Patent Publication Number: US-2018050424-A1

Title: Method and Device for Splitting an Initial Metal Sheet, And Metal-Sheet Part

Description:
The invention relates to a method and to a device for separating a starting sheet metal at a separation location. The invention additionally relates to a sheet metal part which in particular is designed for use in a laminated core, such as a laminated core for a transformer, or an electric machine. 
     A method and a device for punching a starting sheet metal at a separation location are known for example from EP 1758697 B1. There, the starting sheet metal is clamped adjacently to a separation location. A die punch moves completely through the starting sheet metal with a punch edge along the separation location and in so doing separates off a portion of the starting sheet metal. In order to be able to punch high-strength sheet metals, it is proposed to additionally apply a bending moment to the starting sheet metal. 
     When a punching process is performed, a punching tool is moved through the starting sheet metal at the separation location. Other known separation methods for separating a sheet metal are laser cutting or water jet cutting, for example. 
     Proceeding from this basis, the object of the invention can be considered that of creating a method and a device for separating a starting sheet metal and also of creating a sheet metal part that are particularly suitable for use within a magnetic field. 
     This object is achieved by a method having the features of claim  1 , by a device having the features of claim  10 , and by a sheet metal part having the features of claim  15 . 
     In accordance with the invention, the starting sheet metal is divided at the separation location into a first portion and a second portion. The resultant separation edge of the first portion and/or of the second portion of the starting sheet metal runs along the grain boundaries of the material of the starting sheet metal. It has been found that the magnetic flux at the separation edge is thus hindered to a much lesser extent and that the use of a sheet metal part having a side edge that is formed by at least one portion of the separation edge running along the grain boundaries increases the efficiency. It is anticipated that the magnetic flux density can be significantly increased with constant magnetic field strength. 
     In accordance with the invention the starting sheet metal is clamped in a first portion adjacently to the separation location. The second portion of the starting sheet metal is disposed on the side of the starting sheet metal opposite the first portion. Once the starting sheet metal has been clamped, a bending moment is applied to the starting sheet metal about a bending axis extending along the separation location and/or a tensile force directed away from the separation location is applied to the second portion. In contrast to other separation methods, the starting sheet metal is not fully penetrated at the separation location by a blade or edge, and instead the forming of a crack is initiated at the separation location, for example in that a shear stress is applied at an incline or transversely to the plane of extension of the starting sheet metal and/or a notch of shallow depth is formed. The starting sheet metal is not punched through or cut through at the separation location, and instead is merely notched or cut into or scratched into to a limited depth and/or is subjected to a shear stress, such that cracks and preferably microcracks form at the separation location in the starting sheet metal. Due to the bending moment acting at the separation location or due to the tensile force acting on the starting sheet metal, a fracture, preferably a brittle fracture, then forms along the separation location. The starting sheet metal then becomes separated or broken at the separation location between the first portion and the second portion, wherein separation edges are created, which run along the grain boundaries. 
     In order to produce the microcracks at the separation location whilst the bending moment and/or the tensile force are/is effective, a notch of limited depth can be made, wherein the depth of the notch is smaller than the thickness of the starting sheet metal at the separation location at least by a factor of 3 to 5. In addition or alternatively, a shear stress can also be produced on the starting sheet metal at the separation location, at an incline or transversely to the surface. 
     In an exemplary embodiment the notch and/or the tensile moment are/is produced using a mechanical blade acting on the starting sheet metal. Alternatively, it is also possible to form a notch in the starting sheet metal or to cut into said sheet metal by other means, such as lasers. The mechanical blade can act on the starting sheet metal for example at a cutting angle having a value of from 80° to 90° in relation to the plane of extension of the first portion. 
     In one exemplary embodiment the tensile force can act parallel to the second portion of the starting sheet metal. The tensile force acts here in the plane in which the second portion extends starting from the separation location. 
     The starting sheet metal is preferably separated at the separation location by the creation of a brittle fracture. It is particularly preferred if the starting sheet metal is cooled at least at the separation location before or during the separation process. By way of example, at least the separation location of the starting sheet metal can be cooled by a cooling fluid, such as liquid nitrogen (LN). The brittleness of the starting sheet metal can thus be increased, and the separation along the grain boundaries can be improved. 
     It is also advantageous if, after the separation along the separation location, at least one sheet metal part is separated from the first portion and/or the second portion by an arbitrary separation method. This sheet metal part has at least one side edge formed at least by a portion of the separation edge. This side edge thus runs along the grain boundary of the material of the starting sheet metal. This side edge is provided in particular so that, when the sheet metal part is used in a laminated core, magnetic field lines enter the sheet metal part and exit from the sheet metal part. This side edge thus forms a passing area, i.e. an exit and/or entry area, for magnetic field lines and by way of example can border an air gap, as is formed for example between the rotor and the stator of an electric machine. 
