Device for forming a metallic workpiece and method for its production

Abstract

Device for forming a metallic workpiece in the form of two parallel legs, namely a first leg and a second leg, which are connected on one side by means of an arc, wherein at least the legs extend in a common workpiece plane, comprising - a die with an upper die and a lower die, which can be moved relative to each other by means of a lifting device during a die stroke, and - a clamping device for the force-locking fixing of the first leg, wherein the forming device is designed to form the sheet inserted into the lower die by a die stroke, as a result of which the second leg approaches the first leg, The invention is characterized by a slider which can be moved parallel to the workpiece plane and perpendicular to the longitudinal extension of the leg, which is mechanically coupled to the lifting device via a curved slide track and a sliding block guided in this, so that it can be moved by a linear movement of the lifting device in a feed direction corresponding to the approach direction of the second leg, wherein the forming device is designed to form the sheet inserted into the lower die with the first leg fixed by means of the clamping device and the second leg free, and wherein the slide track is shaped such that the slide always bears against the side of the second leg facing away from the first leg during the forming process.

Description

The invention relates to a device for forming a metallic workpiece in the form of two parallel legs, namely a first leg and a second leg, which are connected on one side by means of an arc, wherein at least the legs run in a common workpiece plane, comprisinga die having an upper die and a lower die, which are movable relative to one another by means of a lifting device within the scope of a die stroke, anda clamping device for the force-locking fixing of the first leg,wherein the forming device is configured to form the sheet inserted into the lower die by a die stroke, as a result of which the second leg approaches the first leg.The invention further relates to a method for producing such a forming device.A forming device of the generic type is known from JP 7372398 B1.In the stators of high-performance electric machines, as are used, for example, as traction drives for motor vehicles, very high current intensities flow during operation. It is therefore necessary for the electrical conductors from which the so-called stator windings are constructed to have large cross sections which are as uniform as possible over the entire conductor length and to be manufactured with high precision. Even slight line faults can lead to local heating, which can lead either directly or indirectly to incorrect performance or even damage via thermal expansions. Such disturbances can be present in particular in the form of local cross-sectional variations of the conductors and / or in the form of local mechanical stresses in the conductor material. At the same time, it is necessary to lay the conductors in the stator very close to one another, which leads to complex shapes, in particular in the region of the so-called "hair pins", i.e. in the region of arches in which the direction of extent of the conductors is deflected. Frequently, such a complex shape with regard to production represents a conflict of goals with the required fault-freeness. As a result, sophisticated forming processes are required in any case in order to meet all requirements.EP 3 484 029 A1 discloses the production of such a hair pin by forming a substantially U-shaped blank. The blank consists of two parallel legs with a substantially rectangular cross section, which are connected to one another via an arc of the same cross section. All the shaped elements, i.e. legs such as arches, lie in a common workpiece plane. The said publication proposes forming the sheet and the leg regions directly adjoining it in a sheet die, wherein the sheet receives a curvature about a curvature axis lying centrally between the legs. In this case, a lateral movement of the legs toward one another and their rotation about their longitudinal axis are unavoidable. This curvature of the sheet out of the workpiece plane takes place in a first method step, namely a stroke of the sheet die. The stroke of a die is understood here in general to mean a bringing together of the upper and lower dies, wherein in practice the lower die is usually fixed to a machine base relative to which the upper die performs a vertical movement. The specific configuration of the relative movement of upper and lower dies, which can optionally also be arranged at the same vertical height in horizontal presses, plays no part in the context of the present invention. In the previously known forming device, the curved die is divided into two laterally. In a second method step, its two lateral parts are displaced vertically relative to one another in the clamped state, so that an offset is produced in the arc region clamped between them. This forming step results in an elongation of the short portion of material located between the lateral parts of the arc die and therefore not clamped itself. This is associated with a cross-sectional tapering. In addition, stresses are generated in the material. The offset required for geometric reasons in the region of the hairpin arc, which is also referred to as S-stroke in the technical jargon, therefore offers room for a disturbance, which, as explained above, should be optimally avoided.The generic JP 7372398 B1 mentioned at the beginning discloses a forming device with several