Method for detecting defects in a weld bead and implementation installation

Abstract

The invention relates to a method for detecting defects in a weld bead made at the joint of two parts, and an implementation installation. The method comprises the following steps: welding equipment is provided, including a nozzle, a wire feeding device, and a camera; said nozzle is moved along said joint, while an electric arc is produced to cause the fusion of said two parts and said wire, forming a weld pool area defining a first front and an electric arc area defining a second front; and, a plurality of images of said weld pool area and said electric arc area are recorded.From the aforementioned plurality of images, a first average line (44) of the first front and a second average line (46) of the second front are determined; and a defect in the weld bead is identified when the first average line (44) and the second average line (46) are not substantially parallel to each other. Figure to be published with the abbreviation: Fig. 2.

Description

Title of the invention: Method for detecting defects in a weld bead and implementation installation

[0001] The present invention relates to a method for detecting defects in a weld bead and to an installation for implementing the method.

[0002] One envisaged area of ​​application is that of arc welding processes in which a neutral or reactive gas is injected onto the arc in order to isolate the molten metal from the ambient air. This isolation prevents the formation of oxide.

[0003] It is known to implement a welding equipment fitted with a nozzle and a feed device allowing a welding wire to be fed through the nozzle. A gas supply conduit then opens into the nozzle.

[0004] In addition, such welding equipment can be equipped with a camera oriented towards the nozzle in order to be able to record the scene during the welding operation.

[0005] Thus, to join two adjacent metal parts, generally two parts held perpendicularly to each other, the welding equipment is operated so as to, on the one hand, move the nozzle in translation parallel to and opposite the joint between the two parts, and on the other hand, feed the welding wire, while a potential difference is applied between the wire to be welded and the two parts. An electric arc is thus created between the wire and the parts, which locally melts them. A molten pool then forms at the point of the electric arc, mixing the metal of the two parts and the wire. As the nozzle advances, the molten metals cool and solidify behind the nozzle, forming a weld bead. The weld bead thus joins the two parts together.

[0006] The nozzle drive speeds and wire feed speeds are adjusted relative to each other in order to obtain, as far as possible, a regular weld bead.

[0007] Using a camera equipped with suitable filters, the evolution of the appearance and shape of the molten pool is recorded during the nozzle's advance in order to detect any defects. Indeed, when the molten pool is not sufficiently extensive, a lack of bonding between the two parts can be expected due to insufficient local fusion.

[0008] However, the shape of the weld pool does not, in all circumstances, indicate the quality of the weld.

[0009] Also, a problem which arises and which the present invention aims to solve is to provide a method which makes it possible to better detect defects in weld beads.

[0010] In order to solve this problem, and according to a first objective, a method for detecting a defect in a weld bead made at the joint of two attached parts is proposed, said method being of the type comprising the following steps:

[0011] - Welding equipment is provided comprising, on the one hand, a nozzle and a feeding device adapted to deliver a fusible metal wire through said nozzle, and on the other hand a camera oriented towards said nozzle;

[0012] - said welding equipment is operated so as to drive said nozzle into translation along said joint, while an electric arc is produced to locally cause the melting of the metal of said two pieces and said wire, forming a molten pool zone defining a first front and an electric arc zone defining a second front located upstream of said first front; and,

[0013] - a plurality of images of said bathing area are recorded with said camera fusion and of said electric arc zone.

[0014] Also, from said plurality of images and in the same coordinate system, a first average line of said first front and a second average line of said second front are determined, and a defect in the weld bead is identified when said first average line and said second average line are not substantially parallel to each other.

[0015] Thus, a feature of the invention lies in taking into account not only the molten pool, but also the electric arc, the contours of which can also be discerned thanks to optical filters adapted to the camera. In this way, by means of the images provided by the camera, a first average line is determined, corresponding to the front of the molten pool, that is to say, the transverse line of the area of ​​the pool that extends forward in the direction of advance of the nozzle, and a second average line is also determined, corresponding to the electric arc, that is to say, the transverse line of the area of ​​the electric arc that extends backward relative to the direction of advance of the nozzle.

