METHOD FOR WELDING CELL INTERCONNECTORS AND WELDING ELECTRODE ARRANGEMENT THEREFOR

Abstract

Method for welding one interconnector each of two adjacent electrochemical cells of an accumulator, in particular a lead-acid accumulator (10), wherein the two electrochemical cells are arranged separated from one another by means of a housing partition, wherein the interconnectors are arranged facing one another on two opposite sides of the housing partition, wherein an opening is arranged in a region of the housing partition where the interconnectors are opposite one another, and the method comprising the following steps: - contacting the interconnectors with a welding electrode arrangement, wherein the welding electrode arrangement has at least one pair of welding electrodes, wherein in each case one welding electrode of the at least one pair of welding electrodes contacts one of the interconnectors by means of an insert part (100); - Welding the interconnectors in such a way that, by means of a pressure applied by the insert parts (100) of the welding electrodes and a current applied to the welding electrode arrangement, the material of the interconnectors melts at least in some regions and is bonded through the opening in the housing partition wall, in such a way that the welding surface produced has a surface proportion of plastic inclusions of a maximum of 8% in the welding surface, wherein the insert part (100) has a welding plate (140) on the front side of which a welding projection (110) is formed, which extends from the welding plate (140), and wherein the welding projection (110) has a recess (130).

Description

The present patent application relates to a method for welding interconnectors of a lead-acid accumulator, the lead-acid accumulator, and a welding electrode arrangement for this.Conventionally, a lead-acid battery for a vehicle has a housing including a plurality of chambers. These chambers are separated from one another by means of housing partitions. An electrochemical cell is accommodated or arranged in each of the chambers (in the installed state of the lead-acid accumulator), wherein in each case an electrochemical cell has a multiplicity of positive and negative electrode plates which are separated from one another, in particular are electrically separated from one another, by means of a separator, and an electrolyte. The positive and negative electrode plates may be covered with a positive and negative paste-like active mass, respectively, and optionally a paste-like nonwoven fabric may be disposed on the active mass, holding the active mass on the respective electrode plate and preventing the active mass from coming off the electrode plate. In order to tap off or supply electric current by means of the connection poles of the lead-acid accumulator, the individual electrochemical cells are in electrical connection with one another, so that a series and / or parallel connection of the multiplicity of electrochemical cells can be formed. For this purpose, interconnectors of two adjacent electrochemical cells are welded to one another through the housing separating wall separating the adjacent electrochemical cells. The interconnectors are formed to be electrically connected to the plurality of positive electrode plates and the plurality of negative electrode plates, respectively.Since the housing of the lead-acid accumulator is predominantly made of a plastic material in order to save weight, and the melting point of the interconnectors made of lead or a lead alloy is greater than the melting point of the plastic material, plastic inclusions occur in the welding surface when the interconnectors of two adjacent electrochemical cells are welded. Such plastic inclusions represent a qualitative defect of a welding surface and thereby reduce the strength of the welding surface. In conventional lead-acid batteries, the area proportion of the plastic inclusions in the welding surface is approximately 50% of the welding surface.U.S. Pat. No. 4,429,208 A relates to a conventional electrode structure in which two adjacent electrodes spaced apart from one another by means of a separating wall are welded to one another by means of a conventional welding electrode through an opening in the separating wall.EP 1 983 455 A2 relates to a limit elongation analysis during forming processes in the production of sheet metal parts in the automotive industry.JP S62-165 856 A relates to a lead-acid battery in which two adjacent electrodes spaced apart from one another by means of a separating wall are welded to one another through an opening in the separating wall by means of a conventional welding electrode.The object of the invention is therefore to provide a method for welding interconnectors, which reduces the proportion of enclosed plastic inclusions in the welding surface and which at the same time is simple and cost-effective to implement.The object underlying the present invention is achieved in particular by the subject matter of the independent patent claims. Advantageous further developments are specified in the dependent patent claims.Thus, the subject matter of independent claim 1 relates to a method for welding interconnectors of two electrochemical cells of a lead-acid accumulator spaced apart from one another by means of a housing partition.In this case, the two electrochemical cells are arranged separated from one another by means of a housing partition wall, wherein the interconnectors are arranged facing one another on two opposite sides of the housing partition wall. In other words, the two interconnectors are arranged on two opposite sides of the housing partition in such a way that they are situated opposite one another at least substantially congruently. In a region of the housing partition wall, on which the interconnectors are opposite one another, an opening is arranged. The method has the following steps: contacting the interconnectors with a welding electrode arrangement and welding the interconnectors.In this case, the welding electrode arrangement has at least one pair of welding electrodes, wherein in each case one welding electrode of the at least one pair of welding electrodes makes contact with one of the interconnectors by means of an insert part. The welding of the interconnectors is effected in such a way that by means of a pressure applied by the insert parts of the welding electrodes and a current applied to the welding electrode arrangement, the material of the interconnectors melts at least in regions and connects itself in a materially bonded manner through the opening in the