Abstract:
A two-stage hemming machine has a centrally located press station with an anvil extendable along a vertical axis, and a loading station and an unloading station located on opposite sides of the press station. Separate first and second dies slide on horizontal tracks mounted above the press, the first die movable therealong between the loading station and the press station, and the second die movable between the unloading station and the press station. The dies shuttle back and forth, in unison, between the press station during a production cycle wherein a component to be hemmed is loaded into the first die in the loading station, is carried into the press station along with the first die where the first stage of the hemming operation occurs, and remains on the anvil as the anvil is lowered. The first die then returns to the loading station as the second die moves into the press station. The anvil is extended again to perform a second stage of the hemming operation, the anvil is retracted, the component remaining in contact with the second die, and the second die moves to the unloading station where the component is removed from the press. Spring actuated arms hold the component in connection with the first die as the first die moves to the press station, and a power actuated retaining arm holds the component in connection with the second die as the second die moves to the unloading station.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. Provisional Application Serial No. 60/146,187 filed Jul. 29, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to hemming machines used to join sheet metal panels into a component such as an automobile body assembly. In particular, the invention relates to a method and apparatus for performing a two-stage hemming operation using a single, moveable anvil and two movable dies. 
     BACKGROUND OF THE INVENTION 
     Hemming is a manufacturing technique that is widely used in the automotive industry for joining two sheet metal panels together to form an external body component such as a door, hood or tailgate assembly. Typically, the panel forming the external skin of the component is joined to an inner reinforcing panel around substantially the entire periphery of the component. In the hemming process, this is achieved by folding the outer, peripheral edges of the outer panel over and around the outer edges of the inner panel. 
     At the beginning of the hemming process, any edge of the outer panel that is to be hemmed is already bent to form a flange which extends generally perpendicular to the main portion of the panel. This flange is usually produced during the stamping operation that forms the outer panel. For purposes of description, it will be assumed that the outer panel is oriented so that the flanges extend upwardly. The inner panel is then placed on top of the outer panel so that it nests within the upturned flanges of the outer panel. 
     The folding over or hemming of the outer panel flanges is typically completed in at least two stages. In the first stage, a die or tool strikes the flange to bend it inwardly approximately 35° to 55° from its original vertical orientation. In the second stage, a different die or tool strikes the inward slanting flange to bend it through the remainder of the approximately 90° required to make the flange lay flat against and wrap tightly around the edge of the inner panel. 
     One conventionally known process for performing a two-stage hemming operation on large automotive body components uses two separate presses each including a stationary lower die, commonly known as an anvil, and a vertically movable upper die. The component is placed on top of a first anvil and a first upper die is urged downwardly by a hydraulic or electrically powered press to contact the component and perform the first stage. The component is then removed from the first anvil and placed on a second anvil, which includes a second upper die and is actuated in a similar manner to perform the second stage. This conventional dual press operation incurs the additional cost of purchasing and maintaining two separate presses. Two separate presses also occupy a substantial amount of floor space in a plant. 
     It is also known to execute a two-stage hemming process using a single hemming press in which movable, cam-operated tools are used to change the geometry of the dies between strokes. The panels are placed in the anvil, and the press is actuated with the tools in a first position to perform the first stage. The press is opened, the tools are moved to a second position, and the press is actuated a second time to perform the second stage. In such a process, a finished component is ejected from the machine every two times the press is actuated. 
     As described above, the anvil of a conventional hemming press is stationary and an upper die is urged downwardly by a press to hem the component. An adhesive is typically applied between the panels in the area of the hem to ensure a tight seal between the panels and to prevent corrosion-causing moisture from entering the component. As the component is hemmed, a small amount of excess adhesive squeezes out of the joint and sticks to the upper die which contacts the inner panel. 
     This excess adhesive must be periodically removed from the die, and this is normally accomplished by manually scraping the die while it is in a raised position. In the conventional hemming press described above, the scraped-off excess adhesive falls downwardly onto the anvil, so that the anvil must then be cleaned before production can resume. 
