Patent Publication Number: US-2023142693-A1

Title: Carriage assembly with asymmetrical swage bosses and associated methods

Description:
FIELD 
     This disclosure relates generally to a carriage assembly of a magnetic storage device, and more particularly to a carriage assembly having head-gimbal assemblies with asymmetrical swage bosses. 
     BACKGROUND 
     Magnetic storage devices, such as hard disk drives (“HDDs”), are widely used to store digital data or electronic information for enterprise data processing systems, computer workstations, portable computing devices, digital audio players, digital video players, and the like. Generally, HDDs include a carriage assembly that includes a head stack assembly and at least one head-gimbal assembly. The head stack assembly includes a plurality of carriage arms and a plurality of head-gimbal assemblies. Each one of the head-gimbal assemblies is attached to a corresponding one of the carriage arms by a process known as “swaging”. Typically, during a swaging process, for each head-gimbal assembly, a swage ball is temporarily forced through a swage hole on a carriage arm, which causes a swage boss of the head-gimbal assembly, located within the swage hole, to plastically deform and form a radial interference fit with the swage hole to permanently attach the head-gimbal assembly to the carriage arm. 
     As the storage capacity and number of disks within a HDD has increased, head-gimbal assemblies with a lower profile swage boss have been utilized. However, such lower profile swage bosses have an increased risk of buckling during a swaging process, due to their lower profile, which can result in an insufficient radial interference fit. Additionally, robust swage attachment may require multi-pass swaging, using multiple swage balls or multiple passes by a single swage ball which is a time consuming and expensive process. 
     SUMMARY 
     The subject matter of the present application provides examples of carriage assemblies and associated methods and systems that overcome the above-discussed shortcomings of prior art techniques. The subject matter of the present application has been developed in response to the present state of the art, and in particular, in response to shortcomings of conventional carriage assemblies, methods, and systems. 
     Disclosed herein is a hard disk drive that comprises a housing, defining an interior cavity. The hard disk drive also comprises a plurality of magnetic disks within the interior cavity. The hard disk drive further comprises a carriage assembly, within the interior cavity and movable relative to the plurality of magnetic disks. The carriage assembly comprises a head stack assembly comprising a carriage arm. The carriage arm comprises a carriage-arm tip that comprises a swaging hole centered about a swaging axis and passing through the carriage-arm tip from a first side of the carriage-arm tip to a second side of the carriage-arm tip which is opposite the first side. The carriage assembly also comprises a first head-gimbal assembly comprising a tension baseplate on the first side of the carriage-arm tip and a tension swage boss located within the swaging hole. The tension swage boss is annular, is centered about the swaging axis, has a tension-boss inner diameter, and has a tension-boss outer diameter. The carriage assembly further comprises a second head-gimbal assembly comprising a compression baseplate on the second side of the carriage-arm tip. A compression swage boss is located within the swaging hole and spaced apart from the tension swage boss along the swaging axis. The compression swage boss is annular, is centered about the swaging axis, has a compression-boss inner diameter, and has a compression-boss outer diameter. The tension swage boss comprises an uppercut and a tension-boss undercut. The uppercut extends radially outward, away from the swaging axis, from a first backbore diameter to a second backbore diameter and has an uppercut depth, in a direction parallel to the swaging axis. The tension-boss undercut extends radially, away from the swaging axis, from the tension-boss outer diameter to a first undercut diameter and has a tension-boss undercut depth, in a direction parallel to the swaging axis. The compression swage boss comprises a compression-boss undercut. The compression-boss undercut extends radially outward, away from the swaging axis, from a compression-boss outer diameter to a second undercut diameter and has a compression-boss undercut depth, in a direction parallel to the swaging axis. A swaging ball is insertable through the swaging hole such that, as the swaging ball is inserted through the swaging hole, an interference fit is formed between an outer periphery of the tension swage boss and an inner periphery of the swaging hole and an outer periphery of the compression swage boss and the inner periphery of the swaging hole. The preceding subject matter of this paragraph characterizes example 1 of the present disclosure. 
     The tension swage boss converges, in a force direction along the swaging axis, from the second backbore diameter to the first backbore diameter and to the tension-boss inner diameter. The preceding subject matter of this paragraph characterizes example 2 of the present disclosure, wherein example 2 also includes the subject matter according to example 1, above. 
     The second backbore diameter of the tension baseplate is greater than the inner periphery of the swaging hole and the first backbore diameter of the tension baseplate is less than the inner periphery of the swaging hole. The preceding subject matter of this paragraph characterizes example 3 of the present disclosure, wherein example 3 also includes the subject matter according to any of examples 1-2, above. 
     The second backbore diameter of the tension baseplate is greater than the tension-boss outer diameter and the first backbore diameter of the tension baseplate is less than the tension-boss outer diameter. The preceding subject matter of this paragraph characterizes example 4 of the present disclosure, wherein example 4 also includes the subject matter according to any of examples 1-3, above. 
     The compression swage boss comprises a third backbore diameter. The third backbore diameter of the compression swage boss is less than the second backbore diameter of the tension swage boss. The preceding subject matter of this paragraph characterizes example 5 of the present disclosure, wherein example 5 also includes the subject matter according to any of examples 1-4, above. 
     A minimum thickness of the tension baseplate is less than a minimum thickness of the compression baseplate. The preceding subject matter of this paragraph characterizes example 6 of the present disclosure, wherein example 6 also includes the subject matter according to any of examples 1-5, above. 
     The compression-boss undercut depth is greater than the tension-boss undercut depth. The preceding subject matter of this paragraph characterizes example 7 of the present disclosure, wherein example 7 also includes the subject matter according to any of examples 1-6, above. 
