A method for detecting the surface of a precision metal part

Abstract

The application relates to the field of surface detection, and particularly discloses a precision metal part surface detection method. The precision metal part surface detection method comprises the following steps: starting a laser to point-by-point scan the surface of a precision metal part to be detected; exciting an ultrasonic surface wave at each scanning point; an ultrasonic sensor real-time receives a signal and transmits the signal to a computer after the signal is digitized through a signal acquisition card; 5-10 ultrasonic surface wave signals are collected at each scanning point; the computer carries out filtering processing on the collected signals, extracts time domain features of the filtered signals, and calculates the peak amplitude mean value and standard deviation, the rising time and the falling time of each signal; and when the peak amplitude mean value decreases by more than 20% relative to a standard signal, the standard deviation increases, and the rising time is prolonged by more than 10%, it is judged that a defect exists. The precision metal part surface detection method has the advantages of fast detection speed and high detection precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of surface detection, more particularly, it relates to a precision metal part surface detection method. BACKGROUND

[0002] Precision metal parts play a crucial role in modern manufacturing industry, they are widely used in aerospace, automotive, medical devices and electronic products, etc. These parts usually require high precision, wear resistance and excellent mechanical properties, so the control of surface quality is particularly important. Common materials include stainless steel, aluminum alloy, titanium alloy, etc. Precision machining is carried out by numerical control machine tools, such as turning, milling and drilling operations, to ensure that the geometric shape and size of the parts meet the design requirements. The parts may undergo heat treatment processes such as quenching and tempering to adjust the hardness and corrosion resistance of the material.

[0003] The surface quality of precision metal parts is an important manifestation of their overall performance. Surface defects such as scratches, cracks, pits, etc. not only affect the appearance of the parts, but more importantly, they weaken the mechanical properties and fatigue life of the parts, and may even cause safety accidents. Therefore, it is particularly important to detect the surface of precision metal parts with high precision and high efficiency. Common detection methods include optical microscope inspection and non-destructive testing. Optical microscope inspection has the advantages of being able to quickly identify surface defects, cracks and contamination, but has many limitations in detecting the volume and shape of the object. Non-destructive testing such as ultrasonic testing, eddy current testing, magnetic powder testing can detect surface and internal defects, but the equipment cost is high, usually requires professional skills to operate, and the detection speed is slow, not suitable for mass production. SUMMARY

[0004] In order to improve the detection accuracy, the present application provides a precision metal part surface detection method.

[0005] The precision metal part surface detection method provided by the present application adopts the following technical scheme:

[0006] A precision metal part surface detection method, comprising the following steps:

[0007] After cleaning the precision metal part to be detected, it is fixed on the detection platform;

[0008] Start the laser, scan the surface of the part point by point according to the preset scanning path and angle, excite ultrasonic surface wave at each scanning point, the ultrasonic sensor receives the signal in real time and transmits it to the computer after digitizing the signal through the signal acquisition card, and collects 5-10 times of ultrasonic surface wave signal at each scanning point;

[0009] The computer filters the collected signals by using a band-pass filter, and normalizes the filtered signals to the interval of 0-1.

[0010] The time domain features are extracted, and the peak amplitude mean and standard deviation, rise time and fall time of each signal are calculated. When the peak amplitude mean decreases by more than 20% relative to the standard signal and the standard deviation increases, and the rise time is prolonged by more than 10%, it is judged that there is a defect.

[0011] Through the above scheme, the laser excites the ultrasonic surface wave, and the ultrasonic sensor receives the signal. The whole detection process is non-contact. Unlike the traditional contact detection method (such as using a probe to directly contact the surface of the part for detection), it will not cause scratches, wear and other secondary damage to the originally smooth surface of the precision metal part due to the friction, extrusion and other physical contact between the probe and the surface of the part. It well protects the surface quality of the part, and is especially suitable for the detection of precision metal parts in the fields of aviation, aerospace, high-end electronic equipment and the like which have extremely high requirements on surface precision.

[0012] Through careful processing and feature analysis of the collected ultrasonic surface wave signals, the band-pass filter is used to remove high-frequency noise and low-frequency interference in the signals, which can effectively purify the signals, reduce the influence of irrelevant interference factors on subsequent judgment, and more accurately reflect the real state of the surface of the part. When the peak amplitude mean decreases by more than 20% relative to the standard signal and the standard deviation increases, and the rise time is prolonged by more than 10%, the defect is judged. Such clear and quantified judgment conditions help to accurately identify the subtle abnormal conditions of the surface of the part, and can detect surface defects with a size of tens of microns, greatly improving the accuracy of defect identification. Moreover, 5-10 ultrasonic surface wave signals are collected at each scanning point, and the accidental error of the signals is further reduced through multiple collection and averaging, so as to ensure that the obtained signal features can better represent the real situation of the scanning point, making the detection result more reliable and avoiding misjudgment or omission of defects due to fluctuations in single signal collection.

[0013] Optionally, the laser irradiation angle is 30-60° with the normal of the surface of the part.

[0014] Through the above scheme, within the range of 30-60°, the laser energy can more fully act on a certain depth range of the surface, so that the surface particles produce more regular and sufficient vibration to form ultrasonic surface waves, thereby ensuring that the signals received by the subsequent ultrasonic sensor have high amplitude and good stability, and facilitating more accurate analysis of signal features to detect defects.

[0015] Optionally, the wavelength of the laser output is 1064nm, the pulse width is 10ns, and the energy density is 1-10J / cm 2 .

[0016] Through the above scheme, electrons in the metal have a suitable absorption probability for laser photons of this wavelength, allowing laser energy to be effectively converted into heat energy. This heat-mechanical conversion process is then triggered on the surface of the part based on the thermoelastic effect or ablation effect, efficiently exciting ultrasonic surface waves. Different metal materials have different light absorption characteristics, but the 1064nm wavelength exhibits good excitation effects in many commonly used precision metal materials such as aluminum alloys, stainless steel, and titanium alloys, ensuring that this detection method is applicable to various metal parts. The 10ns pulse width combined with the 1064nm wavelength can transfer high energy to the surface of the metal part in a very short time, instantly creating a strong thermal shock that causes the surface material to expand and contract rapidly, thus generating clear ultrasonic surface waves with sufficient intensity. By adjusting the energy density to 1-10 J / cm², [the method can achieve the desired effect]. 2 Within a certain range, it can avoid irreversible damage to the surface of precision metal parts caused by excessive energy, such as ablation pits, material melting and deformation. While ensuring the effective excitation of ultrasonic surface waves for detection, it maintains the original surface accuracy and quality of the parts.

[0017] Optionally, when the thickness of the precision metal part is 5-10 mm, the energy density of the laser is controlled at 1-5 J / cm². 2 .

[0018] Optionally, the ultrasonic sensors are evenly distributed around the metal part being tested, and the distance between the ultrasonic sensors and the surface of the metal part being tested is 2-3 mm.

[0019] By uniformly distributing ultrasonic sensors around the metal part being tested using the above method, comprehensive capture of ultrasonic surface wave signals propagating from all directions on the part's surface can be achieved. Regardless of the origin or angle of the ultrasonic surface wave on the part's surface, the surrounding sensors have a higher probability of receiving it, avoiding detection blind spots caused by sensor placement limitations. For precision metal parts with complex curved surfaces or irregular shapes, the propagation path of ultrasonic surface waves on their surface is complex and varied. Uniformly distributed sensors ensure that signals propagating from different curved areas can be effectively received, thereby maximizing the acquisition of relevant information from the entire part's surface. The distance between the ultrasonic sensor and the surface of the metal part being tested is set at 2-3 mm. This distance range helps to receive ultrasonic surface wave signals of appropriate intensity and good quality. If the distance is too close, the presence of the sensor may interfere with the propagation of the ultrasonic surface wave, affecting its normal reflection and scattering characteristics. It may also cause the sensor to receive a signal that is too strong, exceeding its optimal receiving range, resulting in signal distortion. If the distance is too far, the ultrasonic surface wave will experience significant energy attenuation during propagation, weakening the signal strength received by the sensor, possibly to the point where it is difficult to accurately distinguish signal characteristics.

[0020] Optionally, the ultrasonic sensor has a frequency response range of 2-8MHz and a minimum detection signal amplitude of 5μV.

[0021] The above scheme ensures that the 2-8MHz frequency response range allows the sensor to capture ultrasonic surface wave signals generated under different conditions, avoiding the loss of certain key signals due to frequency mismatch, thereby improving the versatility for surface inspection of various precision metal parts. The minimum detection signal amplitude of 5μV endows the ultrasonic sensor with high sensitivity, enabling it to capture weak signal changes caused by minute defects, thus making the detection of minute defects possible.

[0022] Optionally, the sampling frequency of the signal acquisition card is 80MHz, and the resolution of the signal acquisition card is 16-bit.

[0023] The combination of high sampling frequency and high resolution enables the signal acquisition card to comprehensively and accurately acquire ultrasonic surface wave signals, thereby more realistically reflecting the surface condition of precision metal parts.

[0024] Optionally, the bandpass filter has a low cutoff frequency of 1.5MHz and a high cutoff frequency of 8.5MHz.

[0025] By setting the low cutoff frequency of the bandpass filter to 1.5MHz and the high cutoff frequency to 8.5MHz, the main frequency range of the ultrasonic surface wave signal can be accurately selected, effectively removing low-frequency interference below 1.5MHz (such as low-frequency fluctuations caused by environmental vibration and power supply interference) and high-frequency noise above 8.5MHz (such as high-frequency thermal noise generated by electronic components). This method greatly purifies the ultrasonic surface wave signal, allowing subsequent signal analysis to focus on the truly relevant information related to the surface condition of the part, reducing the impact of irrelevant interference factors on the test results.

[0026] In summary, this application has the following beneficial effects:

[0027] 1. Since this application uses a laser to scan the surface of the part point by point to excite ultrasonic surface waves for surface inspection, this method adopts non-contact inspection, which avoids secondary damage such as scratches and wear caused by traditional contact inspection to the surface of the part. This is beneficial to protecting the surface quality of precision metal parts in fields such as aerospace and high-end electronic equipment, and greatly improves the accuracy of defect identification.

[0028] 2. In this application, the laser irradiation angle is preferably 30-60° to the normal of the part surface. This allows the laser energy to act on a certain depth range of the surface, causing the surface particles to vibrate regularly and with sufficient intensity to form ultrasonic surface waves with high amplitude and good stability. This facilitates accurate analysis of signal characteristics and defect detection. Furthermore, the laser output wavelength of 1064nm allows electrons in the metal to effectively absorb laser photons and convert them into heat energy. Based on the thermoelastic effect or ablation effect, ultrasonic surface waves are efficiently excited. This method is applicable to various commonly used precision metal materials. A 10ns pulse width, combined with this, can instantly generate a strong thermal shock, producing clear and sufficiently strong ultrasonic surface waves. The pulse strength can be adjusted from 1-10 J / cm. 2 The energy density can effectively excite ultrasonic surface waves for detection while avoiding damage to the surface of the parts, thus maintaining their original accuracy and quality.

[0029] 3. The method of this application is applicable to the surface defect detection of various metal parts, and is not limited by the appearance and shape of the metal parts, thus having high universality. Detailed Implementation

[0030] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0031] Example

[0032] Example 1

[0033] A method for surface inspection of precision metal parts:

[0034] Laser selection and settings

[0035] An Nd:YAG laser with an output wavelength of 1064 nm and a pulse width of 10 ns was selected. The laser was mounted on an optical platform with precisely adjustable angle and position. Through a computer control system, the laser beam could be directed at specific angles to different locations on the surface of the part, achieving comprehensive scanning.

[0036] A piezoelectric ultrasonic sensor with a frequency response range of 2-8MHz was selected to effectively receive ultrasonic surface wave signals generated on the surface of metal parts. The sensor must have high sensitivity, with a minimum detectable signal amplitude of 5μV, to ensure the capture of even the slightest signal changes.

[0037] The sensors are arranged according to the shape and size of the part. For rectangular metal parts, one sensor is installed at the midpoint of each of its four sides; for circular parts, four sensors are evenly arranged along the circumference. The sensors are fixed at a position 2-3 mm away from the surface of the part using high-precision clamps to ensure stable signal reception and without affecting the propagation of ultrasonic surface waves.

[0038] Connect the sensor and signal acquisition card with a low-noise, well-shielded cable to reduce the impact of external electromagnetic interference on the signal.

[0039] A high-speed signal acquisition card is used, with a sampling frequency set to 80MHz, which meets the requirements for ultrasonic surface wave signal acquisition. The acquisition card has a resolution of 16 bits, which can accurately quantize the signal amplitude.

[0040] A high-speed USB 3.2 data transfer interface is used between the signal acquisition card and the computer. Meanwhile, dedicated signal acquisition software is installed on the computer for real-time acquisition, display, and storage of ultrasonic surface wave signals.

[0041] Testing process

[0042] The precision metal parts to be tested are cleaned to remove surface oil, dust and other impurities to ensure a clean surface and avoid interfering with the test results.

[0043] The parts are placed on the testing platform and fixed in place by mechanical clamps to ensure that the parts remain in a stable position during the testing process and do not shift.

[0044] The laser is activated, and the surface of the part is scanned point by point at a 45° angle between the laser beam and the surface normal. The laser energy density is 5 J / cm². 2 At each scanning point, a laser pulse excites and generates ultrasonic surface waves.

[0045] The ultrasonic sensor receives ultrasonic surface wave signals in real time, and the signals are digitized by a signal acquisition card and transmitted to a computer. During the acquisition process, ultrasonic surface wave signals are acquired eight times at each scanning point.

[0046] In the computer, signal processing software is used to filter the acquired signal. A bandpass filter is used, with the low cutoff frequency set to 1.5MHz and the high cutoff frequency set to 8.5MHz, to remove high-frequency noise and low-frequency interference from the signal.

[0047] The filtered signal is normalized using the maximum-minimum normalization method to normalize the signal amplitude to the 0-1 range.

[0048] Extract time-domain features and analyze the peak amplitude, rise time, and fall time of the signal at each scan point. Calculate the mean and standard deviation of the peak amplitude for each signal. If the mean peak amplitude decreases by more than 20% relative to the defect-free standard signal, and the standard deviation increases, a defect exists. Simultaneously, record changes in rise time and fall time; a rise time extension exceeding 10% may indicate an anomaly.

[0049] The extracted signal features are compared with a pre-established defect feature database. The database contains ultrasonic surface wave signal features of different types of defects on the metal part, obtained experimentally. Based on the comparison results, the type of defect is determined.

[0050] Example 2

[0051] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the laser irradiation angle is at a 30° angle to the normal of the part surface.

[0052] Example 3

[0053] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the laser irradiation angle is at a 60° angle to the normal of the part surface.

[0054] Example 4

[0055] A method for surface inspection of precision metal parts: The difference from Example 1 is that the laser output energy density is 1 J / cm². 2 .

[0056] Example 5

[0057] A method for surface inspection of precision metal parts: The difference from Example 1 is that the laser output energy density is 10 J / cm². 2 .

[0058] Example 6

[0059] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that ultrasonic surface wave signals are collected 5 times at each scanning point.

[0060] Example 7

[0061] A method for surface inspection of precision metal parts: The difference from Example 1 is that ultrasonic surface wave signals are collected 10 times at each scanning point.

[0062] Comparative Example 1

[0063] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the laser irradiation angle is at a 20° angle to the normal of the part surface.

[0064] Comparative Example 2

[0065] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the laser irradiation angle is at a 70° angle to the normal of the part surface.

[0066] Comparative Example 3

[0067] A method for surface inspection of precision metal parts: The difference from Example 1 is that the laser output energy density is 12 J / cm². 2 .

[0068] Comparative Example 4

[0069] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the distance between the ultrasonic sensor and the surface of the metal part being tested is 1-2 mm.

[0070] Comparative Example 5

[0071] A method for inspecting the surface of precision metal parts: The difference from Example 1 is that the distance between the ultrasonic sensor and the surface of the metal part being tested is 3-4 mm.

[0072] Detection methods

[0073] A precision-machined shaft with a diameter of 120mm*1250mm was used as the test sample. Surface defect data of the sample was obtained by magnetic particle testing. This data was used as a reference standard, and the test was repeated using the test methods of the example and comparative examples. The difference between the two test results was compared.

[0074] Table 1 Test Data

[0075]

[0076]

[0077] As can be seen from Examples 1-3 and Comparative Examples 1-2, and in conjunction with Table 1, within the 30-60° angle range, laser energy can more fully act on a certain depth range of the surface, causing surface particles to generate more regular and sufficiently strong vibrations to form ultrasonic surface waves. This ensures that the signals received by subsequent ultrasonic sensors have high amplitude and good stability, facilitating more accurate analysis of signal characteristics to detect defects. When the ultrasonic surface wave propagates at an angle of 30-60° with the normal and interacts with the defect, multiple ultrasonic sensors receive the reflected and scattered signals. By combining the propagation characteristics and geometric relationships of the ultrasonic surface wave at a specific angle, the location of the defect on the part surface can be calculated more accurately.

[0078] As can be seen from Examples 1, 4, and 5 and Comparative Example 3, and in conjunction with Table 1, by adjusting the energy density to 1-10 J / cm², [the following method can be used]. 2Within a certain range, it can avoid irreversible damage to the surface of precision metal parts caused by excessive energy, such as ablation pits, material melting and deformation. While ensuring the effective excitation of ultrasonic surface waves for detection, it maintains the original surface accuracy and quality of the parts.

[0079] As can be seen from Example 1 and Comparative Examples 4-5, and in conjunction with Table 1, setting the distance between the ultrasonic sensor and the surface of the metal part being tested at 2-3 mm is beneficial for receiving ultrasonic surface wave signals of suitable intensity and good quality. If the distance is too close, the presence of the sensor may interfere with the propagation of the ultrasonic surface waves, affecting their normal reflection and scattering characteristics. It may also cause the signal received by the sensor to be too strong, exceeding its optimal receiving range and resulting in signal distortion. Conversely, if the distance is too far, the ultrasonic surface waves will experience significant energy attenuation during propagation, weakening the signal strength received by the sensor, potentially to the point where it is difficult to accurately distinguish signal characteristics. Maintaining a distance of 2-3 mm allows the ultrasonic surface waves to propagate to the sensor in a relatively ideal state, ensuring that the signal received by the sensor has sufficient amplitude and a clear waveform, facilitating subsequent accurate signal analysis and processing.

[0080] As can be seen from Examples 1 and 6-7 and Table 1, the random error of the signal is further reduced by averaging multiple acquisitions, ensuring that the acquired signal features are more representative of the real situation of the scanning point, making the detection results more reliable, and avoiding defects such as misjudgment or missed judgment due to fluctuations in a single signal acquisition.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for detecting a surface of a precision metal part, characterized in that, The method comprises the following steps: After cleaning the precision metal part to be detected, it is fixed on the detection platform; Start the laser, and scan the surface of the part point by point according to the preset scanning path and angle, excite the ultrasonic surface wave at each scanning point, the ultrasonic sensor receives the signal in real time, and transmits the signal digitized by the signal acquisition card to the computer, and collects 5-10 ultrasonic surface wave signals at each scanning point; The computer uses signal processing software to filter the collected signals with a band-pass filter, and normalizes the filtered signals to the interval of 0-1; Extract the time domain features, calculate the peak amplitude mean value and standard deviation, rising time and falling time of each signal, and judge whether there is a defect when the peak amplitude mean value decreases by more than 20% relative to the standard signal, the standard deviation increases, and the rising time is prolonged by more than 10%; The laser irradiation angle is 30-60° with the normal of the part surface; The laser output wavelength is 1064nm, the pulse width is 10ns, the energy density of the laser is controlled at 1-5J / cm² when the thickness of the precision metal part is 5-10mm, the ultrasonic sensors are uniformly distributed around the measured metal part, and the distance between the ultrasonic sensor and the surface of the measured metal part is 2-3mm.

2. The method of claim 1, wherein, The frequency response range of the ultrasonic sensor is 2-8MHz, and the minimum detection signal amplitude is 5μV.

3. The method of claim 1, wherein: The sampling frequency of the signal acquisition card is 80MHz, and the resolution of the signal acquisition card is 16 bits.

4. The method of claim 1, wherein: The low cutoff frequency of the band-pass filter is 1.5MHz, and the high cutoff frequency is 8.5MHz.

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