Method for welding a weld part onto a component and use of a weld part

Abstract

Method for welding a weld part (10, 10A) onto a component (30), which is carried out as lift ignition welding with direct current with a pre-current phase (41, 51) in which an arc (L) is formed between the negatively polarized weld part (10, 10A) and the component (30), and a subsequent main current phase (52, 42) for melting material at the joint, where the weld part (10, 10A): a) consisting of a galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, or b) is formed by welding a galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the surface of the sphere is a maximum of 10 micrometers to a connecting element.

Description

[0001] The invention relates to a method for welding a weld part onto a component and the use of a weld part in a welding process.

[0002] German patent application DE 10 2015 211 814 A1 discloses a method for welding a ball onto a component. The method operates on the principle of resistance welding; that is, the ball is pressed onto the component and an electrical voltage is applied, causing an electric current to flow between the ball and the component. As a result, material melts at the point of contact, and the ball is welded to the component.

[0003] If such ball-and-socket joints are to be used in automotive manufacturing, a low tolerance for defects in the joining process is essential. Especially for mass production, it is crucial that the welded joint possesses the necessary strength and can be reliably produced in a reproducible manner. Joining processes in mass production are preferably carried out in automated manufacturing processes. Here, it is desirable that the reliability of the joining process is maintained not only for the welded parts of a single batch but also after a batch change.

[0004] German patent application DE 10 2012 203 217 A1 discloses a method in which a fixing element is welded onto a component. The fixing element has a base that is welded to the component and a functional head projecting from the base, which is formed by at least one spherical element. The base can be in the form of a plate or a plinth. German patent applications DE 10 2013 225 495 A1 and DE 10 2015 209 203 A1 describe further methods for welding a component onto a workpiece.

[0005] Against this background, the object of the present invention is to provide a way in which a ball-component connection can be manufactured in a manner suitable for mass production.

[0006] The problem is solved by a method according to claim 1 and the use of a welded part according to claims 12 and 13. Further advantageous embodiments are described in the dependent claims and the following description.

[0007] The method according to the invention is a direct current (DC) arc welding process in which a workpiece is welded to a component. For this purpose, the workpiece is placed on the component at a joint. In a pre-current phase, a low pre-current is applied, which flows through the workpiece and the component. The workpiece is moved away from the component to a predetermined distance. This results in the formation of a weak arc. The main current phase then follows, in which the pre-current is increased to a main current (welding current). The resulting welding arc causes at least partial melting of the materials of the workpiece and the component. To terminate the process, the workpiece is lowered onto the component or immersed a short distance into the component, and the current is switched off. The molten materials cool to form a metallurgical bond.In direct current arc welding, the direction of current flow is not changed during the process.

[0008] According to the invention, the welded part is negatively polarized. Of central importance for the welding process according to the invention is that the welded part either consists of a galvanized sphere made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere's surface is a maximum of 10 micrometers, or that the welded part is produced by welding such a sphere to a connecting element. Such a welded part consequently includes a spherical segment formed by the galvanized sphere. In the subsequent lift-arc welding process, the weld joint is formed between the component and the sphere, or between the component and the spherical segment of the welded part formed by the sphere.

[0009] If the welded part is formed by welding a galvanized sphere made of C10C with a roundness of G500, where the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, to a connecting element using a welding process, the connecting element can be, for example, a bolt, threaded bolt, rivet or similar.

[0010] In a preferred embodiment, the welded part is a double sphere formed by welding a galvanized sphere made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, to another sphere, preferably of the same type. Various welding processes, such as laser welding or arc welding, can be used to produce the welded part.

[0011] The spheres are made of C10C material, a designation that refers to a quality steel with the material number 1.0214. The chemical composition of the base material is assessed according to DIN EN 10263-2.

[0012] The roundness is specified in accordance with DIN 5401. After the sphere surface has been zinc-plated, it has a roundness of G500.

[0013] Beneath the surface of the sphere formed by the zinc coating, only zinc inclusions with a maximum size of 10 micrometers are permitted. To ensure this, it can be advantageous if the material C10C has a purity grade according to DIN 10247 / 2007-07 / K3 ≤ 15. Furthermore, in a preferred embodiment, it can be advantageous if the spheres have a roundness of G100 and preferably a maximum roughness of Ra = 0.1 and optionally Ra = 0.06 before zinc plating and are subsequently electroplated. The zinc-plated spheres should advantageously also have a core hardness of 220 HV10 ± 30 and a surface hardness of 220 HV10 ± 30.

