Methods for laser welding

Abstract

This invention describes a method for laser welding two joints (1d, 2d), the two joints being held together by an lap joint and made of metallic material. The first joint (1d) has a joint flange with a lap joint, and the second joint (2d) has a joint area (6d) on its flat side. During the laser welding process, the first joint (1d) is held in contact with the joint area (6d) of the second joint (2d) by one side of its joint flange (3d). A gap (10d) is provided between the joints (6d and 2d), which widens in the direction away from the laser action side, and wherein the laser beam (7) is directed at an angle α of 1° to 45° with the plane of the joint (6d) into the groove formed by the joint (6d) and the joint flange (3d), and welding is performed in such a way that the weld (12) formed extends into the gap (10d), and thereby forms a gap bottom (SB) in the gap (10d), through which the opposing surfaces of the joints (1d, 2d) are separated.

Description

[0001] The present invention relates to a method for laser welding having the features of the preamble of claim 1.

[0002] Laser welding is a common method for joining two parts together to fit together. In this process, the two parts are positioned relative to each other and typically held together by clamping devices. A laser beam is then used to melt the joint, thus joining the two parts materially. Laser welding has the advantage that, although sufficiently high energy is introduced locally into the workpiece, the heat-affected zone remains small because the welding speed is high and the introduced energy is very limited, so only a small amount of material is melted. To perform the welding process, the laser head, along with the laser beam, moves relative to the joined parts. Typically, the laser head moves while the joined parts remain stationary.

[0003] For example, a laser welding method is disclosed in document DE 10 2017 105 900 A1. In this known method, two joints are joined together at their joint by orienting them so that they are abutted against each other via flanges and their joints terminate flush with each other. For welding, a laser beam is aligned with the joint gap between the two flanges and thus with the joint. The two joints are positioned at an angle to each other, creating a gap on the side facing away from the laser beam, through which degassing products are expelled. This degassing process does not adversely affect weld formation; these degassing products are primarily generated when welding coated joints, such as galvanized steel sheets.

[0004] A method for joining two steel plates is known from document EP 0 771 605 B1, wherein at least one steel plate has a low-melting-point coating, such as a zinc coating. According to this known method, two joints are arranged at an acute angle to each other for joining. A fillet weld is then formed as a weld, and one plate is welded to the other plate along its end face in this manner. The welding is performed by a laser beam. A laser beam-fillet weld is formed along the joint of one joint by the laser beam. The two joints are positioned and held relative to each other in a clamping device for joining. To degas through the gap formed by the angled arrangement of the two joints, the cut edge of one joint is provided with teeth along its end face. Degassing products of the coating can therefore be discharged through the gap between the teeth and the degassing pathway provided by the angled arrangement of the joints on the side away from the laser beam. The weld is designed as a fillet weld so that it does not penetrate the joint. The gap on the side away from the weld can have an opening angle of 7° to 15° and ends with a zero gap width at the weld.

[0005] The problem here is that this angled arrangement of the components leads to corrosion in the root region of the gap on the side facing away from the laser beam. Due to the high requirements for corrosion resistance, even small corrosion sites that occur during the service life of such components are no longer acceptable. This occurs in the methods described above because the zinc coating evaporates and is removed from the welded area. The gap formed by the angled positioning of the two joints is often not wide enough or the gap angle is too small, making it impossible to apply the desired coating in the areas where the zinc coating has evaporated due to the welding process. While some coatings are feasible, such as wax coatings for cavity protection or new, suitable zinc coatings, this results in higher costs and associated expenses.

[0006] In this context, the technical problem to be solved by the present invention is to propose a laser welding method that can reliably connect two components (joints) and avoid the aforementioned corrosion problems.

[0007] The aforementioned technical problem is solved by the method described at the beginning, characterized in that the first joint has a joint flange with a joint, and the second joint has a joint area on its flat side, wherein, for the laser welding process, the first joint is held in contact with the joint area of ​​the second joint by one side of the joint flange of the first joint, wherein a gap is provided between the two joints, the gap widening in a direction away from the laser action side, and wherein the laser beam is directed at an angle of 1° to 45° to the plane of the joint area into a groove (Kehle or notch) formed by the joint area and the joint flange, and welding is performed in such a way that the weld formed extends into the gap, thereby forming a gap bottom in the gap, through which the opposing surfaces of the joints are separated.

[0008] Advantageous improved design options are described in the dependent claims.

[0009] Surprisingly, in lap joint welding, the arrangement of the laser beam relative to the joint area does not result in the second joint being welded deeper or penetrated within its joint area. Instead, it creates an extremely uniform and deep weld root (or weld base) in the contact and gap area of ​​the two joints—the joint—that curves towards the gap opening and does not linearly follow the angle of light incidence. The weld depth extends through the actual joint until it reaches the gap on the side facing away from the laser beam. Molten metal enters the gap and fills the narrowest gap area. The melt flowing into the gap on the laser-facing side forms a bottom, through which the sides defining the gap boundary of the joints are separated. This gap bottom can be designed to be straight, substantially straight, convex, or even concave. Importantly, through the gap bottom, the gap width between the joints on the laser-facing side does not have zero extension at any location, nor is it so narrow that the desired anti-corrosion coating cannot reach this point. The laser welding process is conducted in a controlled manner—perhaps without any welding additives (Schweiβzugabe). The gap is filled with molten material through a bottom formed by the molten material until the gap width is sufficient to ensure that the material reaches the root of the gap for subsequent coating processes, such as KTL coating. The root in this method is formed by the bottom of the gap created by the welding process. A gap width of approximately 0.2 mm is generally considered sufficient to meet this requirement. This width is adequate so that the entire component can be coated cost-effectively, for example, using a KT coating method (KTL = cathodic dip coating). By filling the root of the gap on the side facing away from the laser beam until the KT paint can be deposited within the gap width, it is ensured that the KTL coating can also be applied to these areas of the component as required.

[0010] The heat introduced into the joint of the first joint's flange by the laser beam partially melts it, thereby providing molten material introduced into the gap through the joint. The second joint acts as a weld support through its joint area. With the laser beam incident on the joint surface at an angle preferably less than 45°, especially less than 30°, the energy introduced into the joint area of ​​the second joint is significantly lower than the energy introduced into the joint of the first joint. The joint of the first joint is thus used as a source of welding material. Using the joint of the first joint's flange as a source or reserve of welding material has the advantage that the laser beam is at least largely loaded into the joint and thus loaded onto the first joint in the direction of material extension rather than laterally. This is advantageous for the welding method because there is no risk of burning through the first joint. The geometric centerline of the laser beam is therefore preferably offset from the joint towards the direction of the first joint, which is formed by the adjacency of the two joints.

[0011] The joint of the engagement flange of the first joint is typically designed to be straight in the direction of its extension along the material thickness.

[0012] The joining flange can be bent relative to the main extension of the joint, and in particular, it can be an outwardly extending flange, such as a bent edge. The transition between the joining flange and other parts of the joint is typically bent radially due to the forming process. In this design, the wall defining the gap is bent at a gradually increasing opening angle.

[0013] Conversely, the second joint has a flat engagement area to which the engagement flange of the first joint is welded. The engagement area is typically distinct from the joint itself. This engagement area is usually spaced from the end of the joint relative to its laser-loaded side. However, the engagement area can also be located in any region of the joint.

[0014] In the laser welding process, the engagement flange of one joint is brought to the engagement area of ​​the other joint, causing the two joints to come into contact to form a joint. The engagement flange of the first joint is recessed relative to the end of the second joint to form a groove. Ideally, the two joints are positioned relative to each other in the joint with a so-called zero-gap. The contact between the two joints can be linear or planar. If the engagement flange and engagement area are planar against each other, care should be taken that the extension of this planar surface in the depth direction of the joint does not exceed the material thickness of the thinner joint. Experiments have shown that, otherwise, the desired weld size in the gap cannot be formed with the specified laser beam energy. Ideally, the first joint is the thinner joint in the engagement area. In this design, a high-strength connection can be reliably achieved by a special process while filling the root of the gap on the side of the joint facing away from the laser beam, so that the gap width in the root region is at least 0.2 mm.

[0015] If the engagement flange of the first joint is bent relative to the adjacent area, the gap is automatically formed by the bending caused by the protrusion of the joint. If both joints are flat, the engagement flange needs to be held at an angle of 5° to 45° onto the joint area to ensure sufficient widening. Of course, the gap angle is chosen such that the gap can be filled with available molten material until the specified minimum gap width is large enough for the anti-corrosion coating to be deposited directly. Possible degassing products can escape through the established gap, especially in cases involving galvanized joints. The gap also serves as a guide line for the weld root; it extends along the gap and thereby connects the two joints along a larger joint surface. This creates a welded connection that is particularly capable of withstanding loads.

[0016] In the preferred design, the two joints are held at an angle of 5° to 20° to each other within the area of ​​the joint.

[0017] The laser beam is focused onto a groove formed by two contacting joints, wherein the center of the laser beam is preferably oriented onto the joint of the first joint. The joint, i.e., the area where the two joints are adjacent, is heated by a ray segment of the laser beam spaced from the geometric center.

[0018] The two joints are typically held in a clamping device under prestress for engagement.

[0019] Particularly preferred is a configuration where the laser energy and the contact surfaces between the joint area and the joint flange are arranged relative to each other, such that a normally raised weld is provided on the side opposite to the laser-loaded side. This provides a weld with a raised surface that adequately fills the gap in the region at the root of the gap, for example, for subsequent KTL coating.

[0020] The advantage is that the method proposed here can be performed without additional welding additives; this greatly reduces the design and structural costs of the welding machine and the process costs.

[0021] The welded joint thus completed can be smoothly coated, for example, with a KTL coating, i.e., a high-viscosity liquid coating applied in the processing state. This coating is particularly durable. This coating is applied after the method described above. Advantageously, the zinc coating, which protects the joint from the laser-loaded side, is not damaged as much as possible in the above method, so the KTL coating is ultimately applied only locally. However, the entire component is usually coated with KTL.

[0022] The invention will now be further described with reference to the accompanying drawings. Wherein:

[0023] Figure 1 : A schematic diagram of the two connecting members according to the first embodiment.

[0024] Figure 2 A schematic diagram of the two connecting members according to the second embodiment.

[0025] Figure 3 A schematic diagram of the two connecting members according to the third embodiment.

[0026] Figure 4a A schematic diagram of the two connecting members according to the fourth embodiment.

[0027] Figure 4b After performing the laser welding process Figure 4a The two connecting parts,

[0028] Figure 5a Microscopic sections passing through the joint heads of two joints joined together by the method according to the invention.

[0029] Figure 1A cross-section is shown showing the edge portions of the first joint 1 and the second joint 2 according to a first embodiment. The first joint 1 includes a joining flange 3 that extends or bends relative to the material 4 defining the boundary of the joint head. The transition between the joining flange 3 and the surrounding material 4 is achieved by a bend 5. The second joint 2 includes a joining area 6. The laser beam is indicated by reference numeral 7.

[0030] The side of the bonding area 6 facing the laser beam 7 is spaced apart from the end 8 of the bonding member 2 and the connector; in this embodiment, the spacing is approximately four times the thickness of the thinner bonding member, wherein in this embodiment, the two bonding members 1 and 2 are of the same thickness.

[0031] The engaging flange 3 of the first connector 1 is arranged on the engaging area 6 formed by the flat side of the second connector 2, forming a stepped layout, i.e., a groove K. A laser beam 7 is focused on the groove K formed by the connector 9 of the engaging flange 3 and the engaging area 6. The angle α between the engaging area 6 and the laser beam 7 is approximately 25° in this embodiment. The center of the laser beam 7 is incident on the lower third of the connector 9 of the first connector 1.

[0032] In the illustrated embodiment, the engagement flange 3 contacts the engagement region 6 in a line contact.

[0033] There is a gap 10 on the side of the arrangement away from the laser beam 7. This gap widens as the opening angle increases due to the bending of the engagement flange 3 relative to the engagement area 6.

