Patent Publication Number: US-6986301-B2

Title: Punch for a ductile material joining tool

Description:
BACKGROUND 
   a. Field of the Invention 
   The present invention relates to a punch for use in a tool for clinch joining ductile materials, such as metal sheets, and in particular to a punch for use with a lanced clinch joiner or a round clinch joiner. 
   b. Related Art 
   It is known to join a plurality of sheets of ductile material by causing these to be deformed into an interlocking configuration in a local area. Such joins are made by ductile material joining tools comprising a die with an aperture that is opposite a punch assembly comprising a punch. The punch has a punch tip, which may have a flat or rounded punch surface. The edges of the punch surface may be radiused, chamfered, or sharp. The punch itself may be surrounded by a stripper mechanism to facilitate removal of the punch from the deformed ductile material. Layers of ductile material are sandwiched between the punch assembly and when the punch tip punch is pressed towards the aperture, material is drawn into the aperture. The material undergoes plastic deformation in the aperture to flow into a shape in which two or more layers are interlocked, for example by the forming of one layer around another layer. 
   The die aperture normally has a base with an anvil having an anvil surface and at least two side walls formed from movable blades. The blades are generally transverse to the anvil surface and extend in the direction in which the die and punch are pressed together. The blades help define the local area, for example a circular, square or rectangular area, in which the deformation of the layers of sheet material takes place. Once the material has been drawn and flows into the aperture, the blades move away from each other in a radial direction as the sheet material is compressed it flows laterally. Some types of die blade pivot outwards about a pivot mechanism below the level of the anvil surface. The pivot mechanism has a pivot axis or pivot point below and laterally outside an edge of the anvil surface. 
   A circular die and punch can be used to form a clinch joint in which sheet material is symmetrically deformed both axially and radially to form a leak-proof button, for example as disclosed in patent documents U.S. Pat. No. 5,150,513 and EP 1 055 467 A2. A square or rectangular die and punch can be used to form a trapezoidal clinch joint (also called a lance joint), in which the sheet material is cut through by the punch along a pair of parallel opposed lines, with the layers of sheet material deformed laterally outwards underneath each of the cuts, as disclosed in patent document GB 2,334,474. The present invention relates a punch for forming these and other types of joints in layers of ductile material. 
   The lifetime of a punch assembly is limited essentially by wear of the punch tip, either of the punch surface itself or edges to the punch tip. Such wear can be minimised if the punch tip is made from hardened steel (62 to 64 RC), but this increases the possibility of the punch tip breaking if the punch is not properly aligned with the die. The clearance between the punch tip and die blades for a lanced joint is normally very close, for example of the order of 50 μm for a 3 mm width punch tip used to join two pieces of 0.7 mm thick metal. The punch tip may therefore be damaged in use if it is not properly aligned with the die. 
   The corner of the die blade facing inwards to the die recess normally forms a sharp edge of about 90°, but this will become dull with excessive use. When clinch joining hard metals, such as stainless steel, the lifetime of a die blade may be as short as 10,000 to 20,000 cycles. In order to maintain join quality, it is necessary to keep to a conservative schedule for changing die blades, which adds to manufacturing cost. 
   When a punch tip becomes worn or damaged, the punch can be removed from the punch assembly and replaced with a new punch. However, because the punch is made from precision machined and hardened steel, each punch is relatively expensive. In addition, a stock of new punch tips may have to be maintained in order to avoid disruption in a production environment. The need to maintain a stock of punches adds to manufacturing cost, particularly if more than one type of punch is to be used with a particular punch assembly. 
   It is an object of the present invention to provide a more convenient punch for use in a tool for joining ductile materials. 
   SUMMARY OF THE INVENTION 
   According to the invention, there is provided a punch for use in a tool for joining ductile materials, comprising a punch body formed around a punch axis, two punch tips extending in opposite directions from the punch body along the punch axis, each punch tip having a punch surface that extends transversely to the punch axis, wherein the punch body has one or more load engagement features by which a punch force for joining ductile materials may be imparted to the punch body along the punch axis so that one or the other of the punch tips may bear against said ductile material. 
