Patent Publication Number: US-2021162699-A1

Title: Combined sheets and method and system for producing same

Description:
FIELD 
     The present application generally relates to sheet materials and, in particular, to combined sheets having two or more joined materials. 
     BACKGROUND 
     Sheet materials are common raw materials for producing products. Sheet metals, for example, may be cut, manipulated, or combined with other materials. Various processes for joining sheet materials include operations for applying adhesives between sheet materials or operations for pressing sheet materials against another. Over time, joined sheet materials may separate. For example, adhesives may deteriorate and lose its tack for keeping the sheet materials joined. In another example, respective sheet materials may be subjected to cyclic environmental conditions and may cause joining forces from mechanical press operations to wean. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made, by way of example, to the accompanying drawings which show example embodiments of the present application, and in which: 
         FIG. 1A  illustrates a cross-sectional view of a first indentation feature, in accordance with an example of the present application; 
         FIG. 1B  illustrates a cross-sectional view of a combined sheet, in accordance with an example of the present application; 
         FIG. 1C  illustrates an exploded, cross-sectional view of the combined sheet of  FIG. 1B ; 
         FIG. 2  illustrates a top view of the combined sheet of  FIG. 1B ; 
         FIG. 3A  illustrates a cross-sectional view of a combined sheet, in accordance with another example of the present application; 
         FIG. 3B  illustrates a first indentation feature of the combined sheet of  FIG. 3A ; 
         FIG. 4  illustrates a perspective view of a combined sheet, in accordance with another example of the present application; 
         FIG. 5A  illustrates a bottom view of the combined sheet of  FIG. 4 ; 
         FIG. 5B  illustrates a cross-sectional, elevation view of the combined sheet of  FIG. 5A ; 
         FIGS. 6A and 6B  illustrate side elevation views of the combined sheet of  FIG. 4 ; 
         FIGS. 7A to 7C  illustrate elevation, cross-sectional views of a combined sheet at various production stages of the combined sheet, in accordance with an example of the present application; 
         FIGS. 8A to 8D  illustrate elevation, cross-sectional views of a combined sheet at various stages of production of the combined sheet, in accordance with another example of the present application; 
         FIGS. 9A and 9B  illustrate perspective views of combined sheets, in accordance with further examples of the present application; 
         FIGS. 10A and 10B  illustrate elevation, cross-sectional views of a combined sheet at different production stages of the combined sheet, in accordance with another example of the present application; 
         FIGS. 11A and 11B  illustrate a perspective view and an elevation, cross-sectional view, respectively, of a corrugated panel formed from a combined sheet, in accordance with an example of the present application; 
         FIGS. 12A and 12B  illustrate perspective views of structural steel profiles, in accordance with examples of the present application; 
         FIGS. 13A and 13B  illustrate an elevation, cross-sectional view and a perspective view, respectively, of a conduit structure formed from a combined sheet, in accordance with an example of the present application; 
         FIG. 14  illustrates a method of producing a combined sheet, in accordance with an example of the present application; 
         FIGS. 15A and 15B  illustrate a side elevation view and a perspective view, respectively, of a machine including a combination of stages for producing a combined sheet, in accordance with an example of the present application; 
         FIGS. 16A and 16B  illustrate a side elevation view and a perspective view, respectively, of a machine including a combination of stages for producing a combined sheet, in accordance with another example of the present application; 
         FIG. 17  illustrates a free-body diagram illustrating force directions applied by a double action press, in accordance with an example of the present application; 
         FIGS. 18A and 18B  illustrate elevation, cross-sectional views of a press apparatus at varying operational stages for forming indentation features, in accordance with an example of the present application; and 
         FIGS. 19A to 19C  illustrate elevation, cross-sectional views of a press apparatus at varying operational stages for forming indentation features, in accordance with another example of the present application. 
     
    
    
     Similar reference numerals may have been used in different figures to denote similar components. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Various examples and aspects of the present application will be described with reference to the details discussed herein. The following description and drawings are illustrative of the present application and are not to be construed as limiting the present application. Numerous details are described to provide a thorough understanding of various embodiments. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of the embodiments of the present application. 
     In one aspect, the present application describes a combined sheet. The combined sheet includes: a main sheet including a first main indentation feature providing a first overhang over a first portion of the main sheet and a second main indentation feature providing a second overhang over a second portion of the main sheet; and a foundation sheet abutting the main sheet, the foundation sheet including a first foundation indentation feature and a second foundation indentation feature, the first foundation indentation feature being crimped to the first main indentation feature and the second foundation indentation feature being crimped to the second main indentation feature, wherein the first overhang and the second overhang provide overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. 
     In another aspect, the present application describes a method of producing a combined sheet. The combined sheet includes a main sheet and a foundation sheet. The method includes: co-locating the main sheet to abut the foundation sheet such that the main sheet is substantially parallel to the foundation sheet; pressing one or more indentation punches to be incident on a sheet combination including the main sheet and the foundation sheet for forming two or more indentation features. The two or more indentation features may include a first indentation feature including a first main indentation feature providing a first overhang over a first portion of the main sheet, the first indentation feature including a first foundation indentation feature crimped to the first main indentation feature; and a second indentation feature including a second main indentation feature providing a second overhang over a second portion of the main sheet, the second indentation feature including a second foundation indentation feature crimped to the second main indentation feature, wherein the first overhang and the second overhang provide overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. 
     Other aspects and features of the present application will be understood by those of ordinary skill in the art from review of the following description of examples in conjunction with the accompanying figures. 
     In the present application, the terms “comprises” and “comprising” are intended to be inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms “comprises” and “comprising” and variations thereof mean the specified features, steps, or components are included. These terms are not to be interpreted to exclude the presence of other features, steps, or components. 
     In the present application, the term “exemplary” means “serving as an example, instance, or illustration”, and should not be construed as preferred or advantageous over other configurations disclosed herein. 
     In the present application, the terms “about”, “approximately”, and “substantially” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. In a non-limiting example, the terms “about”, “approximately”, and “substantially” may mean plus or minus 10 percent or less. 
     In the present application, the term “and/or” is intended to cover all possible combinations and sub-combinations of the listed elements, including any one of the listed elements alone, any sub-combination, or all of the elements, and without necessarily excluding additional elements. 
     In the present application, the phrase “at least one of . . . or . . . ” is intended to cover any one or more of the listed elements, including any one of the listed elements alone, any sub-combination, or all of the elements, without necessarily excluding any additional elements, and without necessarily requiring all of the elements. 
     Examples described herein relate to combined sheets produced from a combination of two or more individual sheet materials. Examples of methods and systems for producing the combined sheets are also described herein. A first sheet metal and a second sheet metal, for example, may be combined via joints. Mechanical processes such as embossing may be used to form joints for joining said materials. In one example, the first sheet metal may be placed adjacent to or abutting the second sheet metal and may be subjected to embossing or stretching by a press. Embossing may be a form of precision stamping in which the sheet metals are subjected to high stress for inducing plastic flow. When a plurality of joints are embossed across the surface of abutting sheet metals, the sheet metals may be joined to form a combined sheet. When a plurality of joints are be provided across the surface of the composite sheet, the plurality of joints may collectively hold one of the sheet material to the other sheet material. 
     In some examples, respective joints may be indentation features and may generally be oriented in a similar direction. For example, the embossing or stretching process may, via a punch, subject a non-penetrating force to the first sheet that is adjacent the second sheet for producing one or more indentation features. The indentation features may extend in a direction from the first sheet metal to the second sheet metal, or vice versa. Each indentation feature may be generally oriented in a direction that is normal or perpendicular to the planar surface of the respective sheets. In some other examples, each respective indentation feature may be generally oriented in a similar direction and may be oriented in a direction that may not be perpendicular to the planar surface of the respective sheets. 
     Over time, however, the respective joints can deform, thereby reducing the force that may hold the sheet metals to another. Deformed joints may cause respective sheet metals to separate from one another, causing finished products to unravel or become disassembled. Because the one or more joints may generally be oriented in a similar direction, a respective sheet metal can separate from the other sheet metal by sliding in a direction opposite to the direction of the respective joints. 
     The present application provides a combined sheet and methods and systems for producing said combined sheet for ameliorating some of the aforementioned disadvantages. 
