CN111007148B - Spot welding ultrasonic quality evaluation method - Google Patents

Spot welding ultrasonic quality evaluation method Download PDF

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CN111007148B
CN111007148B CN201811416890.9A CN201811416890A CN111007148B CN 111007148 B CN111007148 B CN 111007148B CN 201811416890 A CN201811416890 A CN 201811416890A CN 111007148 B CN111007148 B CN 111007148B
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indentation
grid
spot welding
transducer
ultrasonic
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CN111007148A (en
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韩晓丽
肖富城
理华
肖灵
吴文焘
曹政
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Institute of Acoustics CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654—Imaging
    • G01N29/069—Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/023—Solids
    • G01N2291/0234—Metals, e.g. steel
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/267—Welds
    • G01N2291/2672—Spot welding

Abstract

The invention discloses a spot welding ultrasonic quality evaluation method, which comprises the following steps: pre-estimating the indentation position, the indentation depth and the indentation width by using the collected spot welding ultrasonic echo signals, then guiding the selection of ultrasonic C scanning imaging parameters according to the measured surface conditions of the indentation and the welding spot, then performing ultrasonic C scanning imaging and spot welding quality evaluation on the nugget, fusing the actual influence of the indentation into the nugget estimation process, and obtaining the nugget quantification and spot welding quality evaluation results. The method can be used for evaluating the welding quality of spot welding by combining the indentation and nugget size information more comprehensively, and avoids cost waste or unnecessary accidents caused by inaccurate quality evaluation.

Description

Spot welding ultrasonic quality evaluation method
Technical Field
The invention relates to the field of resistance spot welding, in particular to a spot welding ultrasonic quality evaluation method.
Background
Resistance spot welding is widely used for welded joints between metal plates and is recognized as the fastest and most economical welding method. The advantages of spot welding itself make it the most efficient and competitive welding means in automotive, aerospace, metal working industries, and the like. In the automotive industry, resistance spot welding is the most common welding method. Medium-sized passenger vehicles have on average 5000 welding spots, and the reliability of the body structure and the passenger safety depend to a large extent on reliable welding quality. The weld quality of resistance spot welding is affected by a number of factors. During the welding process, the fluctuation of welding parameters can cause the problems of insufficient diameter of a welding core, insufficient welding, over welding, welding defects in the welding core and the like, and the monitoring and the detection of the spot-weld joint are very necessary. The size of a nugget in spot welding is a main characteristic for determining the welding connection strength of spot welding, and is the most key index for evaluating the welding quality of spot welding. Ultrasonic testing of spot welds is the most important nondestructive method of spot welds.
Currently, most spot welding ultrasonic detection methods are based on amplitude attenuation characteristics in the time domain or in the transform domain. Some of the single-chip transducers are placed at fixed positions right above the spot welding to acquire echo signals, and the size of the nugget is estimated by using amplitude attenuation information of the echo signals on different interfaces; some of the methods adopt a single-chip transducer and a mechanical two-dimensional moving mode to collect echo signals at different positions of spot welding, then extract characteristics such as amplitude and the like to form a C scanning image, and further estimate the diameter of a spot welding nugget; and a two-dimensional array transducer is arranged above the spot welding, and echo signals are acquired in a mode of alternately and independently receiving and transmitting different array elements to form a spot welding C scanning image.
When the ultrasonic wave is adopted to estimate the nugget of the spot welding, the indentation on the spot welding surface scatters the incident sound wave, the energy of the transmitted sound wave is influenced, and finally the variation trend of echo signals on different interfaces of the spot welding along with the position is influenced. When the C scanning is adopted for spot welding imaging, the displayed nugget sizes are different when the characteristic value range constraint for imaging is different or different attenuation amplitude ranges of the same characteristic are adopted for imaging, so that the accurate estimation of the nugget sizes and the accurate evaluation of spot welding quality are influenced.
Disclosure of Invention
The invention aims to overcome the technical defects and provides a more accurate spot welding ultrasonic quality evaluation method, which comprises the steps of firstly pre-estimating the indentation position, the indentation depth and the indentation width by utilizing collected spot welding ultrasonic echo signals, then guiding the selection of ultrasonic C scanning imaging parameters according to the measured indentation and the surface condition of a welding spot, then performing ultrasonic C scanning imaging and spot welding quality evaluation on a nugget, and taking the actual influence of the indentation into consideration in the nugget estimation process to obtain more accurate nugget quantification and spot welding quality evaluation results.
