Welding element and welding procedure for joining a welding element to a workpiece

Abstract

Welding element (10) suitable for joining to a workpiece by a welding process, comprising: - a head (14) 14 with a welding surface (22) and a clamping surface (24) oriented in the opposite direction to the welding surface (22), - an anchoring section in the form of a shaft (12) extending between a first end region (18) and a second end region (20) along a longitudinal axis (Xa), wherein the first end region (18) is connected to the clamping surface (24), wherein the welding surface (22) has several regularly distributed pointed projections (26).

Description

Field of invention

[0001] The present invention relates to a welding element, in particular a welding stud, which is suitable for being connected to a workpiece using a welding process, comprising a head with a welding surface and a holding surface facing away from the welding surface and a shaft-shaped anchor section which extends along a longitudinal axis between a first end region and a second end region, wherein the first end region is connected to the holding surface.

[0002] Furthermore, the invention relates to a welding process for joining a corresponding welding element to a workpiece. Background of the invention

[0003] Particularly in automotive body construction, it is common practice to use welded elements to attach parts and components. For this purpose, welding studs are predominantly used, which are attached to a structure in a known manner, for example, by stud welding. Various welding techniques are available for attaching such welded elements, such as arc stud welding. The arc stud welding process belongs to the arc pressure welding processes and serves to permanently join an element, such as a welding stud, pin, bushing, hook, or eyelet, to a corresponding larger component, such as a body panel, a housing, a workpiece, or similar. The head of the welding element is positioned on a workpiece or component and then welded.

[0004] When connecting the welding element or welding stud to the workpiece surface, it is important to ensure that the melting process is uniform and thus the welding is uniform.

[0005] Document DE2227384A1 discloses a fastening element with a head and a shaft-shaped anchor section connected to the head. The fastening element has, on its surface to be connected to the component, a number of protrusions arranged symmetrically around the center point of this surface and radiating outwards in a star shape. DE102013225048A1 discloses another known prior art.

[0006] In many areas of engineering, aluminum alloys have become the dominant material for weight-saving reasons, and / or high-strength or ultra-high-strength body panels with tensile strengths of up to 1500 MPa and various thicknesses (thin and thick) have become established materials, for example in lightweight car bodies, but also in other industrial sectors. The strength of the panels and the different thicknesses depend on the function of the body component. The varying strengths are problematic because the same welding elements cannot be used for every thickness of panel.

[0007] It is therefore the object of the present invention to at least partially overcome the disadvantages described above in a welding element and a welding process for joining the welding element to a workpiece. In particular, it is the object of the present invention to provide a welding element and a welding process by means of which a advantageously durable joining of a welding element to a workpiece is made possible in a simple and cost-effective manner, resulting in improved flexibility and a low risk of perforation of the sheet metal, wherein the strength of the weld joint is primarily consistent compared to known welding elements and welding processes and can preferably even be increased. Summary of the invention

[0008] The above-mentioned problem is solved by a welding stud having the features of claim 1 and by a welding process having the features of claim 8.

[0009] Such a welding element, which is suitable for being joined to a workpiece using a welding process, has a head with a welding surface and a holding surface facing away from the welding surface and a shaft-shaped anchor section which extends between a first end region and a second end region along a longitudinal axis, wherein the first end region is connected to the holding surface, characterized in that the welding surface has several pointed projections regularly distributed over the entire welding surface.

[0010] The term "pointed" is to be understood as a shape that forms a sharp or rounded point or a sharp or rounded corner.

[0011] This weld surface geometry allows the welding characteristic curve to be adapted to both thin and thick sheet metal. The geometry also makes it possible to prevent the risk of through-welding in thin sheets.

[0012] According to the invention, the projections are arranged in parallel rows and separated by two groups of intersecting grooves. Two projections are clearly delineated, and the shape of such separations can be produced without great effort.

[0013] In a preferred embodiment, the weld surface forms a bulge, and the projections are arranged on the bulge. The projections extend over a limited area, which simplifies the welding of the weld element.

