Patent Publication Number: US-2023155461-A1

Title: Conductor forming device and method of manufacturing wave winding coil

Description:
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-187725, filed on 18 Nov. 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a conductor forming device and a method of manufacturing a wave winding coil. 
     Related Art 
     A wave winding coil is generally known as a coil included in a stator for a rotary electric machine such as an electric motor and an electric generator that can reduce environmental burden by reduction of CO, emissions. A wave winding coil has a plurality of straight-shaped, in-slot disposition parts to be disposed in slots of a stator core and a plurality of turning parts (fold parts) each coupling, on an outer side of the stator core in an axial direction, the in-slot disposition parts adjacent to each other in a V or inverted V shape or an arch shape, and is formed into a wave shape along a circumferential direction of the stator core. 
     As such a wave winding coil, there is known a long sheet-shaped wave winding coil having a length that is two or more times the length of the circumference of the stator core. The sheet-shaped wave winding coil is spirally wound, and each in-slot disposition part is inserted into a corresponding slot of the stator core, whereby a coil having a plurality of layers (a plurality of turns) is formed. The sheet-shaped wave winding coil can be formed into a strip shape without the necessity of welding, and therefore can be reduced in weight in comparison with segment coils requiring welding. 
     There is a known method of manufacturing such a sheet-shaped wave winding coil, according to which all of a plurality of inclined-shaped crossover conductors corresponding to the turning parts of the wave winding coil and a plurality of straight-shaped slot conductors corresponding to the in-slot disposition parts of the wave winding coil are formed beforehand in a coil conductor within a plane on which the coil conductor extends, and thereafter, the crossover conductors are sequentially folded at their centers, whereby the resultant fold parts constitute the turning parts of the wave winding coil (for example, see Japanese Unexamined Patent Application, Publication No. 2021-58076). The turning part of the wave winding coil disclosed in Japanese Unexamined Patent Application, Publication No. 2021-58076 is a conductor consisting of at least two unit wires.
     Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2021-58076   

     SUMMARY OF THE INVENTION 
     However, with the above-described known technique, when the turning parts each consisting of two or more unit wires are bent at the same time, twists occur near apex parts formed after bending the turning parts in the respective coil wires (the conductors) arranged in parallel to each other, and variations in individual shapes are caused, in the wave winding coil to be formed due to the influence of the twists, which may adversely affect the workability particularly when automated work is performed. 
     An object of the present invention is to provide a conductor forming device that makes it possible to prevent a twist from occurring at an apex part of a fold part of a conductor while achieving reduction in weight, and a method of manufacturing a wave winding coil. 
     A first aspect of the present invention is directed to a conductor forming device (e.g., a conductor forming device  200 , which will be described later) which folds a group of conductors (e.g., a group of conductors  100 , which will be described later) in thickness directions, the group of conductors including a plurality of conductors (e.g., coil wires  10 , which will be described later) having straight parts (e.g., straight parts  14 , which will be described later). The conductor forming device includes a restrainer (e.g., a restrainer  225 , which will be described later) provided with a plurality of grooves (e.g., grooves  225   a , which will be described later) in which fold parts (e.g., turning parts  12 , which will be described later) of the conductors each consisting of at least two unit wires (e.g., unit wires  10   a , which will be described later) are fitted and which limit a width of each of the conductors to a predetermined distance, when the conductors each consisting of the at least two unit wires are to be folded. 
     The first aspect makes it possible to prevent a twist from occurring near the apex parts after bending the conductors arranged in parallel to each other, and to form the wave winding coil in a uniform state. The first aspect enables improvement of the quality, and improvement of the workability of operations (e.g., straight conveyance, turning conveyance, attachment of jig, and fitting into the slots of the stator) until the completion of fitting of the wave winding coil into the slots of the stator. 
     A second aspect is an embodiment if the first aspect. In the conductor forming device according to the second aspect, the plurality of grooves are arranged in parallel to each other at predetermined intervals in correspondence with the plurality of conductors disposed to be formed at the same time. 
     According to the second aspect, when the plurality of conductors are to be formed at the same time, the plurality of fold parts disposed to be formed at the same time can be arranged in parallel to each other at the predetermined intervals in corresponding with the plurality of grooves, which makes it possible to prevent a twist from occurring, and to form the wave winding coil in a uniform state. 
     A third aspect of the present invention is directed to a method of manufacturing a wave winding coil from coil wire (e.g., a coil wire  10 , which will be described later), the wave winding coil including a plurality of in-slot disposition parts (e.g., in-slot disposition parts  11 , which will be described later) to be disposed in slots (e.g., slots  23 , which will be described later) of a stator core (e.g., a stator core  20 , which will be described later), and a turning part (e.g., a turning part  12 , which will be described later) that couples the in-slot disposition parts adjacent to each other. The method includes a folding step of forming the turning part by folding two or more unit wires (e.g., unit wires  10   a , which will be described later) at the same time in a state where a width of an apex part (e.g., an apex part  12   c , which will be described later) of the turning part consisting of the at least two unit wires is limited to a predetermined distance. 
     The third aspect makes it possible to prevent a twist from occurring near the apex parts after bending the conductors arranged in parallel to each other, and to form the wave winding coil in a uniform state. The third aspect enables improvement of the quality, and improvement of the workability of operations (e.g., straight conveyance, turning conveyance, attachment of jig, and fitting into the slots of the stator) until the completion of fitting of the wave winding coil into the slots of the stator. 
     A fourth aspect is an embodiment of the third aspect. In the method of manufacturing a wave winding coil according to the fourth aspect, in the folding step, the plurality of turning parts disposed to be formed at the same time are arranged in parallel to each other at predetermined intervals. 
     According to the fourth aspect, the plurality of turning parts disposed to be formed at the same time are arranged in parallel to each other at the predetermined intervals, which makes it possible to prevent a twist from occurring, and to form the wave winding coil in a uniform state. 
