| 摘要 |
PURPOSE:To process and harden a recessed part formation surface and to restrict fluidization of an extra thick part in a direction in which the diameter of a lower hole is reduced upon the formation of the recessed part so that precision for recessed part formation can be uniformalized by making the recessed part formation surface be thinned 25% to 50% in its processing factor by the use of a coining process ahead of the formation of the recessed part. CONSTITUTION:A second grid electrode 20 has a slit-shaped recessed part 22 formed on the peripheral part of an electron beam throughhole 21 and it has a ring shaped projecting part 24 around the recessed part 22 on a recessed part formation surface 23. Then, a thickness T of the recessed part formation surface 23 is formed low in the range of 25% to 50% to a thickness T0 of a raw material by the use of a coining process. Namely, when the recessed part formation surface is thinned in advance so as to be made in uniform thickness by the coining process, the recessed part formation surface are processed/ hardened by plastic processing so as to increase a process deformation resistance. Hence, extra thick part's fluidization, which is a cause of generating a dent upon the formation of the recessed part, can be restricted and precision for recessed part formation can be improved.
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