individual forming stations. As the starting workpiece, a straight metal rod is clamped terminally and in radial alignment in a clamping of a gradually rotating round shell. With each rotation step, the workpiece is fed to another forming station and thereby first bent to form a flat hairpin with parallel legs, the first of which is still clamped terminally on the round shell. This preform is supplied in a further rotation step to a die for forming the sheet. Once the sheet is positioned in the lower die, the terminal clamping of the first leg to the round shell is released and an auxiliary clamp is closed further centrally of the first leg to maintain the positioning of the hair pin until the upper die descends into the lower die, so that the sheet is formed. In this case, the auxiliary clamping is released, so that the two legs move substantially freely towards one another and at the same time experience a torsion about their longitudinal axis. This free "flutter" of the legs leads to difficultly reproducible results. Therefore, the hairpin, which is then again exclusively clamped terminally on the round shell, must be transferred to a correction station in which, under video monitoring, the second limb is detected by a movable clamping device and correctly bent into the desired end position. This approach is clearly highly complicated.It is the object of the present invention to design the S-lay configuration of a hairpine in a reliably reproducible manner with little effort.This object is achieved in conjunction with the features of the preamble of claim 1 by a slide which can be moved parallel to the workpiece plane and perpendicular to the limb longitudinal extent and is mechanically coupled to the lifting device via a curved link path and a link block guided therein, such that it can be displaced by a linear movement of the lifting device in a feed direction corresponding to the approach direction of the second limb, wherein the forming device is configured to form the sheet inserted into the lower die when the first limb and the second limb are fixed by means of the clamping device, and wherein the link path is formed such that the slide always bears with force application on the side of the second limb facing away from the first limb during the forming.Preferred embodiments of the invention are the subject of the dependent claims.First, the invention provides for the forming of the sheet to be carried out with the first leg fixed in a force-fitting manner. As a result, during the forming process only the second leg remains movable in order to carry out the required approach movement. This already eliminates one degree of freedom. During the clamping of the first leg, the torsion generated by the curve forming can already be anticipated. For this purpose, the shape of the clamping jaws forming the clamping device is designed such that the first leg is already transferred into its final torsion position and is thus fixed when the clamping device is closed. Due to the shape and material elasticity of the hair pin, this leads to a prestress which presses the sheet firmly into the lower die. During the die stroke, in which the sheet forming takes place, this prestress, which is effected by the clamping device, is relaxed at the same time. However, the opposite case is also conceivable in which the clamping device fixes the first leg in its initial torsion position, so that a torsion stress is built up within the scope of the die stroke, which the first leg elastically follows after the curve forming. However, these details of the first leg clamp are not within the scope of the present invention.This further comprises a mechanical slide which, during the sheet forming process, bears with force application on the outside against the second limb in order to support its approach movement in the direction of the first limb and to prevent "flutter". However, this approach motion is not uniform, i.e., not at a constant speed. Rather, its shape is dependent on the detail processes of the sheet forming. The exact shape can be determined only by considering the details of the particular die shape. In any case, however, this non-uniform movement is realized according to the invention by a correspondingly shaped cam track via which the slide is purely mechanically coupled to the (substantially uniform) die stroke.For determining the specific shape of the curved path or for producing a correspondingly equipped forming device, different approaches are possible. It is conceivable in principle to detect the movement of the second limb by sensor means without a slide according to the invention and to determine the sought curved path shape by corresponding conversion of the actual limb movement. This approach is disadvantageous, however, insofar as the detection of the actual leg movement without a slide also includes the unwanted and unreproducible "flutter" thereof. However, this is to be prevented by the slider. As a refinement of this approach, it would be conceivable to equip the slide with a controllable motor and to provide it with a force control. However, this approach is obviously highly costly. In addition, once this effort is expended, the significantly more cost-effective, purely mechanical slide control by means of a link track could be dispensed with.In contrast to this, it is currently considered to be particularly advantageous to determine the course of the approach movement of the second limb by means of a FEM (Finite Element Method) simulation. Such a simulation allows the ideal movement of the second leg forced by the arc deformation to