JP3037897B2 - Ear ratio measurement method for thin metal plates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to aluminum,
The present invention relates to a method and an apparatus for measuring an ear ratio of a sheet metal manufactured by rolling.

[0002]

2. Description of the Related Art The ear ratio is an index indicating the anisotropy of drawing generated when a metal sheet is deep drawn. The conventional ear ratio measuring method will be described. (Prior Art 1) As shown in FIG. 11, a cup-shaped deep drawing process is performed on a circularly cut thin metal plate using a die and a punch having a predetermined diameter. At this time, the ends of the metal sheet do not have a fixed height but have peaks and valleys, which are called "squeeze cup ears" or "ears". The quantification of the degree of the ear is the "ear ratio", which is calculated as follows. The angle is set clockwise or counterclockwise with the rolling direction of the metal sheet set to 0 °. Assuming that the height of the ear (height from the cup bottom) generated in the angle θ direction is hθ, the ear ratio E (%) is

(Equation 1) Given by Generally, in the case of a rolled aluminum plate, the ear is 0 °,
When the 90 °, 180 °, and 270 ° directions are higher,
There are two types of cases where the directions of 5 °, 135 °, 225 °, and 315 ° increase, and in this case, the ear ratio is negative for the former and positive for the latter (called the negative ear and the positive ear, respectively). The prior art 1 described above is a method based on a destructive test, but the following three examples are all non-destructive methods for measuring ear rate.

(Prior art 2) This is disclosed in Japanese Unexamined Patent Publication No. 7-318.
540 discloses an ear ratio measurement method. The basic principle and implementation method will be briefly described below.
The ears described above occur because the rolled plate is composed of several "textures". The texture is an index indicating whether or not the crystal orientation is biased in a specific direction in a polycrystalline metal structure. When a metal plate is plastically deformed, the deformation does not proceed isotropically, but proceeds in a direction that is easily determined by the crystal orientation. When there is a texture, since the crystal orientation is aligned in a specific direction, a bias occurs in the sliding direction, and plastic deformation proceeds anisotropically, resulting in an ear. If the type and the degree of the texture are different, the slip direction and the slipperiness are different, so that a change in the type or ratio of the texture contained in the rolled sheet appears as a change in ear ratio. Materials with texture, such as rolled materials, are considered to be a mixture of isotropic crystal grains with randomly oriented crystals and single crystal grains with a specific orientation determined by texture. Can be Among them, in the material of the isotropic crystal group, the propagation speed of the ultrasonic wave is constant regardless of the propagation direction. On the other hand, in a material of a single crystal grain group having a specific orientation, the propagation speed of the ultrasonic wave shows a sound velocity anisotropy that changes depending on the propagation direction. Therefore, the prior art 2 attempts to measure the ear rate by detecting the change in the type and ratio of the texture using the sound speed change in the material due to the sound speed anisotropy. A focused ultrasonic probe as shown in FIG. 12 is used for measuring the speed of sound in a material. As shown in the figure, three pairs of transmitting and receiving probes are used to detect the propagation speed of the ultrasonic wave propagating in the rolling direction, 45 ° direction, and the direction perpendicular to the rolling direction in the plane of the rolled plate. The pulsed ultrasonic waves transmitted from the transmitting probes 21a, 21b, and 21c enter the plate 22 to be measured obliquely with respect to the surface normal, diverge, and are transmitted between the front and back surfaces of the plate 22 to be measured. The light propagates with multiple reflections. The ultrasonic wave that has been repeatedly reflected is emitted from the plate to be measured 22 and is received by the receiving probe 23.
a, 23b and 23c. A reflected wave having a predetermined refraction angle is extracted from the received multiple reflected waves, and its propagation time is measured. Since the focusing type ultrasonic probe has the same focal point for transmission and reception for the surface of the plate 22 to be measured, transmission / reception points are specified, and necessary for calculating the sound velocity from the propagation time. The propagation distance can be specified. A predetermined evaluation value is determined from the propagation speeds in the three directions thus determined, and the ear ratio is determined by applying the evaluation value to a correspondence table between the evaluation value and the ear ratio created by a standard sample having a known ear ratio in advance. .