     Reference is made to  FIG. 1A , which illustrates a cross-sectional view of a first indentation feature  190 , in accordance with an example of the present application. The illustrated first indentation feature  190  is an enlarged view of an indentation feature located on a combined sheet. Features of the first indentation feature  190  will be described with reference to  FIG. 1A , while features of said combined sheet will be described elsewhere herein. 
     Features of indentation features may be described with reference to a Cartesian coordinate space, where direction may be referenced according to an illustrated compass rose  180 . For example, positive and negative z-directions may be represented by arrows labelled Z1 and Z2, respectively. Positive and negative x-directions may be represented by arrows labelled X1 and X2, respectively. Although the example illustrated in  FIG. 1A  includes a compass rose  180  that is based on the Cartesian coordinate space, any other coordinate space for describing or referencing direction may be contemplated. 
     The first indentation feature  190  may be a joint produced via a punch during an embossing or stretching process. When a main sheet is placed adjacent to or abutting a foundation sheet  120 , the first indentation feature  190  may be produced when a punch provides a non-penetrating force to the foundation sheet and the main sheet for producing the first indentation feature  190 . For ease of exposition, the first indentation feature  190  may be generally oriented in a direction including a combination of the negative x-direction and the positive z-direction. Although the first indentation feature  190  is illustrated as being generally oriented in a direction including a combination of the negative x-direction and the positive z-direction, in some other examples, the indentation feature may be generally oriented in a direction that is normal to the planar surface of the main sheet or the foundation sheet, or may be generally oriented in any other direction. 
     In  FIG. 1A , the first indentation feature  190  includes a first foundation indentation feature crimped to a first main indentation feature. The first main indentation feature and the first foundation indentation feature may have related shape and related size. For example, the first foundation indentation feature may have a substantially similar shape to the first main indentation feature, but may be appreciably smaller in size as compared to the first main indentation feature such that the first foundation indentation feature may fit within the first main indentation feature. The first main indentation feature and the first foundation indentation feature will be illustrated and described in greater detail herein. 
     The first indentation feature  190  may provide a first overhang  164  over a first portion  160  of a main sheet  172 . In  FIG. 1A , a partial view of the main sheet  172  that is proximal to the first indentation feature  190  is illustrated. The first overhang  164  may be associated with a first direction defined by a first angle  170  between: (a) the first portion  160  of the main sheet  172 ; and (b) an indentation surface  182  of the first overhang  164  that hovers over the first portion  160  of the main sheet  172 . In the example illustrated in  FIG. 1A , the first overhang  164  may extend in a first direction including a combination of the negative x-direction and the positive z-direction. 
     In some examples, the first angle  170  may be an acute angle, such as an angle less than 90 degrees. In some examples, the first angle  170  may be less than 10 degrees. In some examples, the first angle  170  may be near 0 degrees such that the first overhang  164  abuts the first portion  160  of the main sheet  172 . The first angle  170  may, in combination with other features or characteristics, define the first indentation direction for the first indentation feature  190 . 
     The first indentation feature  190  may be a joint for joining the foundation sheet to the main sheet. When a punch imparts a non-penetrating force to the main sheet and the foundation sheet for producing the first indentation feature  190 , high stress imparted by the punch may induce plastic flow and cause the foundation sheet to be joined to the main sheet. However, over time, the joint at the first indentation feature  190  can deform. In the case where the foundation sheet may be joined to the main sheet using a single joint or indentation feature, when the joint deforms, the foundation sheet may separate from the main sheet by sliding in a direction that is opposite to the first direction described above. That is, when the joint deforms, the foundation sheet  120  may separate from the main sheet  172  in a direction including a combination of the negative z-direction and the positive x-direction (in contrast to the first direction that includes a combination of a positive z-direction and the negative x-direction). 
     In another case where the foundation sheet may be joined to the main sheet using two or more joints or indentation features each generally oriented in a similar direction (e.g., the first direction), when the respective joints deform, the foundation sheet may separate from the main sheet by sliding in a direction that may be opposite to the common direction of the respective joints (e.g., a direction that may be opposite to the first direction). Accordingly, it may be desirable to provide a combined sheet for ameliorating some of the aforementioned disadvantages. 
     Reference is now made to  FIG. 1B , which illustrates a cross-sectional view of a combined sheet  100 , in accordance with an example of the present application. The combined plate  100  may include a main sheet and a foundation sheet. Further features of the combined sheet  100  may be apparent with reference to a subsequent exploded view of the combined sheet  100 . 
     The combined sheet illustrated in  FIG. 1B  includes the first indentation feature  190  ( FIG. 1A ) and a second indentation feature  195 . The first indentation feature  190  may be substantially the same size and shape as the second indentation feature  195 , but the first indentation feature  190  may be oriented in a direction that may be different than a direction of the second indentation feature  195 . 
     For example, the first indentation feature  190  may provide a first overhang over a first portion of the main sheet. The second indentation feature  195  may provide a second overhang over a second portion of the main sheet. As was described with respect to  FIG. 1A , the first overhang  164  may be associated with the first direction defined by a first angle between: (a) the first portion  160  of the main sheet  172 ; and (b) an indentation surface  182  of the first overhang  164  that hovers over the first portion of the main sheet  172 . Further, the second overhang may include features similar to the first overhang  164 , but may be provided in a different direction. For example, the second overhang may be associated with the second direction defined by a second angle between: (a) the second portion of the main sheet; and (b) an indentation surface of the second overhang that hovers over the second portion of the main sheet. The first overhang and the second overhang provide overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. 
     In the example illustrated in  FIG. 1B , the first indentation feature  190  may be associated with a first direction that is different than a second direction of the second indentation feature  195 . The first direction may be generally oriented in a direction that includes a combination of the negative x-direction and the positive z-direction, while the second direction may be generally oriented in a direction that includes a combination of the positive x-direction and in the positive z-direction. Over time, even when the respective joints at the first indentation feature  190  and the second indentation feature  195  deform or wean (e.g., joining forces from mechanical press operations weaken), the foundation sheet  120  may not easily separate by sliding away from the main sheet  110 , at least, because the indentation features are oriented in different directions. Because the first indentation feature  190  and the second indentation feature  195  may be features formed from sheet metal material having some rigid properties, separating the main sheet from the foundation sheet may require that the general shape of the respective indentation features be deformed. 
     In some examples, the first direction may be substantially orthogonal to the second direction. That is, the first direction may be spatially oriented in a direction that may be 90 degrees or perpendicular to the spatial orientation of the second direction. 
     Based on the described examples, the foundation sheet  120  may be joined to the main sheet  110  based at least on: (1) joints at the respective indentation features; (2) binding forces due in part to the spatial orientation of the first indentation feature  190  relative to the second indentation feature  195 ; and/or (3) cold welding among sheets of material from one of the example methods described herein. 
     To further illustrate features of the combined sheet  100 , reference is now made to  FIG. 1C , which illustrates an exploded, cross-sectional view of the combined sheet  100  ( FIG. 1B ). 
     The combined sheet  100  may include a main sheet  110  and a foundation sheet  120 . The main sheet  110  may include a first main indentation feature  112 . The first main indentation feature  112  may provide a first overhang over a first portion of the main sheet  110 . The first overhang may be correspond to the first overhang  164  illustrated in  FIG. 1A  and may be associated with a first direction. The main sheet  110  may also include a second main indentation feature  114  providing a second overhang over a second portion of the main sheet. The second overhang may include similar features as the first overhang, while the second overhang may be associated with a second direction that is different than the first direction. 
     The first main indentation feature  112  and the second main indentation feature  114  may protrude from a common side of the main sheet to form a first overhang cavity  186  and a second overhang cavity  188 , respectively. 
     The foundation sheet  120  may be adjacent to or may abut the main sheet  110 . The foundation sheet  120  may include a first foundation indentation feature  122  and a second foundation indentation feature  124 . In some examples, the first foundation indentation feature  122  may be crimped to the first main indentation feature  112  and the second foundation indentation feature  124  may be crimped to the second main indentation feature  114  for joining the foundation sheet  120  to the main sheet  110 . That is, the first foundation indentation feature  122  may be crimped within the first main indentation feature  112 . The second foundation indentation feature  124  may be crimped within the second main indentation feature  114 . 
     Generally, the first indentation feature  190  ( FIG. 1B ) includes the first foundation indentation feature  122  crimped to the first main indentation feature  112 . The second indentation feature  195  ( FIG. 1B ) includes the second foundation indentation feature  124  crimped to the second main indentation feature  114 . 
