Laser welding method to weld two adjacent metal elements of a stator winding with rigid bars for an electric machine

1. A laser welding method to weld two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) of a stator winding ( 8 ) with rigid bars ( 9 ) for an electric machine ( 1 ) for establishing an electrical connection between the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 );

wherein the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) are arranged one beside the other and have respective upper surfaces ( 43 ), which are arranged coplanar to one another and have at least one common edge ( 44 );

the laser welding method comprises the step of aiming at the upper surfaces ( 43 ) of the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 );

a first laser beam ( 38 ), which is suited to melt the metal making up the adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) for forming a first molten metal bath ( 46 ) and is fed along a first straight welding line ( 45 ), which is perpendicular to the common edge ( 44 ) and extends through the common edge ( 44 ); and

a second laser beam ( 38 ), which is suited to melt the metal making up the adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) for forming a second molten metal bath ( 48 ) and is fed along a second straight welding line ( 47 ), which is perpendicular to the common edge ( 44 ), extends through the common edge ( 44 ), is parallel to and spaced apart from the first straight welding line ( 45 ) and has a length that is smaller than the one of the first straight welding line ( 45 );

wherein the second molten metal bath ( 48 ) merges with the previously generated first molten metal bath ( 46 ) for forming a single and common molten metal bath establishing, once cooled down, the electrical connection between the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ).

2. The laser welding method according to claim 1 , wherein the first straight welding line ( 45 ) and the second straight welding line ( 47 ) are not centred relative to one another.

3. The laser welding method according to claim 1 , wherein:

the first straight welding line ( 45 ) is symmetrically divided by the common edge ( 44 ); and

the second straight welding line ( 47 ) is asymmetrically divided by the common edge ( 44 ).

4. The laser welding method according to claim 2 , wherein:

the first straight welding line ( 45 ) and the second straight welding line ( 47 ) extends from a starting point arranged on an adjacent metal element ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) to an arrival point arranged on the other adjacent metal element ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 );

the starting points of the first straight welding line ( 45 ) and the second straight welding line ( 47 ) are arranged at the same distance from the common edge ( 44 ); and

the arrival points of the first straight welding line ( 45 ) and the second straight welding line ( 47 ) are arranged at different distances from the common edge ( 44 ).

5. The laser welding method according to claim 1 , wherein the first laser beam ( 38 ) and the second laser beam ( 38 ) are generated in succession by a single emitting device ( 37 ).

6. The laser welding method according to claim 1 and comprising the further step of pushing the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 )—and keeping them pushed—towards one another along a pushing direction that is perpendicular to the common edge ( 44 ), before generating the first laser beam ( 38 ).

7. The laser welding method according to claim 6 and comprising the further step of keeping the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) pushed towards one another until an at least partial cooling of the molten metal is reached following the action of the first laser beam ( 38 ) and the second laser beam ( 38 ).

8. The laser welding method according to claim 6 , wherein the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 ) are pushed towards one another by means of an internal jaw ( 42 ) and an external jaw ( 42 ), which are mechanically connected to one another, are mounted on the stator winding ( 8 ) before beginning to weld and are removed from the stator winding ( 8 ) at the end of the welding process.

9. The laser welding method according to claim 8 , wherein each jaw ( 42 ) has an annular shape.

10. The laser welding method according to claim 8 , wherein:

the stator winding ( 8 ) has a number of phases and comprises a series of rigid bars ( 9 ), which are “U”-shaped and are inserted through stator slots ( 7 ) defining an entry side ( 12 ), in which the cusps ( 11 ) of the “U”-shaped bars ( 9 ) are placed, and an exit side ( 13 ), in which legs ( 10 ) of the “U”-shaped bars ( 9 ) are placed;

the legs ( 10 ) of the “U”-shaped bars ( 9 ) coming out from the exit side ( 13 ) of the magnetic core ( 6 ) are twisted through relative double folds, each of which comprises an internal fold ( 15 ) in one direction and an external fold ( 16 ) in the opposite direction;

ends of the legs ( 10 ) of the “U”-shaped bars ( 9 ) are electrically connected to one another by means of laser welding so as to form the electrical paths of the stator winding ( 8 );

the internal jaw ( 42 ) is arranged on the inside of the stator winding ( 8 ) in direct contact with the most internal legs ( 10 ); and

the external jaw ( 42 ) is arranged on the outside of the stator winding ( 8 ) in direct contact with most external legs ( 10 ) so as to push the most external legs ( 10 ) towards the most internal legs ( 10 ) and vice versa.

11. The laser welding method according to claim 1 and comprising the further steps of:

capturing a digital image of the two upper surfaces ( 43 ) of the two adjacent metal elements ( 10 ; 18 ; 28 ; 30 ; 32 ; 34 );

analyzing the digital image to determine the position of the external edges of the two upper surfaces ( 43 ); and

controlling the generation of the first laser beam ( 38 ) and the second laser beam ( 38 ) so that the first laser beam ( 38 ) and the second laser beam ( 38 ) are parallel to the external edges of the two upper surfaces ( 43 ), which are perpendicular to the common edge ( 44 ).

12. The laser welding method according to claim 11 and comprising the further steps of:

analyzing the digital image to determine the position of the corners of the external edges of the two upper surfaces ( 43 );

determining the position of the centre of the two upper surfaces ( 43 ) using the position of the corners; and

using the position of the centre of the two upper surfaces ( 43 ) to establish the position of the first and second laser beams ( 38 ).