In order to achieve the above object, the present invention provides a spot welding ultrasonic quality evaluation method, including:
pre-estimating the indentation position, the indentation depth and the indentation width by using the collected spot welding ultrasonic echo signals, then guiding the selection of ultrasonic C scanning imaging parameters according to the measured surface conditions of the indentation and the welding spot, then performing ultrasonic C scanning imaging and spot welding quality evaluation on the nugget, fusing the actual influence of the indentation into the nugget estimation process, and obtaining the nugget quantification and spot welding quality evaluation results.
As a refinement of the above method, the method comprises the steps of:
step 1) placing a non-focusing transducer above spot welding, and collecting ultrasonic echo signals at different positions;
step 2) using the echo data sets of different positions acquired in the step 1), estimating the depth, the spatial position and the width of the surface indentation of the welding spot on different scanning lines by using the time domain signal characteristics, and estimating the parameters of an indentation center ring, an indentation outer ring and an indentation inner ring;
step 3) extracting a characteristic value F (x, y) of the echo signal in a time domain or an envelope spectrum domain by using the data set S of the echo signal acquired in the step 1) and using the depth of the indentation on the surface of the welding spot as a reference;
step 4), taking the characteristic value as a pixel value, and adopting the percentage R to control the display range of the characteristic value to form spot welding C scanning imaging; drawing a spot welding C-scan image by taking the characteristic value F (x, y) of a time domain or an envelope spectrum domain as a pixel value and taking [ R,1] as a characteristic value range;
step 5) drawing the curve of the center circle, the outer circle and the inner circle of the indentation estimated in the step 2) in the C scanning imaging of the step 4);
and 6) in the C scanning imaging of the step 5), judging the nugget size information by combining the position and width information of the indentation.
As an improvement of the above method, the step 1) specifically includes:
step 1-1) establishing a space Cartesian coordinate system, dividing a welding point and a related area around the welding point into a plurality of grids, taking the coordinate of the central point of each grid as the position coordinate of the grid, wherein the length of each grid in the x direction is delta x, the length of each grid in the y direction is delta y, the number of the grids in the x direction is N, and the number of the grids in the y direction is M;
step 1-2) controlling an ultrasonic transducer to send ultrasonic pulse signals at each grid position, receiving ultrasonic echo signals at the grid position, and acquiring a data set S of the echo signals; each element S (x, y, n) of S represents a discrete-time echo signal acquired on the grid (x, y), and n represents a discrete time;
and 1-3) readjusting the sequence of the acquired echo data sets corresponding to each grid according to the increasing sequence of the grid coordinates x and y, wherein the echo data sets correspond to the grid sequence one by one.
As an improvement of the above method, the step 2) specifically includes:
step 2-1) selecting an echo data set corresponding to a grid scanning line, estimating depth information of the surface of a welding spot by using time domain signal characteristics, and calculating the depth of an indentation on the surface of the welding spot by using the position of a peak value of an echo reflected by the upper surface of a sample;
step 2-2) selecting an echo data set corresponding to a grid scanning line, and estimating the spatial position and the width of a spot welding indentation by using the time domain signal characteristic; calculating the position parameters of the indentation center ring, the indentation outer ring and the indentation inner ring;
step 2-3) repeating step 2-1) and step 2-2) on other grid scanning lines, estimating the depth, spatial position and width of the indentation on different scanning lines; and calculating the position parameters of the indentation center ring, the indentation outer ring and the indentation inner ring of different scanning lines.
As an improvement of the above method, the step 2-1) specifically comprises:
step 2-1-1) selecting an echo data set corresponding to a grid scanning line, and setting the sample surfaces at two sides of a welding point as aLOr aRCorresponding echo signals
Figure BDA0001879693240000031
Near the transmitted signal on the time axis, pad surface aCEcho signals further from the transducer surface
Figure BDA0001879693240000032
Distant from the transmitted signal on a time axis;
step 2-1-2) selecting a rectangular time window wt(n) window width satisfies the relationship defined by interface aLAnd aCReflecting the returned primary echo
Figure BDA0001879693240000033
And
Figure BDA0001879693240000034
are contained within the window;
step 2-1-3) respectively calculating the signal envelope of each grid in a window wtMoment of occurrence of internal peak
Figure BDA0001879693240000035
Obtain a one-dimensional vector
Figure BDA0001879693240000036
Each element in the vector represents the y-th0Each grid in the line grid is in a rectangular time window wt(n) a time at which the maximum value within (n) occurs;
step 2-1-4) drawing with x as abscissa
Figure BDA0001879693240000037
Curve, left side of impression read on curve
Figure BDA0001879693240000038
The difference between the maximum value and the minimum value of (1) is delta n; impression Right side
Figure BDA0001879693240000039
The difference between the maximum value and the minimum value is delta n; respectively substituting the maximum depth h of the indentation on the left side and the right side into the formula (1) to calculate:
h＝(Δn)c1/(2fs) (1)
wherein, c1Is the speed of sound of the medium between the transducer surface and the spot weld, fsIs the sampling rate.