     The tension baseplate has a tension baseplate thickness. The tension-boss undercut depth is less than 24 percent of a tension baseplate thickness. The preceding subject matter of this paragraph characterizes example 8 of the present disclosure, wherein example 8 also includes the subject matter according to of any examples 1-7, above. 
     The compression baseplate has a compression baseplate thickness. The compression-boss undercut depth is greater than 24 percent of the compression baseplate thickness. The preceding subject matter of this paragraph characterizes example 9 of the present disclosure, wherein example 9 also includes the subject matter according to of any examples 1-8, above. 
     The second undercut diameter is greater than the first undercut diameter. The preceding subject matter of this paragraph characterizes example 10 of the present disclosure, wherein example 10 also includes the subject matter according to any of examples 1-9, above. 
     The tension-boss inner diameter is less than the compression-boss inner diameter. The preceding subject matter of this paragraph characterizes example 11 of the present disclosure, wherein example 11 also includes the subject matter according to any of examples 1-10, above. 
     The tension-boss inner diameter is at least 0.02 mm less than the compression-boss inner diameter. The preceding subject matter of this paragraph characterizes example 12 of the present disclosure, wherein example 12 also includes the subject matter according to example 11, above. 
     A first height of the tension swage boss is equal to a second height of the compression swage boss. The first height and the second height are less than 0.2 mm. The preceding subject matter of this paragraph characterizes example 13 of the present disclosure, wherein example 13 also includes the subject matter according to any of examples 1-12, above. 
     The first height and the second height is 0.19 mm. The preceding subject matter of this paragraph characterizes example 14 of the present disclosure, wherein example 14 also includes the subject matter according to example 13, above. 
     The swaging ball has a ball diameter. The tension-boss inner diameter is between 4 percent and 15 percent smaller than the ball diameter. The preceding subject matter of this paragraph characterizes example 15 of the present disclosure, wherein example 15 also includes the subject matter according to any of examples 1-14, above. 
     The tension-boss inner diameter is between 5 percent and 8 percent smaller than the ball diameter. The preceding subject matter of this paragraph characterizes example 16 of the present disclosure, wherein example 16 also includes the subject matter according to example 15, above. 
     The plurality of magnetic disks comprises ten magnetic disks. The head stack assembly comprises nine carriage arms, each carriage arm sandwiched between a corresponding first head-gimbal assembly and a corresponding second head-gimbal assembly. The head stack assembly further comprises a top-most carriage arm, positioned above the nine carriage arms. The compression swage boss of a second head-gimbal assembly is located within the swaging hole of the carriage-arm tip of the top-most carriage arm. A bottom-most carriage arm is positioned below the nine carriage arms. The tension swage boss of a first head-gimbal assembly located within the swaging hole of the carriage-arm tip of the bottom-most carriage arm. The preceding subject matter of this paragraph characterizes example 17 of the present disclosure, wherein example 17 also includes the subject matter according to any of examples 1-17, above. 
     Further disclosed herein is a carriage assembly for a hard disk drive. The carriage assembly comprises a head stack assembly comprising a carriage arm. The carriage arm comprises a carriage-arm tip that comprises a swaging hole centered about a swaging axis and passing through the carriage-arm tip from a first side of the carriage-arm tip to a second side of the carriage-arm tip which is opposite the first side. The carriage arm also comprises a first head-gimbal assembly. The first head-gimbal assembly comprising a tension baseplate on the first side of the carriage-arm tip and a tension swage boss is located within the swaging hole. The tension swage boss is annular, is centered about the swaging axis, has a tension-boss inner diameter, and has a tension-boss outer diameter. The carriage arm further comprises a second head-gimbal assembly. The second head-gimbal assembly comprises a compression baseplate on the second side of the carriage-arm tip and a compression swage boss located within the swaging hole and spaced apart from the tension swage boss along the swaging axis. The compression swage boss is annular, is centered about the swaging axis, has a compression-boss inner diameter, and has a compression-boss outer diameter. The tension swage boss comprises an uppercut and a tension-boss undercut. The uppercut extends radially outward, away from the swaging axis, from a first backbore diameter to a second backbore diameter and has an uppercut depth, in a direction parallel to the swaging axis. The tension-boss undercut extends radially, away from the swaging axis, from the tension-boss outer diameter to a first undercut diameter and has a tension-boss undercut depth, in a direction parallel to the swaging axis. The compression swage boss comprises a compression-boss undercut. The compression-boss undercut extends radially outward, away from the swaging axis, from a compression-boss outer diameter to a second undercut diameter and has a compression-boss undercut depth, in a direction parallel to the swaging axis. A swaging ball is insertable through the swaging hole such that, as the swaging ball is inserted through the swaging hole, an interference fit is formed between an outer periphery of the tension swage boss and an inner periphery of the swaging hole and an outer periphery of the compression swage boss and the inner periphery of the swaging hole. The preceding subject matter of this paragraph characterizes example 18 of the present disclosure. 
     The head stack assembly comprises nine carriage arms, each carriage arm sandwiched between a corresponding first head-gimbal assembly and a corresponding second head-gimbal assembly. The head stack assembly further comprises a top-most carriage arm, positioned above the nine carriage arms. The compression swage boss of a second head-gimbal assembly located within the swaging hole of the carriage-arm tip of the top-most carriage arm. The head stack assembly also comprises a bottom-most carriage arm, positioned below the nine carriage arms. The tension swage boss of a first head-gimbal assembly located within the swaging hole of the carriage-arm tip of the bottom-most carriage arm. The preceding subject matter of this paragraph characterizes example 19 of the present disclosure, wherein example 19 also includes the subject matter according to example 18, above. 