be calculated without the secondary effects such as "flutter" occurring in practice. It is this ideal leg movement which is to be reproduced by the slide. The results of the FEM simulation can then be converted into the form of at least one section of the link path. If such specifications are present, it is easy for the person skilled in the art to produce a slide track for the mechanical coupling of the slide to the lifting device, which slide track has at least one central part which corresponds to the slide track section formed in this way. This results in a device according to the invention, the slide of which follows the ideal leg movement by purely mechanical coupling or forces the real leg movement into said ideal leg movement. Such a method represents an independent invention and is the subject of dependent claim 9.Regardless of the specific type of shape determination, a link path is advantageously obtained which has a sequence of regions of different slopes and by means of which a uniform linear movement of the lifting device can be converted into a corresponding sequence of sections of the slide movement at different speeds. In particular, it is preferably provided that the slide track comprises a central part which has a sequence of regions of different inclination, by means of which a uniform linear movement of the lifting device between a first contact of the upper die with the bend and an end position of the die stroke can be converted into a corresponding sequence of sections of the sliding movement at different speeds in the feed direction, which corresponds as a whole to the approach movement of the second limb. This functional section of the slotted guide track, which is referred to here as the central part, corresponds to the realization of the fundamental idea according to the invention explained above.However, the slide track does not have to be limited to said central part. Thus, in a development of the invention, it is provided that the slide track comprises a feed part adjacent to the central part with a uniform pitch, by means of which a uniform linear movement of the lifting device can be converted before the first contact of the upper die with the sheet into a section of the sliding movement at a uniform speed in the feed direction. This is intended to intercept manufacturing tolerances of the starting workpiece. Such tolerances may consist, for example, in an incompletely parallel alignment of the legs. For example, the distance of the legs may increase toward their open ends. If the slide already were to be in the starting position when the workpiece is inserted into the forming device, in which position it would interfere with the workpiece at the beginning of the effective forming process, i.e. at the time when the upper die first contacts the sheet, which would make the insertion more difficult or impossible. The mentioned further development therefore provides that the slide is positioned at the beginning of the die stroke set back from said starting position in order to allow the insertion of imperfect starting workpieces. Within the scope of the first stroke section before the first contact between the upper die and the sheet, the slide is moved by means of the explained leading part of the slide track into said starting position. In the case of an imperfect, bent-up workpiece, the second leg is simultaneously forced into the correct starting position.Alternatively or additionally, it can be provided that the slotted guide path comprises a follow-on part (on the other) adjacent to the central part with a monotonically increasing gradient, by means of which a uniform linear movement of the lifting device can be converted, after reaching the end position of the die stroke, into a section with a monotonically increasing speed in the feed direction. In other words, after completion of the actual sheet forming, the slide is thus advanced further in the feed direction and the second limb is thereby displaced inwardly beyond the end position reached, i.e. towards the first limb. This approach is the result of the finding that the material and shape elasticity of the formed hair pin can lead to a certain amount of outward recovery of the second leg as soon as the force-loaded contact of the slide on the second leg ceases. This is counteracted by bending over the second leg. This bending is served by the explained follow-on part of the slide track. In order to be able to use this follow-on part of the slide track even actually by a corresponding follow-on movement of the slide, it is obviously necessary for the lifting device to continue its movement even after final die closure. This is the case in any case in conventional presses in which the upper die is coupled to the lifting device via a spring.In a preferred embodiment of the invention, the slide track forms a bidirectional guidance of the slide block. This means that the slide is moved back into the starting position by means of reverse positive guidance when the die is opened, i.e. when the lifting device runs through a movement opposite to the forming die stroke.In an alternative embodiment, however, it is provided that the slide track forms an exclusively unidirectional guide of the slide block and the slide is spring-biased counter to its feed direction. In this design, the slide is reset independently of the opening movement of the die by the force of the spring which has tensioned itself during the advancement of the slide. Such a configuration offers more freedom in the selection of the slotted-link path shape, which then only has to allow "smooth" transitions between the individual sections in one direction.In principle, a combination of both embodiments is also conceivable in the sense of a bidirectional positive guidance of the slide with spring support during retraction.Further features and advantages of the invention will become apparent from the following specific description and the drawings.The following are shown: FIG. 1 : a perspective illustration of a preferred embodiment of a workpiece blank, FIG. 2 : the workpiece after forming according to the invention, FIG. 3 is a fragmentary view of a forming apparatus according to the invention, FIG. 4 : shows a schematic detailed illustration of the slide track / slide block coupling of the forming device of FIG. 3 and FIG. 5 : shows a schematic illustration of coupling blocks with a link track according to the invention.Like reference numerals in the figures indicate like or analogous elements.FIG. 1 shows a perspective illustration of the preferred embodiment of a workpiece 10 to be formed according to the invention in a blank stage. In this state, the legs 101 and-in the embodiment shown-the bend 102 connecting them on one side lie in a common workpiece plane which in the embodiment shown is at the same time a plane of symmetry of the substantially rectangular cross section of legs 101 and bend 102.FIG. 2 shows the shaped workpiece 10 according to the invention. At the same time, the legs 101 are moved closer to one another in the lateral direction according to the lateral movement arrows 31. In addition, torsion of the legs 101 about their longitudinal extension axis takes place in accordance with the torsion arrows 32.FIG. 3 shows the workpiece 10 in the lower die 22 of a forming device 20 shown only incompletely, namely without the corresponding upper die. The shaping of the lower die 22 permits, on the one hand, clamping of the first limb 101 aillustrated on the right in FIG. 3 and, on the other hand, migration of the second limb 101 billustrated on the left in FIG. 3 as a result of the forming of the bend 102 within the scope of a die stroke. The basic design, not shown, of the upper die and of a lifting device, by means of which the upper die can be advanced in the direction of the lower die 22 during the die stroke, is familiar to the person skilled in the art.A slide 24, which can be moved into a recess 221 in the lower die 22 and can be moved parallel to the workpiece plane (relative to the workpiece in the blank stage) and perpendicular to the limb longitudinal extension direction, is essential to the invention. During the movement of the second limb 101 bin the direction of the first limb 101 a, it is intended to bear continuously with force on the outside against said second limb 101 bto prevent its "flutter" within the scope of an approaching movement caused by the curve forming. For this purpose, the slide 24 must perform a displacement movement exactly corresponding to the lateral movement of the second limb 101 b.In order to achieve this, the slide 24 is fixed to a coupling block 26 which, as shown in FIG. 4, has a slide track 261 in which a slide block 281 of a coupling element 28 engages. The coupling element 28 is connected to the lifting device and performs a vertical movement (vertical movement arrow 33) predefined by the latter during the die stroke. By engaging the slide block 281 in the slide track 261, this vertical movement is translated into a horizontal movement (horizontal movement arrow 34), namely the advancing movement of the slide 24. The skilled person will recognize that the illustrated selection of a vertical movement of the coupling element 28 and a horizontal movement of the slide 24 is not obligatory and is dependent on the basic orientation of the forming device 20. Also, via the slide track / slide block coupling, other than rectangular motion transmission ratios can be realized.In FIG. 4, the link track 261 is excessively simplified and is shown substantially straight. However, this will generally not meet the complex lateral movement of the second leg 101 b. FIG. 5 shows a particularly preferred shape of the slide track 261. This has essentially three parts, namely a lead part I, a central part II and a lead part III. The central part II is essential to the invention; lead and lead parts I and III represent preferred refinements.It can be seen that the central part II of the slotted guide track 261 is composed of sections of different inclination. A sliding block 281 guided in the sliding track 261 and forced to move vertically uniformly will cause a lateral movement of the coupling block 26 and thus of the slide 24, which is no longer shown in FIG. 5, which is composed of corresponding movement sections with different movement speeds. The desired movement can be determined by means of an FEM simulation of the ideal movement of the second limb 101 bduring the forming process. The curve path 261 required for this can then be easily recomputed by the person skilled in the art.The lead portion I has a uniform, sharp slope and serves to quickly move the slide 24 from a far-removed stand-by position to its starting position at the beginning of the forming process. The initially wide distance from the starting position allows the insertion of workpieces 10 with incorrectly bent-up legs 101 a,b. At the beginning of the forming process, these are bent into a correct starting position when the lead part I is traversed. However, if the workpiece 10 is already correctly shaped during the insertion, only the contact between the slide 24 and the second leg 101 bis established during the passage of the lead part I.The follow-up part III has a monotonically increasing stiffness and is passed through after completion of the actual sheet forming. Here, the second leg 101 bis strongly bent over, which has proven its worth for compensating its intrinsic elasticity.Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative exemplary embodiments of the present invention. The skilled person will be given a wide range of possible variations in the light of the disclosure here. In particular, the specific shape of the gate track 261 has to be selected to suit the specifics of the individual case taking into account the specific S-impact shape and the material properties of the workpiece 10, such as material type, ductility, elasticity, hardness, temperature, etc. The method described above of the FEM simulation is suitable for this purpose.List of reference characters10 Workpiece 101a First leg 101b Second leg 102 Bend 20 Forming device 22 Lower die 221 Recess 24 Slide 26 Coupling block 261 Slide track 28 Coupling element 281 Slide block 31 Lateral movement arrow 32 Torsion arrow 33 Vertical movement arrow 34 Horizontal movement arrow I Lead part of 261 II Central part of 261 III Lead part of 261

Claims

Device (20) for forming a metallic workpiece (10) in the form of two parallel limbs (101a, b), namely a first limb (101a) and a second limb (101b), which limbs are connected on one side by means of a bend (102), wherein at least the limbs (101a, b) run in a common workpiece plane, comprising - a die having an upper die and a lower die (22), which can be moved relative to one another in the course of a die stroke by means of a lifting device, and - a clamping device for fixing the first limb (101a) in a force-fitting manner, wherein the forming device (20) is configured to form the bend (102) inserted into the lower die (22) by means of a die stroke, as a result of which the second limb (101b) approaches the first limb (101a), characterized a slide (24) which can be moved parallel to the workpiece plane and perpendicular to the limb longitudinal extent and which is mechanically coupled to the lifting device via a curved link track (261) and a link block (281) guided therein, such that it can be displaced by a linear movement of the lifting device in a feed direction corresponding to the approach direction of the second limb (101b), wherein the forming device (20) is configured to form the sheet (102) inserted into the lower die (22) when the first limb (101a) and the free second limb (101b) are fixed by means of the clamping device, and wherein the link track (261) is shaped such that the slide (24) always bears with force impact on the side of the second limb (101b) facing away from the first limb (101a) during the forming.Device (20) according to Claim 1, characterized in that the slotted guide track (261) has a sequence of regions of different inclination, by means of which a uniform linear movement of the lifting device can be converted into a corresponding sequence of sections of the slide movement at different speeds.Device (20) according to one of the preceding claims, characterized in that the slide track (261) comprises a central part (II) which has a sequence of regions of different inclination, by means of which a uniform linear movement of the lifting device between a first contact of the upper die with the bend (102) and an end position of the die stroke can be converted into a corresponding sequence of sections of the slide movement at different speeds in the feed direction, which corresponds as a whole to the approach movement of the second limb (101b).Device (20) according to Claim 3, characterized in that the slotted guide track (261) comprises a lead part (I) which is adjacent to the central part (II) and has a uniform pitch, by means of which a uniform linear movement of the lifting device can be converted, before the first contact of the upper die with the bend (102), into a section of the slide movement at a uniform speed in the feed direction.Device (20) according to one of Claims 3 to 4, characterized in that the slotted guide track (261) comprises a follow-on part (III) which is adjacent to the central part (II) and has a monotonically increasing gradient, by means of which a uniform linear movement of the lifting device can be converted, after reaching an end position of the die stroke, into a section having a monotonically increasing speed in the feed direction.Device (20) according to one of the preceding claims, characterized in that the slide track (261) forms a bidirectional guidance of the slide block (281).Device (20) according to one of the preceding claims, characterized in that the slide track (261) forms an exclusively unidirectional guide of the slide block (281), and the slide (24) is spring-biased counter to its feed direction.Device (20) according to one of the preceding claims, characterized in that the shape of the slotted guide track (261) has been determined by conversion of results of an FEM simulation of the approaching movement of the second limb (101b).Method for producing a forming device (20) according to one of the preceding claims, comprising the steps: - determining the course of the approach movement of the second limb (101b) by means of a FEM simulation, - determining a shape of a link path section by converting the determined approach movement, - generating a link path (261) having a central part (II) corresponding to the link path section determined in this way for the mechanical coupling of the slide (24) to the lifting device.

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