Abstract:
A method includes providing a sheet having layers characterized by different softnesses, providing a die component having a leading surface that is generally concave, and causing the leading surface to puncture the sheet thereby to cut a part from the sheet. The method provides improved flatness of parts cut from sheets having layers of varying softness and prevents soft material from exiting the sheet because the peripheral edge of the leading surface applies maximum pressure to the sheet during the puncturing step.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to methods of stamping multilayer sheets with die components characterized by concave leading surfaces. 
       BACKGROUND OF THE INVENTION 
       [0002]    Typically, stamping of metal sheets is performed using a stamping die with female and male components. The male component has a flat surface and fits tightly into a hole formed in the female component. When operating the die, the sheet to be cut is placed between the male and female components. When the male die component is forced into the hole of the female component, the male and female components cooperate to produce a shearing action on the metal sheet that cuts a part from the sheet. The shape of the part cut from the sheet is determined by the shape of the flat surface of the male component and the shape of the hole of the female component. 
         [0003]    Certain sheets include one or more metal layers and one or more layers of material softer than the metal layer. For example, some multilayer sheets include two metal layers and a viscoelastic layer between the two metal layers configured to dampen vibrations. Other sheets may include an adhesive layer. When a sheet that includes a metal layer and layers of softer material is stamped, the pressure applied across the sheet by the flat surface of the male die component may cause the softer material, such as rubber or adhesive, to be forced out of the cut part. This may lead to adhesive build-up in the stamping die and cause the cut part to be outside a specified flatness tolerance. 
       SUMMARY OF THE INVENTION 
       [0004]    A method for stamping multilayer sheets is provided. The method includes providing a sheet having a first layer comprised of a first material and a second layer comprised of a second material that is harder than the first material. The method further includes providing a die component characterized by a leading surface that is generally concave, and causing the leading surface of the die component to puncture the sheet, thereby to cut a part from the sheet. 
         [0005]    Since the leading surface is concave, the perimeter of the leading surface applies maximum pressure to the sheet when the sheet is punctured, and thus the softer first material is prevented from being forced out of the punctured sheet. Accordingly, the method provided herein enables parts that are cut from sheets comprised of layers having different hardnesses and compressibilities to have improved flatness compared to the prior art. In exemplary embodiments, the first material is an elastomer, such as rubber or a viscoelastic material configured to dampen vibrations, and the second material is a metal. 
         [0006]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic, perspective view of a male die component; 
           [0008]      FIG. 2  is a schematic, plan view of the leading surface of the male die component of  FIG. 1 ; 
           [0009]      FIG. 3  is a schematic, sectional view of a portion of the male die component of  FIG. 1 ; 
           [0010]      FIG. 4  is another schematic, sectional view of a portion of the male die component of  FIG. 1 ; 
           [0011]      FIG. 5  is a schematic, cross-sectional view of a multilayer sheet; 
           [0012]      FIG. 6  is a schematic, cross-sectional view of another multilayer sheet; 
           [0013]      FIG. 7  is a schematic, cross-sectional view of a metal forming apparatus with the male die component of  FIG. 1  in a first position and a multilayer sheet positioned for being punched by the male die component; and 
           [0014]      FIG. 8  is a schematic, cross-sectional view of the metal forming apparatus of  FIG. 7  with the male die component in a second position such that a part has been cut from the multilayer sheet. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Referring to  FIGS. 1 and 2 , wherein like reference numbers refer to like components, a male die component  10  is schematically depicted. The male die component  10  is characterized by a body portion  14  and a leading surface  18 . The leading surface  18  is characterized by a generally flat, central portion  22 , a peripheral portion  24  circumscribing the central portion  22 , and a leading edge  30  circumscribing the peripheral portion  24 . The peripheral portion  24  in the embodiment depicted includes segments  26 A- 26 G. The leading edge  30  protrudes further from the body  14  of the male die component  10  than the central portion  22 , and the peripheral portion  24  interconnects the central portion  22  and the leading edge  30 . Each segment  26 A-G of the peripheral portion  24  is inclined such that the segments  26 A-G become more protuberant from the body  14  as they extend radially outward from the central portion  22  toward the leading edge  30 . 
         [0016]    Accordingly, the leading surface  18  is generally concave, with the leading edge  30  being more protuberant than the central portion  22 , and the peripheral portion  24  being angled to interconnect the central portion  22  and the leading edge  30 . The central portion  22 , the peripheral portion  24 , and the leading edge  30  cooperate to define a concavity  32 . 
         [0017]    In the embodiment depicted, the male die component  10  also defines two holes  34 A,  34 B that extend through the body  14  of the component  10 , and that are open at the leading surface  18 . The portions  38 A,  38 B of the leading surface  18  immediately surrounding the holes  34 A,  34 B are protuberant from the central portion  22  of the leading surface  18 . Within the scope of the claimed invention, a male die component may or may not define holes, and any holes defined by the male die component may be characterized by any size or shape. 
