Fuel injector

1. An injector comprising a tubular nozzle body having a nozzle side, receiving a needle valve member, and an actuator side, receiving a tubular magnetic armature and receiving an armature side of a tubular pole piece above the magnetic armature, wherein the nozzle body and the pole piece are welded together through a seam weld line between an inner tubular surface of the actuator side of the tubular nozzle body and an outer tubular surface of the armature side of the pole piece, wherein the actuator side of the tubular nozzle body comprises a constricted area while the outer surface of the armature side of the pole piece comprises a recessed area, the constricted area and the recessed area contacting each other at a level of the seam weld line and providing a friction area reducing hydraulic load on the seam weld line.

2. The injector according to claim 1 , wherein the recessed area is formed through a chamfer of the outer surface in an nozzle to inlet axial direction of the tubular pole piece, the tubular pole piece having a diameter decreasing in the nozzle to inlet axial direction.

3. The injector according to claim 1 , wherein in an nozzle to inlet axial direction the armature side of the pole piece comprises a first diameter providing a contact surface with an inner diameter of the tubular nozzle actuator side and a second diameter above the first diameter, the second diameter being smaller than the first diameter and forming the recessed area.

4. The injector according to claim 1 , wherein the constricted area, provided at the upper end of the actuator side of the tubular nozzle body, reduces the diameter of the nozzle body towards and up to a top of the actuator side of the nozzle body.

5. The injector according to claim 4 , wherein the constricted area and the recessed area extend around the seam weld line.

6. The injector according to claim 4 , wherein the seam weld line is provided at the upper end of the actuator side of the tubular nozzle body and ends the constricted area.

7. The injector according to claim 1 wherein the seam weld line is a continuous annular weld line.

8. A process for manufacturing the injector according to claim 1 , the method comprising applying pressure on the top end of the nozzle body with a tool adapted to apply a preload on the upper end of the actuator side of the nozzle body while laser welding the nozzle body with the pole piece, the tool pressing the upper end of the actuator side of the nozzle body to deform the top end of the nozzle body in a centripetal direction into the constricted area until the constricted area contacts the recessed area of the pole piece during laser welding of the nozzle body and the pole piece.

9. The process for manufacturing an injector according to claim 8 , wherein the tool has a tubular wall provided with an internally conical end pressing the upper end of the actuator side of the nozzle body and wherein the tool, the nozzle body and the pole piece are rotated around a common axis during the laser welding while the beam of the laser is fixed to provide the annular seam weld line and the constricted area contacting the recessed area.

10. The process for manufacturing an injector according to claim 8 , wherein the tool comprises at least one roller pressing the upper end of the actuator side of the nozzle body while the nozzle body and the pole piece are rotated around a common axis during the laser welding and the beam of the laser is fixed thus providing the annular seam weld line and the constricted area contacting the recessed area.