(Prior art 3) This is disclosed in Japanese Patent Application No. 7-242.
This is an ear ratio measurement method proposed in Japanese Patent No. 934. The main difference between this method and the prior art 2 is that longitudinal waves and transverse waves that propagate in the thickness direction are used. The basic principle and implementation method will be briefly described below. FIG. 13 shows an arrangement diagram of an ultrasonic transmission / reception device used in this ear ratio measurement method. Taking a longitudinal wave as an example, as shown in FIG. 13 (a), two magnets are arranged so that a magnetic field is applied in parallel to the thin plate surface, and a transmitting coil and a transmission coil are similarly set in parallel with the thin plate surface. Place the receiving coil. When a high frequency burst wave current is applied to the transmitting coil, an eddy current is generated on the surface of the thin plate in a direction opposite to the coil current. Due to the interaction between the eddy current and the applied magnetic field, Lorentz force acts on the metal atoms in the plate thickness direction, and becomes an exciting force of elastic vibration. The longitudinal ultrasonic wave propagates in the thickness direction in synchronization with the burst wave current of the transmitting coil. The longitudinal wave propagating in the plate thickness direction is a multiple reflected wave reflected on the front and back surfaces of the thin plate. However, since the longitudinal wave reciprocates perpendicularly to the plate surface, the reflected waves overlap and an interference phenomenon occurs. When the wavelength λ of the ultrasonic wave in the thin plate is changed by gradually changing the frequency f of the burst wave current of the transmitting coil, interference that strengthens when an integral multiple of half the wavelength λ / 2 becomes equal to the plate thickness t is obtained. As a result, resonance occurs in which the ultrasonic waves become strong. Since the relationship between the wavelength λ, the longitudinal wave velocity VL, and the frequency f is λ = VL / f, the longitudinal wave velocity VL can be obtained if the thickness t is known. That is, assuming that n is an integer, the resonance wavelength is λc, and the resonance frequency is fc, the longitudinal wave velocity VL can be obtained from the relationship t = n (λc / 2) = nVL / (2fc). Also,
The reception (detection) of the ultrasonic wave is performed by the receiving coil based on the principle opposite to the generation. The transverse wave differs from the longitudinal wave in that the arrangement of the magnets (see FIG. 13B) and the generation of two types of waves having different vibration directions are the same as the longitudinal wave, but the other is the same. The resonance frequencies of the rolling direction and the transverse wave whose vibration direction is perpendicular to the rolling direction are detected. The ear ratio △ e is calculated by the following equation. Δe = a0 + a1 (fc1 + fc2) / fc3 + a2
(Fc1-fc2) / (fc1 + fc2) (where, fc1: resonance frequency of a transverse wave whose vibration direction is the rolling direction, fc2: resonance frequency of a transverse wave whose vibration direction is the direction perpendicular to the rolling direction, fc3: vibration direction of the sheet thickness direction) Resonance frequency of longitudinal wave, a0, a1, a2: coefficient determined by material of thin plate)

(Prior Art 4) This is disclosed in Japanese Patent Laid-Open No. 4-138
No. 310 is an apparatus for evaluating the deep drawability of a thin metal plate proposed in JP-A-310. This apparatus is intended to evaluate the characteristics of a metal sheet in deep drawing by using r-values using ultrasonic waves. The basic principle and implementation method will be briefly described below. An ultrasonic plate wave is used for sound velocity measurement.
An ultrasonic plate wave is generated and detected by using a transmitting probe 31 and a receiving probe 32 for electromagnetic ultrasonic waves as shown in FIG. Both probes are composed of an electromagnet 33 for generating an external magnetic field and a coil 34 arranged in parallel with the surface of the thin metal plate 35, and both are arranged at positions separated by a predetermined distance.
When a pulse current is applied to the coil 34 of the transmitting probe 31, an eddy current is excited on the surface of the thin metal plate 35, and the electromagnet 3
The magnetostriction is generated in the metal thin plate 35 by the magnetic field applied to the surface of the metal thin plate 35 and the eddy current by the eddy current 3, and this is used as an exciting force to generate a plate wave. Receiving probe 32
The plate wave that has propagated immediately below is detected by the receiving probe 32 according to a principle reverse to that at the time of transmission. The propagation time of the plate wave is calculated from the time from transmission to reception. In order to measure the r value, the transmitting and receiving probes are arranged in three directions of 45 ° and 90 ° with respect to the rolling direction and the rolling direction, and the propagation times T0, T45, T90
Is measured, and the average sound speed T is calculated from the following equation. T = (T0 + 2 × T45 + T90) / 4 This T is converted into an r value by a conversion table obtained in advance.

[0006]

However, the above prior art has several problems as described below. (Prior art 1) Since it is a destructive inspection, it takes a long time to measure and cannot be inlined. Due to differences in the lubrication conditions, etc. between the die or punch and the test material, the measured values vary even for the same sample. (Prior art 2) It is difficult to transmit and receive multiple reflected waves at oblique incidence with a thin plate (plate thickness of about 1 mm or less). For example, multiple reflected waves having different numbers of reflections may overlap, making it impossible to separate them. Since the propagation path of the ultrasonic wave is a limited linear area (a zigzag linear range that connects the incident point and the output point of the focused ultrasonic wave and passes through the reflection points on the front and back surfaces of the test material), the local Vulnerable to organizational changes. The required ear ratio is an average value in a region having a certain size, and may differ from the ear ratio obtained by this measurement method. (Prior art 3) It is easy to be affected by the thickness variation. For example, due to uneven thickness in the observation region, no clear resonance occurs, and in extreme cases, a plurality of resonance peaks may be observed. Further, if a small coil is used to remove the influence of the thickness unevenness, the ear ratio indicating the characteristics of the material cannot be expressed due to the unevenness of the texture. A burst oscillator that can change the oscillation frequency with high accuracy is required. (Prior Art 4) The r value and the ear ratio are not a simple relationship, and it is difficult to calculate the ear ratio from the r value. Further, there is no correlation between the rolling direction, the average value of the plate wave sound velocity in the three directions of 45 ° and 90 ° with respect to the rolling direction, and the ear ratio. The sound speed measurement was performed in the rolling direction, 45 ° direction to the rolling direction,
When measuring only in three directions of 90 °, if there is a deviation in the installation angle of the measurement probe with respect to the test material, the measured value tends to fluctuate. (The above will be verified in the embodiments described later.) The present invention has been made in view of the above circumstances, and its purpose is to use an expensive measuring device without using an expensive measuring device.
An object of the present invention is to provide a method and an apparatus for measuring the ear ratio of a thin metal sheet which are non-destructive, are less susceptible to sheet thickness unevenness and installation errors of a measuring device, and can always obtain stable and accurate measurement results.

