JP2002505199A - Method and apparatus for inspecting weld seams - Google Patents

Abstract

  (57) [Summary] Inspecting the weld seam of a butt laser weld presents considerable difficulties. According to the present invention, in order to detect a weld defect, the weld seam height is continuously detected along the weld seam, and the weld defect is detected for a weld seam overhang.

Description

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method and a device for inspecting the weld seam of a welded joint made by deep welding with a laser beam at a butt position, according to the preamble of claim 1.

[0002] Application-specific cut and welded sheet parts, or "tailored blanks (
tailed blanks) "are becoming increasingly widely used, especially in the automotive industry. This can result on the one hand in raw material savings and, on the other hand, simplify process planning and process implementation. Such "tailored blanks" are produced by laser welding at the butting position. At this time, the edges of the two sheet parts, which are machined complementarily to each other, are butted against each other, fixed in position using a clamping device and passed through a welding station equipped with a laser. In particular, high-power lasers capable of performing deep welding, ie "deep welding", are used for this.

[0003] In addition to melting, high power lasers also cause metal evaporation and plasma formation. The vapor pressure of the plasma present above the melt and in the vicinity of the melt opens a narrow and deep capillary in the melt bath. However, the plasma cloud or plasma torch formed above the melting bath, or "weld bath," can be too hot and too dense, resulting in the laser beam being shielded. And the welding process may be interrupted. Therefore, a process gas, usually helium or argon, is generally provided to cool the plasma and thus reduce the density of the plasma. In deep welding using a laser beam, a liquid metal continuously flows into the capillary, and this liquid metal may be explosively released again depending on circumstances. Most of these emissions or spatters flow into a virtual "weld plane" drawn through the weld seam and the laser beam.

[0004] The stability of the deep welding process, and thus the weld seam quality, depends on a number of parameters,
For example, it relates to the welding speed, the properties of the laser and the properties of the workpiece, especially the edge surface and edge shape. In order to obtain reproducible and uniform welding results, the gas dynamic properties, ie the type of process gas supply, the suction of welding fumes and the ventilation of the laser beam tube are very important. All these parameters are set during the welding process
It is in an unstable state of intertwining intricately.

[0005] A loss of balance due to the accidental change of various influence quantities can lead to short interruptions of deep welding and irregular discharge of the melt from the welding bath. . If the released material is relatively small, the locally deficient metal
It is refilled with a liquid welding bath. However, if a large amount of material is released, no recovery takes place and droplet-like material deposits form on the weld seam. Such material deposits extend over the entire weld seam width by a length of 0.5 mm to 5 mm and have a height of about 1 mm. Before such a deposited material deposit in the form of droplets, this released and deposited material no longer flows back into the welding capillary.
Craters, ridges or crevices occur in the weld seam. Such welding defects appear regularly during welding using a high-power laser, and according to the standard for welding seam quality of a welded joint using a laser beam, specified in ISO 13919-1,
Not generally acceptable.

[0006] Therefore, various methods are known for inspecting the quality of a weld seam. Particularly for those skilled in the art, for example, patents. . . . . A method for inspecting a weld seam at the time of butt-type deep welding using a laser beam is known based on (sudronic). The method disclosed in said publication is based on detecting a weld seam profile using an optical system. The evaluation device can then evaluate whether the weld seam profile of the weld connection of the sheet metal part meets the quality requirements. In this method, a welding profile measurement is performed every 15 mm.

[0007] Another known weld seam inspection method, such as that described in US Pat. No. 4,870,099, monitors the welding process itself and includes UV light emitted from the plasma cloud. And the IR radiation emitted from the burning welding spatter. In this method, welding defects are detected by comparing a measured spectral value with a stored reference value. Such a welding process monitoring method requires a time-consuming creation of reference values and also requires a complicated detection structure. Unfortunately, this method often causes false alarms. This is because this method only takes into account substantially two measurands of the complex welding process.

[0008] The object of the invention therefore does not have the disadvantages of the known methods and devices,
In addition, it is an object of the present invention to provide a method and an apparatus for inspecting a weld seam in a butt-type deep welding using a laser beam, so that the weld seam can be inspected simply and reliably.

In particular, welding defects, in particular craters, ridges, crevices and / or material pools, can be easily detected along the welding seam and thus ISO 13919-1.
It is desired to provide a method and apparatus capable of managing whether or not the standards listed in (1) are satisfied.

[0010] The object is achieved according to the invention by a method for welding seam inspection having the features of claim 1 and an apparatus having the features of claim 6. . In particular, in order to detect the welding defect in the welding connection of the thin plate portion, which is performed by deep welding using a laser beam at the butt position, in order to continuously detect the welding seam height along the welding seam. Means are provided. This makes it possible to detect craters, ridges and crevices, as well as the accumulation of material on the weld seam described above.

In deep welding using a high-power laser, welding defects in the weld seam are always
In a preferred embodiment of the method according to the invention, the weld seam is simply a weld seam, which is accompanied by a droplet-shaped material deposit located behind it, which material causes a significant weld seam excess over the entire width of the weld seam. Only overlift is detected.

