METHOD FOR PRODUCING A GAP-FREE AND STRENGTH-FITTING JOINT

Description

[0001] The invention relates to a method for producing a gap-free and force-fit connection between at least three individual metallic components. Such methods are used, for example, for joining segments or laminations of electrical, electromechanical, or electrochemical assemblies such as laminated cores for stators or rotors, or electrochemical cells.

[0002] Several methods for creating a force-fit connection are generally known. Laser welding involves seam welding at an abutment edge. However, the melting of the material leads to high temperature input and thus to a metallurgical change in the base material. The weld bead must be removed in an additional, separate step.

[0003] Consistently high quality is not achievable with ultrasonic welding due to the large and often asymmetrical or curved surface area. Bonding requires a complex process involving surface cleaning, dispensing, assembly, and curing. Furthermore, limitations arise regarding operating temperature and strength.

[0004] The solderless melting of the base materials by external heat supply using inductive or ohmic sources in resistance welding leads to very high temperature input and thus to metallurgical and mechanical changes in the base materials.

[0005] When soft soldering, tin-containing soft solder requires a low melting temperature. However, low strength and low service temperature impair its usability.

[0006] The eutectic high-temperature solder used in brazing melts at temperatures far below the melting point of the components being joined. Energy is preferably supplied by induction or Jouleian / ohmic heating. Brazing is the preferred method because it is proven in series production, can be used flexibly, and meets the required joint strength. However, the brazing alloy forms a thin, undefined gap between the components being joined. Silfos, a silver brazing alloy, can be used as a brazing alloy, for example.

[0007] From DE 195 12 089 C1, it is known to introduce a solder component into a cavity between the formable sheet metal parts to be joined. For joining, the sheet metal parts to be joined are formed under high pressure, and the solder component is brought into a molten state by electrical resistance heating using applied electrodes. The forming processes result in undefined surfaces on the sheet metal parts to be joined. Therefore, a gap-free joining cannot be achieved with this method.

[0008] Although US 2019 / 0363313 A1 discloses a cleaning process in the area of ​​the materials to be soldered before the actual soldering process, it does not suggest a gap-free connection.

[0009] The DD 274 775 A1 specification does reveal soldering surfaces with recesses. However, these grooves or solder deposits are completely filled with solder after soldering has been completed. A defined, gap-free joining is therefore not possible.

[0010] Another similar solution is shown in DE 31 07 665 A1.

[0011] The invention is based on the objective of enabling a mechanically strong and tightly toleranced connection of individual components without bending, warping or deformation in a method for producing a gap-free, tight, chemically resistant and force-fit connection of the type mentioned above.

[0012] The problem is solved according to the invention for a method of the type mentioned at the outset by the features specified in claim 1. Advantageous embodiments are specified in the dependent claims.

[0013] By means of the sequence of process steps according to claim 1, a force-fit, liquid- and gas-tight connection between two or more metal surfaces is obtained in a simple manner. Furthermore, by utilizing proven technologies through the combination of laser and ohmic heating, standard production equipment can be used. Instead of the ablation processes mentioned in step S1 according to claim 1, the recesses can also be created during the casting of the individual components.

[0014] It has proven advantageous to perform the processing of the soldering zones according to step S1 of claim 1 and / or the processing of the surface of the individual components according to claim 1 using a laser. These process steps can be completed in a single process through laser-assisted engraving of the recesses and subsequent surface pretreatment and cleaning.

[0015] Alternatively, the processing of the soldering zones according to step S1 according to claim 1 and / or the processing of the surface of the individual components according to claim 1 can also be carried out according to the invention by means of a mechanical device or by selective electroplating. In the case of mechanical removal or selective electroplating, a thin layer of a solderable material can advantageously be applied to the removed surface so that subsequent soldering can be carried out optimally.

[0016] It has proven advantageous to process the soldering zones according to step S1 according to claim 1 and / or to process the surface of the individual components according to claim 1 on one or both sides.

[0017] It is commendable that the creation of depressions in the area of ​​the soldering zones according to step S1 according to claim 1 is carried out in a trench design and / or groove design.

[0018] An advantage is that the recesses in the groove design have grooves and ridges that are arranged opposite each other, possibly offset.

[0019] Advantageously, the recesses in the groove design can have grooves and ridges of different widths and / or depths.

[0020] It is noteworthy that the application of the brazing component according to step S2 according to claim 1 can be carried out by means of screen printing, stencil printing or dispensers or as a molded part.

[0021] It has proven advantageous to have transverse laser-cut grooves on the webs for better melt distribution.