[0007]

According to a first aspect of the present invention, an ultrasonic wave is applied to a surface of a sheet metal in a rolling direction.
As 0 °, 0 °, 90 °, and θ (where 0 ° <
Propagation when propagating a predetermined distance in the direction of θ <90 °)
The propagation time is measured in each of the above measurement directions.
From the component, a predetermined feature representing the change in sound speed in the plate surface is calculated.
Calculated features and ear ratios obtained in advance using standard samples
By applying the above calculated features to the relationship with
Finding the ear ratio of a thin plate
To measure the above propagation time, only the S0 mode ultrasonic plate wave
And the plus direction for the above θ, and the minor
Metal characterized by measuring the propagation time in the
It is configured as a method for measuring ear ratio of a thin plate. like this
In addition, S0 mode super sound with small speed change due to thickness change
By using corrugated sheet waves, the effect of thickness unevenness is reduced.
And in the plus direction for the above θ,
And by measuring the propagation time in the negative direction.
It is possible to reduce the influence of the installation error of the measuring instrument. That
Time, the feature quantity (Z) is, Z = K {n (T A + T B) - (T +1 + T -1) - ... - (T + n + T -n)} ( here, K: constant n : The number of pairs of propagation time measurement T _A and T _{B in the} above ± θ direction: At the time of propagation in the directions of 0 ° and 90 °, respectively.
During T _+, T _-: each of the above + theta, a -θ direction of propagation time).