     The compression swage boss comprises a compression-boss undercut. The compression-boss undercut extends radially outward, away from the swaging axis, from the compression-boss outer diameter to a second undercut diameter and has a compression-boss undercut depth, in a direction parallel to the swaging axis. The preceding subject matter of this paragraph characterizes example 20 of the present disclosure, wherein example 20 also includes the subject matter according to examples 18 or 19, above. 
     Additionally, disclosed herein is a method of coupling a head-gimbal assembly to a carriage arm. The method comprises positioning a tension baseplate of a first head-gimbal assembly on a carriage-arm tip of a carriage arm. A tension swage boss is located within a swaging hole, on the carriage-arm tip and concentric with a swaging axis of the swaging hole. The method also comprises positioning a compression baseplate of a second head-gimbal assembly on a carriage arm tip of a carriage arm. The carriage arm tip is sandwiched between the tension baseplate and the compression baseplate. A compression swage boss located within the swaging hole and concentric with the swaging axis of the swaging hole and the compression swage boss spaced apart from the tension swage boss along the swaging axis. The method further comprises inserting a swaging ball axially through the swaging hole in an insertion direction and plastically deforming the tension swage boss and the compression swage boss to form an interference fit between an outer periphery of the tension swage boss against an inner periphery of the swaging hole and an interference fit between an outer periphery of the compression swage boss against the inner periphery of the swaging hole. The tension swage boss comprises an uppercut and a tension-boss undercut. The uppercut extends radially outward, away from the swaging axis, from a first backbore diameter to a second backbore diameter and has an uppercut depth, in a direction parallel to the swaging axis. The tension-boss undercut extends radially, away from the swaging axis, from the tension-boss outer diameter to a first undercut diameter and has a tension-boss undercut depth, in a direction parallel to the swaging axis. The compression swage boss comprises a compression-boss undercut. The compression-boss undercut extends radially outward, away from the swaging axis, from a compression-boss outer diameter to a second undercut diameter and has a compression-boss undercut depth, in a direction parallel to the swaging axis. The preceding subject matter of this paragraph characterizes example 21 of the present disclosure. 
     The described features, structures, advantages, and/or characteristics of the subject matter of the present disclosure may be combined in any suitable manner in one or more examples, including embodiments and/or implementations. In the following description, numerous specific details are provided to impart a thorough understanding of examples of the subject matter of the present disclosure. One skilled in the relevant art will recognize that the subject matter of the present disclosure may be practiced without one or more of the specific features, details, components, materials, and/or methods of a particular example, embodiment, or implementation. In other instances, additional features and advantages may be recognized in certain examples, embodiments, and/or implementations that may not be present in all examples, embodiments, or implementations. Further, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the subject matter of the present disclosure. The features and advantages of the subject matter of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the subject matter as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the subject matter may be more readily understood, a more particular description of the subject matter briefly described above will be rendered by reference to specific examples that are illustrated in the appended drawings. Understanding that these drawings depict only typical examples of the subject matter, they are not therefore to be considered to be limiting of its scope. The subject matter will be described and explained with additional specificity and detail through the use of the drawings, in which: 
         FIG.  1    is a schematic perspective view of a magnetic storage device, according to one or more examples of the present disclosure; 
         FIG.  2    is a schematic perspective view of a head stack assembly and a head-gimbal assembly of the magnetic storage device, according to one or more examples of the present disclosure; 
         FIG.  3 A  is a schematic side view of a portion of the head stack assembly, a plurality of disks positioned between adjacent carriage arms of the head stack assembly, according to one or more examples of the present disclosure; 
         FIG.  3 B  is a schematic side view of Box B of the head stack assembly of  FIG.  3 A , according to one or more examples of the present disclosure; 
         FIG.  4    is a schematic cross-sectional view of a carriage-arm tip and two head-gimbal assemblies, before swaging, according to one or more examples of the present disclosure; 
         FIG.  5    is a schematic cross-sectional view of the carriage-arm tip and the two head-gimbal assemblies, before swaging, according to one or more examples of the present disclosure; 
         FIG.  6    is a schematic cross-sectional view of a portion of a carriage assembly during swaging, according to one or more examples of the present disclosure; 
         FIG.  7    is a schematic cross-sectional view of a carriage-arm tip and two head-gimbal assemblies, according to one or more examples of the present disclosure; and 
         FIG.  8    is a schematic flow diagram of a method of coupling a head-gimbal assembly to a carriage arm, according to one or more examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference throughout this specification to “one example,” “an example,” or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present disclosure. Appearances of the phrases “in one example,” “in an example,” and similar language throughout this specification may, but do not necessarily, all refer to the same example. Similarly, the use of the term “implementation” means an implementation having a particular feature, structure, or characteristic described in connection with one or more examples of the present disclosure, however, absent an express correlation to indicate otherwise, an implementation may be associated with one or more examples. 
     Referring to  FIG.  1   , a magnetic storage device  100 , according to one example, is depicted as a hard disk drive (HDD). However, in other examples, the magnetic storage device  100  can be any of various magnetic storage devices without departing from the essence of the subject matter of the present disclosure. The magnetic storage device  100  includes a housing  102  that seals or encloses an interior cavity  114  defined within the housing  102 . The housing  102  includes a base  130  and a cover  132  (shown in dashed lines so as not to obscure internal features of the magnetic storage device  100  within the interior cavity  114  of the housing  102 ). The cover  132  is coupled to the base  130  to enclose the interior cavity  114  from the environment exterior to the housing  102 . In some examples, a seal or gasket is positioned between the base  130  and the cover  132  to promote a seal between the base  130  and the cover  132 . 