   The invention therefore provides a punch that may be used in such a way that the punch force is not borne by the punch tip not in use. 
   The invention also provides a punch assembly for use in a tool for joining ductile materials, comprising a punch, and a punch holder to which the punch may be removably secured, the punch being according to the invention and the punch holder having a load application feature that in use imparts via the load engagement feature said force to the punch body along the punch axis, wherein the punch can be removably secured to the punch holder in either a first orientation or alternatively in a second orientation to dispose respectively one or the other of the punch tips for use to join ductile materials by application of said imparted force along the punch axis. 
   The invention further provides a ductile material joiner for joining two or more layers of ductile material, for example in a round clinch joint or in a lanced clinch joint, comprising a die and a punch assembly with a punch tip disposed in use towards the die, wherein the die has a die aperture matching the punch tip, and the punch assembly is according to the invention. 
   The invention provides cost savings in manufacture of the punch, compared with two conventional punches that each have just one punch tip. This is because it is easier and quicker to fabricate two oppositely directed punch tips on a single punch body, rather than two such tips on different bodies. In addition, because such punch tips normally undergo a final hardening and plating process, cost is saved by halving the number punches which have to hardened and plated. 
   The punch holder may have a recess, for example a cylindrical bore, so that when the punch is secured to the punch holder in either the first orientation or the second orientation, one of said punch tips is retained within the recess while the other of the punch tips may be used to join ductile materials. 
   The punch tips, particularly if the tips are hardened, could be damaged by forces exerted in use by the punch holder. Because such forces are borne by the load engagement feature, rather than the punch tip not in use, the unused punch tip is thereby protected from wear or damage. 
   The load engagement feature may be any feature suitable for transmitting forces used in joining ductile material, for example a projection from the punch body, or a recess in the punch body. In the preferred embodiments of the invention, the load engagement feature is one or more shoulders on the punch body. Such shoulders may be a step in the outer profile of the punch, a protruding flange, or a step in the punch body. The or each shoulder may extend transversely, at least to some extent, from the punch axis. 
   In a preferred embodiment of the invention, a first shoulder and a second shoulder each extend perpendicularly to the punch axis. The shoulders are arranged so that in use a force may be applied either to one of the said shoulders to cause the punch to exert a pressure or to move in a first direction along the punch axis, or to the other of said shoulders to cause the punch to exert a pressure or move in a second direction along the punch axis. 
   When the punch tips face in directly opposite directions, the punch when secured to the punch holder in the first orientation is 180° rotated with respect to the punch when secured to the punch holder in the second orientation. 
   Preferably, the assembly comprises a load spacer which extends between the load engagement feature and the load application feature when the punch is secured to the punch holder. The dimension of the load spacer along the punch axis may be altered, either by fitting a different load spacer to the punch assembly or, for example, by grinding down the length of the load spacer. Such an adjustment is useful in order to vary the length and therefore stoke and pressure exerted by the punch tip. 
   In the preferred embodiments of the invention, the load engagement feature is a shoulder surrounding the punch tip within said recess, the punch tip having one or more side walls extending from the shoulder to the punch surface, and the load spacer having a clearance fit with the or each punch side wall. 
   The load spacer may also be used to help adjust or to set a correct rotational orientation of the punch relative to the punch holder or assembly. In one embodiment of the invention, the load spacer may have a projection that extends transverse to the punch axis to facilitate the making of said adjustment to the rotational orientation of the load spacer. 
   Preferably, the load spacer has one or more location features that are located with one or more matching features of the punch so that the rotational orientation of the punch about the punch axis may be adjusted by making a corresponding adjustment to the rotational orientation of the load spacer. 
   If the punch body has an essentially circular cross-section in a plane perpendicular to the punch axis then, prior to being secured to the punch holder, the punch may be rotated about the punch axis with respect to the punch holder. If at least one of the punch tips has a non-circular cross-section, for example a square or rectangular cross-section, in a plane perpendicular to the punch axis, the rotational orientation of said non-circular cross-section may then be adjusted by rotating the punch about the punch axis prior to securing the punch in the punch holder. 