As an improvement of the above method, the step 2-2) specifically includes:
step 2-2-1) two rectangular time windows w are selectedt1(n) and wt2(n)；wt1(n) sample surface a for selecting both sides of the soldered dotLOr aREcho signal segments reflected for the first time; w is at2(n) for selecting the surface a of the soldered dotCEcho signal segments reflected for the first time;
step 2-2-2) respectively calculating peak values of signal envelopes in two rectangular time windows to respectively obtain one-dimensional vectors Et1And Et2Each element in the two vectors represents the peak of the envelope for each grid in the row of grids;
step 2-2-3) reacting Et1And Et2Drawing in a coordinate system, wherein the abscissa is the position in the x direction, and the ordinate is the peak value of the envelope; calculating the x coordinate of the intersection point of the envelope peak curves of the two time domain windows, namely determining the left position x of the indentation center circledLAnd right position xdR；
Step 2-2-4) is on the left side of the indentation when
Figure BDA0001879693240000041
When reduced to a minimum, the abscissa of the center of the transducer or transducer unit is denoted x4When is coming into contact with
Figure BDA0001879693240000042
When increasing to a maximum, the abscissa of the center of the transducer or transducer unit is denoted x5(ii) a Left indentation width dL＝x5-x4(ii) a The outer ring of the left indentation is positioned
Figure BDA0001879693240000043
The inner ring of the left indentation is positioned
Figure BDA0001879693240000044
D is the aperture of the transducer;
step 2-2-5) on the right side of the indentation when
Figure BDA0001879693240000045
When reduced to a minimum, the abscissa of the center of the transducer or transducer unit is denoted x6When is coming into contact with
Figure BDA0001879693240000046
When increasing to a maximum, the abscissa of the center of the transducer or transducer unit is denoted x8(ii) a The indentation width d on the right sideR＝x8-x6(ii) a The right indentation inner ring is positioned
Figure BDA0001879693240000047
The outer ring of the right indentation is positioned
Figure BDA0001879693240000048
As an improvement of the above method, the step 6) is specifically: reading the diameter of the circular boundary line of the image in the C scanning image; and if the estimated nugget boundary is positioned in the indentation inner ring, the diameter of the circular boundary line is the estimated value of the nugget diameter, if the estimated nugget boundary is positioned near the indentation inner ring, the diameter of the indentation central ring is used as the estimated value of the nugget diameter, and meanwhile, the nugget size is judged to be qualified.
The invention has the advantages that:
the method aims at the ultrasonic nondestructive detection of spot welding, firstly estimates the information of the surface of a welding spot, mainly comprises the information of the indentation depth, the indentation position, the indentation width and the like of the surface of the welding spot, guides the C scanning imaging process of a nugget according to the pre-estimated information, and comprises the characteristic value extraction process and the limitation of the characteristic value range during imaging, so that the C scanning image result is closer to the actual shape of the nugget, when the nugget size is estimated on the basis, the result is more accurate, the welding quality of the spot welding can be comprehensively evaluated by combining the indentation information, the nugget size information, the imaging result and the like, and the cost waste or unnecessary accidents caused by the welding quality problem can be avoided.
Drawings
FIG. 1 is an abstract model of a spot welding ultrasonic scanning inspection process of the present invention;
FIG. 2 is a schematic diagram of grid division during spot welding detection according to the present invention;
FIG. 3 illustrates the selection of echo signal segments using time windows in accordance with the present invention;
FIG. 4 is an echo signal corresponding to a row of grids according to the present invention;
FIG. 5 is an indentation longitudinal cross-sectional profile of the present invention;
FIG. 6 is a time domain peak variation trend of each mesh echo within a specific time window according to the present invention;
FIG. 7 is a schematic view of the parameters of the indentation structure of the present invention;
FIG. 8 is a schematic view of an indentation width estimation process of the present invention;
FIG. 9(a) is a time domain feature extraction for spot welding C-scan imaging of the present invention;
FIG. 9(b) is an extraction of envelope spectral domain features for spot welding C-scan imaging of the present invention;
FIG. 10 is a schematic representation of spot weld C-scan imaging results of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
The invention provides a spot welding ultrasonic quality evaluation method, aiming at the detection of a certain spot welding sample, the specific implementation mode comprises the following steps:
step 1) using a non-focusing transducer to be placed above the spot welding, and collecting ultrasonic echo signals at different positions, as shown in figure 1.