Furthermore, the θ and +45 °, and -45 °, the feature quantity (Z), Z = K { (T A + T B) - (T +45 + T -45)} ( here, K : Constants T _A , T _B : Propagation times in the directions of 0 ° and 90 °, respectively, T ₊₄₅ , T _-45 : Propagation times in the directions of + 45 °, -45 degrees, respectively. Can be detected with higher sensitivity. Further, in the first aspect, the measurement order of the propagation time in each direction may be such that a change due to a temperature change included in the change in the propagation time is canceled in the calculation of the characteristic amount. , And the measurement time interval can also be set. At this time, the measurement order of the propagation time in each direction is set to (1) 0 ° or 90 ° method (2) -45 °
Or 45 ° direction (3) -45 ° or 45 ° remaining direction (4) 0 ° or 90 ° remaining direction, or (1) -4
5 ° or 45 ° direction (2) 0 ° or 90 ° method (3) 0
(4) The remaining direction of (4) is set to −45 ° or the remaining direction of 45 °, and the measurement time interval of the propagation time in each of the directions is set to be equal. The change due to the temperature change included in the change in time is offset. In order to achieve the above objective,
Ming said that the ultrasonic wave is in the plane of the sheet metal and the rolling direction is 0 °.
, 90 °, and θ (where 0 ° <θ <90
The propagation time when the light has propagated a predetermined distance in the direction
Each measurement is performed, and is the change in the propagation time in each of the above measurement directions?
Calculates a predetermined feature representing the change in sound speed in the plate
And the ear ratio calculated using the standard sample in advance.
Applying the calculated feature value to the relationship, the metal sheet
In the method for measuring the ear ratio of a thin metal sheet,
Using only the S0 mode ultrasonic plate wave to measure the propagation time
And the method of measuring the propagation time
Of the ultrasonic plate wave propagating in the
Cross-correlation with reference waveform detected using reference sample
Performs an operation, approximates the result of the operation as a function, and calculates the maximum correlation value.
Find the delay time to be given, and use the delay time as the above propagation time.
Ear ratio measurement of thin metal sheets characterized by being used
It is configured as a fixed method. As a result,
Between it can be measured without having Mochiiruko an expensive measuring device. Ma
And, in the second invention, the feature amount (Z), Z = K { n (T A + T B) -2T 1 - ... -2T n} ( here, K: constant n: the θ direction Propagation time measurement numbers T _A , T _B : Propagation in the directions of 0 ° and 90 ° respectively
During T _n: if so determined by the propagation time of n-th θ direction), unrelated to the ear rate Randa
To obtain the feature quantity that offsets the propagation time caused by the
Can be. In the second invention, the angle θ is
Measure the propagation time in the plus and minus directions
Measures to reduce the effects of measuring instrument installation errors.
be able to.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to facilitate understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention. Here, FIG. 1 is a block diagram showing a schematic configuration of a thin metal ear ratio measuring device according to an embodiment of the present invention, and FIG. 2 is a transmission / reception probe of the thin metal ear ratio measuring device according to the embodiment of the present invention. FIG. 3 is a schematic diagram showing the principle of generation of an ultrasonic plate wave by the transmission probe, FIG. 4 is a diagram showing the mode of the plate wave, and FIG. 5 is a diagram showing the displacement distribution of the plate wave. 6 is a diagram showing the relationship between the frequency x thickness of the plate wave and the sound velocity, FIG. 7 is a diagram showing a method of calculating the propagation time by cross-correlation calculation and function approximation, and FIG. 8 is an example of a measurement result of the sound velocity anisotropy. Fig. 9 and Fig. 9 show the evaluation results of the ear ratio, Fig. 10
FIG. 10 is a diagram showing a result of adopting an average delay time in four directions as an evaluation value in FIG. The ear ratio measuring apparatus for a thin metal plate according to the present embodiment is configured as shown in FIG. First, an ultrasonic plate wave transmission / reception method using the transmission probe 1 and the reception probe 2 and a device configuration thereof will be described with reference to FIGS. Figure 2 shows the transmission probe 1
FIG. 2 schematically shows a plan view and a front view of the receiving probe 2. The transmission probe 1 includes a magnet 14 and a meander coil 15. The meander coil 15 is
As shown in FIG. 2, it is arranged in a plane by a plurality of folds in parallel with the test material 13. Further, the meander coil 15 and the test material 13 are arranged at a distance smaller than a half of a meander pitch L described later. A magnet 14 is arranged above the meander coil 15 so that the direction of the magnetic field is perpendicular to the surface of the test material 13. At this time, the direction of the magnetic field may be either upward or downward.
The receiving probe 2 has exactly the same configuration as the transmitting probe 1 described above. The transmission probe 1 and the reception probe 2
Are arranged such that both meander coils 15 are parallel and both meander coils are perpendicular to a straight line connecting the centers of the two. Further, the transmission probe 1 is connected to a burst wave oscillator 5 via a transmission-side channel switch 7 and a power amplifier 6 (not shown in FIG. 2), and the reception probe 2 is connected to a reception-side channel switch 8 and a high-frequency amplifier 9 (FIG. 2). (Not shown) are connected to the waveform detector 10 respectively. A method of transmitting and receiving an ultrasonic plate wave will be described with reference to FIG. 3, which is an enlarged front view of the transmission probe 1. When a burst wave current is applied from the burst wave oscillator to the meander coil 15 of the transmission probe 1, as shown in FIG. 3, the current alternately flows in the opposite direction due to the folding of the coil on each side of the meander coil 15, An eddy current in the opposite direction to the coil current is excited on the surface of the test material 13. The Lorentz force as shown in the figure acts on each position of the test material 13 by the eddy current and the magnetic field, and an ultrasonic plate wave is generated.

Here, the plate wave will be briefly described. A plate wave is a wave Lamb wave among the waves in a plate.
A longitudinal wave component parallel to the traveling direction and the plate surface and a transverse wave component perpendicular to the traveling direction and the plate surface are combined to form a wave. The actual vibration of a particle is the sum of a longitudinal wave component and a transverse wave component, and generally performs elliptical motion. Plate waves are classified into symmetric waves (symmetric S group) and oblique symmetric waves (oblique symmetric A group) (see FIG. 4). The above symmetrical and obliquely symmetrical waves are further divided by S0, S1, S2,
Modes such as A0, A1, and A2 can be classified (see FIG. 5). The sound velocity of the plate wave is a function of the product fd of the plate wave frequency f and the plate thickness d. FIG. 6 is a graph showing the relationship between fd and sound speed for each mode. From this graph, it can be seen that the speed change due to the fd change is smaller in the S0 mode than in the other modes. In particular, when fd <1 (MHz · mm),
It can be regarded as constant regardless of fd change. Therefore, by using the plate wave in the S0 mode, it is possible to measure the sound velocity without being affected by a change in plate thickness (unevenness). In the transmitting / receiving probe according to the present embodiment, a Lorentz force as shown in FIG. At this time, S0 determined by the plate thickness d, the frequency f of the burst wave, the meander pitch L, fd
Assuming that the sound velocity of the mode is V, an S0 mode plate wave having a meander pitch L of wavelength λ is generated by setting f and L that satisfy V = fL. When the number of turns n of the meander coil 15 is increased, the plate waves generated on each side of the coil interfere with each other, and only the S0 mode is strongly generated, thereby improving the sensitivity. Thus, the S0 mode plate wave generated immediately below the transmission probe 1 propagates directly below the reception probe 2 and induces a current in the reception side meander coil 15 based on a principle opposite to the generation. This induced current is detected as an ultrasonic signal. Four pairs of the transmission probe 1 and the reception probe 2 described above are arranged on the test material 13 as shown in FIG. Each transmission / reception probe pair is arranged such that the transmission probe 1 and the reception probe 2 are at the same distance, and furthermore, a straight line connecting each transmission probe 1 and the reception probe 2 intersects at the same point. Each transmitting and receiving probe pair
Assuming that the rolling direction is 0 °, they are arranged in 0 °, 90 °, and ± 45 ° directions.

