Abstract:
A method for mechanically cutting a continuous circular shaped groove in a foil sheet for use in a metal matrix composite product. In one form the foil sheet is held adjacent a rotating machine tool by vacuum and a cutting tool is moved relative thereto to cut a spiral groove.

Description:
CROSS-REFERENCE TO RELATED APPLICATONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Applications No. 60/231,615 entitled Mechanically Grooved Sheet and Method of Manufacture and No. 60/231,616 entitled Method of Manufacturing a Metal Matrix Composite Structure. The above Provisional Patent Applications were filed on Sep. 11, 2000 and are incorporated herein by reference. This application is related to concurrently filed U.S. patent application Ser. No. ______ entitled Mechanically Grooved Sheet and Method of Manufacture. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to a process for producing a grooved foil material that is utilized in the production of a Metal Matrix Composite (MMC) sheet product. In one form, the process produces a MMC sheet product having a continuous spiral groove. More particularly, the present invention relates to a method of making a grooved foil sheet material that is utilized in fabricating an internally reinforced metal matrix composite ring. Although the present invention was developed for use in gas turbine engines, certain applications may be outside this field.  
           [0003]    Many metal matrix composite structures have been designed to provide the required mechanical properties to operate in a hostile environment. Metal matrix composite structures can be fabricated by a number of techniques including foil-fiber-foil, coated fiber, ribbon wound fiber and wire-fiber. The matrix alloy chosen to form the MMC structure generally determines which of the above fabrication techniques is feasible. For example, a Ti-6-4 MMC structure can wire-fiber. The matrix alloy chosen to form the MMC structure generally determines which of the above fabrication techniques is feasible. For example, a Ti-6-4 MMC structure can generally be fabricated by using any of the above described techniques since the material Ti-6-4 is available in foil, powder, ribbon, and wire form. In contrast, certain high temperature titanium alloys such as Ti-22Al-26Nb (orthorhombic titanium) are only available in a sheet or powder form. Therefore high temperature titanium and titanium-aluminide alloy MMC structures are generally fabricated by the foil-fiber-foil method.  
           [0004]    When fabricating MMC structures with the foil-fiber-foil technique, it is often desirable to utilize grooved foil. A continuous high strength monofilament is laid in the grooved foil and multiple loaded foils are stacked and consolidated to form the structure. The grooving provides a uniform fiber to fiber spacing in the consolidated structure. It is known that grooved foil has successfully been used in producing MMC structures formed of a conventional titanium matrix. One prior technique of producing grooved foil of a conventional titanium material has employed a photolithographic etching technique. However, these photolithographic techniques have proven unsuccessful in producing well-defined grooves in high temperature titanium aluminide alloys such as Ti-22Al-26Nb.  
           [0005]    The present invention allows for the production of a grooved foil sheet product in a novel and nonobvious way.  
         SUMMARY OF THE INVENTION  
         [0006]    One form of the present invention contemplates a method, comprising: providing a machine tool having a backing surface; positioning a sheet of foil adjacent the backing surface; securing the sheet of foil to the machine tool; and, cutting at least one continuous circular shaped groove in the sheet of foil with a cutting tool.  
           [0007]    Another form of the present invention contemplates a method, comprising: providing a machine tool having a backing surface; positioning a sheet of foil adjacent the backing surface; drawing the sheet of foil against the backing surface with a vacuum; mechanically coupling the sheet of foil to the machine tool; and cutting at least one continuous groove through a three hundred and sixty degree revolution in the sheet of foil with a cutting tool.  
           [0008]    Another form of the present invention contemplates a method, comprising: positioning a sheet of orthorhombic titanium foil on a surface of a machine tool; holding the sheet of orthorhombic titanium foil against the surface of the machine tool with one of a vacuum and adhesive; mechanically securing the sheet of orthorhombic titanium foil with the surface of the machine tool; rotating the surface of the machine tool; orienting a single point cutting tool with respect to the orthorhombic titanium foil sheet; and, cutting at least one continuous circular shaped groove on a side of the orthorhombic titanium foil sheet with the cutting tool, wherein a starting point of said cutting is radially inward on the sheet with respect to an ending point of said cutting.  