housing partition wall, namely so that the weld surface produced has an area proportion of plastic inclusions of at most 8% in the weld surface.The insert part has a welding plate on the front side of which a welding projection is formed, which extends from the welding plate and has a recess.The advantages of the present invention are evident. In particular, by using an insert part according to the invention for a welding electrode, the quality of the welding can be increased. In particular, the strength of the connection and the electrical conductivity are improved.Furthermore, only replacement or replacement of the insert part is necessary, while the remaining elements of the conventional welding electrode arrangement can be used further.Welding electrode arrangements which have already been put into operation can therefore also be retrofitted in a simple, cost-effective and quick manner, which can reduce the production, production and assembly costs. Further, the downtime can be limited to less than 5 minutes, whereby interruption of the operation of the welding electrode assembly can be limited to a minimum, which further contributes to a reduction in assembly costs, which also includes costs for necessary downtime.The quality of the accumulator can thus also be increased and improved.According to a further aspect of the invention, the area proportion of plastic inclusions in the welding surface is less than 8%, in particular less than 4%.As a result, the quality of the weld-and in particular the electrical conductivity brought about by it and the strength of the connection-can be further improved, so that a more robust connection with better electrical properties can be ensured.According to a further aspect of the invention, the insert part has been calculated and simulated by means of a finite element method.As a result, weak spots of the conventional insert can be easily and economically found and prevented. This leads to an improved welding surface and thus to a higher quality of the welding.According to a further aspect of the invention, the insert part of each welding electrode has a welding projection which has a shape which has been calculated and simulated in such a way that the proportion by area of plastic inclusions in the welding surface is at most 8%, preferably less than 8%, particularly preferably less than 4%, of the welding surface.This ensures that less scrap is produced, which further reduces manufacturing costs.According to a further aspect of the invention, the welding projection has the recess in such a way that the cross section of the welding projection is at least substantially U-shaped or C-shaped.The weak spots caused by the conventional insert part or conventional welding projection are thus avoided, which leads to an increase in quality.According to a further aspect of the invention, the welding projection has a contact surface which has an at least substantially U-shaped or C-shaped cross section, wherein the welding projection is formed so as to taper towards the contact surface.The weak spots caused by the conventional insert part or conventional welding projection are thus avoided, which leads to an increase in quality.According to a further aspect of the invention, the interconnectors are welded by means of a through-the-partition (TTP) welding process.This is a simple process to carry out, as a result of which the production costs can be further reduced.According to a further aspect of the invention, the interconnectors are welded at a welding temperature of 300° C. to 380° C., in particular 300° C. to 360° C., preferably 300° C. to 340° C., particularly preferably 300° C. to 320° C.In particular, the welding temperature is in the range of the melting point of the interconnectors (±5° C.) or only slightly (i.e. approximately 5° C. to 15° C.) above the melting point of the interconnectors, whereby negative influences on the material of the housing partition wall, which has a lower melting point than the material of the interconnectors, are advantageously reduced. It can thus be ensured that fewer stresses occur in the housing partition wall during the welding process and thus fewer plastic inclusions occur in the welding surface.According to a further aspect of the invention, the housing partition wall is manufactured from plastic which has a melting point of 200° C. to 250° C., in particular 220° C.According to a further aspect of the invention, the housing partition is manufactured from polyamide or a copolymer of polyamide and at least one of polyethylene, polypropylene, and polyoxymethylene.Thus, electrical isolation of the accumulator is ensured in a simple and cost-effective manner and at the same time the weight of the accumulator can also be reduced.According to a further aspect of the invention, the welded interconnectors withstand a torque of at least 12 Nm, in particular of at least 16 Nm.The quality of the produced weld can thus be further increased.According to a further aspect of the invention, there is provided a lead-acid accumulator comprising a housing having a plurality of chambers separated from each other by a plurality of housing partitions and a plurality of electrochemical cells, wherein each electrochemical cell is disposed in a respective chamber, and wherein each electrochemical cell comprises two interconnects for forming an electrical connection,In this case, an interconnector of a first electrochemical cell and an interconnector of a second adjacent electrochemical cell are arranged opposite one another on two opposite sides of a housing partition wall which spatially separates or separates the first and second electrochemical cells from one another. Furthermore, the housing partition wall has an opening in a region at which the interconnectors are opposite one another, through which the interconnectors are connected to one another or are in particular welded, preferably by means of the method described above, wherein the connecting surface or in particular the welding surface has a surface proportion of plastic inclusions of at most 8% of the welding surface.The insert part has a welding plate on the front side of which a welding projection is formed, which extends from the welding plate and has a recess.This advantageously has the consequence that a lead-acid accumulator with improved electrical and mechanical properties can be provided, which is moreover simple and cost-effective to produce.According to a further aspect of the invention, the welded interconnectors maintain a torque of at least 12 Nm, in particular of at least 16 Nm.Furthermore, the