Method for joining components by means of at least one weld seam

Abstract

Method for joining components (2, 3) by means of at least one weld (S), wherein: - defects in a weld (S) produced by a first laser transmission welding process between two components (2, 3) each formed at least partially from a thermoplastic material are identified; - if at least one defect is present, a second laser transmission welding process is carried out in a post-processing step of the weld (S), wherein at least one laser beam (L) is guided through a region of a first component (2) that is transparent to the laser beam (L) onto the weld (S) located in a contact area of ​​the components (2, 3), and the weld (S), or the weld (S) and the second component (3), or the weld (S) and both components (2, 3) are at least partially melted; - at least after melting, a defined post-processing joining pressure (NF) is applied to the components (2, 3).so that the components (2, 3) are pressed against each other in the molten area and the weld seam (S) and / or the second component (3) are compressed in the molten area by a predetermined post-processing settling distance (NW), - the molten area is cured while maintaining the post-processing joining pressure (NF), wherein in the first laser transmission welding process - the first component (2) is positioned on the further component (3) so that the components (2, 3) touch in the contact area, - subsequently at least one laser beam (L) is guided through the area of ​​the first component (2) that is transparent to the laser beam (L) onto an area of ​​the second component (3) located in the contact area and this area is at least partially melted, - by heat conduction from the molten area of ​​the second component (3) the first component (2) is at least partially melted in the contact area,- at least after melting, a defined joining pressure (F) is applied to the components (2, 3) so that the first component (2) is pressed against the second component (3) in the melted area and at least the second component (3) is compressed in its melted area by a predetermined settling distance (W), - the melted area is cured while maintaining the joining pressure (F), and in post-processing, parameters of the laser beam (L) and / or the post-processing joining pressure (NF) are selected such that the post-processing settling distance (NW) is smaller than the settling distance (W) generated by the joining pressure (F).