           [0009]    Yet another form of the present invention contemplates a composite preform, comprising: a foil member having thickness less than about 0.010 inches and at least one continuous circular shaped groove cut therein that is consistent with the mechanical removal of material with a cutting tool, and wherein the circular shaped groove having a width less than about 0.008 inches and a depth less than about 0.004 inches.  
           [0010]    One object of the present invention is to provide a unique method for producing grooved foil.  
           [0011]    Related objects and advantages of the present invention will be apparent from the following description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of an aircraft having a gas turbine engine coupled thereto.  
         [0013]    [0013]FIG. 2 is a partially fragmented side elevational view of a gas turbine engine.  
         [0014]    [0014]FIG. 3 is a cross-sectional view of an unconsolidated MMC configuration.  
         [0015]    [0015]FIG. 3A is a cross-sectional view of an alternate embodiment of an unconsolidated MMC configuration.  
         [0016]    [0016]FIG. 4 is a cross-sectional view of the MMC configuration of FIG. 3 after having been consolidated into an MMC structure.  
         [0017]    [0017]FIG. 5 illustrates a plan view of a sheet product having a continuous spiral groove formed therein.  
         [0018]    [0018]FIG. 6 illustrates a cross-sectional view of the sheet product of FIG. 5 taken along line  6 - 6 .  
         [0019]    [0019]FIG. 7 illustrates a partial cross-sectional view of a grooved sheet product according to one embodiment of the present invention.  
         [0020]    [0020]FIG. 8 illustrates a partial cross-sectional view of a grooved sheet product according to another embodiment of the present invention.  
         [0021]    [0021]FIG. 9 illustrates an enlarged partial cross-sectional view of a groove in the sheet product material.  
         [0022]    [0022]FIG. 10 illustrates one embodiment of a cutting tool utilized in cutting a groove in the sheet material.  
         [0023]    [0023]FIG. 10 a  illustrates another embodiment of a cutting tool utilized in cutting a groove in the sheet material.  
         [0024]    [0024]FIG. 11 illustrates an apparatus having a foil sheet coupled thereto.  
         [0025]    [0025]FIG. 12 illustrates a schematic representation of one embodiment of a vacuum tooling system of the present invention.  
         [0026]    [0026]FIG. 13 illustrates an end view comprising a portion of the FIG. 12 vacuum tooling system.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0028]    The present invention was developed for application in the field of gas turbine engine products. However, the present invention is not intended to be limited to gas turbine engine components unless specifically provided to the contrary. While the present invention is believed applicable to a wide variety of products and components it will nonetheless be described with respect to components suitable for application in gas turbine engines.  
         [0029]    With reference to FIGS. 1 and 2, there is illustrated an aircraft  10  having an aircraft flight propulsion engine  11 . It is understood that an aircraft is generic and includes helicopters, tactical fighters, trainers, missiles and other related apparatus. In one embodiment, the flight propulsion engine  11  defines a gas turbine engine integrating a compressor  12 , a combustor  13 , and a power turbine  14 . Gas turbine engines are just one form of machinery that can utilize the present invention. It is important to realize that there are a multitude of ways in which the components can be linked together. Additional compressors can be added with an inter-cooler connecting between the compressors and reheat combustion chambers can be added between the turbines. Further, gas turbine engines are equally suited to be used for industrial applications. Historically, there has been widespread application of industrial gas turbine engines such as pumping stations for gas and oil transmission lines, electricity generation, and naval propulsion.  
         [0030]    With reference to FIG. 2, there is illustrated electromagnetic thrust bearing  15  having a thrust disk rotor  16  and a stator  17  for positioning a rotating element relative to a static structure. The thrust disk rotor  16  is an example of a structure that can utilize the present invention. However, the present invention is not limited to thrust disks and is applicable to a wide variety of components generally known to those skilled in the art. Components such as, but not limited to, flywheels, fan, compressor and turbine disks and thrust balance pistons are contemplated as ideally suited for fabrication with the present invention. One form of the present invention is particularly useful in the fabrication of ring and/or disk structures.  
