WO2017042116A1

WO2017042116A1 - Method for producing a welded connection in a joint gap, and process monitoring device

Info

Publication number: WO2017042116A1
Application number: PCT/EP2016/070806
Authority: WO
Inventors: Stefan Kaierle; Oliver SEFFER; Philipp VON WITZENDORFF; Anas Moalem
Original assignee: Laser Zentrum Hannover E. V.
Priority date: 2015-09-10
Filing date: 2016-09-05
Publication date: 2017-03-16
Also published as: DE102015115270A1

Abstract

In the production of a welded connection between material flanks (9) in a joint gap (2) of a metallic workpiece (1) using a welding beam generator, by way of which a welding beam (4) is directed onto the joint gap (2) from a first side of the metallic workpiece (1) in order to realize a complete welded connection of the material flanks (9) over the entire depth of the joint gap (2), and an optical detection device (5), by way of which a surface of the workpiece (1) which is averted from the welding beam generator is imaged from a second side of the workpiece (1) in order to optically identify a weld pool (10) formed during the welding process and evaluate said weld bath by way of an evaluation step, process monitoring of the welding process for quality control purposes is performed in a simple manner by virtue of the fact that, by way of the optical detection device (5) and the evaluation stage, the position of the weld pool (10) and the position of the joint gap (2) are simultaneously determined, and the relative position with respect to one another is provided as a parameter for the follow-up regulation of the positioning of the welding beam (4) relative to the joint gap (2).

Description

Method for producing a welded joint in a joint gap and process observation device

The invention relates to a method for producing a welded connection between material flanks in a joining gap of a metallic workpiece using a welding beam generator, with which a welding beam is directed from a first side of the metallic workpiece to the joining gap, in order to ensure complete welding of the material flanks over the entire depth of the To achieve joint gap, and an optical detection means, with a remote from the welding beam generator surface of the workpiece is imaged from a second side of the workpiece to optically detect a process resulting in the welding process melt pool and evaluate with an evaluation stage.

The invention further relates to a process observation device for use in carrying out the method.

For the production of welded joints in a joint gap of a metallic workpiece, it is known to melt the material of the material flanks of the workpiece at the joint gap by means of a laser beam or electron beam to produce a material connection of the material flanks over the joint gap on cooling away. If the joint gap is not sufficiently narrow and can be produced with parallel flanks, in addition to welding with a welding beam in a hybrid method, a further welding method can be used, with which in particular a suitable for the production of the weld compound in liquid form is introduced into the joint gap.

The load capacity of the welded connection produced depends essentially on the fact that the welded connection has been made over the entire height of the material flanks in the joint gap. It is therefore necessary to guide the welding beam accurately along the joint gap and, moreover, to adjust the energy of the welding beam so that the appropriate amount of material of the material fibers is melted to produce the welded joint of the flanks. Is the Energy of the welding beam too low, the Schweäßverbindung occurs only over part of the depth of the joint gap - ie the material strength -. This effect can also occur if the welding beam is not guided precisely along the joint gap.

It is basically known to guide the welding beam along the joint gap by detecting the position of the welding beam on the side of the welding-beam generator relative to the joint gap and possibly tracking it. Since the mere optical observation of the position of the welding beam on the one hand and the joint gap on the other hand, has not been found to be sufficient, methods have been developed to visually estimate the quality of the welding process. It is assumed that the effect of a Schlußlochhole ("keyhole") in the molten bath by the incident welding beam. The energy-transmitting welding beam causes a vaporization of the molten metal in the beam-shaped section, so that a channel is formed in the molten bath within the joining gap, in which metal vapor of the molten metal is located. According to DE 197 16 293 C2, during laser welding, the keyhole is optically detected from the laser side to thereby determine a correct focusing of the laser beam on the material surface. A small keyhole diameter indicates a correct focus, while a defocus leads to an increase in the keyhole diameter. Furthermore, the size of the molten bath is detected, in particular in order to be able to recognize molten metal ejections (in the form of spatters or the like) which can lead to defects of the welded joint. The observation with a camera takes place at an angle to the laser welding beam, whereby the resulting aberrations must be taken into account. A compromise is required between the sharpness of the image and the detectability of the entire molten bath surface.

