METHOD FOR COATING SHEETS USING A LASER

Abstract

A method for coating metal parts, comprising providing a metal part of a first metallic material, applying a sheet of a second metallic material to the metallic material on the metal part in a support area, and irradiating the sheet applied to the metal part in at least part of the support area with a laser.

Description

METHOD FOR COATING SHEETS USING A LASER FIELD OF INVENTION The subject matter refers to a method for the selective coating of metal parts, where a sheet supported on a metal part, or a metal part manufactured by this method, is laser welded to it. BACKGROUND OF THE INVENTION As electrification of mobility progresses, increasingly higher currents are transmitted through cables in motor vehicles. This places significant demands on the cables themselves, but also, and particularly, on the transitions between cables and contact elements, as well as on the transitions between the cables themselves. Such transitions are generally carried out using various types of connections. Common ones include welded connections, and on the other hand, bolted, clamped, and / or pressed connections, hereafter generally referred to as force connections. The type of connection is always chosen according to the connection requirements. For example, welded connections are suitable as permanent connections with low transition resistance. Force connections, on the other hand, can be closed during assembly and reopened later. However, force connections cannot offer the same quality of electrical contact resistance and may therefore have a higher ohmic resistance. It is often necessary to connect the same component to other elements using different types of connections. For example, these might be components that function as connecting pieces at the end of a cable, such as cable terminals. Often, a soldered connection on one side and a removable connection, particularly a crimp connection, on the other side are required and provided on the same component. The respective connections impose different requirements on the components to be connected. In particular, they impose requirements on the surface condition of the components in the connection area. For example, a welded joint requires a clean, smooth surface, i.e., one that is uncontaminated. This allows for the most homogeneous weld possible result with high mechanical stability and low electrical resistance. Force-fit connections (force connections), on the other hand, place particularly high mechanical demands on the components that must be made contact. Firstly, they must be able to absorb pressure. Therefore, the material of the components involved must not be too soft to avoid excessive deformation during connection. However, it is also beneficial for the surface of the contacting components in the connection area to be relatively ductile, at least in its outer layer. This allows for the largest possible bearing area, as irregularities are compensated for by the surface that deforms when force is applied. Furthermore, there are requirements for the material combinations between the contacting part and the components that come into direct contact with it in the connection area.Therefore, it is beneficial to provide homogeneous connections on contact surfaces to avoid contact corrosion, especially between metals of different redox potentials. To prepare the surface of a contact part for a specific type of connection, it is often coated before contact. For this purpose, it is common to coat contact parts made of one material entirely with a second metal in a single step. This means the contact part is essentially coated on all sides with a layer of the second material. Thus, the surface of the contact part is prepared for a particular type of connection for which the applied coating is advantageous. The coating can provide a specific type of connection by matching the material of the element to be contacted. Furthermore, the coating can adjust the surface's mechanical properties, such as making it harder or softer than the substrate material. The coating can also adjust the chemical properties of the contact part's surface, such as redox potential and oxidizability. A coating is not only relevant for the parts in contact. The area where the coating is applied depends on the requirements of the metal part. For example, areas that will later be exposed to specific chemical, mechanical, and / or electrical stresses in the installed state can be coated. The coating can also be applied, for example, to an area where a tool is used during assembly or during connection creation. For instance, the area where a sonotrode and / or anvil of an ultrasonic welding device are attached can be coated. Here, for example, abrasion of the sonotrode and / or anvil can be reduced by using a ductile coating. A complete coating is relatively easy to achieve. However, a second connection is often provided at the contact point, as described earlier. This can place different demands on the surface. In particular, the pure starting material of the contact point, as it was before coating, may be better suited for the second connection than the coated surface. This can be especially true with welded joints. Often, therefore, the base material from which the contact point is primarily formed is exposed again after coating. To address this, the coatings are often removed locally to expose the underlying material. Specifically, it is conceivable, for example, to coat a metal part made of a first metallic material, such as copper, integrally—that is, essentially on all sides—with a thin layer of a second metallic material using electroplating. This second material could be a ductile metal, such as nickel or tin. The surface is now prepared for a bonded connection. However, for a soldered joint, the bare copper must be soldered back in. To restore access to the copper, the coating is then removed locally in a second