The ultrasonic echo signal acquisition method in the step 1) comprises the following steps of:
step 101) establishing a space Cartesian coordinate system, dividing a welding point and a related area around the welding point into a plurality of grids, taking the coordinate of the central point of each grid as the position coordinate of the grid, wherein the length of each grid in the x direction is delta x, the length of each grid in the y direction is delta y, the number of the grids in the x direction is N, and the number of the grids in the y direction is M.
Here, the grid number is 100 × 71, and the scan area is 10mm × 11.2mm, that is, Δ x ═ 11.2/70 mm, Δ y ═ 10/100 mm, M ═ 100, and N ═ 71. As shown in fig. 2.
Step 102) controlling the ultrasonic transducer to send ultrasonic pulse signals at each grid position, receiving ultrasonic echo signals at the grid, and acquiring a data set S of the echo signals. Each element S (x, y, n) of S represents a discrete-time echo signal acquired on the grid (x, y), and n represents a discrete time;
here the sampling rate fS40 MHz. The center frequency of the adopted single crystal transducer is 10MHz, the aperture D is 5mm, the distance between the transducer and the spot welding sample is about 2.1mm, the medium between the transducer and the spot welding sample is water, and the sound velocity c in the water11540m/s, interface aLOr aRThe number of sampling points of the phase difference between the primary echo and the transmitted signal is as follows: (2.1X 2/1000) fS/c1148, interface aLOr aRThe center of the primary echo at time n is approximately 175.
During collection, the single-chip transducer can be fixed by a mechanical movement device to sequentially move to the centers of different grids, stand still and then emit ultrasonic waves and receive echo waves; the single-chip transducer can also be continuously moved by the mechanical movement device, and ultrasonic waves are transmitted and received when the transducer moves to each grid under the control of an electronic system; a plurality of transducers can also be adopted to form a two-dimensional array, and each transducer unit is controlled to transmit and receive ultrasonic waves in turn and independently in an electronic switching mode. The specific scanning path or sequence is not limited. Each grid corresponds to a column of ultrasound echo signals. An example of an ultrasound echo signal on a grid is shown in figure 3.
Step 103) readjusting the sequence of the acquired echo data sets corresponding to each grid according to the increasing sequence of grid coordinates x and y according to the coordinate system shown in fig. 2, wherein the sequence corresponds to the grid sequence one by one.
Step 2) using the echo data set acquired in the step 1) to calculate the depth by using the position of the time domain echo signal peak on the interface a (shown in figure 1); the method specifically comprises the following steps:
201) the echo data set corresponding to a row of grids is selected, and here, the 50 th row of grids is taken as an example for description, and the data subset is S (x,50 Δ y, n), as shown in fig. 4. a isLAnd aRThe interface between the two parts is closer to the surface of the transducer, and corresponding echo signals
Figure BDA0001879693240000061
Closer to the transmitted signal on the time axis, aCEcho signals further from the transducer surface
Figure BDA0001879693240000062
Away from the transmitted signal on the time axis.
202) Selecting a suitable rectangular time window wt(n) the window width should be such that the boundary aLAnd aCReflecting the returned primary echo
Figure BDA0001879693240000063
And
Figure BDA0001879693240000064
are contained within the window;
as shown in fig. 3. Interface aLThe center of the echo at (f) occurs approximately at time n-175, where w is chosent(n) such that n ∈ [160,260 ∈]。
203) Respectively calculating the signal envelope of each grid in a window wtThe time when the peak occurs within (n)
Figure BDA0001879693240000065
Obtain a one-dimensional vector
Figure BDA0001879693240000066
Each element in the vector represents the y-th0Each grid in the row grid is at window wt(n) the time at which the maximum value within (n) occurs.
204) Drawing
Figure BDA0001879693240000067
And according to the curve, the maximum depth h of the indentation on the left side and the right side can be calculated according to the difference delta n between the maximum value and the minimum value on the curve. The calculation formula is as follows:
h＝(Δn)c1/(2fs) (1)
wherein, c1Is the speed of sound of the medium between the transducer surface and the spot weld, fsIs the sampling rate of the acquisition system a/D.