   The invention further provides a method of servicing a punch assembly for use in a tool for joining ductile materials, when the punch assembly is according to the invention, the method comprising the steps of: 
   i) removing the punch from the punch holder when the one of said punch tips disposed for use to join ductile materials has become worn or damaged; 
   ii) returning the punch to the punch holder with the relative orientation of the punch to the punch assembly altered so that the other of said punch tips is disposed for use to join ductile materials. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in further detail, by way of example to the accompanying drawings, in which: 
       FIG. 1  is a partial cross-section view of a ductile material joiner according to a first embodiment of the invention, for joining two or more layers of ductile material, comprising a die and a punch assembly with a punch tip disposed in use towards the die while being used to form a lanced joint in two sheets of ductile material; 
       FIG. 2  is an enlarged partial cross section view of a part of  FIG. 1 , showing the punch tip and die in greater detail; 
       FIG. 3  is a simplified schematic representation of a part of a punch assembly according to a second embodiment of the invention, similar to that of  FIG. 1 , showing a double-ended punch with a cylindrical punch tip suitable for making a round clinch joint, secured within a punch holder; 
       FIGS. 4 ,  5  and  6  are, respectively, two side views and an end view of the punch of  FIG. 3 ; 
       FIG. 7  is a simplified schematic representation similar to that of  FIG. 3 , showing a punch according to a third embodiment of the invention, showing a double-ended punch with a rectangular punch tip suitable for making a lanced joint, secured within a punch holder; 
       FIGS. 8 ,  9  and  10  are, respectively, two side views and an end view of the punch of  FIG. 7 ; and 
       FIGS. 11 ,  12  and  13  are, respectively, two side views and an end view of a load spacer used to set the rotational orientation of the punch of FIG.  7 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a first embodiment of a ductile material joiner  1  according to a first embodiment of the invention. The joiner comprises a punch assembly  2  and a die assembly  4 . The punch assembly  2  and die assembly  4  are aligned along common punch axes  5 , 6 . Between the punch assembly  2  and die assembly  4  are a pair of thin ductile metal sheets  7 , 8  which are aligned transverse to the punch axes  5 , 6 . The sheets  7 , 8  are in contact along a common interface  9 . 
   In a sheet material joining operation, the punch assembly  2  is brought towards the pair of sheets  7 , 8  along a longitudinal direction as indicated by movement arrows  10  until a forward hollow stripper tip  12  of the punch assembly  2  comes into contact with an upper one of the metal sheets  7 , thereby pressing the other lower metal sheet  8  against a base plate  14  surrounding the die assembly  4 . The base  14  plate has a recess  15  in which the die assembly  4  is removably seated. 
   The punch assembly  2  has a lower cylindrical housing  16  referred to herein as a stripper can. The part of the stripper can  16  away from the metal sheets  7 , 8  has an open end  17  within which an open end  18  of a generally cylindrical punch holder  25  is secured by means of a set screw  23 . The other end  19  of the stripper can  16  has a radially inwards directed lip  20  which terminates in a central circular aperture  21  from which the stripper tip  12  extends. The stripper tip  12  has an outwardly directed flange  22  inside the stripper can  16 . An outer cylindrical surface  24  of the stripper tip  12  is a close sliding fit with the matching cylindrical aperture  21  of the stripper can lip  20 . In addition, the stripper tip flange  22  has an outer cylindrical surface  26  which has a close sliding fit with an inner cylindrical surface  27  of the stripper can  16 . The stripper tip  12  is therefore free to slide axially with respect to the stripper can  16  along the longitudinal direction  10 . 
   The sliding fit of the stripper tip  12  within the stripper can  16  is limited in an outwards direction by contact between the stripper can lip  20  and the stripper tip flange  22 . A coil spring  28 , shown schematically in  FIG. 1 , is retained within the stripper can  16  between the punch holder  25  and the stripper tip flange  22 . The coil spring  28  biases the stripper tip  12  outwards so that in a rest condition the stripper tip flange  22  remains in contact with the stripper can lip  20 . The axial sliding movement of the stripper tip  12  with respect to the stripper can  16  is limited in an axially inwards direction by compression of the spring  28  against the punch holder  25 . 
