Method for manufacturing hollow engine valve

Abstract

A method for manufacturing a hollow engine valve includes inserting a half-finished hollow shaft section in sequence into die holes which have different hole shapes, and sequentially drawing so as to reduce the outer diameter and the inner diameter of the hollow shaft section and stretch its length in stages. The half-finished product is subjected to heat treatment so that the hardness thereof is lower than or equal to a predetermined level. A shaft end sealing section is formed by increasing the wall thickness of the opening end of the hollow shaft section toward the inside of the opening and the gap in the shaft end sealing section is welded.

1 . A method for producing a hollow engine valve in which a hollow stem portion of a semi-finished product is shaped into a predetermined shape by sequentially inserting the hollow stem portion into a plurality of shaping holes different in hole shape to sequentially draw the hollow stem portion in such a way that an outer diameter dimension and an inner diameter dimension of the hollow stem portion are reduced stepwise and a length of the hollow stem portion is increased stepwise, the method for producing a hollow engine valve characterized by comprising:
 subjecting the semi-finished product to heat treatment in such a way that a hardness of the semi-finished product becomes equal to or less than a predetermined hardness;   shaping a stem end sealing portion by causing a wall thickness of an opening edge portion of the hollow stem portion to be increased toward an inner side of the opening edge portion, by using a last one of the shaping holes which has a hole diameter adjusted; and   joining gap portions of the stem end sealing portion together.   
     
     
         2 . The method for producing a hollow engine valve according to  claim 1 , characterized by further comprising adjusting a hole diameter of a stem shaping portion in the last one of the shaping holes, the stem shaping portion configured to shape the hollow stem portion. 
     
     
         3 . The method for producing a hollow engine valve according to  claim 1 , characterized by further comprising injecting a coolant into the hollow stem portion before the drawing performed by using the last one of the shaping holes.