Description

The invention relates to a method for joining components by means of at least one weld. The invention further relates to a component arrangement produced by means of such a method. From WO 2015 / 055419 A1, a method for manufacturing a battery casing is known, wherein the method comprises the following steps: providing a battery casing formed from a composite material comprising a thermoplastic polymer matrix and a fiber mat, woven fabric, metal sheet, or metal grid arranged in the thermoplastic polymer matrix; placing a cover on the battery casing; selectively melting a connection area between the battery casing and the cover using a laser beam device; applying mechanical pressure to the cover during the melting process, the pressure pressing the cover against the battery casing; and subsequently solidifying the connection area to join the cover to the battery casing. DE 101 01 240 A1 discloses a method for producing laser-welded composite molded parts, in which a) at least two plastic molded parts are in contact via at least one further molded part, the latter containing a laser-radiation-transmitting material layer on the side facing the direction of incidence of the laser radiation and, connected to or in contact with this layer, a laser-radiation-absorbing material layer, wherein the surface of the material layer in the respective overlap areas with the plastic molded parts is essentially form-fitting, b) laser radiation through the transmitting layer at least in the areas partially or completely strikes the laser-radiation-absorbing layer that overlaps with the molded parts to be joined, c) the distance between the laser-radiation-absorbing layer and the respective molded part surface that essentially covers it in a form-fitting manner,during irradiation with laser light, the temperature is kept substantially constant or reduced, and the areas of the material layer softened or melted by the laser radiation are in contact with the surface of the molded parts for a period of time sufficient to soften or melt these surfaces, and d) the melted or softened areas are allowed to cool. DE 10 2014 009 737 A1 discloses a method for producing a semi-finished product from a semi-finished material having at least one edge. The semi-finished material is melted at least in a section of the edge by means of a heat source, the melted semi-finished material forming a material thickening at the edge. To provide semi-finished products with which a sufficiently high-quality connection between two joining partners can be reliably, and in particular reliably, achieved, the method is characterized in that the material thickening is post-processed to provide a semi-finished product, wherein the solidified and post-processed material thickening has a greater material thickness than the semi-finished material outside the material thickening. US 2017 / 0058860A1 discloses a method for repairing a wind turbine rotor blade. More specifically, in certain embodiments, the rotor blade may consist at least partially of a thermoplastic material reinforced with at least one fiber material. The method thus includes identifying at least one defect on the rotor blade. For example, in certain embodiments, the defects described herein may include a crack, a creep gap, a cavity, a hole, a deformation, a scratch, or any other blade defect. The method also includes applying at least one of the following means: heat, pressure, and / or one or more chemicals to the defect(s) for a predetermined period until the defect is repaired. The invention is based on the objective of specifying a novel method for joining components by means of at least one weld seam and a novel component arrangement produced by means of such a method. The problem is solved according to the invention by a method which has the features specified in claim 1 and by a component arrangement which has the features specified in claim 6. Advantageous embodiments of the invention are the subject of the dependent claims. In the method for joining components by means of at least one weld, defects in a weld produced by a first laser transmission welding process between two components, each formed at least partially from a thermoplastic material, are detected according to the invention. If at least one defect is present, a second laser transmission welding process is carried out in a post-processing step of the weld, wherein at least one laser beam is guided through a region of the first component that is transparent to the laser beam onto the weld located in a contact area of ​​the components, and the weld, or the weld and the second component, or the weld and both components are at least partially melted.At least after melting, a defined post-processing joining pressure is applied to the components, so that the components are pressed against each other in the molten area and the weld seam and / or the second component is compressed by a predetermined post-processing settling distance in the molten area. Subsequently, the molten area is cured while maintaining the post-processing joining pressure. In laser transmission welding, components are welded together using a quasi-simultaneous welding process. The laser beam heats a weld contour almost simultaneously. The concurrently applied joining pressure melts the thermoplastic material, compressing the components to a defined settling depth. Once this settling depth is reached, the joining pressure is maintained briefly to allow cooling in the weld area. This creates a metallurgical bond across the entire joining surface. However, in such a laser transmission welding process, defects can occur in the weld seam due to deviations in the components, for example due to manufacturing tolerances, and / or due to process parameters and / or process conditions and / or damage, which can lead to leaks in the area of ​​the weld seam and in a component arrangement encompassing the components. The present method advantageously and reliably enables the reworking of defective welds, ensuring the aforementioned defects are securely closed. Furthermore, it allows for the enlargement of acceptable height tolerances and the resulting gaps in the weld area between the joining partners. This ensures the tightness of the weld and, consequently, the integrity of the component assembly. The method thus reduces the reject rate in the production of component assemblies, resulting in savings in material, effort, energy, time, and costs. During the reworking process, stresses generated during the remelting of the original weld and the subsequent compression are released and compensated. In the inventive method, in the first laser transmission welding process, the first component is positioned on the second component so that the components are in contact in the contact area. Subsequently, at least one laser beam is guided through the area of ​​the first component that is transparent to the laser beam onto an area of ​​the second component located in the contact area, and this area is at least partially melted. Through heat conduction from the melted area of ​​the second component, the first component is also at least partially melted in the contact area. At least after melting, a defined joining pressure is applied to the components, so that the first component is pressed against the second component in the melted area, and at least the second component is compressed in its melted area by a predetermined settling distance.The molten area is then cured while maintaining the joining pressure. According to the invention, in the post-processing, parameters of the laser beam (L) and / or the post-processing joining pressure (NF) are selected such that the post-processing settling distance (NW) is smaller than the settling distance (W) generated by the joining pressure (F). The laser transmission welding process enables the creation of the weld seam through contactless energy input, without generating any mechanical or oscillating stress on the joining partners. Only a small heat-affected zone is created by the locally limited energy input, thus minimizing thermal stress on sensitive component areas. Furthermore, the welding process does not produce any surface markings and allows for a high degree of design freedom in the components to be welded. The laser transmission welding process is also characterized by its suitability for automation and integration into series production, and it is possible to weld pre-assembled components. Finally, the weld seam is distinguished by its attractive appearance, making it suitable for applications in visible areas. According to the invention, in post-processing, parameters of the laser beam and / or the post-processing joining pressure are selected such that the post-processing insertion path is smaller than the insertion path generated by the initial joining pressure. This minimizes changes in the dimensions of the component arrangement resulting from post-processing. In another possible embodiment of the process, during the curing of the molten area carried out after the first laser transmission welding process, the joining pressure is maintained for a predetermined period in order to allow complete cooling and hardening of the weld seam while minimizing defects. In another possible embodiment of the process, the post-processing joining pressure is maintained for a predetermined period during the curing of the area melted in the post-processing, in order to enable complete cooling and hardening of the