It is known from EP 2 322 312 A1 and US Pat. No. 6,084,205 to make the image of the laser weld seam from the side of the workpiece facing away from the laser beam in the case of a flat workpiece, which may also be designed as a tubular jacket. The size of the keyhole is also detected. However, because of the observation of the welding laser side facing away from a _ _

Minimum size of keyholes considered as quality parameters for the welding process. Sufficient size of the keyholes recognizable by the weld back is considered a measure of penetration through the entire material thickness. The optical recognition thus serves to determine the size of the keyholefläche. According to EP 2 322 3 2 A1, illumination can be performed with a plasma source. Furthermore, it is possible to combine the welding laser, which may have a laser power of more than 15 kW, with a second heat source, for example an arc.

The process monitoring to ensure the quality of the welding process by detecting the size of the keyholes of the molten bath is problematic because it raises significant metrological problems due to the small size of the keyholes and can not detect significant welding defects.

The present invention is therefore based on the object to check the quality of the welded joint during the production of the welded joint with metrologically well detectable parameters and to provide as control or control parameters.

To solve this problem, a method of the type mentioned above according to the invention is characterized in that the position of the molten bath and the position of the joint gap determined with the optical detection device and the evaluation stage and the relative position to each other as a parameter for Nachregeiung the positioning of the welding beam relative to Joint gap is provided.

The invention is thus based on the observation of the weld seam on the rear side of the workpiece facing away from the welding beam generator during the welding process. In the region of the weld root, an ellipsoidal melt pool is typically formed when the energy of the welding beam is sufficient for thorough penetration. In order to check the weld quality, it is relevant in accordance with the invention to determine the position of the molten bath relative to the joint gap. For this, the optical detection device must be suitable, _ _

To detect both the melt and a section of the unprocessed joint gap in time.

In a preferred embodiment, the position of the molten bath can be determined by determining the longitudinal axis of the molten bath when the molten bath is elongated, for example elliptical. For the ellipse shape, the longitudinal axis corresponds to the major axis.

For secure optical detection of both the molten bath and the adjoining not yet processed joint gap, a separate illumination is provided in a preferred embodiment of the invention, which is directed to the molten bath and the not yet processed joint gap.

This makes it possible to at least largely hide the direct radiation of the welding beam generator, in particular when using a welding laser, for the evaluation by using a filtered wavelength range which has a distance from the wavelength range of the welding beam generator for the illumination and / or the optical scanning. The welding beam generator is preferably a laser.

For determining the position of the welding beam relative to the joint gap, a determination of the ratio of the lengths of the semiaxes, ie the main axis and the minor axis, of the at least approximately elliptical molten bath can furthermore be carried out, because conclusions of changes in the ratio can lead to incorrect positioning of the welding beam generator relative to the joint. spait can be pulled, as will be explained in more detail below.

To reduce the influence of stray light and reflected light, it may be expedient if the illumination is carried out with a polarized radiation. The optical scan can then be made with a corresponding polarization filter.

In a particularly preferred structural embodiment of the invention, the entire arrangement of camera and lighting is designed as a single module with a formed in a single housing, which is arranged on the side facing away from the welding beam generator side of the workpiece. It is necessary to integrate a viewing window into the housing for both the illumination beam and the scanning beam. In particular, the viewing window for the scanning beam to the optical detection device should be designed so that a ghost imaging is avoided by a reflection at the glass-to-air transition. For this purpose, an anti-reflection coating could be provided. For harsh operation on a welding device, which can certainly cause splatters of liquid metal, an antireflection coating is easily damaged.

