The ornamental design for a weldinghelmet, as shown and described.
FIG. 1 is a front perspective view of a welding helmet showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing of portions of the welding helmet in FIGS. 1-7 is for the purpose of illustrating environmental structure and forms no part of the claimed design. The oblique line shading shown in FIGS. 1-4 represents a glass surface.