     In some examples, as illustrated in  FIG. 1C , the first foundation indentation feature  122  that is crimped to the first main indentation feature  112  may have related shape and related size. For example, the first foundation indentation feature  122  may have a substantially similar shape to the first main indentation feature  112 , but may be appreciably smaller in size as compared to the first main indentation feature  112  such that the first foundation indentation feature  122  may fit within the first main indentation feature  112 . Similarly, the second foundation indentation feature  124  that is crimped to the second main indentation feature  114  may have related shape and related size. For example, the second foundation indentation feature  124  may have a substantially similar shape to the second main indentation feature  114 , but may be appreciably smaller in size as compared to the second main indentation feature  124  such that the second foundation indentation feature  124  may fit within the second main indentation feature  114 . In the foregoing examples, the first foundation indentation feature  122  may extend within the first overhang  164  of the first main indentation feature. Similarly, the second foundation indentation feature  124  may extend within the second overhang of the second main indentation feature. 
     Reference is now made to  FIG. 2 , which illustrates a top view of the combined sheet  100  of  FIG. 1B , in accordance with an example of the present application. Features of the combined sheet  100  in  FIG. 2  may be referenced according to a second compass rose  282 . For example, positive and negative y-directions may be represented by arrows labelled Y1 and Y2, respectively. Positive and negative x-directions may be represented by arrows labelled X1 and X2, respectively. Although the example illustrated in  FIG. 2  includes the second compass rose  282  that is based on the Cartesian coordinate system, any other coordinate space for describing or referencing direction may be contemplated. 
       FIG. 2  generally illustrates a top view of the first indentation feature  190  and the second indentation feature  195 . Further, the first indentation feature  190  includes the first overhang  164  and the second indentation feature  195  includes a second overhang  266 . The combined sheet  100  is illustrated in  FIG. 2  includes two indentation features. In some other examples, the combined sheet  100  may include any number of indentation features, where each indentation feature may have a respective indentation direction that is different than an indentation direction of another indentation feature. 
     In some examples, the combined sheet  100  may include an indentation rotation point  298 . The indentation rotation point  298  is a reference point. The indentation rotation point  298  may be equidistant to at least one respective feature of the first indentation feature  190  and the second indentation feature  195 . For example, the indentation rotation point  298  may be equidistant to a centroid of the first portion  160  of the main sheet (see e.g.,  FIG. 1A ) and a centroid of the second portion of the main sheet. Although a centroid of a portion of the main sheet (e.g., portion on which an overhang hovers over) is used as another reference point for describing the indentation rotation point  298 , other reference points that can be ascertained for each of the indentation features may be contemplated for identifying an indentation rotation point  298 . 
     The indentation rotation point  298  is be a reference point about which the combined sheet  100  may have rotational symmetry. An object or shape may have rotational symmetry when that object or that shape appears to be the same object or shape when rotated by some angle that is less than 360 degrees. For example, in  FIG. 2 , the combined sheet  100  may have rotational symmetry of order  2 . Order of rotational symmetry refers to the number of times that the combined sheet  100  matches when the combined sheet  100  is rotated 360 degrees about the indentation rotation point  298 . The combined sheet  100  illustrated in  FIG. 2  includes the first indentation feature  190  and the second indentation feature  195  and has rotational symmetry of order two. That is, in  FIG. 2 , the first indentation feature  190  and the second indentation feature  195  may be oriented on the main sheet to have rotational symmetry about the indentation rotation point  298 . When the combined sheet  100  has a rotational symmetry of order two, the first indentation feature  190  may appear as a mirror image of the second indentation feature  195  with respect to a plane that intersects the indentation rotation point  298 . In some examples, the combined sheet  100  may have any number of indentation features and the indentation features may be arranged and oriented to include rotational symmetry of order greater than two. 
     Reference is now made to  FIG. 3A , which illustrates a cross-sectional view of a combined sheet  300 , in accordance with another example of the present application. Features may be described with reference to a third compass rose  380 . The third compass rose  380  may be similar to the compass rose  180  of  FIGS. 1A to 1C . That is, positive and negative z-directions may be represented by arrows labelled Z1 and Z2, respectively. Positive and negative x-directions may be represented by arrows labelled X1 and X2, respectively. 
     The combined sheet  300  includes features that may be similar to the combined sheet  100  of  FIG. 1B . For example, the combined sheet  300  may include a main sheet and a foundation sheet (not explicitly identified in  FIG. 3A ). Further, the combined sheet  300  of  FIG. 3  may include a first indentation feature  390  and a second indentation feature  395 . The first indentation feature  390  may provide a first overhang over a first portion of the main sheet, where the first overhang is oriented in a first direction. The second indentation feature  395  may provide a second overhang over a second portion of the main sheet, where the second overhang is oriented in a second direction. The first direction and the second direction may be different. Similar to the combined sheet  100  of  FIG. 1B , the first indentation feature  390  may include a first foundation indentation feature (not explicitly identified in  FIG. 3A ) crimped to the first main indentation feature (not explicitly identified in  FIG. 3A ) and the second indentation feature  295  may include a second foundation indentation feature (not explicitly identified in  FIG. 3A ) crimped to the second main indentation feature (not explicitly identified in  FIG. 3A ). 
     Reference is now made to  FIG. 3B , which illustrates an enlarged, cross-sectional view of the first indentation feature  390  of  FIG. 3A .  FIG. 3B  features an enlarged view of the first indentation feature  390  located on the combined sheet  300 . 
     The first indentation feature  390  may be a joint produced via a punch during an embossing or stretching process. That is, when the main sheet is placed adjacent to or abutting the foundation sheet, the first indentation feature  390  may be produced when a punch provides a non-penetrating force to the foundation sheet  120  and the main sheet  110 . The first indentation feature  390  may be generally oriented in a direction including a combination of the negative x-direction and the positive z-direction, similar to the first indentation feature  190  illustrated in  FIG. 1 . However, the first indentation feature  390  may have a different indentation angle. 
     The first indentation feature  390  may provide a first overhang  364  over a first portion  360  of the main sheet  372 . In  FIG. 3B , a partial view of the main sheet  372  that is proximal to the first indentation feature  390  is illustrated. The first overhang  364  may be associated with a first direction defined by a first angle  370  between: (a) the first portion  360  of the main sheet  372 ; and (b) an indentation surface  382  of the first overhang  364  that hovers over the first portion  360  of the main sheet  372 . For ease of exposition, the indentation surface  382  is highlighted using a line in  FIG. 3B . In the example illustrated in  FIG. 3B , the first overhang  364  may extend in a first direction including a combination of the negative x-direction and the positive z-direction. It will be appreciated that in some examples, the first indentation feature  390  illustrated in  FIG. 3B  is a result of a multi-step process where: (1) the first overhang  364  may be produced to extend in a direction perpendicular to the main sheet  372 ; and, subsequently, (2) the first overhang  364  may be shaped to extend in another direction, such as the direction illustrated in  FIG. 3B . Example steps of the multi-step process will be described herein. 
     In some examples, the first angle  370  may be an acute angle, such as an angle less than 90 degrees. In some examples, the first angle  370  may be less than 10 degrees. In some examples, the first angle  370  may be near 0 degrees. That is, a punch may be oriented to impart a non-penetrating force to the surface of the foundation sheet for producing the first indentation feature  390  having features illustrated in  FIG. 3B . In some other examples, the first indentation feature  390  illustrated in  FIG. 3B  may be a result of a multi-step process. As will be illustrated in other examples described herein, the embossing or stretching process may produce an indentation feature having a direction that is normal to a planar surface of the combined sheet  300 , and the produced indentation feature may subsequently be rolled or pressed such that the first angle  370  may be less than 10 degrees. 
     Reference is now made to  FIG. 4 , which illustrates a perspective view of a combined sheet  400 , in accordance with another example of the present application. The combined sheet  400  may be similar to the combined sheet  100  of  FIGS. 1A to 1C and 2 ; however, the combined sheet  400  of  FIG. 4  may include a main sheet  410  and a foundation sheet  420  having different features. 