     The present invention provides a conductor forming device that makes it possible to prevent a twist from occurring at an apex part of a fold part of a conductor while achieving reduction in weight, and a method of manufacturing a wave winding coil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front view schematically illustrating a wave winding coil; 
         FIG.  2    is a plan view schematically illustrating a stator; 
         FIG.  3    is a diagram illustrating how a coil wire (conductor) is formed; 
         FIG.  4    is a cross-sectional view taken along line A-A in  FIG.  3   ; 
         FIG.  5    is a front view illustrating a part of the coil wire (conductor) in an enlarged manner; 
         FIG.  6    is a diagram when the coil wire (conductor) illustrated in  FIG.  5    is seen in a direction along Z directions; 
         FIG.  7    is a front view illustrating, in an enlarged manner, a part of a group of conductors in which the plurality of coil wires (conductors) illustrated in  FIG.  5    are arranged in parallel to each other; 
         FIG.  8    is a view when the group of conductors illustrated in  FIG.  7    is seen in the direction along the Z directions; 
         FIG.  9    is a plan view schematically illustrating an outline of a conductor forming device; 
         FIG.  10    is a side view schematically illustrating the outline of the conductor forming device; 
         FIG.  11    is a diagram illustrating a state where clamp parts of the conductor forming device have unclamped the group of conductors; 
         FIG.  12    is a diagram illustrating a state where the clamp parts of the conductor forming device have clamped the group of conductors; 
         FIG.  13    is a plan view of the conductor forming device, illustrating a situation where the group of conductors is conveyed to a position where inclined parts are to be formed; 
         FIG.  14    is a side view of the conductor forming device, illustrating the situation where the group of conductors is conveyed to the position where inclined parts are to be formed; 
         FIG.  15    is a plan view of the conductor forming device, illustrating a situation where inclined parts are being formed on the group of conductors; 
         FIG.  16    is a plan view illustrating an operation of the clamp parts when the inclined parts are being formed on the group of conductors; 
         FIG.  17    is a plan view illustrating the inclined part of the conductor after the inclined part is formed; 
         FIG.  18    is a plan view of the conductor forming device, illustrating a situation where the group of conductors formed with the inclined parts is conveyed to a folding position; 
         FIG.  19    is a plan view of the conductor forming device, illustrating a situation where next inclined parts are being formed on the group of conductors after the inclined parts are formed; 
         FIG.  20    is a side view illustrating an operation of the clamp parts when the inclined parts formed on the group of conductors are being folded; 
         FIG.  21    is a plan view of the conductor forming device, illustrating a situation where inclined parts formed on the group of conductors are folded; 
         FIG.  22    is a perspective view illustrating a restrainer; 
         FIG.  23    is a diagram illustrating a state where a turning part of the coil wire (the conductor) consisting of three unit wires is folded in a groove of the restrainer; 
         FIG.  24    is a plan view illustrating the group of conductors after the inclined parts are folded; 
         FIG.  25    is a diagram illustrating an operation of the clamp parts after the inclined parts are folded; 
         FIG.  26    is a side view illustrating an operation of pressing the folded part with pressing members after the inclined parts are folded; 
         FIG.  27    is a plan view of the conductor forming device, illustrating a situation where next inclined parts are being formed on the group of conductors after the inclined parts are folded; 
         FIG.  28    is a plan view of the group of conductors, illustrating a situation where the inclined parts corresponding to layer switching parts are being folded back in an opposite direction; and 
         FIG.  29    is a plan view illustrating a sheet-shaped, wave winding coil formed from the group of conductors where the layer switching parts are folded back in the opposite direction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a method of manufacturing a wave winding coil using a conductor forming device will be described in detail with reference to the accompanying drawings. A wave winding coil and a stator will be first described with reference to  FIGS.  1  and  2   . A wave winding coil  1  according to the present embodiment is formed, using a plurality of coil wires  10  arranged in parallel to each other, which will be described later, into a long sheet shape extending in Y directions in the figure. The Y directions correspond to circumferential directions of a stator core  20  illustrated in  FIG.  2   . 
     A stator  2  includes the stator core  20  and the wave winding coil  1  to be attached to the stator core  20 . The stator core  20  has a plurality of teeth  22  radially protruding toward a central axial hole  21 . Slots  23  are each formed between the teeth  22  and  22  adjacent to each other. The present embodiment exemplifies the stator core  20  having the seventy-two slots  23 . 
     The wave winding coil  1  has a plurality of in-slot disposition parts  11  and a plurality of turning parts  12 . The in-slot disposition parts  11  are portions to be disposed in the slots  23  of the stator core  20 , and extend straightforwardly in axial directions (Z directions in  FIG.  1   ) of the stator core  20 . The turning parts  12  are each a portion coupling, on an outer side in the axial directions of the stator core  20 , the in-slot disposition parts  11  and  11  adjacent to each other of the coil wires  10  in a V or inverted V shape or an arch shape. The wave winding coil  1  has, at one end, a terminal part  13  for use for electrical connection with a driving circuit. Note that, although the in-slot disposition parts  11  and the turning parts  12  of the wave winding coil  1  are formed from the plurality of coil wires  10 ,  FIG.  1    schematically illustrates the in-slot disposition parts  11 , the turning parts  12 , and the terminal part  13  in plane. 
     The wave winding coil  1  according to the present embodiment has a length corresponding to four turns around the stator core  20 , and forms a coil having eight layers (eight turns) 1T to 8T in total, on the stator core  20 . Therefore, the wave winding coil  1  forms a coil having two layers (two turns) per turn around the stator core  20 , in which layer switching occurs each time the coil is wound around the stator core  20 . Reference signs Ta in  FIG.  1    indicate layer switching parts disposed between the seventh layer (7T) and the sixth layer (6T), between the fifth layer (5T) and the fourth layer (4T), and between the third layer (3T) and the second layer (2T), respectively. 
     The wave winding coil  1  is spirally wound in four turns around the stator core  20 , and is attached to the stator core  20  by disposing the in-slot disposition parts  11  in the slots  23  of the stator core  20 . As a result, the stator  2  is formed. Note that, although an insulator is disposed in each of the slots  23  for insulating the wave winding coil  1  and the stator core  20  from each other, the insulator is not illustrated in  FIG.  2   . 
     Next, each of the coil wires  10  according to an embodiment, which form the wave winding coil  1  will described with reference to  FIGS.  3  to  6   . The coil wire  10  is an electrical conductor made from a copper wire or the like. The coil wire  10  is first cut into a predetermined length, and then is bent at a substantially center portion in extending directions of the coil wire  10 , using an extracting tool  300  that moves in a direction indicated by a white hollow arrow, as illustrated in  FIG.  3   . As illustrated in  FIG.  4   , the coil wire  10  according to the present embodiment includes three unit wires  10   a  that are flat wires and are arranged in the Y directions corresponding to the circumferential directions of the stator core  20 . The coil wire  10  is formed by, in a state in which the three unit wires  10   a  are arranged in the Y directions, integrally bending the three unit wires  10   a  in the arrangement directions using the extracting tool  300 . 