[0012] Of course, the detected height values are transmitted to a device for display and / or evaluation. In particular, the evaluation device can compare the detected values with the various quality stages of ISO 13919-1, indicate the exact location of the welding defect and / or store the measured data.

Thus, the method according to the invention allows a very simple measurement, which enables a simple device construction and provides a simple, inexpensive and reliable method for welding seam inspection and detection of welding defects. Excellent by principle.

Based on such a simple measuring principle, it is possible to use various means for continuously detecting the height of the weld seam along the weld seam. of course,
All distance measuring means known to those skilled in the art can be used. Suitable means include an optical distance measuring device capable of continuously detecting the weld seam.

In another embodiment of the method according to the invention, a mechanically displaceable needle is used. In this case, the displacement of the needle can be converted into an electrical signal using, for example, a piezoelectric crystal.

As a means for detecting the weld seam height along the weld seam, a commercially available device for distance measurement can be used.

In the following, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a welding seam 1 of a welded connection of two sheet metal parts 12, 13 having different thicknesses by deep welding with a laser beam in the form of a butt.
1 is shown. The weld seam width 14, the height profile perpendicular to the weld seam 11, and the surface structure 16 along the weld seam 11 are dependent on various welding parameters, such as the properties of the laser, the properties of the workpiece, especially the edge surface. , The shape of the edge and the nature of the edge preparation as well as the thickness and the welding speed of the sheet edge. That is, for example, the weld seam width 14 is 0.3 to 1.3 m.
m. If the welded joint of the sheet metal part complies with the standard, the weld seam 11 generally has a scale-like surface structure 16, the variation of the weld seam height of this surface structure 16 along the weld seam 11. Is in the range of only a few hundredths of a millimeter, for example 0.02 mm.

As used in this embodiment, the expression “laminate” refers to a flat material of any size, thickness and surface, such as a metal belt, made of metal, preferably of steel. Related to metal sheet or metal plate. The term "weld connection of the sheet parts" described in the present example refers to the connection formed by welding of two sheet edges, in which case the two sheet edges have different thicknesses from one another. And it need not necessarily be from two separate sheets, but may for example belong to one single sheet that has been rolled up beforehand. In the present embodiment, "butt" is used to indicate that the sheet edges of the sheet portion are in a position where they are butted and fixed. “Weld seam height” includes recesses as well as excess ridges in the weld seam.

FIG. 2 schematically shows the situation at the site of the welding process. In this case, the high-power laser beam 21 collides with the thin plate portions 22 and 23 to be welded. The collision energy of the high power laser beam 21 melts the thin plate portions 22, 23 to form a welding bath 27. Further, a plasma 24 is formed by heat generated by the high-power laser beam 21. This plasma 24 enters the welding bath 27
A deep and narrow capillary 25 is formed. High power laser beam 21 and thin plate part 2
Due to the relative movement R with respect to 2 and 23, behind the welding bath 27 there is a zone 26 with hardened welding material, which forms a welding seam. As can be seen from FIG. 2, the liquefied metal 28 located in front of the high-power laser beam 21 moves to the back side 29 of the high-power laser beam 21 during the welding process, based on the relative movement R, and advantageously Deposits above zone 26. At this time, a scale-like surface structure is formed. As can be further seen from the figure, if the equilibrium of the plasma 24 is compromised, the capillary tube 25 will be filled with the liquid welding material, so that no weld connection will be established or only a partial weld connection will be established. When the high power laser beam 21 collides with the already existing welding bath 27, a large amount of liquid welding material may be explosively released. Such emissions often settle on the weld seam behind the welding beam and can be clearly seen as a drop-like deformation.

The weld seam 31 shown in FIG. 3 of the welded joint of the two sheet parts 32, 33 of equal thickness has a weld defect in the form of a crater 34, in this case immediately adjacent to the crater 34. Behind is a droplet-shaped material deposit 35. About 0.1mm
Such craters, also known as pinholes with the above diameters,
It may have different depths, typically does not extend over the entire width of the weld seam, and is especially located in the center of the weld seam. Droplet material deposit 3
5 causes an overhang of the weld seam, such an overhang may extend over the entire width of the weld seam and has a length of about 0.5 mm to about 5 mm and a height of a few millimeters .

The weld seam 41 shown in FIG. 4 between the two sheet parts 42, 43 of equal thickness has a weld defect in the form of a weld seam tear 44, in which case the weld seam Immediately behind the breach 44 there is a droplet of material deposit 45. Such weld seam splits 44 typically have a length of 0.05 to 0.2 mm, and typically have a width of about 0.2 mm rather than extending across the entire weld seam width. are doing. Weld seam splits 44 are often present in the form of holes having a diameter of about 0.2 mm. The material deposits 45 in the form of droplets give rise to weld seam overhangs having a height of a few millimeters.