As shown in fig. 5. Left side of impression read on curve
Figure BDA0001879693240000071
The maximum and minimum values are 176 and 249 respectively, and the difference Δ n between the two is 73; impression Right side
Figure BDA0001879693240000072
The maximum and minimum values are 176 and 249, respectively, and the difference Δ n therebetween is 73. Substituting the formula (1) to calculate that the left and right indentation depths are both 1.05 mm.
And 3) estimating the spatial position and width of the spot welding indentation by using the echo data set acquired in the step 1) and utilizing the characteristics of the time domain echo signal on the interface a (shown in figure 1).
301) Selecting an echo data set S (x, y) corresponding to a row of grids0,n)；
Still taking the 50 th row of grids as an example for explanation here, the data subset is S (x,50 Δ y, n).
302) According to the characteristics of the spot welding surface and the composition of the echo signalTake two appropriate rectangular time windows wt1(n)，wt2(n)。wt1(n) sample surface a for selecting both sides of the soldered dotLOr aRThe echo signal section reflected for the first time, i.e.
Figure BDA0001879693240000073
wt2(n) for selecting the surface a of the soldered dotCThe echo signal section reflected for the first time, i.e.
Figure BDA0001879693240000074
Here, w is selectedt1(n) and wt2(n) are respectively located at [170,180 ]]And [242,256]。
303) Respectively calculating the peak value of the signal envelope in two windows to respectively obtain a one-dimensional vector Et1And Et2Each element in the vector represents the peak of the envelope for each grid in the line of grids.
304) Will Et1And Et2Plotted in a coordinate system with the abscissa being the position in the x-direction and the ordinate being the envelope peak, as shown in fig. 6, the curve describes the trend of the envelope peak with the grid position.
305) According to Et1And Et2And (3) estimating the x coordinate of the central ring of the indentation ring and the indentation width according to the theoretical variation trend and characteristics, as shown in figure 1. The impression structure model is shown in figure 7 when viewed from above the spot welded sample.
Firstly, the positions of the indentations, namely x coordinates of the outer ring, the central ring and the inner ring of the indentations are determined.
When the spread of the beam is not considered, the cross-sectional area of the acoustic field radiated by the transducer or transducer element is equal to the effective aperture area of the transducer or transducer element. Under this assumption, when the center of the transducer or the grid of the transducer unit radiation is moved from left to right, the echoes at different depths of the spot welded sample surface a will exhibit the following law of variation: in position 1, the ultrasonic waves emitted by the transducer or transducer element are all radiated to a, as shown in fig. 8LAt the interface, aLThe echo at the interface reaches a maximumI.e. Et1Reaching a maximum value; in position 2, the ultrasound emitted by the transducer or transducer unit just starts to radiate to aCInterface, just begin to appear aCEcho at the interface, Et2A growing trend just starting from a minimum; in position 3, the ultrasonic waves emitted by the transducer or transducer elements can be radiated simultaneously to aCInterface a andLinterface, echo having an existing aLEcho at the interface, also having aCEcho at the interface, at this time Et1And Et2Are all between respective maximum and minimum values; in position 4, the ultrasonic waves emitted by the transducer or transducer unit do not radiate exactly to aLInterface, aLThe echo at the interface just reaches a minimum, Et1Just to a minimum value, when the abscissa of the center of the transducer or transducer unit is marked x4(ii) a In position 5, the ultrasound emitted by the transducer or transducer unit is radiated exactly in its entirety to aCAt the interface, when Et2Just to a maximum value, when the abscissa of the center of the transducer or transducer unit is marked x5. Similarly, on the right, at position 6, Et2The attenuation is exactly 0, at position 7, Et1And Et2Are all between respective maximum and minimum values; in position 8, Et1Increasing to just the maximum value. Thus, as the grid progresses from left to right along a line, Et1Decreasing first and increasing second to reach a maximum on both sides, Et2Increasing and then decreasing, reaching a maximum in the middle.
According to the above principle, when the center of the transducer or transducer unit is exactly aligned with the center line of the indentation (the position of the center circle of the indentation), as shown in position 3 in fig. 8, the ultrasonic wave emitted from the transducer or transducer unit is radiated to aLInterface a andCthe areas of the interfaces are the same, and when the diffusion attenuation, absorption attenuation and scattering attenuation of the sound beam are neglected, Et1And Et2Exactly equal. By using this characteristic, the curve of the previous step is corrected to let Et1Multiplying by Et2And Et1So that the maximum values of the two curves are the same, and then calculating the x-position coordinates of the intersection point of the two curvesI.e. the position x of the center circle of the indentation is determineddL(left position) and xdR(right position).