[0016] These average lines are curved, and while they remain substantially parallel to each other during the welding operation, surprisingly no defects were observed in the weld bead. In this way, welding defects related to imperfect fusion of the two parts are eliminated.

[0017] Conversely, when the two median lines are no longer parallel during the welding operation, a defect is observed in the weld bead, precisely at the point where the two median lines were no longer parallel. The observed defect consists of the partial melting of at least one of the two parts.

[0018] For example, a defect was subsequently observed in the weld bead, when a portion of the second midline moved closer to the first midline, while an opposite portion moved away from it.

[0019] In this way, it is possible to detect defects in the weld beads, or their absence, without destroying the parts.

[0020] The defects observed essentially lie in the lack of interpenetration between the metal of the wire and the metal of the parts to be joined. To remedy this, the feed speeds of the nozzle and the welding wire must be adjusted. Paradoxically, however, in certain circumstances, defects appear when the nozzle speed is too low. Consequently, adjusting the two speeds is not necessarily intuitive.

[0021] Thus, thanks to the method according to the invention, the relative speeds can be adjusted more precisely to eliminate defects.

[0022] According to a particularly advantageous embodiment of the invention, the center of said electric arc zone is determined, and the plurality of ratios of the distances extending from said center to said first average line and from said center to said second average line are calculated along a plurality of straight lines intersecting said center and said second average line; and, if at least one ratio of distances is far from the average value of the ratios of distances, said first average line and said second average line are not substantially parallel to each other. In other words, two segments extending from the center to the two average lines are considered on each of the straight lines.

[0023] Thus, the center of the electric arc zone is determined. This zone is partially delimited, towards the front, by the second neutral axis of the second front. This electric arc zone is delimited by a closed curve, therefore including the second neutral axis. Its center is also determined by determining its centroid, as will be explained in more detail later in the description.

[0024] Next, a plurality of straight lines are chosen, all intersecting the center and the two midpoints. For each of these lines, the ratios of distances between the center and the first midpoint, and between the center and the second midpoint, are then calculated. If the ratios of distances are approximately equal, it can be deduced that the two midpoints are approximately parallel. Conversely, if at least one of these ratios deviates from the average of the ratios of distances, it can be deduced that the two midpoints are no longer parallel. Consequently, the existence of a defect in the weld bead can be predicted.

[0025] Advantageously, said at least one distance ratio is considered to be far from said average value of the distance ratios when it is less than or greater than 10% of said average value. In other words, if the values ​​of all the If the distance ratios fall within + / - 10% of the average value of the distance ratios, the two average curves are considered to remain substantially parallel. Conversely, if the value of at least one distance ratio is outside the aforementioned range, then the two average curves are no longer substantially parallel, and a hidden defect has been generated in the weld bead.

[0026] Preferably, according to one embodiment of the invention, the extremum of said first mean line is determined, and one of said plurality of lines intersects said extremum. Thus, the first mean line has a curved shape oriented forward in the direction of nozzle movement, and an extremum. The line intersecting the center of the closed curve, delimiting the electric arc zone, and the extremum, extends in a direction substantially parallel to the direction of nozzle movement. Thus, measuring the aforementioned distance ratios along this central line allows for a better understanding of the relative shape of the two mean lines.

[0027] Advantageously, two lines among said plurality of lines are symmetrical to each other with respect to said one of said plurality of lines intersecting said extremum. In other words, the two lines are offset by the same angle from the central line. And consequently, comparing the ratios of distances along these two lines, symmetrical to each other with respect to the ratio of distances along the central line, makes it possible to further improve the relative shape of the two median lines and their parallelism.

[0028] According to a particularly advantageous embodiment, said two lines, symmetrical to each other, form an angle between 40° and 80° with said one of said plurality of lines intersecting said extremum. For example, said two lines, symmetrical to each other, form an angle of 45° with the central line.