According to the invention, it is therefore provided to align at least the viewing window for the optical scanning at the Brewster angle to the beam passing through the viewing window. In particular, when using p-polarized radiation, the reflection is reduced to virtually zero at the Brewster angle, so that a less stable antireflection coating can be avoided and yet no ghosting disturbing the evaluation.

In a further preferred embodiment of the invention, the camera has an objective whose optical axis is arranged inclined to the image plane of the cameras. In this way, the welding area can be observed by the camera without the cameras being arranged in the optical axis of the welding beam. In this case, a pivoting of the optical axis of the lens can be achieved without sacrificing the image sharpness when the lens is used in a Scheimpfluganordnung (tilt optics). As you know, in the

Scheimpfluganordnung in which the image plane is also pivoted relative to the lens plane by a predetermined amount, be sharply mapped when the axes of the object plane, the lens plane and the image plane intersect in a straight line. In a further developed embodiment, it has proven useful to use the lens in a tilt-shift arrangement, in which the lens plane is additionally slightly shifted in order to achieve distortion-free imaging.

It will be apparent to those skilled in the art that the above-described construction of the separate module and the enabling of the sharp image also in a Oblique viewing axis have their own inventive significance and are independent of the evaluation of the molten bath with advantage feasible.

The above-mentioned object is further achieved by a process observing apparatus for carrying out the method, which is provided for being arranged on a second side of a flat workpiece, which is processed on its first side by means of a welding beam directed onto the joining gap, and is characterized by an optical detection device for simultaneously detecting the position of a molten bath occurring during welding and the joint gap and an evaluation stage for determining the position of the molten bath relative to the joint gap.

For the reasons mentioned above, the process monitoring device is preferably designed with a lighting device for illuminating the second side of the workpiece in the area of the welding beam and a distance of the still unprocessed joining gap.

Further features of the process monitoring apparatus result from the implementation of the advantageous embodiments of the above method and from the explanations below of preferred embodiments of the invention with reference to the accompanying drawings. Show it:

Figure 1 shows a schematic arrangement of a welding head on a first

Side of a workpiece and an optical scanning device in the form of a camera and a lighting device on the second side of the workpiece;

Figure 2 is a schematic representation of the formation of a molten bath by an incident at an angle to a joint gap welding beam; Figure 2a is a schematic representation of the formation of a molten bath at an angle joining gap and a non-congruent extending welding beam;

Figure 2b is a schematic plan view of the second side of the workpiece with formation of an elliptical melt bath for proper welding;

Figure 3 is a schematic representation of a control of the positioning of the welding head by detecting the position of the major axis of the elliptical melt pool relative to the joint gap;

Figure 4 is a schematic representation of the regulation of the welding energy in

Dependence on measured nominal lengths of the semiaxes of the elliptical melt bath;

FIG. 5 shows the embodiment of the camera and the illumination according to FIG. 1 as a process observation module;

FIG. 6 shows the formation of an elliptical melt bath in the case of FIG

Length of the joint gap of correctly performed welding;

FIG. 7 shows a representation of three images of the detected molten bath with decreasing welding beam power;

Figure 8 Images of the detected molten bath at an increasing

Deposition of the molten bath relative to the joint gap.

Figure 1 shows schematically an arrangement for producing a welded joint on a workpiece 1, which consists of two sections, which are to be welded together via a joint seam 2. For this purpose, a welding head 3 is arranged on a first side of the workpiece 1, which contains a welding laser in the illustrated embodiment and thus a welding beam 4 in Shape of a laser beam emits.

For process observation is an optical scanning device in the form of a camera 5, the scanning beam 6 is at an angle to the axis of the welding beam 4.

The optical scanning is facilitated by a Beleuchtungsstrahi 7 a lighting device 8 is directed to the second side (bottom) of the workpiece 1 at a corresponding angle. Camera 5 and lighting device 8 are therefore located on the second side of the workpiece 1, which is opposite to the first side on which the welding head 3 is located.

In welding by means of laser or electron beam high demands are placed on the positioning accuracy due to a relatively high aspect ratio (seam depth or weld depth to seam width), especially when joining high material thicknesses. An alignment or positioning of the welding radiation along features on the upper side of the workpiece 1 is not sufficient to ensure a reliable connection over the entire thickness of the material. In particular, edge-banding errors occur especially in the area of the near-root.

This will be clarified with reference to FIG. It schematically shows a misalignment with respect to the angle of incidence of the welding beam. Shown is therefore a section of the workpiece 1 in the region of the joining gap 2, which is bounded by two parallel material edges 9. The ideal direction of incidence for a welding beam 4 is in the middle plane ME of the joining gap. Shown is an incident welding beam 4, which forms an angle α with the center plane ME. Since the welding beam 4 extends in a straight line through the material of the workpiece 1, a molten bath 10 is formed, which undergoes an asymmetrical design with increasing workpiece depth. When the welding beam 4 is adjusted, as desired, to the center of the joining gap 2 on the first upper side of the workpiece 1, a shape of the molten bath 10 is formed on the first side which provides a perfect weld for observation on the first side of the workpiece 1 pretends. With increasing depth, however, the molten bath 10 forms in _G

tapered shape with an increasing distance from the joint gap 2, as shown schematically in Figure 2. Accordingly, from the second side (underside) of the workpiece 1, the molten bath 10 can be seen when the welding beam 4 is strong enough to ensure penetration through to the second surface (back) of the workpiece 1. A process observation on the back of the workpiece, as known in the art, would indicate a proper weld, evaluating the size of the weld pool and the size of the keyhole, although the weld was not properly made at the bottom end of the joint (directed towards the second surface). Rather, only one weld in the Fügespait 2 has taken place.

Already a slight misalignment (tilting) of the axis of the welding beam 4 can therefore lead to insufficient welding results. The causes of a misalignment of the axis of the welding beam, for example, form tolerances of the sheet metal edges or even small angular error of the welding beam axis relative to the flanks of the workpiece 1 in the joint gap 2, despite a precise alignment and positioning of the welding head 3 along features on the workpiece top Flankenbindefehler in the root area the weld result.

Irrespective of a winch error or the positioning of the welding beam 4, in addition to a tilting of the axis of the welding beam, angles may still result due to the workpiece edge quality or the workpiece edge condition, so that edge binding errors can occur in the root area of the connection despite exact alignment and positioning along features on the workpiece top , because relative tilting between the joining edges and the beam axis occur, as illustrated in Figure 2a. Accordingly, this situation generally applies to all non-planar edge qualities that have not undergone any final milling work. With sheet thicknesses of up to 12 mm, frequently no milled edges are used, but Schiagscheren cuts, plasma or laser beam cuts, in which joint edges result without flatness. For larger material thicknesses, primarily saw, plasma, laser beam or water jet cuts are used. As the sheet thickness increases, _{1 Q}

gere edge qualities with respect to the planarity and / or the roughness of the joint edges, so that depending on the application costly milling processes may be required. A similar situation with respect to different, non-planar joining edges results, for example, after a pipe molding in longitudinally welded pipes.

Furthermore, in some applications, no vertical irradiation of the laser beam is possible due to the component, so that a defined tilt of the beam axis is required, the design of which must be adapted to the existing joining edge geometry, so that an exact alignment and positioning along features on the workpiece top Flankenbindefehler in the root area of the connection to May have consequences.

In addition to incorrect positioning, tilting and angle-related joining edge states, fluctuations in the path energy, ie the energy of the welding beam 4, can furthermore lead to differently deep penetration or penetration welding. As the path energy decreases, the welding depth is reduced, which may result in insufficient penetration. By increasing the energy of the track, a larger weld root is formed, which, in addition to a too large increase in root area, can also lead to a seam undershoot with regard to the assessment of the weld quality. Variations in the path energy can be due, for example, to a varying, emitted output power of the radiation of the welding beam source as well as to an altered feed rate of a robot or axis system.

By virtue of the root-side process observation system according to the invention, a decreasing welding depth can be determined, as will be described below.

In addition to varying path energy, changing workpiece conditions, such as variations in material thickness, workpiece geometry or chemical composition, can result in a change in weld depth. By the present invention, a homogeneous root formation can be ensured, which is positioned centrally in the joint gap 2 and has a uniform Wurzelüberhöhung or -ausprägung result. Wetterhin ensures complete flank detection through the weld, thus avoiding the occurrence of flank-tie flaws.

By observing the weld root position in relation to the joint gap, the misalignment or positioning described above during the welding process can be detected.

As is shown in FIG. 2a, with proper welding on the second side of the workpiece 1, it is typically possible to detect an elliptical melt pool 10 which is symmetrical to the joint gap 2, the main axis HA of the ellipse of the melt pool 10 coinciding with the center plane ME of the joint gap 2. A detected lateral deviation thus indicates a no longer proper welding. The main axis HA is made up of the large semiaxes, and the minor axis NA perpendicular to them is composed of the small semiaxes, as is known to the person skilled in the art from the geometry of the ellipse. The major axis HA corresponds to the longitudinal axis of the molten bath 10, which is determinable for elongated molten bath forms that deviate from the elliptical shape.

The detection according to the invention can be implemented with a camera-based observation system as a controllable system. The misalignment or the positional deviation of the beam axis relative to the joint gap is detected via the position of the main axis of the elliptical geometry of the molten bath 10 relative to the joint gap 2 and compensated for by movements of a robot / axis system. A schematic representation of this control process is shown in FIG. As a reference variable of the control process is used to determine the position of the main axis of the elliptical melt bath to the joint gap. If a deviation is detected due to a disturbance variable in the controlled system, a corresponding control of the robot system or axle system for the welding head 3 can be effective in order to eliminate the control deviation. For the regulation of the through-welding, the lengths of the semi-axes of the elliptical melt bath are detected and the control can be effected by adjusting the beam power of the welding beam generator. The corresponding regulation is shown schematically in FIG. The reference variables are the nominal lengths of the semiaxes of the elliptical melt pool. If a disturbance variable in the controlled system leads to a system deviation, the control voltage of the welding beam source, in particular the laser beam source, can serve as a manipulated variable in order to eliminate the control deviation.

In order to detect the deviations described, requirements for the information to be acquired by means of the camera 5 arise for the process observation. These include the exit point of the laser beam on the underside (second side) of the workpiece 1, the position of the joining gap 2 between the material flanks 9 in the still unattached area of the parts of the workpiece 1. Also included is the weld root, so the course of the hardened weld on the Bottom of the workpiece 1.

Depending on the degree of fusion, widths between 5 and 20 mm are expected with regard to the image field size. With regard to a process control, frame rates of 50 fps and resolutions of 640 x 480 are sufficient to detect the described features and relevant faults due to a relatively sluggish reaction of the material and the ability to detect the detection over relatively few points. Optionally, higher frame rates and / or resolutions may be used, for example, where higher subject field sizes are required due to increasing melt pool characteristics.

In a preferred embodiment, the process observing device is implemented as a module in a robust housing. Namely, the process observing device must be robust to process emissions in the form of smoke, steam, spatter and electromagnetic radiation. For protection against these process emissions, the process observation system, if appropriate including the control system, is implemented in a housing 11, as shown schematically in FIG. The housing has integrated Viewing window 12, through which the Beieuchtungsstrahl 8 emerge from the interior of the housing 11 and the scanning beam 6 can enter into the interior of the housing 11. As can be seen from Figure 5, the Beieuchtungsstrahl 8 is directed by the Beieuchtungsvorrichtung 7 against a deflecting mirror 13 and exits after the deflection through the associated viewing window 12. The scanning beam 6 enters through its associated viewing window 12 in the housing 11 and comes to an arrangement of three deflecting mirrors 14 through which the scanning beam 6 is directed into a lens 15, which is provided with a tilt and a shift device to as a tilt-shift lens to meet a modified Scheimpflug condition. Between the lens 15 and the camera 5, a filter cartridge 16 is arranged for a polarizing filter. The polarization filter of the filter cassette 16 corresponds to the polarization of the observation beam emitted by the illumination device 7, which is preferably p-polarized.