     As illustrated in  FIGS.  5  and  6   , the coil wire  10  bent using the extracting tool  300  is formed, using a forming die (not shown), into a substantial U-shape having a turning part  12  with a V or inverted V shape (hereinafter, the turning part  12  first formed in the coil wire  10  may be referred to as a first turning part  12 A) and two straight parts  14  and  14  extending in parallel to each other in the same direction from both ends of the first turning part  12 A. An interval between the two straight parts  14  and  14  of the coil wire  10  according to the present embodiment corresponds to an interval between two slots  23  and  23  which are separated from each other by six slots in the stator core  20 . 
     The first turning part  12 A of the coil wire  10  has a first inclined part  12   a , a second inclined part  12   b , and an apex part  12   c , as illustrated in  FIGS.  5  and  6   . The first inclined part  12   a  and the second inclined part  12   b  are integrally coupled to the straight parts  14  and  14 , respectively, obliquely extend from the respective coupling portions of the straight parts  14  and  14  in directions in which the first inclined part  12   a  and the second inclined part  12   b  come closer to each other, and are then further integrally coupled to the apex part  12   c.    
     As illustrated in  FIG.  6   , a wire width (a width in the radial direction of the stator core  20 ) of the coil wire  10  is denoted by W. The first inclined part  12   a  extends obliquely toward the apex part  12   c  with respect to the straight part  14  to which the first inclined part  12   a  is coupled, without being offset in the X directions. On the other hand, the second inclined part  12   b  is offset by W in an X1 direction with respect to the first inclined part  12   a , and then obliquely extends toward the corresponding straight part  14 , so that the second inclined part  12   b  is offset, at the coupling portion with the straight part  14 , by W in an X2 direction that is an opposite direction to the X1 direction described above. As a result, the two straight parts  14  and  14  are at the same position in terms of the X directions. That is, the two straight parts  14  and  14  are disposed within a single plane extending in the Y directions. Note that the X directions indicated as the X1 direction and the X2 direction correspond to the radial directions of the stator core  20 . 
     A plurality of coil wires  10  formed into a substantial U-shape are arranged in parallel to each other, as illustrated in  FIGS.  7  and  8   , to form the wave winding coil  1 . The plurality of coil wires  10  are arranged in parallel to each other to form a group of conductors  100 . In the present embodiment, six coil wires  10  belonging to three phases are used. The six coil wires  10  are arranged in parallel to each other while being offset by a predetermined pitch in the Y directions to thereby form the group of conductors  100 . At this time, the twelve straight parts  14  are arranged in parallel to each other at equal intervals corresponding to slot intervals on the stator core  20 . The first inclined part  12   a  and the second inclined part  12   b  of each first turning part  12 A are offset by the wire width W of the coil wire  10  in the opposite directions along the X directions, and therefore, when the coil wires  10  and  10  adjacent to each other are stacked together such that the first inclined part  12   a  of one of the first turning parts  12 A and  12 A adjacent to each other and the second inclined part  12   b  of another one of the first turning parts  12 A and  12 A adjacent to each other intersect each other, all the twelve straight parts  14  are therefore disposed within a single plane extending in the Y directions. 
     Next, a method of forming the wave winding coil  1  from the group of conductors  100  including the six coil wires  10  arranged in parallel to each other will be described. A specific configuration of a conductor forming device  200  for use to form the wave winding coil  1  will be first described with reference to  FIGS.  9  and  10   . 
     The conductor forming device  200  includes a loading stand  201  on which the group of conductors  100  is loaded, a first clamp part  202 , a second clamp part  203 , and a third clamp part  204  that hold the group of conductors  100  to form inclined parts and to perform folding, and a holder  205  that holds and conveys the group of conductors  100 . 
     On an upper surface  201   a  of the loading stand  201 , the group of conductors  100  conveyed by a conveyor (not shown) is laid such that the turning parts  12  (first turning parts  12 A) face the first clamp part  202 . 
     The first clamp part  202 , the second clamp part  203 , and the third clamp part  204  are disposed along a conveyance route for the group of conductors  100  to be formed, and are movable upward and downward in the top-bottom direction of the conductor forming device  200  (in vertical direction with respect to the page of  FIG.  9   , and in the top-bottom direction in  FIG.  10   ). The first clamp part  202 , the second clamp part  203 , and the third clamp part  204  are configured to be positioned below the upper surface  201   a  of the loading stand  201  so as not to interrupt the conveyance of the group of conductors  100  when the first, second and third clamp parts  202 ,  203 , and  204  are not clamping the group of conductors  100 , and to move upward to hold the group of conductors  100  when the group of conductors  100  is conveyed to reach a position above the first, second, and third clamp parts  202 ,  203 , and  204 . 
     The first clamp part  202  is disposed most proximally to the loading stand  201 . The first clamp part  202  includes a pair of clamping members  202 A and  202 B that collectively hold the straight parts  14  of the coil wires  10  included in the group of conductors  100 . The clamping members  202 A and  202 B each have a width equal to or greater than the width of the group of conductors  100  in the Y directions illustrated in  FIG.  7   , and are disposed to face the conveyance route for the group of conductors  100  and arranged in parallel to each other at a certain interval in a D1 direction that is a conveyance direction of the group of conductors  100 . The certain interval between the clamping members  202 A and  202 B defines a space  202 C where a holding member  205 A or  205 B of the holder  205 , which will be described later, can be accommodated. 
     The second clamp part  203  is disposed on a side distant from the loading stand  201 , relative to the first clamp part  202 . The second clamp part  203  includes a pair of clamping members  203 A and  203 B that collectively hold the straight parts  14  of the coil wires  10  included in the group of conductors  100 , similarly to the first clamp part  202 . The clamping members  203 A and  203 B also each have a width equal to or greater than the width of the group of conductors  100 , and are disposed to face the conveyance route for the group of conductors  100  and arranged in parallel to each other at a certain interval in the D1 direction that is the conveyance direction of the group of conductors  100 . The certain interval between the clamping members  203 A and  203 B defines a space  203 C where the holding member  205 A or  205 B of the holder  205 , which will be described later, can be accommodated. 
     The third clamp part  204  is disposed on a side further distant from the loading stand  201 , relative to the second clamp part  203 . The third clamp part  204  includes a pair of clamping members  204 A and  204 B that collectively hold the straight parts  14  of the coil wires  10  included in the group of conductors  100 , similarly to the first clamp part  202  and the second clamp part  203 . The clamping members  204 A and  204 B also each have a width equal to or greater than the width of the group of conductors  100 , and are disposed to face the conveyance route for the group of conductors  100  and arranged in parallel to each other at a certain interval in the D1 direction that is the conveyance direction of the group of conductors  100 . The certain interval between the clamping members  204 A and  204 B defines a space  204 C where the holding member  205 A or  205 B of the holder  205 , which will be described later, can be accommodated. 