[0029] According to another embodiment, on the first average curve, two opposite points are considered, spaced from the extremum by the same distance, to establish the two lines symmetrical to each other with respect to the central line.

[0030] Preferably, according to a particular embodiment of the invention, the central line and the two lines symmetrical to each other with respect to the central line are the only three lines considered to evaluate the parallelism of the first and second average lines.

[0031] Also, according to a particular embodiment of the invention, said first and second average lines are determined from the images of said plurality of images recorded during a given time period. The time period adopted depends on the number of images recorded per second by the camera. For example, the camera captures more than 50 images per second. This high frequency is required because This is due to the very rapid evolution of the molten pool and, even more so, of the electric arc. Advantageously, the time period is between one and ten seconds. For example, the time period is three seconds. Consequently, if, for example, the camera captures 50 frames per second, the average lines are determined from 150 frames. In this way, the evolution of the average lines is obtained with good accuracy every three seconds.

[0032] Furthermore, the welding equipment further comprises, according to a first embodiment, a supply of inert gas to the nozzle. This prevents oxidation of the metal during the welding operation.

[0033] According to a second embodiment, said welding equipment further comprises a reactive gas supply to said nozzle. For example, a mixture of argon and carbon dioxide is used.

[0034] According to another object, in accordance with the invention, an arc welding installation is proposed for detecting defects in a weld bead made at the joint of two attached parts, comprising:

[0035] - a welding device comprising, on the one hand, a nozzle and a device a supply adapted to deliver a fusible metal wire through said nozzle, and on the other hand a camera oriented towards said nozzle;

[0036] - an actuator for actuating said welding equipment so as to drive said nozzle in translation along said joint, while an electric arc is produced to locally cause the melting of the metal of said two parts and said wire, forming a molten pool zone defining a first front and an electric arc zone defining a second front located upstream of said first front; and,

[0037] - a memory for recording with said camera a plurality of images of said melt pool area and said electric arc area.

[0038] Also, the installation includes a calculation unit for, on the one hand, determining from said plurality of images and in the same reference frame, a first average line of said first front and a second average line of said second front, and on the other hand, for identifying a defect in the weld bead when said first average line and said second average line are not substantially parallel to each other.

[0039] Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example but not limitation, with reference to the accompanying drawings in which:

[0040] [Fig.1] is a schematic view of a welding installation according to the invention;

[0041] [Fig.2] is a schematic view of an image obtained using the installation illustrated in [Fig.1] according to a first driving mode;

[0042] [Fig.3] is a schematic cross-sectional view of two elements connected together by means of the installation illustrated in [Fig.1] according to said first mode;

[0043] [Fig.4] is a schematic view of an image obtained using the installation illustrated in [Fig.1] according to a second driving mode;

[0044] [Fig.5] is a schematic cross-sectional view of two elements connected together by means of the installation illustrated in [Fig.1] according to said second mode;

[0045] [Fig.6] is a schematic view of an image obtained using the installation illustrated in [Fig.1] according to a third driving mode; and,

[0046] [Fig.7] is a flowchart of the fault detection method according to the invention.

[0047] Fig. 1 illustrates schematically and partially, an installation of Arc welding 10 according to the invention. It includes welding equipment comprising a welding torch 12 which has an end terminated by a welding nozzle 14. The welding equipment also includes a feeding device (not shown) for axially feeding a welding wire 16 through the torch 12 and at the end through the welding nozzle 14.

[0048] The welding equipment also includes a gas supply not shown, extending inside the welding torch to be able to inject gas through the nozzle 14 around the welding wire 16.

[0049] In addition, the welding equipment includes a camera 18 connected to the welding torch 12 by means of a support 20 and oriented towards the welding nozzle 14. Also, the installation includes a robot, not shown, which allows the welding equipment to be operated and the welding torch 12 and the camera 18 to be driven.

[0050] In addition, the installation includes a computing unit 22, or microcontroller, connected to the camera 18. The computing unit 22 includes a memory unit 24 for recording the images collected by the camera 18. Also, the installation includes a display unit 26 connected to the computing unit 22.