     In some examples, the main sheet  410  may be a perforated metal sheet and the foundation sheet  420  may be a non-perforated metal sheet. In other examples (not illustrated), the main sheet  410  may be a non-perforated metal sheet and the foundation sheet  420  may be a perforated metal sheet. The combined sheet  400  of  FIG. 4  may include a first indentation feature  490  and a second indentation feature  495 . In some examples, the main sheet  410  and the foundation sheet  420  are respectively composed of a variant of the same metal. That is, the main sheet  410  may be constructed of stainless steel and the foundation sheet  420  may be constructed of untreated steel, as stainless steel and untreated steel are each types of steel. It can be appreciated that when two different types of metals (e.g., steel and aluminum) are combined, over time, oxidization, galvanic corrosion, or other material by-products can form or result. Thus, it is desirable that the main sheet  410  and the foundation sheet  420  be respectively composed of the same metal or a variant of the same metal. 
     Reference is now made to  FIG. 5A , which generally illustrates a bottom view of the combined sheet  400  of  FIG. 4 . The combined sheet  400  illustrated in  FIG. 5A  includes two indentation features. However, the combined sheet  400  may include any number of indentation features, where each indentation feature has a respective indentation direction that is different than an indentation direction of another indentation feature. 
     Similar to the combined sheet  100  illustrated in  FIG. 2 , the combined sheet  400  illustrated in  FIG. 5A  may have rotational symmetry about an indentation rotation point, where the indentation rotation point may be equidistant to the first indentation feature  490  and the second indentation feature  495 . 
       FIG. 5B  illustrates a cross-sectional, elevation view of the combined sheet  400  of  FIG. 5A  taken along line A-A of  FIG. 5A . The first indentation feature  490  and the second indentation feature  495  may protrude from a common side of the combined sheet  400  to form a first overhang cavity  486  and a second overhang cavity  488 , respectively. The first overhang cavity  486  may have a first cavity opening  496  and the second overhang cavity  488  may have a second cavity opening  498 . In  FIG. 5B , the first cavity opening  496  is not adjacent the second cavity opening  498 . In the example illustrated in  FIG. 5B , the first indentation feature  490  and the second indentation feature  495  may protrude from a side occupied by the foundation sheet  420 . 
     Although the first indentation feature  490  and the second indentation feature  495  may protrude from a common side of the combined sheet  400 , in some examples, the first indentation feature  490  and the second indentation feature  495  may protrude from different sides. Examples of the indentation features protruding from different sides of the combined sheet will be illustrated in other examples described herein. 
     As described, the stretching process for joining the main sheet and the foundation sheet may produce indentation features. Producing the indentation features may produce indentation cavities, such as apertures or voids. Further, as the main sheet  410  illustrated in  FIG. 5B  is a perforated sheet, the combined sheet also includes a plurality of divots  570  (three example divots are identified with reference numeral  570  in  FIG. 5B ). The plurality of divots  570  correspond to the perforations in the main sheet  410 . In some examples, the one or more of the divots  570  may be filled in with one or a combination of non-metal materials, such as epoxy, mineral wool, tar, paper clay (e.g., disposable product), or polystyrene foam (e.g., disposable product). In some examples, the respective indentation features (e.g., first indentation feature  490  and the second indentation feature  495 ) may also be filled with one or a combination of non-metal materials. It can be appreciated that when one or more of the divots  570  are filled in with a non-metal material, the resulting combination of the combined sheet and the non-metal material produces a product that can provide benefits of the respective component materials. For example, the combined sheet made of metal (e.g., perforated main sheet and non-perforated sheet) may form a structured barrier and the non-metal material received within the divots or the indentation features can provide, for example, thermal isolating or insulating properties to the resulting product for ameliorating or preventing condensation. 
     Reference is now made to  FIGS. 6A and 6B , which illustrate further side elevation views of the combined sheet  400  of  FIG. 4 . In  FIG. 6A , the combined sheet  400  may be placed atop a further flat sheet  630  such that an entrance at the planar base of the respective indentation features may be closed. 
     In some examples, the indentation cavities may be filled with non-metal material. For example, as illustrated in  FIG. 6B , the first overhang cavity  486  and the second overhang cavity  488  may respectively be filled with epoxy  636 . In some other examples, the first overhang cavity  486  and the second overhang cavity  488  may be filled with one or a combination of non-metal materials, such as epoxy, mineral wool, tar, paper clay (e.g., disposable product), or polystyrene foam (e.g., disposable product). In some examples, the epoxy  636  may function akin to cement for providing structural integrity to the first indentation feature and the second indentation feature. That is, the epoxy  636  may increase the structural rigidness of the respective indentation features, such that the indentation features may be less prone to collapsing or to being crushed in a direction towards the plane of the combined sheet  400 . 
     Reference is now made to  FIGS. 7A to 7C , which illustrate elevation, cross-sectional views of a combined sheet  700  at various production stages of said combined sheet  700 , in accordance with an example of the present application. Features of indentation features may be described with reference to a Cartesian coordinate space, where direction may be referenced according to an illustrated compass rose  780 . 
       FIG. 7A  illustrates a combined sheet  700  including a main sheet joined to a foundation sheet. The combined sheet  700  may include a first indentation feature  790 , a second indentation feature  792 , a third indentation feature  794 , or a fourth indentation feature  796 . Four indentation features are illustrated in  FIG. 7A , however the combined sheet  700  may include any number of indentation features. 
     In  FIG. 7A , the first indentation feature  790  and the third indentation feature  794  protrude from a different side of the combined sheet  700  than the second indentation feature  792  and the fourth indentation feature  796  from the combined sheet  700 . The respective indentation features may be formed during an embossing or stretching process, where a double action press is used for forming the respective indentation features. 
     In  FIG. 7A , the first indentation feature  790  may provide a first overhang and may have a first indentation direction including a combination of the positive x-direction and positive z-direction. The second indentation feature  792  may provide a second overhang and may have a second indentation direction including a combination of the negative x-direction and negative z-direction. In some examples, the first indentation direction may be substantially opposite to the second indentation direction, as illustrated in  FIG. 7A . 
     The third indentation feature  794  may provide a third overhang and may have a third indentation direction including a combination of the negative x-direction and the positive z-direction. The fourth indentation feature  796  may provide a fourth overhang and may have a fourth indentation direction including a combination of the positive x-direction and negative z-direction. In the example combined sheet  700  illustrated in  FIG. 7A , the respective indentation features have an indentation direction different than at least one other indentation feature of the combined sheet  700 . 
     The first overhang includes a first cavity opening  770  and the second overhang includes a second cavity opening  772 . Similarly, the third overhang includes a third cavity opening  774  and the fourth overhang includes a fourth cavity opening  776 . In some examples, the first indentation feature  790  may provide the first overhang over the second cavity opening  772 . Similarly, the second indentation feature  792  may provide the second overhang over the first cavity opening  770 . In the foregoing example, although the first indentation feature  790  and the second indentation feature protrude from or extend from opposite sides of the combined sheet, the first cavity opening  770  may be adjacent to the second cavity opening  772 , as illustrated in  FIG. 7A . 
     Similarly, the third indentation feature  794  may provide the third overhang over the fourth cavity opening  776  and the fourth indentation feature  796  may provide the fourth overhang over the third cavity opening  774 . The third cavity opening  774  may be adjacent to the fourth cavity opening  776 , as illustrated in  FIG. 7A . 
     Other examples of indentation feature configurations may be contemplated. For example, a first indentation feature and a second indentation feature may protrude from a common side of the combined sheet, where the respective indentation features provide overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. In this example, it can be contemplated that the respective overhang cavity openings can be adjacent. 
     The indentation features of the combined sheet  700  in  FIG. 7A  may be formed using a double action press. An example double action press will be described and illustrated in a subsequent embodiment herein.  FIG. 7A  illustrates a first stage in formation of a combined sheet  700 , where the respective indentation features are formed using one or more punches. The foundation sheet may be joined to the main sheet for forming the combined sheet  700  based at least on: (1) the joints produced using the punch of a double action press at each of the respective indentation features; or (2) binding forces due in part to the spatial direction of a given indentation feature relative to another indentation feature, such that separating the foundation sheet from the main sheet may require that the general shape of the respective indentation features need to be deformed. 
       FIG. 7B  illustrates a subsequent stage in formation of the combined sheet  700 . The combined sheet  700  illustrated in  FIG. 7A  are subsequently pressed or rolled such that the respective indentation features are manipulated to be nearer to the plane of the combined sheet  700 . For example, the first overhang  760  (identified in  FIG. 7B ) of the first indentation feature  790  may be pressed or rolled nearer to the second cavity opening of the adjacent second indentation feature  792 . The second overhang  762  (identified in  FIG. 7B ) of the second indentation feature  792  may be pressed or rolled nearer to the first cavity opening of the adjacent first indentation feature  790 . 