     The second clamp part  203  and the third clamp part  204  are provided with pressing members  203 D and  204 D, respectively, which are movable upward and downward in the top-bottom direction. The pressing members  203 D and  204 D are each formed from a plate-like member for pressing, with its surface, the group of conductors  100 . The pressing member  203 D of the second clamp part  203  is provided on a side distant from the loading stand  201 , and is disposed proximally to and in parallel to the clamping member  203 B. The pressing member  204 D of the third clamp part  204  is provided on a side proximal to the loading stand  201 , and is disposed proximally to and in parallel to the clamping member  204 A.  FIG.  10    illustrates a state in which the pressing members  203 D and  204 D are at respective positions after being moved downward. At this time, upper surfaces of the pressing members  203 D and  204 D are disposed below upper surfaces of the clamping members  203 A,  203 B,  204 A, and  204 B so as not to interrupt the conveyance of the group of conductors  100  and a holding operation and a conveyance operation for the group of conductors  100  by each clamping member  203 A,  203 B,  204 A,  204 B. 
     As illustrated in  FIGS.  9  and  10   , the clamping member  202 B, which belongs to the first clamp part  202  and is disposed on a side distant from the loading stand  201 , is separated by a distance L 1  from the clamping member  203 A, which belongs to the second clamp part  203  and is disposed on a side proximal to the loading stand  201 . The clamping member  203 B, which belongs to the second clamp part  203  and is disposed on a side distal from the loading stand  201 , is separated by a distance L 2  from the clamping member  204 A, which belongs to the third clamp part  204  and is disposed on a side proximal to the loading stand  201 . The distance L 2  is shorter than the distance L 1 . 
     The third clamp part  204  is disposed to be offset, with respect to the first clamp part  202  and the second clamp part  203 , in one direction (a D2 direction in  FIG.  9   ) of width directions of the conductor forming device  200  (D2-D3 directions in  FIG.  9   ). The D2-D3 directions are directions orthogonal to the D1 direction that is the conveyance direction of the group of conductors  100 . An amount of offset of the third clamp part  204  in the D2 direction with respect to the second clamp part  203  corresponds to one-half of the width of the group of conductors  100 , i.e., a pitch for the six straight parts  14  of the coil wires  10 . 
     The second clamp part  203  and the third clamp part  204  are movable integrally with each other by means of a movement mechanism (nor shown) in the width directions of the conductor forming device  200 . In contrast, the first clamp part  202  is immovable. Therefore, when the second clamp part  203  moves relative to the first clamp part  202  in one of the width directions of the conductor forming device  200  in a state in which at least the first clamp part  202  and the second clamp part  203  hold the group of conductors  100 , the straight parts  14  of the group of conductors  100  disposed between the first clamp part  202  and the second clamp part  203  can be obliquely bent to form inclined parts  15  illustrated in  FIG.  15   . Accordingly, the first clamp part  202  and at least the second clamp part  203  constitute an inclined part forming mechanism  206  in the conductor forming device  200 . 
     The third clamp part  204  is configured to rotationally move by means of a rotational movement mechanism (not shown). As illustrated in  FIG.  25   , the third clamp part  204  can be placed over the second clamp part  203  by way of folding along a folding line R (see  FIG.  9   ) extending in the width directions between the second clamp part  203  and the third clamp part  204 . With the rotation movement of the third clamp part  204 , the clamping member  204 B, the clamping member  204 A, the space  204 C, and the pressing member  204 D are placed over the clamping member  203 A, the clamping member  203 B, the space  203 C, and the pressing member  203 D, respectively. Thus, the conductor  100  held by the second clamp part  203  and the third clamp part  204  is folded along the folding line R in thickness directions (the X1-X2 directions in  FIG.  8   ). Accordingly, the second clamp part  203  and the third clamp part  204  constitute a folding mechanism  207  in the conductor forming device  200 . 
     As illustrated in  FIG.  10   , the holder  205  is disposed above the upper surface  201   a  of the loading stand  201 , and is configured to move upward and downward with respect to the group of conductors  100  disposed below the holder  205 , by means of an ascend/descend mechanism (not shown). The holder  205  includes the pair of holding members  205 A and  205 B each having a width equal to or greater than the width of the group of conductors  100 . The pair of holding members  205 A and  205 B have the same structure. The holding members  205 A and  205 B are disposed to be separated from each other by a certain distance in the D1 direction, and the holding member  205 B is disposed to be offset with respect to the holding member  205 A in the D2 direction. 
     The holder  205  according to the present embodiment is provided separately from the second clamp part  203  and the third clamp part  204  constituting the folding mechanism  207 . This configuration makes it possible to constantly maintain a folding position in the folding mechanism  207  unchanged, which enables a suitable positional accuracy to be achieved for the folding position. 
     The holder  205  is movable relative to the first clamp part  202 , the second clamp part  203 , and the third clamp part  204  in the D1 direction. In the present embodiment, the holder  205  is movable in the D1 direction. Therefore, the holder  205  conveys the group of conductors  100  held thereon, along the conveyance route in the D1 direction, and changes a relative position with respect to the first clamp part  202 , the second clamp part  203 , and the third clamp part  204 . 
     In an initial state illustrated in  FIG.  9   , the interval between the pair of holding members  205 A and  205 B in the D1 direction is slightly narrower than the interval between the space  202 C of the first clamp part  202  and the space  203 C of the second clamp part  203 , and is equal to the interval between the space  203 C of the second clamp part  203  and the space  204 C of the third clamp part  204 . An amount of offset of the holding member  205 B with respect to the holding member  205 A in the D2 direction is equal to the amount of offset of the third clamp part  204  with respect to the second clamp part  203  in the D2 direction. 
     Specific structures, for holding the group of conductors  100 , of the clamping members  202 A,  202 B,  203 A,  203 B,  204 A, and  204 B and the holding members  205 A and  205 B may be identical to each other, among the clamping members  202 A,  202 B,  203 A,  203 B,  204 A, and  204 B and the holding members  205 A and  205 B. As illustrated in  FIGS.  11  and  12   , a structure for holding the group of conductors  100  can be configured with, for example, a plurality of blocks  210  arranged in parallel to each other in an openable and closable manner in width directions (the Y directions in  FIG.  7   ) of the group of conductors  100 . The blocks  210  each have a groove  210   a  having a width slightly narrower than a width of the straight part  14  of each of the coil wires  10  constituting the group of conductors  100  (a width in the Y direction in  FIG.  4   ). The grooves  210   a  extend in the D1 direction that the extending directions of the straight parts  14  of the group of conductors  100 . 
