Spark plug for internal combustion engine having ground electrode with thick, thin and stepped portion and method for producing the spark plug

A spark plug for an internal combustion engine, said spark plug comprising:

• a rod-shaped center electrode extending in a direction of an axis line;
• a substantially cylindrical insulator disposed on an outer periphery of the center electrode;
• a cylindrical metal shell disposed on an outer periphery of the insulator;
• a ground electrode having a base end joined to a leading end portion of the metal shell in the direction of the axis line and a distal end portion bent toward the axis line, said ground electrode comprising:
• a thick portion provided on a base end side;
• a thin portion provided on a distal end side;
• and
• a stepped portion provided on an inner peripheral surface between the thick portion and the thin portion;
• a noble metal tip joined to and partially embedded in an inner peripheral surface of the thin portion, the noble metal tip being disposed to form a gap between the same and the leading end portion of the center electrode;
• and
• a bulge portion provided on the inner peripheral surface of the thin portion between the stepped portion and the noble metal tip and formed of substantially a same metal component contained in the ground electrode,
• wherein, when viewed from a side surface of the ground electrode, a following relationship is satisfied:
• [a protruding height of the noble metal tip from the inner peripheral surface of the thin portion]≧[a protruding height of the bulge portion from the inner peripheral surface of the thin portion].