FIG. 5 schematically shows an apparatus for performing the method according to the invention. To detect the weld seam height along the weld seam 51 of the weld joint of the two sheet metal parts 52, 53 having different thicknesses, it is advantageous if optical means 54 are used. In this embodiment, the optical means 54 comprises three optical distance measuring devices equipped with semiconductor lasers, these distance measuring devices being 3 from the surface normal.
Advantageously, it is arranged at an inclination angle of 0 °.

In another embodiment, instead of an optical detector, a detection needle guided along the welding seam 51 is used. The displacement of the detection needle can be converted into an electric signal using a piezoelectric crystal. This electrical signal is processed by a corresponding threshold circuit. Of course, the person skilled in the art can also use other distance measuring devices that he sees fit for the person skilled in the art, for example an ultrasonic sensor. Since the structure of these detectors is not directly important to the present invention, a detailed description of the detector structure will be omitted. Critical to selecting an appropriate detector is the ability of the detector to reliably and easily detect height differences on the order of a few tenths of a millimeter. It would be desirable to be able to detect weld seam overhangs, especially in this order.

An advantage of the method according to the invention or the device according to the invention lies in the fact that welding defects can be easily detected in deep welding with a high-power laser, in particular only by detecting a weld seam excess ridge. Further, by continuously probing the weld seam, reliable detection of such welding defects is provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of a weld seam without defects.

FIG. 2 is a schematic diagram showing a deep welding process.

FIG. 3 is a schematic view of a weld seam with crater formation.

FIG. 4 is a schematic view of a weld seam having a tear.

FIG. 5 is a schematic diagram showing an advantageous embodiment of the device according to the invention.

[Explanation of symbols]

11 Weld seam, 12, 13 Thin plate part, 14 Weld seam width, 15
Height profile, 16 surface structure, 21 high power laser beam, 22
, 23 Thin plate, 24 Plasma, 25 Capillary, 26 Zone, 2
7 welding bath, 28 liquefied metal, 29 backside, 31 weld seam,
32,33 sheet part, 34 crater, 35 material deposit, 41 weld seam, 42,43 sheet part, 44 weld seam rift, 45 material deposit, 51 weld seam, 52,53 sheet part, 54 optical means

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] March 8, 2000 (200.3.8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006] Therefore, various methods are known for inspecting the quality of a weld seam. Particularly for those skilled in the art, for example, patents. . . . . A method for inspecting a weld seam at the time of butt-type deep welding using a laser beam is known based on (sudronic). The method disclosed in said publication is based on detecting a weld seam profile using an optical system. The evaluation device can then evaluate whether the weld seam profile of the weld connection of the sheet metal part meets the quality requirements. In this method, a welding profile measurement is performed every 15 mm.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007] Another known weld seam inspection method, such as that described in US Pat. No. 4,870,099, monitors the welding process itself and includes UV light emitted from the plasma cloud. And the IR radiation emitted from the burning welding spatter. In this method, welding defects are detected by comparing a measured spectral value with a stored reference value. Such a welding process monitoring method requires a time-consuming creation of reference values and also requires a complicated detection structure. Unfortunately, this method often causes false alarms. This is because this method only takes into account substantially two measurands of the complex welding process. GB 2259269 describes the detection of welding defects based on acoustic signals emitted from a plasma.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008] The object of the invention therefore does not have the disadvantages of the known methods and devices,
In addition, it is an object of the present invention to provide a method and an apparatus for inspecting a weld seam in a butt-type deep welding using a laser beam, so that the weld seam can be inspected simply and reliably.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

In particular, welding defects, in particular craters, ridges, crevices and / or material pools, can be easily detected along the welding seam and thus ISO 13919-1.
It is desired to provide a method and apparatus capable of managing whether or not the standards listed in (1) are satisfied.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM , HR, HU, ID, IL, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, V N, YU, ZW (71) Applicant Industriestrasse 35, CH-9962 Bergdietikon, Switzerland Land F term (reference) 2F069 AA16 AA42 AA60 AA61 BB19 CC06 GG01 GG04 GG06 CC09 GG01 GG00H09 CC06 GG01 GG01 H09

Claims (10)

[Claims] 1. A method for inspecting a weld seam of a weld joint of a thin plate portion performed by a deep welding using a laser beam at a butt position, wherein the weld seam height is welded to detect a weld defect. A method for inspecting a welded seam, characterized by detecting continuously along the seam. 2. The method of claim 1, wherein welding defects are detected for weld seam overhangs. 3. The method according to claim 1, wherein the weld seam height is detected by a mechanical needle. 4. The method according to claim 1, wherein the weld seam height is detected by an optical distance measuring device. 5. The welding seam height is detected by an acoustic distance measuring device.
The method according to claim 1. 6. Apparatus for performing the method of claim 1, wherein the apparatus continuously detects a weld seam height along the weld seam to detect a weld defect. An apparatus for inspecting a weld seam, characterized by having the apparatus. 7. Apparatus according to claim 6, wherein said detection device comprises means for detecting a weld seam overhang. 8. The device according to claim 6, wherein the detection device has at least one mechanical needle. 9. The device according to claim 6, wherein the detection device has at least one optical distance measuring device. 10. The device according to claim 6, wherein the detection device comprises at least one acoustic distance measuring device.