Abstract:
A method of forming acoustic holes in a composite sound-insulating material includes creating a image of at least a portion of an array of holes and transferring the image to an ultraviolet (UV) radiation transparent medium. The method continues with positioning the medium in contact with a UV-curable mask and exposing the medium-covered mask to UV radiation to cure the UV-exposed areas. The method further includes removing the uncured mask material to create an abrading mask that includes a plurality of holes in a desired pattern. The method also includes positioning the abrading mask in contact with the sound-insulating material and directing a stream of abrasive matter at the abrading mask to create perforations in the sound-insulating material that correspond to the pattern of holes in the abrading mask.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate to the creation of acoustic holes in a sound insulating material. More particularly, embodiments of the present invention relate to a method of creating acoustic holes in a sound insulating material using an ultraviolet radiation curing mask. 
         [0003]    2. Description of the Related Art 
         [0004]    Aircraft engines include sound insulating material to reduce the amount of noise that they produce. The sound insulating material may include a plurality of acoustic holes to enhance its sound insulating ability. Such acoustic holes are typically produced by applying pressure to a polymeric pin mat that is in contact with the sound insulating material. Unfortunately, there are drawbacks to this procedure. Pin mats may be difficult to utilize on sound insulating surfaces that possess varying contours. It is also possible that one or more pins on the mat may break and not create the appropriate perforations, thereby diminishing the sound insulating ability. Correction of this problem may require manual creation of the acoustic holes, often by hand drilling. Furthermore, pin mats are generally fabricated using metal dies, which produce a fixed pattern of pins. Modification of the pin hole pattern requires modification of the metal die, which may be costly and time-consuming. 
       SUMMARY OF THE INVENTION 
       [0005]    Embodiments of the present invention solve the above-mentioned problems and provide a distinct advance in the art of creating acoustic holes in a sound insulating material. More particularly, embodiments of the invention provide a method of creating acoustic holes in a sound insulating material using an ultraviolet radiation curing mask that is easily created and modified. In addition, the mask is flexible to match varying contours and includes no protruding parts that can detach or break. 
         [0006]    The method of forming acoustic holes in a composite sound-insulating material includes creating a positive image of at least a portion of a desired array of holes and transferring the image to an ultraviolet (UV) radiation transparent medium. The method continues with positioning the medium in contact with a UV-curable mask and exposing the medium-covered mask to UV radiation to cure the UV-exposed areas. The method further includes removing the uncured mask material to create an abrading mask that includes a plurality of holes in a desired pattern. The method also includes positioning the abrading mask in contact with the sound-insulating material and directing a stream of abrasive matter at the abrading mask to create perforations in the sound-insulating material that correspond to the pattern of holes in the abrading mask. 
         [0007]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0008]    Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0009]    A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0010]      FIG. 1  is a plan view of a target material showing perforations in the material created using a method in accordance with various embodiments of the present invention; 
           [0011]      FIG. 2  is a flow diagram of steps of the method; 
           [0012]      FIG. 3  is a plan view of an ultraviolet (UV) radiation transparent sheet and a UV curing mask; 
           [0013]      FIG. 4  is a plan view of the UV radiation transparent mask aligned with the UV curing mask and a profile view of the two masks receiving UV radiation; 
           [0014]      FIG. 5  is a profile view of the UV curing mask held against a firm surface while uncured material is removed from a liquid source in order to create an abrading mask; 
           [0015]      FIG. 6  is a plan view and a cross-sectional view of the abrading mask showing holes formed in the mask; 
           [0016]      FIG. 7  is a plan view of the abrading mask aligned with a target surface; and 
           [0017]      FIG. 8  is a sectional view of the abrading mask aligned with the target surface receiving a stream of abrasive material. 
       
    
    
       [0018]    The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
         [0020]      FIG. 1  shows a target material  10  that includes an array of acoustic holes  12  created using a method in accordance with various embodiments of the present invention. The target material  10  may be acoustic damping material for use in an aircraft engine or any other material in which holes are formed. The target material  10  may include varying contours or shapes and may be flat or curved as seen in  FIG. 1 . The array of acoustic holes  12  may be regular with uniform spacing between the holes or may be irregular with non-uniform spacing. The holes  12  may be of varying shape and dimension. 
         [0021]    The steps of the method of making acoustic holes using ultraviolet (UV) curing masking material are outlined in  FIG. 2 . The method includes creating an image  14  of at least a portion of the array of acoustic holes as shown in step  101 . The image  14  may include just a portion of the array  12 , if the array  12  includes a repeated pattern, as shown in  FIG. 3 . It is possible that the image  14  may be stepped and repeated in later steps of various embodiments of the present invention. Thus, the image  14  may include only the portion of the array  12  that is a repeated pattern, or the image  14  may include multiple copies of the repeated pattern to minimize stepping and repeating in later steps of various embodiments of the present invention. Furthermore, the image  14  may include the entire array  12  of holes if there is no portion of the array  12  that is repeated. In addition, the image  14  may include alignment features, as are known in the art. 
         [0022]    The image  14  may include a positive representation of the array  12 , as shown in  FIG. 3 , wherein the black features represent areas where the holes will exist. Or, the image  14  may include a negative representation of the array  12 , wherein the black and white features of the array are inverted, such that the desired array of holes are white that are surrounded by a black background. The type of UV-sensitive material used in later steps of various embodiments of the present invention determines whether a positive representation or a negative representation is used. 
         [0023]    The image  14  may be created using computer software, such as computer-aided drafting or design (CAD) programs, word-processing or desktop publishing programs, spreadsheet programs, data presentation preparation programs, photographic or video editing programs, combinations thereof, and the like. The image  14  may also be created by using manual drafting techniques either alone or in combination with computer software techniques. 
