Manufacturing method of differential device

A manufacturing method of a differential device, the differential device including:

• a differential case that houses a differential mechanism drivingly coupled to an output shaft and that has a first abutting surface disposed so as to extend in an axial direction, a first welding surface disposed along an entire circumference, and a first facing surface disposed on a downstream side in an irradiating direction of an energy beam with respect to the first welding surface so as to extend along the entire circumference;
• and
• a differential ring gear that is welded by the energy beam on an outer peripheral side of the differential case and that has a second abutting surface disposed so as to extend in the axial direction, a second welding surface disposed along the entire circumference and disposed so as to face the first welding surface, a second facing surface disposed on the downstream side in the irradiating direction with respect to the second welding surface so as to extend along the entire circumference and face the first facing surface, the manufacturing method of the differential device comprising:
• an installing step of inserting the first abutting surface and the second abutting surface while relatively moving the first abutting surface and the second abutting surface in the axial direction, determining positions of the differential case and the differential ring gear in the axial direction, installing the differential case and the differential ring gear so that a separation portion is formed so that the first welding surface and the second welding surface are spaced away from each other and so as to have a non-linear portion that has a non-linear shape in a section passing through an axial center of the energy beam, and installing the differential case and the differential ring gear so that a void is formed between the first facing surface and the second facing surface that are spaced away from each other by a distance larger than that of the separation portion and is in communication with the separation portion;
• and
• a welding step of irradiating the energy beam to the separation portion and welding the first welding surface and the second welding surface.