PROBLEM TO BE SOLVED: To provide autofrettage processing which can reduce part consumption due to wear as much as possible.;SOLUTION: An apparatus for autofrettage processing inserts a piston that forms a clearance having a predetermined average clearance amount (h) and a first axial length (a), between an inner wall on one end side of a workpiece and a side surface along an axial direction of the piston at a predetermined feed speed (v) while the piston is driven by a pressurizing part and in a pre-pressuring state of the pressurizing part, to apply autofrettage processing to the workpiece. The apparatus for autofrettage processing sets a clearance with a second axial length (b) longer than the first axial length (a) when a first critical feed speed (Vca) equivalent to the greatest leakage flow amount (Qmax (a)) per unit time in the first axial length (a) of a hydraulic oil leaking out from the clearance is higher than a preset piston critical feed speed (V0).;COPYRIGHT: (C)2013,JPO&INPIT
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