On-line quantitative evaluation method for stability of welding process

Abstract

An on-line quantitative evaluation method for the stability of a welding process includes the steps of monitoring and acquiring the arc voltage U and the welding current I during the welding process, and drawing a phase diagram of each U-I cycle; converting the phase diagram of each U-I cycle into a binary image K; obtaining an area J.sub.N through which a dynamic working curve passes in the binary image K; obtaining a welding process stability evaluation index P according to the formula (1), where J.sub.N is the area of a U-I curve, N is the number of cycles passed, L is the total number of samples in N cycles, and P is the repetition rate of the i-th U-I cycle and other cycles (i=1 . . . N); and evaluating the stability of the welding process according to the obtained welding stability evaluation index P.

Claims

1. An on-line quantitative evaluation method for the stability of a welding process, comprising: monitoring and acquiring the arc voltage U and the welding current I during the welding process, and drawing a corresponding phase diagram of a U-I cycle; converting the phase diagram of each U-I cycle into a binary image K; obtaining an area J.sub.N through which a dynamic working curve passes in the binary image K; obtaining a welding process stability evaluation index P according to formulas (1) and (2); $\begin{array}{cc}{J}_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}};& \left(1\right)\\ \frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}};& \left(2\right)\end{array}$ where J.sub.N is the area of a U-I curve, N is the number of cycles passed, L is the total number of samples in N cycles, P is the repetition rate of the i-th U-I cycle and other cycles (i=1 . . . N), Q is the sum of non-background areas obtained by using a command sum (L(:)) after L is inverted in a binary image matrix L=bwlabel(K), and M is the number of elements in the binary image matrix L=bwlabel(K); and evaluating the stability of the welding process according to the obtained welding stability evaluation index P.

2. The method according to claim 1, wherein the specific step of acquiring is: obtaining a corresponding phase diagram of each U-I cycle according to the values of the arc voltage U and the welding current I acquired by a group control system in real time.

3. The method according to claim 1, wherein the specific step of converting the phase diagram of the U-I cycle into the binary image K is: saving the U-I phase diagram as “UI.jpg”, importing the image into MATLAB by using a command I=imread(‘UI.jpg’), and converting the U-I phase diagram file into the binary image K through a binary conversion function im2bw( ).

4. The method according to claim 3, wherein in the binary image K, the gray value is 0 in the place where the U-I dynamic working trajectory passes, and otherwise is 1.

5. The method according to claim 1, wherein the specific steps of obtaining an area J.sub.N through which a dynamic working curve passes are: inverting L by making the binary image matrix L=bwlabel(K), at this time the number of “1” in the image matrix being the total number of points or area through which the UI curve passes; obtaining the sum Q of non-background areas by using a command sum (L(:)), the area of unit voltage and current in the U-I phase diagram is assumed to be 1, and the area J.sub.N through which the dynamic working curve passes in the U-I phase diagram can be obtained from $\frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}}.$

6. An application of the method according to claim 1 in CO.sub.2 gas shielded welding, MAG/MIG welding, and occasions where the output characteristics are double variables and high consistency.

7. An on-line quantitative evaluation apparatus for the stability of a welding process, comprising: a detection apparatus, configured to monitor the arc voltage U and the welding current I during the welding process and acquire various detection data; an input device, configured to transmit the various detection data to a processor; the processor, configured to process the various detection data to obtain a welding process stability evaluation index P; an output device, configured to output the welding process stability evaluation index P obtained by the processor; and a display, configured to display the result output by the output device, wherein the specific steps of processing the various detection data are: 1) drawing a corresponding phase diagram of a U-I cycle according to the values of the arc voltage U and the welding current I of each cycle during the welding process; 2) converting a phase diagram of each U-I cycle into a binary image K; 3) obtaining an area J.sub.N through which a dynamic working curve passes in the binary image K; and 4) obtaining a welding process stability evaluation index P according to formulas (1) and (2); $\begin{array}{cc}{J}_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}};& \left(1\right)\\ \frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}};& \left(2\right)\end{array}$ where J.sub.N is the area of a U-I curve, N is the number of cycles passed, L is the total number of samples in N cycles, P is the repetition rate of the i-th U-I cycle and other cycles (i=1 . . . N), Q is the sum of non-background areas obtained by using a command sum (L(:)) after L is inverted in a binary image matrix L=bwlabel(K), and M is the number of elements in the binary image matrix L=bwlabel(K).