[0014] During the welding process, a dome-shaped surface of the galvanized sphere or spherical section of the weld part faces the component. It was expected that the arc, moving uncontrollably and randomly across the dome surface, would result in a welding process that was difficult to control. However, trials surprisingly showed that using a weld part as described above in the described DC lift-arc ignition method resulted in a well-controlled welding process characterized by high reproducibility and strength of the weld results.It is assumed that the random movement of the arc across the dome-shaped surface of the workpiece, in conjunction with the direction of the welding current, the roundness and base material of the sphere, and the limitation of the size of the zinc inclusions, leads to a particularly complete and spatter-free zinc burn-off without explosive zinc eruptions and to uniform melting of the base material, which in turn increases the strength of the weld. The quality of the welding results was also demonstrated in tests with spheres from different production batches. As long as the spheres met the requirements described above, an adjustment of the welding parameters after a batch change was either unnecessary or only required to a minimal extent. This makes the described welding process particularly suitable for (large-scale) series production in vehicle manufacturing.

[0015] The described beneficial effect can be observed more strongly when the zinc layer thickness of the galvanized sphere is in the range of 6 to 12 micrometers. Using spheres with this zinc layer thickness, welded joints with a strength sufficient to meet the requirements of vehicle construction could consistently be produced.

[0016] The welded parts can, in principle, be welded onto any component whose material composition makes it suitable for welding to the galvanized ball described above. However, it is particularly preferred to weld the parts onto a sheet metal component, and especially onto a steel sheet component. Steel sheet components also include those made from steel sheets with a corrosion-resistant coating, such as galvanized steel sheets. The steel sheets preferably have a thickness in the range of 0.5 mm to 3 mm.

[0017] The components are preferably body parts of a motor vehicle, although the method and its use are not limited to such components. The welded parts attached to the component can subsequently be used, for example, for aligning, temporarily fixing, or permanently attaching other components, such as body (add-on) parts.

[0018] The lift-ignition welding process can be carried out using a lift-ignition welding device known to those skilled in the art. In one embodiment, the lift-ignition welding is performed such that a single main current value is specified during the main current phase. More precisely, the welding current is increased to the specified main current value at the beginning of the main current phase and only reduced again at the end of the welding process. The main current phase lasts for a predetermined welding time. This process is hereinafter referred to as "single-phase main current welding" and can be particularly advantageous for welding components to parts with a thickness in the range of 0.7 mm to 1.5 mm or for welding double spheres to parts.

[0019] For welding components consisting of the sphere described above, a process has proven particularly advantageous in which the main current phase comprises three successive main current sub-phases, each using different main current values. The pre-current phase is followed by a first main current sub-phase in which a first main current value is set. This is followed by a second main current sub-phase in which a second main current value, lower than the first, is set. The second main current sub-phase is followed by a third main current sub-phase in which a third main current value is set, lower than the first and higher than the second.

[0020] The three main current phases each have different tasks. In the first main current phase, a relatively high current value is used to vaporize the zinc and any zinc inclusions that may be present in the sphere. This happens relatively quickly, so the welding time for the first phase can be kept short.

[0021] To prevent overheating of the melt forming in the base materials during the first main current phase, the first main current phase is followed by a second main current phase with a low second main current value. However, the second main current value is still significantly higher, for example, by a factor of 2, than the pre-current value from the pre-current phase. Overheating can be avoided if this second phase has only a short duration. In the subsequent third main current phase, the necessary welding energy for the weld is applied. Accordingly, the main current value is increased again, although not to the value of the first main current phase. The third main current phase has the longest duration of the three main current phases.

[0022] For welding processes with three main current phases, it has proven particularly advantageous if the first, second, and third main current values ​​and the corresponding durations of the phases lie within the value ranges described below. These values ​​refer to a reference main current value and a reference time. The reference main current value indicates the main current value, and the reference time indicates the welding time, that would be determined and used for a single-phase welding process of the same weld part and component to achieve a proper weld. Compared to these reference values, the first main current value should preferably be 130% to 150%, and particularly 140%, of the reference main current value, and the duration of the first main current phase should preferably be 10% to 15%, and particularly 12.5%, of the reference time.The second main current value should preferably be 23% to 43% and particularly 33% of the reference main current value, and the duration of the second main current sub-phase should preferably be 10% to 15% and particularly 12.5% ​​of the reference time. The third main current value should preferably be 70% to 90% and particularly 80% of the reference main current value, and the duration of the third main current sub-phase should be 50% to 70% and particularly 60% of the reference time.