subject matter of independent patent claim 14 relates to a welding electrode arrangement for welding a respective interconnect of two adjacent electrochemical cells of an accumulator, in particular of a lead-acid accumulator.The interconnectors are separated from one another by means of a housing partition and arranged opposite one another on opposite sides of the housing partition, wherein the housing partition has an opening in a region at which the interconnectors are opposite one another.For this purpose, the welding electrode arrangement has at least one pair of welding electrodes, wherein each welding electrode of the at least one pair of welding electrodes has an insert part which is designed to contact a corresponding interconnector and to weld the interconnectors through the opening in the housing partition wall in such a way that an area proportion of plastic inclusions in the welding area is at most 8% of the welding area.The insert part has a welding plate on the front side of which a welding projection is formed, which extends from the welding plate and has a recess.With the aid of this recess, the detected weak spots of the conventional welding projection are bypassed, whereby a weld can be produced which has both higher or better mechanical and higher or better electrical properties.In particular, the quality of the weld can be increased by using an insert part according to the invention for a welding electrode arrangement. In particular, the strength of the connection and the electrical conductivity are improved.Furthermore, only replacement or replacement of the insert part is necessary, while the remaining elements of the conventional welding electrode arrangement can be used further.Welding electrode arrangements which have already been put into operation can therefore also be retrofitted in a simple, cost-effective and quick manner, which can reduce the production, production and assembly costs. Further, the downtime can be limited to less than 5 minutes, whereby interruption of the operation of the welding electrode assembly can be limited to a minimum, which further contributes to a reduction in assembly costs, which also includes costs for necessary downtime.The quality of the accumulator can thus also be increased and improved.According to a further aspect of the invention, the insert part has been calculated and simulated by means of a finite element method.As a result, weak spots of the conventional insert can be easily and economically found and prevented. This leads to an improved welding surface and thus to a higher quality of the welding.According to a further aspect of the invention, the welding projection has at least substantially the shape of a prism with a base surface of a round-end rectangle and the recess has at least substantially the shape of a prism with a trapezoidal base surface.According to a further aspect of the invention, the welding projection has a contacting surface for contacting the interconnector, wherein the welding projection is formed tapering towards the contacting surface.According to a further aspect of the invention, the contact surface has an at least substantially U-shaped or C-shaped cross section.According to a further aspect of the invention, a protrusion for inserting the insert into a groove in the welding electrode formed complementarily to the protrusion is provided on the rear side of the welding plate, wherein the insert is attachable or attached to the welding electrode by means of a fastening bore arranged on the rear side of the welding plate.As a result, the changing or replacing of the insert part can take place in a simple (and in particular releasable) manner, which can reduce the costs for assembly and the time required for it. In addition, the centering of the insert is simplified.According to a further aspect of the invention, the welding projection and / or the protrusion are formed integrally with the welding plate.As a result, the production costs of the insert can advantageously be reduced, since it can be produced, for example, cost-effectively by means of a casting process with optional subsequent post-processing.The invention is explained in more detail below on the basis of the description of embodiments with reference to the attached drawings.These show in: FIG. 1 is a schematic illustration of a vehicle; FIG. 2 shows a schematic illustration of an insert part according to the invention for a welding electrode; FIG. 3 is a schematic illustration of a front view of the insert part according to the invention for a welding electrode; FIG. 4 shows a detailed view of the welding projection according to the invention; FIG. 5 shows a schematic illustration of a side view of an insert part according to the invention for a welding electrode; FIG. 6 is a schematic illustration of a rear view of the insert part according to the invention for a welding electrode; and FIG. 7 is a schematic view showing a front view of a conventional welding electrode insert.The method according to the invention and the welding electrode arrangement according to the invention are described in more detail below with reference to the illustrations in FIGS. 1 to 7. Identical or identically acting elements and functions are provided with the same or similar reference numerals.The supply of energy, in particular with electricity, to a vehicle plays an increasingly important role with the constantly increasing number of energy consumers, in particular electricity consumers, and specifically both in internal combustion engine-based vehicles and in electric vehicles and in hybrid vehicles. In particular, when starting an internal combustion engine, high currents are produced which are provided by a starter battery of the vehicle.The vehicle can be an aerial or watercraft, a track-guided vehicle, an off-road vehicle or preferably a road vehicle, wherein road vehicle can be understood to mean a passenger car, a truck, a bus or a motorhome. Furthermore, hybrid vehicles can be understood to mean any vehicle which has both an internal combustion engine and an electric motor as energy source. Hybrid vehicles may be divided into micro-hybrid, mild hybrid, full hybrid, and plug-in hybrid vehicles.In particular, lead-acid batteries or lead-acid accumulators are used as starter batteries. These are designed to provide the electrical current required to start the motor. One design of a lead-acid storage battery is, for example, an absorbent glass mat (AGM) storage battery, in which the electrolyte is bonded in a fleece made of glass fibers. In comparison with wet