         [0018]    Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1-2 , at least a portion of the leading edge  30  is coplanar about a plane  42  that is parallel to the central portion  22 . The leading edge  30 , and therefore the plane  42 , is spaced a distance apart from the central portion  22 , which, in an exemplary embodiment, is  0 . 35  millimeters. The most protuberant part of portions  38 A,  38 B are coplanar with the leading edge  30  about plane  42 . Segment  26 F of the peripheral portion  24  defines an angle α with the plane  42 . Angle α is at least five degrees, and α is preferably at least twelve degrees. In the embodiment depicted, α is twenty degrees. The relationship between segment  26 F and the plane  42  is representative of the relationships between segments  26 A-E,  26 G and the plane  42 . That is, each of the other segments  26 A-E,  26 G likewise define a respective angle with the plane  42  that is at least five degrees and preferably at least twelve degrees. The angles formed between each segment  26 A-G of the peripheral portion  24  and the plane  42  may or may not be equal to one another within the scope of the claimed invention. 
         [0019]    Correspondingly, and with reference to  FIG. 4 , segment  26 F of the peripheral portion  24  defines an angle β with the central portion  22  of the leading surface. Angle β is no greater than 175 degrees, and angle β is preferably no greater than 168 degrees. In the embodiment depicted, angle β is 160 degrees. The relationship between segment  26 F and the central portion  22  of the leading surface  18  is representative of the relationships between the other segments  26 A-E,  26 G and the central portion  22 . That is, each of the other segments  26 A-E,  26 G likewise define a respective angle with the central portion  22  that is no greater than 175 degrees and preferably no greater than 168 degrees. The angles formed between each segment  26 A-G of the peripheral portion  24  and the central portion  22  may or may not be equal to one another within the scope of the claimed invention. 
         [0020]    Referring to  FIG. 5 , a cross section of a sheet  44  is schematically depicted. The sheet  44  is composed of multiple layers  48 ,  52 ,  56 ,  60 . In an exemplary embodiment, layers  48  and  60  are comprised of adhesive, layer  52  is steel, and layer  56  is comprised of an elastomer, e.g., a textured rubber coating. Layers  48 ,  56 , and  60  span the entirety of layer  52 . In an exemplary embodiment, layers  48  and  60  are characterized by a thickness of approximately 0.051 mm, layer  52  is characterized by a thickness of 0.45 mm, and layer  56  is characterized by a thickness of 0.12 mm. As understood by those skilled in the art, steel is significantly harder, and less compressible, than rubber. Other multilayer sheet compositions may be employed within the scope of the claimed invention. For example, and with reference to  FIG. 6 , sheet  44 A includes layers  64 ,  68 ,  72 , and  74 . Layers  64  and  68  are steel, layer  72  is comprised of a viscoelastic material, and layer  74  is comprised of an elastomer such as rubber. 
         [0021]    Referring to  FIG. 7 , wherein like reference numbers refer to like components from  FIGS. 1-6 , a metal forming apparatus  76  is schematically depicted. The metal forming apparatus  76  includes the male die component  10  and a female die component  80 . The female die component  80  defines an aperture, namely hole  84 , sufficiently sized and shaped to receive the male die component  10  therein. The male die component  10  is mounted to a press  88  that is configured to selectively move the male die component  10  between a first position, as shown in  FIG. 7 , in which no part of the male die component  10  is within the hole  84 , and a second position, as shown in  FIG. 8 , in which the male die component  10  is at least partially within the hole  84  of the female die component  80 . The male die component  10  is positioned such that the leading surface  18  faces the hole  84 . Hole  84  is open in the direction of the die component  10 . 
         [0022]    During operation of the metal forming apparatus, the multi-layer sheet  44  is supported by the female die component  80  such that the sheet  44  spans the hole  84  and is positioned between the male die component  10  and the hole  84 . The press  88  is activated to move the male die component to the second position. Referring to  FIG. 8 , as the male die component moves from the first position to the second position, the leading surface  18  contacts the sheet  44 . Since the leading edge  30  is more protuberant than the other portions of the leading surface  18 , the leading edge  30  contacts the sheet  44  before any other portion of the male die component  10 . The central portion  22  of the leading surface is perpendicular to the surface of the sheet  44 . As the male die component  10  moves to the second position, it punctures the sheet  44 , thereby causing removal of a portion  90  of the sheet  44 . More specifically, the male and female die components  10 ,  80  cause a shearing force on the sheet  44 , which causes portion  90  to separate from the remainder of the sheet  44 . 
         [0023]    Portion  90  is configured as a brake shim, and is characterized by a perimeter that has the same shape as the leading edge  30  of the leading surface  18 . The portion  90  also includes two holes  94 A,  94 B that are cut by portions  38 A,  38 B of the leading surface  18 . 
         [0024]    Within the scope of the claimed invention, the method disclosed herein may be employed in a single stage tool or a multistage tool in which a component is formed in a plurality of successive steps. 
         [0025]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.