     SUMMARY OF THE INVENTION 
     It is desirable in the present invention to provide a method and apparatus for producing hemmed sheet metal components in a faster and more economical manner than is possible with conventional hemming presses. A hemming machine according to the present invention can include a power-actuated press station which moves an anvil along a press axis between a retracted position and an extended position, a die movable between a first stamping position aligned with the press axis and a loading position wherein the first die is offset from the press axis, and a second die movable between the stamping position and an unloading position wherein the second die is offset from the press axis. 
     The hemming machine provided by the present invention is operated by loading the component to be hemmed into the first die when it is in the loading position, moving the first die and the attached component to the stamping position and extending the press to urge the anvil into contact with an un-hemmed component to perform the first stage of the hemming operation. The component remains in contact with the anvil as it is lowered, and the first die is then returned to the loading position. The second die then moves from the unloading position to the stamping position, and the anvil is extended again to perform a second stage of the hemming operation. The anvil is then returned to the retracted position, the component remaining in contact with the second die, and the second die is moved to the unloading position where the component is removed from the press. 
     A hemming machine according to the invention is more compact than the prior designs using two separate presses. The machine and method provided herein offers a short cycle time, since the first stage of the hemming operation can be performed while a completed part is removed from the second hemming die, and the second stage of the hemming operation can be performed while a new part is loaded into the first die. 
     In a preferred embodiment of the invention, the press axis is oriented vertically and extension of the press moves the anvil upwardly toward the first and second dies, which have their component-contacting surfaces oriented downwardly. The first and second dies are linearly movable along horizontal axes. Accordingly, a component to be hemmed is loaded into a centrally-located press station from a first side of the press, both the first and second stage of the hemming operations take place in the press station, and the finished hemmed component is unloaded from the press station on a different side of the press, creating a very efficient work flow. 
     According to another feature of the invention, means are provided for holding the component in connection with the first die as it moves from the loading position to the stamping position in the press station, and for releasing the component after the first hemming stage is complete, so that the component remains in contact with the anvil as it is retracted downwardly. In this fashion, the component is automatically transferred from the loading position into the press station by the movement of the first die, and remains in the press station as the first die returns to the loading position and the second die moves into the press station in preparation for the second stage hemming stroke. 
     The hemming machine of the present invention also preferably includes means disposed on the second die for engaging the component when the component is raised into contact with the second die during the second stroke of the press station, and holding the component in connection with the second die as it moves to the unloading position after completion of the second hemming stroke. In this fashion, the finished component is automatically transferred out of the press station to the unloading station by the movement of the second die. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view of a hemming machine according to the present invention; 
     FIGS. 2A through 2F are a series of partially cut-away elevation views depicting the operating sequence of the invention hemming machine; 
     FIG. 3 is a detail view of a component being loaded into a first die; 
     FIG. 4 is a detail view of the component during the first stage of the hemming operation; 
     FIG. 5 is a detail view of the component resting on top of the press die after the first hemming stage; and 
     FIG. 6 is a detail view of the component being retained in connection with the second die. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-6, a hemming machine  10  according to the present invention is depicted along with a loading carriage  12  for loading a component  14  to be hemmed into the machine  10  and an unloading carriage  16  for removing the component from the machine after hemming. The component  14  depicted herein is a door for an automotive vehicle, but it is to be understood that the present invention can be employed to hem any type of sheet metal component or assembly. The component  14  includes an upper panel or reinforcing panel  14   a , a lower panel or outer skin  14   b  and a flange  14   c  that are nested together (see FIG. 3) prior to being joined into a unitary assembly in the hemming operation. 
     The hemming machine  10  includes a centrally located press station  18 , a loading station  20  disposed on a first side of the press station  18 , and an unloading station  22  disposed on an opposite, second side of the press station  18 . A top frame  24  extends across substantially the full length of the hemming machine  10  above the loading station  20 , the press station  18  and the unloading station  22 . The top frame  24  is preferably constructed of steel castings bolted and keyed together to form a truss. First and second side frames  26  are also constructed of steel castings, and extend from the top frame  24  downwardly to the floor on either side of the press station  18 . One or both of the side frames  26  preferably have a viewing window  28  formed therein which are covered with high-strength, transparent polycarbonate sheet. Support pillars  30  are located at each of the four corners of the top frame  24  and extend downwardly to the floor. Adjustable leveling feet  32  are located at the bottoms of the support pillars  30  and at points along the lower edges of the side frames  26  so that the machine  10  can be made level and true when installed on a shop floor. 