accumulators in which the electrolyte is present in liquid form, AGM accumulators have the advantage that no electrolyte can leak even when the accumulator is tilted. Furthermore, AGM batteries are distinguished by a low internal resistance.Hereinafter, the lead-acid battery and the welding electrode assembly will be described such that relative terms refer to the installation state of the lead-acid battery. For example, "in an upper region" means an upper region when the lead-acid battery is in the installed state, "in a lateral region" means a region when in the installed state and in the traveling direction, which is located in a front, rear, left or right region, and "in a lower region" means a lower region when in the installed state.FIG. 1 shows a schematic illustration of a vehicle V. The lead-acid accumulator 10 can be arranged here in a region of the vehicle V which is at the front in the direction of travel, in a rear region of the vehicle V and / or in a region below the seats, in particular below the driver's seat.As shown in FIG. 1, the lead-acid battery 10 is disposed in a front portion of the vehicle, particularly in a front engine room below the front door.The lead-acid battery 10 includes a housing configured to house a plurality of electrochemical cells. For this purpose, the housing has a housing lower part defining an interior, the upper side or upper side surface of which is open in the installed state, and a cover which is designed to close the upper side of the housing lower part which is open in the installed state.The housing base further includes a plurality of housing partitions arranged such that the interior of the housing base is divided into a plurality of chambers, each configured to receive an electrochemical cell.The housing lower part and the cover can be connected or connected to one another, in particular welded or welded, in such a way that a connection sealed with respect to liquids and gases or gas mixtures can be produced. For this purpose, the cover can be connected to the housing lower part in particular in a materially bonded and / or force-fit manner. For example, the cover can be connected to the housing lower part via a screw connection.The cover can have a positive connection pole and a negative connection pole, which can be electrically and mechanically connected to electrical consumers or loads. However, the cover can just as well have, instead of the positive and the negative terminal pole, an at least substantially planar positive and negative electrical contact surfaces. As a result, the size and in particular the height of the lead-acid accumulator 10 can be reduced in an advantageous manner.The housing, i.e. the lower housing part including the housing partitions and the cover, can be made at least in regions, in particular completely, from plastic in order to be able to design the lead-acid accumulator 10 as easily as possible. The material selected may be, for example, polyolefin, acryl-butadiene-styrene, polycarbonate, polyamide, polyvinyl chloride, polyethylene terephthalate, polyoxymethylene or a copolymer thereof. In particular, the housing of the lead-acid storage battery 10 can be manufactured from polyamide, polypropylene or polyethylene or a copolymer thereof.The material of the housing has a melting point of 120° C. to 260° C., in particular 150° C. to 250° C., preferably 200° C. to 250° C., particularly preferably 220° C. to 240° C., in particular about 220° C. For the purposes of the present application, about 220° C. means 220° C.±5° C.However, it is equally conceivable to produce only the housing partitions from a plastic material described above. The housing lower part and / or the cover can be manufactured from a metal or a metal alloy. However, in this case, an electrical insulation of the housing must additionally be provided or arranged and ensured.Each electrochemical cell includes a plurality of positive electrode plates and a plurality of negative electrode plates, the plurality of positive electrode plates and the plurality of negative electrode plates being arranged alternately and spaced apart from each other and electrically separated from each other by a separator, respectively.The positive electrode plates may be covered with a positive paste-like active mass, which may optionally be covered with a paste-like nonwoven fabric that holds the positive paste-like active mass on the positive electrode plate and prevents the positive paste-like active mass from becoming detached. Similarly, the negative electrode plates may be covered with a negative paste-like active material which may in turn be covered with a paste-like nonwoven fabric which holds the negative paste-like active material on the negative electrode plate and prevents the negative paste-like active material from coming off the negative electrode plate.Furthermore, the electrochemical cell comprises an electrolyte. This may be in the form of a liquid. It is equally conceivable to use an electrolyte bonded in a glass fiber fleece. When using an electrolyte bonded in a glass fiber fleece, one also speaks of an absorbent glass mat (AGM) accumulator.Each electrochemical cell further includes a pair of interconnects. In particular, each electrochemical cell includes a positive interconnect electrically connected to the plurality of positive electrode plates and a negative interconnect electrically connected to the plurality of negative electrode plates. By means of the positive and negative interconnectors, an electric current is discharged from the corresponding electrochemical cell or supplied to it.The interconnectors of two adjacent electrochemical cells separated from one another by a housing separating wall are electrically connected to one another via the separating wall, in particular through an opening in the separating wall, so that the plurality of electrochemical cells are connected to one another in series and / or parallel to one another. By means of this connection, the total current or the total voltage that can be output by the lead-acid accumulator 10 is determined. The rated voltage of the lead-acid accumulator 10 is in particular approximately 12 V. For this purpose, the plurality of electrochemical cells is electrically connected to one another, in particular in series.For connecting the plurality of electrochemical cells in series, the positive interconnect of a first cell is electrically connected to the negative interconnect of a second adjacent electrochemical cell. Similarly, the positive interconnect of the second electrochemical cell is electrically