Patent Publication Number: US-8978431-B1

Title: Punch and method for piercing holes with a retention structure

Description:
TECHNICAL FIELD 
     This disclosure relates to an apparatus and method for punching holes in a hydro-formed part. 
     BACKGROUND 
     Holes are formed in tubular hydro-formed parts that may function, for example, as locator holes or for receiving fasteners. 
     Tubular parts may be hydro-formed in a die with a pressure medium, such as water, being injected inside a tubular blank to form the blank to a desired shape. The part may be pierced in the hydro-forming machine with a hydro-piercing tool. 
     A hydro-piercing tool includes a punch that is advanced to engage an outer surface of the part while the inner surface is supported by the pressure medium. Hydraulic cylinders are actuated to drive the punch through the part to form a hole. When the hole is formed a slug is removed from the part forming a hole. 
     Loose slugs created in the hydro-piercing process can create problems if not properly managed. Loose slugs can become trapped in the interior of the part and may cause a rattling noise. Loose slugs can damage the hydro-forming die if they are dislodged from the part and fall into the die. 
     Several systems have been developed in an effort to control slugs created in the hydro-piercing process. One proposal is to punch a slug leaving a short retaining tab attaching the slug to the part. The slug is then folded back on the tab into the interior of the part. This proposal may be acceptable for ductile steel materials, but is not suitable for other materials such as aluminum and high-strength steel. Folding the slug into the interior of the part on the tab when applied to aluminum may result in the slug being fractured from the part. In addition, edge cracks may tend to form on the part proximate the hole when the hole is formed. 
     Referring to  FIGS. 1A and 1B , a specialized punch is proposed that has two recessed portions for forming tabs that hold the slug in place after punching the hole. This punch may be used for aluminum but undesirable distortion may occur proximate the hole. This punch may not be well suited for circular holes. 
     This disclosure is directed to solving the above problems and other problems as summarized below. 
     SUMMARY 
     The disclosure provides a punch method and system for controlling slugs formed during hydro-piercing hydro-formed parts. 
     According to one aspect of this disclosure, a punch for a hydro-forming tool is disclosed. The punch comprises a shearing edge formed on an outer periphery of the punch that is partially recessed from a distal end of the punch and a cutting edge formed at the distal end of the punch inboard of the shearing edge. The punch further comprises at least two ramp surfaces provided between the shearing edge and the cutting edge. Each of the ramp surfaces extend about a portion of a periphery of the punch and extend at an angle from the distal end to a recessed portion of the shearing edge. 
     According to an alternative embodiment of the punch, each of the at least two ramp surfaces may extend perpendicular to a longitudinal axis of the punch in a radial direction between the cutting edge and the shearing edge. 
     According to an alternative embodiment of the punch, the at least two ramp surfaces may include three ramp surfaces that extend at a first incline angle and then at a second incline angle. The three ramp surfaces may be spaced 120 degrees apart. 
     The distal end may have a central portion and at least two outer portions extending outwardly from the central portion to the periphery of the punch. The at least two outer portions may be disposed at diametrically opposed locations on the central portion and may include a cut-off face extending between the cutting edge disposed on the outer portion and the ramp surface proximate the recessed portion of the shearing edge. The central portion may be circular in shape or may be elongated in shape having two semi-circular ends that are connected by flat sides. In the elongated central portion configuration, the two outer portions may be disposed at the semi-circular ends. 
     According to another aspect of this disclosure a method is disclosed for forming a hole in a part. The method comprises punching the part with a punch that has a cutting edge for cutting a slug in the part. A portion of the part is sheared to form an outer periphery of the hole outboard of the slug. Punching and shearing the part creates arms that connect the slug to the outer periphery of the hole. The punch advancing into the part bends the arms into the part and holds the slug in a recessed location on the part. 
     The method may further include detaching the arms from the part to remove the slug from the part and produce a finished hole. 
     According to other aspects of the method, the slug may be sheared by a shearing edge formed on a periphery of the punch. The punch may further include at least two ramp surfaces formed between the shearing edge and the cutting edge. The ramp surfaces may extend about a portion of the periphery of the punch and extend at an angle from the distal end to a recessed portion of the shearing edge. The ramp surface may engage the arms to bend the arms into the part during the punching operation. 
