METHOD FOR PITCH SEAM WELDING

Description

[0001] The invention relates to a method for spot welding according to the preamble of claim 1.

[0002] To retain heat within a vehicle's exhaust system and / or prevent damage to surrounding components / objects from radiant heat, exhaust systems are partially or completely insulated. This insulation is typically applied to the outside of the exhaust system during the final stages of the manufacturing process (by welding, bolting, or clamping). Welding often involves welding a very thin outer sheet to the thick exhaust system's inner tube using numerous micro-welds (e.g., one weld every 10 mm), which is very time-consuming. Another challenge is the geometric constraints imposed by the insulation, which can necessitate welding in locations that are difficult to work in (poor accessibility). Furthermore, the strength of the individual weld points is low. Welding very thin sheets is also difficult because excessive heat input can lead to the sheet metal burning away.

[0003] Manufacturing with micro-spot welds is characterized by long production times, high demands on the geometric tolerances of the external surfaces to be joined, and potentially poor accessibility when welding individual spots, as well as low strength of the individual spots. Furthermore, special welding equipment is required (MAG welding systems cannot be used). Welding using MAG welding currently requires thicker sheets (more weight, more material usage, higher demands on deep-drawing tools, a stiffer component with potential strength problems due to differences in thermal expansion).

[0004] In an exemplary process, a hole seam welding is performed in which a thin sheet metal part is joined to a support part that is thicker than the thin sheet metal part in a fusion welding process.

[0005] A heat shield arrangement for an exhaust system is known from CN 208 564 720 U. A component assembly for a structural part of a vehicle exhaust system is known from EP 3 748 142 A1. Further exhaust systems with a heat-insulating insulating sheet are known from US 9 671 056 B2 and CN 207 245 808 U. WO 2018 / 042680 A1 discloses a method for arc spot welding for joining dissimilar materials, as well as a joining aid and a weld joint made of dissimilar materials. Improvements relating to the welding process are known from GB 865 483 A.

[0006] The object of the invention is to provide a method for spot welding, specifically for welding a thin-walled heat insulation sheet to a vehicle exhaust system, which, compared to the prior art, enables a reliable connection between the thin sheet part and the support part in a manufacturing-technically simple manner.

[0007] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] The invention relates to a method for spot welding in which a thin sheet metal part is joined to a carrier part that is thicker than the thin sheet metal part in a fusion welding process. According to claim 1, a locally limited material thickening is provided at the joint to be welded on the side of the thin sheet metal part facing away from the carrier part. This thickening melts during the fusion welding process. After completion of the fusion welding process, the material thickening is therefore metallurgically bonded to the carrier part, with the thin sheet metal part clamped between them. Preferably, the thin sheet metal part can be joined to the carrier part solely by this clamping. Alternatively, the thin sheet metal part can also be welded to a limited extent together with the carrier part and the locally limited material thickening.

[0009] According to the invention, the support element is a vehicle exhaust system component (such as an exhaust system funnel), while the thin sheet metal part is a heat-insulating sheet (for example, 0.15 mm thick). This can be attached to the exhaust system funnel at, for example, three points. The respective insulating sheets have pre-drilled holes (hereinafter referred to as pilot holes). When attaching the insulation to the exhaust system funnel, for example, 1.5 mm thick ring washers (similar to a washer) are first placed over the holes from the outside and then welded to the funnel using, for example, a MAG weld. Each ring washer is now metallurgically bonded to the funnel. The thin insulating sheet is welded in place, or at least clamped at several points. The added washer acts as a partial thickening, thus preventing the thin insulating sheet from burning away.

[0010] In the application described above, a strong (often material-bonded) connection between the insulation with the very thin insulating sheet (for example, ≤0.2 mm) and the funnel can be created using preferably only three MAG spot welds. The insulating sheet itself does not need to be thick enough for MAG welding, as the melting and weld pool are achieved by means of the 1.5 mm thick annular washer.

[0011] In a comparative method not covered by the invention, in which the thin sheet metal is attached using, for example, micro-welds, the strength of the individual points is low, so that a very large number of points are required (e.g., 30 points), which results in a long production time and thus high costs. In other methods, where the insulating sheet is welded to the funnel using MAG welding, the sheet metal has a significantly greater wall thickness (e.g., ≥ 1 mm) to prevent burn-through.

[0012] The following are key aspects of the invention highlighted in detail: According to the invention, the locally limited material thickening is a ring-shaped disc, which is pressed against the carrier part as a separate component with the thin sheet metal part interposed. This disc can be placed on the joint to be welded with a holding force. In this case, a hold-down device can optionally press the ring-shaped disc against the carrier part with the thin sheet metal part interposed. The fusion welding process can then be carried out. During the fusion welding process, the inner circumference of the ring-shaped disc can melt. The inner cross-section of the ring-shaped disc can then be filled with the weld pool. After completion of the fusion welding process, the inner cross-section of the ring-shaped disc is therefore filled with a weld bead that bonds the ring-shaped disc to the carrier part in a metallurgical bond.With regard to a permanently reliable welded joint, it is preferred if the ring disc and the support part are made of a material similar or identical to that of a weldable material, in particular stainless steel.