[0051] The actuator carries the welding torch 12 so that the end of the welding wire 16 is positioned directly above a weld point 28 at the joint of two parts defining a straight line 30. The actuator also carries the welding torch 12 inclined relative to the vertical V at an angle B of approximately 15° in [Fig. 1], and is adapted to drive it in translation along the arrow F, parallel to the line 30 of the joint, while the optical axis A of the camera 18 is oriented substantially in front of the end of the welding wire 16. The welding operation is then called "push welding." However, the method according to the invention is applicable to other types of welding.

[0052] Reference will now be made to [Fig.3] and then to [Fig.2] illustrating the implementation of the welding equipment shown in [Fig.1].

[0053] Thus, [Fig.3] shows partially and in right section, a first right parallelepiped piece 32 on which a second right parallelepiped piece 34 is fitted perpendicularly. The two pieces 32, 34 thus define a joint 36 and an angle C substantially right.

[0054] Also, using the welding equipment, a weld bead 38 is then produced in the corner at the joint 36 of the two parts 32, 34. The weld bead 38 has a substantially triangular cross-section, and it will be observed that there is no discontinuity with the two parts 32, 34, and that the bead 38 and the parts 32, 34 are locally interpenetrated. In other words, the bond between the two parts 32, 34 is optimal.

[0055] Consequently, the surface melting of the material of the two parts 32, 34 took place in the same way as that of the filler metal by means of the welding wire.

[0056] In accordance with the invention, and unexpectedly, such weld quality, as well as conversely, defects in welds, could be correlated with visual parameters during the welding process, which visual parameters had not been explored until then.

[0057] Thus, [Fig.2] schematically illustrates, from a top view, a reconstructed image corresponding to the images captured by camera 18.

[0058] Before describing the said reconstructed image, giving optimal weld quality, the mode of cooperation of the camera 18 and the computing unit 22 will be described by means of the logic diagram shown in [Fig.7].

[0059] First, the camera 18 acquires images of the scene taking place in front of the welding nozzle 14, at a predetermined frequency between 25 and 70 Hz. In other words, the camera 18 records between 25 and 70 images per second. For example, it records 60 images per second, which it stores in the memory unit 24. Thus, according to a first step 40 of the process of the invention, while the welding nozzle 12 is driven in translation at a speed of 20 cm / min, for example, and the wire is unwound at a speed of 8.7 m / min, the memory unit 24 stores 60 images per second of the scene taking place under the welding nozzle 14 in the angle between the two parts 32, 34.

[0060] These images show a molten pool area and, within it, an electric arc area, or halo. The invention consists of considering a first front corresponding to the downstream boundary of the molten pool and a second front corresponding to the upstream boundary of the electric arc.

[0061] These two front lines are determined on the images, in a second step 41, by means of an image analysis device 42, illustrated in [Fig.1].

[0062] In the embodiment described here, the image analysis unit 42 further determines the contours of the halo of the electric arc, which includes said second front.

[0063] Also, taking into account the instability of the arc, it is carried out, in accordance with a third step of the process 43, to process the images at regular time intervals, for example every three seconds, in order to establish an average relating to the shape of the halo of the electric arc and the first front corresponding to the melt pool.

[0064] Thus, at a frequency of 60 Hz, for three seconds, 180 images are obtained which allow the relative average shapes of the contours of the halo of the electric arc and of the first front to be determined.

[0065] Figure 2 schematically shows a first average line 44 of the first front, corresponding to the downstream boundary of the molten pool, and behind it, a second average line 46 of the second front, corresponding to the boundary of the electric arc. The second average line 46 constitutes a portion of the closed average curve 48, corresponding to the halo of the electric arc.

[0066] It will be observed that the first 44 and second 46 average lines, although curved, are substantially parallel to each other.

[0067] And the merit of the invention lies in highlighting a relationship between the quality of the weld and the parallelism of these average lines 44, 46.

[0068] In order to quickly and easily measure this parallelism, or conversely this lack of parallelism, in order to be able to identify the position of the defect, calculations of distance ratio Rd are carried out.