     According to another aspect of this disclosure, a slug control system is disclosed for a hydro-formed part. The system comprises a hydro-forming tool for forming the hydro-formed part and a hydro-piercing punch operable to partially form a hole having a predetermined periphery in the part. The hydro-piercing punch advances into the part to form a slug having a first arm and a second arm connecting a central portion of the slug to the periphery of the hole. The punch advances into the part to cause the first and second arms to partially sever from the part. The arms wrap around the periphery of the hole. The arms also extend from the periphery of the hole to the central portion of the slug. The punch when fully advanced causes the central portion, the first arm and the second arm to be retained in a recessed position on the part. 
     A tool maybe used to remove the slug from the part to produce a finished hole. 
     The above aspects of this disclosure and other aspects are described in greater detail below with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a prior art punch. 
         FIG. 1B  is a perspective view of a part having a slug formed by the prior art punch of  FIG. 1A . 
         FIG. 2  is perspective view of a part having holes formed according to one exemplary embodiment of the present disclosure. 
         FIG. 3  is a perspective view of a circular punch made according to one embodiment of the present disclosure. 
         FIG. 4  is a perspective view of an oval punch made according to an alternative embodiment of the present disclosure. 
         FIG. 5  is a perspective view of a circular punch made according to an alternative embodiment of the present disclosure that includes three ramp surfaces. 
         FIG. 6  is a perspective view of a circular punch made according to an alternative embodiment of the present disclosure that includes ramped surfaces that extend at two different inclined angles. 
         FIG. 7  is a side view of the punch shown in  FIG. 6 . 
         FIG. 8  is a perspective view of a slug formed in the part by the punch of  FIG. 4 . 
         FIG. 9  is a diagrammatic cross-sectional view of a hydro-forming tool. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
     Referring to  FIG. 2 , a portion of a hydro-formed part  10  is shown with a two-way locator hole  12  and a four-way locater hole  14 . The two-way locator hole  12  and four-way locator hole  14  are produced by the punch that is used in the disclosed method and system. 
     Referring to  FIG. 3 , one example of a punch  16  is shown for use with a hydro-forming tool. The punch  16  has a shank  20  attached to the hydro-forming tool (shown in  FIG. 9 ) and a distal end or tip  22  that is first to engage the part  10  during the punching process. The punch  16  may be circular as shown in  FIG. 3  or may be a different shape. The punch  16  has a shearing edge  24  formed on an outer periphery  26  of the punch  16 . A cutting edge  28  is formed on the punch  16  inboard of the shearing edge  24  and is disposed on the distal end  22  of the punch  16 . A ramp surface  30  is formed between the shearing edge  24  and the cutting edge  28 . The ramp surface  30  extends about a portion of the periphery  26  and extends at an angle from the distal end  22  to a recessed portion  32  of the shearing edge  24 . 
     The punch  16  includes two symmetrical ramp surfaces  30 . Each of the two ramp surfaces  30  extends perpendicular to the longitudinal axis of the punch  16  in a radial direction to form a flat, angled surface that wraps around a portion of the periphery  26  of punch  16 . The ramped surfaces  30  provide a gradual cut into the part  10  and reduce distortion of the part  10  around the hole being cut. 
     The distal end  22  includes a central portion  34  and two diametrically opposed outer portions  36  extending outwardly from the central portion  34  to the periphery  26 . The central portion  34  may be circular in shape as shown in  FIG. 3  or may have an elongated shape as shown in  FIG. 4 . Each of the outer portions  36  includes a cut-off face  42  extending longitudinally between the cutting edge  28  disposed on the outer portion  36  and the recessed portion  32  of the shearing edge  24 . The cut-off face  42  extends radially between the central portion  34  and the outer periphery  26 . 
       FIG. 4  illustrates an oval punch having elongated central portion  34  and two semi-circular ends  38  that are symmetrical about the minor axis “M”. Two flat sides  40  extend between and connect the semi-circular ends  38 . Each of the outer portions  36  are disposed at the semi-circular ends  38  and extend radially between the ends  38  and the periphery  26  of the punch  16 . 