8. The apparatus according to claim 7, wherein the specific step of converting the phase diagram of the U-I cycle into the binary image K is: saving the U-I phase diagram as “UI.jpg”, importing the image into MATLAB by using a command I=imread(‘UI.jpg’), and converting the U-I phase diagram file into the binary image K through a binary conversion function im2bw( ); in the binary image K, the gray value is 0 in the place where the U-I dynamic working trajectory passes, and otherwise is 1.

9. The apparatus according to claim 7, wherein the specific steps of obtaining an area J.sub.N through which a dynamic working curve passes are: inverting L by making the binary image matrix L=bwlabel(K), at this time the number of “1”s in the image matrix being the total number of points or area through which the U-I curve passes; obtaining the sum Q of non-background areas by using a command sum (L(:)), the area of unit voltage and current in the U-I phase diagram is assumed to be 1, and the area J.sub.N through which the dynamic working curve passes in the U-I phase diagram can be obtained from $\frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}}.$

10. An application of the method according to claim 2 in CO.sub.2 gas shielded welding, MAG/MIG welding, and occasions where the output characteristics are double variables and high consistency.

11. An application of the method according to claim 3 in CO.sub.2 gas shielded welding, MAG/MIG welding, and occasions where the output characteristics are double variables and high consistency.

12. An application of the method according to claim 4 in CO.sub.2 gas shielded welding, MAG/MIG welding, and occasions where the output characteristics are double variables and high consistency.

13. An application of the method according to claim 5 in CO.sub.2 gas shielded welding, MAG/MIG welding, and occasions where the output characteristics are double variables and high consistency.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The drawing accompanying the Description and constituting a part of the present application is used for providing a further understanding of the present application, and the schematic embodiments of the present application and the descriptions thereof are used for interpreting the present application, rather than constituting improper limitations to the present application.

(2) FIG. 1 shows a U-I phase diagram of a welding process, where the parts (a), (b) are U-I phase diagrams of different welding processes.

DETAILED DESCRIPTION OF EMBODIMENTS

(3) It should be pointed out that the following detailed descriptions are all exemplary and aim to further illustrate the present application. Unless otherwise specified, all technological and scientific terms used herein have the same meanings generally understood by those of ordinary skill in the art of the present application.

Embodiment 1

(4) A U-I phase diagram of a welding process is shown in FIG. 1. A welding process stability evaluation index P is defined, which represents an average repetition rate of a U-I cycle and other cycles. When P=100%, it indicates that the changes in each cycle and previous cycles are completely consistent, and such welding process is absolutely stable. On the contrary, the smaller P is, the more irregular the changes in the arc voltage and the welding current of the welding process are, and the poorer the consistency of welding quality is.

(5) It is assumed that, after the first U-I cycle the number of points on the phase diagram is:
J.sub.1=α

(6) After the second cycle, the first cycle and the second cycle have Pα points repeated. At this time, the number of points on the U-I phase diagram increases by (1−P)α points, and the total number of points is:
J.sub.2=α+α−Pα=α+(1−P)α

(7) After the third cycle, the number of points increasing on the U-I phase diagram is (1−P)α−P(1−P)α, and at this time the total number of points is:
J.sub.3=α+(1−P)α+(1−P)α−P(1−P)α=α+(1−P)α+(1−P).sup.2α

(8) After the N-th cycle, α may be replaced with the number of points evaluated per cycle

(9) $\frac{L}{N},$
where L is the total number of samples over a period of time, and the following can be obtained by mathematical induction:

(10) $J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}$

(11) In the formula, only J.sub.N and P are unknown, and the average repetition rate P can be obtained just by obtaining J.sub.N. Practically, J.sub.N represents an area through which the U-I curve passes. In the present invention, the area of the curve in the U-I phase diagram is obtained by using an image binarization method. The specific steps are as follows:

(12) (1) A U-I phase diagram is obtained according to the values of the arc voltage U and the welding current I obtained by a group control system in real time, and saved as “UI.jpg”, and the image is imported into MATLAB by using a command I=imread(‘UI.jpg’).