   A double-ended punch  30  is axially centered on the punch axis  5 . The punch  30  has a body portion  31  with a cylindrically stepped outer surface, a lower and upper third of which  29 , 29 ′ have the same dimensions with a reduced diameter compared with a central third  39 . The central portion  39  of the punch body  31  makes a tight siding fit inside a cylindrical bore  32  of the punch holder  25 . The punch  30  is secured to the punch holder  25  by a securing bolt  33  that is threaded through a tapped hole  35  in the punch holder  25  to engage with a flat  38  on the central portion  39  of the punch body  31 , so that the punch  30  extends axially inside the punch holder  25  and along the centre of the stripper can  16  into the stripper tip  12 . 
   The upper and lower thirds  29 , 29 ′ of the punch body  31  each terminate at a right-angled shoulder  41 , 41 ′, in the form of a surface that extends inwardly towards a rectangular (or square) punch tip  34 , 34 ′. The shoulders  41 , 41 ′ therefore define respective boundaries between the punch body and the punch tips  34 , 34 ′, and the shoulder at each boundary extends in a ring around the respective punch tip  34 , 34 ′. Each punch tip  34 , 34 ′ is unitary with the punch body and extends from the punch body  31  in opposite directions centered along the punch axis  5 , and each has a flat punch surface  11 , 11 ′ that extends perpendicularly to the punch axis  5 . 
   One punch tip  34  protrudes in use through the stripper tip  12 , while the other punch tip  34 ′ is concealed within the cylindrical bore  32  of the punch holder  25 . The concealed punch tip  34 ′ is partially surrounded by a load spacer  50 , which has an outer surface  51  matching the width of the bore  32 , and a rectangular inner surface  52  matching rectangular side walls  58 ′ of the punch tip  34 ′. The load spacer has parallel upper and lower surfaces  53 , 54  that contact respectively a flat end surface  55  of the bore  32  and the shoulder  41 ′ surrounding the punch tip  34 ′. The spacing between the parallel upper and lower surfaces  53 , 54  of the load spacer  50  is greater than the extension of the punch tip  34 ′ from the shoulder  41 ′, so that the punch surface  11 ′ of the concealed punch tip  34 ′ is free from contact with any surfaces within the punch holder  25 . This helps to protect the concealed punch surface  11 ′ from damage or wear. 
   The stripper tip  12  terminates in a neck  36  with a rectangular inner surface  37  that has a clearance fit with the rectangular side walls  58  of the protruding punch tip  34 . 
   The operation of the punch assembly  2  to join ductile material  7 , 8  will now be described. When the punch assembly  2  is moved  10  up against the metal sheet  7  the stripper tip  12  comes first into contact with the upper metal sheet  7 . Further movement  10  then causes the stripper tip  12  to slide axially with respect to the stripper can  16 , with the result that the spring  28  begins to be compressed whilst the protruding punch tip  34  continues with the motion  10  towards the metal sheet  7 . 
   As this is happening, the base  14  plate and the die assembly  4  provide a restoring force against the other metal sheet  8 . Most of the restoring force is provided through the die base plate  14 . 
   As shown most clearly in  FIG. 2 , the die assembly  4  has a unitary die body  40  which is rectangularly symmetric about the die axis  6 . The die body  40  has at one end a lower stem  42  that in use is seated in a tool holder (not shown) to which the base plate  14  is also securely affixed. At the opposite end of the die body  40  is a die anvil  44  with a flat anvil surface  46 . 
   A pair of die blades  56 , 57  are arranged either side of the die anvil  44 , which has a similarly rectangular cross-section shape. Each die blade  56 , 57  extends longitudinally above and below the anvil surface  46  and forms with the anvil surface  46  a rectangular die aperture  66  for the punch tip  34 . 