connected to the negative interconnect of a third electrochemical cell adjacent to the second electrochemical cell, etc. The negative interconnect of the first cell is electrically connected to the negative terminal of the lead-acid battery 10. The positive interconnector of the last electrochemical cell is electrically connected analogously to the positive terminal pole of the lead-acid accumulator 10, so that the accumulated voltage of the individual electrochemical cells can be tapped via the negative and positive terminal poles of the lead-acid accumulator 10.In order to electrically connect the interconnectors of two adjacent electrochemical cells to one another, an opening is provided or arranged in the housing partition wall, through which the interconnectors of the adjacent electrochemical cells are electrically connected to one another. In particular, a welded connection is formed between the interconnectors of the adjacent electrochemical cells.For this purpose, an interconnector of a first electrochemical cell is welded through the opening in the housing partition to an interconnector of a second electrochemical cell spaced from the first electrochemical cell by means of the housing partition by means of a through-the-partition (TTP) welding method.In particular, the electrical contacting of two interconnectors of two adjacent electrochemical cells, which are separated from one another by a housing partition, takes place in such a way that an opening is arranged in the housing partition, namely at the location at which the two interconnectors of the respective cells are opposite one another.In other words, the interconnectors to be connected or welded are arranged at least substantially congruently on two mutually opposite sides of the housing partition in a welding region of the housing partition. In this context, "substantially congruent" means that the contours of the interconnectors on two opposite sides of the housing partition overlap with at least 90% of the surface enclosed by them or that the contours of the interconnectors are (completely) congruently arranged on the two opposite sides of the housing partition.The opening is furthermore arranged in the welding region. The opening has a contour of a rectangle with rounded corners or a round-end rectangle. A round-end rectangle is understood to mean a rectangle whose end sides or shorter sides are at least substantially semicircular or rounded. In particular, the opening has a shape such that the longer side of the opening is smaller than the width of the interconnectors, so that the opening is completely covered by the interconnectors and is closed by them.For example, the opening can have an area of 80 mm 2 to 120 mm 2 in particular 90 mm 2 to 100 mm 2.The interconnectors of the plurality of electrochemical cells are made of lead or a lead alloy. The melting point of lead or lead alloy is in the range of about 300°C to 350°C.To carry out the method known from TTP welding methods, a welding arrangement according to the invention is used. The welding arrangement has at least one pair of welding electrodes according to the invention. In this case, a respective pair of welding electrodes is designed to produce a welded connection; i.e. six welded connections can be carried out, in particular simultaneously, with a welding electrode arrangement having six pairs of welding electrodes. In this case, each pair of welding electrodes can be assigned a control unit for monitoring and controlling the welding process. It is equally conceivable to provide or arrange a (central) control unit which monitors and controls all pairs of welding electrodes.In the following, the method according to the invention and the welding electrode arrangement according to the invention are explained in more detail using an example with a pair of welding electrodes. Of course, this embodiment is purely exemplary and applies accordingly also to welding electrode arrangements with at least one pair or more pairs of welding electrodes according to the invention.In an exemplary embodiment, the welding electrode assembly includes a pair of welding electrodes. Each welding electrode has a specifically formed insert 100 at a distal end. In particular, the welding electrode arrangement is arranged in such a way that a welding electrode with a specifically designed insert part 100 engages a corresponding interconnect, namely in such a way that the insert parts 100 of the welding electrodes contact and compress the interconnects.In particular, the pair of welding electrodes can be designed as a type of clamp which can apply a predetermined force to the interconnectors. For example, the interconnectors can be pressed against one another with a force of 4 kN to 10 kN, in particular with 5 kN to 6 kN.An electric current is then supplied to the welding electrodes in such a way that a welding temperature of approximately 300° C. to 380° C., in particular 300° C. to 360° C., particularly preferably 300° C. to 320° C., is achieved. This can be easily checked by means of a control unit connected and communicating with the pair of welding electrodes via suitable sensors and can be observed by means of corresponding control.When the welding temperature is reached, the interconnectors are melted at least in regions at the point at which the insert part 100 abuts the interconnectors. By the pressure applied by means of the welding electrodes, at least a part of the melted material of the interconnectors is pressed into the opening in the housing partition wall, so that the interconnectors arranged on both sides of the housing partition wall fuse with one another.After a predetermined melting time, the welding electrode is still held for a defined holding time without a current supply, but with application of a predetermined contact pressure to the interconnectors, so that the fusion or cohesive connection of the interconnectors in the opening can be ensured. This results in a welding of the interconnectors after solidification of the melted material of the interconnectors. In the sense of this application, welding is understood to mean the cohesive connection of the interconnectors after carrying out the welding process, wherein the connection is defined or characterized by a produced welding surface between the interconnectors.The welding surface that arises corresponds at least substantially to the surface of the opening in the housing partition wall and is preferably located in a plane with the latter. Furthermore, the welding surface has at least substantially a contour corresponding to