step, for example, by etching, laser etching, mechanical ablation, etc. The problem with the described procedure is that coating removal / ablation is never perfect, and the surface after removal / ablation is not as pure as it was before the coating. Often, coating and / or tool residue remains after removal / ablation. Furthermore, the material surface is often no longer as smooth as it was before the coating and removal steps. Sometimes, the steps are also time-consuming (etching) and do not easily fit into a production line. It is possible to locally cover the metal part before coating, which is then removed after the coating step. However, this is an expensive method that would raise production costs too high for the cost-conscious market. / frfrCfrn / eznz / q / YiAi BRIEF DESCRIPTION OF THE INVENTION Therefore, the matter was based on the objective of locally coating a metal piece in a favorable manner without changing the surface of the uncoated areas. This objective is achieved by means of a method according to claim 1 and a metal part according to claim 17. It has been recognized that it is possible to locally coat a metal part by welding a metal sheet onto the metal part with a laser. First, a metal part is provided for this purpose. The metal part may be made of a solid material, in particular a single metallic material such as copper or copper alloys, or aluminum or aluminum alloys. It is also possible for the metal part to be made of several different metallic materials, in particular two different metallic materials. The metal part may also not be made of a solid material but may have cavities. Furthermore, the metal part may be made only partially of one metal and partially of another material, such as a non-conductor. For example, a non-conductive material may act as a carrier material, and the metallic material may act as a conductive contact material. The metal part can be molded, stamped from sheet metal, cut, milled, forged, or similarly shaped. Its form is preferably substantially cuboid, at least in some areas. Round cross-sections are also possible, at least partially. The metal part can also be a sheet of metal, a wire, or a machine component such as a piston, bolt, fin, etc. Therefore, the present method is not limited to connecting parts. One result of the method—local adaptation of the surface material of a metal part without altering other surface areas—is relevant to many different metal parts. The metal part may have connection areas for non-positive connections on one side. These can be connection terminals, such as sleeves, lugs, wire terminals, threaded or unthreaded holes, bolts, etc., where items can be pressed, squeezed, clamped, screwed, riveted, fastened, plugged, or otherwise connected by pressure. These areas may also be called bearing areas, bolting areas, etc., depending on the type of connection. In addition, connection areas for welded connections can be provided. These can be areas on the surface of the metal part and / or separate connection terminals such as tabs, bolts, sleeves, wire terminals, etc. The surface of the metal part can be prepared for welded connections. For example, it can be roughened, such as by ribs, protrusions, grooves, or have other rough surface structures. The surface can also be smoothed, in particular by brushing, grinding, and / or polishing. And / or the surface can be cleaned. For a connection, the metal part can also have a recess in the area of ​​the weld joint. Another aspect of the present method involves providing a sheet. The sheet, which will subsequently be at least partially bonded to the metal part, can be a metal plate. This can have, for example, a thickness of 1 µm, 3 µm, 10 µm, 30 µm, or 100 µm. This coating thickness can also be achieved through selective laser coating, which involves welding a sheet onto the metal workpiece. It's important to note that the thickness of the sheet used doesn't necessarily have to match the coating thickness. Rather, depending on the laser beam configuration, the final coating can be thinner or thicker than the original sheet. If the coating is thinner than the sheet, some of the sheet material will vaporize during the coating process. If the coating thickness is greater than the sheet thickness, the sheet contracts longitudinally due to the thermal effect of the laser beam, but the volume of the sheet material remains the same or less. Therefore, the volume of the laser-applied coating is constant relative to the volume of the original sheet. The thickness of the film can be adapted to the specific application. For example, for a purely chemical protective effect on the surface, a thin layer in the range of a few micrometers, particularly between 5 µm and 20 µm, may be sufficient. On the other hand, for a mechanical function, such as when the surface has to absorb static and / or dynamic forces, for example, as a contact surface for a sonotrode in ultrasonic welding, a thicker coating in the range of 30 to 100 µm may be suitable. This prevents damage to the coating and exposure of the underlying material. Furthermore, the coating thickness can be adapted to the material of the film used. The metal sheet can be made of metallic materials such as tin, nickel, copper, aluminum, silver, or gold, or alloys thereof. The metallic material of the sheet can be matched to the metallic material of the metal part. In particular, the metallic material of the sheet can be identical to that of the metal part. Alternatively, the sheet can be made of a different metallic material than the metal part. In this way, the mechanical, electrical, and / or chemical properties of the metal part's surface in the coated area can be different from those of the uncoated areas of the metal part's surface. It is also possible that the sheet consists of two or more layers of different metallic materials arranged one on top of the other. These metal layers may already be physically