         [0031]    Referring now to FIG. 3, there is illustrated a schematic representation of one embodiment of an unconsolidated MMC structure  30 . The MMC structure  30  includes a plurality of sheets  32  and reinforcement fibers  36 . The term plurality is intended to be broadly construed and is not limited to the number of layers of material shown in the figures. In one embodiment the MMC structure includes as few as two sheets and one layer of reinforcement fiber  36 . In one form of the present invention each sheet  32  has groove(s)  34  formed on both sides (FIG. 3). Further, a top and bottom sheet  32   a  have grooves formed on one side. However, in an alternate form the MMC structure  30   a  utilizes the sheets  32   a  having grooves only on one side (FIG. 3A). The MMC structure will be described generally with reference to sheet  32 , however, it is understood that it is applicable to the other sheets described herein unless specifically provided to the contrary. The grooves  34  provide a uniform fiber to fiber spacing in the consolidated MMC structure  30   b  (FIG. 4). The sheet material can be selected from any of a variety of intermetallic materials, metallic materials and/or metallic alloys. Typical materials to form sheet  32  from include titanium alloys, iron-cobalt alloys and aluminum alloys. In one embodiment the sheet  32  is formed from a high temperature titanium aluminide alloy. One type of high-temperature titanium aluminide is Ti-22 Al-26Nb (orthorhombic titanium). MMC structures formed from these alloys are generally fabricated with the foil-fiber-foil method. A continuous reinforcement fiber  36  is laid within the groove  34  on each layer of the MMC structure  30 . In a preferred form, the reinforcement fiber  36  is a continuous high strength monofilament having the desired mechanical properties to provide the required strength. In an alternate embodiment of the present invention multiple reinforcement fibers  36  are utilized on a single layer instead of a single continuous reinforcement fiber. The separate sheets  32  are stacked upon one another and consolidated to form an integral MMC structure  30   b  as shown in FIG. 4. Applying a combination of pressure and thermal cycles onto the structure  30  can form the combined structure  30   b.    
         [0032]    With reference to FIGS. 5 and 6, there is illustrated one form of a disk  32 . Referring to FIG. 5, there is illustrated a plan view of a single sheet  32  having a continuous circular shaped groove formed therein. The term circular shaped which may be utilized to define the groove is intended to be read quite broadly and will include geometrically circular, geometrically elliptical, spiral, archimedes spiral unless specifically provided to the contrary. In one form the groove will extend through at least one 360 degree revolution on the single sheet  32 . It has been discovered that producing the grooves using conventional photolithographic techniques for the high temperature titanium-aluminide alloy produces unacceptable grooves. During etching, the mask tends to lift and the material under the mask is etched. This produces a sheet having a rough surface and misshaped grooves. A groove that does not have the desired geometry can cause the fiber to be misaligned, touch and/or break, which in turn can create an inferior structure.  
         [0033]    It has been discovered that the desired groove geometry can be created by mechanically cutting the groove  34  into the sheet  32 . It is also contemplated in the present invention that a plurality of continuous grooves  34  can be formed on the sheet  32 . In one form, the sheet  32  has a ring shape in order to fit around a shaft such as in a turbine. However, it is also contemplated that the sheet  32  has a different configuration than shown in the drawings. Furthermore, in a preferred form, the circular continuous groove  34  has a spiral shape. The continuous groove  34  can have even spacing between the adjacent 360-degree revolutions or can have non-even spacing between the adjacent complete 360-degree revolutions. However, it is also contemplated that the circular continuous groove  34  have a different configuration than the one shown, such as a configuration with concentric circular grooves  34 . It has been discovered that cutting the groove  34  with a cutting tool provides adequate groove geometry. As shown in FIG. 5, the cut can be initiated at point  40  and can end at point  42  which is located radially outward with respect to point  40 . In one form of the present invention, the cutting starting point  40  and ending point  42  are controlled to provide a predetermined relationship between the start point and end point of the groove  34 .  