     A device according to the invention for separating a starting sheet metal has a clamping means, with which the first portion can be securely clamped adjacently to the separation location. The device also has an acting arrangement, which is adapted to apply a bending moment to the starting sheet metal about a bending axis extending along the separation location and/or to apply a tensile force directed away from the separation location to the second portion of the starting sheet metal. In addition, a tool is provided which for example can have a mechanical blade or another means, with which the forming of a crack can be initiated in the starting sheet metal at the separation location, for example by forming a notch in said sheet metal or by scratching into said sheet metal, and/or with which a shear stress can be produced at the separation location, which stress is directed at an incline or right angle to a plane in which the first portion of the starting sheet metal extends. The tool does not fully cut through the starting sheet metal at the separation location, but instead penetrates said sheet metal at most to a limited depth. Alternatively or additionally, an appropriate shear stress can also be created at the separation location in order to initiate the separation or breaking at the separation location. As a result of the shear stress or the notching at the separation location, as long as the acting arrangement applies the bending moment and/or the tensile force, the forming of a crack is initiated in the starting sheet metal at the separation location and the starting sheet metal is separated or fractured. A separation edge is formed at the first portion or at the second portion and runs along the grain boundary of the material of the starting sheet metal. 
     In a preferred embodiment the acting arrangement has a first acting unit and a second acting unit, which are movable relative to one another in a working direction. The tool is preferably movable in a working direction independently of the acting arrangement, but can also be connected to the first acting unit and therefore can move together with the first acting unit. The notching or application of the shear stress is preferably performed on the starting sheet metal in the working direction by the tool. 
     In one exemplary embodiment the first acting arrangement can have a first press part with a first press face and the second acting arrangement can have a second press part with a second press face. The press faces are each intended to rest on the second portion of the starting sheet metal when the bending moment and/or the tensile force are/is applied. The starting sheet metal is thus supported on opposite sides, specifically on one side of the separation location by the clamping means and on the other side of the separation location by the two acting units. An accidental plastic deformation of the first and the second portion during the separation process can thus be avoided. 
     It is also advantageous if the two press parts are mounted so as to be movable at an incline or right angle to the working direction. A tensile force can thus be applied to the second portion of the starting sheet metal in a very simple manner. 
     In one exemplary embodiment the press faces are oriented parallel to one another and at an incline to the working direction. As a result of the relative movement of the two press parts in the working direction, a tensile force can thus be applied additionally to the second portion (similarly to a wedge surface gear) without the need for a separate drive for this purpose. 
     The invention additionally relates to a sheet metal part that in particular can be used in a laminated core that conducts magnetic field lines. The sheet metal part is produced from a starting sheet metal by at least one separation process. The sheet metal part has at least one side edge, which runs along the grain boundaries along the material of the starting sheet metal. This side edge can be used particularly preferably in order to guide magnetic field lines into the sheet metal part and out from the sheet metal part. With constant magnetic field strength, it has been found that the side edge extending along the grain boundaries does not hinder the forming of the magnetic flux, and therefore a large magnetic flux density can be achieved. 
    
    
     
       Advantageous embodiments of the invention will become clear from the dependent claims, the description, and the drawing. Preferred embodiments will be explained in greater detail hereinafter with reference to the accompanying drawings, in which 
         FIGS. 1 and 2  show, respectively, a schematic partial illustration of a rotor lamination and a stator lamination of an electric machine in a side view, 
         FIGS. 3 to 5  each show a schematic illustration of a plurality of teeth of the rotor lamination and the stator lamination according to  FIGS. 1 and 2 , 
         FIGS. 6 to 8  each show a block diagram of an exemplary embodiment of a device for separating a starting sheet metal at a separation location in different situations during the separation process, and 
         FIGS. 9 to 11  each show a schematic basic diagram of the production of a sheet metal part from a starting sheet metal separated at a separation location. 