     Similarly, the third overhang  764  (identified in  FIG. 7B ) of the third indentation feature  794  may be pressed or rolled nearer to the fourth cavity opening of the adjacent fourth indentation feature  796 . The fourth overhang  766  (identified in  FIG. 7B ) of the fourth indentation feature  796  may be pressed or rolled nearer to the third cavity opening of the adjacent third indentation feature  794 . 
     In some examples, it may be desirable to produce a substantially planar or flat combined sheet. Accordingly, it may be desirable to press or roll a combined sheet including indentation features into a substantially planar or flat product. 
       FIG. 7C  illustrates a subsequent stage in formation of the combined sheet  700 . The combined sheet  700  may be subsequently pressed or rolled such that the respective indentation features become substantially co-planar with a general plane of the combined sheet  700 . 
     In some examples, production of the combined sheet  700  may not include pressing or rolling said combined sheet  700  to be substantially planar or flat. Material properties of the main sheet or the foundation sheet may make it undesirable or impractical to do so. For example, if rolling or pressing the indentation features to be substantially co-planar with the combined sheet  700  required that the metal be stretched past a point of fracture, it may be desirable in some examples to produce the combined sheet  700  illustrated in  FIG. 7B  without any further subsequent pressing or rolling. 
     Reference is now made to  FIGS. 8A to 8D , which illustrate elevation, cross-sectional views of a combined sheet  800  at different stages of production of said combined sheet  800 , in accordance with another example of the present application. Indentation features may be described with reference to a Cartesian coordinate space, where direction may be referenced according to an illustrated compass rose  880 . 
     Similar to the combined sheet  700  illustrated in  FIG. 7A , in  FIG. 8A , the combined sheet  800  may include a first indentation feature  890 , a second indentation feature  892 , a third indentation feature  894 , and a fourth indentation feature  896 . The indentation features illustrated in  FIG. 8A  may be formed using a double action press. However, other methods of forming the indentation features may be contemplated, such as a rolling punch apparatus. 
     The indentation features illustrated in  FIG. 8A  may have an indentation direction that is substantially perpendicular or normal to the surface of the combined sheet  800 . In contrast, the combined sheet  700  illustrated in  FIG. 7A  may have respective indentation directions that are not substantially perpendicular or normal to the surface of the combined sheet  700 . 
     The combined sheet  800  of  FIG. 8A  may also include one or more embossed or stretched indentations  840 . The stretched indentations may be located at periodic locations across the combined sheet  800  and are joints for joining a foundation sheet of the combined sheet  800  to the main sheet of the combined sheet  800 . In  FIG. 8A , the foundation sheet is joined to the main sheet based at least on joints formed by: (1) the first indentation feature  890 , the second indentation feature  892 , the third indentation feature  894 , the fourth indentation feature  896 ; and (2) the one or more stretched indentations  840  located at various locations across the surface of the combined sheet  800 . 
       FIGS. 8B and 8C  illustrate a subsequent stage and a further subsequent stage in formation of the combined sheet  800  that was illustrated in  FIG. 8A . The combined sheet  800  may subsequently be pressed or rolled such that the respective indentation features are located nearer to the surface of the combined sheet  800 . Similar to the illustration in  FIG. 7B , the respective indentation features may include an indentation angle that may be nearer to 0 degrees. 
       FIG. 8D  illustrates another subsequent stage in formation of the combined sheet  800 . The combined sheet  800  may be pressed or rolled such that the respective indentation features or the stretched indentations  840  may become substantially co-planar with the general plane of the combined sheet  800 . 
     Reference is now made to  FIGS. 9A and 9B , which illustrate perspective views of combined sheet, in accordance with further examples of the present application. In  FIG. 9A , the combined sheet  900 A includes a plurality of indentation features across the combined sheet. For illustration, the combined sheet  900 A may include a first indentation feature  990  and a second indentation feature  992 , where a first indentation direction of the first indentation feature  990  and a second indentation direction of the second indentation feature  992  may be in opposite directions. The first indentation feature  990  and the second indentation feature  992  may be similar to the first indentation feature  790  and the second indentation feature  792  of  FIG. 7A . 
     In  FIG. 9A , the first indentation feature  990  and the second indentation feature  992  may be grouped such that an overhang cavity opening of the first indentation feature  990  may be adjacent to an overhang cavity opening of the second indentation feature  992 . In  FIG. 9A , groups of indentation features may be formed in an alternating direction relative to an adjacent group of indentation features. In  FIG. 9B , the combined sheet  900 B includes groups of indentation features having indentation directions that may alternate from a row of groups of indentation features to a subsequent row of groups of indentation features. It can be appreciated that the perspective views of the example combined sheets in  FIGS. 9A and 9B  may correspond to the combined sheet  800  illustrated in  FIG. 8B . That is, the perspective views of the combined sheets in  FIGS. 9A and 9B  may be a result of a method step where respective indentation features have been pressed or rolled such that the respective indentation features are located nearer to the surface of the combined sheet. Further, it can be appreciated that a plurality of indentation features may be provided to produce a combined sheet, and that the plurality of indentation features may be arranged to collectively form a pattern on the surface of the combined sheet. It will be understood that the illustrated examples of indentation features forming a pattern are illustrative and not restrictive, and that the pattern of indentation features can vary or be different from a combined sheet to another combined sheet. 
     Reference is now made to  FIGS. 10A and 10B , which illustrate elevation, cross-sectional views of a combined sheet  1000  at different production stages of said combined sheet  1000 , in accordance with an example of the present application. 
     The combined sheet  1000  includes a first indentation feature  1090  and a second indentation feature  1095 . The first indentation feature  1090  may be spaced from the second indentation feature  1095 . The combined sheet  1000  may include one or more stretched indentations  1040  across the surface of the combined sheet  1000 . The stretched indentations  1040  may be similar to the stretched indentations  840  of  FIG. 8  and may be formed as joints for joining a foundation sheet of the composite plate  1000  to a main sheet of the combined sheet  1000 . 
     In  FIG. 10A , the first indentation feature  1090  and the second indentation feature  1095  may have indentation directions that are substantially normal to or perpendicular to a general plane of the combined sheet  1000 . 
       FIG. 10B  illustrates a subsequent stage in formation of the combined sheet  1000  that was illustrated in  FIG. 10A . The combined sheet  1000  may be subsequently pressed or rolled such that the respective indentation features may be located nearer to the surface of the combined sheet  1000 . In  FIG. 10A , the respective indentation features may have an indentation angle of substantially 90 degrees. Subsequently, the respective indentation features may be rolled or pressed such that the respective indentation features may have an indentation angle that is an acute angle. For example, in  FIG. 10B , the respective indentation features may be rolled or pressed such that the respective indentation angles may be an acute angle, such as 85 degrees, 45 degrees, 25 degrees, 10 degrees, or any angle less than 90 degrees. In  FIG. 10B , a respective indentation feature may be oriented in a spatial direction that is different than another spatial direction of another indentation feature. As described, when an indentation feature may be oriented in a spatial direction that is different than another spatial direction of another indentation feature, the indentation features oriented in different directions may provide binding forces for joining a main sheet to a foundation sheet due in part to the spatial orientation of the respective indentation features. When the respective indentation directions are different, separating the foundation sheet from the main sheet may require that the general shape of the respective indentation features be deformed. 
     The examples described herein include joining a foundation sheet to a main sheet for producing a combined sheet. In some examples, the term “sheet” may be utilized for describing material having a thickness of 3 mm or less. Further, in some examples, the term “plate” may describe material having a thickness of more than 3 mm. The features described herein may be implemented for both combined sheet materials and combined plate materials. In some examples, the terms “sheet” and “plate” may be used interchangeably and should be considered to be illustrative and not restrictive. 
     In some examples described herein, the example combined sheets include at least a foundation sheet joined to a main sheet. That is, the combined sheet includes joining of two layers. In some other examples, any number of sheets may be joined via the features, methods, or apparatus described herein. For example, at least one additional sheet abutting a foundation sheet/main sheet combination may be joined to the foundation sheet/main sheet combination to form another example combined sheet. For example, the at least one additional sheet may include indentation features crimped to indentation features of the foundation sheet/main sheet combination. For example, referring again to the combined sheet  100  of  FIG. 1C , at least one additional sheet may include a first additional indentation feature crimped to the first foundation indentation feature  122  and a second additional indentation feature may be crimped to the second foundation indentation feature  124  for joining the additional sheet to the foundation sheet  120  and the main sheet  110 . 