     Referring now to FIGS. 2A-2F, a press  34  is disposed in the press station  18  and includes a piston  38  extending from a base  40 . An anvil  42  is attached to the upper end of the piston  38  for vertical movement therewith, sliding up and down along vertical tracks  44  mounted to or integral with, the side frames  26  (shown in FIG.  1 ). The inner surface  46  of the anvil  42  (shown in FIG. 4) is shaped to match the particular component that the hemming machine  10  is designed to hem. Generally, the inner surface  46  is concave so that the component  14  can rest thereon. The press  34 , as depicted, is hydraulically powered. However, press  34  can be powered by a flywheel with clutch and brake, or by any other power source known in the art. 
     Overhead tracks  48  are attached to, or integral with, the lower side of the top frame  24  and extend horizontally from the loading station  20  through the press station  18  and to the unloading station  22 . A first die  50  is mounted to slide along one end of the overhead tracks  48  (as viewed in FIGS.  2 A- 2 F), between the loading station  20  and the press station  18 . A hydraulic actuator  52  (as shown in FIG. 1) or other power drive means is disposed on the top frame  24  and is connected with the first die  50  to provide the motive force for sliding the first die  50  back and forth along the overhead tracks  48 . A plurality of retaining arms  54  extend downwardly from the first die  50  at locations around its perimeter. A second die  56  is slidingly mounted to the overhead tracks  48  for movement there along between the unloading station  22  and the press station  18 , and is powered by a second hydraulic actuator  58  mounted on the top frame  24 . At least one retaining arm  60  extends downwardly from the second die  56  (as shown in FIGS. 2A-2B) The loading carriage  12  has a bed  62  for receiving the component  14  to be hemmed and can include means for vertical movement such as a chain drive actuated by an electric motor, or a hydraulic or pneumatic ram. The loading carriage  12  is movable between a first position immediately adjacent the loading station  20  (as shown in FIG. 1) and a second position within the loading station  20  directly beneath the first die  50 . The loading carriage  12  can roll along guide tracks  64  disposed on the floor to allow for precise positioning within the loading station  20 . The unloading carriage  16  (see FIG. 2F) is generally similar to the loading carriage  12  in construction and operation and is movable between a first position within the unloading station  22  and a second position outside of and adjacent to the unloading station. 
     The sequence of operation of the hemming machine  10  is as follows. Starting with the loading carriage  12  adjacent the loading station  20 , the un-hemmed component  14  is positioned on the bed  62  of the loading carriage  12 , as illustrated in FIG.  1 . The loading carriage  12  is movable into the loading station  20 . At this stage of the operating sequence, as seen in FIG. 2A, the first die  50  is in the loading station  20 , the second die  56  is in the press station  18 , and the press  34  is retracted so that the anvil  42  is in a lowered position. 
     The loading carriage bed  62  is raised to bring the component  14  into contact with the first die  50 . As seen in FIG. 3, the first die  50  has a lower or contacting surface  51  shaped to receive the component  14 , and the component  14  fits between the retaining arms  54 . Each retaining arm  54  has a finger  66  which pivots about a hinge pin  68  located near the lower end of the arm. The finger  66  is biased inwardly, toward the center of the first die  50 , by a spring  70 . As used herein, “inwardly” refers to direction generally towards said the center of first die  50 . A cam surface  72  is formed on the inward-facing side of the finger  66 . As the loading carriage bed  62  lifts the component  14  upwardly toward the first die  50 , the outer edge of the component  14  contacts the cam surface  72  of the finger  66  to urge the finger  66  outwardly, against the force of the spring  70 , so that the component  14  can pass between the retaining arms  54  and into contact with the first die  50 . When the component  14  reaches the fully loaded position, as shown in FIG. 3, the fingers  66  snap inwardly to support the component  14  from beneath and hold the component in contact with the first die  50  when the bed  62  is lowered. 