[0013] In contrast to resistance spot welding with a welding gun, the fusion welding process is preferably designed so that only a single-sided welding access is required. The welding access can preferably be from the side where the locally limited material thickening (i.e., the ring disc) is located.

[0014] From a manufacturing perspective, the fusion welding process can be easily implemented as a gas metal arc welding process, such as MAG welding. The welding electrode used in the fusion welding process can be a consumable electrode, the material of which, together with the material of the locally limited material thickening, the base material, and, if applicable, the thin sheet material, forms the weld nugget.

[0015] According to a first process variant, the thin sheet metal part can be provided with a pilot hole before the fusion welding process. The pilot hole diameter can be dimensioned larger than the inner diameter of the ring washer. Furthermore, it is preferred that the pilot hole and the ring washer are aligned concentrically with each other at the joint to be welded.

[0016] In an alternative process, the thin sheet metal can be positioned at the joint to be welded without a pilot hole before the fusion welding process. In this case, the pilot hole forms during the fusion welding process due to burn-off. After the pilot hole has formed, the locally limited material thickening then bonds to the substrate material in a metallurgical bond.

[0017] In one specific, but not limiting, embodiment, the thin sheet metal part can, for example, have a material thickness ranging from 0.15 mm to 0.20 mm. The thickened material can have a thickness ranging from 0.60 mm to 0.90 mm. Furthermore, the pilot hole diameter in the thin sheet metal part can, for example, be in the range of 7 mm, while the inner diameter of the ring disc is dimensioned slightly smaller and can, for example, be in the range of 6.4 mm.

[0018] According to the invention, the support element is a vehicle exhaust system component, specifically an exhaust system funnel. The thin sheet metal part, according to the invention, is an insulating sheet that insulates the heat radiation from the exhaust system component to surrounding components. The insulating sheet can be part of an insulation system consisting of the insulating sheet and an insulating element (for example, a fiber mat).

[0019] Exemplary embodiments of the invention are described below with reference to the accompanying figures.

[0020] They show: Figure 1 shows an exhaust system with a welded-on insulating plate; Figures 2 to 4 show views illustrating a method for producing the welded joint; and Figure 5 shows a view according to the Figure 3 a second embodiment.

[0021] In the Figure 1A vehicle exhaust system is shown with an exhaust system component, in particular an exhaust system funnel, which forms a support part 3 according to the invention, to which an insulating thin sheet metal part 1 is attached at welded joints F. The thin sheet metal part 1 is part of an insulation that insulates against heat radiation from the exhaust system component to surrounding components.

[0022] In the Figure 2 One of the weld joints F is shown in a cross-sectional view. In the weld joint, the thin sheet metal part 1 is joined to the support part 3, which has a greater material thickness than the thin sheet metal part 1. For example, the thin sheet metal part 1 can have a material thickness s1 of 0.15 mm, while the material thickness s2 of the support part 3 can be, for example, 2 mm. As can be seen from the Figure 1 As can be seen, a ring disc 5 is positioned on the side of the thin sheet metal part 1 facing away from the support part 3, the inner cross-section of which is 7 (only in the Figure 3 (shown) is filled with a weld bead 9. The weld bead 9 is bonded to the ring disc 5 by a material bond on one side. On the other side, the weld bead 9 extends through a pilot hole 11 in the thin sheet metal part 1 and is bonded to the carrier part material by a material bond.

[0023] In the Figure 1 For example, the pilot hole diameter d1 is dimensioned so large that no direct weld connection is formed between the thin sheet metal part 1 and the weld bead 9. Alternatively, the thin sheet metal part 1 can also be partially bonded to the weld bead 9. However, the thin sheet metal part 1 is primarily held not by a bond, but rather by clamping between the ring washer 5 and the support part 3.

[0024] The following will be based on the Figures 3 and 4 Process steps for the production of the in the Figure 1The weld joint shown is described as follows: First, in the Figure 3 The ring disc 5 is positioned on the joint F to be welded using a singulation unit 13, for example by means of a compressed air supply (alternatively by gravity or other means). The ring disc 5 is then held in place using a hold-down device 15 ( Figure 4 ) with the thin sheet metal part 1 interposed against the support part 3. In this state, a fusion welding process starts, preferably implemented as a MAG welding process. For the fusion welding process, according to the Figure 4A welding nozzle 16 is guided to the joint F. The welding nozzle 16 has an electrode feed 18, by means of which a consumable welding electrode 17 is guided to the joint F in a protective gas atmosphere. Under the protective gas atmosphere 22 and with the formation of an arc 20, the annular disc 5 melts on its inner circumference. The resulting molten weld metal 24 is enclosed by the annular disc 5. The weld nugget 9 is formed from the material of the annular disc 5, the electrode material, the base material, and, if applicable, the thin sheet metal part material.