Next, a processing procedure of the ear ratio measuring apparatus according to the present embodiment will be described with reference to FIG. First, the sound velocity measurement direction (propagation direction) of the ultrasonic plate wave is determined, and a signal is output from the channel switching signal generator 3. With this signal, the transmission-side channel switch 7 and the reception-side channel switch 8 are operated, and a target transmission / reception probe pair is selected. At the same time, the ear ratio calculator 1
1, the measurement direction is indicated, and a trigger signal is output from the trigger signal generator 4. The burst wave oscillator 5 receiving the trigger signal outputs a burst wave current of a predetermined frequency and is amplified by the power amplifier 6. The amplified burst wave current is applied to the transmission probe 1 selected by the transmission-side channel switch 7 and transmits the S0 mode plate wave to the test material 13 according to the principle described above. The plate wave that has propagated through the test material 13 is detected as a burst current by the reception probe 2 selected by the reception-side channel switcher 8.
After being amplified by the high-frequency amplifier 9, it is output to the waveform detector 10. The waveform detector 10 samples the detected waveform by A / D conversion using the trigger signal from the trigger signal generator 4 as a reference time, executes a cross-correlation calculation with a previously stored reference waveform, and determines the maximum value. Delay time T to be given
Is calculated. (Each device used in the above procedure corresponds to a propagation time measuring means.) Here, the reference waveform is, for example, a waveform detected as follows. First, a reference plate having the same thickness as the test material is prepared. One of the transmission / reception probe pairs is selected, and the reference plate is installed such that the plate wave propagation direction matches the rolling direction of the reference plate. The plate wave waveform captured in this state is used as a reference waveform of the transmission / reception probe. This operation is performed for all the transmitting and receiving probe pairs, and four waveforms are stored as reference waveforms of each transmitting and receiving probe pair. The stored reference waveforms of the transmission and reception probe pairs are used at the time of the cross-correlation calculation.

In this manner, the correlation value for each sampling time Δt is obtained by the cross-correlation calculation.
If the above-mentioned delay time T is directly obtained from each correlation value, only the resolution of Δt can be obtained. However,
The delay time change (sound speed change) corresponding to the actual ear rate change is slight. For example, in the case of an aluminum cold-rolled sheet having a thickness of 0.3 mm, a change in delay time corresponding to a change in ear ratio of 1% is about 10 to 20 nsec when the propagation distance is 55 mm.
The above resolution when performing A / D conversion of 50 MHz is 20
Since it is nsec, in this case, only the ear rate of 1% unit can be obtained. Therefore, in order to increase the measurement resolution, it is conceivable to increase the plate wave frequency and increase the accuracy of the signal detection device. To increase the plate wave frequency by the electromagnetic ultrasonic method, it is necessary to increase the frequency of the excitation signal and downsize the transmission coil (to reduce the meander pitch). However, in this case, problems such as an increase in equipment cost and difficulty in manufacturing a coil occur. In addition, a high-speed A / D converter corresponding to a high frequency is required, and the device cost is also high here. Therefore, as shown in FIG. 7, a cross-correlation operation between the reference waveform and the measured waveform is performed, and a delay time at which the maximum value is obtained is obtained by function approximation.
Using a relatively low-frequency plate wave that can be realized with a low-cost device, it is possible to measure the change in the propagation time with high accuracy and stably.

The above-described processing is performed for all of the above four propagation directions by changing the channel setting. The ear ratio calculator 11 (corresponding to a feature amount calculating unit and an ear ratio calculating unit) calculates an evaluation value Z by the following equation using each channel, that is, the delay time Tn (n = 1 to 4) in each propagation direction. _{Z = K {(T A +} T B) - (T +45 + T -45)} ‥‥‥‥ (1) ( here, K: constant T _A, T _B: each of the above 0 °, 90 ° direction Propagation time T ₊₄₅ , T _-45 : Propagation time in the above + 45 ° and -45 ° directions, respectively) The propagation time itself includes the propagation time due to isotropic random tissue unrelated to the change in ear ratio. Therefore, the absolute value of the propagation time itself has no correlation with the ear rate. Therefore, the above equation (1) cancels the propagation time caused by the random tissue. Further, by adding the delay times in the ± 45 ° direction, errors in the delay time due to installation errors of the transmission / reception probes are canceled out. Details of these will be described later. The estimated value Z is applied to a correspondence table between the evaluated value Z and the ear ratio created from a standard sample whose ear ratio is known in advance to obtain an estimated ear ratio, which is displayed on the display 12.

