Abstract:
A method for machining a component. The method includes providing a machining apparatus configured to induce vibrations such that a vibration direction of the machining apparatus is substantially aligned with respect to a machining direction of the component, and vibrating the machining apparatus in the vibration direction to machine the component in the machining direction.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to machining techniques, and more specifically to methods and apparatus for ultrasonic machining.  
           [0002]    At least some known components include features that require ultrasonic machining. More specifically, complex-shaped components, for example gas turbine engine blades, often have geometric constraints which may limit the use of conventional machining methods. For example, blind holes which have non-circular and/or tapered cross-sections may be inaccessible to conventional machining heads. Typically, ultrasonic machining is a “directional” machining process, wherein to optimize performance an amplitude of a sonic vibration is aligned with a direction of desired material removal. However, aligning the sonic vibration amplitude may limit the usefulness of ultrasonic machining when applied to complex-shaped components.  
           [0003]    At least some known ultrasonic machining methods use trial and error to machine complex-shaped components. More specifically, in at least some known ultrasonic machining methods, various curved or irregularly-shaped tuning forks or cutters are fabricated, and an amplitude of vibration is bent or redirected into alignment with geometry of the tuning fork or cutter. However, bending or redirecting an amplitude into alignment with the geometry of the tuning fork or cutter may inhibit the amount of energy directed to a machining surface or material, and thus may limit the effectiveness of the ultrasonic machining.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0004]    In one aspect, a method is provided for machining a component. The method includes providing a machining apparatus configured to induce vibrations such that a vibration direction of the machining apparatus is substantially aligned with respect to a machining direction of the component, and vibrating the machining apparatus in the vibration direction to machine the component in the machining direction.  
           [0005]    A machining tool is provided for machining a component. The tool includes a body including a first projection extending therefrom and a second projection extending therefrom. The first projection is spaced a distance across the body from the second projection. The body is configured to vibrate in a direction substantially aligned with a machining direction of the component. The tool further includes a cross-bar removably coupled to the body between the first and second projections. The cross-bar includes at least one machining surface. The cross-bar and the machining surface are configured to vibrate with the body in a direction substantially aligned with respect to the machining direction of the component such that the machining surface machines the component in the machining direction.  
           [0006]    A machining tool assembly is provided for machining a gas turbine engine blade. The assembly includes a base, a fixture coupled to the base and configured to couple to the component such that the component is fixedly secured in position during machining of the component, an ultrasonic vibration unit coupled to the base, and a machining tool coupled to the ultrasonic vibration unit. The machining tool is configured to vibrate in a direction substantially aligned with respect to a machining direction of the component to machine the component in the machining direction. The ultrasonic vibration unit is configured to control vibration of the machining tool. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a perspective view of an exemplary gas turbine engine blade;  
         [0008]    [0008]FIG. 2 is a perspective view of an exemplary machining tool assembly for machining a component, such as the gas turbine engine blade shown in FIG. 1;  
         [0009]    [0009]FIG. 3 is a perspective view of an exemplary machining tool that may be included in the machining tool assembly shown in FIG. 2;  
         [0010]    [0010]FIG. 4 is a front view of the machining tool shown in FIG. 3 illustrating the machining tool before assembly; and  
         [0011]    [0011]FIG. 5 is a front view of the machining tool shown in FIG. 3 illustrating the machining tool after assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    As used herein the terms “machining”, “machine”, and “machined” may include any process used for shaping a component. For example, processes used for shaping a component may include turning, planing, milling, grinding, finishing, polishing, and/or cutting. In addition, and for example, shaping processes may include processes performed by a machine, a machine tool, and/or a human being. The above examples are intended as exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the terms “machining”, “machine”, and “machined”. In addition, as used herein the term “component” may include any object that has been or may be machined. Furthermore, although the invention is described herein in association with a gas turbine engine, and more specifically for use with an engine blade for a gas turbine engine, it should be understood that the present invention may be applicable to any component and/or any machining process. Accordingly, practice of the present invention is not limited to the machining of engine blades or other components of gas turbine engines. In addition, as used herein the term “machining apparatus” may include any device used to machine a component.  
