less than the first standard value and greater than or equal to the second standard value, the difference of the current material to be processed is analyzed; When the comprehensive evaluation value is less than the second standard value, it is determined that the current material to be processed has a difference problem and does not meet the semi-precision processing requirements.

3. The multifunctional tool fine numerical control processing method according to claim 2, characterized in that: The process of analyzing the differences in the current material to be processed includes: Detecting the curved surface of the material to be processed, dividing a number of measurement points into convex points and concave points, extracting the maximum convex point and the maximum concave point to identify key areas of the curved surface of the material to be processed, wherein the key areas include convex areas and concave areas; When the depth of the largest concave point in the concave area is less than the critical value of the semi-precision machining allowance, it is determined that the concave surface of the material to be processed can be compensated; When the depth of the largest concave point in the concave area is greater than or equal to the critical value of the semi-precision machining allowance, it is determined that the concave surface of the material to be machined cannot be overcome.

4. The multifunctional tool fine numerical control processing method according to claim 3, characterized in that: When the material to be processed does not have any discrepancies and meets the semi-precision processing requirements and the concavity of the surface of the material to be processed can be compensated, semi-precision processing is performed; When the concave surface of the material to be processed cannot be overcome or the difference problem does not meet the semi-precision processing requirements, an early warning will be issued to remove the current material to be processed; When the concave surface of the material to be processed can be compensated, the tool is adjusted to move to the initial semi-finishing coordinate for starting semi-precision machining according to the three-dimensional coordinates of the feature point located at the initial semi-finishing coordinate, and the feed amount of semi-precision machining is corrected accordingly.

5. The multifunctional tool fine numerical control processing method according to claim 4, characterized in that: The process of calculating the hidden danger index to determine whether to start the hidden danger analysis includes calculating the hidden danger index according to the maximum convex point and the maximum concave point and the key area; When the hidden danger index is greater than the critical index, it is determined that there is a hidden danger risk in semi-precision machining of the current material to be machined, and the hidden danger type is determined by hidden danger analysis during the semi-precision machining process; When the hidden danger index is greater than the critical index, it is determined that there is no hidden danger risk in performing semi-precision machining on the current material to be processed.

6. The multifunctional tool fine numerical control processing method according to claim 5, characterized in that: The process of analyzing hidden dangers and determining the type of hidden dangers includes collecting the high-frequency vibration signal of the tool during semi-precision machining, extracting and calculating the characteristic parameters of the high-frequency vibration signal; The characteristic parameters include a frequency band energy ratio and a phase correlation. When the frequency band energy ratio is greater than a first parameter value and the phase correlation is greater than a second parameter value, it is determined to be a precursor to chattering and the spindle speed of the tool is dynamically adjusted.

7. The multifunctional tool fine numerical control processing method according to claim 6, characterized in that: Acquire the acoustic emission signals generated by the tool during semi-precision machining, and determine the number of burst signals per unit time and the changing trend of the frequency band in which the signal energy is concentrated according to the initial detection period; Calculate the event count rate based on the number of burst signals per unit time, and calculate the energy proportion of the normal frequency band and the specific frequency band in the total energy; If the ratio of the energy proportion of the specific frequency band in two consecutive current initial detection cycles to the energy proportion of the specific frequency band in the historical initial detection cycle is greater than the reference threshold, it is determined that the main frequency band offset occurs.

8. The multifunctional tool fine numerical control processing method according to claim 7, characterized in that: When the growth rate of the event count rate is greater than a critical percentage and a main frequency band shift occurs, it is determined that the tool is chipping or has initial wear.

9. The multifunctional tool fine numerical control processing method according to claim 8, characterized in that: The process of determining the cause of tool chipping or initial wear includes calculating the entropy value of the acoustic emission signal; If the entropy value changes more than the change amplitude within the standard time, it is determined that the cutting resistance has suddenly changed and is about to penetrate the interlayer interface, and the spindle speed is adjusted nonlinearly; When it is determined that there is a sudden change in cutting resistance, the cause of tool chipping or initial wear is determined to be a change in cutting resistance, and the spindle speed is nonlinearly pre-adjusted before the interface penetrates; When it is not determined that there is a sudden change in cutting resistance, it is determined that the cause of tool chipping or initial wear is not a change in cutting resistance, and the initial detection cycle is reduced.

10. The multifunctional tool fine numerical control processing method according to claim 9, characterized in that: The process of determining whether the machining accuracy meets the requirements includes calculating the comprehensive evaluation value of the machined workpiece; When the comprehensive evaluation value of the workpiece is less than the first standard value, it is determined that the machining accuracy of the workpiece does not meet the requirements, and the first standard value and the second standard value are increased according to the ratio of the first standard value to the comprehensive evaluation value of the workpiece.

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