Next, a description will be given of a measurement example using the ear ratio measuring apparatus. As the test material 13,
A cold rolled aluminum plate of 28 to 0.32 mm is used. FIG. 8 shows the results obtained by measuring the delay time while sequentially changing the propagation direction at a pitch of 10 ° with respect to the rolling direction, with the meander pitch being 4 mm and the interval between the transmitting and receiving probes being 55 mm. The measurement was performed on three types of test materials having different ear ratios. In this measurement, a measurement waveform in the rolling direction of each test material is used as a reference waveform when performing a cross-correlation calculation. Therefore, when the rolling direction is set to the propagation direction, the delay times are all 0 (nse
c). Comparing the three graphs, looking at the difference in delay time between each test material in the same propagation direction, the difference is the largest when the propagation direction is around 45 °. It can be seen that it appears remarkably in the delay time around 45 °. Therefore, by using the delay time in the 45 ° direction with respect to the rolling direction, the change in the sound velocity anisotropy can be detected with the highest sensitivity. When the same waveform is used for three kinds of test materials as the reference waveform in obtaining the delay time, each graph shifts up and down within a range of several nsec, although the shape of the graph in FIG. 8 does not change. FIG. 8 shows the relative change of the plate wave propagation time with respect to the rolling direction.
This indicates that the absolute value (or average value) of the propagation time is different for each test material. As will be described later, the ear ratio measurement requires a relative change in the propagation time, and the absolute value or average value of the propagation time has no correlation with the ear ratio. Also,
Under the same conditions as above, with a meander pitch of 4 mm and a transmission / reception probe interval of 55 mm, the delay time in four propagation directions was measured for a plurality of test materials, and the evaluation value Z was obtained using the above equation (1). FIG. The abscissa represents the ear ratio obtained by the method of the above-mentioned prior art 1. A clear correlation is seen, and the ear ratio can be estimated from the evaluation value Z by making this table a table. The variation in each value in FIG. 9 is considered to be caused by an error in the ear ratio measurement according to the related art 1 described above. As a result of measuring the same sample a plurality of times, the repetition error of the evaluation value Z was about ± 4 nsec, and the ear rate error was about ± 1.5%. It is reasonable to assume that errors are the cause.

Next, the effect of the installation error of the transmission / reception probe (deviation of the installation angle) will be considered. From the results in Fig. 9, the ear ratio is 1%.
Is detected as a change of about 25 nsec in the evaluation value Z. Looking at the amount of change in the measured value of the delay time due to the 1 ° displacement of the installation angle of the transmitting and receiving probe from FIG. 8, the point is an extreme point in the rolling direction (0 °) and the sheet width direction (90 °). Therefore, it is almost 0, and about 1.5 nsec near the 45 ° direction. Assuming that the installation angle of the transmitting / receiving probe is shifted from the rolling direction by 5 °, the delay time change in the propagation direction of 45 ° is 7.5 nsec, which is simply converted to the ear ratio using FIG. %
become. However, by measuring ± 45 °, the changes in the delay time due to the installation angle shift of the transmission / reception probe cancel each other, and the evaluation value Z hardly changes. For example, in the graph of ear ratio + 4.7 (%) in FIG.
The delay time in the ° direction is about 42 nsec, but if the installation angle of the transmitting and receiving probe is shifted by -5 ° from the rolling direction, the actual delay time in the 50 ° direction is measured.
The delay time in the 45 ° direction is measured as about 36 nsec. However, since the above graph is symmetric with respect to the rolling direction, in this case, the delay time in the −45 ° direction is equal to the actual −40 °.
Since the delay time in the ° direction is measured, that is, about 47 nsec, the evaluation value Z hardly changes as a result. Therefore, by measuring ± 45 °, it is possible to improve the ear ratio measurement accuracy when there is an installation error of the transmission / reception probe. In addition, the test material used in FIG.
FIG. 10 shows the relationship between the average sound velocity of the three-way propagation time and the ear ratio proposed in (1). Thus, it can be seen that there is no simple correlation between the average sound speed and the ear rate.

In the above-described ear ratio measuring apparatus, a method for preventing deterioration of the ear ratio measurement accuracy due to a change in the temperature of the test material will be described. As an example, consider ear ratio measurement on an aluminum plate immediately after cold rolling. Immediately after cold rolling, the temperature of the aluminum plate has risen to about 100 to 200 ° C., which falls to room temperature over time. Since the speed of sound in a material is also a function of temperature, the speed of sound changes as the material temperature decreases. As in the present embodiment, the transmission and reception probes are sequentially switched, and the plate wave propagation time (delay time) in each direction.
If the measurement is performed when the material temperature changes abruptly as described above, each measured delay time includes the change due to the ear rate and the change due to the material temperature, and this is the ear rate measurement. This may cause deterioration of accuracy. The following shows the degree to which the temperature change affects the ear ratio measurement accuracy. For example, in the case of medium speed of aluminum rod, 195 ° C →
With a temperature change of -1 ° C, the sound speed is 4974m / s → 507
It changes by about 1 m / s, that is, about -2.4% (ultrasonic testing, Nikkan Kogyo Shimbun). In addition, 50 ° C → room temperature (about 30
° C) was about 0.2%. The sound velocity anisotropy in the rolling plane of a normal aluminum cold rolled sheet is about 0.6%, and the change in sound velocity corresponding to a difference in ear ratio of 1% is 0.
Considering that it is about 1%, it is expected that an actually possible temperature change will have a non-negligible effect on the ear ratio measurement value.

