CN-121972912-A - Method for treating centrifugal compressor impeller with prolonged low cycle fatigue life

Abstract

The present invention relates to a method for treating a centrifugal compressor impeller to extend the low cycle fatigue life. A method for treating a centrifugal compressor wheel includes a combination of cold expansion of at least a portion of a bore of the wheel to induce residual compressive stress in an area surrounding the bore and surface peening of at least a portion of the compressor wheel such as a rear disk and portions of blades.

Inventors

• M. Morrisi
• F. Alan
• LI XIAODONG
• Q. Roberts
• P. Reynolds

Assignees

• 盖瑞特动力科技(上海)有限公司
• 盖瑞特动力科技(武汉)有限公司

Dates

Publication Date

20260505

Application Date

20221122

Priority Date

20211122

Claims (12)

1. 1. A method for producing a centrifugal compressor wheel, comprising the steps of: Providing a manufactured centrifugal compressor wheel made of ductile metal having tensile yield strength, the compressor wheel including a hub and a back plate and a plurality of blades joined to the hub and the back plate, the plurality of blades defining a lead-in portion of the compressor wheel configured for axial air ingress into the compressor wheel and defining a lead-out portion of the compressor wheel configured for radial air egress out of the compressor wheel, each blade having a blade root fillet at a junction of the blade and the hub, the compressor wheel having a first face and an opposite second face, the compressor wheel defining a bore extending centrally through the hub and the back plate in a downstream axial direction, and The manufactured compressor wheel is processed by: (a) A hole treatment step comprising forcibly expanding the diameter of the hole to cold work the metal at the inner surface of the hole to exceed the tensile yield strength in a circumferential direction around the hole so as to induce compressive residual hoop stress in the metal adjacent the inner surface of the hole, and (B) A back plate treatment step comprising surface peening at least a portion of the back plate of the compressor wheel.
2. 2. The method for producing a centrifugal compressor wheel according to claim 1, wherein the hole processing step is performed only along an incomplete portion of the hole, the hole not being forcibly expanded outside the incomplete portion.
3. 3. The method for producing a centrifugal compressor wheel according to claim 2, wherein a starting point of said incomplete portion of said hole is spaced axially downstream from a leading edge of said blade root fillet.
4. 4. The method for producing a centrifugal compressor wheel of claim 1, further comprising surface peening at least some regions of the blades.
5. 5. The method for producing a centrifugal compressor wheel according to claim 4, wherein the surface-peened region of the blade comprises a suction surface and a pressure surface of the blade.
6. 6. The method for producing a centrifugal compressor wheel of claim 5, further comprising surface peening the blade root fillet and the hub.
7. 7. The method for producing a centrifugal compressor wheel according to claim 6, wherein the surface peening is performed at an intensity of from 0.15mm to 0.6mm measured on an Almen N scale.
8. 8. The method for producing a centrifugal compressor wheel according to claim 6, wherein the surface peening is performed at an intensity of from 0.2mm to 0.35mm measured on an Almen N scale.
9. 9. The method for producing a centrifugal compressor wheel according to claim 6, wherein the surface peening is performed at an intensity of from 0.25mm to 0.35mm measured on an Almen N scale.
10. 10. The method for producing a centrifugal compressor wheel of claim 1, wherein the hole treating step includes disposing a split bushing within the hole about a mandrel, and pulling the mandrel axially through the split bushing to expand the split bushing radially outward.
11. 11. The method for producing a centrifugal compressor wheel according to claim 1, wherein said hole treatment step produces a retained expansion of at least 1.2% at said inner surface of said hole.
12. 12. The method for producing a centrifugal compressor wheel according to claim 1, further comprising the step of machining said inner surface of said bore to remove surface irregularities created during said bore treatment step.

Description

Method for treating centrifugal compressor impeller with prolonged low cycle fatigue life The present application is a divisional application of application number 202211469775.4 entitled "method of treating centrifugal compressor impeller to extend low cycle fatigue life", filed on day 2022, 11 and 12. Technical Field The present application relates generally to centrifugal compressor wheels, such as for use in turbochargers for internal combustion engines. Background Typically, the life limiting mode of the centrifugal compressor wheel is a Low Cycle Fatigue (LCF) failure mode. Various failure modes may occur. In one LCF failure mode, one or more cracks may initiate at or near the surface of the through hole of the impeller. In other modes, the rear disk of the impeller may form a crack in a chordal or "pizza-lump" configuration. Disclosure of Invention The object leading to the current technical development of the invention described herein is to improve the LCF life of centrifugal compressor wheels. The present disclosure describes a treatment method for a centrifugal compressor impeller that can significantly extend the LCF life of the impeller. This method requires the continuous application of two operations on the impeller. In one operation, the inner surface of at least a portion of the length of the hole is cold worked by forced expansion of the hole diameter, thereby creating a compressive residual hoop stress region in the metal surrounding the hole. In a second operation, surface peening is performed on at least a portion of the compressor wheel to induce compressive residual stresses in the surface of the wheel. Advantageously, the hole cold working achieves a retained expansion of at least 1.2% and the surface peening is performed at an intensity of 0.15mm to 0.6mm measured on the Almen N scale. In one embodiment described herein, a method of processing includes the steps of: Providing a centrifugal compressor wheel made of ductile metal having a tensile yield strength, the compressor wheel comprising a hub and a back plate and a plurality of blades joined to the hub and the back plate, the plurality of blades defining a lead-in portion of the compressor wheel configured for axial entry of air into the compressor wheel and defining a lead-out portion of the compressor wheel configured for radially outward discharge of air from the compressor wheel, each blade having a blade root fillet at the juncture of the blade and the hub, the compressor wheel having a first face and an opposite second face, the hub of the compressor wheel defining a bore extending centrally through the hub and the back plate in a downstream axial direction; Cold working the metal at the inner surface of the hole to exceed the tensile yield strength in a circumferential direction around the hole, thereby inducing compressive residual hoop stress in the metal adjacent the inner surface of the hole, and At least a portion of the compressor wheel is surface peened, excluding the inner surface of the bore. In some embodiments, the cold working step includes exerting a radially outward pressure on the inner surface of the bore. This may be accomplished mechanically, such as by using a mechanical tool to exert radially outward pressure on the inner surface of the bore. For example, the cold working step may include drawing a tool axially through the hole in a downstream axial direction, the diameter of the tool exceeding the initial diameter of the hole prior to the cold working step. Various mechanical tools may be employed, non-limiting examples of which include a radially expandable mandrel (or "split mandrel") that may be triggered at a desired location along the hole, after which the expanded mandrel is then pulled axially along the hole to cold work the hole, or alternatively a split sleeve and mandrel, wherein the split sleeve is located in the hole and the mandrel is pulled through the sleeve to expand the sleeve radially outward and thus cold work the hole. Ball pushing is yet another technique that may be employed. The cold working may be applied to the entire axial length of the bore, or alternatively may be applied to only a portion of the length. When only a portion of the bore length is to be cold worked, a larger diameter countersink may be provided in the region of the bore not ready for cold working, and the machine tool may be initially activated in the countersink before being pulled through the smaller diameter main bore portion. As an alternative to using mechanical tools, cold working of the bore may be accomplished by non-mechanical means (non-limiting examples of which may include laser treatment of the bore surface or chemical treatment of the bore surface). Drawings Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: FIG. 1 is a cross-sectional view through a compressor wheel prior to a tr