     The description herein provides numerous examples of combined sheets including a foundation sheet joined to a main sheet. A foundation sheet may be joined to a main sheet when two or more indentation features form joints and when respective indentation directions of the two or more indentation features are in different spatial directions. The features of the combined sheets described herein may ameliorate some disadvantages of utilizing one or more joints (e.g., embossed joints) oriented in a single or unitary spatial direction. 
     When combined sheets including features described herein are produced, said combined sheets may be cut and/or shaped into products for subsequent stages of product manufacturing. 
     Reference is now made to  FIGS. 11A and 11B , which illustrate a corrugated panel  1100  formed from a combined sheet  1110 , in accordance with an example of the present application.  FIG. 11A  illustrates a perspective view of a combined sheet  1110  shaped into a corrugated panel  1100 . The combined sheet  1110  may include a plurality of first indentation features  1190 . The first indentation features  1190  may be located periodically across a surface of the combined sheet  1110 . Once the first indentation features  1190  are formed, the combined sheet  1110  may be shaped into the corrugated panel  1100 . 
       FIG. 11B  illustrates an elevation cross-section view of the corrugated panel  1100  of  FIG. 11A . In some examples, the first indentation features  1190  may be periodically spaced such that the first indentation features  1190  are located at regular intervals of the corrugated pattern. The combined sheet  1110  may also include second indentation features  1195  located at regular intervals of the corrugated pattern. Before the combined sheet  1110  may be shaped into the corrugated panel  1100 , the first indentation features  1190  may be oriented in a first direction and the second indentation features  1195  may be oriented in a second direction, such that the first direction is different than the second direction. 
     Reference is now made to  FIGS. 12A and 12B , which illustrate perspective views of a first structural steel profile  1200 A and a second structural steel profile  1200 B, in accordance with an example of the present application. In  FIG. 12A , the first structural steel profile  1200 A may be formed from a first combined sheet  1210  having a plurality of indentation features  1290 . Once indentation features  1290  are formed, the first combined sheet  1210  may be roll formed, for example, to provide the first structural steel profile  1200 A. 
     In  FIG. 12B , the second structural steel profile  1200 B may be formed from a second combined sheet  1220  having a plurality of indentation features  1292 . The indentation features  1292  in  FIG. 12B  may have a different overall length than the overall length of the indentation features  1290  in  FIG. 12A . Once indentation features  1292  are formed, the second combined sheet  1220  may similarly be roll formed, for example, to provide the second structural steel profile  1200 B. 
     Reference is now made to  FIGS. 13A and 13B , which illustrate a conduit structure  1300  formed from a combined sheet  1310 , in accordance with an example of the present application. The combined sheet  1310  may include a main sheet and a foundation sheet that are joined. The foundation sheet may be joined to the main sheet via a first indentation feature  1390  and a second indentation feature  1392 . The first indentation feature  1390  and the second indentation feature  1392  may be similar to the indentation features described herein and may be formed by embossing or stretching steps. Before the combined sheet  1310  may be formed into the conduit structure  1300 , the first indentation feature  1390  may be formed such that a first indentation direction of that first indentation feature  1390  may be in a different direction than a second indentation direction of the second indentation feature  1392 . Accordingly, the foundation sheet may be joined to the main sheet via indentation features spatially oriented in different directions. 
     In some examples, once the combined sheet  1310  is produced, the combined sheet  1310  may be roll formed to produce the conduit structure  1300 . Roll forming the combined sheet  1310  is one example of producing the conduit structure  1300 , however other methods of producing the conduit structure  1300  from the combined sheet  1310  may be contemplated. 
     In some examples, two or more sheet materials may be joined to a main sheet. It may be desirable to join sheet materials that may be placed adjacent to another, such that the combination of joined sheet materials may be more rigid or may be more resistant to bending. In some examples, it may be desirable to join sheet materials having variant properties. For example, it may be desirable to join an untreated steel sheet to stainless steel sheet for producing building structures. The stainless steel sheet may face a weathered environment, whereas the untreated steel sheet may face a temperate environment. When two or more indentation features may be formed for joining two or more sheet materials, adhesives or other adhesive like materials may not be required thereby reducing material costs for producing combined sheets. It can be appreciated when two different types of metals are combined, over time, galvanic corrosion, oxidization or other material by-products can result. Thus, it is desirable that each of the two or more sheet materials be respectively composed of the same metal or a variant of the same metal (e.g., stainless steel being a variant of steel). 
     In some examples, the conduit structure  1300  may include an edge formation  1360  for joining edges of the combined sheet  1310  for forming the conduit structure  1300 . 
     Reference is now made to  FIG. 14 , which illustrates a method  1400  of producing a combined sheet, in accordance with an example of the present application. The combined sheet may include a main sheet and a foundation sheet. The method  1400  may be implemented by a machine or a collection of machines along a production line for producing the combined sheet. 
     At  1410 , the machine may be configured to co-locate the main sheet to abut the foundation sheet such that the main sheet may be substantially parallel to the foundation sheet. In some examples, the foundation sheet may be placed atop the main sheet, such that the foundation sheet may be abutting the main sheet, and the combination of sheets may be conveyed through or along a production line. 
     At  1420 , the machine may be configured to press one or more indentation punches to be incident on a sheet combination including the main sheet and the foundation sheet for forming two or more indentation features. In some examples, the punch may include a double action press that may provide a non-penetrating force to the sheet combination for forming the indentation features. The indentation features may include those described herein. In other examples, a plurality of punches may be provided on a roller and the roller may be configured to press the plurality of punches on the sheet combination being conveyed along the production line. 
     In some examples, the two or more indentation features may include a first indentation feature including a first main indentation feature providing a first overhang over a first portion of the main sheet. The first indentation feature may include a first foundation indentation feature crimped to the first main indentation feature. The two or more indentation features may also include a second indentation feature including a second main indentation feature providing a second overhang over a second portion of the main sheet. The second indentation feature may include a second foundation indentation feature crimped to the second main indentation feature. The first overhang and the second overhang may be overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. The two or more indentation features may collectively be formed for joining the foundation sheet to the main sheet. 
     In some examples, the indentation punches may include a first indentation punch and a second indentation punch. At  1420 , when pressing the indentation punch to be incident on the sheet combination, the machine may be configured to: (a) press the first indentation punch to be incident on the sheet combination to translate a force in a direction normal to a surface of the sheet combination into a force in a first direction; and (b) press the second indentation punch to be incident on the sheet combination to translate a force in a direction normal to a surface of the sheet combination into a force in the second direction. In some examples, the first direction may be different than the second direction. In some examples, described below, the first direction and the second direction may both be a direction that may be substantially normal to or perpendicular to the general plane of the sheet combination and the indentation features may be subsequently formed. In some examples, pressing the first indentation punch and the second indentation punch may be performed substantially simultaneously. In some examples, the pressing of the first indentation punch may be offset in time from the pressing of the second indentation punch. 
     In some examples described herein, indentation features may be formed by one or more stages. For instance, the machine may be configured to press the indentation punch in a direction that is normal to the combined sheet surface to form two or more indentation features having indentation directions defined by a normal direction that is perpendicular to the combined sheet. For example, referring again to  FIG. 10A  as an illustrative example, at  1420 , the machine may be configured to press the indentation punches to be incident on the sheet combination for forming indentation features having indentation directions that are substantially normal to or perpendicular to the plane of the sheet combination. 
     Referring again to  FIG. 10B  as an illustrative example, at  1430 , the machine may be configured to roll form the two or more indentation features such that a first indentation feature is roll formed in a first indentation direction and a second indentation feature is roll formed in the second indentation direction. That is, in  FIG. 10B , the first indentation feature  1090  may be pressed or rolled such that the first indentation direction is a combination of the positive x-direction and the positive y-direction. Further, the second indentation feature  1095  may be pressed or rolled such that the second indentation direction is a combination of the negative x-direction and the positive y-direction. The operation at  1430  may provide a combined sheet that may be cut or shaped for producing other finished products. 