[0069] Thus, according to a fourth step 50, thanks to the calculating element 22, on the one hand, the center O of the electric arc zone is determined, for example by calculating the barycenter of a plurality of points of the average closed curve 48, and on the other hand, the extremum E of the downstream of the first average line 44 is determined. By the same means, the relative position of the intermediate point I corresponding to the intersection of the segment OE and the second average line 46 is evaluated.

[0070] In this fourth step 50, the calculating element 22 determines on the first mean line 44 two points opposite each other J, K substantially equidistant from the extremum E. For example, the two points J, K chosen are spaced apart by a distance substantially equal to the distance OC extending from the center O to the extremum E. The calculating element 22 then evaluates the relative position of the two other intermediate points L, M corresponding respectively to the intersection of the segments OJ and OK with the second mean line 46.

[0071] And in a fifth step 52, the calculating unit 22 evaluates the three distance ratios, OE / OI, OJ / OL and OK / M, and compares them with each other. If these distance ratios are substantially equivalent, then the second average line 46 and the first average line 44 are substantially parallel to each other.

[0072] Conversely, if one of the distance ratios deviates from the other distance ratios, then the two average lines 44, 46 are not parallel to each other, and the weld bead 38 is considered to have a defect.

[0073] According to a particular, but in no way limiting, embodiment, and in a sixth step 54, the average Moy of the three distance ratios OE / OI, OJ / OL and OK / M is calculated, and if one of the three distance ratios Rd deviates, more or less than 10% from the average, then the weld bead 38 is considered to have a defect.

[0074] Also, from that moment on, according to the process, in a seventh storage step 56, the images corresponding to the identified defect are then stored in a special memory so as to be able to locate the defect later on the welded parts.

[0075] Next, according to an eighth step 58, we check whether the predetermined length of the weld bead 38 is reached.

[0076] If not, according to the process, we return to the first step 40 and the memory organ 24 continues recording the images provided by the camera 18. And if yes, the welding process stops.

[0077] Reference is made to [Fig. 4], which illustrates a situation in which a defect is generated in the weld bead 38' shown in [Fig. 5] during the welding operation. Indeed, in [Fig. 5], the two parts 32', 34' are arranged in a manner analogous to that of [Fig. 4]. It will be observed that the weld bead 38' exhibits a cohesion defect 60 with one 32' of the two parts 32', 34'. This defect results from the imperfect local fusion of one 32' of the two parts.

[0078] Also, on [Fig.4] where, as on [Fig.2], the first 44' and second 46' average lines corresponding to the situation where the defect 60 appears appear, it will be observed that the distance ratios O'J' / O'L' and O'K' / O'M' are close to 1.5, while the distance ratio O'E7OT is close to 2.

[0079] Therefore, the absolute value of the difference between the distance ratio O'E7OT and the average value, which is 1.66, is much greater than 0.17. As a result, a defect is indeed obtained in the weld bead 38'.

[0080] The 10% limit of the mean (Moy), used to determine whether a defect appeared in the weld bead, proved conclusive in the observed situations. However, in certain circumstances, or with particular metals, it is possible that this limit could be adjusted downwards or upwards.

[0081] Notwithstanding, it can be clearly seen in [Fig. 4] that the first average line 44' deviates from parallelism with the second average line 46'

[0082] Reference will now be made to [Fig.6] showing a situation in which a defect was also observed in the weld bead produced.

[0083] We also find the first average line 44" and the second average line 46" corresponding to the two fronts. It is even more evident here that these two average lines 44" and 46" are not parallel to each other.

[0084] Furthermore, using the same reference points as in [Fig.2] and [Fig.4], marked with a double prime sign: «” », the ratios O”E” / O”I”, O”J” / O”L” and O”K” / O”M” are respectively: 1.77; 1.71; 1.43, i.e. an average Mey of 1.64. Therefore, the difference between the ratio of distances O”K” / O”M” and the average Mey is well greater than 10% of this average Mey.