bonded together, at least in certain areas, or pressed or rolled onto one another by friction, or simply overlapped. In a beneficial configuration, the metallic material of the sheet is made of a more ductile material than the metal part itself. Therefore, it has a lower hardness than the metallic material of the metal. The hardness of the material can be determined using the Martens method (DIN EN ISO 14577), the Rockwell method (DIN EN ISO 6508-1), the Brinell method (EN ISO 6506-1 to EN ISO 6506-4), and / or other methods. This has the particular advantage with force connections that they can make contact over a larger area. This is because the ductile surface deforms when force is applied. Specifically, irregularities in the contact surfaces of the metal part on one side and the element to be contacted on the other can be compensated for. In this way, contact is not limited to areas that protrude from the contact surfaces of the metal part and the element to be contacted. Contact over a larger area reduces the electrical contact resistance between the metal part and the element to be contacted. It is also possible to select the metallic material of the coating based on its chemical properties, particularly its redox potential. Thus, a bimetallic contact part can be manufactured from the first metallic material of the contact part, on the one hand, and the metallic material of the coating, on the other. Specifically, the metallic material of the coating can be matched to the material of the contacting element. In particular, these can be substantially the same. By matching the two metallic materials, contact corrosion between a contact part made of one material and a contacting element made of a second, different metallic material can be prevented by means of a coating placed between them in the connected state. / frfrCfrn / eznz / q / YiAi For the present method, the foil is placed on a support area on one side of the metal part. After application, the foil can rest on the metal part substantially without air inclusions, at least in parts of the support area. It is also possible that the foil initially makes only minimal contact with the metal part. The surface of the metal part is substantially flat in the support area and possibly in areas close to it. It is also possible that the surface is curved, particularly convex and / or concave. The shape of the surface can be adapted to the element to be contacted. The surface in the support area can also be structured in another way, such as domed, grooved, slotted, etc. In particular, raised areas can serve to fix the foil in position. An essentially flat surface is also possible.This facilitates readjusting the position of the sheet in the applied state. The support area may extend to at least one limiting edge of the respective surface of the metal part and thus be limited by the metal part itself. However, the support area may also be entirely within the respective surface of the metal part and have a distance from the edges that limits the surface in all directions. The sheet can define the support area by its size. Thus, the sheet can rest precisely on the support area of ​​the metal part, and the area it occupies can correspond exactly to the support area. It is also possible for the sheet to be larger than the support area, with only a portion of it in contact with the metal part. When the foil is applied to the metal workpiece, it can be placed on a support area. Therefore, the placement can determine the foil's position on the metal workpiece. This placement can be carried out without any special bonding between the foil and the metal workpiece at this stage. The foil can simply rest loosely on the metal workpiece. Alternatively, the foil can be pressed down, for example, by means of a roller, a support that moves towards the metal workpiece, a stamp, etc. When the foil is pressed down, it can already adhere at least partially to the metal workpiece. In particular, a frictional and / or material connection can form at an interface, such that its position is fixed, at least temporarily, to some extent. Preferably, a frictional connection can be achieved at this stage. / frfrCfrn / eznz / q / YiAi If a surface texture is present in the metal workpiece's support area, this texture can contribute to a stronger bond, regardless of whether the sheet is applied by pressure or other means. For example, positioning buttons can be provided on the metal workpiece in the support area, particularly on the sides of the support area and / or the sheet, especially in the case of a rectangular sheet, at the corners. An optimized fit between the sheet and the surface, particularly during pressing, can also be achieved with a raised surface texture in the support area. Ideally, the sheet is pre-cut to a specific shape before being placed on the metal workpiece. This shape can correspond to the shape of the bearing area, but the sheet can also be larger or smaller. A sheet larger than the bearing area can compensate for positioning errors. Alternatively, the sheet can be laser-forged at the edge of the generated coating, separating the coating from the exposed, unforged sheet. Minor displacements of the sheet from its correct position do not result in any parts of the bearing area remaining uncovered. It is also possible to avoid cutting the sheet altogether, instead placing a small section of a relatively large piece of sheet onto the metal workpiece and preventing the rest of the sheet from making contact.On the other hand, it may be desirable for the sheet not to extend beyond the support area. In this case, a sheet with a smaller surface area than the support area is advantageous, since even errors in sheet positioning do not necessarily cause it to extend beyond the support area. The sheet can be held in place with a vacuum clamp, a carrier roll, by hand, with a mechanical clamping tool, or other clamping methods before