[0022] It has proven effective to choose the surface area ratio between individual components and the brazing part in such a way that, during brazing, the temperature of the base material of the individual components remains below the threshold critical for the application, so that, for example, no deformation of the base materials occurs.

[0023] Advantageously, the recesses can be arranged axially, concentrically and / or radially.

[0024] A commendable feature is the method of securing the brazed part by squeezing the excess brazing material into lateral overflow channels.

[0025] The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. The drawing shows: Figure 1: Arrangement for creating gap-free solder joints according to the invention between several aligned metal components; Figure 2: Enlarged view of detail D of the Figure 1 Figure 3 shows a representation extended to include current paths. Figure 2Figures 4 and 5 show a soldering zone for processing a component stack according to the trench design, Figures 6 to 9 show soldering zones for processing a component stack according to the groove design, Figures 10 to 13 show soldering zones for coaxial processing of a component stack, and Figures 14 and 15 show soldering zones for radial processing of a component stack.

[0026] In the Figure 1A component stack 1 consisting of four metallic individual components 2 is shown, which are provided with surface layers 3, for example, surface contaminants or protective layers. In the area of ​​the solder joints to be produced, the solder zones 4, these surface layers 3 were removed, as described below. In these solder zones 4, recesses 5 were also formed in the individual components 2. Brazing elements 6 are arranged between the individual components 2 in the recesses 5, which keep the individual components 2 at a distance. Such a solder zone 4 is shown as detail D in the Figure 2 Shown enlarged.

[0027] Component stack 1 is calculated according to Figure 1The components are held together in the desired position by two electrodes 7. The electrodes 7 also serve as electrical contacts for the regulated electrical energy source 9, which can be current-, voltage-, or power-regulated. The brazing elements 6 are located in the soldering zones 4, which have been processed, for example, by a laser. In the base material of the individual components 2, the current I supplied via the electrodes 7 is distributed over the entire cross-sectional area A of the base material. In the brazing elements 6, the current is only conducted over the narrow brazing cross-section. This is illustrated by the current paths 10.

[0028] In the Figure 3 Detail D, with the labeled current paths 10, is now shown enlarged. A current I1 flows through the cross-sectional area A1 of the upper component 2. A current I2 flows through the brazing element 6 with a cross-sectional area A2. A current I3 flows through the cross-sectional area A3 of the lower component 2.

[0029] As can be seen from the heating formula, this area ratio, in addition to the material properties Hx, is the decisive factor for the different heating of the base materials of the individual components 2 and the brazing alloy 6. A full-surface brazing foil would therefore, on the one hand, result in an undesirably high heating of the base material and, on the other hand, require a very high current.

[0030] In typical applications, a very short and high current pulse is used. This achieves rapid heating of the soldering zones 4, which leads to the melting of the hard solder parts 6 and the soldering, before the heat dissipates again via the base material of the individual components 2 and the electrodes 7.

[0031] The heating formula "heating ΔTx" describes the dependence of the heating of an arbitrary metal layer on the flowing current Ix, the conductor cross-section Ax, the duration tx, and the material factor Hx. Since the material factor is determined by the material selection, and the current should be as high as possible and the duration as short as possible, simple optimization can be achieved by the contact area of ​​the brazing alloy. The reproducible width of the grooves 15 and webs 16 is of great importance for the repeatability of the welding process. Without these limits, the brazing alloy spreads more or less undefined, and the welding process is subject to a large variation, as is known from the aforementioned prior art. Erwärmung Delta Tx = Ix ∧ 2 * Hx * tx / Ax ∧ 2

[0032] The formula for the ratio of the heating of two materials illustrates this. In the given pairing, with a full-surface solder foil, the area ratio would be 1:1. Therefore, at a solder melting temperature of 800°C, the temperature of the base material would rise to at least 400°C. With an area ratio of 1:10, the base material remains at room temperature. It will heat up due to heat flow from the soldering zone, but within the permissible range. Verhältnis Delta T = I 1 ∧ 2 * H 1 * t / A 1 ∧ 2 / I 2 ∧ 2 * H 2 * t / A 2 ∧ 2 = H 1 * A 2 ∧ 2 / H 2 * A 1 ∧ 2 = 207 : 1 d . h . Lotmaterial erwämt sich ∼ 200 mal stärker als Basismaterial for A1 / A2 = 10 , H1 = 28 (iron) , H2 = 58 (silfos) with A1 = Area of ​​base material (top) A2 = Area of ​​brazing part 6 A3 = Area of ​​base material (bottom) I1 = Current through base material (top) H1 = Coefficients of base material (top) I3 = Current through base material (bottom) I2 = Current through brazing part 6 H2 = Coefficients of brazing part 6 H3 = Coefficients of base material (bottom)

[0033] Magnetic materials lose certain physical properties when the Curie temperature is exceeded. At approximately 400°C, scaling (Fe₂O₃) begins in ferrous materials. Even higher temperatures lead to changes in the material's microstructure.