   The constricted rectangular die aperture  66  may be between 4 mm to 12 mm in length along a long axis, for example perpendicular to the drawing if  FIG. 2 , in which case the dimension of the recess  15  in the base plate  14  will be between, respectively, 8 mm to 18 mm. The width of the aperture  66  between the die blades  56 , 57  may then be between 2 mm to 8 mm. The depth of the aperture will depend on the separation between the die blades and thickness of sheet material to be joined, but typically will be between 0.5 mm to 2 mm. The die blades  56 , 57  are flush to 0.05 mm below the surrounding base plate  14 , so that that the die blades may pivot outwards as the metal layers  7 , 8  are compressed by the punch tip  34  against the anvil surface. 
   The die blades  56 , 57  are biased against the die anvil  44  to constrict the die aperture  66  by a spring biasing means  80 , seen most clearly in FIG.  2 . The biasing means  80  are under tension even when the die blades  56 , 57  are against the die anvil  44 . 
   The type of joint formed by the die tool  1  is a lanced type joint in which sheet material  7 , 8  is cut along two parallel lines formed by the scissor-like contact between each die blade and the punch tip  34 . Compression of the ductile sheet materials  7 , 8  in the longitudinal direction into the die aperture  66  and against the anvil surface  46  by the die punch tip surface  11  causes the sheet materials  7 , 8  to shear and then to flow mainly in two opposite lateral directions towards each die blade  56 , 57 . This flow causes the die blades  56 , 57  to be pushed outwards and the sheet materials  7 , 8  to flow underneath the cuts initially formed in the materials, in a process referred to as a “drawing process”. 
   The forces involved in the drawing process will depend on the ductility of the material, but will usually be substantial, for example of the order of  1  tonne. This force is imparted from the flat end surface  55  of the punch bore  32  to the punch body  31  via the load spacer  50  and the shoulder  41 ′. In the terminology of the claims, the flat end surface  55  of the bore  32  is an example of a load application feature and the shoulder  41 ′ is an example of a load engagement feature, the load being transmitted between the two by the load spacer  50 . The load spacer protects the unused punch tip  34 ′ from any damage or wear that might otherwise be caused by such forces if these forces were imparted via the unused punch tip  34 ′. 
   When the longitudinal pressure is relieved, the die punch tip  34  is withdrawn under the action of the coil spring  28  that was compressed in the drawing process. The punch tip  34  is then removed from the upper metal sheet  7 , and at the same time the die  4  is removed from the lower metal sheet  8 , whereupon each die blade  56 , 57  springs back against the die anvil  44  under the biasing action of the spring biasing means  80 . 
   The cutting action will, over time, cause wear on the cutting die blades  56 , 57 , which would then be replaced with new die blades. The punch tip will also become worn. 
   The invention permits the double-ended punch  30  to be reoriented so that the second punch tip  34 ′ may be used. The set screw  23  is first removed, allowing the stripper can  16 , stripper tip  12  and spring  28  to be separated form the punch  30  and punch holder  25 . Then, the securing bolt  33  is loosened, allowing the punch  30  to be withdrawn from the punch holder  25 . Because the punch is symmetric about a central point  60  on the punch axis  5 , the second punch tip  34 ′ can be oriented for use by inverting the punch  30  by 180° relative to the punch holder  25 . The punch  30  is then reinserted into the punch holder  25  with a second flat  38 ′ positioned so that when the securing bolt  33  is tightened, the punch  30  is secured within the holder  25  with the second punch tip  34 ′ oriented for use. Finally, the stripper can  16 , stripper tip  12  and spring are reassembled and reconnected to the punch  30  and punch holder  25 . 
     FIGS. 3  to  6  show in a simplified schematic representation, a second embodiment  102  of the punch assembly in which components similar to those of the first embodiment  2  are indicated by reference numerals incremented by 100. Also shown schematically are other components of the punch assembly that work in the same manner as described above, in particular, the stripper assembly  116 . 
   The second embodiment  102  differs from the first embodiment  2  in that the punch  130  has a pair of cylindrical punch tips  134 , 134 ′, suitable for making a circular clinch joint in sheets of ductile material. Each shoulder  141 , 141 ′ is therefore-annular in shape, and the load spacer  150  has cylindrical outer and inner surfaces  151 , 152 . 