the circumference of the opening.Since the melting temperature of the housing and in particular of the housing partition wall is significantly below the welding temperature or the welding temperature range, the housing partition wall is melted at least in regions in a region around the opening during welding. In this context, the term "well below" is understood to mean a temperature difference of at least 100° C., in particular about 100° C. to 150° C., between the material of the interconnectors and the material of the housing partition wall.Due to the pressure applied by the welding electrodes and the resulting stresses, parts of the melted material of the housing partition wall may migrate into the opening.Thus, plastic inclusions can arise in the welding surface, which reduce the quality of the weld.Thus, on the one hand, the strength of the weld is reduced by a high plastic inclusion and, on the other hand, the electrical conductivity is also lowered.In this connection, Fig. 7 shows a conventional welding electrode insert 100'. The conventional insert 100' has a welding plate 140' for this purpose, on which a conventional welding projection 110' is arranged. The conventional welding projection 110' contacts the element to be welded, namely an interconnector, with a contact surface 120'.The conventional contact surface 120' has at least substantially the shape of a rectangle with rounded corners or the shape of a round-end rectangle. This means that the end faces, i.e. the short sides of the rectangle, are designed in particular to be semicircular.In other words, the conventional contact surface 120' has at least substantially a shape corresponding to the contour of the opening.During the welding process, the material of the housing partition is thereby melted around the opening to a greater extent. In particular, performing the TTP welding method using a conventional insert 100' increasingly leads to plastic inclusions in the welding surface.In particular, when the conventional insert 100' is used, the area ratio of the resin inclusions after the welding operation is 50% or more of the welding area.This represents a considerable quality problem, since both the strength of the weld (i.e. the welded elements) and the electrical conductivity of the weld or of the welded interconnectors are adversely affected and in particular are reduced.In order to reduce the surface proportion of plastic inclusions, an insert part 100 according to the invention is specified with this, which is illustrated in FIGS. 2 to 6.In particular, the TTP welding process was simulated by means of a finite element method (FEM) and the weak points of the conventional insert 100' were optimized in such a way that during the welding process lower stresses are applied to the region around the opening in the housing partition wall or are present in the region around the opening in the housing partition wall, which leads to a reduced plastic inclusion in the resulting welding surface.In particular, the contacting surface 120 according to the invention is optimized by means of the finite element method starting from the conventional contacting surface 120' in such a way that in the resulting welding surface the surface proportion of the plastic inclusions is at most 8%, in particular less than 8%, preferably less than or equal to 4%, of the total welding surface. Particularly preferably, the area proportion of the plastic inclusions in the resulting welding surface is at least substantially 0%; i.e. no plastic inclusions are present in the resulting welding surface.This has the advantage that both the electrical conductivity of the weld or of the welded interconnectors is improved and the strength of the weld is increased. In particular, the weld should be able to withstand a (torsional) torque of at least 12 Nm before the weld fails.For this purpose, the contact surface 120 of the welding projection 110 according to the invention on the welding plate 140 can have at least substantially the shape of a short-leg "U" or at least substantially the shape of a banana or boomerang.In other words, in comparison with the conventional at least substantially round-end rectangular-shaped contacting surface 120', the contacting surface 120 according to the invention has a recess 130, so that the welding temperature arising during the welding process is at least partially lower, whereby the stresses between the opening in the housing partition wall and the interconnector during the welding are reduced.The recess 130 is preferably arranged at a location at which the highest voltages and temperatures were detected by means of the FEM method during the welding process with a conventional welding electrode or with a conventional insert 100' and determined in the simulation. In other words, the recess 130 is arranged at a location at which the majority of the plastic inclusions arise in the welding surface. By means of an insert part 100 optimized in this way, in particular the contact of the melted material of the interconnectors with the material of the housing partition wall can be reduced or reduced in a region around the opening, which leads to lower stresses in the housing partition wall and to lower melting of the housing partition wall.As a result, the surface proportion of plastic inclusions in the welding surface formed can be reduced, wherein at the same time the strength of the weld or of the welded interconnectors is not adversely affected. In particular, the interconnectors welded by means of an insert part according to the invention can withstand a (torsion) torque between the interconnectors which is greater than the specification value of 11 Nm.In particular, the welding surface between the interconnectors fails only at about 16 Nm.In particular, the contour of the contacting surface 120 is formed continuously; i.e. at least substantially without corners and angles. For this purpose, all (sharp) corners and angles are rounded, so that the contour of the contact surface 120 and the lateral surface of the welding projection 110 have a smooth course. Soft running is understood to mean that no corners, sharp edges and / or angles occur in a surface or an outline or periphery. This makes it possible to prevent stresses from being applied to the housing partition wall during a welding process or at least reducing the latter.FIG. 2 shows a schematic illustration of an insert part 100 according to the invention, which has a welding plate 140. On the front side of the welding plate 140, which faces the element to be welded (in this case an interconnector), the