     
    
    
       FIGS. 1 and 2  schematically illustrate, respectively, a stator lamination  15  and a rotor lamination  16 . Such laminations are combined, respectively, in stators and rotors of electric machines to form laminated cores. They have a ring part  17 , from which teeth  18  extend radially inwardly and outwardly respectively, said teeth having a tooth head  19  at their free end. Exemplary embodiments of teeth  18  for a stator lamination  15  or a rotor lamination  16  are illustrated in  FIGS. 3 to 5 . The teeth  18  can be connected to one another from a plurality of individual sheet metal parts  20  at the illustrated joint lines  21 . A form-fitting and/or frictionally engaged connection can be produced at the joint lines  21 . At the tooth head  19 , each tooth  18  has a passing area  22 , through which magnetic field lines exit from the tooth  18  and enter the tooth  18 . The passing area  22  can be arranged on a single sheet metal part  20  or in portions on a number of interconnected sheet metal parts  20 . 
     It goes without saying that, in a modification from  FIGS. 3 to 5 , each tooth  18  can be formed merely from a single sheet metal part  20  without seam and joint. 
     It should be noted at this juncture that the invention can relate not only to rotary electric machines, but also to linear drives. The stator lamination  15  and the rotor lamination  16  then are not formed annularly in a peripheral direction, but instead extend in a straight line. The shape of the teeth  18  can be provided here too in the manner as has been illustrated schematically in  FIGS. 3 to 5 . 
     The at least one sheet metal part  20  is produced by at least one separation process from a starting sheet metal  27 . It is separated at a separation location  28 , wherein at least one separation edge  29 , and in accordance with the example two separation edges  29  ( FIGS. 9 to 11 ), are created at the separation location and extend along a grain boundary of the material of the starting sheet metal  27 . In accordance with the example the starting sheet metal  27  is separated at the separation location  28  into a first portion  30  and a second portion  31 , wherein each of the two portions  30 ,  31  has a separation edge  29 , which extends along the grain boundary of the material of the starting sheet metal  27 . One or more sheet metal parts  20  can be separated off from these portions  30 ,  31  in subsequent separation processes, for example by punching, cutting, laser cutting, water jet cutting, etc., as is shown schematically in  FIGS. 9 to 11 . These sheet metal parts  20  have a side edge  32 , which is formed in each case by a portion of the separation edge  29 . Each side edge  32  can form a passing area  22  of a tooth  18  or an area portion  22   a  of a passing area  22  (see also  FIGS. 3 to 5  by way of example). 
     An exemplary embodiment of a device  35  for separating the starting sheet metal  27  at the separation location  28  into the first portion  30  and the second portion  31  is illustrated in  FIGS. 6 to 8 . The device  35  has a machine frame  36 . A clamping means  37  comprising a first clamping part  37   a  and a second clamping part  37   b  is arranged on the machine frame  36 . The two clamping parts  37   a ,  37   b  are movable relative to one another in a working direction A. In accordance with the example the second clamping part  37   b  is fixed relative to the machine frame  36 , whereas the first clamping part  37   a  is movable in the working direction A along the machine frame  36  and relative to the second clamping part  37   b . The clamping means  37  is adapted to clamp the first portion  30  of the starting sheet metal  27  between the two clamping parts  37   a ,  37   b.    
     Adjacently to the clamping means  37 , the device  35  has an acting arrangement  38 . The acting arrangement  38  is adapted to produce, at the separation location  28  of the starting sheet metal  27 , a bending moment M about a bending axis B extending parallel or tangentially to the separation location  28 . The acting arrangement  38  is also adapted to produce a tensile force Z parallel to the second portion  31  of the starting sheet metal  27 , away from the separation location  28 . In a modified embodiment, merely the bending moment M or merely the tensile force Z can also be produced, by way of an alternative. 
     The acting arrangement  38  has a first acting unit  38   a  and a second acting unit  38   b , which are movable relative to one another in the working direction A. The first acting unit  38   a  has a ram  39 , which is guided movably in the working direction A along the machine frame  36  and which can be moved in the working direction A by a drive (not illustrated). On the side facing towards the second acting unit  38   b , a first press part  40  is arranged on the ram  39 . The first press part  40  is supported on the ram  39  so that the force exerted by the ram  39  in the working direction A can be transferred to the first press part  40 . 
     The first press part  40  is mounted on the ram  39  at an incline or right angle to the working direction A by means of a first bearing means  41  so as to be movable in a transverse direction Q. The press part optionally can also be mounted additionally on the machine frame  36 . The first press part  40  has, on its side facing towards the second acting unit  38   b , at least one first press face  42 , by means of which it bears against the second portion  31  of the starting sheet metal so as to exert the bending moment M and/or the tensile force Z. In the case of the exemplary embodiment described here, protrusions  43 , such as spikes, nubs or the like, are provided in the region of the at least one press face  42  so that a force can also be applied via the first press part  40  parallel to the plane in which the at least one press face  42  extends. This plane is arranged in the exemplary embodiment at an incline to the working direction A. If the first press part  40  is disposed in a starting position at a distance from the second portion  31  of the starting sheet metal  27 , the part of the at least one press face  42  that is arranged at a greater distance from the separation location  28  in the transverse direction Q is disposed closer to the starting sheet metal  27 , as considered in the working direction A ( FIG. 6 ). 