Therefore, in order to prevent deterioration of the ear ratio measurement accuracy due to the temperature change of the test material as described above, the measurement order of the plate wave propagation time in each direction and the measurement time intervals are as follows. (1) The measurement order of the plate wave propagation time in each direction is 0 ° or 90 ° direction -45 ° or 45 ° direction -45 ° or remaining direction of 45 ° direction 0 ° or 90 ° direction of remaining direction or 45 ° or 45 ° direction 0 ° or 90 ° direction 0 ° or 90 ° remaining direction −45 ° or 45 ° remaining direction. (2) The measurement time intervals in each of the above directions are made equal. The effect of the above method will be described. For the sake of simplicity, the rate of decrease in the material temperature is assumed to be constant, and the change in sound speed due to temperature change is also assumed to be constant. , The second measurement can be set to 0 sec, the second to δsec, the second to 2δsec, and the third to 3δsec.
Therefore, when the feature amount Z is obtained by using the above equation (1), the change due to the temperature change is (0 + 3δ) − (δ + 2δ) = 0, and the change in the delay time due to the temperature change is cancelled. Therefore, by setting the measurement order of the plate wave propagation time in each direction and the measurement time interval as described above, it is possible to prevent deterioration of the ear rate measurement accuracy due to a temperature change of the test material.

As described above, the ear-rate measuring apparatus for a thin metal plate according to the present embodiment can measure the ear-rate in a non-destructive manner by measuring the change in the plate wave propagation time. Since the plate wave used is limited to the S0 mode,
No waveform separation is required, and the generator can be simplified.
In addition, since a wide area of the test material is used as a propagation path by the plate wave, an average ear rate less affected by local tissue changes can be obtained. In addition, the sound velocity of the plate wave can be considered to be substantially constant at about 10 μm, which is the actual thickness fluctuation of the metal sheet, and the ear rate measurement which is hardly affected by the thickness fluctuation can be performed. In addition, in addition to the rolling direction and the sheet width direction, the 45 ° direction where the change in the propagation time accompanying the change in ear ratio is most remarkable is measured as the direction of propagation of the plate wave, and the ± direction is measured. The influence of the installation error is reduced, and the ear ratio can be measured with high sensitivity. Further, in the above equation (1) for calculating the evaluation value Z, the ear rate is measured based on the relative change of the propagation time required for the ear rate measurement by canceling the propagation time due to the random tissue not related to the ear rate. be able to.

[0019]

[Embodiment] In the above embodiment, a pair of transmission / reception probes are installed in each measurement direction, and each transmission / reception probe is switched by channel switching for measurement. The installation angle of the transmission / reception probe may be changed. When the test material is a non-magnetic material such as an aluminum plate, the configuration of the magnet and the meander coil of the transmission / reception probe may be such that the test material is sandwiched between the magnet and the meander coil.

[0020]

As described above, according to the present invention,
Non-destructive method that does not use expensive measuring equipment, is less susceptible to thickness unevenness and installation errors of measuring equipment, and can always obtain stable and accurate measurement results. And an apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a metal sheet ear ratio measuring apparatus according to an embodiment of the present invention.

FIGS. 2A and 2B are a plan view and a front view of a transmission / reception probe of the metal thin plate ear ratio measuring apparatus according to the embodiment of the present invention. FIGS.

FIG. 3 is a schematic diagram showing the principle of generating an ultrasonic plate wave by the transmission probe.

FIG. 4 is a diagram showing modes of a plate wave.

FIG. 5 is a diagram showing a displacement distribution of a plate wave.

FIG. 6 is a diagram showing the relationship between the frequency of a plate wave × the plate thickness and the speed of sound.

FIG. 7 is a diagram showing a method of calculating a propagation time by cross-correlation calculation and function approximation.

FIG. 8 is a diagram showing an example of a measurement result of sound velocity anisotropy.

FIG. 9 is a view showing evaluation results of ear ratio.

FIG. 10 is a diagram showing a result of employing the average delay time in four directions as an evaluation value in FIG. 9;

FIG. 11 is a diagram showing an ear ratio measuring device according to the related art 1.

FIG. 12 is a diagram showing an ear ratio measuring device according to Conventional Technique 2.