     The magnetic storage device  100  includes various features located within the interior cavity  114  of the housing  102 . In some examples, the magnetic storage device  100  includes a carriage assembly  103 , disks  115 , a spindle motor  121 , and a voice coil motor (VCM)  125  within the interior cavity  114 . The carriage assembly  103  includes a head stack assembly  107  that includes a plurality of carriage arms  105  and at least one head-gimbal assembly  109  (e.g., suspension) coupled to a carriage-arm tip  106  (e.g., distal tip) of each carriage arm  105  of the plurality of carriage arms  105 . Each head-gimbal assembly  109  includes a suspension assembly  135  and a slider  142 . The slider  142  includes at least one read-write head coupled to (e.g., embedded in) the slider  142 . Although the magnetic storage device  100  in  FIG.  1    is shown to have five carriage arms  105  and four disks  115 , in other examples the magnetic storage device  100  can have fewer or more than five carriage arms  105  (e.g., eleven carriage arms  105 ) or fewer or more than four disks  115  (e.g., ten disks  115 ). In one example, each side of each carriage arm  105  facing a disk  115  has a head-gimbal assembly  109  (e.g., each of bottom and top carriage arms  105  has one head-gimbal assembly  109  and each of middle carriage arms  105 , which are between two of the disks  115  and between the bottom and top carriage arms  105 , have two head-gimbal assemblies  109 ). Similarly, although the magnetic storage device  100  is shown to have one spindle motor  121  and one VCM  125 , in other examples, the magnetic storage device  100  can have any number of spindle motors  121  and VCMs  125 . 
     The spindle motor  121  is coupled to the base  130 . Generally, the spindle motor  121  includes a stationary portion non-movably fixed relative to the base  130  and a spindle that is rotatable relative to the stationary portion and the base  130 . Accordingly, the spindle of the spindle motor  121  can be considered to be part of or integral with the spindle motor. Generally, the spindle motor  121  is operable to rotate the spindle relative to the base  130 . The disks  115 , or platters, are co-rotatably fixed to the spindle of the spindle motor  121  via respective hubs  122 , which are co-rotatably secured to respective disks  115  and the spindle. As the spindle of the spindle motor  121  rotates, the disks  115  correspondingly rotate. In this manner, the spindle of the spindle motor  121  defines a rotational axis of each disk  115 . The spindle motor  121  can be operatively controlled to rotate the disks  115 , in a rotational direction  190 , a controlled amount at a controlled rate. 
     Each of the disks  115  may be any of various types of magnetic recording media. Generally, in one example, each disk  115  includes a substrate and a magnetic material applied directly or indirectly onto the substrate. For example, the magnetic material of the disks  115  may be conventional granular magnetic recording disks or wafers that have magnetic layer bits with multiple magnetic grains on each bit. In granular magnetic media, all of the bits are co-planar and the surface  116  of the disk is substantially smooth and continuous. In one example, each bit has a magnetic dipole moment that can either have an in-plane (longitudinal) orientation or an out-of-plane (perpendicular) orientation. 
     As the disks  115  rotate in a read-write mode, the VCM  125  electromagnetically engages voice coils of the carriage arms  105  to rotate the carriage arms  105 , and the head-gimbal assemblies  109 , which are coupled to the carriage arms  105 , relative to the disks  115  in a rotational direction along a plane parallel to read-write surfaces  155  of the disks  115 . The carriage arms  105  can be rotated to position the read-write head of the head-gimbal assemblies  109  over a specified radial area of the read-write surface  155  of a corresponding disk  115  for read and/or write operations. The VCM  125  is fixed to the base  130  in engagement with the voice coils of the carriage arms  105 , which are rotatably coupled to the base  130  via a spindle  127  extending through the carriage assembly  103 . Generally, the spindle  127  defines a rotational axis about which the carriage arms  105  rotate when actuated by the VCM  125 . 
     The carriage arms  105  are non-movably fixed to (e.g., integrally formed as a one-piece unitary monolithic body) and extend away from a base of the carriage assembly  103  in a spaced-apart manner relative to each other. In some examples, the carriage arms  105  are spaced an equi-distance apart from each other and extend parallel relative to each other. A respective one of the disks  115  is positioned between adjacent carriage arms  105 . In an idle mode (e.g., when read-write operations are not being performed), the VCM  125  is actuated to rotate the carriage arms  105 , in a radially outward direction relative to the disks  115 , such that the head-gimbal assemblies  109  are parked or unloaded onto a ramp support  117  secured to the base  130 . 
     As shown in  FIG.  2   , another example of a carriage assembly  103  is shown. The carriage assembly  103  includes the head stack assembly  107 , which includes carriage arms  105 A-N, each having a corresponding one of a plurality of carriage-arm tips  106 A-N, and a plurality of head-gimbal assemblies  109 . For the sake of simplicity, only one head-gimbal assembly  109  of the plurality of head-gimbal assemblies  109  is illustrated and it is shown in exploded view adjacent to the carriage arms  105 A-N. However, it is noted that each one of the carriage arms  105 A-N may have another head-gimbal assembly  109  on an opposite side of the carriage arm  105 , that mirrors the head-gimbal assembly  109  shown (see, e.g.,  FIG.  3 A ). In some examples, only one head-gimbal assembly  109  is coupled to each one of the carriage-arm tip  106 A of the carriage arm  105 A and the carriage-arm tip  106 N of the carriage arm  105 N, and two head-gimbal assemblies  109  are coupled to each one of the carriage-arm tips  106 B-J of the carriage arms  105 B-J. In the current reference number nomenclature, ‘N’ represents any whole number to indicate that the carriage assembly  103  can have any whole number of corresponding features without departing from the essence of the present disclosure. 