     In some examples, where desirable and where the materials may have large material plasticity to be rolled or pressed without fracturing, the machine may be configured to press or roll the respective indentation features such that the combination sheet is a planar sheet or a flat sheet. That is, in some examples, the machine may be configured to roll mill the combination sheet having indentation features into a flat sheet, such that the first indentation feature and the second indentation feature become planar with the surface of the combination sheet. In some examples, the machine may be configured to press the combination sheet having the indentation features into a flat sheet using a flat press. In some other examples, to increase plasticity of the sheet materials being rolled or pressed, the methods described herein may include heating steps. That is, heating the sheet materials can result in greater sheet material malleability. Increasing plasticity using heat of the sheet material may be desirable when producing a flat combined sheet having the features described herein. For example, metals may not have sufficient plasticity for indentation features to be rolled or pressed without causing metal fractures. Thus, it may be desirable to include method steps for heating the sheet material during one or more method steps described herein. 
     At  1440 , the machine may be configured to roll form the combined sheet into various structures. For example, the machine may be configured to roll form the combined sheet into example corrugated panels (see e.g.,  FIGS. 11A, 11B ), example structural steel profile (see e.g.,  FIG. 12A, 12B ), or example conduit structures (see e.g.,  FIG. 13A, 13B ). 
     Reference is now made to  FIGS. 15A and 15B , which illustrate a machine  1500  including a combination of stages for producing a combined sheet including a main sheet and a foundation sheet, in accordance with an example of the present application.  FIG. 15A  illustrates a side elevation view of the machine depicting example stages of the machine for producing a combined sheet.  FIG. 15B  illustrates a perspective view of the machine illustrated in  FIG. 15A . 
     The machine  1500  includes a first coil opener  1502  and a second coil opener  1504 . The first coil opener  1502  may be for unravelling one of a foundation sheet or a main sheet. The second coil opener  1504  may be for unravelling another one of a main sheet or a foundation sheet. In some examples, the main sheet or the foundation sheet may be a metal sheet. In some examples, the main sheet or the foundation sheet may be perforated sheets or non-perforated sheets. 
     The machine  1500  includes a first leveler  1506  and a second leveler  1508 . The first leveler  1506  may be downstream from the first coil opener  1502 . The second leveler  1508  may be downstream from the second coil opener  1504 . The first leveler  1506  and the second leveler  1508  may be for conditioning and positioning sheet material being conveyed along the machine and to be feed into a feeding system  1510 . 
     The machine  1500  includes the feeding system  1510 . The feeding system  1510  may be configured for positioning or co-locating the main sheet to abut the foundation sheet such that the main sheet may be parallel to the foundation sheet. The feeding system  1510  may be downstream from each of the first leveler  1506  and the second leveler  1508 . 
     The machine  1500  may include a heater  1512  downstream from the feeding system  1510 . The heater  1512  may increase the temperature of the foundation sheet and the main sheet material being conveyed through the machine. The foundation sheet and the main sheet may be heated, for example, to increase the material plasticity of the respective sheet materials for forming indentation features or for roll forming the sheet materials into finished products, such as structures. 
     The machine  1500  may include a double action press  1520  for forming indentation features on the sheet materials for joining the foundation sheet to the main sheet. The indentation features may include features described in the present application. In some examples, the double action press  1520  may include punches on both a top plate and a bottom plate such that a subset of indentation features formed in the sheet materials may protrude from a top portion of the combined sheet and another subset of indentation features formed in the sheet materials may protrude from a bottom portion of the combined sheet. For example, the double action press  1520  may be configured to form indentation features to produce the combined sheet illustrated in  FIG. 8A . In  FIG. 8A , indentation features are illustrated to be grouped in pairs, where indentation features in a pair may have a respective overhang cavity opening that is adjacent to another overhang cavity opening. In some other examples, the double action press  1520  may be configured to form indentation features such that respective overhang cavity openings are spaced apart from other overhang cavity openings. In some other examples, the double action press  1520  may be configured to form indentation features in the sheet materials such that the indentation features protrude from a single side of the combined sheet. In some examples, the double action press  1520  may be configured to perform a two step process, including: (1) pressing punches to be incident on the sheet materials for producing the indentation features; and (2) rolling or pressing the respective indentation features such that an overhang or indentation surface may be nearer to the plane of the combined sheet than before said step (2). 
     The machine  1500  may include a mill roll former  1530  for further forming the produced combined sheet. The mill roll former  1530  may be downstream from the double-action press machine. In some examples, the mill roll former  1530  may be an optional production stage. 
     The machine  1500  may include a combined sheet leveler  1535  that is downstream from the double action press  1520 . The combined sheet leveler  1535  may condition the produced combined sheet (e.g., including the foundation sheet joined to the main sheet) for subsequent stages in the production process for producing finished products that incorporate the produced combined sheet. 
     Reference is now made to  FIGS. 16A and 16B , which illustrate a machine  1600  including a combination of stages for producing a combined sheet including a main sheet and a foundation sheet, in accordance with an example of the present application.  FIG. 16A  illustrates a side elevation view of the machine depicting example stages of the machine for producing a combined sheet.  FIG. 16B  illustrates a perspective view of the machine illustrated in  FIG. 16A . 
     The machine  1600  includes a first coil opener  1602 , a second coil opener  1604 , a first leveler  1606 , a second leveler  1608 , a feeding system  1610 , a heater  1612 , an indentation roll former  1620 , a mill roll former  1630 , and a combined sheet leveler  1635 . The first coil opener  1602 , the second coil opener  1604 , the first leveler  1606 , the second leveler  1608 , the feeding system  1610 , the heater  1612 , the mill roll former  1630 , and the combined sheet leveler  1635  may be similar to the first coil opener  1502 , the second coil opener  1504 , the first leveler  1506 , the second leveler  1608 , the feeding system  1510 , the heater  1512 , the mill roll former  1530 , and the combined sheet leveler  1535  illustrated in  FIGS. 15A and 15B . 
     The indentation roll former  1620  may be configured to form indentation features at two or more locations across the combination of the foundation sheet and the main sheet. That is, the indentation roll former  1620  may include a roller configured with a plurality of punches. The roller may be configured to press the plurality of punches onto the sheet combination (e.g., the foundation sheet and the main sheet) being conveyed along the production line. 
     As described, in some examples, the double action press  1520  of  FIGS. 15A and 15B  may include punches on both a top plate and a bottom plate such that a subset of indentation features formed in sheet materials may protrude from a top portion of the combined sheet and another subset of indentation features formed in the sheet material may protrude from a bottom portion of the combined sheet. In some examples, the double action press  1520  may be configured to translate a force in a direction that is normal or perpendicular to a surface of the sheet combination (e.g., the foundation sheet and the main sheet) into a force in a direction for an indentation feature. To illustrate, reference is now made to  FIG. 17 , which illustrates a free-body diagram illustrating force directions being applied by the example double action press  1520  of  FIGS. 15A and 15B . 
     The double action press  1520  of  FIGS. 15A and 15B  may include a top plate and a bottom plate. The top plate may be configured to impart a first normal force  1702  that is perpendicular to a sheet combination surface  1750 . The bottom plate may be configured to impart a second normal force  1704  that is also perpendicular to the sheet combination surface  1750 . The first normal force  1702  and the second normal force  1704  may be applied from opposing sides of the sheet combination surface  1750 . 
     Further, the double action press  1520  may be configured to translate the first normal force  1702  and the second normal force  1704  into a force having a direction corresponding to a direction of one or more respective indentation features. For example, the double-action press  1520  may be configured to translate the first normal force  1702  into a third force  1710  having a third direction (illustrated in  FIG. 17 ). The double-action press  1520  may also be configured to translate the first normal force  1702  into a fourth force  1712  having a fourth direction (illustrated in  FIG. 17 ). 
     Further, the double-action press  1520  may be configured to translate the second normal force  1704  into a fifth force  1720  having a fifth direction (illustrated in  FIG. 17 ). The double action press  1520  may also be configured to translate the second normal force  1704  into a sixth force  1722  having a sixth direction (illustrated in  FIG. 17 ). 
     To illustrate a double action press apparatus configured to impart forces in the various directions that are illustrated in  FIG. 17 , reference is now made to  FIGS. 18A and 18B , which illustrate a press apparatus including one or more indentation punches for forming indentation features in sheet material, in accordance with another example of the present application. The press apparatus  1800  in  FIG. 18A  is illustrated at a first stage and the press apparatus  1800  in  FIG. 18B  is illustrated at a second stage. The press apparatus  1800  at the second stage is in response to the first normal force  1702  and the second normal force  1704  being applied. 