[0014] In another preferred embodiment, the bulge has a circular cross-section. The bulge is centered on the longitudinal axis.

[0015] In a particularly preferred embodiment, each projection has a pyramid-like shape with a square base. The shape of the projection enables efficient and targeted melting. Furthermore, the shape of the projection is simple to produce, particularly by embossing. In another embodiment, knobs or conical protrusions may be provided.

[0016] In a particularly preferred embodiment, each projection has four flat cylindrical surfaces, and two opposing cylindrical surfaces are enclosed by an angle between 75 and 85 degrees. Such an angle allows for good and targeted melting.

[0017] According to a further preferred embodiment, the tips of two adjacent projections (26) are spaced between 0.5 millimeters and 2.0 millimeters apart. This distance allows for good ignition of all tips and uniform melting across the entire weld surface.

[0018] In a particularly preferred embodiment, the projections are produced during the forming of the welding element by a suitable cold forming process. No further step is required to produce the projections. The projections are integral with the head.

[0019] Furthermore, the above task is solved by a welding process for joining a welding element to a workpiece, which comprises the following steps: Providing a welding element as described above, providing a workpiece with a first and a second surface and a sheet thickness, providing a welding machine, arranging the welding surface of the welding element on the first surface of the workpiece, controlling the welding machine depending on the sheet thickness, welding the welding element to the workpiece by melting at least part of the protrusions and pressing the welding element against the workpiece.

[0020] In a particularly preferred embodiment, the projections along the longitudinal axis have a projection height that depends on the sheet thickness.

[0021] In a particularly preferred embodiment, the workpiece is provided with a zinc layer on its second surface. This method only minimally affects the zinc layer on the reverse side of the base material.

[0022] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention. Description of the accompanying drawings

[0023] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description. They show: Fig. 1 a perspective schematic view of a welding element according to the invention with a head and an anchor section, wherein the head has a first surface structure; Fig. 2 a side view of the welded element made of Fig. 1 ; Fig. 3 a top view of the surface structure of the weld element made of Fig. 1 ; Fig. 4a longitudinal sectional view of an embodiment of a welding element according to the invention, arranged on a surface of a workpiece and with a schematic welding device; Fig. 5 a side view of a welded element according to a further embodiment. Detailed description of preferred embodiments of the present invention

[0024] Fig. 1 Figure 1 shows a welding element 10 designed as a welding stud with a shaft-shaped anchor section 12 and a head 14 (or stud head).

[0025] The shaft-shaped anchor section 12 has a base body 16, a first and a second end region 18, 20.

[0026] The base body 16 extends along a longitudinal axis Xa between the first end region 18 and the second end region 20. The base body 16 of the anchor section 12 can assume the desired shaft shape. As in Fig. 1, Fig. 2 and Fig. 4As shown, the base body 16 can have a circular cross-section, essentially constant over its length. In other embodiments, the anchor section could also have a rectangular, triangular, or trilobular cross-section. Also in other embodiments, the base body 16 could not be constant over its length.

[0027] The in Fig. 1 The weld element 10 shown is advantageously a substantially cylindrical connecting element, the anchor section 12 of which has a thread. With regard to the weld element 10 according to the Fig. 1 and Fig. 2It should therefore be noted that the weld studs shown here are each provided with threads on their anchor sections 12, which is only intended to indicate that after welding, the weld studs in question can of course be provided with a screw connection for attaching any further component or for other purposes. Various thread forms and thread dimensions may be provided.

[0028] The second end region 20 of the anchor section 12 is preferably round, but other end region shapes could also be provided. For example, the second end region could have a cut edge.