     As shown in  FIG.  2   , the head stack assembly  107  includes eleven carriage arms  105 A-N. However, in other examples, the head stack assembly  107  can have fewer or more than eleven carriage arms. The head stack assembly  107  of  FIG.  2    includes a top-most carriage arm  105 A, nine middle carriage arms  105 B-J, and a bottom-most carriage arm  105 N. Each of the carriage arms  105 A-N has a carriage-arm tip at the distal region of the carriage arm. More specifically, the top-most carriage arm  105 A has a top-most carriage-arm tip  106 A, each one of the nine middle carriage arms  105 B-J has a carriage-arm tip  106 B-J, and the bottom-most carriage arm  105 N has a carriage-arm tip  106 N. Each one of the carriage-arm tips  106 A-N includes a swaging hole  108  that passes through the carriage-arm tip from a first side  111  of the carriage-arm tip to a second side  112  of the carriage-arm tip, where the second side  112  is opposite the first side  111 . The swaging hole  108  is centered about a swaging axis  110  which is perpendicular relative to an arm axis  113 , parallel to a length of each one of the plurality of carriage arm  105 A-N. 
     Each one of the head-gimbal assemblies  109  includes a baseplate  118 , a load beam  123 , and a flexure  141 . The baseplate  118  is utilized to directly interconnect the carriage arm  105  and the load beam  123 . More specifically, the baseplate  118  spans between and couples together the carriage-arm tip  106  of the carriage arm  105  and the load beam  123 . The baseplate  118  has a flange  119  and a swage boss  124 , protruding from the flange  119 . The flange  119  is a relatively flat plate and the swage boss  124  has an annular shape. The slider  142 , with at least one read-write head, is coupled to a distal end portion of the load beam  123  via a tip portion of the flexure  141 . 
     In one example, the baseplate  118  of the head-gimbal assembly  109  is a compression baseplate  118 A and configured to be coupled to the second side  112  of a corresponding one of the carriage arms  105 A-N. Accordingly, the swage boss  124  of the compression baseplate  118 A is a compression swage boss  126  that is configured to protrude upwards into the swaging hole  108  from the second side  112  of the corresponding one of the carriage arms  105 A-N. In another example, the head-gimbal assembly  109  has a tension baseplate  118 B (see, e.g.,  FIG.  3 A ) that is configured to be coupled to the first side  111  of a corresponding one of the carriage arms  105 A-N. Accordingly, the tension baseplate  1118 B has a swage boss  124  that is a tension swage boss  128  that is configured to protrude downwards into the swaging hole  108  on a corresponding one of the carriage arms  105 A-N. 
     A side, elevation view of a portion of one example of the carriage assembly  103 , after a swaging process, is shown in  FIGS.  3 A and  3 B . The top-most carriage arm  105 A is coupled (i.e. swaged) to a single one of the plurality of head-gimbal assemblies  109 . The head-gimbal assembly  109  swaged to the carriage arm  105 A includes a compression baseplate  118 A. The compression baseplate  118 A includes a compression swage boss  126  that is located within and protrudes upwards into the swaging hole  108  from the second side  112  of the carriage-arm tip  106 A of the carriage arm  105 A. The compression baseplate  118 A is annular and centered about the swaging axis  110 . Likewise, the bottom-most carriage arm  105 N is coupled (i.e., swaged) to one head-gimbal assembly  109 . The head-gimbal assembly  109  swaged to the carriage arm  105 N includes a tension baseplate  118 B. The tension baseplate  118 B includes a tension swage boss  128  that is located within and protrudes downwards into the swaging hole  108  from the first side  111  of the carriage-arm tip  106 N of the carriage arm  105 N. The tension baseplate  118 B is annular and centered about the swaging axis  110 . Each one of the middle carriage arms  105 B-J is coupled to two of the head-gimbal assemblies  109 . Accordingly, each one of the middle carriage arms  105 B-J is coupled to a first head-gimbal assembly  109 , having a tension baseplate  118 B and a tension swage boss  128 , and a second head-gimbal assembly  109 , having a compression baseplate  118 A and a compression swage boss  126 . 
     A respective one of the plurality of disks  115  is positioned between adjacent corresponding carriage arms  105 A-N, such that ten disks  115  are shown positioned between the eleven carriage arms  105 A-N. As shown in  FIG.  3 B , the disks  115  are spaced apart from each other by a distance defined as a disk pitch  133 . The disk pitch  133  is measured parallel to the swaging axis  110 , from a midpoint of a first disk  115  to the midpoint of a second adjacent disk  115 . In one example, in order to increase the number of disks  115  that can fit within a universally sized magnetic storage device  100 , without increasing the space within the interior cavity  114 , the disk pitch  133  can be decreased. In other words, the distance between each disk  115  can be shortened to allow more disks  115  within a magnetic storage device  100  having the same sized interior cavity  114  as previous designs. In some examples, in order to shorten the disk pitch  133  a lower profile swage boss  124  can be used. 
     Referring to  FIG.  4    and  FIG.  5    is a cross-sectional view of the carriage-arm tip  106  of the carriage arm  105  and two head-gimbal assemblies  109  with asymmetrical swage bosses, prior to swaging. Each one of the head-gimbal assemblies  109  includes a load beam  123  and a baseplate  118 . The first head-gimbal assembly  109  has a tension baseplate  118 B on the first side  111  of the carriage arm  105 . The tension swage boss  128  is located within the swaging hole  108  on the carriage-arm tip  106  and extends from the first side  111  of the carriage-arm tip  106  into the swaging hole  108 . The swaging hole  108  is centered about the swaging axis  110  and the tension swage boss  128  is annular about the swaging axis  110 . The tension swage boss  128  has a tension-boss inner diameter ID T  and a tension-boss outer diameter OD. 
     Additionally, the second head-gimbal assembly  109  has a compression baseplate  118 A on the second side  112  of the carriage arm  105 . The compression swage boss  126  is located within the swaging hole  108  on the carriage-arm tip  106  and extends from the second side  112  of the carriage-arm tip  106  into the swaging hole  108 . The compression swage boss  126  is also annular about the swaging axis  110 . The compression swage boss  126  has a compression-boss inner diameter ID C  and a compression-boss outer diameter OD. In one example, the carriage-arm tip  106  has a thickness such that the tension swage boss  128  and the compression swage boss  126  are spaced apart from each other (i.e., not in contact with each other). The tension swage boss  128  and the compression swage boss  126  are made of stainless steel, in one example. 
     In certain examples, the tension-boss inner diameter ID T  and the compression-boss inner diameter ID C  are equal. For example, the tension-boss inner diameter ID T  and compression-boss inner diameter ID C  can both be equal to or less than 1.51 mm. Alternatively, in some examples, the tension-boss inner diameter ID T  and the compression-boss inner diameter ID C  are not equal. For example, the tension-boss inner diameter ID T  can be less than the compression-boss inner diameter ID C . In one example, the tension-boss inner diameter ID T  is at least 0.02 mm less than the compression-boss inner diameter ID C . In yet another example, the tension-boss inner diameter ID T  is equal to or less than 1.49 mm and the compression-boss inner diameter ID C  is equal to or less than 1.51 mm. In some examples, the tension-boss outer diameter OD is equal to the compression-boss outer diameter OD. 
     The tension swage boss  128  includes an uppercut  137  and a tension-boss undercut  138 . The uppercut  137  extends radially outward, away from the swaging axis  110 , from a first backbore diameter BB 1  to a second backbore diameter BB 2 . In other words, the tension swage boss  128  converges, in the force direction  137  along the swaging axis  110 , from the second backbore diameter BB 2  to the first backbore diameter BB 1  and to the tension-boss inner diameter ID T . In one example, the second backbore diameter BB 2  of the tension baseplate  118 B is greater than the inner periphery  154  of the swaging hole  108  and the first backbore diameter BB 1  of the tension baseplate  118 B is less than the inner periphery  154  of the swaging hole  108 . In another example, the second backbore diameter BB 2  of the tension baseplate  118 B is greater than the tension-boss outer diameter OD and the first backbore diameter BB 1  of the tension baseplate  118 B is less than the tension-boss outer diameter OD. The uppercut  137  has an uppercut depth D 1  in a direction parallel to the swaging axis  110 . 
     The tension-boss undercut  138  extends radially, away from the swaging axis  110 , from the tension-boss outer diameter OD to a first undercut diameter TU D . The tension-boss undercut  138  has a tension-boss undercut depth D 2  in a direction parallel to the swaging axis  110 . 
     The portion of the tension swage boss  128  between the first backbore BB 1  and the tension-boss outer diameter OD defines a neck  129  of the tension swage boss  128 . During swaging, the tension swage boss  128  can rotate at the neck  129  (see, e.g.,  FIG.  7   ). 
     The compression swage boss  126  also includes a compression-boss undercut  140 . The compression-boss undercut  140  extends radially outward, away from the swaging axis  110 , from a compression-boss outer diameter OD to a second undercut diameter CU D . The compression-boss undercut  140  has a compression-boss undercut depth D 3  in a direction parallel to the swaging axis  110 . In one example, the compression undercut depth D 3  is greater than the tension undercut depth D 2 . 
     The tension baseplate  118 B has a tension baseplate thickness T TB . In one example, the tension-boss undercut depth D 2  is less than 50 percent of the tension baseplate thickness T TB . In another example, the tension-boss undercut depth D 2  is less than 24 percent of the tension baseplate thickness T TB . In yet another example, the tension-boss undercut depth D 2  is between 24 and 50 percent of the tension baseplate thickness T TB . The compression baseplate  118 A has a compression baseplate thickness T CB . In another example, the compression-boss undercut depth D 3  is greater than 50 percent of the compression baseplate thickness T CB . In yet another example, the compression-boss undercut depth D 3  is greater than 24 percent of the compression baseplate thickness T CB . In yet another example, the compression-boss undercut depth D 3  is between 24 and 50 percent of the compression baseplate thickness T CB . In some examples, the compression undercut depth D 3  is at least 1.5 times larger than the tension undercut depth D 2 . In yet another example, the compression undercut diameter CU D  is greater than the tension undercut diameter TU D . 
     The compression swage boss  126  also includes a third backbore diameter BB 3 . The portion of the compression swage boss  126  between the third backbore BB 3  and the compression-boss outer diameter OD defines a neck  131  of the compression swage boss  126 . During swaging, the compression swage boss  126  can both rotate and expand at the neck  131  (see, e.g.,  FIG.  7   ). In one example, the second backbore diameter BB 2  of the tension swage boss  128  is greater than the third backbore diameter BB 3  of the compression swage boss  126 . 
     The tension baseplate  118 B has a minimum thickness T 1 , that extends from the uppercut  137  to the tension-boss undercut  138 . The compression baseplate  118 A also has a minimum thickness T 2 , extending from an outer surface  144  of the compression baseplate  118 A to the compression-boss undercut  140 . In one example, the minimum thickness T 1  of the tension baseplate  118 B is less than the minimum thickness T 2  of the compression baseplate  118 A. 