     The press apparatus  1800  may operate when the first normal force  1702  ( FIG. 17 ) and the second normal force  1704  ( FIG. 17 ) is applied to a ram press  1820 . The ram press  1820  may include a pair of components including a top portion and a bottom portion associated with a top ram press and a bottom ram press. In some examples, the first normal force  1702  may be applied at substantially the same time as the second normal force  1704 . In some other examples, the first normal force  1702  may be applied at a time that is offset from the second normal force  1704 . 
     When at least one of the first normal force  1702  and the second normal force  1704  is applied to the ram press  1820 , at least one of the third force  1710 , the fourth force  1712 , the fifth force  1720 , or the sixth force  1722  may be applied to one or more indentation punches  1830 . When at least one of the aforementioned forces may be applied to the one or more indentation punches  1830 , the indentation punches  1830  may be thrust towards a sheet receiving space  1802 . The sheet receiving space  1802  can be described as a material receiving slot. The sheet receiving space  1802  may be configured to receive combination sheet material, including a foundation sheet that may abut a main sheet for producing a combined sheet. The respective indentation punches  1830  may be thrust towards the sheet receiving space  1802  for producing indentation features described herein. The respective indentation punches  1830  may be thrust towards the sheet receiving space  1802  in a direction corresponding to an indentation direction of respective indentation features. 
     For example, referring again to  FIG. 7A , the first indentation feature  790  ( FIG. 7A ) may be formed using one of the indentation punches  1830 , and the indentation punch  1830  may be thrust towards the sheet receiving space  1802  in the first indentation direction including a combination of the positive x-direction and positive z-direction (see e.g.,  FIG. 7A ). 
     Further, the respective indentation punches  1830  may be thrust towards the sheet receiving slot  1802  with guidance of respective guides  1810 . That is, the respective guides  1810  may allow the indentation punches  1830  to be thrust towards the sheet receiving space  1802  at specified or preconfigured directions. 
     In some examples, the press apparatus  1800  may also include a roller interface  1812 . The roller interface  1812  may couple the ram press to respective indentation punches  1830  for thrusting the respective indentation punches  1830  towards the sheet receiving space  1802 . 
     The press apparatus  1800  may be operated in a first state ( FIG. 18A ) and a second state ( FIG. 18B ). In the first state ( FIG. 18A ), the indentation punches  1830  may be in a retracted configuration and the sheet receiving space  1802  may be available for receiving sheet materials. Once sheet materials are received in the sheet receiving space  1802 , the first normal force  1702  ( FIG. 17 ) and the second normal force  1704  ( FIG. 17 ) may be imparted on the ram press  1820  and the press apparatus  1800  will be transitioned to the second state ( FIG. 18B ). In the second state, the indentation punches  1830  may be thrust towards the sheet receiving space  1802  for forming indentation features in the combination of the main sheet and the foundation sheet. In some examples, the first normal force  1702  and the second normal force  1704  may be applied to the ram press  1820  at preconfigured periodic intervals, such that the main sheet and the foundation sheet being propagated along the machine (see e.g.,  FIG. 15A, 15B, 16A, 16B ) may be provided with indentation features when the sheet materials are propagated through the sheet receiving space  1802 . It can be appreciated that, in some examples, the press apparatus  1800  illustrated in  FIGS. 18A and 18B  may be used for producing the combined sheet illustrated in  FIG. 7A . 
     Reference is now made to  FIGS. 19A, 19B, and 19C , which illustrate a press apparatus  1900  including one or more indentation punches for forming indentation features in sheet material, in accordance with another example of the present application. 
     The press apparatus  1900  may operate when the first normal force  1702  ( FIG. 17 ) and the second normal force  1704  ( FIG. 17 ) is applied to a ram press  1920 . In some examples, the ram press  1920  may include a top portion and a bottom portion, where the first normal force  1702  may be applied to the top portion and the second normal force  1704  may be applied to the bottom portion. In some examples, the first normal force  1702  may be applied at substantially the same time as the second normal force  1704 . In some other examples, the first normal force  1702  may be applied at a time that is offset from the second normal force  1704 . 
     When the second normal force  1704  is applied to the ram press  1920 , at least the fifth force  1720  or the sixth force  1722  may be applied to indentation punches  1930 . When at least one of the aforementioned forces may be applied to the one or more indentation punches  1930 , the indentation punches  1930  may be thrust towards a sheet receiving space  1902 . The sheet receiving space  1902  may be configured to receive combination sheet material, including a foundation sheet that may abut a main sheet for producing a combined sheet. The respective indentation punches  1930  may be thrust towards the sheet receiving space  1902  in a direction corresponding to an indentation direction of respective indentation features. 
     Further, the respective indentation punches  1930  may be thrust towards the sheet receiving space  1902  with guidance of guides  1910 . That is, the guides  1910  may allow the indentation punches  1930  to be thrust towards the sheet receiving space  1902  at specified or preconfigured directions. 
     In some examples, the press apparatus  1900  may also include a roller interface  1912 . The roller interface  1912  may couple the ram press to indentation punches  1930  for thrusting the respective indentation punches  1930  towards the sheet receiving space  1902 . 
     The press apparatus  1900  may be configured to form indentation features (described herein) on a combination of a foundation sheet and a main sheet, such that the indentation features may protrude from a common side of the produced combined sheet. For example, the press apparatus  1900  may include indentation punches  1930  adjacent to a ram press  1920 , such that indentation punches  1930  may be thrust into the sheet receiving space  1902  from a single side. 
     In some examples, the press apparatus  1900  may include one or more sheet retention blocks  1970 . When the first normal force  1702  ( FIG. 17 ) may be applied to the ram press  1920 , the press apparatus  1900  may be configured to thrust the sheet retention blocks  1970  towards the sheet receiving space  1902 . When the sheet retention blocks  1970  are thrust towards the sheet receiving space  1902 , the sheet material received in the sheet receiving space  1902  may be held in place, in part, by the sheet retention blocks  1970 , such that the indentation punches  1930  may form indentation features in the sheet materials. To illustrate,  FIG. 19A  illustrates a first state, where the first normal force  1702  ( FIG. 17 ) and the second normal force  1704  ( FIG. 17 ) has not yet been applied to the ram press  1920 . 
       FIG. 19B  illustrates a second state, where the first normal force  1702  ( FIG. 17 ) and the second normal force  1704  ( FIG. 17  may be applied to the ram press  1920  and the sheet retention blocks  1970  may be urged against at least one of the guides  1910 . 
       FIG. 19C  illustrates a third state, where the first normal force  1702  and the second normal force  1704  may be released subsequent to the indentation punches  1930  being thrust towards the sheet receiving space  1902  for forming the indentation features. Once the indentation punches  1930  have been thrust towards the sheet receiving space  1902  for forming the indentation features, the foundation sheet is joined to the main sheet for forming the combined sheet portion. That combined sheet portion forms a portion of the combined sheet being formed and conveyed along the machine (see e.g.,  FIGS. 15A, 15B, 16A, 16B ). 
     From the examples described herein, a combined sheet may include two or more indentation feature. A first indentation feature may include a first main indentation feature providing a first overhang over a first portion of the main sheet. A first foundation indentation feature may be crimped to the first main indentation feature. A second indentation feature may include a second main indentation feature providing a second overhang over a second portion of the main sheet. The second indentation feature may include a second foundation indentation feature crimped to the second main indentation feature. The first overhang and the second overhang may be overhangs in different directions to prohibit separation of the foundation sheet from the main sheet. 
     The two or more indentation features may be formed for joining the foundation sheet to the main sheet. Thus, the foundation sheet may be joined to the main sheet based at least on: (1) plastic flow occurring during joint creation at respective indentation features; and/or (2) binding forces due in part to the spatial orientation/direction the first indentation feature relative to the second indentation feature. Because the first indentation feature and the second indentation feature may include features formed from sheet metal material having some rigid properties, separating the foundation sheet from the main sheet may not occur unless the general shape of the respective indentation features is deformed. Based at least in part on the rigid material properties of the first indentation feature and the second indentation feature and on the respective indentation features providing overhangs that may be oriented in different directions, the main sheet and the foundation sheet may be formed without the use of adhesives or other materials providing bonds between materials. 
     Certain adaptations and modifications of the described embodiments can be made. Therefore, the above discussed embodiments are considered to be illustrative and not restrictive.