application. Alternatively, the sheet can be joined using another welding method, such as resistance welding. It can be advantageous to position the sheet directly onto the metal workpiece using the appropriate clamping method. This allows for reproducible positioning relative to the metal workpiece. For example, sheets that have already been cut to size can be held on a roll and then laminated onto the metal workpiece. Unlike conventional laser welding, the material to be applied is supplied in sheet form. The sheet is applied locally and selectively. The metal part can be precisely coated, for example, over a bolted surface, while the rest of the metal part can remain uncoated. The transition between the coated and uncoated areas can be locally sharp without the need for a transition area. The application method can take place in a specially prepared environment. For example, the ambient temperature can be maintained. Depending on the sheet material, the sheet may have a softer consistency (measured according to one of the methods mentioned above) due to the temperature, particularly a higher temperature than would normally be expected, compared to its consistency at room temperature. Specifically, the sheet temperature can be adjusted close to its melting point. A softer consistency can facilitate better adaptation of the sheet to the surface of the metal part and, in particular, achieve more extensive contact between the sheet and the metal part immediately after application. It is also possible to lower the temperature compared to ambient, thus producing a harder sheet.This can prevent the sheet from breaking. It is possible to apply a second or more sheets (immediately or after a certain time has elapsed) to the metal part after the first sheet has been applied. These can overlap each other, in particular completely overlapping, but they can also be placed on completely separate support areas. In another step of the present method, the sheet placed on the metal workpiece is irradiated with a laser, at least in parts of the contact area. The laser heats the sheet locally, causing it to melt, or even remelt. The material of the metal workpiece beneath the sheet can also be heated in this step and, if necessary, melt locally, or even remelt. This creates a bond between the sheet and the metal workpiece. The sheet can then be laser-welded or welded to the metal workpiece. The laser can be a pulsed laser, particularly an ultrashort pulse laser, or a continuous-wave laser with a continuous laser beam. Such lasers are well-known and already used to expose coated surfaces as described above, for example, after coating a metal part. By using an existing laser, the present method can be easily integrated into existing production lines. In particular, the laser can be a / frfrCfrn / eznz / q / YiAi Nd:YAG, a CO-2, a diode, or a disk laser. Other types of lasers are possible. The laser allows for a precisely defined, spatially defined connection between the sheet and the workpiece. By moving the laser over at least a portion of the bearing area, a bond can be achieved over the desired part of the bearing area. The area within which the sheet is welded to the workpiece will henceforth be referred to as the weld surface. This may include portions of the bearing area. In particular, the weld surface may substantially coincide with the bearing area. The bond between the sheet and the workpiece can be achieved in parts of the weld surface. However, a bond with substantially no gaps between the sheet and the workpiece can also be achieved over the entire weld surface. Since the laser cannot heat the entire welding surface at once, it is proposed to move the laser along a welding pattern across the surface. This welding pattern can be traced along a line that at least partially fills the welding surface in a continuous motion. Alternatively, it is possible to traverse a grid step by step with the laser and weld the sheet point by point at each step at a different grid point on the metal workpiece. It is advantageous to laser weld the central areas of the weld surface first, and then weld progressively more distant areas. This prevents the sheet from shrinking or expanding on one side. It also prevents air pockets from forming between the sheet and the metal workpiece. The outline of the weld surface can also be welded first, at least spot-welded. Only then can the laser be moved further inward from the outside. This minimizes sheet shrinkage. It is also beneficial to arrange the areas on the weld surface so that the areas heated by the laser beam (laser spots) partially overlap. This prevents unwelded areas within the weld surface and ensures a bond across essentially the entire surface between the sheet and the metal workpiece. Due to the laser effect, the sheet may contract or expand during welding. To counteract this, the order of the welding grid positions can be adjusted as mentioned previously. Therefore, the outer grid positions can be welded first. Furthermore, for this reason, the sheet can be made larger or smaller than the welding surface and / or the support surface. In this way, the welding surface remains covered even if the sheet contracts slightly or expands significantly beyond the limits of the support area. The sheet can also be initially fixed to a coarse grid of spot welds and then welded with progressively finer spacing, so that any deformations of the sheet remain only very localized. If the area of ​​the welding surface is smaller than the size of the applied foil, the laser can remove the excess foil. To do this, the edge of the foil is removed with the laser beam, thus allowing the foil to be cut. A higher laser power can be used for cutting, or the same laser power used for welding can be used. For laser foil cutting, it is advantageous that the foil is not in direct contact with the metal workpiece in the cutting area. This allows the foil to separate locally, specifically