     Each groove  210   a  is formed by cutting out a portion from the block  210 , from one side surface of the in its width directions to a substantial half of an upper surface of the block  210 , and a remaining half of the upper surface of the block  210  forms a pinching piece  210   b  that pinches one of the straight parts  14  of the coil wires  10 . One groove  210   a  and one pinching piece  210   b  are formed on each block  210 . The grooves  210   a  and the pinching pieces  210   b  are greater in number than the straight parts  14  of the group of conductors  100 . Specifically, in the present embodiment, one clamping member  202 A,  202 B,  203 A,  203 B,  204 A,  204 B or one holding member  205 A,  205 B has at least the twelve grooves  210   a  and at least the twelve pinching pieces  210   b.    
     As illustrated in  FIG.  11   , when the blocks  210  move away from each other, each of the clamping members  202 A,  202 B,  203 A,  203 B,  204 A, and  204 B and the holding members  205 A and  205 B is brought into an open state. At this time, the width of the groove  210   a  between the pinching pieces  210   b  and  210   b  adjacent to each other becomes wider than the width of the straight part  14  of the coil wire  10 . Therefore, the straight part  14  of the coil wires  10  can be accommodated in or removed from the groove  210   a.    
     On the other hand, as illustrated in  FIG.  12   , when the blocks  210  are in full contact with each other, each of the clamping members  202 A,  2028 ,  203 A,  2038 ,  204 A, and  204 B and the holding members  205 A and  2058  is brought into a closed state. At this time, the width of the groove  210   a  between the pinching pieces  210   b  and  210   b  adjacent to each other becomes slightly narrower than the width of the straight part  14  of the coil wire  10 . Therefore, the straight parts  14  of the coil wires  10 , which are accommodated in the respective grooves  210   a , are each individually pinched between the pinching pieces  210   b  and  210   b  adjacent to each other. Thus, the group of conductors  100  is held. 
     In this way, each of the clamping members  202 A,  202 B,  203 A,  203 B,  204 A, and  204 B and the holding members  205 A and  205 B for holding the group of conductors  100  holds the straight parts  14  of the coil wires  10  in the width directions. The width directions of the straight parts  14  (the Y directions illustrated in  FIGS.  4  and  7   ) correspond to a stacking direction of the plurality of unit wires  10   a  included in each coil wire  10 . Therefore, even when there is variation in the thickness direction (the X directions illustrated in  FIG.  4   ) between the plurality of unit wires  10   a , it is possible to integrally pinch and hold the plurality of unit wires  10   a  included in each of the coil wires  10 . In addition, no separate pressing member is required for pressing the coil wires  10  to prevent the unit wires  10   a  from becoming loose, making it possible to reduce the size of the device. 
     Note that,  FIGS.  11  and  12    illustrate a case where the straight parts  14  of the group of conductors  100  are held from below. The case corresponds to a case where the clamping members  202 A,  202 B,  203 A,  203 B,  204 A, and  204 B hold the straight parts  14  of the group of conductors  100  from below. A case where the holding members  205 A and  205 B hold the straight parts  14  of the group of conductors  100  from above corresponds to a configuration resulting from vertical reversal of the configuration illustrated in  FIGS.  11  and  12   . 
     Next, a specific forming operation when the conductor forming device  200  performs forming on the group of conductors  100  will be described. As illustrated in  FIGS.  9  and  10   , the group of conductors  100  including the six coil wires  10  is first loaded on the upper surface  201   a  of the loading stand  201  with the turning parts  12  (the first turning parts  12 A) facing toward the first clamp part  202 . 
     When the holder  205  moves toward the group of conductors  100  on the loading stand  201 , and the holding member  205 A on the side proximal to the loading stand  201  reaches a position above the group of conductors  100 , the holder  205  moves downward and the holding member  205 A holds each of the straight parts  14  that lie in proximity to the turning parts  12  (the first turning parts  12 A) of the group of conductors  100 . At this time, the other holding member  205 B stays between the loading stand  201  and the first clamp part  202 , and does not hold the group of conductors  100 . The holder  205  having the group of conductors  100  held hereon linearly moves in the D1 direction along the extending direction of the straight parts  14  to thereby convey, as illustrated in  FIG.  13   , the group of conductors  100  to a position above the first clamp part  202  and the second clamp part  203  constituting the inclined part forming mechanism  206 . 
     Reference numeral  208  in  FIG.  13    indicates guide members that are a plurality of pins disposed between the loading stand  201  and the first clamp part  202 . After the turning parts  12  (the first turning parts  12 A) of the group of conductors  100  have passed above the first clamp part  202 , the guide members  208  move upward from below the group of conductors  100 , and each enter a space between the straight parts  14  and  14  adjacent to each other. Consequently, the straight parts  14  of the group of conductors  100  being conveyed are prevented from interfering with each other, and the group of conductors  100  being conveyed are thus smoothly guided. 
     As illustrated in  FIGS.  13  and  14   , after the holding member  205 A holding the group of conductors  100  moves to a position above the space  203 C of the second clamp part  203 , the first clamp part  202 , the second clamp part  203 , and the third clamp part  204  integrally move upward, whereby the holding member  205 A is accommodated in the space  203 C. When the first clamp part  202  and the second clamp part  203  move upward, the clamping members  202 A,  202 B,  203 A, and  203 B are in an open state, as illustrated in  FIG.  11   . Therefore, as the first clamp part  202  and the second clamp part  203  move upward, the straight parts  14  of the group of conductors  100  are accommodated in respective grooves  210   a  each of which is between pinching pieces  210   b  and  201   b  adjacent to each other. After the straight parts  14  are accommodated in the grooves  210   a , the clamping members  202 A,  202 B,  203 A, and  203 B are closed, and hold the group of conductors  100 . 
     As illustrated in  FIGS.  13  and  14   , holding target parts  140  and  140  of the straight parts  14  that the first clamp part  202  and the second clamp part  203  hold, respectively, are portions corresponding to the in-slot disposition parts  11  of the wave winding coil  1 . Therefore, the interval between the pair of clamping members  202 A and  202 B in the extending direction of the straight parts  14  (a length in the D1 direction of the first clamp part  202  including the space  202 C) and the interval between the pair of clamping members  203 A and  203 B (a length in the D1 direction of the second clamp  203  including the space  203 C) are each substantially equal to a length of each of the in-slot disposition parts  11  of the wave winding coil  1 . 
     As illustrated in  FIGS.  13  and  14   , on the straight parts  14  of the group of conductors  100 , portions  141  disposed between the first clamp part  202  and the second clamp part  203  are portions of the group of conductors  100  in which the inclined parts  15  are to be formed, and are also portions corresponding to the turning parts  12  of the wave winding coil  1 . A length of each of the portions  141 , i.e., the distance L 1  between the first clamp part  202  and the second clamp part  203  illustrated in  FIGS.  9  and  10   , is substantially equal to a length of each of the turning parts  12  of the wave winding coil  1  when the turning part  12  is stretched straightforwardly. 