     With the component  14  properly retained in connection with the first die  50 , the hydraulic actuators  52 , 58  are actuated to slide the first die  50  into the press station  18  and the second die  56  into the unloading station  22 , as seen in FIG.  2 B. This movement positions the first die  50  in direct alignment with the vertical axis of the press  34 . At this time, the loading carriage  12  can be moved out of the loading station  20 . 
     As seen in FIG. 2C, the press  34  is then actuated to urge the press die  42  upwardly into contact with the first die  50  and the attached component  14 . The contacting surface  51  of the first die  50  and the inner surface  46  of anvil  42  coact to perform a first stage of the hemming operation. In the first stage of the hemming operation, a flange  14   c  extending upwardly around the edges of the outer skin  14   b  is bent inwardly approximately 45° so that the peripheral flange  14   c  wraps partially around the outer perimeter of the reinforcing panel  14   a.    
     As the anvil  42  moves upwardly towards the component  14  and first die  50 , the anvil  42  passes between the retaining arms  54  and contacts the cam surfaces  72  of the fingers  66  (see FIG.  4 ), urging the fingers  66  outwardly so that the retaining arms  54  release their engagement with the component  14 . As the anvil  42  moves downward after the first stage of the hemming operation, anvil  42  continues to hold fingers  66  outwardly (see FIG. 5) so that the component  14  drops away from the first die  50  and remains on inner surface  46  (see FIG. 4) of anvil  42  to move downwardly therewith. 
     After the first stroke of press  34  has accomplished the first stage of the hemming operation, first die  50  slides back to the loading station  20  (see FIG. 2D) and second die  56  slides into the press station  18  and into alignment with the press axis  34 . Also at this time, the loading carriage  12  with a second, un-hemmed component  74 , positioned on bed  62 , moves into the loading station  20  beneath the first die  50  to prepare for loading of the second component  74  into the first die  50 . 
     As seen in FIGS. 2A-2F, the press  34  is then actuated a second time to urge the anvil  42  and the component  14  lying thereon upwardly into contact with the second die  56 , having contact surface  57 , to perform the second stage of the hemming operation and produce a completed component  14   d . In the second stage of the hemming operation, the flange  14   c  of the outer skin  14   b  of the component is crimped tightly around the outer perimeter of the reinforcing panel  14   a  of the component  14 . Prior to, or simultaneously with, the anvil  42  moving away from second die  56 , retaining arm  60 , extending from second die  56 , is actuated to hold the component  14   d . The hemmed component  14   d  is removed from anvil  42  as the anvil  42  retreats to the retracted position. In a preferred embodiment of the invention, as shown in FIG. 6, the retaining arm  60  includes a shaft  76  which extends downwardly through an aperture  77  in hemmed component  14   d  and has a finger  78  extending radially outward therefrom. Shaft  76  is rotatable by a power-actuated linkage  80  between a first angular position  82  shown in phantom line and a second angular position  84  shown in hidden line beneath reinforcing panel  14   a . Shaft  76  is in first angular position  82  when anvil  42  moves upward to perform the second stage of the hemming operation, and the linkage  80  is actuated to move shaft  76  to second angular position  84  prior to the anvil  42  lowering so that the component  14   d  is held in contact with the second die  56 . 
     As seen in FIG. 2F, after anvil  42  lowers from second die  56 , the hydraulic actuator  58  is actuated to slide the second die  56  and the attached hemmed component  14   d  into unloading station  22 , and a vertically movable bed  86  of the unloading carriage  16  is raised into contact with the hemmed component  14   d  as seen in FIG.  2 F. The retaining arm  60  is actuated to release the hemmed component  14   d  so that the finished, hemmed component  14   d  rests on the bed  86  of the unloading carriage  16  and can be lowered away from the second die  56  and removed from the unloading station  22 . As the second die  56  and the hemmed component  14   d  move to the unloading station  22 , the first die  50 , now bearing the second, un-hemmed component  74 , is simultaneously moved into press station  18  so that the press  34  can be extended to perform the first stage of the hemming operation on the second component  74  in a continuous production cycle. As is apparent from the foregoing description, the hemming machine  10  is particularly well suited for a continuous production cycle. 