to evaporate. To achieve a seamless transition between the foil and the uncoated surface of the metal part, it can be beneficial to first roll the foil or bring it close to the metal part after cutting. The pressed edge area of ​​the weld surface can then be scanned again with the laser, and any remaining unwelded foil can be re-fused onto the metal part. Alternatively, these pressing steps can be omitted, and any remaining protruding foil can simply be vaporized with the laser. It has been recognized that the foil can be welded onto the metal workpiece or vaporized under the action of the laser, depending on the contact with the metal. If there is contact between the two, welding occurs; otherwise, the foil separates. This can be used to achieve a combined full-area and cut weld of the foil. For this, the foil can contact the metal workpiece only in the area of ​​the desired weld surface. It can extend beyond this weld surface, but without touching the metal workpiece. As the laser moves along the foil, including its edge areas, the foil welds in the areas that make contact with the metal workpiece. In the areas where there is a gap between the foil and the metal workpiece, it vaporizes. The weld surface is automatically welded and cleanly cut in a single pass.Furthermore, immediately after placement, especially while the clamping tool is still holding the sheet in position, the laser can perform the cut around the sheet's contour. Subsequently, the sheet can be re-melted with the laser. The described procedure of combined welding and cutting is especially useful if the sheet is larger than the welding surface or has not yet been cut into any shape. For example, the sheet can be unwound from a large stock, such as a continuous belt, and pressed onto the metal workpiece in the support area, especially without cutting it first. The cut sheet can also be only slightly larger than the welding surface, for example, 10%, 20%, 30%, 40%, or 50%, to compensate for positioning errors and / or possible shrinkage of the sheet under the laser action. The sheet can also be made smaller, for example, 10%, 20%, or 30% smaller than the welding surface, to compensate for any expansion that might occur. The laser can now first weld the foil to a support area where it is in contact with the metal workpiece. Subsequently, the laser can cut the foil's contour where it is no longer directly over the metal workpiece. Any excess foil can then be vaporized, for example. Steps 1 (trimming the contour) and 2 (melting the foil to the weld surface) can also be interchanged. The result is selective coating in a combined welding and cutting step. There is no need to cut the foil before positioning and / or welding. Furthermore, difficulties in positioning the foil relative to the metal workpiece are eliminated, as the cutting process determines the foil's area. It can be beneficial to apply the foil to the metal workpiece under a specific surrounding gas composition and / or machine it using a laser. For example, negative pressure can be created in the vicinity of the metal workpiece and the foil, resulting in a near-gas-free vacuum. This largely prevents air inclusions. It is also possible to apply the foil under a shielding gas atmosphere, such as nitrogen, argon, argon-helium, etc. This prevents chemical changes to the foil, especially oxidation. The shielding gas can temporarily surround parts of the assembly, particularly parts of the foil, or the foil and / or the metal workpiece can be enveloped in a shielding gas atmosphere throughout the entire process. In particular, a shielding gas atmosphere can be useful during laser welding to prevent changes in the material's properties, especially oxidation. / bfrCfrn / rznz / q / YiAi Often, the purpose of local coating is to prepare the metal part for joining. These can be press connections, and screw connections, in particular, are common. For press connections, the coated surface may be located within the contact area of ​​the joint, where the metal part and the part to be joined make contact. Specifically, the contact area may be located entirely within the weld surface. In this case, the part to be joined only comes into contact with the foil coating, not with the uncoated material of the metal part. This method allows for coating a metal part around a gap, particularly around a hole. This is achieved by placing the foil on the metal part in the bearing area as previously described, which now includes one or more gaps, such as holes. During the welding process, the laser moves over the welding surface and melts it. In this case, the welding surface does not enclose the gaps (but the bearing area already does). Once the welding process is complete, the gaps can be exposed using the laser. This is done by tracing the edges with the laser. The foil evaporates in these areas and can therefore be cleanly removed from the gap area. The foil simply needs to be laser-cut at the edge of the gaps and can then be removed.It is also possible for the laser to first explore the edge areas of the gaps outside the gaps themselves—that is, in areas where the metal part is still beneath the sheet metal—thus creating a weld in the edge area. Only then can the rest of the weld surface be joined. After that, the gaps can be cut out. Such a sequence of laser-formed areas can be integrated into a welding pattern described earlier. For forced connections, but also for other types of connections, one or more gaps can often be provided in the metal part, as mentioned previously. In particular, holes are possible. For this method, the laser intensity, or power, is of vital importance. If the intensity is too high, the foil will be damaged or deformed. If the intensity is too low, a reliable bond will not be achieved. The laser power must be adjusted according to the layer density, as well as the foil and workpiece materials, the operating temperature, and other factors. The