FIG. 13 is a diagram showing an ear ratio measuring device according to a conventional technique 3;

FIG. 14 is a diagram showing an ear ratio measuring device according to Conventional Technique 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transmission probe 2 ... Reception probe 3 ... Channel switching signal generator 4 ... Trigger signal generator 5 ... Burst wave oscillator 6 ... Power amplifier 7 ... Transmission-side channel switching device 8 ... Reception-side channel switching device 9 ... High-frequency amplifier 10 ... Waveform detector 11 Ear ratio calculator 12 Display 13 Test material 14 Magnet 15 Meander coil

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Norio Suzuki 2-3-1 Shinhama, Arai-machi, Takasago-shi, Hyogo Kobe Steel, Ltd. Inside Takasago Works (56) References JP-A-7-318540 (JP, A) JP-A-1-301162 (JP, A) JP-A-7-328727 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (8)

(57) [Claims] (1) An ultrasonic wave is applied in a plane of a sheet metal in a rolling direction.
As 0 °, 0 °, 90 °, and θ (where 0 ° <θ
At the time of propagation at a predetermined distance in the direction of <90 °)
And the change in propagation time in each of the above measurement directions
From the minutes, a predetermined feature representing the change in the speed of sound in the plate is performed.
And the ear ratio and the feature quantity obtained using the standard sample in advance.
By applying the calculated feature value to the relationship
In the method for measuring the ear ratio of a thin metal plate, which determines the ear ratio of a plate, only the S0 mode ultrasonic plate wave is used to measure the above propagation time.
When used, the above θ is propagated in the plus and minus directions
Ear ratio measurement of thin metal sheets characterized by measuring the gap
Method. Wherein said characteristic quantity (Z) is, Z = K {n (T A + T B) - (T +1 + T -1) - ... - (T + n + T -n)} ( here, K : Constant n: Propagation time T _A , T _{B in the} above ± θ direction: Propagation in the directions of 0 ° and 90 °, respectively.
2. The ear ratio measuring method for a metal sheet according to claim 1 , wherein the intervals T ₊ and T ₋ are the propagation times in the + θ and −θ directions, respectively . Wherein said θ is 45 °, the feature quantity (Z) _{is, Z = K {(T A} + T B) - (T +45 + T -45)} ( here, K: constant T _A, T _B : When propagating in the directions of 0 ° and 90 °, respectively.
Between T ₊₄₅ , T _-45 : + 45 ° and -45 ° directions above
Claim 1 or 2 ears ratio measurement method for a sheet metal according to a propagation time). 4. A temperature change included in the change in the propagation time.
The change due to the quantization is canceled out in the calculation of the feature amount.
The measurement order of the propagation time in each direction is
The method according to any one of claims 1 to 3, wherein an interval is set.
Ear ratio measurement method for thin metal plates. 5. The method according to claim 1, wherein the temperature change included in the change in the propagation time.
The change due to the quantization is canceled out in the calculation of the feature amount.
As described above, the measurement order of the propagation time in each direction is defined as follows: (1) 0 ° or 90 ° method (2) -45 ° or 45 ° method
Direction (3) -45 ° or 45 ° remaining direction (4) 0 ° or
90 ° remaining direction, or (1) -45 ° or 45 ° direction (2) 0 ° or 90 ° direction
Modulo (3) 0 ° or 90 ° remaining direction (4) -45 ° or
The remaining direction shall be 45 °, and the measurement time intervals of the propagation time in each direction shall be equal.
The method for measuring ear ratio of a metal sheet according to claim 4. 6. An ultrasonic wave is applied in the rolling direction in the plane of the sheet metal.
As 0 °, 0 °, 90 °, and θ (where 0 ° <θ
At the time of propagation at a predetermined distance in the direction of <90 °)
And the change in propagation time in each of the above measurement directions
From the minutes, a predetermined feature representing the change in the speed of sound in the plate is performed.
And the ear ratio and the feature quantity obtained using the standard sample in advance.
By applying the calculated feature value to the relationship
In the method for measuring the ear ratio of a thin metal plate, which determines the ear ratio of a plate, only the S0 mode ultrasonic plate wave is used to measure the above propagation time.
In addition to the above , the method for measuring the propagation time detects the waveform of the ultrasonic plate wave propagating in each of the propagation directions, and compares the waveform with a reference waveform previously detected using a reference sample.
Performs a cross-correlation operation using the function and approximates the result of the operation as a function to provide the maximum correlation value.
The delay time and use the delay time as the above propagation time
A method for measuring the ear ratio of a thin metal plate, comprising: 7. The characteristic quantity (Z) is, Z = K {n (T A + T B) -2T 1 - ... -2T n} ( here, K: constant n: number of measuring the θ direction of propagation time T _A , T _B : Propagation in the directions of 0 ° and 90 ° respectively
7. The method for measuring the ear ratio of a thin metal plate according to claim 6, wherein the interval T _{n is the} n-th propagation time in the θ direction.
Law. 8. The method according to claim 1, wherein said θ is a plus direction and a minor direction.
7. The thin metal sheet according to claim 6, wherein the propagation time in the metallization direction is measured.
How to measure the ear ratio of a board.