Abstract:
A hydropnuematic riveter system is described, having features that allow for a reduction in size and weight over traditional rivet squeezers and rivet pullers. The riveter system also provides for greater versatility by permitting the operator to connect different rivet forming heads to the pressure intensifier portion, via a single flexible conduit with fluid-tight quick disconnect fittings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED R&amp;D 
       [0002]    Not Applicable 
       REFERENCE TO A SEQUENCE LISTING 
       [0003]    Not Applicable 
       FIELD OF THE INVENTION 
       [0004]    The present invention relates to rivet forming tools, or tools serving a similar function, powered by a combination of air pressure and hydraulic pressure. 
       BACKGROUND OF THE INVENTION 
       [0005]    The invention relates to rivet forming tools, historically used in the aerospace industry or other industries during the process of joining metal sheets together by compressing solid metal rivets or by pulling blind rivets. 
         [0006]    Several different types of tools exist for forming the heads of rivets, in order to join sheet metal parts into an assembled unit. These include rivet guns/bucking bars, hand squeezers, hand blind riveters, pneumatic squeezers and pneumatic blind riveters. Of these types, pneumatic squeezers and pneumatic blind riveters produce the most consistently formed rivets with the least operator fatigue. Pneumatic rivet squeezers have been used for many years. There are two basic types; C-yoke and Alligator type squeezers. C-yoke types allow for different yokes to be used, dependent on the geometry of the parts to be fastened, while Alligator types allow the tool squeezer jaws to get into tighter areas. 
         [0007]    The inventor of the present invention, while assembling an amateur built aircraft kit, discovered several limitations of present pneumatic squeezers. The inventor undertook designing a new riveter which would overcome these limitations. The invention disclosed represents a preferred embodiment of the basic configuration, but not all possible embodiments. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Pneumatic riveters of the known art are durable and reliably form rivets, or perform alternate operations such as crimping, swaging, staking and hole punching. One of the earliest examples is represented by U.S. Pat. No. 2,140,658 by Paul Van Sittert. These riveters come in various sizes and configurations in order to accommodate a myriad of riveting requirements typically found on aircraft of metallic construction. U.S. Pat. No. 7,219,526 by James Herod is a recent example of an alligator type squeezer, in this case incorporating composite materials to minimize weight. The riveters are able to generate several thousand pounds of force, necessary for compressing or pulling typical rivets, using a relatively low air pressure supply of approximately 90 psi. Notwithstanding the effectiveness of existing riveters, these riveters have several disadvantages, which the present invention remedies. 
         [0009]    A first disadvantage of existing riveters is the inability to access some tightly confined areas, such as internal wing structures. This is a result of packaging the riveter into an integrated unit, whereby the portion of the unit forming the rivet head and the portion of the unit creating the force are rigidly joined. Although recent inventions have attempted to minimize the size of the unit, such as that for an alligator type squeezer detailed in U.S. Pat. No. 7,290,431 by Boris Spivak, the size of these units still prohibit access to some confined structural areas. Other types of riveters also have a need for compactness, as evidenced by a hydropneumatic blind riveter detailed in U.S. Pat. No. 6,704,986 by Pao-Fang Liu. However, despite an attempt to allow for greater flexibility of the unit referenced by employing a rotational head, the unit is still prohibited from very confined areas, and it makes for a relatively heavy unit for the operator to hold. 
         [0010]    A primary object of the present invention is to create a highly compact and lightweight riveter. The present invention accomplishes this by separating the force generation portion (pressure intensifier) of the riveter from the rivet forming portion (forming head) of the riveter. Control of the riveter is packaged at the force generation portion to further reduce the size and weight of the forming portion. The pressure intensifier of the riveter comprises a low pressure air actuated piston, which is attached to a high pressure hydraulic piston. The forming head of the present invention comprises a piston housing and a moving piston, which interfaces with the rivet to be compressed or pulled. The two portions are connected via a flexible metal-braided conduit and a quick disconnect fitting may also be employed. By separating these two portions, the forming head of the present invention can fit into more tightly confined areas, and the riveter is lighter for the operator to hold. The weight reduction for the rivet squeezer forming head of the present invention is approximately 3 lb, or 60% of the weight of a pneumatic squeezer with similar force capability. Those skilled in the art can readily appreciate the advantages of such a compact and lightweight riveter. 