     FIGS. 7  to  9  show in a simplified schematic representation, a third embodiment  202  of the punch assembly in which components similar to those of the first embodiment  2  are indicated by reference numerals incremented by 200. Also shown schematically are other components of the punch assembly that work in the same manner as described above, in particular, the stripper assembly  216 . 
   The third embodiment  202  is similar to the first embodiment  2  in that each punch tip  234 , 234 ′ is generally rectangular in a cross-section perpendicular to the punch axis  205 . The punch tips  234 , 234 ′ extend, however, in one direction fully to the cylindrical outer surface of the punch body  231 . Each punch tip also has a pair of chamfered edges  90  either side of a nearly square punch surface  211 , 211 ′. This type of punch tip is well known in the art, and is suitable for making a trapezoidal lance joint. The double-ended punch  230  can be inverted to present a fresh punch tip  234 ′ in the same way as described above. 
   The main difference between the third embodiment  202  and the first embodiment  2  is the form of the load spacer  250 , shown in more detail in  FIGS. 11  to  13 . Each shoulder  241 , 241 ′ does not extend in a ring around the punch tip  234 , 234 ′, but rather is formed in two separate halves each with a similar arcuate shape having one curved side truncated by a straight base. Because the bore  232  of the punch holder  225  is essentially cylindrical, it is not possible for the load spacer to extend fully around the concealed punch tip  234 ′. The punch holder therefore has an opening (not shown) that extends perpendicular to the plane of the drawing in  FIG. 3  into the cylindrical bore  232 , so that the load spacer  250  can be inserted into the bore  232  in a direction perpendicular to the punch axis  205 . 
   As shown in  FIGS. 11  to  13 , the load spacer therefore has an elongate rectangular body  91  extending along an axis  92 , and having a square or rectangular cross-section. A pair of similarly shaped rectangular fingers  95  extends axially from the load spacer body  91 , spaced equidistantly on opposite sides of the axis  92 . In use, the fingers  95  are inserted into the cylindrical bore  232  to serve as the load transmitting element between the punch holder  225  and punch shoulder  241 , 241 ′. The outer spacing of the finger  95  matches the inner spacing of the bore  232 , and the inner spacing between the fingers  95  matches the width of the rectangular punch tip  234 , 234 ′. The benefit of this is that the load spacer  250  is rotationally aligned to the bore  232  about the punch axis  205 , and each the punch tip  234 , 234 ′ is aligned to the load spacer  250 . This therefore sets the rotational orientation of the rectangular punch tip about the punch axis  205 , and therefore helps to prevent misalignment between the punch tip  234 , 234 ′ and a similarly shaped rectangular die aperture, such as the die aperture  66  shown in FIG.  2 . 
   Alternatively, there may be some play between the load spacer outer surfaces  251  and the bore  232  so that the load spacer body  91  can be moved to rotate the load spacer  250  and hence punch  230  about the punch axis  205  in order to adjust the rotational orientation of the punch tip  234 . In this case, the load spacer can be fixed in the correct orientation by a fixing bolt through an aperture  98  in the load spacer body  91 . 
   As with the other embodiments, the longitudinal extent of the load spacer  250  can be altered, for example by grinding, in order to vary the position of the exposed punch tip  234 , or the pressure exerted by the punch tip. 
   It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately, or in any suitable combination. 
   The punches  30 , 130 , 230  and punch assemblies  2 , 102 , 202  described above can each be used with suitable conventional die assemblies. The deformation process in making the joint in ductile material is unaffected by the invention, which can therefore readily be implemented in existing punch machinery. The double-ended punch also provides a significant cost saving compared with two separate punches, and can also help reduce the time needed to change a worn punch tip, owing to the fact that for half of such changes it is not necessary to locate or retrieve another punch. The invention therefore provides a convenient and economical punch for use in a tool for joining ductile materials. 
   It is to be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately, or in any suitable combination. 
   It is to be recognized that various alterations, modifications, and/or additions may be introduced into the constructions and arrangements of parts described above without departing from the spirit or scope of the present invention, as defined by the appended claims.