Importance

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Abstract

A method of press forming a turbine shell 5a is provided for suppressing the reduction in thickness of a radially inner corner portion 52 of the turbine shell 5a without increasing a radius of the radially inner corner portion 52. The preferred method of forming the turbine shell 5a with the radially inner corner portion 52 is performed by bending a thin sheet material or plate with a press in basically a first preliminary pressing operation and second finish pressing operation. In the preliminary pressing operation, the thin sheet material or plate is subjected to compressive force to provide a preliminary form having a radially inner corner portion 52, a blade-carrying portion 51 and a flat portion 53. The blade-carrying portion 51 extends radially outward from the radially inner corner portion 52. The flat portion 53 extends radially inward from the radially inner corner portion 52. During the preliminary pressing operation, the compressive force is applied to form the radially inner corner portion 52, which is longer than the finished form of the radially inner corner portion 52. During the finish pressing operation, the preliminary form of the radially inner corner portion 52 is subjected to a pressing force, which generates a compressive force in the preliminary form of the radially inner corner portion 52. The compressive force generated in the corner portion 52 is directed in a direction substantially transverse to a direction of the thickness of the radially inner corner portion 52. In other words, the thickness of the corner portion 52 is reduced during the preliminary pressing operation and then increased during the finish pressing operation.

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First Claim