         [0011]    Another object of the present invention is to produce a riveter with a constant actuation force. The rivet squeezer of the present invention utilizes a compression pin driven by hydraulic pressure only, and as such the force does not vary with varying rivet lengths. This is in contrast to rivet squeezers of the known art, whereby the compression force varies as the rivet is squeezed. The variability is due to the fact that the rivet is compressed by a pin or jaw which is further driven by an air piston driven profiled wedge. As the interfacing tip of the pin or jaw moves in relation to the profiled wedge, the mechanical advantage changes. For a ⅛ inch rivet being squeezed, it is necessary to upset the shank of the rivet by approximately 0.110 inch. However the inventor has found that a typical pneumatic squeezer force may drop from 3,800 lbf to only 2,000 lbf in 0.030 inch of travel of the profiled wedge. Those skilled in the art will recognize that this variability may require the operator to make additional adjustments to the squeezer, or require the operator to squeeze the rivet twice to set the final rivet head size. 
         [0012]    A further object of the present invention is to produce a riveter which is more cost effective, by offering greater flexibility to the operator. The present invention allows the operator to purchase one force generation portion to power a variety of rivet forming portions, thereby saving the expense of multiple force generation portions. A disadvantage of existing riveters is related to their intrinsic inseparable assembly. Since the force generation portion and forming head portion of these riveters are inseparable, the end user is essentially buying additional force generation portions each time a different forming head is needed, which results in a higher cost burden to the operator. 
         [0013]    Thus, for the aforementioned reasons those skilled in the art will readily appreciate that the hydropneumatic riveter of the present invention offers distinct advantages over traditional pneumatic and hydropneumatic riveters. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of the riveter, with a C-yoke forming head portion attached to a pressure intensifier portion via a flexible conduit. The conduit is approximately six feet in length and is therefore not shown in its entirety. 
           [0015]      FIG. 2  is a perspective view of a blind rivet forming head portion, which may be attached to the pressure intensifier portion of the riveter shown in  FIG. 1  via a flexible conduit. 
           [0016]      FIG. 3  is a perspective view of an alligator forming head portion, which may be attached to the pressure intensifier portion of the riveter shown in  FIG. 1  via a flexible conduit. 
           [0017]      FIG. 4  is an exploded view of the pressure intensifier portion of the riveter shown in  FIG. 1 . 
           [0018]      FIG. 5  is a top view of the pressure intensifier portion of the riveter shown in  FIG. 1 . 
           [0019]      FIG. 6  is a partial sectional view of the pressure intensifier portion taken along cutting plane  6 - 6  of  FIG. 5 . 
           [0020]      FIG. 7  is a top view of the C-yoke forming head shown in  FIG. 1 . 
           [0021]      FIG. 8  is a partial sectional view of the C-yoke forming head taken along cutting plane  8 - 8  of  FIG. 7 . 
           [0022]      FIG. 9  is an exploded view of the C-yoke forming head shown in  FIG. 1 , with an example of an alternate C-yoke also shown. 
           [0023]      FIG. 10  is a partial sectional view of the blind rivet forming head taken along cutting plane  10 - 10  of  FIG. 2 . 
           [0024]      FIG. 11  is a partial sectional view of the blind rivet forming head taken along cutting plane  11 - 11  of  FIG. 2 . 
           [0025]      FIG. 12  is a top view of the alligator forming head shown in  FIG. 3 . 