The arrangement of the adjustable mirror allows a deflection of the beam paths of camera 5 and lighting device 7 to a compact arrangement. Due to a more compact design of the lighting device and the camera, a direct lighting without deflection is possible. To illuminate the observation zone on the second side (underside) of the workpiece 1, a light source, for example a helium-neon or diode laser beam source is optionally used.

Since viewing windows 12 can lead by partial reflections to so-called Geisterbiidern, the reflectivity of the observation-side viewing window 12 must be reduced. Usually, antireflection coatings are applied to the glass surfaces for this purpose. However, such surface coatings are prone to spatter and smoke and can be damaged by manual cleaning. According to the invention, the ghost biiders are avoided by arranging the windows in the so-called Brewster angle and p-polarizing the illumination radiation with a polarization filter. At the Brewster angle, the reflectivity for p-polarized radiation has a minimum of the theoretical value of zero. Due to the unnecessary surface coating a longer life of the viewing window 12 is achieved and the windows can cost if necessary, because without surface finish, replaced become.

Possible embodiments of the process observation device and experimental arrangements are explained in the following examples.

example 1

For the execution of experiments, a camera manufacturer Imaging Source type DFM 22BUC03-ML was used. The observation camera 5 was combined with a Nikon type PC-E Micro-Nikkor Tilt-Shift Lens 85 mm - F / 2.8. The camera has a resolution of 640 x 80 and a frame rate of 76 fps. The lens has a maximum magnification of 1: 2 and a minimum focusing distance of 390 nm.

In the filter cartridge 16, a band pass filter has been used which has a wavelength characteristic (CWL = 660 nm ± 2 nm, FWHM = 10 nm ± 2 nm) which allows complete transmission for wavelengths of 660 nm ± 2 nm.

The illumination device used was a laser diode with a maximum output power of 55 mW and a wavelength of 659 nm as an optional illumination module.

Example 2

For the welding tests, a diode-pumped solid-state disk laser beam source from TRUMPF Laser- und Systemtechnik GmbH type TruDisk 16002 was used as the beam source. With output powers of up to 16 kW on workpiece 1 and a high beam quality of 8 mmomrad, this laser source is suitable both for welding and for cutting metals. The output wavelength is 1,030 nm.

The disk laser beam source combines the advantages of a solid state laser beam source with those of a diode laser beam source. Energy-efficient diode laser _

- 5 -

Beam sources deliver the excitation energy as a pump source and ensure high efficiency, while the disk as a solid-state laser causes the high beam quality.

Furthermore, due to the high beam quality, large working distances can be realized. The laser beam source is equipped with several optical fibers and can be flexibly integrated into production lines as well as combined with industrial robots or other handling systems thanks to a fiber-guided beam guidance system.

In the welding tests carried out, the laser beam was guided over a light waveguide with a fiber diameter of 200 μm to the water-cooled laser beam welding optics.

Example 3

The laser beam welding optics used was a machining head from TRUMPF Laser GmbH with a rigid, lens-based beam shaping system. The machining head basically consists of a fiber receptacle for the fiber optic cable, a collimator (200 mm focal length focal length), a focusing (focusing focal length 200 mm), a protective glass receptacle and a crossjet module.

From the optical waveguide with a fiber diameter of 200 μm used, a focus diameter of 200 μm results in combination with the laser beam optics used (imaging ratio of 1: 1).

