A method of establishing a weld joint between at least a first part and a second part, comprising the step of projecting an energy beam onto an interface area between the parts, wherein the beam is projected onto the interface area so as to produce a primary spot on the interface area, and wherein the beam is repetitively scanned in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the object, the effective spot having a two-dimensional energy distribution, wherein the effective spot is displaced along a track over the interface area so as to progressively melt mating portions of the first part and the second part so as to form the weld joint, and being characterised in that: the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot along the track, wherein during at least a portion of the displacement of the effective spot along the track, said two-dimensional energy distribution is asymmetric - in relation to any line extending through the effective spot in parallel with the track, and/or - in relation to any line extending through the effective spot perpendicularly to the track, and wherein: the two-dimensional energy distribution of the effective spot is dynamically adapted so that it is different when the effective spot is in an area adjacent to a recess, opening, through hole or projection in one of the parts, than when it is in an area remote from said recess, opening, through hole or projection, respectively, or the two-dimensional energy distribution is dynamically adapted in correspondence with variations in the thickness and/or material of at least one of the two parts in the interface area, or the two-dimensional energy distribution is dynamically adapted so that it is different at a curved portion of the track than at a straight portion of the track. wherein the beam is projected onto the interface area so as to produce a primary spot on the interface area, and wherein the beam is repetitively scanned in two dimensions in accordance with a scanning pattern so as to establish an effective spot on the object, the effective spot having a two-dimensional energy distribution, wherein the effective spot is displaced along a track over the interface area so as to progressively melt mating portions of the first part and the second part so as to form the weld joint, and being characterised in that: the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot along the track, wherein during at least a portion of the displacement of the effective spot along the track, said two-dimensional energy distribution is asymmetric - in relation to any line extending through the effective spot in parallel with the track, and/or - in relation to any line extending through the effective spot perpendicularly to the track, and wherein: the two-dimensional energy distribution of the effective spot is dynamically adapted so that it is different when the effective spot is in an area adjacent to a recess, opening, through hole or projection in one of the parts, than when it is in an area remote from said recess, opening, through hole or projection, respectively, or the two-dimensional energy distribution is dynamically adapted in correspondence with variations in the thickness and/or material of at least one of the two parts in the interface area, or the two-dimensional energy distribution is dynamically adapted so that it is different at a curved portion of the track than at a straight portion of the track. the two-dimensional energy distribution of the effective spot is dynamically adapted during displacement of the effective spot along the track, wherein during at least a portion of the displacement of the effective spot along the track, said two-dimensional energy distribution is asymmetric - in relation to any line extending through the effective spot in parallel with the track, and/or - in relation to any line extending through the effective spot perpendicularly to the track, - in relation to any line extending through the effective spot in parallel with the track, and/or - in relation to any line extending through the effective spot perpendicularly to the track, and wherein: the two-dimensional energy distribution of the effective spot is dynamically adapted so that it is different when the effective spot is in an area adjacent to a recess, opening, through hole or projection in one of the parts, than when it is in an area remote from said recess, opening, through hole or projection, respectively, or the two-dimensional energy distribution is dynamically adapted in correspondence with variations in the thickness and/or material of at least one of the two parts in the interface area, or the two-dimensional energy distribution is dynamically adapted so that it is different at a curved portion of the track than at a straight portion of the track. the two-dimensional energy distribution of the effective spot is dynamically adapted so that it is different when the effective spot is in an area adjacent to a recess, opening, through hole or projection in one of the parts, than when it is in an area remote from said recess, opening, through hole or projection, respectively, or the two-dimensional energy distribution is dynamically adapted in correspondence with variations in the thickness and/or material of at least one of the two parts in the interface area, or the two-dimensional energy distribution is dynamically adapted so that it is different at a curved portion of the track than at a straight portion of the track.