     The second acting unit  38   b  has a support part  46 , on which a second press part  47  can be mounted movably in the transverse direction Q by means of a second bearing means  48 , similarly to the mounting of the first press part  40 . The second press part  47  has at least one second press face  49 , which bears against the starting sheet metal  27  in order to produce the bending moment M and/or the tensile force Z. The at least one second press face  49  extends in a plane that is oriented parallel to the plane in which the at least one press face  42  extends. Similarly to the first press face  42 , protrusions  43  are also provided in the region of the at least one second press face  49  in accordance with the example. 
     In accordance with the example, the support part  46  is supported on the machine frame  36  or a base spring-elastically in the working direction A. In a modification hereto, it could also be arranged movably in the working direction A, similarly to the ram  39 . 
     A drivable tool  52  that is mounted movably in the working direction A additionally belongs to the device  35  and in the exemplary embodiment is embodied as a mechanical cutting tool having a blade  53 . The tool  52  serves to form a notch at the separation location  28 , said notch having a shallow depth T that is smaller than the thickness of the starting sheet metal  27  at the separation location  28 . The depth T is preferably smaller than the thickness D of the starting sheet metal  27  at least by a factor of 3 to 5. In the exemplary embodiment the tool  52  is movable in the working direction A so that it acts on the starting sheet metal  27  at a cutting angle of approximately 90° relative to the plane of extension of the first portion  30 . 
     Instead of the notching, a tool  52  can also be provided which produces a shear stress at the separation location  28  by means of a force exerted onto the starting sheet metal  27  preferably in the working direction A. 
     In any case, the tool  52  is adapted to produce small microcracks at the separation location  28  in order to initiate the breaking of the starting sheet metal  27  at the separation location  28 . The tool  52  does not perform a cutting or punching operation and does not fully sever the starting sheet metal  27  at the separation location  28 . A material flow is thus at least largely avoided. The grain boundaries are maintained at the resultant separation edges  29  of the two portions  30 ,  31 , which improves the course of magnetic field lines at the separation edges  29  if a sheet metal part produced from the starting sheet metal is located within a magnetic field. 
     In order to increase the brittleness, the starting sheet metal can be cooled optionally, at least at the separation location  28 . The cooling can be performed before the starting sheet metal  27  is introduced into the device  35 . It is also possible to provide a coolant feed  55  at the device  35  in order to feed a cooling fluid K to the separation location  28 . By way of example, liquid nitrogen LN can be used as cooling fluid K. 
     The method for separating the starting sheet metal  27  at the separation location  28  along the grain boundary of the material of the starting sheet metal  27  is as follows: 
     Firstly, a starting sheet metal  27  is provided and is introduced into the device  35 . The first portion  30  of the starting sheet metal  27  is then clamped between the two clamping parts  37   a ,  37   b , adjacently to the separation location  28 . 
     In order to produce a brittle fracture at the separation location  28  or in order to improve the breaking at the separation location  28  along the grain boundary, at least the separation location  28  or the entire starting sheet metal  27  can be cooled by a cooling fluid K before or after the clamping of the starting sheet metal  27 . 
     The second portion  31  of the starting sheet metal  27  is acted on by the acting arrangement  38  so that the second portion  31  of the starting sheet metal  27  is held between these press faces  42 ,  49 . On account of the press faces  42 ,  49  extending from the first portion  30  at an incline to the working direction, a bending moment M about a bending axis B is produced at the separation location  28 , at a right angle to the working direction A and the transverse direction Q. In addition, a tensile force Z is produced parallel to the direction of the course of the second portion  31 . The direction of the tensile force Z runs parallel to the planes in which the press faces  42 ,  29  extend. 
     In order to produce the bending moment M and the tensile force Z, the ram  39  is moved towards the starting sheet metal  27  or the second acting unit  38   b . In so doing, the second portion  31  of the starting sheet metal  27  firstly comes into contact with the first press part  40  and is then bent about the bending axis B until the second portion  31  is held between the two press faces or the two press parts  40 ,  47 . As a result of the bearing means  41 ,  48 , the two press parts  40 ,  47  can move away from the separation location  28  in the transverse direction Q. This results in the tensile force Z. The second portion  31  can be held for this purpose in a frictionally engaged and/or form-fitting manner between the two press faces  42 ,  49 . 