[0029] The head 14 extends from the first end region 18. The head 14 is, for example, circular and concentric with a head axis Xk. For example, the head axis Xk and the longitudinal axis Xa coincide. The head 14, which is advantageously designed in the form of a disc (or a flange), has a weld surface 22 and a holding surface 24 facing away from the weld surface 22. The distance along the longitudinal axis Xa between the weld surface 22 and the holding surface 24 constitutes the thickness of the head 14. The greater the distance, the thicker the head. The first end region 18 of the anchor section 12 is connected to the holding surface 24. The head 14 has the weld surface 22 on its side facing away from the anchor section 12.

[0030] The weld surface 22 extends, for example, in a plane (or is fairly flat). In another embodiment, the weld surface 22 can have two weld sections which together form an angle of 7 degrees or 9 degrees.

[0031] The holding surface 24, for example, has the following properties as shown in Fig. 2 The figure shows a head diameter Dk that is larger than that of the anchor section. The weld surface can also be circular and have a weld diameter Ds. The head diameter Dk and the weld diameter Ds can coincide, as shown in Fig. 2 depicted.

[0032] In another embodiment, the head diameter Dk can be larger than the weld diameter Ds, as shown in Fig. 4 The welding surface 22 can in this case be centered on the holding surface 24.

[0033] As in Fig. 5In another embodiment, the welding surface 22 can be annular and form a ring, so that the holding surface has a recess 48 which is aligned concentrically to the head axis Xk.

[0034] As from Fig. 1, Fig. 2 , Fig. 3, Fig. 4 and Fig. 5 It can be seen that the welding surface 22 of the head 14 is not flat, but has several protrusions 26.

[0035] In particular, a "protrusion" shall be understood to mean a head section or head part projecting from the weld surface 22, such as a protrusion, a bump, etc.

[0036] The projections 26 are pointed. The term "pointed" refers to a shape that forms an edge, a point, or a corner. The tip 28 of the projection 26 can be sharp or rounded. Preferably, the tips 28 of the projection 26 will be rounded to simplify storage and transport. In particular, the weld elements with rounded tips will not damage the packaging during transport. The tip forms a free end of the projection. The projection extends along the longitudinal axis Xa from the tip to a base 30, which rests on a plinth of the head. The plinth is wider than the tip.

[0037] The projections 26 are made of material that can be melted in an electric arc.

[0038] The projections 26 are arranged at regular intervals on the weld surface 22. Each projection 26, for example, has a substantially pyramidal shape with a square base 30 and four substantially planar lateral surfaces 32 that form the apex 28. The four lateral surfaces 32 converge to form the apex 28.

[0039] Preferably, two opposing cylindrical surfaces 32 are enclosed by an angle α between 70 and 90 degrees, particularly between 75 and 85 degrees. Two opposing cylindrical surfaces 32 can be enclosed by an angle α of approximately 80 degrees. Such an angle allows for a good distribution of the projections and, at the same time, simple fabrication of the weld element (or the weld surface).

[0040] The angle α between two opposing lateral surfaces 32 of a projection 26 can be the same or different from the angle α between the two other opposing lateral surfaces 32. The distance between two adjacent projections 26 (in particular between two tips 28 of two adjacent projections 26) can be between 0.5 millimeters (mm) and 2.0 millimeters (mm).

[0041] In another embodiment (not shown), each projection has knobs or cone-shaped protrusions.

[0042] Each projection 26 has a projection height Hv along the longitudinal axis Xa. The projection height Hv of all projections 26 can be the same. In another embodiment, the projections 26 have different projection heights Hv. For example, the projection heights Hv can be between 0.2 and 1.1 millimeters (mm), and in particular between 0.3 and 1.0 millimeters (mm). The projection height Hv can preferably be 0.3 millimeters.

[0043] The projections 26 are aligned in parallel rows, as in Fig. 3 The projections 26 are separated by two groups of intersecting grooves 34a, 34b (or lines). The first group of grooves 34a (or lines) can, for example, be orthogonal to the second group of grooves 34b (or lines). In another embodiment, the first group of grooves 34a (or lines) can form an angle β of more or less than 90 degrees with the second group of grooves 34b.