[0034] The individual components 2 can be soldered sequentially or in parallel. This means that the component stack 1 is built up component by component, or that the component stack 1 is created and joined simultaneously in a single welding operation, as is done in the Figure 1 is shown.

[0035] In addition to double-sided laser processing, other combinations such as single-sided engraving and / or cleaning are also possible. However, a loss of quality is to be expected with a single-sided cleaning step.

[0036] The surface of the individual components 2 to be joined is, due to the preceding processes, covered with thin surface layers 3, a contamination layer often detectable only with special analytical methods. In addition to the known oxide layers, layers or spots containing sulfide, carbon-containing, and / or halogen-containing compounds are also found. In some applications, the surface layers 3 of the individual components 2 are specifically protected with nitride layers or lacquer / adhesive layers. All these layers negatively affect solderability. The use of fluxers is only effective in the case of oxides.

[0037] In addition to purely mechanical pretreatment methods, the use of a laser is recommended here. With a laser, the cleaning of the surface layers 3, the engraving of the recesses 5, and the marking can be carried out in a single process step in the soldering zones 4.

[0038] For surface treatment of metals, wavelengths are required that lead to partial or complete absorption of the laser light in the base material. Generally, short-wavelength radiation is more suitable than long-wavelength radiation. However, when iron is used as the base material for the components, a CO₂ laser with a wavelength of approximately 10 µm is also well-suited.

[0039] The beam power can be applied continuously or in pulses. Overall, the wavelength, laser pulse duration, peak power, beam cross-section, beam velocity, and Raleigh length play an important role in the dimensioning.

[0040] Depending on these parameters, the surface layers 3 of the individual components 2 can be cleaned, roughened and / or engraved. To achieve a gap-free solder joint, the cross-sectional area of ​​the recesses 5, the engraving, is selected so that the molten solder fits completely within them.

[0041] In summary, the following advantages are achieved through the prior laser processing of the soldering zones: Removal of surface contaminants or protective layers, control of the direction of spread of the solder melt, complete absorption of the molten solder in the trenches or grooves, reproducible surfaces and thus uniform soldering conditions, and defined contact surface through the shaping of the ridges.

[0042] The width and depth of the laser ablation for creating the recesses 5 are calculated so that the solder material fits completely within the recesses 5, whether on one or both sides. Only a small circumferential border forms the tolerance volume or tolerance space 17 for compensating for dimensional variations of the solder material and the grooves. The height of the solder material is chosen so that the two components are sufficiently spaced apart to prevent a short circuit during the formation of the melt phase. As already described, heating therefore takes place throughout the entire solder wire and, on the component side, in the recesses 5 of the soldering zones 4.

[0043] Typically, the engraving can be executed as a groove or a grooved zone. The grooved design offers an enlarged wetting zone across the side wall of the webs and therefore allows for higher tensile and shear forces.

[0044] Because the current flows through precisely manufactured ridges in the groove design, the contact area is defined very accurately and reproducibly. This also means that the heat generation, which depends on the contact area, is also defined very accurately and reproducibly.

[0045] The angled surface is created by reducing the laser energy input. Therefore, significantly less weld bead is to be expected there. This bead is formed as molten residue when the base material of the component is removed.

[0046] In accordance with the state of the art, an ultrashort pulse laser with pulse widths in the range of ps (picoseconds) or fs (femtoseconds) should be used.

[0047] The brazing alloy can be applied technically as a pre-formed part using a handling system, or as a paste or powder using a dispenser, stencil printer, or screen printer. Adding flux material can improve solderability. It is advantageous if the pre-formed part is pressed into the groove / trough in a separate step so that it is securely anchored and cannot be displaced during subsequent steps. Spot welding of the brazing alloy onto the base material in a separate step is also suitable. The position of the pre-formed part during the welding process is crucial for quality. For safety, the pre-formed part can be monitored inline using a scanner or camera system.

[0048] The positioning of the ridges and grooves moves the molten solder during the melting process and forces it into the grooves. This strengthens the metallurgical bond in the interface zone and thus increases its strength.

[0049] Transverse channels between the grooves allow process gases and trapped air to escape.

[0050] For the production of the depressions 5, the trench design and the groove design are suitable. Based on the Figures 4 and 5 The trench design of depressions 5 will now be explained in more detail.