     After the first clamp part  202  and the second clamp part  203  hold the group of conductors  100 , the holder  205  releases the holding of the group of conductors  100  and moves back upwardly to a position above the group of conductors  100 . After that, for the preparation for a next holding operation, as illustrated in  FIG.  15   , the holding member  205 A moves to a position above the space  202 C of the first clamp part  202 . 
     Next, the conductor forming device  200  causes, from a state where the first clamp part  202  and the second clamp part  203  are holding the group of conductors  100 , the second clamp part  203  and the third clamp part  204  to move relative to the first clamp part  202  in the D2 direction, as illustrated in  FIG.  15   . Specifically, the first turning parts  12 A of the coil wires  10  in the group of conductors  100  and the holding target parts  140  held by the second clamp part  203  are caused, within a plane on which the coil wires  10  included in the group of conductors  100  extend (within a plane of the page of  FIG.  15   ), to be offset in the direction (the D2 direction) intersecting the extending directions of the straight parts  14 . Consequently, the portions  141  including the twelve straight parts  14  disposed between the first clamp part  202  and the second clamp part  203  are inclined in the offset direction (the D2 direction), thereby forming respective first inclined parts  15  (inclined parts  15 A) on the coil wires  10  included in the group of conductors  100 . 
     An inclination angle of each of the inclined parts  15  relative to the straight parts  14  is, as illustrated in  FIG.  5   , substantially equal to the inclination angle of each of the first inclined parts  12   a  or the second inclined parts  12   b  of the turning parts  12  formed on the coil wires  10 . Forming the inclined parts  15  on the group of conductors  100  causes a side adjacent to the turning parts  12  (the first turning parts  12 A) of the group of conductors  100  held by the second clamp part  203  to be disposed and offset, with respect to the straight parts  14  held by the first clamp part  202 , in the D2 direction by an amount of offset corresponding to one-half of the width of the group of conductors  100 , i.e., a pitch for the six straight parts  14  of the coil wires  10 . 
     The conductor forming device  200  according to the present embodiment is configured to not cause, when the inclined parts  15  are to be formed, the side adjacent to the second clamp part  203  to move straightforwardly in the D2 direction, but, as illustrated in  FIG.  16   , to cause the side adjacent to the second clamp part  203  to move in an arc shape centered on bending points P serving as boundary points between the inclined parts  15  and the straight parts  14  that are continuous from the inclined parts  15  and are held by the first clamp part  202 , at a radius corresponding to a length of each of the inclined parts  15 . At this time, the side adjacent to the second clamp part  203  keeps the parallelism to the first clamp part  202 , and moves in the arc shape. Consequently, as illustrated in  FIG.  17   , the inclined part  15  (the portion  141 ) is pulled in opposite directions and formed, whereby the straightness of the inclined part  15  after being formed becomes satisfactory, thereby improving the forming accuracy for the inclined part  15 . 
     When the second clamp part  203  is offset in the D2 direction to form the inclined parts  15 , as illustrated in  FIG.  15   , the interval between the space  202 C of the first clamp part  202  and the space  203 C of the second clamp part  203  becomes slightly smaller, and becomes coincident with the interval between the pair of holding members  205 A and  205 B. Therefore, after formation of the first inclined parts  15  (the inclined parts  15 A) of the group of conductors  100 , when the holder  205  lying at the position illustrated in  FIG.  15    moves downward toward the group of conductors  100 , the holding members  205 A and  205 B are accommodated in the spaces  202 C and  203 C, respectively, which makes it possible to hold the group of conductors  100 . 
     At this time, since the pair of holding members  205 A and  205 B hold the group of conductors  100  at two points on the straight parts  14  and  14  disposed on both sides with respect to the inclined parts  15 , respectively, the group of conductors  100  is less likely to become loose. Thereafter, as the holder  205  holds the group of conductors  100 , the first clamp part  202  and the second clamp part  203  release the holding of the group of conductors  100 , move downward and also move in the D3 direction, and return to the positions in the initial state. 
     Thereafter, the holder  205  holding the group of conductors  100  moves in the D1 direction to convey the group of conductors  100 , as illustrated in  FIG.  18   , until the holding member  205 A reaches a position above the space  203 C of the second clamp part  203 , and the holding member  205 B reaches a position above the space  204 C of the third clamp part  204 . The third clamp part  204  is offset beforehand in the D2 direction with respect to the first clamp part  202  and the second clamp part  203  by one-half of the width of the group of conductors  100 , and the holding member  205 B of the holder  205  is similarly offset with respect to the holding member  205 A. Therefore, as the first clamp part  202 , the second clamp part  203 , and the third clamp part  204  move upward, the holding members  205 A and  205 B holding the group of conductors  100  having the first inclined parts  15  (the inclined parts  15 A) are formed thereon are accommodated in the space  203 C of the second clamp part  203  and the space  204 C of the third clamp part  204 , respectively. 
     After moving upward, the first clamp part  202 , the second clamp part  203 , and the third clamp part  204  hold the straight parts  14  of the group of conductors  100 , and then the holder  205  releases the holding of the group of conductors  100 . At this time, the inclined parts  15  formed on the group of conductors  100  are disposed between the clamping member  203 B of the second clamp part  203  and the clamping member  204 A of the third clamp part  204 . That is, the distance L 2  between the clamping member  203 B and the clamping member  204 A is substantially equal to a distance between the straight parts  14  and  14  that are adjacent to each other with the inclined parts  15  interposed therebetween. The portions  141  to be then newly formed as the inclined parts  15  are also disposed between the first clamp part  202  and the second clamp part  203 . After retracting upward to a position above the group of conductors  100 , the holder  205  moves, for the preparation of next holding, as illustrated in  FIG.  19   , to the position above the space  202 D of the first clamp part  202  and the space  203 C of the second clamp part  203 . 
     Thereafter, similar to the case illustrated in  FIG.  15   , the second clamp part  203  and the third clamp part  204  are caused to move in the D2 direction to form, as illustrated in  FIG.  19   , each of second inclined parts  15  (the inclined parts  15 B) between the first clamp part  202  and the second clamp part  203  (inclined part forming step). 
     Next, at the center portion of each of the first inclined parts  15 A disposed between the second clamp part  203  and the third clamp part  204 , i.e., at points along the folding line R disposed between the second clamp part  203  and the third clamp part  204  (see  FIGS.  9  and  19   ), the third clamp part  204  performs a rotation movement to be placed over the second clamp part  203 , as illustrated in  FIG.  20   , to fold the first inclined parts  15 A (folding step). 