     In accordance with the example the tensile stress Z is caused by the tool  52 . The tool  52  has a wedge face  52   a , on which the first press part  40  is supported. By means of a movement of the tool  52  towards the second acting unit  38   b , the second press part  40  is moved away from the separation location  28  in the transverse direction Q. On account of the frictionally engaged and/or form-fitting coupling of the second press part  41  to the second portion  31 , the second press part  41  is also moved away from the separation location  28  in the transverse direction Q. This situation is illustrated schematically in  FIG. 7 . 
     The tool  52 , and in accordance with the example the blade  53 , then forms a notch of shallow depth T in the surface region of the starting sheet metal  27  at the separation location  28  ( FIG. 8 ). In so doing, the forming of a crack is initiated at the separation location  28 , with the crack continuing from the notched surface, which is subject to a tensile stress, through the thickness of the starting sheet metal  27  at the separation location  28 . The starting sheet metal  27  is separated between the first portion  30  and the second portion  31  by an initiated breaking operation, wherein a separation edge  29  is created at both portions  30 ,  31 , said separation edges running along the grain boundaries of the material of the starting sheet metal  27 . 
     It is advantageous when the clamping means  37  to a certain extent releases the pressure on the first portion  31  of the sheet metal at least in the region of the separation location  28  after the notching procedure. The sheet metal can thus be moved back from the blade  53 , reducing the wear of the blade  53  or of the tool  52 . 
     As a result of this separation method, a flow of the material of the starting sheet metal  27  at the separation location  28  is avoided or reduced to a minimum. The following is true for the method according to the invention: 
       σ v √{square root over ((σ B +σ Z ) 2 +3 τ     2   )}
 
     with 
     σ V : comparison stress 
     σ B : bending stress 
     σ Z : tensile stress 
     τ: shear stress 
     The tensile stress σ Z  is provided here by the tensile force Z, and the bending stress σ B  is provided by the bending moment M. The shear stress τ is caused by the tool  52 . 
     The separation location  28  in accordance with the example has a straight course, at least in part, but can also have an at least partially curved course. 
     As shown in  FIGS. 9 to 11  and already explained, a sheet metal part  20  can then be separated off from the two portions  30 ,  31  of the starting sheet metal  27  by an arbitrary separation method, said sheet metal part having a side edge  32  formed at least by a portion of the separation edge  29 . 
     The invention relates to a sheet metal part  20  that is produced from a starting sheet metal  27  and has at least one side edge  32 , which extends along the grain boundaries of the material of the starting sheet metal  27 . A method and a device for separating or breaking the starting sheet metal  27  at a separation location  28 , with said separation/breaking being initiated by forming a notch in the starting sheet metal or by scratching or cutting into the starting sheet metal, are also proposed. The starting sheet metal is clamped via a first portion  30  adjacently to the separation location  28 . On the side of the separation location  28  opposite the first portion  30 , there is disposed a second portion  31  of the starting sheet metal  27 , which second portion is acted on in order to produce a bending moment M about a bending axis B at the separation location  28  and/or in order to produce a tensile force Z directed away from the separation location  28 . By forming a notch of limited depth and/or by producing a shear stress at the separation location  28 , the forming of a crack is preferably initiated at the separation location  28 , and separates the second portion  31  from the first portion  30  along the grain boundary of the material of the starting sheet metal  27 . 
     LIST OF REFERENCE SIGNS 
     
         
           15  stator lamination 
           16  rotor lamination 
           17  ring part 
           18  tooth 
           19  tooth head 
           20  sheet metal part 
           21  joint line 
           22  passing area 
           22   a  area portion of the passing area 
           27  starting sheet metal 
           28  separation location 
           29  separation edge 
           30  first portion 
           31  second portion 
           32  side edge 
           35  device 
           36  machine frame 
           37  clamping means 
           37   a  first clamping part 
           37   b  second camping part 
           38  acting arrangement 
           38   a  first acting unit 
           38   b  second acting unit 
           39  ram 
           40  first press part 
           41  first bearing means 
           42  first press face 
           43  protrusion 
           46  support part 
           47  second press part 
           48  second bearing means 
           52  tool 
           53  blade 
           55  coolant feed 
         α cutting angle 
         σ B  bending stress 
         σ V  comparison stress 
         σ Z  tensile stress 
         τ shear stress 
         A working direction 
         B bending axis 
         K cooling fluid 
         M bending moment 
         T depth 
         Z tensile force