Patent ID: 8156779
Filing Date: 2012-04-17
Classification: B21H,H01T

Abstract:
1. An apparatus for producing a spark plug, comprising: a workpiece supporting portion for rotatably holding a workpiece about a center axis, said workpiece being a shaft-like workpiece which is to be formed as a metal shell of said spark plug, and in which a gas seal portion is formed on an outer peripheral surface of a basal end side of a to-be-threaded portion while being radially outward projected; a die which is rotationally drivable in a rolling performing direction by die rotation driving means, for performing a thread rolling process on an outer peripheral surface of said workpiece held by said workpiece supporting portion; workpiece conveying means for conveying said workpiece supporting portion, to which said workpiece is attachable, from a retracting position for preparation of rolling to a rolling position which is determined in a form where a predetermined rolling relief gap extending along the center axis of the workpiece remains between an end face of said gas seal portion on a side of said to-be-threaded portion, and an end face of said die corresponding to a positioning end face on a side of said workpiece; approach driving means for, in order to start the thread rolling process, performing an approach drive of relatively approaching said die in a rotationally driven state and said workpiece to each other in a radial direction; rolling relief gap displacement amount specifying means for, in advance of a start of the approach drive, measuring a value of the rolling relief gap formed between said workpiece conveyed to the rolling position and the die, and specifying a rolling relief gap displacement amount which is a displacement amount from a target value of said rolling relief gap; thrust direction correcting means for thrust-correcting a positional relationship between a threaded portion formed in said die and said workpiece, in a direction along which the specified rolling relief gap displacement amount is eliminated; approach driving condition calculating means for calculating the approach driving conditions on a basis of the specified rolling relief gap displacement amount so that, in a circumferential direction of said workpiece, a positional relationship between a starting position of said threaded portion which is rolling-formed, and a joining position of a ground electrode to a tip end face of said workpiece is constant; and approach drive controlling means for controlling an operation of said approach driving means on the basis of the calculated approach driving conditions.