机械加工中涡轮叶片变形的研究翻译

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附录 A 英文原文

Energy and Power Engineering, 2016, 8, 1-12 Published Online January 2016 in SciRes.

http://www.scirp.org/journal/epe http://dx.doi.org/10.4236/epe.2016.81001

Research on the Deformation of

Turbine Blades at Machining

—Part 1. Properties of Materials and Features of

Chips

Masu Yamada1, Keiji Sonoya2, Takahito Sobayashi3, Hiroshi Satoh4

1TBM Corporation, Nagano, Japan

2Department of Mechanical Systems, Yamanashi University, Kofu, Japan

3Nichia Tanko Co. Ltd., Tomioka, Japan

4Oridea Inc., Mishima, Japan

Received 1 December 2015; accepted 26 January 2016; published 29 January 2016

This work is licensed under the Creative Commons Attribution International

License (CC BY).

Abstract

Along with the recent expansion of demand for electricity, the production of

steam turbine blades has increased, and various materials forged of 12Cr ferritic heat-

resistant types of steel have become widely used for this purpose. Although this

material seems to be an excellent choice as heat-resistant steel, it requires a post-

correction process for deformation after machining and thus lowers productivity.

Therefore, we started basic experimental research, and through a series of tests, we

found that 12Cr steel is a sticky material; the residual stresses after machining

concentrate in the vicinity of the surface; and this influences the deformation of

blades.

Keywords

Turbine Blade, Machining, Deformation, 12Cr Steel

1. Introduction

The production of steam turbine blades continues to increase along with the

recent expansion of demand for electricity. As electric plants seek larger capacity

and increased efficiency, the recent trend is to produce larger turbine blades that

demand dimensional control with high accuracy. The materials typically used for

turbine blades are chrome alloy steel, nickel alloy steel, and titanium, as well as

austenitic stainless steel for special environments and 17-4PH steel with high

strength. The contents of the additives vary slightly among turbine manufacturers.

One material among them, the forged material 12Cr steel, which is a ferritic heat-

resistant steel, began to be used as a turbine blades material[1]. Although

considerable time has passed since the development of the fundamental

technological background, there are a lot of complaints when this material is seen

from the standpoints of forging suppliers and machining workers, who report that

“care must be taken in the heat-treatment of removing stress after forging”, and

“there is unexplained transforming behavior at machining”. Moreover, although

there is some research on creep strength, etc., for this material as heat-resistant

steel[2][3], there is little research on its characteristics upon machining. In terms of

the amount of deformation at machining of the turbine blades, foregoing research

does not exist at all.

Considering this current situation, we started research on the engineering

issue: how can this machining deformation be brought as close as possible to zero?

In a series of experimental research projects, first, we examined the cutting

resistance and investigated how it is influenced by the number of teeth and the

depth of the cut made by the tool[4][5]. Next, we tried to acquire basic data that tend

to be lacking, such as the tensile and compression test, and investigated the work-

affected layers[6]. Consequentially, their thicknesses were obtained by the hardness

method, and it was calculated that the values were larger than the ones seen in the

reference. Moreover, we have not come to an understanding of the situation of the

metallographic structure and residual stress. As a result, we found that 12Cr steel is

a sticky material; the residual stresses after machining concentrate in the

neighborhood of the surface; and this influences the deformation of blades.

2. Experiments and Measurements

2.1. Material Properties and Blades Deformation State

Although it depends on the product shape after machining, these forged

materials are delivered from turbine manufacturers via forging suppliers to us, as

the fabricator, in the state of cutting stock of about 4 mm thickness remaining on

both sides to be finished with two rounds of machining.

The machining is done using simultaneous NC milling for such materials, and

the deformation correction of a deformed blade, which is discussed in this paper, is

done using a press machine as shown in Figure 1(a) and Figure 1(b), respectively.

Here, in Figure 1(a), when the amount of the deformation during machining

increases, it is likely to end only in a rising vibration value or in an abnormal

warning in the index table, or both at the same time. In this case, a worker is forced

to do corrective work using a press, shown in Figure 1(b). There is a loss of

productivity because this work must rely on the worker’s intuition and experience.

When restraint of the work materials on the milling bed during machining is

relieved, and after supporting the root part of the blades that are the working

reference of the machined blades and other parts are freed, the run-outs of the

blade center have no fixed form, as well as magnitudes and directions. One sample

in which all blades are distorted in the direction of the back is shown in Figure 2.

This figure was obtained through data on blades for a 700 MW electric generating

plant, 400 mm in length for 45 blades after finishing, and it is known that large

deformations close to 1.5 mm developed for the tolerance of 0.2 mm. In the age of

NC versatile machines, although the introduction of improved cutting methods

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摘要：

附录A英文原文EnergyandPowerEngineering,2016,8,1-12PublishedOnlineJanuary2016inSciRes.http://www.scirp.org/journal/epehttp://dx.doi.org/10.4236/epe.2016.81001ResearchontheDeformationofTurbineBladesatMachining—Part1.PropertiesofMaterialsandFeaturesofChipsMasuYamada1,KeijiSonoya2,TakahitoSobayashi3,HiroshiSa...

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