laser power must also be adjusted according to the foil thickness and the workpiece material. / frfrCfrn / eznz / q / YiAi If two or more sheets are to be welded onto the metal workpiece, they can first be placed onto the workpiece during the placement step. Subsequently, the sheets can be laser-welded individually or, if they overlap, joined together in a single step in this overlap area, as described above. It is also possible to place and weld one or more initial sheets first. Then, in a second or subsequent pass, one or more sheets can be placed onto the already coated metal workpiece and subsequently welded. The method can be repeated with any number of additional sheet layers. Such two-step or multi-step welding can be advantageous for achieving a multi-layer coating. For example, contact between two metallic materials with particularly different redox potentials can be facilitated by inserting an intermediate compensating layer.The contact areas and / or weld surfaces of different sheets welded successively onto the metal part may be completely separated from each other in space; that is, they may not overlap. It is also possible for them to overlap. In particular, a subsequently applied sheet may completely enclose the previously applied sheet. Furthermore, the first applied sheet may completely enclose the area occupied by the last applied layer. Another aspect relates to a metal part produced according to the described method. Such a metal part consists of a first metallic material and is coated in an area of ​​its surface with a second metallic material. The remainder of the metal part's surface, away from the coated area, may be uncoated and has no residue or traces of metallic coating removal in the uncoated areas. The metal part produced by this method can be a connecting part. Such a connecting part can, on one hand, have an area for making a welded connection. Preferably, this area is uncoated and has not been stripped of a coating. In other words, it was not coated during the manufacturing process of the connecting part, and its coating was subsequently removed. Furthermore, the connecting part provides a connection terminal for a forced connection. This can be a screw connection, but also a clamp, press, riveted, or other type of connection. Therefore, a threaded or unthreaded hole is provided in the connecting part in the area where the screw connection is to be made. In the area of ​​the hole, the surface of the connecting part is coated according to this method. The coating can be applied to both sides of the connector, which are connected by the hole.It is also possible for the coating to be applied to only one side. The size of the coating on the respective side may depend on the size of the element to be contacted. Thus, the element to be contacted may be positioned with its entire contact surface exclusively on the coated area (weld surface). Alternatively, only portions of the contact surface may be coated on the metal part. BRIEF DESCRIPTION OF THE FIGURES The subject is then explained in more detail with reference to a diagram showing different modalities. The diagram shows: Figures la-1c show one modality of the present method. Figure 2 shows one modality of a structured support area. Figures 3a-3c are modalities of various continuous welding patterns. Figures 4a-4c are modalities of various grid welding patterns. Figures 5a-5c are modalities of various grid welding patterns with edge fixing. Figures 6a, 6b are a modality of a combination of remelting and cutting. Figures 7a-7e are a modality of a connecting part manufactured in accordance with the present method. Figure 8 shows ultrasonic welding modes of a metal part coated by the present method. DETAILED DESCRIPTION OF THE INVENTION Figures 1a-1c show the main features of the coating method in question. First, a metal part 10 and a metal sheet 20 are provided, see Figure 1a. A support area 12 can already be defined on the metal part 20 on which the sheet will be placed. In Figure 1b, sheet 20 is placed on metal piece 10 in the area of ​​the support area 12. Sheet 20 can be placed loosely, as described above, or it can be pressed onto the metal piece with a certain force. The size of the sheet and the support area 12 do not have to correspond, so sheet 20 can be larger or smaller than the support area 12. Figure 1c shows the irradiation of a laser beam 32 from a laser 30 onto sheet 20. The laser 30 can melt around sheet 20, thus achieving a material bond between sheet 20 and the metal part 10 in the laser's area of ​​effect. A material bond is achieved in at least parts of the support area 12 on a weld surface. When referred to in this document as a laser, this can mean either the laser beam or the laser apparatus. To improve the attachment of the sheet 20 to the metal part 10 after application, the surface of the metal part 10 can be textured in the area of ​​the support area 12. In particular, protrusions 18 can be provided in the support area 12. Specifically, positioning protrusions 18 can be provided in the edge areas of the support area 12 as shown in Figure 2. In the case of a rectangular sheet 20, the protrusions 18 can be located in the corner areas of the sheet 20 and / or the support area 12. Since the laser 30 can only heat and remelt the sheet 20 locally, it must move across the weld surface to create a two-dimensional connection between the sheet 20 and the metal part 10. This is done in a weld pattern 40. Figures 3a–3c show some exemplary and advantageous weld patterns. Here, the laser 30 can be moved in a continuous motion across the sheet 20. Figure 3a shows a serpentine weld pattern 40 extending from a starting point 42 in parallel paths across the sheet 20. This pattern has the advantage that many sheet shapes can be traversed uniformly in a single pass without switching off and / or repositioning the laser. Alternatively, as shown in Figure 3b, the laser 30 can move outwards