           [0026]      FIG. 13  is a partial sectional view of the alligator forming head taken along cutting plane  13 - 13  of  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    According to a preferred embodiment of the invention, there is described a hydropneumatic riveter having features that allow for a more compact size, lower weight, consistent force and greater versatility. Referring to  FIG. 1 , a hydropneumatic riveter  10  can be generally divided into two main sub-assemblies; a forming head  12  and a pressure intensifier  14 . The forming head  12  shown in  FIG. 1  is a C-yoke type, so named due to the shape of the anvil which forms the rivet. The two sub-assemblies are interconnected via a flexible wire-braided reinforced conduit  16 , which may comprise a fluid-tight female quick disconnect  17 . The conduit  16  is generally permanently attached to the pressure intensifier  14 , but could alternately be permanently attached to the forming head  12 . The forming head  12  may likewise comprise a fluid-tight male quick disconnect  18 , for selectively coupling and uncoupling the forming head  12  from the conduit  16  attached to the pressure intensifier  14 . The conduit  16 , female disconnect  17  and male disconnect  18  are capable of withstanding pressures of up to 4,000 psi. The female disconnect  17  and male disconnect  18  prevent fluid leakage during connection and disconnection, and minimizes air inclusion during those processes. 
         [0028]    The pressure intensifier  14  may be used to power alternate types of rivet forming heads, as depicted in  FIGS. 2 and 3 . The intensifier  14  is sized so that it displaces a volume of pressurized fluid that meets the flow requirements of the various forming heads. A blind rivet forming head  20  is shown in  FIG. 2 . This type of rivet former is useful for installing blind type rivets, also known commercially as “pop” rivets. An alligator forming head  22  is shown in  FIG. 3 . Alligator riveters typically have an advantage over C-yoke type rivet squeezers in that the jaws of an alligator riveter can be inserted into more confined areas. It should however be noted that the C-yoke forming head  12  of the present riveter invention  10  can often fit into equally confined areas, and sometimes more confined areas depending on the surrounding structure. 
         [0029]    Referring to  FIGS. 1 ,  4  and  5 , the intensifier  14  primarily comprises cylindrical components including a low pressure housing assembly  30 , a high-pressure housing  32 , a low-pressure piston  34  and a high-pressure piston  36 . The high pressure housing  32  is mounted to the low pressure housing assembly  30  with screws  38 . Alternatively, the high pressure housing  32  and low pressure housing  30  may be integrally manufactured such as by casting. Referring to  FIG. 6 , the low pressure housing  30  is further comprised of a upper end cap  40 , a lower end cap  42  and a cylinder  44 , which together with the low-pressure piston  34  define two cavities; an upper retraction cavity  46  and a lower extension cavity  48 . The low-pressure piston  34  and a high-pressure piston  36  are rigidly connected by a locking nut  50  on a threaded end  51  of the high-pressure piston  36 . Air is prevented from leaking between these two parts by an o-ring  52  installed in a groove of the low-pressure piston  34 . The upper end cap  40  and lower end cap  42  are sealed to the cylinder  44  by o-rings  53  in grooves  54  ( FIG. 4 ) of the cylinder  44 . The low pressure housing  30  is mounted to a base plate  55  by cap screws  56 . The low pressure piston  34  is in axially slidable contact with an internal bore  57  of the cylinder  44 . The housing assembly  30  is mounted in a vertical orientation as referenced to the ground, but may alternately be mounted in a horizontal position. A four port double acting control valve  58  is adjacent the housing assembly  30 , and affixed to the base plate  55  with screws  59 . Control of the valve  58  is accomplished via a foot pedal  60 . Rubber pads  62  may be affixed to the bottom of the base plate  54 , to help prevent the intensifier  14  from sliding on the floor. 
