Sand mould strength on-line non-destructive testing method and device

Abstract

The application discloses a sand mold strength online nondestructive detection method and device, and relates to the field of sand mold strength detection. The method comprises the following steps: emitting high-frequency ultrasonic waves to the surface of a sand mold to be detected through an ultrasonic emission probe; receiving reflected waves reflected by the surface of the sand mold through an ultrasonic receiving probe and converting the reflected waves into electric signals; converting the electric signals into digital signals through a data collector; pre-processing the digital signals through a computing device, calculating an ultrasonic wave propagation time difference, correcting the propagation time difference, calculating the internal stress of the sand mold based on the corrected propagation time difference, and calculating the strength of the sand mold based on the internal stress of the sand mold. The application can realize nondestructive, online detection and real-time monitoring, and ensure the quality stability of each sand mold in the production process.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and more specifically to a method and apparatus for online nondestructive testing of sand mold strength. Background Technology

[0002] In casting production, the strength of the sand mold directly affects the quality of the castings and production efficiency. Insufficient sand mold strength can lead to defects in the castings, such as deformation, cracks, or even scrap. Therefore, sand mold strength testing is a crucial and indispensable step in the casting process. Existing methods for testing sand mold strength mainly rely on destructive testing, such as compressive strength tests and tensile strength tests. While these traditional methods can provide strength data, they have several significant drawbacks in practical applications.

[0003] First, traditional destructive testing requires sampling, which means that part of the sand mold needs to be destroyed during the testing process. This portion of the mold is usually unusable for actual production. For large-scale production processes, frequent sampling and testing not only wastes materials but also increases production costs and reduces efficiency. Second, these methods are often offline inspections, making it impossible to monitor the sand molds in use on the production line in real time. This means that problems caused by insufficient sand mold strength may not be detected and corrected in time during the casting process, thus increasing production risks and scrap rates.

[0004] Therefore, how to provide an ultrasonic surface wave non-destructive testing method and device for sand mold strength, and successfully overcome the problems of complex testing process, low accuracy, and poor real-time performance, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides an online non-destructive testing method and device for sand mold strength, which can realize non-destructive, online testing and real-time monitoring, ensuring the quality stability of each sand mold during the production process. Combined with signal processing technology, a non-linear relationship between sand mold strength and ultrasonic propagation time difference is established, which improves the accuracy and reliability of the test results.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for online non-destructive testing of sand mold strength, comprising:

[0008] High-frequency ultrasonic waves are emitted onto the surface of the sand mold to be tested using an ultrasonic transmitting probe.

[0009] The reflected waves from the surface of the sand mold under test are received by an ultrasonic receiving probe and converted into electrical signals;

[0010] The electrical signal is converted into a digital signal using a data acquisition device;

[0011] The digital signal is preprocessed by a computing device to calculate and correct the ultrasonic propagation time difference. The internal stress of the sand mold is calculated based on the corrected propagation time difference, and the strength of the sand mold is calculated based on the internal stress of the sand mold.

[0012] Preferably, the preprocessing includes adaptive median filtering, Savitzky-Golay filtering, and cubic spline interpolation.

[0013] Preferably, the ultrasonic wave propagation time difference is calculated using the digital correlation method, and the calculation formula is as follows:

[0014] R 12 (τ)=∫S1(t)·S2(t+τ)dt

[0015] In the formula, τ is the time delay, and R 12 (τ) reaches its maximum value when τ = Δt, where Δt is the time difference of ultrasonic wave propagation from the transmitting probe to the receiving probe. R 12 (τ) is the cross-correlation function of the transmitted waveform S1(t) and the received waveform S2(t).

[0016] The preferred and corrected formula for calculating the propagation time difference is as follows:

[0017] Δt′=Δt+C r =Δt+αR a

[0018] In the formula, Δt′ is the corrected propagation time difference, and R a C represents the average deviation of the sand mold surface profile. r As a correction factor, α represents the degree of influence of roughness on the time difference, and Δt represents the ultrasonic wave propagation time difference from the ultrasonic transmitting probe to the ultrasonic receiving probe.

[0019] Preferably, the process also includes calibrating the acoustoelastic coefficient of the material, the specific process of which is as follows:

[0020] Select representative sand mold material samples, ensuring that the samples are uniform and free of obvious defects, and that the sample size meets the standard, so as to ensure that the propagation of ultrasonic signals is not affected by edge effects.

[0021] Under stress-free conditions, ultrasonic waves are excited on the surface of a sand-shaped material sample and the propagation signal is detected. The initial propagation time t0 and propagation distance L of the ultrasonic waves are measured, and the initial ultrasonic propagation velocity v0 = L / t0 is calculated.

[0022] A known stress σ is gradually applied to the sand mold material sample. i The ultrasonic wave propagation velocity was measured repeatedly under each stress state, and the propagation time t was recorded for each measurement. i And calculate the propagation velocity v under stress state.i =L / t i ;

[0023] According to the theory of acoustoelasticity, the relationship between the propagation velocity of ultrasonic waves and the internal stress of the sand mold is expressed as:

[0024]

[0025] Where E is the elastic modulus of the material, u is Poisson's ratio, ρ is the density of the material, and σ is the internal stress of the sand mold;

[0026] For different stresses σ i The corresponding propagation velocity v is measured at i = 1, 2, ..., n. i Through formula Calculate y under each stress state i For data points (σ) i ,y i Linear regression was performed to obtain the acoustoelastic coefficient K of the material:

[0027]

[0028] Where, σ i It is the i-th stress value, n represents the number of different stress states, y i It is related to the i-th stress σ i The corresponding function of the speed of ultrasonic wave propagation. It is stress σ i The mean, It is y i The mean.

[0029] Preferably, the formula for calculating the internal stress of the sand mold is:

[0030]

[0031] Where σ is the internal stress of the sand mold, and Δt0 is the propagation time difference under stress-free conditions.

[0032] Preferably, the formula for calculating the strength of the sand mold is:

[0033] σ max =a·σ 2 +b·σ+c

[0034] Where a, b, and c are coefficients obtained through fitting, and σ is the internal stress of the sand mold. max The strength of the sand mold.

[0035] An online non-destructive testing device for sand mold strength includes: an ultrasonic transmitting probe, an ultrasonic receiving probe, a pulse transmitting receiver, a data acquisition unit, and a computing unit. The ultrasonic transmitting probe and the ultrasonic receiving probe are respectively connected to the pulse transmitting receiver, the pulse transmitting receiver is connected to the data acquisition unit, and the data acquisition unit is connected to the computing unit.

[0036] The ultrasonic transmitting probe is used to emit high-frequency ultrasonic waves onto the surface of the sand mold to be tested.

[0037] The ultrasonic receiving probe is used to receive the reflected waves reflected from the surface of the sand mold under test and convert them into electrical signals;

[0038] The pulse transmitter and receiver are used to generate high-energy pulses to excite the ultrasonic transmitter probe and to receive electrical signals sent by the ultrasonic receiver probe.

[0039] The data acquisition device is used to convert electrical signals into digital signals;

[0040] The computing device is used to preprocess digital signals, calculate and correct ultrasonic propagation time difference, calculate internal stress of sand mold based on the corrected propagation time difference, and calculate sand mold strength based on internal stress of sand mold.

[0041] Preferably, it also includes an oscilloscope, which is connected to the data acquisition unit for real-time monitoring and analysis of ultrasonic waveforms.

[0042] Preferably, the high-frequency ultrasonic frequency is in the range of 1-5MHz, and the sampling frequency of the data acquisition device is at least twice the high-frequency ultrasonic frequency.

[0043] As can be seen from the above technical solution, compared with the prior art, the present invention discloses an online non-destructive testing method and device for sand mold strength. Compared with the traditional destructive testing method, the present invention avoids sample damage and realizes non-destructive testing. Through preprocessing techniques such as median filtering and spline interpolation, the signal quality is improved, noise interference is suppressed, and the reliability of the test results is enhanced.

[0044] By introducing the digital correlation method and calibrating the acoustic elastic coefficient, the relationship between ultrasonic propagation time difference and sand mold strength was accurately correlated, enabling precise assessment of sand mold strength and greatly improving the level of sand mold quality control. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the structure of an online non-destructive testing device for sand mold strength provided by the present invention.

[0047] Figure 2 The present invention provides a flowchart of an online non-destructive testing method for the strength of sand molds.

[0048] Among them, 1. Ultrasonic transmitting probe, 2. Ultrasonic receiving probe, 3. Pulse transmitting receiver, 4. Data acquisition device, 5. Calculation device, 6. Oscilloscope, 7. Sand mold to be tested, 8. Universal testing machine. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention discloses an online non-destructive testing device for sand mold strength, such as... Figure 1 As shown, it includes: an ultrasonic transmitting probe 1, an ultrasonic receiving probe 2, a pulse transmitting receiver 3, a data acquisition unit 4, and a computing device 5. The ultrasonic transmitting probe 1 and the ultrasonic receiving probe 2 are respectively connected to the pulse transmitting receiver 3, the pulse transmitting receiver 3 is connected to the data acquisition unit 4, and the data acquisition unit 4 is connected to the computing device 5.

[0051] The ultrasonic transmitting probe 1 is used to transmit high-frequency ultrasonic waves to the surface of the sand mold 7 to be tested;

[0052] The ultrasonic receiving probe 2 is used to receive the reflected waves reflected from the surface of the sand mold 7 under test and convert them into electrical signals;

[0053] The pulse transmitter receiver 3 is used to generate high-energy pulses to excite the ultrasonic transmitter probe and to receive electrical signals sent by the ultrasonic receiver probe.

[0054] Data acquisition unit 4 is used to convert electrical signals into digital signals;

[0055] The computing device 5 is used to preprocess the digital signal, calculate and correct the ultrasonic propagation time difference, calculate the internal stress of the sand mold based on the corrected propagation time difference, and calculate the strength of the sand mold based on the internal stress of the sand mold.

[0056] Specifically, the ultrasonic transmitting probe 1 converts electrical signals into high-frequency ultrasonic waves, ensuring that the ultrasonic waves can effectively propagate on the sand mold surface. The generated high-frequency ultrasonic waves have a short wavelength, allowing for sensitive detection of minute changes and defects on the sand mold surface.

[0057] When ultrasonic waves propagate on the surface of a sand mold, they are reflected when they encounter structural discontinuities or changes in material density. The ultrasonic receiving probe 2 captures these reflected signals and converts them back into electrical signals.

[0058] Data acquisition unit 4 is responsible for converting the electrical signals received by the pulse transmitter and receiver into digital signals for further analysis and processing by computing device 5. To improve the real-time performance of the system, data acquisition unit 5 also supports direct signal transmission to oscilloscope 6 for real-time monitoring and analysis of ultrasonic waveforms.

[0059] The computing device 6 is specifically a computer, responsible for processing the digital signals from the data acquisition unit 4, and analyzing, modeling, and visualizing the data through software. Through the computer's real-time data processing capabilities, the system can quickly analyze and calculate the time difference of ultrasonic wave propagation and its correction value, and obtain real-time stress and strength assessment results for the sand mold.

[0060] This invention's online testing device can quickly calculate the stress and strength of sand molds. The test results can be displayed instantly on the operating interface and can be correlated with manufacturing parameters (such as sand mold formulation, temperature, humidity, etc.) for timely adjustments to the production process, ensuring the stable quality of each sand mold. Through this online testing method, the strength data of the sand molds is continuously monitored and analyzed, enabling intelligent management of the production process, improving production efficiency, and reducing scrap rates.

[0061] Based on the above-described apparatus, this embodiment provides an online non-destructive testing method for sand mold strength, such as... Figure 2 As shown, it includes:

[0062] High-frequency ultrasonic waves are emitted onto the surface of the sand mold to be tested via ultrasonic transmitting probe 1;

[0063] The ultrasonic receiving probe 2 receives the reflected waves from the sand mold surface and converts them into electrical signals;

[0064] The electrical signal is converted into a digital signal by the data acquisition unit 4;

[0065] The computing device 5 preprocesses the digital signal, calculates and corrects the ultrasonic propagation time difference, calculates the internal stress of the sand mold based on the corrected propagation time difference, and calculates the strength of the sand mold based on the internal stress of the sand mold.

[0066] In this embodiment, ultrasonic surface waves are excited in a designated area on the sand mold surface, and a receiving probe is used to receive the propagated signal. To meet the requirements of acoustic attenuation characteristics and detection sensitivity of the sand mold material, the ultrasonic frequency is selected in the range of 1-5MHz. The data acquisition unit records the transmitted waveform S1(t) and the received waveform S2(t), and the sampling frequency should be at least twice the signal frequency to ensure the accuracy of data acquisition.

[0067] In this embodiment, preprocessing the collected ultrasonic surface wave signals is a crucial step in the nondestructive testing process, decisively impacting the accuracy of subsequent analysis results. The main objectives of preprocessing are to improve signal quality, suppress noise interference, and lay the foundation for accurate time difference measurement. First, an adaptive median filtering technique is employed to address the random noise prevalent in ultrasonic signals. Median filtering, as a nonlinear digital filtering method, significantly enhances the suppression of impulse noise by replacing the center point value with the median value of the data points within a window, while preserving the signal's edge features. To further optimize the filtering effect, an adaptive window size strategy is introduced. This strategy dynamically adjusts the filtering window based on the signal's local statistical characteristics, increasing the window size in areas of strong noise to improve denoising capabilities, and decreasing the window size in areas of drastic signal changes to preserve signal details. Next, to further improve signal smoothness and ensure the preservation of its higher-order features, a Savitzky-Golay filter is applied after median filtering. This filter achieves signal smoothing through local polynomial fitting, effectively removing noise while preserving the signal's higher-order moments. Finally, to further improve the accuracy of time difference measurement, cubic spline interpolation was performed on the preprocessed signal.

[0068] In this embodiment, the digital correlation method is used to calculate the ultrasonic wave propagation time difference. The digital correlation method calculates the cross-correlation function R between the transmitted waveform S1(t) and the received waveform S2(t). 12 (τ) Determines the time difference using the formula:

[0069] R 12 (τ)=∫S1(t)·S2(t+τ)dt

[0070] In the formula, τ is the time delay, and R 12 (τ) reaches its maximum value when τ=Δt, where Δt is the time difference of ultrasonic wave propagation from the ultrasonic transmitting probe to the ultrasonic receiving probe.

[0071] In this embodiment, during sand mold inspection, surface roughness affects the propagation characteristics of ultrasonic waves, including scattering and attenuation, which in turn affects the accuracy of time difference measurement. To improve measurement accuracy, the propagation time difference is corrected.

[0072] Roughness R a The average deviation of the sand mold surface profile is represented by the correction factor C. r It is proportional to roughness:

[0073] C r =αR a

[0074] α represents the degree of influence of roughness on time difference.

[0075] Corrected propagation time difference Δt′:

[0076] Δt′=Δt+C r =Δt+αR a

[0077] In this embodiment, to correlate the corrected propagation time difference Δt′ with the internal stress σ of the sand mold, it is necessary to calibrate the acoustoelastic coefficient of the material. The calibration process includes the following steps:

[0078] First, select representative sand mold material samples, ensuring the samples are uniform and free of obvious defects. The sample dimensions should conform to standards to ensure that the propagation of the ultrasonic signal is not affected by edge effects. Under stress-free conditions, by exciting ultrasonic waves on the surface of the sand mold material and detecting the propagation signal using a pulse transmitter and receiver, measure the initial ultrasonic wave propagation time t0 and propagation distance L, thereby calculating the initial ultrasonic wave propagation velocity v0 = L / t0. Then, gradually apply a known uniform stress σ to the sample using a universal testing machine 8. i The ultrasonic wave propagation velocity was measured repeatedly under each stress state, and the propagation time t was recorded for each measurement. i And calculate the propagation velocity v under stress state. i =L / t i According to the theory of acoustoelasticity, the relationship between the propagation velocity of ultrasonic waves and the internal stress of the sand mold can be expressed as:

[0079]

[0080] Where E is the elastic modulus of the material, u is Poisson's ratio, ρ is the material density, and v0 is the ultrasonic velocity under stress-free conditions.

[0081] For different stresses σ i Measure the corresponding ultrasonic propagation velocity v under (i = 1, 2, ..., n) i Using the formula Calculate y under each stress statei For data points (σ) i ,y i Perform linear regression to obtain the slope K, which is the acoustoelastic coefficient of the material. The calculation formula is:

[0082]

[0083] Where, σ i It is the i-th stress value, n represents the number of different stress states, y i It is related to the i-th stress σ i The corresponding function of the speed of ultrasonic wave propagation. It is stress σ i The mean, It is y i The mean.

[0084] Using the corrected propagation time difference Δt′ and the calibrated acoustoelastic coefficient K, the internal stress σ of the sand mold can be derived:

[0085]

[0086] Where Δt0 is the propagation time difference under stress-free conditions, v0 is the ultrasonic propagation speed under stress-free conditions, and K is the acoustoelastic coefficient.

[0087] In this embodiment, the key to sand mold strength assessment lies in establishing the relationship between the measured stress σ and the material's ultimate strength σ. max The relationship between them can be calculated using the following formula:

[0088] σ max =a·σ 2 +b·σ+c

[0089] Where a, b, and c are coefficients obtained through fitting.

[0090] By applying this model, the measured stress can be effectively converted into the ultimate strength of the sand mold material, thereby achieving an effective assessment of the sand mold strength.

[0091] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0092] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for online non-destructive testing of sand mold strength, characterized in that, include: High-frequency ultrasonic waves are emitted onto the surface of the sand mold to be tested using an ultrasonic transmitting probe. The reflected waves from the surface of the sand mold under test are received by an ultrasonic receiving probe and converted into electrical signals; The electrical signal is converted into a digital signal using a data acquisition device; The digital signal is preprocessed by a computing device to calculate and correct the ultrasonic propagation time difference. The internal stress of the sand mold is calculated based on the corrected propagation time difference, and the strength of the sand mold is calculated based on the internal stress of the sand mold.

2. The online non-destructive testing method for sand mold strength according to claim 1, characterized in that, Preprocessing includes adaptive median filtering, Savitzky-Golay filtering, and cubic spline interpolation.

3. The online non-destructive testing method for sand mold strength according to claim 1, characterized in that, The time difference of ultrasonic wave propagation is calculated using the digital correlation method. The formula is as follows: R 12 (τ)=∫S1(t)·S2(t+τ)dt In the formula, τ is the time delay, and R 12 (τ) reaches its maximum value when τ = Δt, where Δt is the time difference of ultrasonic wave propagation from the transmitting probe to the receiving probe. R 12 (τ) is the cross-correlation function of the transmitted waveform S1(t) and the received waveform S2(t).

4. The online non-destructive testing method for sand mold strength according to claim 1, characterized in that, The corrected formula for calculating the propagation time difference is: Δt′=Δt+C r =Δt+αR a In the formula, Δt′ is the corrected propagation time difference, and R a C represents the average deviation of the sand mold surface profile. r As a correction factor, α represents the degree of influence of roughness on the time difference, and Δt represents the ultrasonic wave propagation time difference from the ultrasonic transmitting probe to the ultrasonic receiving probe.

5. The online non-destructive testing method for sand mold strength according to claim 1, characterized in that, This also includes calibrating the acoustoelastic coefficient of the material, the specific process of which is as follows: Select representative sand mold material samples, ensuring that the samples are uniform and free of obvious defects, and that the dimensions meet the standards, so as to ensure that the propagation of ultrasonic signals is not affected by edge effects; Under stress-free conditions, ultrasonic waves are excited on the surface of a sand-shaped material sample and the propagation signal is detected. The initial propagation time t0 and propagation distance L of the ultrasonic waves are measured, and the initial ultrasonic propagation velocity v0 = L / t0 is calculated. A known stress σ is gradually applied to the sand mold material sample. i The ultrasonic wave propagation velocity was measured repeatedly under each stress state, and the propagation time t was recorded for each measurement. i And calculate the propagation velocity v under stress state. i =L / t i ; According to the theory of acoustoelasticity, the relationship between the propagation velocity of ultrasonic waves and the internal stress of the sand mold is expressed as: Where E is the elastic modulus of the material, u is Poisson's ratio, ρ is the density of the material, and σ is the internal stress of the sand mold; For different stresses σ i The corresponding propagation velocity v is measured at i = 1, 2, ..., n. i Through formula Calculate y under each stress state i For data points (σ) i ,y i Linear regression was performed to obtain the acoustoelastic coefficient K of the material: Where, σ i It is the i-th stress value, n represents the number of different stress states, y i It is related to the i-th stress σ i The corresponding function of the speed of ultrasonic wave propagation. It is stress σ i The mean, It is y i The mean.

6. The online non-destructive testing method for sand mold strength according to claim 5, characterized in that, The formula for calculating the internal stress of a sand mold is: Where σ is the internal stress of the sand mold, and Δt0 is the propagation time difference under stress-free conditions.

7. The online non-destructive testing method for sand mold strength according to claim 1, characterized in that, The formula for calculating the strength of sand molds is: s max =a·s 2 +b·s+c Where a, b, and c are coefficients obtained through fitting, and σ is the internal stress of the sand mold. max For sand mold strength.

8. An online non-destructive testing device for sand mold strength, characterized in that, include: An ultrasonic transmitting probe, an ultrasonic receiving probe, a pulse transmitting receiver, a data acquisition device, and a computing device are provided. The ultrasonic transmitting probe and the ultrasonic receiving probe are respectively connected to the pulse transmitting receiver. The pulse transmitting receiver is connected to the data acquisition device, and the data acquisition device is connected to the computing device. The ultrasonic transmitting probe is used to emit high-frequency ultrasonic waves onto the surface of the sand mold to be tested. The ultrasonic receiving probe is used to receive the reflected waves reflected from the surface of the sand mold under test and convert them into electrical signals; The pulse transmitter and receiver are used to generate high-energy pulses to excite the ultrasonic transmitter probe and to receive electrical signals sent by the ultrasonic receiver probe. The data acquisition device is used to convert electrical signals into digital signals; The computing device is used to preprocess digital signals, calculate and correct ultrasonic propagation time difference, calculate internal stress of sand mold based on the corrected propagation time difference, and calculate sand mold strength based on internal stress of sand mold.

9. The online non-destructive testing device for sand mold strength according to claim 8, characterized in that, It also includes an oscilloscope, which is connected to the data acquisition unit for real-time monitoring and analysis of ultrasonic waveforms.

10. The online non-destructive testing device for sand mold strength according to claim 8, characterized in that, The high-frequency ultrasonic frequency is in the range of 1-5MHz, and the sampling frequency of the data acquisition device is at least twice the high-frequency ultrasonic frequency.

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