A process for the injection of an electric motor rotor, said rotor comprising: a lamination stack (10) having a central axial bore (11) and a plurality of axial channels (12); and a cage (30) of aluminum, which is formed by an upper end ring (31) and a lower end ring (32), which are interconnected by a plurality of bars (33) molten in the axial channels (12). The process comprises the steps of: mounting, at the upper end portion of the central axial bore (11), a stamping pin (40), which has a widened head (41) seated against the upper end lamination of the lamination stack (10); heating the lamination stack, as well as an upper cavity (21) and a lower cavity (22) of a mold (20); positioning the lamination stack (10) inside the mold (20); rotating the mold (20) and pouring the aluminum into the inside thereof through the inlet channel (23); removing, from the mold (20), the rotor (R) with the cage (30) already formed and comprising an upper plate (35) that covers the stamping pin (40); and axially extracting the stamping pin (40) in order to break, centrally, the upper plate (35), transforming it in the upper ring (31) of the cage (30).