(13) (2) The U-I phase diagram file is converted into a binary image K through a binary conversion function im2bw( ). At this time, the U-I phase diagram may show a black and white effect: the gray value is 0 in the place where the UI dynamic working trajectory passes, and otherwise is 1.

(14) (3) The obtained binary image matrix L=bwlabel(K), and the number of elements thereof is M To facilitate the calculation, L is inverted, so that the number of “1” in the image matrix is the total number of points or area that the U-I curve passes through.

(15) (4) The sum Q of non-background areas is obtained by using a command sum (L(:)), the area of unit voltage and current in the U-I phase diagram is assumed to be 1, and the area J.sub.N through which the dynamic working curve passes in the U-I phase diagram can be obtained from

(16) $\frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}}.$

(17) (5) The repetition rate P can be obtained according to the previous formula

(18) $J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}.$
The stability of the system can be determinated based on P.

(19) By the calculation above, the repetition rate P.sub.1 in part (a) of FIG. 1 is 0.0701, and the repetition rate P.sub.2 in part (b) of FIG. 1 is 0.0305. P.sub.1 greater than P.sub.2 indicates that the welding process shown in part (a) of FIG. 1 has good stability and high welding consistency, which achieves the same effect as human intuitive determination.

Embodiment 2

(20) The evaluation of the stability of a CO.sub.2 gas shielded welding process. A welding process stability evaluation index P is defined, which represents an average repetition rate of a U-I cycle and other cycles. When P=100%, it indicates that the changes in each cycle and previous cycles are completely consistent, and the welding process is absolutely stable. On the contrary, the smaller P is, the more irregular the changes in the arc voltage and the welding current of the welding process are, and the poorer the consistency of welding quality is.

(21) It is assumed that, after the first U-I cycle the number of points on the phase diagram is:
J.sub.1=α

(22) After the second cycle, there are Pα points repeated between the first cycle and the second cycle. At this time, the number of points on the U-I phase diagram increases by (1−P)α points, and the total number of points is:
J.sub.2=α+α−Pα=α+(1−P)α

(23) After the third cycle, the number of points increasing on the U-I phase diagram is (1−P)α−P(1−P)α, and at this time the total number of points is:
J.sub.3=α+(1−P)α+(1−P)α−P(1−P)α=α+(1−P)α+(1−P).sup.2α

(24) After the N-th cycle, α may be replaced with the number of points evaluated per cycle

(25) $\frac{L}{N},$
where L is the total number of samples over a period of time, and the following can be obtained by mathematical induction:

(26) 0$J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}$

(27) In the formula, only J.sub.N and P are unknown, and the average repetition rate P can be obtained just by obtaining J.sub.N. Practically, J.sub.N represents an area through which the U-I curve passes. In the present invention, the area of the curve in the U-I phase diagram is obtained by using an image binarization method. The specific steps are as follows:

(28) (1) A U-I phase diagram is obtained according to the values of the arc voltage U and the welding current I obtained by a group control system in real time, and saved as “UI.jpg”, and the image is imported into MATLAB by using a command I=imread(‘UI.jpg’).

(29) (2) The U-I phase diagram file is converted into a binary image K through a binary conversion function im2bw( ). At this time, the U-I phase diagram may shows a black and white effect: the gray value is 0 in the place where the UI dynamic working trajectory passes, and otherwise is 1.

(30) (3) The obtained binary image matrix L=bwlabel(K), and the number of elements thereof is M. To facilitate the calculation, L is inverted, so that the number of “1”s in the image matrix is the total number of points or area that the U-I curve passes through.