         [0034]    The groove pitch of groove  34  is proportional to a fiber volume fraction for a given thickness of the sheet  32 . Traditionally, fiber volume fractions for ring structures  32  are typically 20-45%. However, the present invention is not limited to these volume fractions and other volume fractions are contemplated herein. The method described herein can readily accommodate this range since in one form the tool traverse speed needs only to be adjusted to change the groove pitch. In addition, to vary the stiffness of the formed ring structure  30 , the groove pitch in sheet  32  can be varied from the inside diameter (ID) to the outside diameter (OD). In another embodiment the groove pitch remains constant from the inside diameter (ID) to the outside diameter (OD). A change in groove pitch is often desirable when a variation in ring stiffness of the structure  32  from the inside diameter ID to the outside diameter OD is sought. In one embodiment, a non-linear tool traverse speed is used to create the change in groove pitch.  
         [0035]    Referring now to FIG. 7, a partial cross-sectional view of the grooved sheet material  32  for one embodiment is shown. In this embodiment, the continuous groove  34  is formed on only one side of the sheet  32 . In contrast, as shown in FIG. 8, in another embodiment of the present invention, continuous grooves  34  are formed on both sides of sheet  32 .  
         [0036]    Referring now to FIG. 9, a partial, cross-section of one embodiment of the sheet  32  is shown. The groove  34  has a radius  44  and a width  46 . The present invention is particularly applicable to cutting grooves having a width less than about 0.008 inches and a radius less than about 0.004 inches in the thin foil material. The thin foil material/sheet generally has a thickness less than about 0.010 inches. In one form of the present invention, the radius  44  is about 0.003 inches and the groove  34  has a width  46  of about 0.006 inches. The sheet  32  has a thickness  48  that is within a range of about 0.004 inches to about 0.020 inches. In a preferred form, the thickness  48  of the sheet  32  is from about 0.0045 inches to about 0.0075 inches, and in a more preferred form, the thickness  48  of the sheet  32  is about 0.007 inches. However, other sheet thickness, groove sizes and groove geometry are contemplated herein.  
         [0037]    Referring now to FIG. 10, one form of a cutting tool is illustrated. In a preferred form, the cutting tool is formed of a tool steel, a carbide cutting tool material or a ceramic metallic (cermet) cutting tool material. The cutting tool  50  includes a cutting member  52  and a body  60 . As can be seen in FIG. 10, the cutting tool  50  has a single cutting member (point)  52 . By having only a single cutting point  52 , the cutting member  50  is adapted to cut variable groove pitches. In a preferred form, the cutting member  52  has a width  54  between about 0.0055 inches and about 0.0065 inches, a minimum length  56  of about 0.005 inches and a curvature radius from about 0.0025 inches to about 0.0035 inches. Also, in a preferred form of the present invention, the body  60  of the cutting tool  50  is formed to have an angle  62  of about sixty-degrees (60°). In addition, the cutting tool  50  can have a blend radius  64  of about 0.005 inches. However, the present invention is not limited to the specific tool and other cutting tools having other geometries, sizes, angles, etc. are contemplated herein.  
         [0038]    With reference to FIG. 10 a , there is illustrated another embodiment of a cutting tool  500 . In a preferred form, the cutting tool  500  is formed of a tool steel, a carbide cutting material or a ceramic metallic (cermet) cutting tool material. The cutting tool  500  includes a cutting member  520  and a body  600 . The cutting member  520  has a point with a radius formed thereon, and a width W. In a preferred form the width W is within the range of about 0.006 inches to about 0.008 inches. In a more preferred form the width W is about 0.008 inches. Further, the radius of the point preferably has a radius within the range of about 0.003 inches to about 0.004 inches, and more preferably is about 0.004 inches. Cutting tools having other geometry, size and properties are contemplated herein.  