[0034] Figure 2 A cross-section of the second embodiment is shown. Unlike the first embodiment, in this embodiment, the first joint 1a is designed to be straight, while the second joint 2a has a joint area 6a with a curved portion 5a and thus a segmental bend. In this embodiment, the joint flange 3a of the joint 1a and the joint area 6a of the second joint 2a also contact each other on a line.

[0035] Figure 3 A cross-section of another arrangement according to the invention is shown. In this embodiment, the straight engagement flange 3b of the first engagement member 1b is arranged at an angle to the straight engagement region 6b of the second engagement member 2b, specifically at an angle β of approximately 25°. Here, the engagement flange 3b also contacts the engagement region 6b linearly.

[0036] Figure 4a A cross-section of another embodiment is shown. In this embodiment, the engagement flange 3c of the first connector 1c contacts the engagement region 6c of the second connector 2c in a facet manner. It can be clearly seen in the cross-section that the facet contact in the direction transverse to the side facing the laser beam 7c is substantially equivalent in the width direction B to the thickness D of the thinner engagement flange 3c of the first connector 1c in this example.

[0037] Figure 4b The following is shown after the laser welding process is completed: Figure 4a The layout is as follows. As can be seen in the schematic diagram, the weld has been formed along the contact surfaces of the two joints 1c and 2c, and the two joints 1c and 2c are therefore connected by the joint flange 3c, or joint area 6c. The molten material is indicated by reference numeral 11. It can be seen that, due to the widening of the gap 10c in the direction of the first joint 1c, the weld bends towards the first joint 1c.

[0038] The gap 10c, arranged on the side facing away from the laser beam 7d, can thus be filled until the gap width S is greater than or equal to 0.2 mm and therefore until this minimum width is filled. The gap bottom SB is formed by molten metal entering the gap 10c, and the gap width S is defined by this gap bottom in the region facing the end of the molten material 11. The remaining minimum gap width S is chosen such that an anti-corrosion coating, such as a KTL coating, can be smoothly introduced into the gap up to the gap bottom SB formed by the molten material. Therefore, no uncoated wedge-shaped portions are left in the gap 10c.

[0039] Figure 5a Micrographs of samples of two joints 1d and 2d welded according to the present invention are shown. Welding was performed by a laser beam with a diameter of approximately 0.8 mm. The first joint 1d is 1.5 mm thick, and the second joint 2d is 2 mm thick. How weld 12 is formed along the contact surface between the joint flange 3d and the joint area 6d can be clearly seen. A bulge is formed on the side opposite to the laser loading, creating a convex weld at the bottom SB of the gap.

[0040] It can also be seen that the joint side of the 3d flange is partially melted. Of course, the amount of melted material is only what is required for the joint connection of the two joints 1d and 2d, including the amount needed to fill the root of the gap to form the bottom SB of the gap. This material is represented by the material introduced into the gap 10d through the joint. The gap width S is still 0.4 mm in this embodiment.

[0041] exist Figure 5a In the diagram, the perimeter of weld 12, i.e., the molten area, is represented by dashed lines. The original surfaces of the two joint members 1d and 2d within the joint area are represented by dotted lines. It can be clearly seen that the material molten by the laser welding method flows into gap 10d, and through this material, the minimum width of gap 10d has reached the width of the gap bottom SB, which has a gap width S. Figure 4b The schematic diagram also shows the arc-shaped direction of weld 12.

[0042] The present invention has been described with reference to embodiments. Many other solutions will be apparent to those skilled in the art without departing from the scope of the claims, and need not be described in detail within the scope of these designs.

[0043] List of reference numerals in the attached diagram:

[0044] The letters in the attached figures indicate the same parts in another design.