     With the rotation movement of the third clamp part  204 , the first inclined parts  15 A of the group of conductors  100  are folded in one of the thickness directions of the group of conductors  100 . The folding line R extends in the D2-D3 directions along the width directions of the group of conductors  100 , and intersects with the inclined parts  15 A. Therefore, as the inclined parts  15 A are folded, the folded parts newly serve as the twelve turning parts  12  (second turning parts  12 B) each having a V or inverted V shape (a triangular shape) having the apex parts (the apex parts  12   c ) at the folding line R. In the present embodiment, the rotation movement of the third clamp part  204  causes the inclined parts  15 A to be folded forward along the folding line R in a direction toward the near side on the plane of the page of  FIG.  19    (an R1 direction). 
       FIG.  24    illustrates only the group of conductors  100  after the first inclined parts  15 A are folded. As illustrated in  FIG.  24   , after the first inclined parts  15 A are folded, the holding target parts  140  and  140  of the straight parts  14  held by the second clamp part  203  and the third clamp part  204  partially overlap with each other to be parallel to each other. Specifically, six out of the twelve holding target parts  140  held by the second clamp part  203  and six out of the twelve holding target parts  140  held by the third clamp part  204  overlap with each other. Consequently, the in-slot disposition parts  11 , a total width of which corresponds to a total width of the  18  straight parts  14 , are formed. 
     Note that, in the present embodiment, before the folding step is performed for the first time on the group of conductors  100 , the two inclined parts  15  (the inclined parts  15 A and  15 B) are formed. Therefore, as illustrated in  FIG.  21   , the turning parts  12  (the first turning parts  12 A) of the group of conductors  100  after folding are disposed to overlap with the secondly formed inclined parts  15  (the inclined parts  15 B). Therefore, the turning parts  12  after folding do not interfere with the straight parts  14  of the group of conductors  100 . 
     As illustrated in  FIG.  20   , when the inclined parts  15  are to be folded, a folding jig  220  may be inserted between the second clamp part  203  and the third clamp part  204 . The folding jig  220  has a triangular shape in cross section, and a peripheral part  220   a  having an acute apex is inserted along the folding line R on the inclined parts  15 . This enables the third clamp part  204  to accurately fold the inclined parts  15  along the folding line R. Before the folding operation is completed, the folding jig  220  is removed from between the second clamp part  203  and the third clamp part  204 . 
     As illustrated in  FIGS.  20  and  21   , when the inclined parts  15  are to be folded, a restrainer  225  that restrains the apex parts  12   c  of the turning parts  12  may be disposed at the apex parts  12   c  (the first turning parts  12 A) of the turning parts  12  in the midst of folding. 
     The restrainer  225  has a rectangular parallelepiped shape, as illustrated in  FIG.  22   . The restrainer  225  has a predetermined length in the D1 direction as illustrated in  FIG.  21   , and extends longer in the D2-D3 directions than a range in which the plurality of turning parts  12  of the group of conductors  100  are arranged in the D2-D3 directions and has a predetermined height in the top-bottom direction as illustrated in  FIG.  20   . 
     As illustrated in  FIGS.  21  and  22   , the restrainer  225  has a plurality of grooves  225   a  that are arranged side by side in the D2-D3 directions to face the apexes of the turning parts  12  (the first turning parts  12 A) of the group of conductors  100 . The plurality of groove  225   a  are arranged in parallel to each other in the D2-D3 directions at predetermined intervals, in correspondence with the plurality of coil wires  10  arranged to be formed at the same time. 
     The plurality of grooves  225   a  are formed to be recessed in a U shape in cross section from a surface of the restrainer  225  adjacent to the turning parts  12  (the first turning parts  12 A) of the group of conductors  100 , and extend in the top-to-bottom direction. 
     As illustrated in  FIG.  23   , when the coil wires  10  each consisting of at least two unit wires  10   a  are to be folded, the apex part  12   c  of the turning part  12  (the first turning part  12 A) of the coil wire  10  consisting of at least two unit wires  10   a  is fitted in each of the plurality of grooves  225   a , and the groove  225   a  limits the width of the coil wire  10  in the D2-D3 directions to a predetermined distance. 
     In the folding step, in a state where the width in the D2-D3 directions of each of the apex parts  12   c  of the turning parts  12  (the first turning parts  12 A) each consisting of at least two unit wires  10   a  is limited to the predetermined distance by the restrainer  225 , the two or more unit wires  10   a  are folded at the same time to form the turning part  12  (the first turning part  12 A). In the folding step, the apex parts  12   c  of the plurality of turning parts  12  (the first turning parts  12 A) arranged to be formed at the same time are fitted into the plurality of grooves  225   a  of the restrainer  225 , whereby the plurality of turning parts  12  (the first turning parts  12 A) arranged to be formed at the same time are arranged in parallel to each other in the D2-D3 directions at the predetermined intervals. 
       FIG.  20    illustrates a timing at which the restrainer  225  is attached. After the plurality of turning parts  12  (the first turning parts  12 A) are folded at a folding angle α (for example, an angle α=150°), the restrainer  225  is moved from a side away from the turning parts  12  (the first turning parts  12 A) toward the turning parts  12  (the first turning parts  12 A) to thereby be attached to the plurality of turning parts  12  (the first turning parts  12 A). Thereafter, in a state where the restrainer  225  is attached, the plurality of turning parts  12  (the first turning parts  12 A) are further folded at an increased folding angle of 180°, and then the restrainer  225  is moved away from the turning parts  12  (the first turning parts  12 A) so as to be detached. Attachment and detachment of the restrainer  225  may be performed by an automatic operation of an automatic machine or a human operation. 
     As described above, the restrainer  225  provided with the plurality of grooves  225   a  is disposed to the apex parts  12   c  of the turning parts  12  (the first turning parts  12 A) in the midst of folding, which makes it possible to prevent twists from occurring near the apex parts  12   c  after bending the coil wires  10  arranged in parallel to each other, and to form the wave winding coil  1  in a uniform state. This makes it possible to improve the quality, and improve the workability of operations until the completion of fitting of the wave winding coil  1  into the slots  23  of the stator core  20  (e.g., straight conveyance, turning conveyance, attachment of jig, and fitting into the slots  23  of the stator core  20 ). 