According to the analysis of the previous step, when the transducer or transducer unit is located at position 4 shown in fig. 8,
Figure BDA0001879693240000081
just to a minimum value, when the abscissa of the center of the transducer or transducer unit is denoted x4The outer ring of the left indentation is positioned
Figure BDA0001879693240000082
When the transducer or transducer unit is in position 5 shown in fig. 8, this time
Figure BDA0001879693240000083
Just increasing to a maximum value, when the abscissa of the center of the transducer or transducer unit is marked x5The inner ring of the left indentation is positioned
Figure BDA0001879693240000084
Left side impression width dL＝x5-x4I.e. the difference between the radii of the left indentation outer ring and the inner ring. In the same way, the width d of the right indentationR＝x8-x6The inner ring of the right indentation and the outer ring of the right indentation are respectively positioned
Figure BDA0001879693240000085
Figure BDA0001879693240000086
And
Figure BDA0001879693240000087
the position of the center circle of the indentation is first determined. Neglecting the diffusion attenuation, absorption attenuation, and scattering attenuation of the sound beamt1And Et2The exact equal position is the position of the center circle of the indentation. In fig. 6, the x-coordinate of the intersection point of the envelope peak curves of the two time domain windows is calculated, i.e. the position of the center circle of the left indentation is determinedIs set to xdL5.4mm and the position of the center circle of the right indentation is xdR＝11.0mm。
Then, the width of the indentation is calculated. When the transducer or transducer unit is in position 4 shown in figure 8,
Figure BDA0001879693240000091
just to a minimum value, when the abscissa of the center of the transducer or transducer unit is marked x467 Δ x; when the transducer or transducer unit is in position 5 shown in fig. 8, this time
Figure BDA0001879693240000092
Just to a maximum value, when the abscissa of the center of the transducer or transducer unit is marked x571 Δ x. Left side impression width dL＝x5-x40.64mm, the difference between the radii of the left indentation outer ring and the inner ring. Similarly, the width d of the right indentation can be calculatedR＝x8-x6＝0.64mm。
And finally, determining the positions of the outer ring and the inner ring of the indentation. The positions of the outer ring and the inner ring of the left indentation are x respectivelyILL5.08mm and xILR5.72 mm; the positions of the outer ring and the inner ring of the right indentation are x respectivelyIRR11.32mm and xIRL＝10.68mm。
Step 4) repeating steps 2) and 3) on all different scan lines, depth, position, width information of the indentation on different scan lines can be estimated.
And 5) extracting the characteristic value of the echo signal in a time domain or an envelope spectrum domain by using the data set S of the echo signal acquired in the step 1) to form a characteristic value matrix F.
The following describes how to extract the feature value F of the echo signal in the time domain or the envelope spectrum domain. The extraction process of the time domain feature value is shown in fig. 9(a), and the extraction process of the envelope spectrum domain is shown in fig. 9 (b). In the time domain feature extraction process, a time domain window is selected, the depth of the extracted surface (including the indentation) of the welding spot is used as a reference, the starting point of the time domain window is selected after the echo time corresponding to the surface a of the welding spot at the corresponding grid, and the time width of the time window is wideDegree generally not greater than the ultrasonic signal from aCRound trip time of interface to c interface (as shown in FIG. 1); in the process of extracting the characteristics of the envelope spectrum domain, the selection of the starting point of the time window is the same as the time domain characteristic extraction process, and the time width of the time window generally meets the requirement that the ultrasonic signal is extracted from aCThe integer multiple of the round trip time from interface to c-interface, i.e. the multiple echoes from c-interface are contained within the time window. Let the selected time domain window be wc(n) the signal segment intercepted by the time domain window is
Figure BDA0001879693240000093
The frequency domain window is centered at frequency fwF ofwJust satisfying equation (2). Wherein H-H is the thickness of the upper and lower surfaces of the solder joint, c2Is the speed of sound of the solder joint material. The width of the frequency domain window should be such that at all pad surface locations (depth of the pad surface) the repetition frequency of echoes going back and forth between the upper and lower surfaces of the pad is almost within the frequency window.
1/fw＝2(H-h)/c2 (2)
Here, when extracting temporal features for C-scan imaging, the starting point of the temporal window is selected to be n-287, and the window width is 7. When the envelope spectrum domain features are extracted and used for C scanning imaging, the time domain window starts from n 263 with the width of 400; the length of the FFT is 8192; the center of the frequency domain window is determined according to equation (2), frequency fw1.53MHz, where h0＝2mm，c26100 m/s; the width of the frequency domain window is chosen to be 0.665MHz, containing 10 FFT spectral lines.