from a central position 42 of the support area 12 or the sealing area in paths substantially concentric with the starting point 42. This has the advantage that the sheet 20 does not move to one side of the support area 12. In addition, the risk of air entrapment is low. Alternatively, as shown in Figure 3c, the laser 30 can start from the edge of the applied sheet 20 at a starting point 42 and advance from there towards the center of the sealing surface. This has the advantage that the edge area of ​​the sheet 20 is already firmly bonded to the metal part 10, and therefore the sheet 20 can no longer move; in particular, it cannot contract or expand. This ensures that the weld surface is covered by the sheet 20. / frfrCfrn / eznz / q / YiAi Instead of, or in combination with, continuous movement of the laser 30 along a welding pattern 40, it is also possible to have the laser 30 act on the sheet 20 at one point 44 at a time on a grid 40. In this case, the laser 30 does not move during light emission, but rather between individual irradiation events. The sheet 20 is remelted at each point. Nevertheless, the laser scans a pattern 40, albeit point by point. Figures 4a–4c show the patterns 40 of Figures 3a–3c with point-by-point laser action. To minimize any displacement, contraction, expansion, or other changes in the position or shape of the sheet 20 due to the laser beam 32, the sheet 20 can be welded at individual positioning points 46 before the entire area is melted. Subsequently, the connection of the entire surface between the sheet 20 and the metal part 10 can be completed using the laser 30. Figure 5a shows an example of four positioning points 46 at the corners of a rectangular support area 12. Depending on the shape of the welding surface, more or fewer positioning points 46 can be established and positioned differently. Positioning points 46 at central locations on the welding surface are also possible. An unshown procedure is also possible, in which a coarse grid of welding points is melted first, followed by progressively finer grids.It is also possible to have an initial grid that is essentially uniformly distributed, which is then followed by a sweep of the entire surface, for example according to one of the patterns in Figures 3a-3c. Figure 5b shows a complete area of ​​back-melting of sheet 20 onto metal part 10 after the application of positioning points 46. This can occur in a serpentine pattern as in Figure 5b, but it can also occur essentially concentrically from the outside in as in Figures 3c and 4c, from the inside out as in Figure 5c, or in other ways. The pattern 40 in Figure 5c has the advantage of preventing air pockets through outward-extending remelting and, at the same time, avoiding sheet deformation due to the outward-facing positioning points 46. Figures 6a-6b show the combined remelting and cutting of sheet 20 by laser 30. When sheet 20 comes into contact with metal part 10 in the bearing area 12, laser 30 has a remelting effect and welds sheet 20 and metal part 10 together. However, when sheet 20 does not rest directly on metal part 10, laser 30 cuts sheet 20. Therefore, a properly positioned sheet 20 can be remelted and materially bonded to metal part 10 either in the central bearing area 12 or on the weld surface enclosed by it. Conversely, laser 30 has a cutting effect in the edge areas of the bearing area 12 where sheet 20 is not in contact. Thus, sheet 20 is remelted and cut in a single pass through laser 30. The sequence between cutting the contour and remelting the sheet on the welding surface can be reversed. Figures 7a-7e show a connecting part produced by the present method. This part is formed from a metallic material and comprises, on one side, a welding terminal 16, which may have a surface prepared for the welding method, which may be smooth or, as shown in Figure 7a, rough, particularly provided with grooves. Furthermore, the connecting part has a hole 14. This may be provided, for example, for a screw connection; a riveted or similar connection is also possible. The area with the hole 14 is therefore provided for a press fit. According to the present method, a sheet 20 is now placed in the perforated area of ​​the rear force connection, see Figures 7a, 7b. As shown in Figure 7c, the sheet 20 is then joined by means of a laser 30 in the bearing area and / or the weld surface. The hole is excluded from the weld pattern 40 (not shown). In a further step (Figure 7d), the hole is then exposed using the same or a different laser 30. To do this, the laser cuts the sheet in the area of ​​the hole's contour, specifically by vaporizing it. Figure 7e shows the completed connection portion. On one side, it is prepared for a welded connection and has a completely clean surface. On the other side, it is prepared for a force connection due to the sheet coating. For example, the coated surface may be more ductile than the rest of the metal surface. A coating using sheet 20 can also be used for purposes other than improved contact. For example, a surface that is softer in some areas (lower hardness according to one of the measurement methods mentioned above) than the rest of the metal surface is useful for ultrasonic welding. If the sonotrode 50 of an ultrasonic device touches a metal surface that is too hard, the collision of two hard materials can result in high abrasion, and welding times must be reduced. / frfrCfrn / eznz / q / YiAi Here it is useful, as shown in Figure 8, to coat the contact surface of the sonotrode on a first metal piece 10 with a foil 20. When ultrasonically welded to a second metal piece 60, the sonotrode now comes into contact with a coated area of ​​the first metal piece 10 and can apply energy to it for a longer time without causing too much abrasion. LIST OF REFERENCE NUMBERS Metal part Support area Holes Bumps Sheets Laser Laser beam Welding pattern Starting point Grid dot Positioning points Sonotrode Metal part