Example 4

The laser beam machining head was mounted on a KUKA Roboter GmbH type KR 60 HA six-axis robot. By means of special gearboxes, accurate measurement and a high rigidity of the mechanics, the KR 60 HA achieves a high positioning accuracy, with point repeat accuracy of ± 0.05 _{1 f} ,

mm and linear trajectory repeatability of +0.16 mm. In terms of high torsional and bending strength, this type has a CAD- and FEM-optimized structure, resulting in a high rigidity of the mechanism, which ensures a high process accuracy even at contact.

Example 5

Work piece plates of steel grade S700MC were used for the prototype demonstration of functionality presented as examples. The weld samples had a plate thickness of 7 mm, a length of 300 mm and a width of 120 mm.

Example 6

For the laser beam welding process of the welding tests for the prototype functionality demonstration, a laser beam power of 4 kW, a feed rate of 1 m / min and a focus position of the laser beam on the upper side of the sheet (workpiece top side) were used.

Example 7

FIG. 6 shows, as a reference, exemplary process observation images of a welding process that proceeds correctly without disturbances. Images of the process zone on the underside of the workpiece at different times as well as the associated weld root are shown.

By means of the root-side process observation and control module, penetration can be clearly detected. With constant welding parameters and workpiece conditions (variations or tolerances of the material thickness and workpiece geometry, local differences in the chemical composition of the material) has the elliptical geometry of the melt 10 over the duration of the welding process (position a), position b) and position c)) no changes , Accordingly, the images for the positions a), b) and c) show matching configurations of the molten bath 10. Example 8

By contrast, FIG. 7 shows root side recordings which have been carried out for a welded connection with decreasing laser power. The laser power is initially kept constant in accordance with the curve figure 7 shown on the top right and is then lowered linearly with a ramp shape. While full laser power is effective at position a), position b) has been reduced and laser power has been reduced for position c).

As a result of the decreasing laser beam power, the root exaggeration decreases and changes into root recession. If the beam power is reduced further, the path energy required for penetration through welding is undershot and only welding is achieved, as a result of which the lower region of the material flanks 9 in the root region is not detected. The images of the positions a), b) and c) show a dependence between the size of the formation of the elliptical Schmelzbadgeometrie and the Laserstrahlletstung so that a change in the process conditions can be determined on the basis of recordings. In addition to a decreasing laser beam power but also an increasing feed rate or an increase in material thickness can cause line energy changes in this form.

Example 9

A welding test was carried out in which an exact positioning of the welding beam 5 with respect to the joining gap 2 is present at the beginning of the process. Over a connecting length of the joining gap, an increasing linear depopulation is carried out so that, at the connection end, the root area of the weld seam is positioned offset laterally next to the joining gap 2.

FIG. 8 illustrates the increasing linear deviation in the positions a), b) and c).

Due to the excessive deposition are the weld end to the The workpiece edges of the fixed joint partners positioned in the joint are no longer detected, resulting in a lack of connection with flank bond defects or no connection. The process observation images a, b and c show an extension of the elliptical geometry of the molten bath 10 when the joint gap 2 is no longer detected, so that a change in the process conditions can be determined on the basis of the images. The elongation of the elliptical melt pool increases with increasing deposition. The lateral deviation is clearly visible.

The examples carried out serve to illustrate the invention without any intention to limit it to the examples carried out. The invention can be used for different metallic materials, for example other steel materials, aluminum or copper alloys. It can be used for different material thicknesses (from thin to thick sheet metal). The description for planar workpiece geometries also includes the use of curved sheet geometries, for example for pipes. In this case, the workpiece processing with the welding device from the outside of the tube and the process observation from the inside of the tube can be made, for example, to ensure the quality of a tube longitudinal seam. Of course, other laser beam sources with different wavelengths can be used. Likewise, the invention can be used for electron beam welding.

In this case, the beam welding methods can also be combined with other welding methods (hybrid welding), in particular in order to possibly introduce additional materials into the weld seam.

