CN104655564A - Detection method for hole defect of double-shaft-shoulder friction stir welding seam - Google Patents
Detection method for hole defect of double-shaft-shoulder friction stir welding seam Download PDFInfo
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- CN104655564A CN104655564A CN201510024502.2A CN201510024502A CN104655564A CN 104655564 A CN104655564 A CN 104655564A CN 201510024502 A CN201510024502 A CN 201510024502A CN 104655564 A CN104655564 A CN 104655564A
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Abstract
The invention discloses a detection method for a hole defect of a double-shaft-shoulder friction stir welding seam. The detection method comprises the steps that a torque low-frequency signal TL and a rectilinear oscillation signal To are extracted from an original welding torque signal T according to the original welding torque signal T, and an hour at which the hole defect possibly exists is judged according to change situations of minimum values of an amplitude value AL of the low-frequency signal TL and an amplitude value Ao of the rectilinear oscillation signal To. Based on a frequency spectrum of a double-shaft-shoulder friction stir welding torque, according to the change situations of the amplitude values of the low-frequency signal and the rectilinear oscillation signal, the hole defect of the welding seam is judged, so that the detection method for the hole defect of the double-shaft-shoulder friction stir welding seam is simple; huge investment on methods and equipment of X-ray detection and the like is not required, so that the cost is low; and the welding seam is not damaged, so that the method is suitable for occasions with low requirements on the joint strength and without damaging the welding seam for detection.
Description
Technical field
The present invention relates to and relate to stirring friction welding seam defects detection field, be specifically related to a kind of double-shaft shoulder stirring friction welding seam hole defect detection method.
Background technology
A kind of solid-state bonding process that friction stir welding (FSW) is proposed in 1991 by Britain's institute of welding (TWI).Compared with traditional melt welding method; it is tiny that friction stir welding has crystal grain, fatigue behaviour, tensile property and bending property be good, without the cloud of dust, pore-free, without splashing, energy-conservation, use blanket gas, the rear unrelieved stress of welding without the need to not needing when welding wire, welding and be out of shape the advantages such as little.Friction stir welding is at first for aluminium alloy, and along with going deep into of research, friction stir welding not only may be used for the welding of aluminium alloy.Also can be used for the welding between other metals such as copper, titanium and different metal.
But stirring friction welding seam is not perfect in every way, also can produce various defect, as common hole defect, tunnel defect, surperficial overlap etc.To the hole defect being present in surface, available visualize; To the hole or the tunnel defect that are present in weld seam inside, the nondestructiving detecting means such as x-ray detection, ultrasonic inspection can be adopted at present, or weld seam is directly blocked inspection.Though adopt nondestructiving detecting means to realize testing goal, operating comparatively loaded down with trivial details, blocking inspection as adopted, as blocked inspection, then more loaded down with trivial details, and weld seam is thoroughly destroyed.
Therefore, how improving or to propose new lossless detection method, is Welder author's pursuit always.
Summary of the invention
Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides a kind of double-shaft shoulder stirring friction welding seam hole defect detection method, the amplitude situation of change according to low frequency signal and periodic oscillation signal judges weld seam hole defect, and method is simple and easy.
Technical scheme: for solving the problems of the technologies described above, a kind of double-shaft shoulder stirring friction welding seam hole defect detection method of the present invention, for the moment of torsion that stirring-head in stir friction welding process bears, extract the low frequency signal in torque signal and periodic oscillation signal respectively, then the amplitude situation of change of low frequency signal amplitude and periodic oscillation signal is detected, when there is flex point and minimal value in the amplitude of low frequency signal and periodic oscillation signal amplitude exceedes threshold values, can judge now to weld and occur Weak link, judge that weld seam inside exists hole defect thus.
Described double-shaft shoulder stirring friction welding seam hole defect detection method, specifically comprises the following steps:
The first step: the rotational speed ω (unit is rpm) according to stirring-head determines correction factor k, k=0.00274 ω-0.0689;
Second step: the scope determining the frequency f of periodic oscillation signal,
3rd step: extract the low frequency signal T in original welding torque signal T by wave filter
lwith periodic oscillation signal T
o, to T
l, T
othe overall length of sequence revise, make overall length be whole 10 times of L, L is to 60*f
s/ ω rounds, f
sbe original welding torque signal T sample frequency, from T
l, T
orow first open the beginning, get respectively a segment length be 10L signal composition s
l, s
o, as initial ranging data source;
4th step: search s
lflex point A
g, to low frequency signal s
ldiscrete signal ask for first order derivative and second derivative, when both are zero and corresponding first order derivative is flex point A by bearing the point become corresponding to positive moment
g, if any, then turning next step, as not having, proceeding to the 7th step;
5th step: search minimal value A
mIN, flex point A
gafter appearance, continue to detect and A
gadjacent minimum point, when first order derivative be zero, the second derivative point that is greater than zero is minimum point A
mIN, judge A
mINwhether be less than or equal to the threshold values A of low frequency signal
f1if, A
mINbe less than or equal to A
f1, then the 6th step is carried out; If be greater than A
f1, then to the 7th step;
6th step: to periodic oscillation signal s
ocarry out solving first order derivative and second derivative, when first order derivative be zero, the second derivative point that is greater than zero is minimum point, search s
othe minimal value of middle appearance, gets the absolute value A of arithmetic mean
m, judge A
mwhether be more than or equal to periodic oscillation signal s
othreshold value A
f2, in this way, then judge herein as defect possibility origination point, and record, for subsequent review; As A
mbe less than A
f2, then normal point is considered as;
7th step: judge T
lwhether read complete, if read complete, proceeded to the 9th step; If do not read complete, proceed to next step;
8th step: keep search source s
l, s
osegment length 10L is constant, and move according to the order of sequence to row tail direction, movable length is L, forms new search data source, proceeds to the 4th step;
9th step: detect and terminate.