And 6) controlling the display range according to the percentage R, and forming spot welding C scanning imaging.
Let R be 1/2, and draw a spot-welded C-scan image with the time-domain or envelope-spectrum domain feature value F (x, y) as a pixel value and [ R,1] as a feature value range, as shown in fig. 10.
And 7) drawing the curve of the center circle, the outer circle and the inner circle of the indentation estimated in the step 3) in the C scanning imaging of the step 6).
And 8) in the C-scan imaging of the step 6), judging the nugget size information by combining the position and width information of the indentation.
The diameter of the image's circular border line is read in the C-scan image. If the estimated nugget boundary is located in the indentation inner ring, the nugget is smaller, and the diameter of the circular boundary line can be used as the estimated value of the nugget diameter at the moment, and the estimation is more accurate; if the estimated nugget boundary is located near the inner ring of the indentation, the diameter of the circular boundary line is used as the estimated value of the nugget diameter, the uncertainty range is the width of the indentation, the actual nugget boundary is located below the annular region of the indentation, the diameter of the central ring of the indentation is used as the estimated value of the nugget diameter, and the nugget size can be basically considered to be qualified. And further evaluating whether welding defects exist in spot welding and whether the welding quality is qualified according to the image and the estimation result of the nugget size.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (6)

1. A spot welding ultrasonic quality evaluation method comprises the following steps:
pre-estimating the indentation position, the indentation depth and the indentation width by using collected spot welding ultrasonic echo signals, then guiding the selection of ultrasonic C scanning imaging parameters according to the measured surface conditions of the indentation and the welding spot, then performing ultrasonic C scanning imaging and spot welding quality evaluation on the nugget, fusing the actual influence of the indentation into the nugget estimation process, and obtaining nugget quantification and spot welding quality evaluation results;
the method comprises the following steps:
step 1) placing a non-focusing transducer above spot welding, and collecting ultrasonic echo signals at different positions;
step 2) using the echo data sets of different positions acquired in the step 1), estimating the depth, the spatial position and the width of the surface indentation of the welding spot on different scanning lines by using the time domain signal characteristics, and estimating the parameters of an indentation center ring, an indentation outer ring and an indentation inner ring;
step 3) extracting a characteristic value F (x, y) of the echo signal in a time domain or an envelope spectrum domain by using the data set S of the echo signal acquired in the step 1) and using the depth of the indentation on the surface of the welding spot as a reference;
step 4), taking the characteristic value as a pixel value, and adopting the percentage R to control the display range of the characteristic value to form spot welding C scanning imaging; drawing a spot welding C-scan image by taking the characteristic value F (x, y) of a time domain or an envelope spectrum domain as a pixel value and taking [ R,1] as a characteristic value range;
step 5) drawing the curve of the center circle, the outer circle and the inner circle of the indentation estimated in the step 2) in the C scanning imaging of the step 4);
and 6) in the C scanning imaging of the step 5), judging the size information and the quality condition of the nugget by combining the position and the width information of the indentation.
2. The spot welding ultrasonic quality evaluation method according to claim 1, characterized in that the step 1) specifically includes:
step 1-1) establishing a space Cartesian coordinate system, dividing a welding point and a related area around the welding point into a plurality of grids, taking the coordinate of the central point of each grid as the position coordinate of the grid, wherein the length of each grid in the x direction is delta x, the length of each grid in the y direction is delta y, the number of the grids in the x direction is N, and the number of the grids in the y direction is M;
step 1-2) controlling an ultrasonic transducer to send ultrasonic pulse signals at each grid position, receiving ultrasonic echo signals at the grid position, and acquiring a data set S of the echo signals; each element S (x, y, n) of S represents a discrete-time echo signal acquired on the grid (x, y), and n represents a discrete time;
and 1-3) readjusting the sequence of the acquired echo data sets corresponding to each grid according to the increasing sequence of the grid coordinates x and y, wherein the echo data sets correspond to the grid sequence one by one.
3. The spot welding ultrasonic quality evaluation method according to claim 2, wherein the step 2) specifically includes:
step 2-1) selecting an echo data set corresponding to a grid scanning line, estimating depth information of the surface of a welding spot by using time domain signal characteristics, and calculating the depth of an indentation on the surface of the welding spot by using the position of a peak value of an echo reflected by the upper surface of a sample;
step 2-2) selecting an echo data set corresponding to a grid scanning line, and estimating the spatial position and the width of a spot welding indentation by using the time domain signal characteristic; calculating the position parameters of the indentation center ring, the indentation outer ring and the indentation inner ring;
step 2-3) repeating step 2-1) and step 2-2) on other grid scanning lines, estimating the depth, spatial position and width of the indentation on different scanning lines; and calculating the position parameters of the indentation center ring, the indentation outer ring and the indentation inner ring of different scanning lines.