         [0013]    [0013]FIG. 1 is a perspective view of an engine blade  10  that may be used with a gas turbine engine (not shown). In one embodiment, a plurality of turbine blades  10  form a high-pressure turbine rotor blade stage (not shown) of the gas turbine engine. Each blade  10  includes a hollow airfoil  12  and an integral dovetail  14  that is used for mounting airfoil  12  to a rotor disk (not shown) in a known manner. Alternatively, blades  10  may extend radially outwardly from a disk (not shown), such that a plurality of blades  10  form a blisk (not shown). Each airfoil  12  includes a first contoured sidewall  16  and a second contoured sidewall  18 . First sidewall  16  is convex and defines a suction side of airfoil  12 , and second sidewall  18  is concave and defines a pressure side of airfoil  12 . Sidewalls  16  and  18  are joined at a leading edge  20  and at an axially-spaced trailing edge  22  of airfoil  12 . More specifically, airfoil trailing edge  22  is spaced chordwise and downstream from airfoil leading edge  20 . First and second sidewalls  16  and  18 , respectively, extend longitudinally or radially outward in span from a blade root  24  positioned adjacent dovetail  14 , to an airfoil tip  26 .  
         [0014]    [0014]FIG. 2 is a perspective view of a machining tool assembly  50  used for machining blade  10  (shown in FIG. 1). FIG. 3 is a perspective view of a machining tool  52  included within machining tool assembly  52 . Tool assembly  50  includes machining tool  52 , a base  54 , an ultrasonic vibration unit  56 , a fixture  58 , at least one abrasive particle guide  60 , and a shield  62 . Fixture  58  is coupled to base  54  and is configured to fixedly secure blade  10  during machining. Fixture  58  is coupled to base  54  using any suitable means, such as, but not limited to, threaded bolts (not shown) and threaded openings (not shown). Furthermore, fixture  58  fixedly secures blade  10  during machining using any suitable means. For example, in one embodiment, fixture  58  includes a plurality of clamps (not shown) that fixedly secure blade  10  with respect to fixture  58 . Ultrasonic vibration unit (UVU)  56  is coupled to base  54  and includes a vibration head  64 . Ultrasonic vibration unit  56  is coupled to base  54  using any suitable means, such as, but not limited to, threaded bolts (not shown) and threaded openings (not shown). Vibration head  64  is coupled to UVU  56  such that vibration head  64  can oscillate, or vibrate, along an axis  66  at varying frequencies and amplitudes.  
         [0015]    Machining tool  52  is removably coupled to vibration head  64  and extends outwardly from vibration head  64  along axis  66 . Machining tool  52  is removably coupled to vibration head  64  using any suitable means, such as, but not limited to, threaded bolts (not shown) and threaded openings (not shown). Machining tool  52  is configured to vibrate with vibration head  64  along axis  66  and includes at least one cutter  68  that extends outwardly from a portion of machining tool  52 . In one embodiment, machining tool  52  includes a plurality of machining surfaces  68  for machining blade  10 .  
         [0016]    Machining surfaces  68  are referred to herein as cutters  68 . Cutters  68  are configured to vibrate with machining tool  52  and vibration head  64  along axis  66 . Abrasive particle guide  60  is coupled to base  54  and is in fluid communication with a supply of abrasive particles (not shown). In the exemplary embodiment tool assembly  50  includes a plurality of abrasive particle guides  60 . Abrasive particle guide  60  supplies abrasive particles to cutters  68  during machining of blade  10 . In one embodiment, abrasive particles are delivered from the supply through abrasive particle guide  60  using a pump (not shown). Furthermore, in one embodiment, abrasive particles include at least one of aluminum oxide, boron carbide, diamond chip, and silicone carbide grains. In addition, and in one embodiment, the abrasive particles are contained in a 50% water slurry.  
