Importance

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Abstract

Thread rolling dies are disclosed which are provided with a band of roughness extending along the flanks of the thread forming grooves in the dies. The roughened bands provide traction between the blank and the dies so as to establish rolling without slippage at about the initial blank diamter. The roughened band is produced by electric discharge machining or grinding, using a precision-formed electrode. The electrical power applied during the formation of the roughened band is controlled so that the greatest amount of roughness, and in turn traction, is provided at the start end of the die and the band is provided with a progressively decreasing amount of roughness as it extends toward the finish end of the die. The band of roughness ends at a location spaced from the finish end of the die so that the flanks of the thread formed on the blank are smooth at the completion of the rolling operation. Improved quality threads are achieved by controlling the slippage between the die and the blank without producing objectionable laps in the finished thread. Also, wavy or drunken threads are eliminated because the blank tends to remain in match as it rolls along the die faces. Better die life is also achieved because the match between the blank and the dies is maintained.

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First Claim