         [0030]    Referring to  FIG. 6 , the high-pressure housing  32  has an inner bore  64  which is slightly larger than the diameter of the a high-pressure piston  36 , so as to minimize wear on the piston  36  when it traverses the length of the housing  32 . The high-pressure housing  32  and high-pressure piston  36  define a cavity  66  which contains the high pressure fluid. High pressure fluid is also contained in the flexible conduit  16 . A high level of concentricity is achieved between the low pressure housing assembly  30  and high-pressure housing  32  by a close fit between a bore  68  of the upper end cap  40  and a cylindrical step  70  of the high-pressure housing  32 . Concentricity between all moving parts is important to assure low seal wear. An o-ring  72  is used to seal air that would otherwise leak from the retraction cavity  46 . The screws  38  that attach the high-pressure housing  32  to the low pressure housing assembly  30  are installed into threads  74  tapped into the upper end cap  40  ( FIG. 4 ). For the intensifier presently designed, these threads collectively resist a separation force of approximately 600 lbf, created when the internal pressure of the fluid in the cavity  66  is elevated to approximately 3,000 psi. Typically an oil such as automotive transmission fluid, is sealed within the cavity  66  by a high pressure cup shaped seal  76 . The high pressure seal  76  is oriented so that a cup on the seal  76  faces the fluid in the cavity  66 , and expands as necessary to seal the fluid at elevated pressures. The seal  76  is retained in a bore  78  of the high-pressure housing  32  by a seal spacer  80 . The high pressure piston  36  is guided by a bushing  82 . The length of the piston  36  and housing  32  are set so as to achieve a desired swept volume in the cavity  66 , which is slightly greater than the fluid volumetric requirements of the filler heads  12 ,  20  or  22 . 
         [0031]    In operation, the intensifier  14  is first filled with a hydraulic fluid, using a syringe or other device. The fluid volume of the system is on the order of 80 cc, so filling is relatively simple. Fluid is injected into a bleed fitting  84  located on the periphery of the high-pressure housing  32 , until all unwanted trapped air is removed from the cavity  66  and the flexible conduit  16  and replaced with the fluid. The trapped air is allowed to escape from a similar bleed fitting located on the various forming heads  12 ,  20  or  22 , and these heads can be filled with fluid in conjunction with filling the intensifier  14 . Periodically it may be necessary to remove unwanted air which may begin to accumulate from repeated connections of the quick disconnects  17  and  18 . 
         [0032]    Next, pressurized air is supplied at approximately 90 psi to a conventional quick disconnect air fitting  86  ( FIG. 5 ) installed into a pipe elbow  88 , which is further installed in the double acting control valve  58 . The foot operated valve  58  is spring energized, so that the pedal  60  on the valve  58  remains in an upper position. In the normal condition, pressurized air flows through the valve  58  and into a retraction air supply tube  90 , which delivers the air to a port  92  in the upper end cap  40 , and further into the retraction cavity  46 . This normal condition ensures the low pressure piston  34  is fully retracted against the lower end cap  42  (as shown), and the high pressure piston  36  is thereby not exerting pressure on the fluid in the cavity  66 . When it is desirable to create high fluid pressure in the cavity  66 , the operator depresses the pedal  60  on the foot valve  58 , causing compressed air to switch from pressurizing the air supply tube  90  to pressurizing an extension air supply tube  96 . Since the valve  58  is double acting, air which had been pressurizing the cavity  46  is allowed to vent out of the valve  58  through a muffler  98 . The compressed air pressurizing the supply tube  96  is routed to a port  100  in the lower cover  42  and into the extension cavity  48 . The supply tubes  90  and  96  are connected to the valve  58  and low pressure housing  30  via quick air disconnects  102 . The compressed air in the cavity  48  is now acting differentially on the lower side of the low pressure piston  34 , exerting a force on the attached high pressure piston  36 . The low pressure piston  34  has seals  104  which prevent compressed air from escaping the cavity  48  along the internal bore  57  of the cylinder  44 . The area ratio of the low pressure piston  34  to the high pressure piston  36  is approximately 30:1. This ratio multiplies the input air pressure thereby creating a pressure within the high-pressure housing cavity  66  of approximately 3,000 psi. This fluid pressure provides the motive force for the forming heads  12 ,  20  and  22 . 
         [0033]    The C-yoke forming head  12 , blind rivet forming head  20  and alligator forming head  22  of the present invention are comprised of similar components, and therefore similar components will use like item numbers in the figures and following descriptions. The C-yoke head  12  will be described in detail, with the alternate heads  20  and  22  described where they differ. 