[0051] A wide groove 11 in the lower component 2 serves to receive the solder. The brazing element 6 is placed on the bottom of the lower groove 11. The volume of the brazing element 6 is smaller than the total volume of the grooves 11. Since the cross-section of the brazing element 6 is also smaller than the cross-section of the grooves 11, the brazing element 6 projects upwards beyond the lower component 2. The upper component 2 is positioned on the assembly such that contact occurs only in the area of ​​the brazing element 6 and the grooves 11. A lateral slope 12 of the groove 11 prevents a molten bead from forming if the material does not completely vaporize during the soldering process. After completion of the soldering process, both components 2 are positioned as described above. Figure 5The components are flush against each other. An interface zone 13 has formed between the solder and the base material in the grooves 11. Lateral, solder-free tolerance spaces 14 serve to compensate for the volume of the solder. Only the surface in the area of ​​the bottom of the groove 11 is wetted. The groove 11 can be formed on one side only on a single component 2 or, as shown, on both sides.

[0052] In the Figures 6 to 9 Various versions of the groove design are shown. Figure 6Figure 1 shows a groove design with offset ridges before soldering. The individual components 2 are provided with several grooves 15 in the soldering zones to receive the solder, which are separated from each other by ridges 16. At least two grooves 15 must be provided laterally as tolerance space 14 for the solder melt. The tolerance space 14 serves to receive the solder that is not required to fill the grooves 15. The lateral chamfer 12 of the outer grooves 15 prevents a bead of melt if the base material should not completely vaporize during material removal.

[0053] On the webs 16, transverse, laser-cut grooves (recesses) can be formed by means of ridges 17, acting as flow channels for the solder, which lead to a better distribution of the solder in the grooves 15. Process gases can also escape to the outside via these transverse grooves.

[0054] The component stack 1 is now formed such that the brazing elements 6 lie on the webs 16 or on the ridges 17 of the individual components 2, so that contact only occurs in the area of ​​the brazing elements 6 and the webs 16. Thus, heat of fusion is generated only there.

[0055] After the soldering process, both individual components 2 are positioned according to Figure 7 The parts fit together without gaps. The interface zone 13 between the solder and the base material has formed in the grooves 15. The lateral solder-free tolerance spaces 14 serve to compensate for the volume of the solder. The entire surface in the area of ​​the grooves 15 and the webs 16 is wetted.

[0056] A groove-like engraving instead of a trench 11 offers the advantage of increasing the wettable surface area of ​​the base material. Various configurations are possible. The ridges 16 are positioned opposite each other, or the ridge 16 of one component 2 is located within the grooves 15 of the other component 2. In contrast to conventional brazing systems, the contact area is precisely defined by the ridge / groove design.

[0057] In the Figures 8 and 9 A groove design with opposing ribs 16 is now shown. The state before soldering is shown. Figure 8 , in which the brazing components 6 to be melted are arranged between the individual components 2 on the webs 16. After the melting process already described, the following is formed in Figure 9The shown condition is one in which the interface zone 13 between solder and base material has formed in the grooves 15, while the tolerance spaces 14 have remained free laterally.

[0058] In the Figures 10 and 11 A component stack 1 with round individual components 2 is shown, which undergo axial laser processing. The solder zone 4 is designed coaxially. The number and width of the grooves are determined by the overall design. The entire solder zone 4 determines the durability and strength of the solder joint. Figure 11 shows a cross-section through component stack 1 along line AA.

[0059] The disc-shaped individual components 2 are provided with round bores 18. The soldering zone 4 is annular and arranged at a short distance from the edge of the disc. In this case, the component stack 1 consists of three individual components 2, which are separated by the hard solder parts 6 resting on the soldering zones 4. As detail E, the soldering zone 4 is pre-drilled before soldering. Figure 12 shown. Here it becomes clear that the brazed parts 6 rest on the webs 16. The Figure 13 The image now shows the same area after the soldering process, with the individual components 2 touching without gaps. The grooves 15 are filled with solder except for the tolerance spaces 14 in the interface zone 13.

[0060] The Figures 14 and 15 Figure 1 shows a component stack whose soldering zone 4 is arranged radially. Here too, the number and width of the soldering zones 4, and thus the engraving zones, are determined by the overall design.

[0061] The individual components 2, which are also provided with bores 18, have solder zones 4 arranged between the bores 18, pointing radially outwards. Figure 15 Figure 1 shows the component stack 1 in cross-section along line BB. The component stack 1 also consists of three individual components 2, which are separated by the hard solder parts 6 resting on the webs 16 of the soldering zones 4. The details correspond to those shown in the figure below. Figures 12 and 13 described training programs.

