TECHNICAL FIELD

The present disclosure relates to a method for machining a free-form surface on an elongated material.

BACKGROUND ART

When an elongated material is machined into a turbine blade, conventionally, a blade root portion and a blade tip portion are kept in hold from roughing to finishing. In this case, strain occurs in the elongated material during roughing, and if the turbine blade is further machined as it is, the accuracy of a final finished state of the turbine blade degrades. Although not relating to machining of a turbine blade, Patent Document 1 discloses that, when machining an elongated material, the holding of one end of the elongated material is released after rough machining to release strain of the elongated material, and the end of the elongated material free from strain is held again before finishing.

CITATION LIST

Patent Literature

Patent Document 1: JPH10-76437A

SUMMARY

Problems to be Solved

However, in machining of an elongated material, the elongated material is generally held in a horizontal orientation. When one end of the elongated material in this state is released after rough machining, although strain generated during rough machining can be released, stress associated with deformation due to the own weight of the elongated material supported by only the other end remains. If the end of the elongated material is held again for finishing while leaving the stress associated with deformation due to its own weight, a desired final finished state of a product of the elongated material with the machined free-form surface may not be obtained.

In view of the above, an object of at least one embodiment of the present invention is to provide a method for machining a free-form surface on an elongated material whereby it is possible to improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

Solution to the Problems

(1) A method for machining a free-form surface on an elongated material having a first end region and a second end region with respect to a longitudinal direction according to at least one embodiment of the present invention comprises: a step of holding the first end region and the second end region; a first machining step of machining the free-form surface on the elongated material with the first end region and the second end region held; a step of releasing holding of the first end region; a step of determining a re-holding position obtained by correcting a position of the first end region after the holding of the first end region is released by a deformation amount of the elongated material due to a weight of the elongated material; a step of holding the first end region again at the re-holding position; and a second machining step of further machining the free-form surface on the elongated material after holding the first end region again.

With the above method (1), since the second machining step is performed in a state free from the strain of the elongated material generated in the first machining step and the stress associated with deformation of the elongated material due to its own weight, it is possible to improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

(2) In some embodiments, in the above method (1), the deformation amount of the elongated material due to the weight of the elongated material is determined by an analysis or an experiment in advance, and, in the step of determining the re-holding position, a position shifted from the position of the first end region after the holding of the first end region is released by the deformation amount is determined as the re-holding position.

With the above method (2), since it is unnecessary to individually determine the deformation amount of the elongated material due to the own weight of the elongated material in the step of determining the re-holding position, it is possible to rapidly perform the method for machining the free-form surface on the elongated material.

(3) In some embodiments, in the above method (1) or (2), the deformation amount is a difference between a position of the first end region relative to the second end region when the elongated material is horizontally oriented and a position of the first end region relative to the second end region when the elongated material is vertically oriented.

With the above method (3), it is possible to accurately and easily obtain the deformation amount of the elongated material due to the own weight of the elongated material.

(4) In some embodiments, the above method (1) further comprises a step of vertically orientating the elongated material, with the holding of the first end region being released, after the step of releasing the holding of the first end region, and, in the step of determining the re-holding position, a position of the first end region relative to the second end region when the elongated material, with the holding of the first end region being released, is vertically oriented is determined as the re-holding position.

With the above method (4), since the re-holding position is determined in consideration of the deformation due to the own weight of the individual elongated material, it is possible to further improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

(5) In some embodiments, in any one of the above methods (1) to (4), after the second machining step, the step of releasing the holding of the first end region to the second machining step are repeated at least once.

With the above method (5), even when the step of machining the free-form surface is repeatedly performed, the free-form surface can be machined in a state free from the strain generated during machining of the free-form surface and the stress associated with deformation of the elongated material due to its own weight. Thus, it is possible to improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

(6) In some embodiments, any one of the above methods (1) to (5) further comprises a step of subjecting the free-form surface to surface treatment after the second machining step.

With the above method (6), it is possible to improve the mechanical properties of a product of the elongated material with the machined free-form surface.

(7) In some embodiments, in the above method (6), a deformation amount of the elongated material due to residual stress caused by the surface treatment is predicted in advance, and the free-form surface is machined in the second machining step in consideration of a predicted value.

With the above method (7), when strain generated by the surface treatment is applied to the elongated material with the machined free-form surface, a desired final finished state of a product of the elongated material with the machined free-form surface is obtained. Thus, it is possible to improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

(8) In some embodiments, in any one of the above methods (1) to (7), the first end region of the elongated material has a projection protruding from the first end region, and the first end region is held by holding the projection.

With the above method (8), since the projection protrudes from the first end region, the projection can be easily held, and machining can be easily performed.

(9) In some embodiments, in any one of the above methods (1) to (8), a product of the elongated material on which the free-form surface is machined is a blade.

With the above method (9), it is possible to provide a finished blade of a rotary machine with an improved accuracy.

(10) In some embodiments, in the above method (9), the first end region and the second end region are held so that a chordwise direction is oriented in a vertical direction at a blade tip side of the blade.

Since the blade is thinner on the blade tip side than on the blade root side, the blade tends to easily deform at the blade tip side upon application of a force in the out-of-plane direction (a direction perpendicular to the chordwise direction). However, with the above method (10), when the holding of the first end region is released so that only the second end region is supported, a force due to the weight of the blade acts in the in-plane direction (chordwise direction) of the blade at the blade tip side, which suppresses the deformation due to the weight of the blade. When the deformation due to the own weight of the blade is suppressed, variation in the re-holding position of the first end region among the individual blades is reduced. Thus, it is possible to effectively release the stress associated with deformation due to the own weight of the elongated material when holding the first end region again.

Advantageous Effects

According to at least one embodiment of the present invention, by performing the second machining step in a state free from the strain of the elongated material generated in the first machining step and the stress associated with deformation of the elongated material due to its own weight, it is possible to improve the accuracy of a final finished state of a product of the elongated material with the machined free-form surface.