[0023] Such a process with three main current partial phases achieves excellent results for (steel) sheets with a thickness of up to 0.7 mm in the thin sheet range and from 1.5 mm in the thick sheet range, which are better rated in terms of strength and reproducibility than comparable welds with a "single main current phase welding".

[0024] Furthermore, the use of a galvanized sphere made of C10C with a roundness of G500, as described above, wherein the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, is specified in the described method for lift ignition welding.

[0025] The use of a welded component in the aforementioned method is also described. This component is formed by welding a galvanized sphere made of C10C, as described above, with a roundness of G500, where the size of any zinc inclusions below the sphere's surface is a maximum of 10 micrometers, to a connecting element. The connecting element can be, for example, a bolt, threaded stud, or rivet. In particular, the connecting element can be another galvanized sphere made of C10C, as described above, with a roundness of G500, where the size of any zinc inclusions below the sphere's surface is a maximum of 10 micrometers.

[0026] Further advantages, features and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings.

[0027] The features mentioned in the claims and the description can be essential to the invention, either individually or in any combination. Where the term "can" is used in this application, it refers to both the technical possibility and the actual technical implementation.

[0028] The following are examples of implementation explained with reference to the accompanying drawings. These show: Fig. 1 and Fig. 2 schematic representations of welded parts that are welded onto a component using lift-arc welding. Fig. 3 exemplary welding characteristic curves for carrying out the process.

[0029] Fig. 1 and Fig. Figures 2 each show a weld part 10 which is received in a lifting ignition device 20 for use in the method.

[0030] First, the welding part 10 is placed onto a component 30 using the lifting ignition device 20. The component 30 can, for example, be a sheet steel component for a motor vehicle. The welding part 10 and the component 30 are connected to a welding power source (not shown), with the welding part 10 being negatively polarized. The welding part 10 is then lifted from the component 30 using the lifting ignition device 20, while a pre-current is passed through both, causing an arc L to ignite. In the subsequent main current phase, the current flowing between the welding part 10 and the component 30 is increased. As a result, the base material of the component 30 and the welding part 10 melts. After a predetermined welding time, the welding part 10 is lowered again and pressed into the molten metal. After cooling, a metallurgical bond is formed.

[0031] According to Fig. 1 is used as weld part 10 a galvanized ball 1 made of C10C with a roundness G500, wherein the size of any zinc inclusions below the surface of the ball is a maximum of 10 micrometers. Fig. Figure 2 shows another welded part 10A in the form of a double sphere, which is formed by welding a galvanized sphere 1 made of C10C with a roundness of G500, where the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, to a second such sphere 1. Other alternative welded parts, not shown, can be formed, for example, by a sphere 1 welded to a connecting element, such as a bolt, threaded stud, or rivet. In each case, the welding between the welded part and the component is carried out in such a way that the sphere 1 is placed onto the component.

[0032] Fig. Figure 3 shows two exemplary welding characteristic curves 40, 50 of lift-arc welding for welding a weld part 10, which consists of a sphere 1, to the component 30. The diagram represents the welding current I over time t.

[0033] The welding characteristic curve 40 shown in dashed lines in Fig. 3 describes a welding process as it relates to Fig. 1 is described. Such a welding process, referred to in this application as a “single-phase welding process”, has, following a pre-phase 41, a main phase 42 with a single main current value IH, which is constant for the duration of the main phase 42.

[0034] The welding characteristic curve designated with reference numeral 50 is particularly suitable for welding the sphere 1 to a thin sheet of 1.5 mm thickness or less. Fig. 3. This process is characterized by the fact that the main current phase 52 is divided into three main current sub-phases 53, 54 and 55, in which welding is carried out with different main current values ​​IH1, IH2, IH3.

[0035] After a preliminary phase 51, the current is increased to a first main current value IH1 in a first main current sub-phase 53. In the subsequent second main current sub-phase 54, the main current is reduced to a second main current value IH2, which, however, is still higher than the value of the preliminary phase IV. In the last, third main current sub-phase 55, the current is increased again, with the third main current value IH3 lying between the first main current value IH1 and the second main current value IH2. The first and second main current sub-phases 53 and 54 each last only a very short time; the energy input for melt formation occurs mainly in the third main current sub-phase 55, which accordingly lasts a longer time.