reworked weld without defects. In another possible embodiment of the process, the period for maintaining the post-processing joining pressure is chosen to be longer than the period for maintaining the joining pressure. This further minimizes the risk of defects occurring. In another possible embodiment of the process, the post-processing joining pressure is maintained for a period of more than 10 seconds, for example, for 15, 20, 25, or 30 seconds. Such a period has proven particularly effective in minimizing defects within the weld seam. The component arrangement according to the invention comprises at least two components, wherein the components are connected by means of a weld seam that has been post-processed in a previously mentioned method. Due to the post-processing of the weld seam, the component arrangement is media-tight in the area and thus exhibits a minimal leakage rate. In one possible embodiment of the component arrangement, it is designed as a battery housing for an electrical energy storage device, with one component being a lid and the other a housing body closed by the lid. Due to the post-processing of the weld seam, the battery housing is media-tight and thus exhibits a minimal leakage rate, which does not exceed a value of, for example, 5.4 * 10⁻⁵ mbar * l / s. Therefore, it is possible to contain a temperature control medium within the battery housing without any leakage. Because of its tightness and minimal leakage rate, the battery housing advantageously meets the requirements of a helium leakage test necessary for its use. In another possible embodiment of the component arrangement, additional components coupled to openings in the battery housing, such as further covers, media connections, electrical connections, etc., can be reliably and securely coupled to the battery housing using welds produced and finished using the aforementioned method. It is also possible for the components themselves to be manufactured from several sub-elements using this method in a media-tight manner. Exemplary embodiments of the invention are explained in more detail below with reference to drawings. Figure 1 schematically shows a device for joining components by means of at least one weld, Figure 2 schematically shows a sectional view of a section of two components, Figure 3 schematically shows a sectional view of a further section of the components according to Figure 2, Figure 4 schematically shows a sectional view of a section of two components, Figure 5 schematically shows a sectional view of a further section of the components according to Figure 4, and Figure 6 schematically shows a process for joining components by means of a weld. Corresponding parts are marked with the same reference symbols in all figures. Fig. 1 shows a possible embodiment of a device 1 for joining components 2, 3 formed at least partially from thermoplastic material by means of at least one weld seam S produced in a laser transmission welding process and shown in more detail in Fig. 6. The device 1 comprises a scanner optic 1.1-1.2, a bridge plate 1.3, a printing stamp 1.4, a tool carrier 1.5 and a linear drive 1.6. To create the weld seam S, component 2, for example a cover for a battery housing, is arranged together with component 3, for example a housing element for the battery housing, on the tool carrier 1.5 such that components 2 and 3 are already positioned in a desired subsequent position. The pressure die 1.4 is arranged on component 2. The web plate 1.3 is arranged above the pressure die 1.4. For example, the pressure die 1.4 is attached to the web plate 1.3. A joining pressure F, shown in more detail in Fig. 6, is applied to components 2 and 3 by means of the linear drive 1.6, and at least one laser beam L is generated by means of the scanner optics 1.1-1.2. To weld components 2 and 3 together in a quasi-simultaneous welding process, the laser beam L is guided through a transparent area of ​​component 2 onto a region of component 3 in contact with the component 3 that exhibits a high absorption coefficient for the laser beam L, causing this region to melt at least partially. Heat conduction from the melted region of component 3 also melts component 2 at least partially in the contact area. The laser beam L is guided in such a way that it melts a weld contour "almost completely simultaneously." The simultaneously applied joining pressure F causes at least the thermoplastic material of component 3 to melt, thereby compressing component 3 to a defined settling distance W, also shown in Fig. 6.Once the settling distance W is reached, the joining pressure F is maintained for a defined period to allow cooling and hardening of the thermoplastic material in the weld area. Thus, a material-bonded connection is created across the entire joining surface between components 2 and 3 by means of the weld seam S. Component 2, designed as a cover, is welded to component 3, for example, to close an opening formed on the upper side of component 3, which is designed as a housing element for the battery housing. In a manner not shown in detail, a further component, also designed as a cover, can be welded to the housing element in the same way, through an opening formed on the underside of the housing element. Furthermore, other components not shown in detail can also be welded using components 2 and 3 in an analogous manner to the described laser transmission welding process. Figures 2, 3, 4 to 5 show sectional views of sections of different embodiments of components 2, 3 to be welded by means of a laser transmission welding process carried out analogously to the description of Figure 1. Component 2 is transparent to the laser beam L, at least in the contact area with component 3. Component 3 exhibits a high absorption coefficient for the laser beam L in the contact area with component 2. In all embodiments, it is provided that a flat side of component 2 is joined to an end face of component 3 by means of a weld seam S produced in the laser transmission welding process, as schematically illustrated in Fig. 2, Fig. 3, Fig. 4 to Fig. 5. Fig. 6 shows a process of a possible embodiment of a method for joining components 2, 3 by means of a weld seam S. The process can also be applied analogously to the production of weld seams S of other components. In a first process step V1, the components 2, 3 are positioned such that the components 2, 3 touch each other in a contact area. Subsequently, in a second process step V2, a laser transmission welding process is carried out, for example analogously to the description in Fig. 1, whereby the joining pressure F and the power P of the laser beam L are set such that the settling distance W is achieved. The joining pressure F is, for example, 3.5 N / mm² to 5 N / mm², for example, 4 N / mm². The settling distance W is, for example, 0.3 mm to 0.5 mm, for example, 0.4 mm. After reaching the settling distance W, the joining pressure F is maintained for a defined period of, for example, 5 seconds to 7 seconds, for example, 6 seconds, to allow the cooling and curing of the thermoplastic material in the weld area. During the production of the weld seam S, defects may occur in the produced weld seam S due to deviations in the components 2, 3 and / or due to process parameters and / or process conditions and / or damage, which can lead to leaks in the area of ​​the weld seam S and in the component arrangement 5 comprising the components 2, 3. To eliminate these defects, it is necessary to first identify them. This identification can be carried out, for example, using leak tests, such as a helium leak test, or imaging techniques, such as an X-ray procedure. If defects are identified, at least a second laser transmission welding process is carried out in a further process step V3 in a post-processing of the weld seam. For this purpose, the component arrangement 5 is positioned in the same device 1 in which the original laser transmission welding process was carried out. Subsequently, using device 1 in the second laser transmission welding process, at least one laser beam L is guided through the area of ​​component 2 that is transparent to the laser beam L onto the weld seam S located in the contact area of ​​components 2 and 3, so that the weld seam S, or the weld seam S and component 3, or the weld seam S and both components 2 and 3 are at least partially melted. The joining pressure F and the power P of the laser beam L are adjusted such that a post-processing settling distance NW is achieved. The post-processing joining pressure NF is, for example, 3.5 N / mm² to 5 N / mm², for example, 4 N / mm². The post-processing settling distance NW is, for example, 0.15 mm to 0.2 mm, for example, 0.17 mm.After reaching the post-processing settling distance NW, the post-processing joining pressure NF is maintained for a defined period of, for example, more than 10 seconds, e.g., 12 seconds, 15 seconds, or 20 seconds, to allow complete cooling and curing of the thermoplastic material in the weld area. The features and advantages described herein relating to a method for joining components may also apply to the component arrangement described herein and vice versa. Reference symbol list 1 Device 1.1 Scanner optics 1.2 Scanner optics 1.3 Bridge plate 1.4 Pressure stamp 1.5 Tool holder 1.6 Linear drive 2 Component 3 Component 5 Component arrangement F Joining pressure L Laser beam NF Post-processing joining pressure NW Post-processing insertion path P Power S Weld V1 to V3 Process step W Insertion path