[0044] Essentially, the projections 26 form a "waffle-like pattern". The projections 26 can be oriented with varying slopes, depths, and paths.

[0045] The weld surface 22 forms, for example, a bulge 36, and the projections 26 can be arranged on the bulge 36. For example, the bulge 36 has a circular cross-section. The bulge 36 can be centered on the longitudinal axis Xa.

[0046] In another embodiment, the welding element 10 has no bulge and the welding surface 22 forms a flat plane opposite the holding surfaces.

[0047] In another embodiment, the weld surface 22 is ring-shaped and the projections 26 form a ring around the head axis Xk.

[0048] The welding element 10 is made of a single material. The welding element 10 is preferably made of steel or stainless steel. Other metals, such as aluminum, or other materials can also be used. The welding element 10 is manufactured, for example, by cold forming, and the projections 26 are formed during the cold forming process. The projections are formed, for example, by embossing.

[0049] The weld element can be manufactured in several steps. For example, in a first step the surface is extruded. In a second step, pressing to the weld diameter can be carried out. In a third step, the "waffle pattern" (or the projections 26) can be pressed, for example with an embossing die.

[0050] The welding element 10 is formed in one piece or monolithically, so that in particular the anchor section 12 and also the head 14 with the corresponding projections 26 are manufactured from one component (or workpiece) to form the welding element 10.

[0051] In other embodiments, the welding element 10 could be multi-part.

[0052] The welding element 10 is suitable for joining to a workpiece 38 by a welding process (in particular by arc welding). The workpiece 38 is, for example, a car body panel and has a first surface 40, a second surface 42, and a sheet thickness Tb. The workpiece 38 can be made of various weldable materials, such as metal or alloys, or other materials.

[0053] The first surface 40 has a connecting section 44. A zinc layer (or other surface layer such as a paint layer, corrosion protection layer, etc.) can, for example, be provided on the second surface 42 of the workpiece 38.

[0054] In a first step, the welding element 10 is positioned in the area of ​​the connection section 44. The projections 26, and in particular a (distal) tip 28 of the projections 26, come into contact with the connection section 44 of the workpiece 38, at least partially. However, the contact zone between the workpiece and the welding element, formed by the tip 28, is distributed across several point contacts and is not continuous. This allows for a better distribution of the compressive force over the entire weld surface during the placement of the welding element 10 onto the workpiece 38. The anchor section 12 extends away from the holding surface 24 of the head 14 of the welding element 10.

[0055] The welding element 10 and the workpiece 38 are each connected to a power source via power lines to receive an electric current. When the projections 26 are arranged or contacted with the connecting section 44 of the workpiece 38, a closed circuit is formed, through which an electric arc can be generated. In such welding processes, a pilot current and a main current are used. The voltage required for the welding process depends on the material of the welding element and the workpiece 38, as well as on the size of the elements.

[0056] First, the welding element 10 is initially placed onto the workpiece 38. With (or after) this placement, the pre-current is ignited. The immediate contact zone between the welding element 10 and the workpiece 38 (i.e., the contact zone between the tip 28 and the workpiece 38) heats up as a result of the current flow. Then, the main current is ignited to begin the melting phase. This prepares the joining zone. The welding element is pressed against the workpiece 38. The joint is formed by crystallization of the molten metal.

[0057] The geometry of the weld surface 22 (i.e., with the protrusions) creates an extension of the weld area. The protrusions allow for good distribution of the welding energy across the entire weld surface. Due to their shape, the molten metal spreads from the tip of the protrusion to its base. The shape of the protrusions ensures a uniform distribution of the molten metal across the entire weld surface and a fairly constant melting depth of the tip. The tips will melt, particularly at the beginning of the welding process. The welding energy will then spread along the longitudinal axis Xa in the direction of the holding surface. The molten metal spreads along the longitudinal axis Xa across the entire weld surface up to the flat plane on which the bases of the protrusions are located. The regularly distributed, pointed protrusions ensure stable arc burning on the weld surface.This prevents uncontrolled arc propagation to the outside.