[0085] It is therefore natural to find a defect in the weld bead.

[0086] Also, the invention also relates to the welding installation described in [Fig.1].

[0087] Furthermore, although the invention has been described in connection with several particular embodiments, it is by no means limited to them and includes all technical equivalents of the means described as well as combinations thereof if these fall within the scope of the invention. For example, to determine the parallelism of the two center lines, which indicates the absence or presence of a defect, five straight lines are determined intersecting the center and the two center lines.

[0088] Furthermore, the use of the verb "to include", "to understand" or "to include" does not exclude the presence of other elements or steps than those stated in a claim.

Claims

Demands

1. A method for detecting a defect in a weld bead (38) made at a joint (36) of two joined parts (32, 34), said method being of the type comprising the following steps: - a welding equipment is provided comprising, on the one hand, a nozzle (14) and a feeding device adapted to deliver a consumable metal wire (16) through said nozzle, and on the other hand, a camera (18) directed towards said nozzle (14); - said welding equipment is operated so as to move said nozzle (14) in translation along said joint (36), while an electric arc is produced to locally cause the metal of said two parts (32, 34) and said wire (16) to melt, forming a weld pool zone defining a first front and an electric arc zone defining a second front located upstream of said first front; and, - a plurality of images of the said melt pool area and of the said electric arc area are recorded with said camera (18);characterized in that, from said plurality of images and in the same coordinate system, a first average line (44) of said first front and a second average line (46) of said second front are determined; and in that a defect in the weld bead (38) is identified when said first average line (44) and said second average line (46) are not substantially parallel to each other.

2. A defect detection method according to claim 1, characterized in that the center C of said electric arc zone is determined, and the plurality of distance ratios extending from said center C to said first average line (44) and from said center C to said second average line (46) is calculated along a plurality of straight lines intersecting said center and said second (46) average lines; and, if at least one distance ratio is far from the average value of the distance ratios, said first average line (44) and said second average line (46) are not substantially parallel to each other.

3. A defect detection method according to claim 2, characterized in that said at least one distance ratio is far from said average value of distance ratios, when it is less than or greater than 10% of said average value.

4. A defect detection method according to claim 2 or 3, characterized in that the extremum E of said first mean line (44) is determined, and in that one of said plurality of lines intersects said extremum E.

5. A defect detection method according to claim 4, characterized in that two lines among said plurality of lines are symmetric to each other with respect to said one of said plurality of lines intersecting said extremum E.

6. A defect detection method according to claim 5, characterized in that said two lines symmetrical to each other form an angle between 40° and 80° with said one of said plurality of lines intersecting said extremum E.

7. A defect detection method according to any one of claims 1 to 6, characterized in that said first (44) and second (46) average lines are determined from the images of said plurality of images recorded during a given period of time.

8. A defect detection method according to any one of claims 1 to 7, characterized in that said welding equipment further comprises a neutral gas supply to said nozzle (14).

9. A method for detecting defects according to any one of claims 1 to 7, characterized in that said welding equipment further comprises a reactive gas supply to said nozzle.

10. An arc welding installation for detecting defects in a weld bead (38) made at a joint (36) of two parts (32, 34), comprising: - welding equipment including, on the one hand, a nozzle (14) and a feeding device adapted to deliver a consumable metal wire (16) through said nozzle, and on the other hand, a camera (18) directed towards said nozzle; - an actuator for actuating said welding equipment so as to move said nozzle (14) in translation along said joint (36), while an electric arc is produced to locally melt the metal of said two parts (32, 34) and said wire (16) by forming a weld pool defining a first front and an electric arc zone defining a second front located upstream of said first front; and, - a memory (24) for recording with said camera (18) a plurality of images of said melt pool area and of said electric arc area; characterized in that it comprises a calculation element (22) for, on the one hand, determining from said plurality of images and in the same frame of reference, a first average line (44) of said first front and a second average line (46) of said second front, and on the other hand, for identifying a defect in the weld bead when said first average line and said second average line are not substantially parallel to each other.

Images