The evaluation of the size and characteristics of the molten bath 0 allows a process observation that is largely independent of the material thicknesses and materials used. Due to a higher molten volume of material, the weld roots of thicker workpieces have larger dimensions, but without changing their basic geometric shape.

Furthermore, it is possible according to the invention, also workpiece parts of different _G

Materials to connect to a workpiece 1, provided that the materials are compatible for a welded joint.

Claims

claims:

1 . Method for producing a welded connection between material flanks (9) in a joint gap (2) of a metallic workpiece (1) using a welding beam generator, with which a welding beam (4) from a first side of the metallic workpiece (1) onto the joint gap (2) in order to achieve a complete welding connection of the axial flanks (9) over the entire depth of the joining gap (2), and an optical detection device (5), with which a surface of the workpiece (1) facing away from the welding beam generator from a second side of the Workpiece (1) is imaged to optically detect a melt during the welding process (10) and evaluate with an evaluation stage, characterized in that the position of the molten bath (10) and the position. With the optical detection means (5) and the evaluation stage of the joining gap (2) and determines the relative position to each other as a parameter for the Nachr Regulation of the positioning of the welding beam (4) relative to the joint gap (2) is provided.

2. The method according to claim 1, characterized in that for the optical image, a separate illumination (7) is directed to the molten bath and the not yet processed joint gap (2).

3. The method according to claim 1, characterized in that with the optical detection means (5) and the evaluation stage also determines a change in the ratio of the lengths of mutually perpendicular semi-axes of the molten bath (10) and as a parameter for the readjustment of the position of the Schweißstrahis ( 4) is used relative to the joint gap (2).

4. The method according to claim 2 or 3, characterized in that

Lighting is done with a P-polarized radiation.

5. The method according to any one of claims 1 to 4, characterized in that the entire arrangement of camera and lighting as a single module with a single housing (1 1) is formed, which arranged on the welding beam generator side facing away from the workpiece (1) becomes.

A method according to claim 5, characterized in that the optical scanning is performed by at least one viewing window (12) of the housing (11), which is aligned at Brewster angle to the passing scanning beam (6).

Method according to one of claims 1 to 6, characterized in that the optical scanning device (5) has a lens (15) whose optical axis is arranged inclined to the image plane of the scanning device (5).

A method according to claim 7, characterized in that the lens is used in a Scheimpflug arrangement (tilt optics).

Method according to one of claims 1 to 8, characterized in that the position of the molten bath (10) by determining a longitudinal axis (main axis HA) takes place.

Process observation device for carrying out the method according to one of Claims 1 to 9 for arrangement on a second side of a flat workpiece (1) which is machined on its first side by means of a welding beam (4) directed onto a joint gap, characterized by an optical detection device ( 5) for the simultaneous detection of the position of a molten bath (10) occurring during welding and of the joining gap (2) and an evaluation stage for determining the position of the molten bath (10) relative to the joint gap (2).

11. Process monitoring device according to claim 8, characterized by a lighting device (7) for illuminating the second side of the workpiece (1) in the region of the welding beam (4) and a distance of the still unprocessed joining gap (2).

12. Process monitoring device according to claim 10 or 11, characterized in that the evaluation stage is further adapted to determine the ratio of the lengths of the semiaxes of the molten bath (10).

13. Process observation device according to claim 11 or 12, characterized by a polarization filter for generating a P-polarized light of the illumination device (7).

14. Process monitoring device according to one of claims 10 to 13, characterized in that the entire arrangement of scanning device (5) and lighting as a single module in a single housing (11) is formed.

15. Process observation device according to claim 14, characterized in that in the housing (11) at least one viewing window (12) is integrated, which is aligned at Brewster angle to an optical axis formed in the scanning device for a scanning beam (6).

16. Process observation device according to one of claims 10 to 15, characterized in that the scanning device (5) has a lens (15) whose optical axis is arranged inclined to the image plane of the scanning device (5).

17. Process monitoring device according to claim 16, characterized in that the lens has a Scheimpflug arrangement (tilt optics).