welding projection 110 according to the invention is arranged, which substantially has the contour of the contacting surface 120 according to the invention. The welding projection 110 according to the invention extends from the front side of the welding plate 140 towards the contact surface and is in particular formed tapering towards the latter. The welding projection 110 has a recess 130 on the lower side in FIG. 2, whereby the contacting surface 120 has the above-mentioned specific shape according to the invention.As shown in FIG. 2, the recess 130 has a substantially prismatic shape with a symmetrical trapezoid as a base. The welding projection 110 has at least substantially a prismatic shape with a round-end rectangle as the base surface, a part of which is missing in the shape of the recess 130 in such a way that the welding projection 110 has the contacting surface 120 with a cross section of a (upside down) short-leg "U". Just as well, the contact surface 120 can have a substantially C-shape or a U-shape.However, it is equally conceivable for the contact surface 120 to have a different shape. In this context, it is only important that a welding of interconnectors can be achieved in which the surface proportion of plastic inclusions is less than 8%, in particular less than (or equal to) 4%, of the total welding surface and wherein the welding maintains a (torsion) torque of at least 12 Nm. In other words, the welding surface may have a maximum surface proportion of 8%, preferably less than 4%, of plastic inclusions and must withstand a torsion moment of at least 12 Nm before the weld fails.This is effected in particular by simulating the welding process with the conventional insert part 100' by means of a FEM method in which the weak points of the conventional welding projection 110' and the conventional contact-making surface 120' are detected and evaluated. This is effected in particular in that a relationship between the stresses and temperatures arising during the welding process and the plastic inclusions (and their position in the welding surface) occurring in the produced welding surface is determined. On the basis of these results, an alternative shape of the contacting surface 120 according to the invention is then determined, in which the weak points can be prevented or at least reduced. Weak points are understood in this context to mean regions in which high stresses and / or temperatures occur during the welding process in a region around the opening in the housing partition wall, and at which plastic inclusions increasingly occur in the produced welding surface after the welding process has been carried out.FIG. 3 shows the front view of an insert part 100 according to the invention for the welding electrode. Here, the welding plate 140 has substantially the shape of a "T". By such a shaping, in particular an alignment of the insert part 100 according to the invention on the welding electrode can already be provided or formed.Furthermore, a circle indicates in FIG. 3 a region which is shown in more detail in a detailed view IV in FIG. 4.FIG. 4 shows the detailed view IV of the welding projection 110 according to the invention, indicated in FIG. 3, with the recess 130 and the contacting surface 120 according to the invention.FIG. 5 shows a side view of the insert part 100 according to the invention. It can be seen here that a protrusion 160 is formed on a rear side of the welding plate 140, namely the side which is opposite the welding projection 110, which protrusion essentially has the shape of a feather key formed in a round end on one side.In addition, a fastening bore 150 passing through the protrusion 160 and ending in the welding plate 140 is arranged in the insert part 100 with a thread, by means of which the insert part 100 can be fastened to the welding electrode, namely by means of a screw.As a result, the insert part 100 can be changed or replaced easily and quickly, which on the one hand lowers the tool costs since it is not necessary to replace the entire welding electrode arrangement or the entire welding electrode, and on the other hand reduces the time required for the replacement or replacement of the insert part 100, which can reduce production costs and, for example, prevent or at least shorten a production stop.In particular, the fastening bore 150 is arranged substantially at the height of the welding projection 110.FIG. 6 shows a rear view of the insert 100, on which the rear side of the welding plate 140 can be seen. In FIG. 6, the shape of the protrusion 160 can also be seen in more detail, which is semicircular at an upper end and has a chamfer at a lower end.In this case, the protrusion 160 can be inserted into a correspondingly complementarily configured groove in the welding electrode, as a result of which the insert part 100 can be centered on the welding electrode. Subsequently, in order to fasten the insert 100 to the welding electrode, a screw can be screwed through the welding electrode into the fastening bore 150 of the insert 100.Thus, the insert part 100 according to the invention can be easily mounted and removed on welding electrodes, which leads to improved handling or easier handling, and thus reduces mounting costs and the susceptibility to errors during mounting. Furthermore, welding electrodes already put into operation can be easily, economically and quickly retrofitted with the insert part 100 according to the invention. In particular, it is not necessary to replace the entire welding electrodes, but it is sufficient to replace only the conventional insert 100' with the insert 100 according to the invention. This can take place in particular within an exchange time of less than 5 minutes.With the aid of the insert part 100 according to the invention, the interconnectors of the electrochemical cells of the lead-acid accumulator 10 can thus be welded in such a way that the area proportion of plastic inclusions in the welding surface between the interconnectors is at most 8%, in particular less than 8%, particularly preferably at most or less than 4% of the entire welding surface, wherein at the same time the strength of the weld between the interconnectors is designed in such a way that the weld resists a torsion moment of at least 12 Nm, in particular at least 16 Nm (without failure).For example, by using the insert part 100 according to the invention in an opening with an area in the order of magnitude of 90 mm 2 to 100 mm 2 the area proportion of plastic inclusions in the welding area can be reduced from 36 mm 2 to 51 mm 2 to 0 mm 2 to 15 mm 2, preferably to 0 mm 2 to 5 mm 2.List of reference charactersV vehicle 10 accumulator 100 welding electrode insert 110 welding projection 120 contact surface 130 recess 140 welding die 150 mounting bore 160 protrusion 100' conventional welding electrode insert 110' conventional welding projection 120' conventional contact surface 140' conventional welding die