4. The ultrasonic quality evaluation method for spot welding according to claim 3, wherein the step 2-1) specifically comprises:
step 2-1-1) selecting an echo data set corresponding to a grid scanning line, and setting the sample surfaces at two sides of a welding point as aLOr aRCorresponding echo signals
Figure FDA0002671655990000021
Near the transmitted signal on the time axis, pad surface aCEcho signals further from the transducer surface
Figure FDA0002671655990000022
Distant from the transmitted signal on a time axis;
step 2-1-2) selecting a rectangular time window wt(n) window width satisfies the relationship defined by interface aLAnd aCReflecting the returned primary echo
Figure FDA0002671655990000023
And
Figure FDA0002671655990000024
are contained within the window;
step 2-1-3) respectively calculating the signal envelope of each grid in a window wtMoment of occurrence of internal peak
Figure FDA0002671655990000025
Obtain a one-dimensional vector
Figure FDA0002671655990000026
Each element in the vector represents the y-th0Each grid in the line grid is in a rectangular time window wt(n) a time at which the maximum value within (n) occurs;
step 2-1-4) drawing with x as abscissa
Figure FDA0002671655990000027
Curve, left side of impression read on curve
Figure FDA0002671655990000028
The difference between the maximum value and the minimum value of (1) is delta n; impression Right side
Figure FDA0002671655990000029
The difference between the maximum value and the minimum value is delta n; respectively substituting the maximum depth h of the indentation on the left side and the right side into the formula (1) to calculate:
h＝(Δn)c1/(2fs) (1)
wherein, c1Is the speed of sound of the medium between the transducer surface and the spot weld, fsIs the sampling rate.
5. The ultrasonic quality evaluation method for spot welding according to claim 4, wherein the step 2-2) specifically comprises:
step 2-2-1) two rectangular time windows w are selectedt1(n) and wt2(n)；wt1(n) sample surface a for selecting both sides of the soldered dotLOr aREcho signal segments reflected for the first time; w is at2(n) for selecting the surface a of the soldered dotCEcho signal segments reflected for the first time;
step 2-2-2) respectively calculating peak values of signal envelopes in two rectangular time windows to respectively obtain one-dimensional vectors Et1And Et2Each element in the two vectors represents the peak of the envelope for each grid in the row of grids;
step 2-2-3) reacting Et1And Et2Drawing in a coordinate system, wherein the abscissa is the position in the x direction, and the ordinate is the peak value of the envelope; calculating the x coordinate of the intersection point of the envelope peak curves of the two time domain windows, namely determining the left position x of the indentation center circledLAnd right position xdR；
Step 2-2-4) is on the left side of the indentation when
Figure FDA0002671655990000031
When reduced to a minimum, the abscissa of the center of the transducer or transducer unit is denoted x4When is coming into contact with
Figure FDA0002671655990000032
When increasing to a maximum, the abscissa of the center of the transducer or transducer unit is denoted x5(ii) a Left indentation width dL＝x5-x4(ii) a The outer ring of the left indentation is positioned
Figure FDA0002671655990000033
The inner ring of the left indentation is positioned
Figure FDA0002671655990000034
D is the aperture of the transducer;
step 2-2-5) on the right side of the indentation when
Figure FDA0002671655990000035
When reduced to a minimum, the abscissa of the center of the transducer or transducer unit is denoted x6When is coming into contact with
Figure FDA0002671655990000036
When increasing to a maximum, the abscissa of the center of the transducer or transducer unit is denoted x8(ii) a The indentation width d on the right sideR＝x8-x6(ii) a The right indentation inner ring is positioned
Figure FDA0002671655990000037
The outer ring of the right indentation is positioned
Figure FDA0002671655990000038
6. The spot welding ultrasonic quality evaluation method according to claim 5, wherein the step 6) is specifically: reading the diameter of the circular boundary line of the image in the C scanning image; and if the estimated nugget boundary is positioned in the indentation inner ring, the diameter of the circular boundary line is the estimated value of the nugget diameter, if the estimated nugget boundary is positioned near the indentation inner ring, the diameter of the indentation central ring is used as the estimated value of the nugget diameter, and meanwhile, the nugget size is judged to be qualified.
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