[0036] In Fig.Figure 3 further specifies the welding durations of the entire main current phase for "single-main-phase welding" (characteristic curve 40, reference numeral t40) and for welding with three main current sub-phases (characteristic curve 50, reference numeral t50). If the welding time t40 and the main current value IH of characteristic curve 40 are considered as reference values, the first main current value IH1 should preferably be 130% to 150% and particularly 140% of the reference main current value IH, and the duration t1 of the first main current sub-phase 53 should preferably be 10% to 15% and particularly 12.5% ​​of the reference time t40. The second main current value IH2 should preferably be 23% to 43% and in particular 33% of the reference main current value IH, and the duration t2 of the second main current sub-phase 54 should preferably be 10% to 15% and in particular 12.5% ​​of the reference time t40.The third main current value IH3 should preferably be 70% to 90% and in particular 80% of the reference main current value IH, and the duration t3 of the third main current sub-phase 55 should be 50% to 70% and in particular 60% of the reference time t40. Reference symbol list 1 ball 10, 10A welding part 20 Lift ignition welding device 30 components 40 Welding characteristic curve 41 Pre-current phase 42 Main current phase 50 Welding characteristic curve 51 Pre-current phase 52 Main phase 53, 54, 55 Main current sub-phases I current IH, IH1, IH2, IH3 Main current value IV Lead-current value t time t1, t2, t3 Duration of main current partial phase t40, t50 Welding duration of the main current phase

Claims

[1] Method for welding a weld part (10, 10A) onto a component (30) by direct current arc welding with a pre-current phase (41, 51) in which an arc (L) is formed between the negatively polarized weld part (10, 10A) and the component (30), and a subsequent main current phase (52, 42) for melting material at the joint, where the weld part (10, 10A): a) consisting of a galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, or b) is formed by welding a galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the surface of the sphere is a maximum of 10 micrometers to a connecting element. [2] Method according to claim 1, wherein the welded part (10A) is designed as a double sphere by welding a galvanized sphere (1) made of C10C with a roundness G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, to a second such sphere (1). [3] Method according to claim 1 or 2, wherein the material C10C of the galvanized sphere (1) has a purity level according to DIN 10247 / 2007-07 / K3 ≤ 15. [4] Method according to one of claims 1 to 3, wherein the galvanised sphere (1) is a sphere which has a roundness of G100 before coating to form the zinc layer. [5] Method according to one of the preceding claims, wherein the thickness of the zinc layer of the zinc-plated sphere (1) is in the range of 6 to 12 micrometers. [6] Method according to one of the preceding claims, wherein the component (30) is a sheet steel component. [7] Method according to one of the preceding claims, wherein the component (30) is a body component of a motor vehicle. [8] Method according to any one of claims 1 to 7, wherein a single main current value (IH) is specified during the main current phase (42) and the main current phase lasts for a specified welding time (t40). [9] Method according to any one of claims 1 to 7, wherein the welded part (10) consists of the galvanized ball (1) and the main current phase (52) has three successive main current sub-phases (53, 54, 55), where in the first main current sub-phase (53) a first main current value (IH1) is specified, in the second main current sub-phase (54) a second main current value (IH2) is specified that is reduced compared to the first main current value (IH1) and In the subsequent third main current sub-phase (55) a third main current value (IH3) is specified, which lies between the first main current value (IH1) and the second main current value (IH2). [10] Method according to claim 9, wherein - the first main current value (IH1) is 130% to 150% and in particular 140% of a reference main current value (IH) and the duration of the first main current sub-phase (53) is 10% to 15% and in particular 12.5% ​​of a reference time (t40), - the second main current value (IH2) is 23% to 43% and in particular 33% of the reference main current value (IH) and the duration (t2) of the second main current phase (54) is 10% to 15% and in particular 12.5% ​​of the reference time (t40), and - the third main current value (IH3) is 70% to 90% and in particular 80% of the reference main current value (IH) and the duration (t3) of the third main current phase is 50% to 70% and in particular 60% of the reference time (t40), wherein the reference main current value (IH) and the reference time (t40) correspond to the main current value and the welding time that would be specified for welding the same weld part (10) with the same component (30) in a method according to claim 6. [11] Method according to claim 9 or 10, wherein the component (30) is a thin sheet with a sheet thickness of 0.7 mm or less or a thick sheet with a sheet thickness of 1.5 mm or greater. [12] Use of a welding part (10) in a lift-arc welding process according to one of the preceding claims, wherein the welding part (10) consists of a galvanized sphere (1) made of C10C with a roundness G500, wherein the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers. [13] Use of a weld part (10A) in a lift-arc welding process according to any one of claims 1 to 8, wherein the weld part (10A) is formed by welding a galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers, to a connecting element, in particular to another galvanized sphere (1) made of C10C with a roundness of G500, in which the size of any zinc inclusions below the sphere surface is a maximum of 10 micrometers.

Images