Claims

Method for welding in each case one interconnector of two adjacent electrochemical cells of an accumulator, in particular a lead-acid accumulator (10), wherein the two electrochemical cells are arranged separated from one another by means of a housing separating wall, wherein the interconnectors are arranged facing one another on two opposite sides of the housing separating wall, wherein an opening is arranged in a region of the housing separating wall at which the interconnectors are opposite one another, and wherein the method comprises the following steps: - contacting the interconnectors with a welding electrode arrangement, wherein the welding electrode arrangement comprises at least one pair of welding electrodes, wherein in each case one welding electrode of the at least one pair of welding electrodes contacts one of the interconnectors by means of an insert part (100); welding the interconnectors in such a way that by means of a pressure applied by the insert parts (100) of the welding electrodes and a current applied to the welding electrode arrangement, the material of the interconnectors melts at least in regions and connects in a materially integral manner through the opening in the housing partition wall, namely so that the welding surface produced has an area proportion of plastic inclusions of at most 8% in the welding surface, wherein the insert part (100) has a welding plate (140), on the front side of which a welding projection (110) is formed, which extends from the welding plate (140), and wherein the welding projection (110) has a recess (130).Method according to claim 1, wherein the area proportion of plastic inclusions in the welding surface is less than 8%, in particular less than 4%.Method according to claim 1 or 2, wherein the insert part (100) has been calculated and simulated by means of a finite element method.Method according to one of Claims 1 to 3, wherein the welding projection (110) of the insert (100) has a shape which has been calculated and simulated in such a way that the proportion by area of plastics inclusions in the welding surface is at most 8%, preferably less than 8%, particularly preferably less than 4%, of the welding surface.Method according to one of Claims 1 to 4, wherein the welding projection (110) has the recess (130) in such a way that the cross section of the welding projection (110) is at least substantially U-shaped or C-shaped.Method according to claim 4 or 5, wherein the welding projection (110) has a contact surface (120) which has an at least substantially U-shaped or C-shaped cross section, wherein the welding projection (110) is formed tapering towards the contact surface (120).The method of any one of claims 1 to 6, wherein the interconnectors are welded using a through-the-partition (TTP) welding process.Method according to one of Claims 1 to 7, wherein the interconnectors are welded at a welding temperature of 300°C to 380°C, in particular 300°C to 360°C, preferably 300°C to 340°C, particularly preferably 300°C to 320°C.Method according to one of Claims 1 to 8, wherein the housing partition wall is produced from plastic which has a melting point of 200°C to 250°C, in particular 220°C.The method according to claim 9, wherein the housing partition is made of polyamide or a copolymer of polyamide and at least one of polyethylene, polypropylene, polyoxymethylene.Method according to one of Claims 1 to 10, wherein the welded interconnectors withstand a torque of at least 12 Nm, in particular of at least 16 Nm.Welding electrode arrangement for welding in each case one interconnector of two adjacent electrochemical cells of an accumulator, in particular a lead-acid accumulator (10), wherein the interconnectors are separated from one another by means of a housing separating wall and are arranged opposite one another on opposite sides of the housing separating wall, wherein the housing separating wall has an opening in a region at which the interconnectors are opposite one another, wherein the welding electrode arrangement has at least one pair of welding electrodes, wherein at least one, in particular each, of the welding electrodes of the at least one pair of welding electrodes has an insert part (100) which is designed to contact a corresponding interconnector, and to weld the interconnectors through the opening in the housing separating wall in such a way that an area proportion of plastic inclusions in the welding surface is at most 8% of the welding surface, wherein the insert part (100) has a welding plate (140), on the front side of which a welding projection (110) is formed, which extends from the welding plate (140), and wherein the welding projection (110) has a recess (130).Welding electrode arrangement according to claim 12, wherein the insert part (100) has been calculated and simulated by means of a finite element method.Welding electrode arrangement according to claim 12 or 13, wherein the welding projection (110) has at least substantially the shape of a prism with a base surface of a round-end rectangle and the recess (130) has at least substantially the shape of a prism with a trapezoidal base surface.Welding electrode arrangement according to one of Claims 12 to 14, wherein the welding projection (110) has a contact surface (120) for contacting the interconnect, wherein the welding projection (110) is formed so as to taper towards the contact surface (120).Welding electrode arrangement according to claim 15, wherein the contact surface (120) has an at least substantially U-shaped or C-shaped cross section.Welding electrode arrangement according to one of claims 12 to 16, wherein a protrusion (160) is formed on the rear side of the welding plate (140) for inserting the insert part (100) into a groove formed in the welding electrode in a complementary manner to the protrusion (160), wherein the insert part (100) is attachable or attached to the welding electrode by means of a fastening bore (150) arranged on the rear side of the welding plate.The welding electrode assembly of any one of claims 12 to 17, wherein the welding protrusion (110) and / or the protrusion (160) are integrally formed with the welding die (140).

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