         [0017]    UVU  56  is configured to direct vibration of vibration head  64  and machining tool  52  along axis  66 , and to control the amplitude and frequency of vibration of vibration head  64  and machining tool  52 , as desired for machining blade  10 . Ultrasonic vibration units  56  used to vibrate a machining tool for machining components are known in the art. During machining, when UVU  56  vibrates vibration head  64 , machining tool  52 , including cutters  68 , vibrates along axis  66 . Abrasive particles are supplied by abrasive particle guide  60  between cutters  68  and a surface (not shown) of blade  10  being machined. Vibration of cutters  68  excites the abrasive particles causing the abrasive particles to remove material from blade  10 . Shield  62  is coupled to base  54  and is configured to facilitate containing material removed from blade  10  and the abrasive particles within at least a portion of tool assembly  50 . Shield  62  is coupled to base  54  using any suitable means, such as, but not limited to, threaded bolts (not shown) and threaded openings (not shown).  
         [0018]    [0018]FIG. 4 is a front view of machining tool  52  before assembly, and FIG. 5 is a front view of machining tool  52  after assembly. More specifically, in the exemplary embodiment and before machining blade  10 , a portion of machining tool  52  is assembled about a portion of blade  10 , such that a portion of blade  10  is received within a portion of machining tool  52 . Machining tool  52  includes a body  70 , having a first projection  72  and a second projection  74 , and a cross-bar  76 . Tool body  70  extends a length  78  measured between a first end  80  and a second end  82 . Tool body  70  also extends a length  84  measured between a first side  86  and a second side  88 .  
         [0019]    First projection  72  is adjacent tool body first side  86  and extends outwardly from a portion of tool body  70  to a first projection end  90 . Second projection  74  is adjacent tool body second side  88  and extends outwardly from a portion of tool body  70  to a second projection end  92 . First projection  72  and second projection  74  are spaced apart along tool body length  84  by a gap  94 . In the exemplary embodiment, gap  94  receives at least a portion of blade  10  therein. The geometry of tool body  70  facilitates distributing vibrational energy substantially evenly across tool body  70 . For example, in the exemplary embodiment tool body  70  is symmetrical about axis  66  to facilitate evenly distributing vibrational energy. Furthermore, the material and/or geometry of tool body  70  may facilitate efficient and optimal transmittal of vibrational energy. For example, in one embodiment tool body  70  is symmetrical about axis  66  to facilitate efficient and optimal transmittal of vibrational energy. Furthermore, in another embodiment tool body  70  is constructed from a material having a high material modulus, for example high carbon steel, stainless steel, a nickel-based alloy, a carbon-epoxy composite, and graphite, to facilitate efficient and optimal transmittal of vibrational energy. Accordingly, the material properties and/or geometry of tool body  70  may be selected to optimize a desired vibratory response.  
         [0020]    Cross-bar  76  extends a length  96  measured between a first end  98  and a second end  100 . Cross-bar length  96  is slightly smaller than projection gap  94  such that cross-bar  76  is received within projection gap  94 . Cross-bar first end  98  includes a mating surface  102 , and cross-bar second end  100  includes a mating surface  104 . Cross-bar  76  is removably coupled to tool body  70  between first projection  72  and second projection  74 . Cross-bar  76  may be coupled to tool body  70  using any suitable means. For example, in the exemplary embodiment cross-bar  76  is coupled to tool body  70  using threaded bolts  106  and threaded openings (not shown) in cross-bar  76 . When cross-bar  76  is coupled to tool body  70 , mating surfaces  102  and  104  contact a first projection mating surface  108  and a second projection mating surface  110 , respectively. In one embodiment, mating surfaces  102 ,  104 ,  108 , and  110  are serrated to facilitate efficient and optimal transmission of vibrational energy. In addition, in another embodiment, mating surfaces  102  and  108  are coupled together using an adhesive, and mating surfaces  104  and  110  are coupled together, using an adhesive, to facilitate efficient and optimal transmission of vibrational energy. For example, in one embodiment, mating surfaces  102  and  108  are coupled together with epoxy.  