As preferably, described 3rd step median filter comprises low-pass filter and bandpass filter, and the cutoff frequency of low-pass filter is 3Hz, and original welding torque signal T extracts low frequency signal T by described low-pass filter
l, the upper cut off frequency of bandpass filter is
lower limiting frequency is
k is correction factor, and original welding torque signal T extracts periodic oscillation signal T by described bandpass filter
o.
In the present invention, to s
ldiscrete signal ask for first order derivative and second derivative, when both are zero and corresponding first order derivative is flex point A by bearing the point become corresponding to positive moment
g; Flex point A
gafter appearance, continue to detect and A
gadjacent minimum point, when first order derivative be zero, the second derivative point that is greater than zero is minimum point A
mIN, in the present invention, low frequency signal s
lbe greater than zero.
In the present invention, to s
odiscrete signal ask for first order derivative and second derivative, when first order derivative be zero, the second derivative point that is greater than zero is just minimum point; Due to s
oabout time shaft symmetrical for periodic oscillation signal, very big or minimizing absolute value is exactly the amplitude of signal, therefore can detect s
othe minimal value occurred, gets the absolute value of these minimizing arithmetic means, is amplitude mean value, is designated as A
m.
Method of the present invention, is applicable to normally at the uniform velocity weld the stage, and be the double-shaft shoulder agitating friction welding incipient stage, part metals can be extruded weld seam by stirring-head, and cause torque signal unstable, described detection method is invalid; Double-shaft shoulder friction stir welding connects finishing phase, and when namely weld seam forms U-shaped opening, torque signal is unstable equally, and described detection method is invalid.
Beneficial effect: double-shaft shoulder stirring friction welding seam hole defect detection method of the present invention, has the following advantages:
(1) based on the frequency spectrum of double-shaft shoulder agitating friction welding moment of torsion, the amplitude situation of change according to low frequency signal and periodic oscillation signal judges weld seam hole defect, and method is simple and easy;
(2) the method is with low cost, without the need to a large amount of inputs of the method equipment such as x-ray detection;
(3) the method not butt welded seam destroy, be suitable for low strength of joint requirement, without the need to destroying the occasion of weld seam detection.
Accompanying drawing explanation
Fig. 1 is process flow diagram of the present invention.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further described.
The collection of the welding moment of torsion original signal that the present invention relates to, existing correlation technique is open, can directly adopt.
With the rotational speed of stirring-head be 600rpm, thickness for 6mm model be the aluminium alloy of 6061, the sample frequency f of raw torque signal
sfor 50Hz is example, testing process refers to Fig. 1:
Step1: according to rotational speed ω=600rpm, k=0.00274 ω-0.0689, determine correction factor k=1.5751;
Step2: according to formula
determine that the frequency f scope of periodic oscillation signal is for [18.54Hz, 20Hz];
Step3: design low-pass filter, cutoff frequency is 3Hz;
Step4: design bandpass filter, upper cut off frequency is 20Hz, and lower limiting frequency is 18.54Hz;
Step5: with original welding torque signal T be low-pass filter, the input of bandpass filter, then record corresponding output low frequency signal T respectively
l, periodic oscillation signal T
o;
Step6: to T
l, T
othe overall length of sequence revise, make overall length be whole 10 times of L (L=5); Respectively from T
l, T
orow first open the beginning, get the s of a segment length
l, s
osignal as initial ranging data source, signal length is 10L;
Step7: search search source s
lflex point A
g, if any, then turning next step, as not having, proceeding to Step10;
Step8: search minimal value A
mIN, judge A
mINwhether be less than or equal to the threshold values A of low frequency signal
f1(now set A
f1=15), if A
mINbe less than or equal to A
f1, then Step9 is carried out; If be greater than A
f1, then to Step10;
Step9: search search source s
omiddle occurred minimizing arithmetic mean, and the A that takes absolute value
m, judge A
mwhether be more than or equal to the threshold value A of periodic oscillation signal
f2(now set A
f2=5), in this way, then judge herein as defect possibility origination point, and record; As A
mbe less than A
f2, then normal point is considered as.
Step10: judge T
lwhether read complete, if read complete, proceeded to Step12; If do not read complete, proceed to next step.
Step11: keep search source s
l, s
osegment length 10L is constant, and move according to the order of sequence to row tail direction, movable length is L, forms new search data source, proceeds to Step7.
Step12: detect and terminate.
In the 11 step, original search source is moved to the row tail of original signal, and movable length is L, as new search source s
l, s
o, new search source s
lbe used in the 7th step, the 9th step; When proceeding to the 7th step, search s
lnew flex point A
o; In 9th step, calculate new periodic oscillation signal s
oall minimal values, and calculate all minimal value arithmetic mean, and the absolute value of averaging.
After the above step is finished, the detection of double-shaft shoulder stir friction welding process Hole defect can be completed; This detection method, is extracted the information of torque signal medium and low frequency and radio-frequency component especially, more truly reflects defect characteristic all sidedly, and detection mode is simple simultaneously.
The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (5)
1. a double-shaft shoulder stirring friction welding seam hole defect detection method, it is characterized in that: the moment of torsion born for stirring-head in stir friction welding process, extract the low frequency signal in torque signal and periodic oscillation signal respectively, then the amplitude situation of change of low frequency signal amplitude and periodic oscillation signal is detected, when there is flex point and minimal value in the amplitude of low frequency signal and periodic oscillation signal amplitude exceedes threshold values, can judge now to weld and occur Weak link, judge that weld seam inside exists hole defect thus.
2. double-shaft shoulder stirring friction welding seam hole defect detection method according to claim 1, is characterized in that comprising the following steps:
The first step: determine correction factor k according to the rotational speed ω of stirring-head, k=0.00274 ω-0.0689;
Second step: the scope determining the frequency f of periodic oscillation signal,
3rd step: extract the low frequency signal T in original welding torque signal T by wave filter
lwith periodic oscillation signal T
o, to T
l, T
othe overall length of sequence revise, make T
l, T
othe overall length of sequence be whole 10 times of L, L is to 60*f
s/ ω rounds, f
sbe original welding torque signal T sample frequency, respectively from T
l, T
orow first open the beginning, get respectively a segment length signal composition s
l, s
o, as initial ranging data source, signal length is 10L;
4th step: search s
lflex point A
g, to low frequency signal s
ldiscrete signal ask for first order derivative and second derivative, when both are zero and corresponding first order derivative is flex point A by bearing the point become corresponding to positive moment
g, if any, then turning next step, as not having, proceeding to the 7th step;
5th step: search minimal value A
mIN, flex point A
gafter appearance, continue to detect and A
gadjacent minimum point, when first order derivative be zero, the second derivative point that is greater than zero is minimum point A
mIN, judge A
mINwhether be less than or equal to the threshold values A of low frequency signal
f1if, A
mINbe less than or equal to A
f1, then the 6th step is carried out; If be greater than A
f1, then to the 7th step;
6th step: to periodic oscillation signal s
ocarry out solving first order derivative and second derivative, when first order derivative be zero, the second derivative point that is greater than zero is minimum point, search s
othe minimal value of middle appearance, gets the absolute value A of arithmetic mean
m, judge A
mwhether be more than or equal to periodic oscillation signal s
othreshold values A
f2, in this way, then judge herein as defect possibility origination point, and record, for subsequent review; As A
mbe less than A
f2, then normal point is considered as;
7th step: judge T
lwhether read complete, if read complete, proceeded to the 9th step; If do not read complete, proceed to next step;
8th step: keep search source s
l, s
osegment length 10L is constant, and move according to the order of sequence to row tail direction, movable length is L, forms new search data source, proceeds to the 4th step;
9th step: detect and terminate.
3. double-shaft shoulder stirring friction welding seam hole defect detection method according to claim 2, it is characterized in that: described 3rd step median filter comprises low-pass filter, the cutoff frequency of low-pass filter is 3Hz, and original welding torque signal T extracts low frequency signal T by described low-pass filter
l.
4. double-shaft shoulder stirring friction welding seam hole defect detection method according to claim 2, is characterized in that: described 3rd step median filter comprises bandpass filter, and the upper cut off frequency of bandpass filter is
lower limiting frequency is
k is correction factor, and original welding torque signal T extracts periodic oscillation signal T by described bandpass filter
o.
5. double-shaft shoulder stirring friction welding seam hole defect detection method according to claim 2, is characterized in that: in the described first step, when determining correction factor k according to the rotational speed ω of stirring-head, should be in and normally at the uniform velocity weld the stage; Be the double-shaft shoulder agitating friction welding incipient stage, part metals can be extruded weld seam by stirring-head, and detection method is invalid; Double-shaft shoulder friction stir welding connects finishing phase, and when weld seam forms U-shaped opening, detection method is invalid.
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| CN201510024502.2A CN104655564B (en) | 2015-01-16 | 2015-01-16 | Detection method for hole defect of double-shaft-shoulder friction stir welding seam |
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| CN109570729A (en) * | 2018-11-28 | 2019-04-05 | 湘潭大学 | A method of stirring friction welding seam penetration quality dynamic is detected based on torque |
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