[0062] Any number of variations can be derived from these basic shapes. The alignment and fixing of the individual components 2 can be carried out in axial, radial, and rotational directions.

[0063] The soldered area is crucial for achieving the required strength. The ratio of the conductor cross-sections of component 2 to the brazing element 6 is important for the heating of the individual component 2.

[0064] In summary, it can be stated that the inventive method described above enables a force-fit, gap-free, tightly toleranced connection of individual components, in which the width of the trenches, ridges and grooves determines the contact zone and thus the durability and strength of the soldered joint.

[0065] Even when joining individual components using other joining techniques, e.g., soft soldering or gluing, the recesses can serve to hold the soft solder or adhesive, so that gap-free joining of individual components is possible even with these joining techniques. Reference symbol list

[0066] 1 Component stack 2 Individual components 3 Surface layers 4 Soldering zones 5 Recesses 6 Brazing component 7 Electrodes 8 Contact pressure 9 Energy source 10 Current paths 11 Trench 12 Slope 13 Interface zone between solder and base material 14 Tolerance space 15 Grooves 16 Ridges 17 Beads 18 Holes

Claims

1. A method for producing a gap-free and non-positive connection between at least three metallic individual components (2), having the following steps: S1creating depressions (5) in the region of soldering zones (4) of at least one individual component (2),S2applying at least one hard solder part (6) in the depressions (5) of at least one of the individual components (2) forming part of the soldered connection,S3fixing the individual components (2) to be connected,S4applying electrodes (7) to the component stack with an adjustable contact pressure (8),S5applying electrical energy to the electrodes (7) for transferring the hard solder parts (6) into a molten state under contact pressure (8) by electrical resistance heating by means of the electrodes (7),S6adjusting the electrodes by applying pressure until the at least three individual components have the predetermined connection,S7interrupting the energy between the two electrodes (7),S8cooling and hardening the solder parts formed andS9relieving pressure from the electrodes (7), characterized in that depressions (5) are created in the region of soldering zones (4) of at least one individual component (2) according to step S1 by an ablation process, in that before step S2 the surface of the individual components (2) is treated at least in the region of the soldered connections to be produced in the soldering zones (4) for the removal of surface layers (3) which are different from the base material, and in that during step S2, for forming a tolerance space (14), the volume of the hard solder part (6) or the sum of the volumes of the hard solder parts is less than the sum of the volumes of the depressions (5) of a soldered connection and in that the at least one hard solder part (6) is arranged in the depressions (5) such that the at least one hard solder part (6) holds the individual components (2) at a distance.

2. The method according to Claim 1, characterized in that the treatment of the soldering zones (4) according to step S1 and / or the treatment of the surface of the individual components (2) is carried out by means of a laser.

3. The method according to Claim 1, characterized in that the treatment of the soldering zones (4) according to step S1 and / or the treatment of the surface of the individual components (2) is carried out by means of a mechanical device or by selective galvanic etching.

4. The method according to Claim 3, characterized in that, during the mechanical ablation or during the galvanic etching, a thin layer of a solderable material is applied to the ablated surface so that it can be subsequently soldered in an optimal manner.

5. The method according to one of Claims 1 to 4, characterized in that the treatment of the soldering zones (4) according to step S1 and / or the treatment of the surface of the individual components (2) is carried out on one side or on both sides.

6. The method according to one of Claims 1 to 5, characterized in that depressions (5) are created in the region of the soldering zones (4) according to step S1 in a trench design and / or groove design.

7. The method according to Claim 6, characterized in that in the groove design the depressions (5) have grooves (15) and webs (16) which are arranged opposingly or optionally offset.

8. The method according to Claim 6 or 7, characterized in that in the groove design the depressions (5) have grooves (15) and webs (16) of a different width and / or depth.

9. The method according to one of Claims 1 to 8, characterized in that the application of the hard solder part (6) according to step S2 is carried out by means of screen printing, stencil printing or a dispenser or as a moulded part.

10. The method according to one of Claims 7, 8 or 9, when Claim 9 is dependent on one of Claims 7 or 8, characterized in that transversely running laser-cut furrows are provided on the webs (16) for improved melt distribution.

11. The method according to one of Claims 1 to 10, characterized in that the surface ratio between the individual components (2) and the hard solder part (6) is selected such that during brazing the temperature of the base material of the individual components (2) remains below the critical threshold for the application.

12. The method according to one of Claims 1 to 11, characterized in that the depressions (5) are arranged axially, concentrically and / or radially.

13. The method according to one of Claims 1 to 11, characterized in that the hard solder part (6) is fixed in the depression (5) in step S2 by squeezing the excess solder into lateral overflow channels.