Claims

Method for joining components (2, 3) by means of at least one weld (S), wherein: - defects in a weld (S) produced by a first laser transmission welding process between two components (2, 3) each formed at least partially from a thermoplastic material are identified; - if at least one defect is present, a second laser transmission welding process is carried out in a post-processing step of the weld (S), wherein at least one laser beam (L) is guided through a region of a first component (2) that is transparent to the laser beam (L) onto the weld (S) located in a contact area of ​​the components (2, 3), and the weld (S), or the weld (S) and the second component (3), or the weld (S) and both components (2, 3) are at least partially melted; - at least after melting, a defined post-processing joining pressure (NF) is applied to the components (2, 3).so that the components (2, 3) are pressed against each other in the molten area and the weld seam (S) and / or the second component (3) are compressed in the molten area by a predetermined post-processing settling distance (NW), - the molten area is cured while maintaining the post-processing joining pressure (NF), wherein in the first laser transmission welding process - the first component (2) is positioned on the further component (3) so that the components (2, 3) touch in the contact area, - subsequently at least one laser beam (L) is guided through the area of ​​the first component (2) that is transparent to the laser beam (L) onto an area of ​​the second component (3) located in the contact area and this area is at least partially melted, - by heat conduction from the molten area of ​​the second component (3) the first component (2) is at least partially melted in the contact area,- at least after melting, a defined joining pressure (F) is applied to the components (2, 3) so that the first component (2) is pressed against the second component (3) in the melted area and at least the second component (3) is compressed in its melted area by a predetermined settling distance (W), - the melted area is cured while maintaining the joining pressure (F), and in post-processing, parameters of the laser beam (L) and / or the post-processing joining pressure (NF) are selected such that the post-processing settling distance (NW) is smaller than the settling distance (W) generated by the joining pressure (F). Method according to claim 1, characterized in that during the curing of the molten area carried out according to the first laser transmission welding method, the joining pressure (F) is maintained for a predetermined period of time. Method according to one of the preceding claims, characterized in that during the curing of the area melted in the post-processing, the post-processing joining pressure (NF) is maintained for a predetermined period. Method according to claim 3, characterized in that the period of maintenance of the post-processing joining pressure (NF) is selected to be longer than the period of maintenance of the joining pressure (F). Method according to claim 3 or 4, characterized in that the maintenance of the post-processing joining pressure (NF) is carried out for a period of more than 10 s. Component arrangement (5) comprising at least two components (2, 3) wherein the components (2, 3) are connected by means of a weld seam (S) reworked in a method according to one of the preceding claims. Component arrangement (5) according to claim 6, configured as a battery housing for an electrical energy storage device, wherein one of the components (2) is a lid and the other component (3) is a housing body closed by means of the lid.

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