Abstract:
A force generating apparatus includes a housing, a piston movably mounted in a cavity and a punch and die mounted in the housing. The punch and die are normally spaced apart to receive two overlapping sheets of metal. The piston moves a wedge against the punch toward the die in order to clinch two overlapping sheets together.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to metal working apparatuses and more particularly to hand held devices utilizing a mechanical multiplication scheme with a low pressure fluid.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    There is often a need to join two or more pieces of sheet material to form various assemblies and subassemblies. There are several ways of accomplishing this. One such way is to deform the sheet material to form an interlocking and leakproof clinched joint.  
           [0003]    In clinched joints, several pieces of sheet material are plastically deformed in such a manner that they are locked or pierced together. Depending on the thickness, strength, and/or the number of pieces of material to be joined, a great amount of force is required to accomplish this plastic deformation.  
           [0004]    An apparatus and method for accomplishing a clinched joint of sheet material are disclosed in commonly assigned U.S. Pat. Nos. 5,027,503, 4,910,853, 4,757,609, the disclosures of which are expressly incorporated herein by reference. As is disclosed in these patents, the sheets of material to be joined are placed between complementary die and punch members. A suitable press is then activated to provide the force and displacement necessary to deform the material between the die members thereby joining the sheets of material together.  
           [0005]    In the embodiments disclosed in the above U.S. patents, the dies are generally attached to relatively large presses thus requiring the sheets to be joined to be manipulated with respect to the press. In contrast, portable spot welding devices have been in existence for many years. These smaller devices allow for the joining tool to be manipulated with respect to the workpiece thereby making it easier to work with large workpieces. Smaller portable tools are available which can provide the necessary clamping force to join the sheets and which allow for manipulation of the joining tool with respect to the workpiece and thus allow for easier operations with larger workpieces. One such tool is a riveting tool shown in U.S. Pat. No. 2,313,843. This tool uses pneumatic pressure in a cavity to move a pair of pistons arranged in tandem to create a portable rivetor. The pistons move linearly in the cavity to urge a reciprocating toggle mechanism to move a punch in a bore that is substantially perpendicular to the axis of the cavity to urge a rivet toward an anvil in order to rivet the workpiece. While the tool is designed to be portable, it is bulky and the level of force that is generated by this tool is limited by the size of the cavity that can be incorporated into the tool while maintaining its portability.  
           [0006]    Another such tool is disclosed in commonly assigned U.S. Pat. No. 4,878,284, the disclosure of which is expressly incorporated by reference herein. This tool incorporates a pneumatic or hydraulic cylinder to provide the force and displacement necessary for sheet material joining and clamping. Unfortunately, the level of force generated by this device is limited by the size of the cylinder which can be incorporated into the tool while still maintaining the compact, light weight nature of a hand held portable tool.  
           [0007]    Still another such tool is described in U.S. Pat. No. 5,431,089 and also owned by the assignee of the present application. The device has a body and an anvil which is connected to the body. The body has an actuating chamber with a generally arcuate surface and a flat surface against which a ram is contained. The ram is made of spring sheet steel. In a relaxed state, the ram has a generally arcuate shape corresponding to the arcuate surface in the chamber with a forward tang that engages the punch. Air pressure is used to bear against the ram causing the ram to deflect and move the punch longitudinally toward the anvil. This provides a “toggle-like” mechanical advantage which creates a force multiplying effect.  
           [0008]    This device is limited by the size and shape of the actuating chamber and the size of the ram. Additionally, the device is complex and limited by the size of the cavity which can be encapsulated into the hand held tool while maintaining its compact and lightweight features.  
           [0009]    Thus, there is a need for a hand held device that is simple and inexpensive and yet provides a force multiplying effect that is not limited by the size of the actuating chamber to provide the displacement necessary in order to produce the force necessary to cold forming two or more sheets of metal and does not require a force intensifier as is common in the prior art.  
           [0010]    In accordance with the present invention, a joining apparatus provides an inexpensive and simple hand held device that deforms two or more overlapping workpieces with a low pressure fluid source in combination with a wedge shaped force multiplier.  
           [0011]    Another aspect of the present invention is directed to an apparatus adapted for cold forming or clinch joining at least two overlapping sheets of metal wherein the apparatus has a housing, a punch and a die member aligned on a central axis and normally spaced apart a sufficient distance to receive the overlapping sheets therebetween.  
           [0012]    In a further aspect of the present invention, the apparatus includes a piston movably mounted in the housing and a wedge between the piston and the punch. The wedge urges the punch along the central axis toward the die and against the two overlapping sheets of metal whereby the sheets are cold formed.  
           [0013]    The present invention apparatus is advantageous over conventional devices since the present invention provides a hand held device that has an inclined force multiplication device acting on the end of a punch to cold form sheets of metal that is simple and inexpensive to make and does not require a force intensifier. Additionally the device is compact, rugged, light weight and easy to operate.  
           [0014]    These and other features and advantages of the present invention will become apparent from the subsequent description and claims taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1 is a side view with a partial cross section of the apparatus according to the present invention with the die spaced apart from the punch;  
         [0017]    [0017]FIG. 2 is a side view with a partial cross section of the apparatus according to the present invention with the die against the punch;  
         [0018]    [0018]FIG. 3 is a cross-sectional view of the piston along line  3 - 3  in FIG. 1;  
         [0019]    [0019]FIG. 4 is a cross-sectional view of a wedge along line  4 - 4  in FIG. 2;  
         [0020]    [0020]FIG. 5 is a cross-sectional view of a spacer along line  5 - 5  in FIG. 2; and  
         [0021]    [0021]FIG. 6 is an exploded view of the top of the piston, spacer, wedge, and the rod and shaft of the hand apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    The present invention is described for illustrative purposes embodied in a pneumatically actuated hand held portable sheet material forming tool. It will be appreciated, however, that the principles of the present invention are readily adaptable to a number of manufacturing processes which involve force generation or joining including clinching, clamping, piercing and holding.  
         [0023]    FIGS.  1 - 6  show the preferred embodiments of a sheet material joining apparatus or force generating device  100  of the present invention. Apparatus or device  100  includes a body  10 , a punch member  24 , a piston  40 , an inclined force multiplication member  50  and a jaw  80 .  
         [0024]    Although only two pieces of sheet metal are shown in FIGS. 1 and 2 to be clinched, it is to be understood that more than two pieces may be clinched or joined depending on sheet thickness and/or sheet material properties. The sheets may be made of metal or polymeric material. The joint so formed, and the method and apparatus for forming it, are shown and described in the herein-above referenced U.S. Pat. Nos. 4,459,735 and 4,757,609, the disclosures of both of which are expressly incorporated herein by reference.  
         [0025]    Body or housing  10  has a contoured surface  12 , an actuating chamber  14 , a first central bore  16  and a second central bore  18 . Contoured surface  12  defines a hand grip and is mounted on a cover plate  13 . Cover plate  13  is conventionally fastened (not shown) to the body  10 . A seal (not shown) is sandwiched between cover  13  and body  10  to enclose and seal pneumatic pressure in chamber  14 . Actuating chamber  14  has a generally cylindrical shape with an oval cross-section for a purpose to be described later on. First central bore  16  is aligned with second central bore  18  and defines a central axis  11 . First central bore  16  has an open end and a first closed end  17 . Second central bore  18  also has an open end and a closed end  19 . First closed end  17  and second closed end  19  are adjacent but spaced apart from each other. A passage  15  extends axially along central axis  11  to communicate with the first and second bores  16 ,  18  respectively. Body  10  is preferably made of a light weight material such as aluminum or other suitable material.  
         [0026]    A punch member  24  is disposed in first central bore  16 . Punch member  24  has an axially extending shaft  22 , a radial groove  23  on its outer surface with an O-ring seal  27 . O-ring seal  27  is made of a suitable polymeric material such as nitrile and is disposed in the groove  23  to sealingly engage shaft  22  with inner radial surface of first bore  16  and to seal pneumatic pressure in body  10 . One end of shaft  22  has a punch die and the other end has an inclined end  26  with a threaded bore  28 . End  26  will be described in more detail later on.  
         [0027]    Rod  34  is disposed in passageway  15 . Rod  34  has a threaded end  35  which engages threaded bore  28  in punch member  24 . Rod  34  also has an opposite threaded end  37  which extends axially into second bore  18 . Spring  32  is placed in second bore  18  and surrounds rod  34  adjacent to threaded end  37 . Spring  32  is preferably a coil spring that abuts against closed end  19  of second bore  18 . Spring  32  is retained in second bore  18  by a washer  36  with a hole. Threaded end  37  extends through the hole in washer  36  and is engaged by threaded nut  38 . Spring  32  urges punch member  24  towards first closed end  17  in bore  16 . The biasing force of spring  32  is adjusted by the diameter of spring  32 , coil spring thickness and number of coils in spring  32  and by advancing threaded nut  38  on threaded end  37  axially toward or away from second closed end  19  of bore  18  as is well known in the prior art. A circular groove is formed in body  10  near passageway  15  and an O-ring seal is retained therein. The O-ring seal abuts against a cylindrical outer portion of rod  34  which is between ends  35 ,  37  respectively to sealingly engage rod  34  between first bore  16  and second bore  18  and to seal pneumatic pressure in body  10 .  
         [0028]    Piston  40  is disposed in actuating chamber  14 . Chamber  14  is located adjacent to but spaced away from bores  16 ,  18  respectively. Piston  40  has a cylindrical shape with an oval cross-section which generally corresponds to the shape of chamber  14  so that piston  40  travels axially along the axis of chamber  14  from one end adjacent to cover plate  13  to a second end adjacent but spaced away from bores  16 ,  18  respectively. Piston  40  has an outer rim with a medial annular groove  42 . Elastomeric seal  44 , which is made of a suitable polymeric material such as nitrile, is retained in groove  42  to sealingly engage inner radial side walls of chamber  14  and to seal pneumatic pressure therein. Piston  40  has a longitudinal slot  46  extending radially along top  43  of piston  40 . Slot  46  has an undercut  47  formed in piston  40  that connects with cavity  48  that is formed on one end of slot  46 . Piston  40  is made of aluminum or other suitable material.  
         [0029]    Inclined force multiplication member  50  is inserted into slot  46  in piston  40 . Member  50  includes a wedge  51 , a spacer  60  and half spacer  68 . Wedge  51  has a top planar portion, a pair of edges and a bottom portion. The top planar portion has a first inclined surface  52  and an opposite second inclined surface  54  as best shown in FIGS. 1, 2 and  6 . Bottom portion has a locking member  57  defining a T-shaped configuration which is inserted into slot  46  in the piston  40 . Wedge  51  is inserted into cavity  48  and then is slidingly positioned in slot  46  so that member  57  lockingly engages undercut  47  as best shown in FIG. 4. Wedge  51  thus can slide in slot  46  axially but is prevented from being disengaged from piston  40  because the extending arms of locking member  57  are captured in undercut  47  in slot  46 . Preferably, there are three wedges  51  inserted into slot  46  however, optionally there may be between one to five wedges  51  inserted therein. The angle β between a vertical axis and the inclined surfaces  52 ,  54  respectively is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the forming tool  100 , the force required to clinch the sheets and the number of wedges and spacers used. Returning back to FIG. 1, wedge member  51  extends axially from the top of piston  40  into cavity  20  formed in first bore  16  between end  26  of shaft  22  and closed end  17  of bore  16 . Wedge  51  has a notch  56  in the top portion to permit wedge  51  to slide past rod  34  and slidingly engage spacer  60  as wedge  51  is moved into cavity  20  by piston  40  as will be discussed later on.  
         [0030]    As is best shown in FIGS. 5 and 6, spacer  60  has a bore  66  and is formed in a wedge shape. Spacer  60  has a first slanted surface  62  on one side and a second slanted surface  64  on the opposite side. The angle β′ between a vertical axis and surfaces  62 ,  64  respectively is 5 degrees and may be between 3 to 7 degrees and optionally may be between 2 to 10 degrees depending on the length of the forming tool  100 , the force required to clinch the sheets and the number of wedges and spacers used. Similarly, the angle β″ from vertical axis for inclined end  26  is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the forming tool  100 , the force required to clinch the sheets and the number of wedges and spacers used.  
