| 摘要 |
Forming of a valve head portion (1) of a hollow engine valve (V) comprising a material particularly satisfactory in heat resistance is performed by cold forging. On this occasion, the material with excellent heat resistance is worked to form a valve head portion semifinished product (11) having a hollow hole (S11) whose inner diameter (Phi11) is equal to the maximum inner diameter (Phi11) of a hollow hole (S1) of a finished product of the valve head portion (1), and having a diameter-increased section (111) whose maximum outer diameter (Phi12) is equal to the maximum outer diameter (Phi12) of a diameter-increased section (1a) of the finished product. Parts of the valve head portion semifinished product other than a central part to a lower part of the diameter-increased section (111) are necked down by cold forging performed a plurality of times to obtain the finished product of the valve head portion (1). This method of obtaining the finished product is provided by the present invention.
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