         [0021]    In one embodiment, at least a portion of cross-bar  76  includes a cross-sectional geometry that facilitates distributing vibrational energy substantially evenly across cross-bar  76 , and also efficient and optimal transmittal of vibrational energy. For example, in one embodiment cross-bar  76  includes a generally square cross-section. However, it should be understood that the cross-sectional geometry of cross-bar  76  may be any shape producing a desired vibration response, such as, for example, a rectilinear, I-beam, Pi-beam, or T-beam cross-sectional shape. Furthermore, in one embodiment, cross-bar  76  and cutters  68  are at least partially hollow and abrasive particles are delivered through cross-bar  76  to cutters  68 . In addition, in one embodiment at least a portion of cross-bar  76  includes a structural stiffness facilitating even distribution of vibrational energy, and efficient and optimal transmittal of vibrational energy. Furthermore, in one embodiment at least a portion of cross-bar  76  includes a material stiffness facilitating even distribution of vibrational energy, and efficient and optimal transmittal of vibrational energy. For example, in one embodiment cross-bar  76  is constructed from a material having a high material modulus, for example carbon steel, to facilitate efficient and optimal transmittal of vibrational energy.  
         [0022]    Cross-bar  76  includes at least one cutter  68  that extends outwardly therefrom. In the exemplary embodiment, cross-bar  76  includes a plurality of cutters  68  that are integrally formed with cross-bar  76 . Integrally forming cutters  68  with cross-bar  76  facilitates reducing vibratory fatigue loading thereby facilitating a longer operational life for cutters  68 . In an alternative embodiment, cutters  68  are formed independently from cross-bar  76  and are coupled to cross-bar  76  using any suitable means. Cutters  68  may be configured in any suitable size and shape based on with the geometry of blade  10  that is to be machined. For example, in the exemplary embodiment blade  10  includes a plurality of openings  112  to be machined by machining tool  52 , and cutters  68  are shaped to ultrasonically machine openings  112 . In the exemplary embodiment, cutters  68  include a generally square cross-sectional shape. Furthermore, openings  112  may be an size and shape desired to be machined by machining tool  52 . For example, openings  112  may have, but are not limited to, a generally constant circular cross-sectional shape, a generally elliptical cross-sectional shape, a slot/race track cross-sectional shape, or a combination of the above or other cross-sectional shapes. In addition, in one embodiment, cross-bar  76  and cutters  68  are at least partially hollow and abrasive particles are delivered through cross-bar  76  to cutters  68  and ultimately to a surface being machined by cutters  68 , for example openings  112 .  
         [0023]    Before machining blade openings  112 , machining tool  52  is disassembled such that cross-bar  76  is not coupled to tool body  70  and gap  94  is open between first projection  72  and second projection  74 . When blade  10  is fixedly secured to fixture  58  and in position for machining, tool assembly  50  positions machining tool  52  adjacent blade  10  such that a portion of blade  10  is received within gap  94  between first projection  72  and second projection  74 . Machining tool  52  is then re-assembled such that cross-bar  76  is fixedly coupled to tool body  70  and a portion of blade  10  is received within gap  94 . Machining tool assembly  50  then aligns axis  66  parallel with a machining direction  114  of openings  112 , and aligns cutters  68  with openings  112 . UVU  56  then vibrates vibration head  64  along axis  66 , and the vibration of head  64  is transmitted through machining tool body  70  and cross-bar  76  to cutters  68  for machining openings  112 . By aligning axis  66  parallel with machining direction  114 , tool assembly  50  aligns the vibration direction of head  64 , tool body  70 , cross-bar  76 , and cutters  68  with cutting direction  114 , thereby to facilitate transmitting a sufficient amount of vibrational energy to cutters  68  for machining openings  112 .  
         [0024]    The above-described tool is cost-effective and highly reliable for machining a component. The tool permits complex geometry to be machined ultrasonically within a gas turbine engine blade. More specifically, the tool aligns a direction of vibration of the machining tool with a cutting direction to facilitate directing sufficient vibrational energy to a blade machining surface. As a result, the tool facilitates reducing machining costs in a cost-effective and reliable manner.  
         [0025]    Exemplary embodiments of tool assemblies are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. Each tool assembly component can also be used in combination with other tool assembly components.  
         [0026]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.