[0058] The welding process (in particular the welding process parameters such as the required energy and process duration) can be selected such that only the tips 28 (or a specific protrusion height Hv) of the projection 26 are melted. This may be sufficient to create a joint between the welding element 10 (or welding stud) and the workpiece 38 with thin sheet metal without penetration. Alternatively, the welding process (in particular the welding process parameters such as the required energy and process duration) can be selected such that the entire projections 26 and part of the base are melted. The depth of the base that is melted depends on the sheet thickness.

[0059] The thickness of the sheet metal can be, for example, between 0.5 and 3 millimeters. Thin sheets preferably have a thickness between 0.5 and 0.7 millimeters. Thick sheets preferably have a thickness between 0.8 and 2 millimeters. When welding thick materials (sheets), the process energy is increased or the welding time is extended to achieve sufficient melting of the joining partners and thus generate a satisfactory joint.

[0060] A control device is provided to automatically control the parameters of the welding process according to the thickness of the workpiece 38. In particular, the thickness of the workpiece 38 is measured by a sensor and the voltage of a welding machine 46 is controlled by the control device in such a way as to prevent through-welding of the workpiece and to optimize the welding process.

Claims

1. Welding element (10) which is suitable for being connected to a workpiece using an arc welding method, having: - a head (14) with a welding surface (22) and a stop surface (24) facing away from the welding surface (22), - a shaft-shaped anchor section (12) which extends between a first end region (18) and a second end region (20) along a longitudinal axis (Xa), wherein the first end region (18) is connected to the stop surface (24), wherein the welding surface (22) has a plurality of regular, pointed projections (26) distributed over the entire welding surface (22), characterized in that the projections (26) are aligned in parallel rows, wherein the projections (26) are separated by two groups of intersecting grooves (34a, 34b), and wherein the welding element (10) is made of a single material, wherein the material is a material that can be melted by electric arc, so that stable arc burning is ensured on the welding surface.

2. Welding element (10) according to claim 1, wherein the welding surface (22) forms a bulge (36), and wherein the projections (26) are arranged on the bulge (36).

3. Welding element (10) according to claim 2, wherein the bulge (36) has a circular cross-section, and wherein the bulge (36) is centered on the longitudinal axis (Xa).

4. Welding element (10) according to any one of claims 1 to 3, wherein each projection (26) has a pyramidal shape with a square base.

5. Welding element (10) according to claim 4, wherein each projection (26) has four flat lateral surfaces which form a point (28) of the projection (26), and wherein two opposite lateral surfaces (32) are included at an angle (a) between two between 75 and 85 degrees.

6. Welding element (10) according to any one of claims 1 to 5, wherein the projections (26) have a projection height (Hv) of between 0.3 and 1.0 millimeters (mm).

7. Welding element (10) according to any one of claims 1 to 6, wherein the points of two adjacent projections (26) are spaced apart from one another by between 0.5 millimeters and 2.0 millimeters.

8. Welding method for connecting a welding element (10) to a workpiece (38), comprising the following steps: - providing a welding element (10) according to any one of the preceding claims 1 to 7, - providing a workpiece (38) with a first and a second surface (40, 42) and a sheet thickness (Tb), - providing a welding device (46), - arranging the welding surface (22) of the welding element (10) on the first surface (40) of the workpiece (38), - controlling the welding device (46) depending on the sheet thickness (Tb), - welding the welding element (10) to the workpiece (38) by arc welding and by melting at least a part of the projections (26) and pressing the welding element against the workpiece.

9. Welding method according to claim 8, wherein the projections (26) have a specific projection height (Hv) along the longitudinal axis (Xa), wherein the projection height (Hv) to be melted is determined depending on the sheet thickness (Tb).

10. Welding method according to claim 8 or claim 9, wherein the workpiece (38) is provided with a zinc layer on its second surface (42).

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