         [0031]    Spacer  60  is disposed in cavity  20  and rod  34  extends through bore  66  to capture spacer  60  in cavity  20 . The wedge shape of spacer  60  slidingly engages the inclined surface of wedge  51  to move shaft  22  axially along central axis  11  towards jaw  80 . Preferably, multiplication member  50  is lubricated with a suitable lubricating fluid such as grease or oil to reduce friction, or optionally, inclined surfaces  26 ,  52 ,  54  respectively and slanted surfaces  62 ,  64  respectively are chrome plated or coated with a layer of lubricious material such as polytetrafluoride or PTFE. Preferably, there are two spacers  60  and a half spacer  68  in cavity  20 . Optionally, the number of spacers  60  may be varied between one to four or alternatively, spacer  60  may be eliminated and only half spacer  68  inserted into cavity  20  where only one wedge  51  is used. Those skilled in the art will recognize that the angle of the surfaces  62 ,  64  respectively may be varied to increase or decrease the force multiplication and travel of the device as required.  
         [0032]    Half spacer  68  has only one inclined surface  67  to engage an inclined surface of wedge  51 . The other surface of spacer  68  abuts the closed end of bore  16 . Half spacer  68  also has a bore  69  to permit rod  34  to capture it in bore  16 . The angle β′″ from vertical of the inclined surface  67  is 5 degrees and may be between 3 to 7 degrees and optionally between 2 to 10 degrees depending on the length of the total  100 , the force required to clinch the sheets and the number of wedges and spacers used.  
         [0033]    Jaw  80  is secured to body  10  by a dowel and screw as is well known in the art. Jaw  80  has a die member  86 . As described in greater detail in the aforementioned U.S. patents, punch member  24  and die  86  are operable to plastically deform and thereby clinch a number of sheets of material upon translation movement of punch member  24  relatively towards die member  86 . Preferably, punch member  24 , die member, and multiplication member  50  are made of hardened steel or any other suitable material.  
         [0034]    A 4-way power valve  90  is disposed on contoured surface  12 . Valve  90  receives air from fitting  98  and it controls whether air is to be supplied to chamber  14  or optionally cavity  20 . Valve  90  communicates air supplied from a hose  97  and fitting  98  through bores  92 ,  94 ,  96  respectively to chamber  14  and alternatively supplies air through a bore (not shown) to cavity  20 . As noted, when air is supplied to chamber  16 , piston  40  moves upwardly toward bores  16 ,  18  respectively and wedge  51  slidingly engages spacer  60  and/or half spacer  68  to urge shaft  22  toward the jaw  80 . Conversely, when air is supplied to cavity  20 , wedge  51  slidingly engages spacer  60  and/or half spacer  68  and moves toward cover plate  13 . Spring  32  biases shaft  22  to move away from jaw  80  as piston  40  moves downwardly toward cover plate  13 . Compressed air flows from a source (not shown) and into hose  97  and fitting  98  and is supplied through a filter-regulator-lubricator (not shown) to pressurize trigger valve  90  on contoured surface  12  to cause valve  90  to pressurize chamber  14 .  
         [0035]    By way of a nonlimiting example, the force generation attributes of device  100  will now be described. The force generated by a wedge moving perpendicular to the axis of a punch is described by the following formula which is disclosed in page  109  of  Machinery&#39;s Handbook  (24 th  ed.) and is modified herein for the sake of clarity.  
         [0036]    Q=½ p cot β 
         [0037]    where: Q=mechanical force  
         [0038]    p=pneumatic force on the piston (pressure×area)  
         [0039]    β=is the half angle of inclination of the inclined surface relative to the axis of travel of the piston  
         [0040]    With air pressure of 80 psi and piston surface area of 18.9 sq. inches, and β=5 degrees,  
         [0041]    Q=½ (80×18.9) (cot 5°)=½ (1512) (11.43003)  
         [0042]    Q=8641 pounds of force  
         [0043]    Q=4.32 tons  
         [0044]    Thus, 80 psi of pressure on the piston generates 4.32 tons of force generation between the punch and die to form clinched metal sheets.  