     The tension swage boss  128  has a first height H 1  extending from an inner surface  145  of the tension baseplate  118 B to a tension-boss inner surface  146 . The compression swage boss  126  has a second height H 2 , extending from an inner surface  143  of the compression baseplate  118 A to a compression-boss inner surface  147 . In one example, the first height H 1  and the second height H 2  are equal. For example, the first height H 1  and the second height H 2  are less than 0.2 mm. In other examples, the first height H 1  and the second height H 2  are 0.19 mm. In yet other examples, the first height H 1  and the second height H 2  are not equal. The first height H 1  and the second height H 2  are a factor for determining how many disks  115  can fit within the magnetic storage device  100 . Accordingly, the first height H 1  and the second H 2  are of sufficient height to avoid excessive buckling of the swage boss  124 , resulting in a poor interference fit of the swage boss  124  and the carriage-arm tip  106 , while allowing a greater number of disks  115  to fit within the magnetic storage device  100 . 
     A swaging ball  136  is insertable into the swaging hole  108 . During the swaging process, the swaging ball  136  having a diameter D large enough to interfere with the tension-boss inner diameter ID T  and the compression-boss inner diameter ID C , is forced through the tension swage boss  128  and the compression swage boss  126  located within the corresponding swaging hole  108 . In one example, the tension-boss inner diameter ID T  is between 4 percent to 15 percent smaller than the ball diameter D. Likewise, in some examples, the compression-boss inner diameter ID C  is between 4 percent and 15 percent smaller than the ball diameter D. In another example, the tension-boss inner diameter ID T  is between 5 percent to 8 percent smaller than the ball diameter D. 
     During the swaging process, the swaging ball  136  is forced through the swaging hole  108  and an interference fit is formed between an outer periphery  150  of the tension swage boss  128  (e.g., the portion of the tension swage boss  128  defining the tension-boss outer diameter OD) and an inner periphery of the swaging hole  108 . Additionally, an interference fit is formed between an outer periphery  152  of the compression swage boss  126  (e.g., the portion of the compression swage boss  126  defining the compression-boss outer diameter OD) and the inner periphery  154  of the swaging hole  108 . In one example, the swaging ball  136  is forced in a force direction  137 , parallel to the swaging axis  110 , through the swaging hole  108 . After swaging, the outer periphery  150  of the tension swage boss  128  and the outer periphery  152  of the compression swage boss  126  tightly engages and is radially preloaded against the inner periphery  154  of the corresponding swaging hole  108  in the carriage-arm tip  106 . 
     Referring to  FIG.  6    is a cross-sectional view of a portion of the carriage assembly  103  during swaging, according to one example. The carriage assembly  103  includes a top-most carriage arm  105 A, two middle carriage arms  105 B and  105 C, and a bottom-most carriage arm  105 D. The carriage assembly  103  further includes six head-gimbal assemblies  109 , in the process of being coupled, by swaging, to the corresponding carriage arm  105 . 
     During the swaging process, the swaging ball  136  is forced axially through the plurality of swaging holes  108  in the force direction  137 . In one example, the swaging ball  136  is forced in the force direction  137  by a tool, not shown, that forces the swaging ball  136  in the force direction  137  through the plurality of swaging holes  108 . In some examples, additional tools may be used to help control the motion of the swaging ball  136  during the swaging process. Comb spacer tools  160  may be temporarily positioned between the carriage arm  105 A,  105 B,  105 C, and  105 D, respectively, to limit axial carriage arm deflection caused by the force applied in the force direction  137 . 
     The passing of the swaging ball  136  through the swaging hole  108  causes the tension swage boss  128  and/or compression swage boss  126  to plastically deform within the corresponding swaging hole  108  and cause an interference fit with the corresponding swaging hole  108 . For example, the swaging ball  136  has been forced axially through the swaging hole  108  in carriage arm  105 A and  105 B, such that each of the swage bosses with the swaging holes  108  have formed an interference fit with the corresponding swaging hole  108 . Accordingly, the compression swage boss  126  has formed an interference fit with the carriage arm  105 A and the tension swage boss  128  and the compression swage boss  126  has formed an interference fit with the carriage arm  105 B. By contrast, the swaging ball  136  has not yet been forced axially through the swaging hole  108  in carriage arms  105 C and  105 D. Therefore, a radial clearance C exists between the inner periphery  154  of the swaging hole  108  and the corresponding swage bosses in carriage arms  105 C and  105 D. 
     In some examples, the swaging process is performed with a single swaging ball  136  and a single pass through the carriage assembly. Multi-pass swaging, where the necessary total radial plastic deformation is created by swaging more than one time with progressively larger swage balls and/or by forcing the swage ball(s) through the swage holes in alternative directions, can be a time consuming and an expensive process. Accordingly, obtaining a good interference fit using a single swage boss and a single pass is preferred in some instances. 
     Referring to  FIG.  7   , a cross-sectional view of the carriage-arm tip  106  and two head-gimbal assemblies  109  is shown. During swaging, a number of forces are generated in the head-gimbal assemblies  109  and the carriage-arm tip  106 . In order to avoid a poor interference fit between the swage bosses and the carriage-arm tip  106  from forces such as excessive buckling, baseplate deformation, carriage-arm tip deformation, and residual stress within the carriage-arm tip, it can be beneficial to balance the forces during the swaging process. Accordingly, the tension swage boss  128  and the compression swage boss  126  have asymmetrical profiles, such that the stresses along axis  170 , perpendicular to the swaging axis  110  are symmetrical during swaging. Symmetrical stress along axis  170  can minimize the carriage-arm tip  106  deformation, as well as, the baseplate deformation in the tension baseplate  118 B and the compression baseplate  118 A. 