         [0024]    The image  14  may be transferred to a UV-transparent medium  16  as listed in step  102 . Opaque material corresponding to the image  14  is applied to the medium  16  and filters UV radiation from transmitting through the medium  16 . The transfer may be performed by printers, plotters, copiers, graphic reproduction machines, combinations thereof, and the like. It is also possible that the image  10  may be formed directly on the UV-transparent medium  16 . Manual drafting techniques using permanent, opaque ink on the medium  16  may be utilized or manual placement of patterned opaque stickers or masking tape onto the medium  16  may also be employed. 
         [0025]    The UV-transparent medium  16  is positioned in contact with a UV-curable material  18  as listed in step  103  and shown in  FIG. 4 . The medium  16  may be aligned to alignment features on the UV-curable material  18  and the medium  16  and the material  18  may be temporarily adhered to one another. 
         [0026]    The UV-curable material  18  may include monomers, oligomers, or prepolymers as are known in the art. Photosensitive resins may also be included. The thickness of the UV-curable material may be between approximately 0.002 inches and 0.010 inches. 
         [0027]    The UV-transparent medium  16  and the UV-curable material  18  are both exposed to a UV-wavelength radiation source  20  as listed in step  104  and shown in  FIG. 4 . Typically the exposure occurs in a closed chamber with one or more bulbs or tubes providing the UV radiation. The duration of the UV exposure may depend on the intensity of the UV source  20  and the properties of the UV-curable material  18 , such as thickness. If the medium  16  is substantially the same size in area as the material  18 , then one exposure is all that is necessary to properly expose the UV-curable material  18 . 
         [0028]    In certain embodiments, if the desired array of acoustic holes  12  is a regular, repeated pattern, then it is possible to use a smaller UV-transparent medium  16  than the UV-curable material  18 , such that the medium  16  is repeatedly exposed in different locations across the material  18 . The UV-transparent medium  16  is aligned to one location on the UV-curable material  18  and exposed to UV radiation while the rest of the material  18  is covered (or masked) with UV-opaque material to prevent unwanted UV exposure. The UV-transparent medium  16  is aligned with another location on the UV-curable material  18  and exposed to UV radiation while the rest of the material  18  is covered. This process continues until all areas of the UV-curable material  18  have been exposed to UV radiation. 
         [0029]    The uncured material is removed from the UV-curable material  18 , leaving behind the cured material which forms an abrading mask  22  as listed in step  105  and shown in  FIG. 5 . Typically, the UV-curable material  18  is held against a solid surface  24 , such as wood or metal, and the uncured material is removed with a high pressure jet  26  (approximately 120 psi) of warm water. Removal of the uncured material may be accomplished with other liquids and variations in the pressure and temperature of the liquids are possible. What remains after the removal of the uncured material is the abrading mask  22  as shown in  FIG. 6 . The abrading mask  22  includes a plurality of holes  28  that extend through the thickness of the mask  22 , wherein the holes  28  are formed in the pattern of at least a portion of the desired array of acoustic holes  12 . 
         [0030]    The abrading mask  22  is positioned in contact with the surface of the target material  10  as listed in step  106  and shown in  FIG. 7 . The mask  22  may be aligned with alignment features on the surface of the target material  10 . The mask  22  may also be affixed temporarily to the target material  10  surface. 
         [0031]    The abrading mask  22  and the target material  10  are exposed to a stream of abrasive material  30  from an abrasive material source  32  as listed in step  107  and shown in  FIG. 8 . The abrasive material  30  is typically a solid and may be a powder or small-particulate form of silicon carbide (SiC) or alumina (Al 2 O 3 ) or similar abrasive material. The abrasive material  30  may have a particle size of approximately 190 μm to 270 μm. The abrasive material source  32  may be a pressurized solid or powder material sprayer. The duration of the exposure of the abrading mask  22  and target material  10  to the abrasive material source  32  and the pressure of the abrasive material stream  30  may be varied and may depend on factors such as the density of the target material  10 , the size and depth of the desired acoustic holes  12 , the particle size and flow rate of the abrasive stream  30 , etc. The range of the pressure of the abrasive material stream  30  may be between approximately 50 pounds per square inch (psi) and approximately 100 psi. Typically, the abrasive stream  30  is scanned across the surface of the target material  10  until all of the holes  28  in the mask  22  have been exposed to the stream  30  and perforations have been created in the target material  10  that correspond to the holes of the mask  22 . The mask  22  is then removed from the surface of the target material  10 . 
         [0032]    In certain embodiments, the desired array of acoustic holes  12  includes a pattern that is repeated. Thus, the abrading mask  22  may be smaller in size than the size of the array of acoustic holes  12  and may include just the pattern of holes that is to be repeated. Typically, the mask  22  includes more than one copy of the pattern to minimize the stepping and repeating process. The abrading mask  22  is aligned and temporarily affixed to one area of the target material  10 . The rest of the surface of the target material is covered with a protective coating to prevent undesired abrasion or damage. The stream of abrasive material  30  is directed at the mask  22  and the target material  10  and is scanned across all of the holes  28  in the abrading mask  22  to create perforations in the target material  10 . The mask  22  is moved to the next location where it is aligned and temporarily affixed to the target surface  10 . The abrasive material stream  30  is scanned across all holes  28  in the abrading mask  22 . This process is repeated until all necessary areas of the target material  10  have been exposed to the abrasive stream  30  and the desired array of acoustic holes  12  has been created. 
         [0033]    Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.