         [0034]    Referring to  FIGS. 7 ,  8  and  9  a C-yoke forming head  12  is used to compress a solid rivet, and is comprised of a generally rectangular piston housing  120 , enclosing a high-pressure piston  122  and mounting a C-yoke  124 . The housing  120  is shaped to ergonomically fit the user&#39;s hand, and is optimized to be as small and lightweight as practical. Referring to  FIG. 7 , the housing has a V-shaped end  125  which is intended to fit within the V formed by the thumb and forefinger of the user&#39;s hand. The piston  122  utilizes the fluid pressure delivered by the intensifier  14  to compress a solid rivet against the C-yoke  124 . The C-yoke  124  is attached to the housing  120  by quick connect shear pins  126 , located in close tolerance holes  128  in a clevis end  129  of the housing  120 , and similarly spaced holes  130  in the C-yoke  124 . The pins  126  carry shear forces created resisting a moment applied to the C-yoke  124  during compression of the rivet. A commercially available rivet die  132  is attached to the C-yoke  124  and a compression pin  133 , and is useful for forming various rivet head shapes and sizes. 
         [0035]    The C-yoke  124  and compression pin  133  have bores  134  and  135  respectively for receiving a shank  136  in the rivet die  132 . The piston  122  and compression pin  133  have a threaded bore  138  and threaded shank  140  respectively, for adjusting the distance of the pin  133  relative to the piston  122 . This threaded pair is used in turn to adjust the distance between the die  132  installed in the pin  133  and the die  132  installed in the C-yoke  124 , to accommodate different rivet lengths. For the preferred embodiment, the thread pitch for the bore  138  and shank  140  is 32 threads per inch. Adjustment of the distance can be accomplished by a wrench flat  141  on the piston  122  and a wrench flat  142  on the pin  133 . The piston  122  is guided in the housing  120  by a bushing  144 . C-yokes come in different shapes in order to clear various structure. An alternate C-yoke  143 , known as a flange C-yoke, is shown in  FIG. 9 . The forming head  12  further comprises a return spring  145 , which assists in retracting the piston  122  following compression of the rivet. A threaded plug  146  is used to cover a bore  148  of the housing  120 . The plug  146  may further comprise a bleed nipple  150 , which is used to remove any unwanted air bubbles from the fluid in a cavity  152  defined by the extents of the piston  122 , cylinder  148  and plug  146 . Alternately the bleed nipple  150  may be installed in the housing  120 . An o-ring  154  is installed in a groove  156  of the plug  146  to prevent fluid leakage past the wall of the bore  148 . A backup ring  158  may be installed adjacent to the o-ring  154  to prevent extrusion of the o-ring  154 . A high pressure cup shaped seal  160  is installed on the piston  122  to prevent fluid leakage from the cavity  152 . The male disconnect  18  is installed in a tapered threaded port  166  of the housing  120 . 
         [0036]    Referring to  FIG. 9 , the piston  122  has a large diameter end  170  and a small diameter end  172 . The large end  170  is used to convert the high fluid pressure in the cavity  152  into a compressive force, which will cause the piston  122  to move in axial alignment with the rivet being compressed. The large end  170  has a groove  174  which is used to retain the high-pressure seal  160 . The seal  160  is retained in the groove  174  by a tapered lip  176 , on the end of the piston  122 . The diameter of the lip  176  is only slightly greater than the groove  174 , in order to minimize distortion of the seal  160  during installation. The lip  176  is also tapered in order to further ease installation of the seal  160 . 