         [0045]    The operation of force generating device  100  will now be described in detail with reference to FIGS. 1 and 2. Cold forming apparatus  100  is actuated by depressing valve  90  on hand grip  12 . Preferably, air pressure of approximately 80 to 100 psig flows from hose  97 , through fitting  98 , into valve  90  through bores  92 ,  94  and  96  and into actuating chamber  14 . Air pressure bears on bottom surface  41  of piston  40  causing piston  40  to move toward central axis  11 . This causes inclined surfaces  52 ,  54  respectively of wedge  51  to slidingly engage slanted surfaces  62 ,  64  respectively of spacers  60  and inclined surface  67  on half spacer  68  and inclined end  26  of shaft  22 . Thus, shaft  22  overcomes the biasing force of spring  32  and translates longitudinally along central axis  11  towards die member  86 . Sheet materials A, B are inserted between die  86  and punch  24  before actuation of apparatus  100 . When the apparatus is actuated, sheets A, B are plastically deformed or clinched as described in the aforementioned patents.  
         [0046]    Since piston  40  has a relatively large surface area on its bottom  41 , a large upward force is generated by the air pressure acting on this surface area. This force is exerted against wedge  51 , spacer  60 , half spacer  68  and inclined end  26  of shaft  22 . The upward force overcomes the biasing force of spring  32  acting on shaft  22  and causes wedge  51  to slide on slanted surfaces  62 ,  64  respectively of spacer  60 , the slanted surface of half spacer  68  and inclined end  26  of shaft  22 . Wedge  51 , spacers  60 , half spacer  68  and inclined end  26  cause the upward force of the air pressure acting on piston  40  to be translated into longitudinal movement of shaft  22 . Additionally, the force acting on piston  40  is multiplied as the movement of wedges  51  against spacer  60 , half spacer  68  and end  26  acting on their respective inclined/slanted surfaces as described earlier. This results in force multiplication that is sufficient to permit clinching of sheet materials A, B respectively when shaft  22  axially translates punch  24  to engage die  86 .  
         [0047]    After sheet materials A, B respectively are clinched, pressure in chamber  14  is released by pressing the trigger in one position which causes valve  90  to evacuate chamber  14  through passages (not shown) to a muffler (not shown). As best shown in FIG. 2, when the pressure is released from chamber  14 , piston  40  moves downward so that bottom surface  41  moves toward cover plate  13  in body  10 . Optionally, to assist the downward movement of piston  40  in chamber  14 , air is introduced into cavity  20  by depressing the trigger in another position so that the air bears on top  43  of piston  40  causing wedge  51  to move away from central axis  11  and slide on the inclined surface of end  26  of shaft  22 , inclined surface  67  of half spacer  68 , and slanted surfaces  62 ,  64  respectively of spacer  60 . Spring  32  assists in biasing punch member  24  away from die  86 . This permits sheet materials A, B to be removed from apparatus  100 . It should be appreciated that die  86  may be replaced with clamping jaws or other tooling devices to accomplish a variety of tasks. It is also possible to mount a number of force generating units equipped with appropriate tools to create a work fixture into which a workpiece may be inserted and a number of operations performed simultaneously.  
         [0048]    Those skilled in the art will recognize that while the device was described with pneumatic pressure, hydraulic pressure, an electric motor may alternately be employed to move piston  40  or any another suitable mechanism in the chamber  14 .  
         [0049]    While it is apparent that the preferred embodiment of the invention disclosed is well calculated to provide the advantages and features above stated, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the subjoined claims. For example, the apparatus may be stationarily mounted to a factory floor or fixture. The apparatus may also be attached to an articulating robotic arm. Furthermore, extra linkages or cams can couple the wedges to the joining dies. Pierced or riveted joints can also be performed with the present apparatus. Other materials and dimensions can be substituted for those disclosed. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of this invention.