Method of manufacturing a valve for an internal combustion engine
A method of manufacturing a valve for an internal combustion engine, comprises: (i) a primary step of forging a bulging portion at one end of a rod material to form a generally disk-shape valve head of the valve having a tapered periphery; (ii) an thickness adjustment step of machining an excessively thick portion of the valve head; and (iii) a secondary step of forging a peripheral region of the valve head to create radial slip deformations therein to form a valve face of the valve head. In the step of thickness adjustment, only the front end of the disk-shape valve head is machined without harming dense grain flow lines induced in the tapered face ( 16 a ) in the primary forging while advantageously saving the valve material and reducing thickness adjustment time. In the secondary forging, the hardness of the valve face is further enhanced.
1. A method of manufacturing a valve for an internal combustion engine, comprising:
a step of primary forging in which a bulging portion at one end of a rod material is forged to form a generally disk-shape valve head of the valve by means of a primary forging die unit having a first die and a first punch;
a step of adjusting a thickness of the disk-shape valve head formed in the step of primary forging by machining an excessively thick portion thereof; and
a step of secondary forging in which a periphery of the disk-shape valve head is forged to create therein radial slip deformations by means of a secondary forging die unit having a second die and a second punch, the periphery being associated with a valve face that comes into contact with a valve seat of the internal combustion engine,
the method further comprising:
the primary forging die unit is provided on the first die thereof for forging the valve head with a peripheral taper forming face for forming a tapered face associated with the valve face; and
a predetermined tapered face that corresponds to the valve face is formed in the step of primary forging along the periphery of the disk-shape valve head, in conjunction with the valve head and in preparation for the secondary forging; and
only a front end opposite the valve face of the disk-shape valve head formed in the primary step is machined in the step of adjusting the thickness.
2. The method of manufacturing a valve according to claim 1 , wherein an angle of inclination of a pressing face provided on the first die of the primary forging die unit for forming the tapered face associated with the valve face has a predetermined angle smaller than an inclination angle of a pressing face provided on the second die of the secondary forging die unit for forming the valve face.