         [0037]    The blind rivet forming head  20  depicted in  FIGS. 2 ,  10  and  11  is comprised of components similar to the C-yoke forming head  12 , such as a piston housing  120 , a high pressure piston  122 , a bleed fitting  150 , and male disconnect  18 . Note that the bleed fitting is installed in the housing  120 . In operation, the blind rivet head  20  essentially works in reverse of the C-yoke head  12 , whereby the high pressure piston  122  moves away from a blind rivet to be formed. This is accomplished by directing high pressure fluid from the intensifier  14  into a cavity  180  defined by the extents of the housing  120  and the piston  122 . Fluid is contained within the cavity  180  by a high pressure piston seal  160  mounted on the piston  122 , and a similar but smaller high pressure housing seal  184  restrained in a bore  186  of the housing  120 . The high pressure fluid causes the piston  122  to move axially away from a nose-piece  188  mounted at a tip  189  of the housing  120 . The nose-piece  188  is installed in the tip  189  by a threaded end  190  of the nose-piece  188  installed into a threaded bore  191  of the tip  189 . As the piston  122  moves axially, an internal tapered bore  192  of the piston  122  comes into diametrical contact with a pair of tapered split jaws  194 , forcing the jaws  194  to collapse radially inward about the stem of the blind rivet to be formed. 
         [0038]    The split jaws  194  are initially held in a diametrically enlarged state, by a taper  196  on the nose-piece  188  and by a wedge  198  on a ram  200 . This allows the blind rivet to be installed into the nose-piece  188 , prior to forming. The ram  200  is forced by a spring  145  toward the nose-piece  188 . The spring  145  also serves to return the piston  122  to a retracted state, once fluid pressure is removed. The jaws  194  have serrations  202  on an inner diameter, which serve to grasp the stem of the blind rivet. A hollow spacer  204  may be used to tailor the preload force applied to the ram  200  by the spring  145 . A threaded plug  206  is used to close a housing bore  148 , however unlike the plug  146  of the C-yoke head  12 , this plug  206  does not seal fluid, and is used as a back stop for the spring  145 . A threaded hollow spacer  208  may be used to fine adjust the preload force of the spring  145 . The ram  200 , spacer  204 , plug  206  and threaded spacer  208  are hollow to allow the stem of the blind rivet to escape the forming head  20 , once the rivet has been formed. 
         [0039]    The alligator forming head  22  depicted in  FIGS. 3 ,  12  and  13  is comprised of components similar to the C-yoke forming head  12 , such as a piston housing  120 , a high pressure piston  122 , a threaded plug  146 , a high pressure seal  160 , a bleed fitting  150 , and male disconnect  18 . Some of these components may be interchangeable between the various forming heads, which reduces acquisition cost. The alligator head  22  compresses a rivet via a set of rotatable jaws; an upper jaw  210  and a lower jaw  212 . The upper jaw  210  and lower jaw  212  have a central bore  214  and  216  respectively, and are each pinned to a mount end  218  of the piston housing  120  by shear pins  220 , which allows the upper jaw  210  and lower jaw  212  to pivot about their respective shear pins  220 . The upper jaw  210  and lower jaw  212  have internal ends  222  and  224  respectively, that have axle bores  226  and  228  respectively. Roller bearings  230  are mounted to jaw internal ends  222  and  224  by shear pins  232 . Jaws  210  and jaw  212  have external ends  234  and  236  respectively, which are used to compress the rivet to be formed. 
         [0040]    In operation, the alligator head  22  is selectively coupled to the flexible conduit  16  which supplies fluid pressure from the intensifier  14 . Fluid pressure from the conduit  16  acts on a surface of the piston  122 , forcing the piston toward the jaws  210  and  212 . The piston  122  contacts a tapered wedge  238 , forcing the wedge  238  into the roller bearings  230  mounted on the jaw internal ends  222  and  224 . The wedge  238  creates mechanical advantage, to force the jaws  210  and  212  to rotate about their respective central bores  214  and  216 , thereby compressing a rivet installed between the internal ends  222  and  224 . A jaw return spring  240  is used to cause the jaws  210  and  212  to rotate in an opposite direction once pressure from the cavity  152  is relieved and the piston  122  is returned to a refracted state by a piston return spring  145 . 
         [0041]    To those skilled in the art, it should be readily apparent that the invention described herein has significant advantages over existing tools in terms of size, weight and versatility. While the invention has been described in terms of various specific embodiments and use for forming rivets, those skilled in the art will recognize that the invention can be practiced with modification and alternative purpose within the spirit and scope of the claims.