     As illustrated in  FIG.  25   , after completion of folding of the inclined parts  15 , the third clamp part  204  may also be caused to slightly move, in a state where the group of conductors  100  are held, relative to the second clamp part  203  in arrangement directions of the straight parts  14  and in width directions of the folded parts (the D2-D3 directions). This makes it possible to suppress occurrence of springback that is a phenomenon in which the turning parts  12  after the inclined parts  15  are folded open while returning to the original shape. It is also possible to adjust a pitch between adjacent ones of the six straight parts  14  that has been folded. 
     In the folding step, after the inclined parts  15  are folded, and in a state where the second clamp part  203  and the third clamp part  204  overlap with each other, as illustrated in  FIG.  26   , the pressing member  203 D of the second clamp part  203  moves upward relative to the second clamp part  203 , and the pressing member  204 D of the third clamp part  204  also moves upward relative to the third clamp part  204 , and the turning parts  12  that are the folded parts of the group of conductors  100  are thus pinched between the pressing members  203 D and  204 D and pressed in the thickness directions. This makes it possible to suppress expansion of the turning parts  12  in the thickness directions due to the springback and to further improve the forming accuracy for the turning parts  12 . It is also possible to immediately press the turning parts  12  that have been formed by the second clamp part  203  and the third clamp part  204 , thereby simplifying the device and the process steps, without the necessity of providing a separate station for pressing. 
     After the second turning parts  12 B are formed, the holder  205  further conveys the group of conductors  100  in the D1 direction to dispose the secondly formed inclined parts  15 B between the second clamp part  203  and the third clamp part  204 . Thereafter, similar to the case illustrated in  FIG.  19   , third inclined parts  15  (inclined parts  15 C) are formed on the straight parts  14  disposed between the first clamp part  202  and the second clamp part  203 , as illustrated in  FIG.  27   . 
     Subsequent to the foregoing process, the folding step for the second inclined parts  15 B, the inclined part forming step for forming the fourth inclined parts, the folding step for the third inclined parts  15 C, and subsequent necessary steps are alternately and repeatedly executed in the same manner as described above until the wave winding coil  1  formed from the group of conductors  100  has a predetermined length corresponding to four turns around the stator core  20 . Thus, the wave winding coil  1 , which has a sheet shape forming eight layers (eight turns) and in which the in-slot disposition parts  11  are offset by an amount corresponding to six in-slot disposition parts  11  between two adjoining layers, is formed. Thus, in the wave winding coil  1  formed by the conductor forming device  200 , where forming of the inclined parts  15  and folding of the inclined parts  15  are alternately repeated, formation errors that may occur when the coil wires  10  are folded are not accumulated in the inclined parts  15 . Therefore, the in-slot disposition parts  11  and the turning parts  12  are formed with satisfactory forming accuracy. 
     When the coil wires  10  are formed from the plurality of unit wires  10   a  arranged in the thickness directions (the Y directions) as described in the present embodiment, it is inevitable that, when the inclined parts  15  are folded, a perimeter difference occurs among the unit wires  10   a  due to an angular difference between the extending directions and the folding direction of the inclined parts  15  before folding. In a case where all the inclined parts are formed beforehand as in the known art, there is a disadvantage that a perimeter difference that occurs at the time of the folding among the unit wires  10   a  affects the already formed inclined parts, causing shoulder bending parts of the formed inclined parts (starting points at which the inclined parts are bent) to be displaced. In contrast, alternately performing the inclined part forming step and the folding step as described in the present embodiment makes it possible to substantially cancel out, by way of forming of the next inclined parts  15 , the adverse effects of a perimeter difference among the unit wires  10   a  caused by the folding. Therefore, even though the coil wires  10  are each formed from the plurality of unit wires  10   a  arranged in the thickness directions, it is possible to manufacture the wave winding coil  1  with improved forming accuracy. 
     Note that, the sheet-shaped wave winding coil  1  produced as described above has a two-layer structure where the in-slot disposition parts  11  overlap with each other, and further has, as illustrated in  FIG.  1   , the layer switching parts Ta at which the layers (turns) switch in the radial directions of the stator core  20 , every length corresponding to one turn around the stator core  20 . In the case of forming the wave winding coil  1  having this structure, in order to prevent layers from interfering with each other in the layer switching parts Ta, the folding step may include folding the inclined parts  15  corresponding to the layer switching parts Ta in a direction (an R2 direction) opposite to the previous folding direction (the R1 direction), as will be described below. 
     As illustrated in  FIG.  28   , in the folding step where the inclined parts  15  corresponding to the layer switching parts Ta are folded along the folding line R, the inclined parts  15  are folded back in the opposite direction (the R2 direction) that is opposite to the folding direction (the R1 direction) of the inclined parts  15  in the previous folding step. Specifically, in the case of the wave winding coil.  1  according to the present embodiment, as illustrated in  FIG.  1   , the layer switching parts Ta are present at three locations in total, i.e., between the seventh layer (7T) and the sixth layer (6T), between the fifth layer (5T) and the fourth layer (4T), and between the third layer (3T) and the second layer (2T). Accordingly, the inclined parts  15  are folded back in the opposite direction only in the folding step for the inclined parts  15  corresponding to the layer switching parts Ta, as described above. As a result, as illustrated in  FIG.  29   , in the layer switching parts Ta, an offset direction along one of the thickness directions of the turning parts  12  (the radial directions of the stator core  20 , and the X directions in  FIG.  29   ) is reversed, making it possible to prevent the layers from interfering with each other in the layer switching parts Ta when the wave winding coil  1  is attached to the stator core  20 . 
     The sheet-shaped wave winding coil  1  described above does not require a common dominant technique in which a plurality of coil segments are formed, inserted into slots, and thereafter, coil ends of the coil segments are welded. Thus, it is not necessary to use, for example, a high-purity copper material for the coil to be subjected to heat process at weld points, making it possible to use recycled copper material containing impurities and contribute to achievement of the recycling and reusing of resources. 
     The wave winding coil  1  described above includes the six coil wires  10  arranged in parallel to each other, but the number of the coil wires  10  arranged in parallel is not limited to six, and the number may be appropriately increased or reduced. The coil wires  10  includes the three unit wires  10   a  arranged in parallel to each other, but the number of the unit wires  10   a  is not limited to three, and the number may also be appropriately increased or reduced. 
     The wave winding coil is not limited to one formed from the coil wires  10  formed into a substantial U-shape, and the wave winding coil may be formed by alternatively performing the inclined part forming step and the folding step on the straight coil wire. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1 : Wave winding coil 
           10 : Coil wire (conductor) 
           10   a : Unit wire 
           11 : In-slot disposition part 
           12 : Turning part (Fold part) 
           12   c : Apex part 
           20 : Stator core 
           23 : Slot 
           100 : Group of conductors 
           225 : Restrainer 
           225   a : Groove