Claims

1. A method of coating metal parts, characterized in that it comprises: - providing a metal part from a first metallic material, - applying a sheet of a second metallic material onto the metal part in a bearing area, - irradiating the sheet applied onto the metal part in at least a portion of the bearing area with a laser, wherein the bearing area of ​​the metal part comprises a hole and is at least partially a bolted area, - materially bonding the applied sheet to the metal part in the bearing area, - evaporating the sheet by the laser in the area of ​​the hole.

2. The method according to claim 1, further characterized in that the sheet is at least partially remelted on a welding surface by means of the laser and in particular forms a material bond with the metal piece.

3. The method in accordance with any of the preceding claims, further characterized in that the sheet is smaller than the support area or the sheet is larger than the support area or the area of ​​the sheet is substantially the same size as the area of ​​the support area.

4. The method in accordance with any of the preceding claims, further characterized in that the weld surface constitutes a part of the bearing area or the weld surface substantially fills the entire bearing area.

5. The method in accordance with any of the preceding claims, further characterized in that the first metallic material is different from the second metallic material and / or the first metallic material is the same as the second metallic material.

6. The method according to any one of the preceding claims, further characterized in that the laser is an ultrashort pulse laser, in particular an Nd:YAG-, CO2- or diode laser.

7. The method in accordance with any of the preceding claims, further characterized in that holes are laser cut from the metal piece in the support area / frfrCfrn / eznz / q / YiAi and / or the outer contour of the sheet is laser cut.

8. The method in accordance with any of the preceding claims, further characterized in that the metal piece is a cable terminal.

9. The method in accordance with any of the preceding claims, further characterized in that the sheet is heated close to the melting point during application.

10. The method in accordance with any of the preceding claims, further characterized in that a structure is arranged in the support area, in particular one or more elevations, in particular positioning protrusions.

11. The method according to any of the preceding claims, further characterized in that the support area is traversed at least partially by the laser in a grid of regularly spaced welding positions and the sheet is welded and / or reshaped in the respective welding positions in an essentially point-like area and / or the support area is continuously traversed by the laser in at least partially a continuous line and the sheet is welded and / or formed along the line.

12. The method in accordance with any of the preceding claims, further characterized in that the sheet is made of nickel, tin, silver, gold or alloys thereof.

13. The method in accordance with any of the preceding claims, further characterized in that the metal part is made of copper, a copper alloy, aluminum, or an aluminum alloy.

14. The method according to any of the preceding claims, further characterized in that at least a second sheet is applied to the metal piece at least on a second welding surface by means of a laser, wherein the first welding surface and the second welding surface do not overlap or at least partially overlap.

15. The method in accordance with any of the preceding claims, further characterized in that a shielding gas is applied over at least a portion of the support area before and / or after and / or during the application of the sheet and / or the laser irradiation.

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