     Referring to  FIG. 5 , an alternative design of punch  16  is shown. The distal end  22  of the punch  16  includes a circular central portion  34  with three outer portions  36  spaced 120 degrees apart. Three ramp surfaces  30  are formed on the punch  16  and extend between adjacent outer portions  36 . Each of the ramp surfaces  30  are disposed radially between the center portion  34  and the outer periphery  26  and extend at an angle from a first edge  44  on the outer portion  36  to a cut-off face  42  formed on an adjacent outer portion  36 . 
     The ramp surface  30  may extend from the distal end  22  to a recessed portion  32  at a single linear angle, multiple linear angles, or along a continuously variable path. Changing the angle or angles of the ramp surface  30  allows the punch to be adapted for use with parts of different thicknesses.  FIGS. 6 and 7  illustrate the multiple linear angles alternative. Each ramp surface  30  extends between the distal end  22  and the recessed portion  32  at a first angle  48  and then at a second angle  50 . The multiple angle alternative is shown on a circular punch but it is equally applicable to non-circular punches. 
     Referring to  FIG. 8 , a part  10  post hydro-piercing is shown. The part  10  has a hole  60  and a slug  18  retained within the hole  60 . The slug  18  has a recessed central portion  52  connected to first and second arms  54 , both of which are connected to the part  10  at the periphery  58  of the hole  60  and retain the slug  18  on the part  10 . Each of the arms  54  have a first end  62  connected to the hole periphery  58  and a second end  64  connected to the central portion  52 . The first end  62  is completely detached from the central portion  52  and the second end  64  is completely detached from the part  10 . The first end  62  includes an end-face  66  extending radially inward from an outer side  68  proximate the hole periphery  58  to an inner side  70  of the arm  54 . 
     Referring to  FIGS. 4 and 8 , the punch  16  is driven into the part  10  partially forming the hole  60  and the slug  18 . The punch  16  is initially advanced to cause the distal end  22  to first engage the part  10 . The cutting edges  28  cut the part  10  to begin formation of the central portion  52 , and the inner side  70  of the arms  54 . The shearing edge  24  disposed at the periphery  26  of the outer portions  36  shear a portion of the part defining the periphery of the hole  60 . 
     The shearing edge  24  disposed on the ramp surfaces  30  is advanced to shear the part  10  further cutting more of the periphery of the hole  60  and forming the outer-side  68  of the arms  54 . The cutting edge  28  cuts the inner-side  70  to partially detach a portion of the arms  54  from the central portion  52 . The ramp surfaces  30  bend the arms. The arms  54  are bent into the hole  60  as the inner side  70  and outer side  68  of the arms  54  are formed by the shearing and cutting edges of the punch  16 . The arms  54  bend at an angle corresponding to the angle of the ramp surfaces  30  and have a similar shape. The cutting edge  28  disposed along the cut-off face  42  of the punch  16  cuts the end-face  66  of the slug  18  and creates a gap  72  between the first end  62  of the first arm  54  and the second end  64  of the second arm  54 . 
     The central portion  34  of the punch  16  pushes the central portion  52  of the slug into a fully recessed position upon full advancement of the punch. The cutting edges  28  partially cut the inner side  70  of the arms  54  except at the second end  64  where the part  10  is not cut to ensure a strong connection between the arms  54  and the central portion  52 . The shearing edge  24  has at least partially cut the hole  60  except at the first end  62  where the slug  18  is not cut to ensure a strong connection between the arms  54  and the part  10 . 
     Referring to  FIG. 9 , a hydro-forming tool  74  is shown for use with the slug control system. The tool  74  includes a first die  76  and a second die  78 . The tool  74  is opened and a part  10  is placed between the first die  76  and the second die  78 . The tool  74  is closed and a fluid, such as water, is supplied under high pressure inside the part  10  to form the part  10  into the desired shape. After the part  10  is formed, the tool  74  actuates the hydro-piercing punch  16  to partially form the hole  60  with the slug  18  being retained inside the part  10 . The part  10  is then removed from the tool  74 . The slug  18  may then be removed by a manual tool or a robotic system. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. The words used in the specification are words of description rather than limitation. Changes may be made to the illustrated embodiments without departing from the spirit and scope of the disclosure as claimed. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts.