Method and system of welding for inductive windings of electrical machines

A method of welding for inductive windings of electrical machines starting from U-shaped conducting elements with a bridge joining a pair of shanks, wherein said conducting elements are arranged in a ferromagnetic core of an electrical machine with said shanks oriented parallel to an axis of symmetry of said ferromagnetic core, and wherein each shank of said conducting elements comprises an end, each end being adjacent to an end of another conducting element for welding together according to a predefined electrical connection diagram;

• wherein said method comprises the steps of:
• arranging said ferromagnetic core containing said conducting elements in a welding zone, with said ends of said conducting elements facing a programmable focusing optic scanner controlled by an electronic control unit, said programmable focusing optic scanner being configured to project a laser welding beam;
• gripping said ends to be welded together, which are mutually adjacent and aligned, an axial interspace of separation being leaved between said ends;
• scanning said laser welding beam, by following a preset cyclic path and passing through at least one first end and at least one second end of said ends of said conducting elements, wherein said preset path is scanned for a plurality of cycles, for the generation of a well of molten metal in said at least first and second ends in order to close said interspace that separates them, each cycle of said scan having a preset duration;
• cooling said well of molten metal, by means of shutting off said laser welding beam, up until solidification of said well of molten metal, said solidification resulting in a weld that stably connects said at least first and second ends of said adjacent conducting elements, said cooling having a preset duration;
• monitoring at least one real signal of an optical emission in said steps of scanning and cooling in order to control a quality of said weld between said pair of ends of said conducting elements of an inductive winding of a stator, via at least one optical sensor device and said electronic control unit;
• where said step of monitoring comprises the steps of:
• detecting and acquiring said optical emission originating from said weld for said duration of said steps of scanning and cooling of each welding operation between said pair of ends of said conducting elements;
• obtaining at least one real signal from said optical emission, said real signal being a time trend constituted by one of either a continuous time series or a plurality of consecutive discrete values of a discrete time series;
• comparing characteristics of said at least one real signal of said optical emission with respective characteristics of at least one respective reference signal of said optical emission, and identifying defects of said weld on the basis of the relationship between said compared characteristics;
• and
• classifying said at least one real signal on the basis of a comparison of said characteristics of said at least one real signal with said respective characteristics of said at least one respective reference signal, said classifying of said at least one real signal including identifying any defects and/or estimating mechanical properties of said weld on the basis of the single relationship between said compared characteristics;
• wherein, prior to said steps of scanning and cooling, the method comprises the step of:
• selecting a predefined welding program, where said welding program comprises instructions and operating parameters with which said electronic control unit is to execute said steps of scanning and cooling, where said welding program further comprises at least one reference signal of said optical emission relating to said welding program, and where said welding program further comprises at least one time window for monitoring in said steps of scanning and cooling corresponding to a phase of said welding operation;
• and wherein said step of monitoring further comprises, prior to said step of comparing, the steps of:
• extracting values corresponding to said phase defined by said at least one time window from said at least one real signal of said optical emission and from said at least one respective reference signal of said optical emission of each welding operation;
• and
• calculating at least one physical indicator relating to said phase of said welding operation, starting from said values which are contained in said at least one time window and extracted from said at least one real signal and from said at least one respective reference signal;
• and wherein said step of comparing further comprises the step of:
• comparing said at least one physical indicator of said phase of said at least one real signal with said at least one respective physical indicator of said phase of said at least one reference signal.

A system of welding for inductive windings of electrical machines starting from U-shaped conducting elements with a bridge joining a pair of shanks, wherein said conducting elements are arranged in a ferromagnetic core of an electrical machine with said shanks oriented parallel to an axis of symmetry of said ferromagnetic core, and where each shank of said conducting elements comprises an end, each end being adjacent to an end of another conducting element for welding together according to a predefined electrical connection diagram;

• wherein said system is configured for:
• arranging said ferromagnetic core containing said conducting elements in a welding zone, with said ends of said conducting elements facing a programmable focusing optic scanner controlled by an electronic control unit, said programmable focusing optic scanner being configured to project a laser welding beam;
• gripping said ends to be welded together, which are mutually adjacent and aligned, an axial interspace of separation being leaved between said ends;
• scanning said laser welding beam, by following a preset cyclic path and passing through at least one first end and at least one second end of said ends of said conducting elements, wherein said preset path is scanned for a plurality of cycles, for the generation of a well of molten metal in said at least first and second ends in order to close said interspace that separates them, each cycle of said scan having a preset duration;
• cooling said well of molten metal, by means of shutting off said laser welding beam, up until solidification of said well of molten metal, said solidification resulting in a weld that stably connects said at least first and second ends of said adjacent conducting elements, said cooling having a preset duration;
• monitoring at least one real signal of an optical emission in said steps of scanning and cooling in order to control the quality of said weld between said pair of ends of said conducting elements of an inductive winding of a stator, via at least one optical sensor device and said electronic control unit;
• wherein said system is further configured for:
• detecting and acquiring said optical emission originating from said weld for said duration of said steps of scanning and cooling of each welding operation between said pair of ends of said conducting elements;
• obtaining at least one real signal from said optical emission, said real signal being a time trend constituted by one of either a continuous time series or a plurality of consecutive discrete values of a discrete time series;
• comparing characteristics of said at least one real signal of said optical emission with respective characteristics of at least one respective reference signal of said optical emission, and identifying defects of said weld on the basis of the relationship between said compared characteristics;
• and
• classifying said at least one real signal on the basis of the comparison of said characteristics of said at least one real signal with said respective characteristics of said at least one respective reference signal, said classifying of said at least one real signal including identifying any defects and/or estimating mechanical properties of said weld on the basis of the single relationship between said compared characteristics;
• wherein said system is further configured for:
• selecting a predefined welding program, where said welding program comprises instructions and operating parameters with which said electronic control unit is to execute said steps of scanning and cooling, where said welding program further comprises at least one reference signal of said optical emission relating to said welding program, and where said welding program further comprises at least one time window for monitoring in said steps of scanning and cooling corresponding to a phase of said welding operation;
• extracting values corresponding to said phase defined by said at least one time window from said at least one real signal of said optical emission and from said at least one respective reference signal of said optical emission of each welding operation;
• and
• calculating at least one physical indicator relating to said phase of said welding operation, starting from said values which are contained in said at least one time window and extracted from said at least one real signal and from said at least one respective reference signal;
• and
• comparing said at least one physical indicator of said phase of said at least one real signal with said at least one respective physical indicator of said phase of said at least one reference signal.