         [0039]    In order to cut the grooves, it is contemplated that the sheet  32  can remain stationary and the cutting tool  50  can move to cut the desired circular groove  34 . It is also contemplated that the cutting tool  50  can remain stationary and the sheet  32  move relative to the cutting tool  50  so that the circular groove  34  can be cut into the sheet. It is also contemplated that relative movement of both the sheet  32  and the cutting tool  50  can occur so that the circular groove  34  can be formed.  
         [0040]    A preferred form of cutting the groove  34  in the sheet  32  is shown in FIG. 11. A cutting machine  70  such as a lathe includes a securing mechanism  72  that secures the sheet during the machining process. In one embodiment the securing mechanism includes hard tooling  74  which can abut the inside diameter (ID) and the outside diameter (OD) regions of the sheet  32 , and/or a magnetic chuck for magnetic alloys, and/or a vacuum chuck and/or a temporary adhesive  76  to temporarily bond the sheet  32  to the securing mechanism  72 . Multiple combinations of these approaches can also be applied. The sheet  32  can be flattened either before or after the cutting of the sheet  32 . In a preferred form, the flattening of the sheet  32  is accomplished by creep forming. The securing mechanism  32  in the preferred form is rotated and the cutting tool contacts the sheet  32  to begin cutting the groove  34 . The cutting tool is preferably moved relative to the rotating sheet  32 . The traverse speed of the cutting tool  50  can be adjusted to create the desired pitch variation of the groove  34 . The cutting speed and the rake angle of the cutting tool can be adjusted to provide the desired cutting characteristics for the sheet material. In one embodiment, a cutting speed of 300 surface feet per minute produced acceptable grooves in orthorhombic titanium foil. In addition, it has been found that a neutral rake angle produces acceptable grooves in the orthorhombic titanium foil.  
         [0041]    With reference to FIGS. 12 and 13, there is illustrated a vacuum tooling system  150  adapted for holding the sheet material  32  during the cutting of the groove. In one embodiment the vacuum tooling system  150  includes a vacuum pump  151  operatively coupled to the vacuum chuck  152 . The vacuum pump  151  is in fluid communication with the vacuum chuck  152  through a first fluid passageway  153 , a rotating coupling  154  and a second passageway  155 . In a preferred form the second passageway  155  is defined within a rotating structure.  
         [0042]    The vacuum chuck  152  includes a housing  156  and a vacuum faceplate  157  which define therebetween an internal plenum  158 . Removeably secured to the vacuum faceplate is an inner clamping ring  159  and an outer clamping ring  160 . The rings  159  and  160  are removable to allow the positioning of the sheet material  32  on the surface  161  of the vacuum faceplate  157 . The rings  159  and  160  are placed over a portion of the sheet material  32  and thereafter mechanically coupled to the vacuum faceplate  157  by a plurality of mechanical fasteners  162 . The surface  161  of the vacuum faceplate  157  has a plurality of apertures  165  formed therein and disposed in fluid communication with the internal plenum  158 . The vacuum from the vacuum pump draws the sheet material securely adjacent the surface  161  of the vacuum faceplate  157  during the cutting of the material. The plurality of apertures  165  preferably has a size within the range of about 0.010 inches to about 0.030 inches. In one preferred form, the plurality of apertures  165  has a size of about 0.020 inches. Preferably the size of the plurality of apertures is selected to minimize the dimpling of the thin sheet material by preventing any substantial movement of the sheet material into the aperture  165 . The plurality of apertures are preferably equally spaced with an area ratio (total aperture area/sheet area) within a range of about 2%-4%. More specifically, in one form, the area ratio is about 2.7%. Further, in one form the vacuum draws up to minus one atmosphere.  
         [0043]    With reference to FIG. 13, there is illustrated one form of tooling system  150 . In one embodiment of the present invention, a plurality of alignment pins  166  extend from the vacuum face plate  157 . In one form, the present invention contemplates four alignment pins, however, other quantities of alignment pins are contemplated herein. The alignment pins  166  are adapted to receive a sheet material  32  with corresponding openings formed therethrough. The alignment pins  166  and corresponding opening in the sheet material  32  function to align and orient the sheet material for cutting grooves therein. However, in another form of the present invention there are not alignment pins or corresponding openings within the sheet material.  
