Abstract:
A multi-axis machine includes a controller operable to control a nozzle which ejects a particulate material relative to a part surface to maintain a compound angle and predetermined stand off distance to remove surface and near-surface crack initiation sites.

Description:
BACKGROUND 
       [0001]    The present disclosure claims priority to U.S. Provisional Patent Disclosure Ser. No. 61/352,483, filed Jun. 8, 2010. 
         [0002]    The present disclosure relates to a surfacing technique, and more particularly to an abrasive machining technique that eliminates crack initiation sites. 
         [0003]    Conventional machining of alloy 718 material may introduce damage to surface and near surface carbide particles inherent to the 718 alloy. These surface carbide particles are cracked by interaction of the machining tools and the brittle carbides. Under fatigue loading conditions, these carbides may serve as preferential locations for crack initiation which may limit the useful life of the material. 
       SUMMARY 
       [0004]    A multi-axis machine according to an exemplary aspect of the present disclosure includes a controller operable to control a nozzle which ejects a particulate material, relative to a part surface to maintain a compound angle and predetermined stand off distance to remove surface and near-surface crack initiation sites. 
         [0005]    A method of surface machining according to an exemplary aspect of the present disclosure includes removing surface and near-surface crack initiation sites with a particulate matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0007]      FIG. 1  is a general schematic view of a multi-axis system for use with the present disclosure; 
           [0008]      FIG. 2  is a schematic view of a nozzle position with respect to a workpiece to illustrate a first component of the compound angle; 
           [0009]      FIG. 3  is a sectional view of the workpiece in  FIG. 2  taken along line  3 - 3  to illustrate a second component of the compound angle; and 
           [0010]      FIG. 4  is a perspective view of a nozzle position with respect to an example workpiece. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  schematically illustrates a multi-axis system  20 . The system  20  generally includes a particulate matter supply  22 , a nozzle  24  to dispense the particulate matter, a positioning apparatus  26  and a control  28 . The nozzle  24  is located relative a workpiece W by the positioning apparatus  26  under direction of the control  28 . The particulate matter supply  22  in the disclosed non-limiting embodiment supplies a 500 grit aluminum oxide powder through the nozzle  24  which may be a 5/16″ (7.9375 mm) diameter nozzle. The positioning apparatus  26  provides multi-axis motion with variable velocity control to consistently position the nozzle  24  relative to each surfaces S of the workpiece W under direction of the control  28 . The control  28  is utilized to implement the operational functionality of the positioning apparatus  26  to direct the nozzle  24  relative to the workpiece W. In terms of hardware architecture, the computing device can include a processor, memory, and one or more input and/or output (I/O) device interface(s) that are communicatively coupled via a local interface. It should be understood that the system  20  is schematically depicted herein with conventional systems, however, various other configurations may alternatively or additionally provided to effectuate the surface machining technique disclosed herein. 
         [0012]    The surface machining technique disclosed herein utilizes the multi-axis motion with variable velocity control through the positioning apparatus  26  to assure a uniform erosion rate is achieved upon the desired surfaces S of the workpiece W. The control  28  locates the nozzle  24  relative to the surface S of the workpiece W at a constant compound angle and predetermined stand off distance which is consistently maintained as the nozzle  24  traverses the various surfaces S 1 -Sn ( FIGS. 2 and 3 ) of the workpiece W. The compound angle generally includes an alpha (α) and beta (β) component which may or not may not remain same relative to each surface S 1 -Sn of the workpiece W ( FIG. 3 ) depending on desired amount of erosion at each surface of the workpiece. 
         [0013]    As the particulate matter strikes the workpiece W, the particulate matter erodes the material to produce a surface free of the damaged layer caused by previous conventional machining operations. That is, the previous conventional machining operations result in a damaged layer with surface and near-surface crack initiation sites. The surface machining technique disclosed herein eliminates this damaged layer to improve the fatigue life up to ten times compared to the life of conventionally machined alloy 718. 
         [0014]    The surface machining technique uniformly removes high amounts of material as compared to conventional abrasive blasting processes. In other words, rather than a surface treatment/cleaning process typical of conventional abrasive blast processing, the disclosed surface machining technique uses specific media, machining angles and gun distances to achieve tightly controlled and relatively significant material removal rates more typical of a machining processes. Material removal typical of the surface machining technique in one non-limiting embodiment disclosed herein is 0.002-0.003″ (0.05-0.07 mm) of material removal compared to a conventional abrasive surface treatment/cleaning process that removes only approximately 0.0005″ (0.001 mm) of surface contaminants with little regard to final product size. 
         [0015]    The material removal rate disclosed herein is for alloy 718 and may be varied dependant on the surface damage experienced by other alloys. That is, use of different grit sizes and materials may be utilized to remove surface damage of any type. The surface machining technique disclosed herein has been found to remove both hard surface material conditions and slightly distorted surface structure with equal efficiency on several high strength aerospace alloys, with no compromise in size control. 
         [0016]    Since the surface machining technique enhances Low Cycle Fatigue (LCF) life, the surface machining technique disclosed herein provides for a competitive advantage over those that use a typically-processed alloy 718 part. Possible components that could necessitate enhanced LCF life are: different flight envelopes which increase stresses or temperatures, requirements for larger surface damage, i.e., handling damage, allowances in the field, or reverse engineering a material in a gas turbine engine program with lower life margins. 
         [0017]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
         [0018]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0019]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.