[0025] It should be emphasized that the invention is not limited to the embodiment shown in the figures. Alternatively, the ring disc 5 can also be pre-attached to the thin sheet metal part 1. In this case, the ring disc 5 would no longer need to be fed to the thin sheet metal part 1 by means of a feeding unit.

[0026] In the Figure 2, 3 and4 The inner circumference of the ring disk 5 is positioned concentrically to the pilot hole 11 of the thin sheet metal part 1. The pilot hole diameter d 1 is oversized by an interference Δd / 2 ( Figure 3 ) larger than the inner diameter of the ring disc d 2 ( Figure 3 ).

[0027] In the Figure 5 is in a view according to the Figure 3 A second embodiment is shown. In the second embodiment, the same process sequence is carried out as in the first embodiment above. Therefore, reference is made to the preliminary description. In contrast to the first process ( Figures 2 to 4 ) will be according to the Figure 5The thin sheet metal part 1, without a pilot hole 11, is positioned at the joint F to be welded. The pilot hole 11 only forms at the beginning of the fusion welding process due to burn-off. After this pilot hole formation, the weld nugget 9 can form during the further course of the welding process, which is metallurgically bonded to both the support part 3 and the inner circumference of the ring disc 5. Reference symbol list

[0028] 1 Thin sheet metal part 3 Support part 5 Locally limited material thickening or ring washer 7 Ring washer inner cross-section 9 Welding lens 11 Pre-hole 13 Singling unit 15 Hold-down device 17 Welding electrode 18 Electrode feeder 20 Arc 22 Shielding gas atmosphere 24 Liquid weld metal F Jointing point s 1 Material thickness of the thin sheet metal part s 2 Material thickness of the support part d 1 Pre-hole diameter d 2 Ring washer inner diameter Δd / 2 Oversize

Claims

1. Method for plug welding, in which, in a fusion welding process, a thin sheet metal part (1) is joined to a carrier part (3) which is thicker in material than the thin sheet metal part (1), a locally delimited material thickening (5) being provided at a joint (F) to be welded, on the side of the thin sheet metal part (1) facing away from the carrier part (3), which material thickening is at least partially melted in the fusion welding process and is integrally welded to the carrier part (3) after the fusion welding process, in particular with the thin sheet metal part (1) being clamped therebetween, the carrier part (3) being an exhaust system component, namely an exhaust system funnel, and the thin sheet metal part (1) being an insulating sheet in order to insulate the heat radiation from the exhaust system component to surrounding elements, characterized in that the locally delimited material thickening (5) is an annular disk which is pressed against the carrier part (3) as a separate element with the thin sheet metal part (1) interposed therebetween.

2. Method according to claim 1, characterized in that the thin sheet metal part (1) is joined to the carrier part (3) solely by means of the intermediate clamping, or in that the thin sheet metal part (1) is welded to a small extent to both the carrier part (3) and the locally delimited material thickening (5).

3. Method according to claim 1 or 2, characterized in that in the fusion welding process, the annular disk (5) melts on the inner circumference and / or the annular disk inner cross section (7) is filled with a weld nugget (9) after the fusion welding process, which weld nugget integrally bonds the annular disk (5) to the carrier part (3), and / or in that the annular disk (5) and the carrier part (3) are made identically or similarly in terms of material from weldable material, in particular stainless steel.

4. Method according to any of the preceding claims, characterized in that in the fusion welding process, only one-sided weld access takes place, namely from the side on which the locally delimited material thickening (5) is arranged.

5. Method according to any of the preceding claims, characterized in that the fusion welding process is a gas metal arc welding process, such as MAG welding, and / or in that the welding electrode (17) used in the fusion welding process is a consumable electrode, the material of which, together with the material of the locally delimited material thickening (5), the carrier part material and optionally the material of the thin sheet metal part (1), forms the weld nugget (9).

6. Method according to any of the preceding claims, characterized in that before carrying out the fusion welding process, the thin sheet metal part (1) is provided with a pilot hole (11), and in that in particular the pilot hole diameter (d1) is dimensioned to be larger than the inner diameter (d2) of the annular disk (5) by an oversize (Δd / 2), and / or in that the pilot hole (11) and the annular disk (5) are positioned concentrically with respect to one another at the joint (F) to be welded.

7. Method according to any of claims 1 to 5, characterized in that before carrying out the fusion welding process, the thin sheet metal part (1) is provided without a pilot hole (11) at the joint (F) to be welded, and in that during the fusion welding process, the pilot hole (11) is formed due to melting loss, such that in the further course of the process, the locally delimited material thickening (5) becomes integrally bonded to the carrier part material.