         [0044]    The drawings and above text has provided details regarding many embodiments of the present invention. The following text describes these and other embodiments further. There is no intention to limit the present invention by the following description of embodiments.  
         [0045]    1. One embodiment comprises:  
         [0046]    securing a sheet of high temperature titanium alloy foil on a securing mechanism; and  
         [0047]    cutting at least one continuous circular shaped groove on a side of the sheet with a cutting tool.  
         [0048]    2. Another embodiment comprises the embodiment of 1 and further comprising:  
         [0049]    arranging at least one reinforcement fiber within the groove.  
         [0050]    3. Another embodiment comprises the embodiment of 2 and further comprising:  
         [0051]    stacking a second sheet of high temperature titanium alloy foil on the sheet.  
         [0052]    4. Another embodiment comprises the embodiment of 1 and further comprising:  
         [0053]    rotating the securing mechanism.  
         [0054]    5. Another embodiment comprises the embodiment of 1 and further comprising:  
         [0055]    orienting the cutting tool to have a neutral rake angle with respect to the sheet.  
         [0056]    6. Another embodiment comprises the embodiment of 1 and wherein the cutting includes moving the cutting tool so that the groove has a spiral shape.  
         [0057]    7. Another embodiment comprises the embodiment of 1 and wherein the cutting includes varying a traverse speed of the cutting tool with respect to the sheet to vary pitch.  
         [0058]    8. Another embodiment comprises the embodiment of 1 and wherein the cutting includes imparting a cutting speed of about 300 surface feet per minute between the sheet and the cutting tool.  
         [0059]    9. Another embodiment comprises the embodiment of 1 and wherein the securing includes magnetically fastening the sheet.  
         [0060]    10. Another embodiment comprises the embodiment of 4 and wherein the securing includes fastening the sheet with a vacuum and a temporary adhesive.  
         [0061]    11. Another embodiment comprises the embodiment of 1 and wherein the high temperature titanium alloy foil includes orthorhombic titanium foil.  
         [0062]    12. Another embodiment comprises the embodiment of 1 and further comprising:  
         [0063]    cutting at least one second continuous circular shaped groove with the cutting tool on an opposite side of the sheet which is opposite the side having the groove cut therein.  
         [0064]    13. Another embodiment comprises the embodiment of 1 and further comprising:  
         [0065]    flattening the sheet by creep forming.  
         [0066]    14. Another embodiment comprises the embodiment of 13 and wherein the cutting tool includes a single point ceramic tool.  
         [0067]    15. Another embodiment comprises the embodiment of 1 and wherein a starting point of the cutting is radially inward on the sheet with respect to an ending point of said cutting.  
         [0068]    16. Another embodiment, comprising:  
         [0069]    flattening a sheet of orthorhombic titanium foil by creep forming;  
         [0070]    securing the sheet on a securing mechanism with a vacuum and an adhesive;  
         [0071]    orienting a cutting tool to have a neutral rake angle with respect to the sheet, the cutting tool being a single point ceramic tool;  
         [0072]    rotating the securing mechanism;  
         [0073]    cutting at least one first continuous spiral shaped groove on a side of the sheet with the cutting tool at a cutting speed of  300  surface feet per minute, wherein a starting point of the cutting is radially inward on the sheet with respect to an ending point of said cutting;  
         [0074]    varying a traverse speed of the cutting tool with respect to the sheet to vary pitch;  
         [0075]    cutting at least one second continuous spiral shaped groove with the cutting tool on an opposite side of the sheet which is opposite the side having the first groove cut therein;  
         [0076]    arranging at least one reinforcement fiber within the first groove; and  
         [0077]    stacking a second sheet of high temperature titanium alloy foil on said sheet after said arranging.  
         [0078]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. It should be understood that while the use of the word preferable, preferably or preferred in the description above indicates that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one,” “at least a portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.