(31) (4) The sum Q of non-background areas is obtained by using a command sum (L(:)), the area of unit voltage and current in the U-I phase diagram is assumed to be 1, and the area J.sub.N through which the dynamic working curve passes in the U-I phase diagram can be obtained from

(32) $\frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}}.$

(33) (5) The repetition rate P can be obtained according to the previous formula

(34) $J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}.$
The stability of the system can be determinated based on the P.

(35) By the calculation above, the same U-I welding process having large repetition rate P has good stability and high welding consistency, which achieves the same effect as human intuitive determination.

Embodiment 3

(36) The evaluation of the stability of an MAG/MIG welding process. A welding process stability evaluation index P is defined, which represents an average repetition rate of a U-I cycle and other cycles. When P=100%, it indicates that the changes in each cycle and previous cycles are completely consistent, and the welding process is absolutely stable. On the contrary, the smaller P is, the more irregular the changes in the arc voltage and the welding current of the welding process are, and the poorer the consistency of welding quality is.

(37) It is assumed that after the first U-I cycle the number of points on the phase diagram is:
J.sub.1=α

(38) After the second cycle, there are Pα points repeated between the first cycle and the second cycle. At this time, the number of points on the U-I phase diagram increases by (1−P)α points, and the total number of points is:
J.sub.2=α+α−Pα=α+(1−P)α

(39) After the third cycle, the number of points increasing on the U-I phase diagram is (1−P)α−P(1−P)α, and at this time the total number of points is:
J.sub.3=α+(1−P)α+(1−P)α−P(1−P)α=α+(1−P)α+(1−P).sup.2α

(40) After the N-th cycle, α may be replaced with the number of points evaluated per cycle

(41) $\frac{L}{N},$
where L is the total number of samples over a period of time, and the following can be obtained by mathematical induction:

(42) $J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}$

(43) In the formula, only J.sub.N and P are unknown, and the average repetition rate P can be obtained just by obtaining J.sub.N. Practically, J.sub.N represents an area through which the U-I curve passes. In the present invention, the area of the curve in the U-I phase diagram is obtained by using an image binarization method. The specific steps are as follows:

(44) (1) A U-I phase diagram is obtained according to the values of the arc voltage U and the welding current I obtained by a group control system in real time, and saved as “UI.jpg”, and the image is imported into MATLAB by using a command I=imread(‘UI.jpg’).

(45) (2) The U-I phase diagram file is converted into a binary image K through a binary conversion function im2bw( ). At this time, the U-I phase diagram may show a black and white effect: the gray value is 0 in the place where the UI dynamic working trajectory passes, and otherwise is 1.

(46) (3) The obtained binary image matrix L=bwlabel(K), and the number of elements thereof is M. To facilitate the calculation, L is inverted, so that the number of “1” in the image matrix is the total number of points or area that the U-I curve passes through.

(47) (4) The sum Q of non-background areas is obtained by using a command sum (L(:)), the area of unit voltage and current in the U-I phase diagram is assumed to be 1, and the area J.sub.N through which the dynamic working curve passes in the U-I phase diagram can be obtained from

(48) $\frac{Q}{M}=\frac{J_N}{\mathrm{total}\mathrm{area}\mathrm{of}\mathrm{UI}\mathrm{phrase}\mathrm{diagram}}.$

(49) (5) The repetition rate P can be obtained according to the previous formula

(50) $J_N=\frac{L\left(1-{\left(1-P\right)}^N\right)}{\mathrm{NP}}.$
The stability of the system can be determinated based on the P.

(51) By the calculation above, the welding process having large repetition rate P has good stability and high welding consistency, which achieves the same effect as human intuitive determination.

(52) Described above are merely preferred embodiments of the present application, and the present application is not limited thereto. Various modifications and variations may be made to the present application for those skilled in the art. Any modification, equivalent substitution, improvement or the like made within the spirit and principle of the present application shall fall into the protection scope of the present application.