Abstract: Steel rod stock is shaped into a fuel injector tip having a central axis and including a shank extending between a mating end and a nozzle end. An inner surface of the fuel injector tip includes a conical needle valve seat and defines a nozzle chamber and a sac on opposite sides of the needle valve seat. The mating end includes a injector stack surface and an injector body contact surface. After shaping the fuel injector tip, it is a case hardened to a hardness in excess of HRC 55. Next, the nozzle end is shaped, after the case hardening step, to include a plurality of nozzle surfaces that each define one of a plurality of nozzle outlets extending between the sac and the outer surface. The inner surface and the nozzle surfaces are then autofrettaged to induce compressive residual stress at the case hardened needle valve seat, the case hardened sac and at least a portion of the nozzle surfaces closest to the sac.

Abstract: A production robust autofrettage process for strengthening fuel injector nozzle tips includes applying a vacuum to the interior volume of the nozzle tip. Plugs are suctioned over each of the nozzle outlets. Nozzle outlets are blocked by pressing the plugs between the nozzle tip and a fixture component. The nozzle tip is then autofrettaged at least in part by pressurizing the interior volume with an autofrettage liquid. The plugs are then removed from the nozzle outlets leaving the nozzle tip strengthened with compressive residual stress, especially in the sac region of the interior volume of the nozzle tip.

Abstract: Steel rod stock is shaped into a fuel injector tip having a central axis and including a shank extending between a mating end and a nozzle end. An inner surface of the fuel injector tip includes a conical needle valve seat and defines a nozzle chamber and a sac on opposite sides of the needle valve seat. The mating end includes a injector stack surface and an injector body contact surface. After shaping the fuel injector tip, it is a case hardened to a hardness in excess of HRC 55. Next, the nozzle end is shaped, after the case hardening step, to include a plurality of nozzle surfaces that each define one of a plurality of nozzle outlets extending between the sac and the outer surface. The inner surface and the nozzle surfaces are then autofrettaged to induce compressive residual stress at the case hardened needle valve seat, the case hardened sac and at least a portion of the nozzle surfaces closest to the sac.

Abstract: A production robust autofrettage process for strengthening fuel injector nozzle tips includes applying a vacuum to the interior volume of the nozzle tip. Plugs are suctioned over each of the nozzle outlets. Nozzle outlets are blocked by pressing the plugs between the nozzle tip and a fixture component. The nozzle tip is then autofrettaged at least in part by pressurizing the interior volume with an autofrettage liquid. The plugs are then removed from the nozzle outlets leaving the nozzle tip strengthened with compressive residual stress, especially in the sac region of the interior volume of the nozzle tip.

Abstract: A fuel injector is disclosed. The fuel injector has an injector body and an injector needle located inside the injector body. At least one of the injector body and injector needle has a portion configured to be exposed to a combustion chamber, the portion including maraging or carburizing steel and having a nitrided outer layer.