[0045] 1 First joint

[0046] 2 Second joint

[0047] 3. Engaging flange

[0048] 4. Surrounding materials

[0049] 5. Bending section

[0050] 6. Joint area

[0051] 7. Laser beam

[0052] 8 ends

[0053] 9 connectors

[0054] 10 gaps

[0055] 11 Welding

[0056] 12 Welds

[0057] K groove

[0058] D Material thickness

[0059] B width

[0060] S-gap width

[0061] SB gap bottom

[0062] β Joint Angle

[0063] α laser beam angle

Claims

1. A method for laser welding two joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d), wherein the two joints are held together by an lap joint and are made of metallic material, characterized in that, The first joint (1, 1a, 1b, 1c, 1d) has a joint flange (3, 3a, 3b, 3c, 3d) with a joint (9), and the second joint (2, 2a, 2b, 2c, 2d) has a joint area (6, 6a, 6b, 6c, 6d) on its flat side. During the laser welding process, the first joint (1, 1a, 1b, 1c, 1d) contacts the second joint (2, 2a, 1b, 1c, 1d) through one side of the joint flange (3, 3a, 3b, 3c, 3d) of the first joint. The joint areas (6, 6a, 6b, 6c, 6d) of the two joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d) are maintained, wherein a gap (10, 10a, 10b, 10c, 10d) is provided in the contact area between the two joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d), the gap being widened in the direction away from the laser action side, and wherein the laser beam (7) is directed at an angle of 1° to the plane of the joint areas (6, 6a, 6b, 6c, 6d). An angle (α) of 45° is directed into the groove (K) formed by the joint area (6, 6a, 6b, 6c, 6d) and the joint flange (3, 3a, 3b, 3c, 3d), and welding is performed such that the formed weld (12) extends into the gap (10, 10a, 10b, 10c, 10d), and thereby forms the gap bottom (SB) in the gap (10, 10a, 10b, 10c, 10d), and the joints (1, 2; 1a, 2a; 1b, 2b); The opposing surfaces of 1c, 2c; 1d, 2d) are separated by the bottom of the gap, such that the gap width between the joints on the side away from the laser beam does not have zero extension at any position or is not so narrow that the desired anti-corrosion coating cannot reach there, and wherein, after the welding process, the joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d) are provided with an anti-corrosion layer at least in the area at the bottom of the gap (SB).

2. The method according to claim 1, characterized in that, The engagement flanges (3, 3a, 3b, 3c, 3d) of the first joint (1, 1a, 1b, 1c, 1d) are constructed and held onto the engagement regions (6, 6a, 6b, 6c, 6d) of the second joint (2, 2a, 2b, 2c, 2d) such that the engagement flanges (3, 3a, 3b, 3c, 3d) and the engagement regions (6, 6a, 6b, 6c, 6d) are in line contact or contact through a surface on the side facing the laser beam (7), the width (B) of which is transverse to the laser loading side is consistent with the material thickness (D) of the thinner joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d) in the engagement regions (6, 6a, 6b, 6c, 6d).

3. The method according to claim 2, characterized in that, The first joint (1, 1a, 1b, 1c, 1d) is a thinner joint (1, 1a, 1b, 1c, 1d) among the two joints (1, 2; 1a, 2a; 1b, 2b; 1c, 2c; 1d, 2d) in the joint area (6, 6a, 6b, 6c, 6d).

4. The method according to claim 1 or 2, characterized in that, The laser beam is directed at an angle (α) of 7° to 30° relative to the plane of the joint areas (6, 6a, 6b, 6c, 6d) into the groove (K) formed by the joint areas and the joint flange.

5. The method according to claim 1, characterized in that, The mating flanges (3, 3a, 3b, 3c, 3d) are held at an angle (β) of 5° to 45° on the mating areas (6, 6a, 6b, 6c, 6d).

6. The method according to claim 5, characterized in that, The angle (β) is between 7° and 30°.

7. The method according to claim 1, characterized in that, At least one joint is provided with a zinc coating that evaporates from the joint area (6, 6a, 6b, 6c, 6d) during the welding process.

8. The method according to claim 1, characterized in that, A raised weld is formed on the side away from the laser loading in the gaps (10, 10a, 10b, 10c, 10d).

9. The method according to claim 1, characterized in that, The welding process is performed without welding additives.

10. The method according to claim 1, characterized in that, The anti-corrosion layer is a KTL coating.

11. The method according to claim 4, characterized in that, The laser beam is directed at an angle (α) of 15° to 25° relative to the plane of the joint areas (6, 6a, 6b, 6c, 6d) into the groove (K) formed by the joint areas and the joint flange.

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