     During the swaging process, the tension swage boss  128  rotates, along a rotation axis  162  at the neck  129  of the tension swage boss  128 . The rotation of the neck  129  causes the outer periphery  150  of the tension swage boss  128  to tightly engage (i.e., clamp) with the inner periphery  154  of the swaging hole  108 . The rotation along the rotation axis  162  causes the tension swage boss  128  to deform at an angle and downward, in a direction towards the axis  170 , to a maximum deformation height H D . In one example, the maximum deformation height H D  does not extend past the axis  170 . Additionally, a tensile force  163  is generated in the tension baseplate  118 B, during swaging. Due to the uppercut  137  in the tension swage boss  128 , the tensile force  163  is perpendicular to the swaging axis  110  and located adjacent the inner surface  145  of the tension baseplate  118 B, such that the tension baseplate  118 B is pushed tightly into the carriage-arm tip  106  to minimize tension baseplate  118 B deformation and carriage-arm tip  106  deformation. 
     Additionally, during the swaging process, the compression swage boss  126  experiences multiple forces, including a clamping force  166 , compression force  164 , and a buckling force  168 . The clamping force  166  forces the outer periphery  152  of the compression swage boss  126  against the inner periphery  154  of the swaging hole  108 . The compression force  164  forces the compression swage boss  126  at an angle away from the swaging axis  110  towards the outer surface  144  of the compression baseplate  118 A. The buckling force forces the compression swage boss  126  downward, parallel to the swaging axis  110  in the force direction  137 . Together, the clamping force  166 , the compression force  164 , and the buckling force  168  cause the outer periphery  152  of the compression swage boss  126  to tightly engage (i.e., clamp) with the inner periphery  154  of the swaging hole  108 . Additionally, a push force  169  is generated in the compression baseplate  118 A during swaging. The push force  169  is perpendicular to the force direction  137  in the compression baseplate  118 A and located adjacent the outer surface  144  of the compression baseplate. 
     Now referring to  FIG.  8   , one example of a method  300  of coupling a head-gimbal assembly  109  to a carriage arm  105  is shown. The method  300  includes (block  302 ) positioning a tension baseplate  118 B of a first head-gimbal assembly  109  on a carriage-arm tip  106  of a carriage arm  105 . A tension swage boss  128  is located within a swaging hole  108 , of the carriage-arm tip  106 , and is concentric with a swaging axis  110  of the swaging hole  108 . The method  300  also includes (block  304 ) positioning a compression baseplate  118 A of a second head-gimbal assembly  109  on a carriage-arm tip  106  of a carriage arm  105 , such that the carriage-arm tip  106  is sandwiched between the tension baseplate  118 B and the compression baseplate  118 A. A compression swage boss  126  is located within the swaging hole  108 , of the carriage-arm tip  106 , and is concentric with the swaging axis  110  of the swaging hole  108 . The compression swage boss  126  is spaced apart from the tension swage boss  128  along the swaging axis  110 . The method further includes (block  306 ) inserting a swaging ball  136  axially through the swaging hole  108  in an insertion direction and plastically deforming the tension swage boss  128  and the compression swage boss  126  to form an interference fit between an outer periphery  150  of the tension swage boss  128  against an inner periphery  154  of the swaging hole  108  and an interference fit between an outer periphery  152  of the compression swage boss  126  against the inner periphery  154  of the swaging hole  108 . 
     The tension swage boss  128  includes an uppercut  137  and a tension-boss undercut  138 . The uppercut  137  extends radially outward, away from the swaging axis  110 , from a first backbore diameter BB 1  to a second backbore diameter BB 2  and has an uppercut depth D 1 , in a direction parallel to the swaging axis  110 . The tension-boss undercut  138  extends radially, away from the swaging axis  110 , from the tension-boss outer diameter OD to a first undercut diameter TU D  and has a tension-boss undercut depth D 2 , in a direction parallel to the swaging axis  110 . The compression swage boss  126  comprises a compression-boss undercut  140 . The compression-boss undercut  140  extends radially outward, away from the swaging axis  110  from a compression-boss outer diameter OD to a second undercut diameter CU D  and has a compression-boss undercut depth D 3 , in a direction parallel to the swaging axis  110 . 
     Although described in a depicted order, the method may proceed in any of a number of ordered combinations. 
     In the above description, certain terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” “over,” “under” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object. Further, the terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise. Further, the term “plurality” can be defined as “at least two.” 
     Additionally, instances in this specification where one element is “coupled” to another element can include direct and indirect coupling. Direct coupling can be defined as one element coupled to and in some contact with another element. Indirect coupling can be defined as coupling between two elements not in direct contact with each other, but having one or more additional elements between the coupled elements. Further, as used herein, securing one element to another element can include direct securing and indirect securing. Additionally, as used herein, “adjacent” does not necessarily denote contact. For example, one element can be adjacent another element without being in contact with that element. 
     As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of” means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example, without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination. 
     Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to, e.g., a “second” item does not require or preclude the existence of, e.g., a “first” or lower-numbered item, and/or, e.g., a “third” or higher-numbered item. 
     As used herein, a system, apparatus, structure, article, element, component, or hardware “configured to” perform a specified function is indeed capable of performing the specified function without any alteration, rather than merely having potential to perform the specified function after further modification. In other words, the system, apparatus, structure, article, element, component, or hardware “configured to” perform a specified function is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the specified function. As used herein, “configured to” denotes existing characteristics of a system, apparatus, structure, article, element, component, or hardware which enable the system, apparatus, structure, article, element, component, or hardware to perform the specified function without further modification. For purposes of this disclosure, a system, apparatus, structure, article, element, component, or hardware described as being “configured to” perform a particular function may additionally or alternatively be described as being “adapted to” and/or as being “operative to” perform that function. 
     The schematic flow chart diagrams included herein are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one example of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. 
     The present subject matter may be embodied in other specific forms without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.