     An un-hemmed component  14  is loaded into press station  18  each time the first die  50  moves into press station  18 , and a completed, fully hemmed component  14   d  is removed from press station  18  each time the second die  56  moves to unloading station  22 . When operated in this continuous production mode, the dies  50 , 56  preferably move simultaneously and in coordination with one another. That is, the first die  50 , carrying an un-hemmed component  14 , moves into press station  18  simultaneously with second die  56 , carrying a fully hemmed component  14   d , moving out of press station  18  to the unloading station  22 . In the same fashion, the empty first die  50  moves back to the loading station  20 , to receive a new, second component  74 , simultaneously with the empty second die  56  moving back into press station  18 , to perform the second stage of the hemming operation. The component  14  need not be manually handled between the time it is loaded in an un-hemmed condition into the loading station  20 , and removal of the completed, fully hemmed component  14   d  from the unloading station  22 . 
     A break in the continuous production cycle occurs when it becomes necessary to clean the dies. An adhesive (see FIGS. 3-4) is typically applied around the edges of the upper and/or lower panels  14   a ,  14   b  of the component  14  prior to loading. This adhesive  88  dries to form a corrosion resistant, moisture-tight seal at the locations where the outer skin  14   b  and reinforcing panel  14   a  are hemmed together. During the hemming operation, a certain amount of adhesive  88  is forced out of the overlaps between the panels and sticks to the first and second dies  50 ,  56 . This dried, excess adhesive must be cleaned off of the dies  50 ,  56  at certain intervals to maintain proper functioning of the machine. The hemming machine  10  of the present invention has an advantage over prior art machines when cleaning must be performed. Cleaning is accomplished by positioning the first die  50  in the loading station  20  and the second die  56  in the unloading station  22 , with neither of the dies  50 ,  56  carrying a component  14 ,  14   d . The dried adhesive can then be scraped or otherwise cleaned off of the dies  50 ,  56  and, since the dies  50 ,  56  are not above the anvil  42 , the adhesive falls to the floor in the loading and unloading stations  20 , 22  rather than onto surface  46  of the anvil  42 . The cleaning of the present invention does not cause debris to fall into anvil  42 , so the production process can then immediately resume without the need to clean adhesive scrapings off from the anvil  42 . It should be noted that during the normal production sequence of the hemming machine  10 , the first and second dies  50 , 56  are effectively joined so that the dies  50 ,  56  remain adjacent one another as the dies  50 ,  56  move between stations. It is only during cleaning that the first and second dies  50 , 56  are separated so that neither one is located in the press station  18 . This is in contrast to conventional hemming presses where upper dies are always positioned directly over the anvil and any adhesive scraped off from the die falls into the anvil. This requires the scraped off adhesive to be removed before the hemming operation can resume. 
     It has been found that a hemming machine  10  according to this invention is well adapted for operation with a much shorter press stroke than a conventional hemming press. Specifically, while a conventional hemming press has a stroke averaging thirty to forty inches, a hemming machine according to the present invention has been found to operate effectively using a stroke of only approximately eight inches. This shorter stroke length is a result of the manner in which the components  14 ,  14   d  are shuttled into and out of the press station in connection with the first and second dies  50 ,  56 , and results in a significantly reduced cycle time during production, and hence greater efficiency 
     In one possible alternative to the preferred embodiment depicted herein, one or both of the loading and unloading carriages  12 , 16  can be oriented to roll into and out of the loading and unloading stations  20 ,  22  in directions perpendicular to the axis along which the dies travel. In another possible alternative configuration, the axes of sliding movement of the first and second dies  50 ,  56  can be oriented at 90° to one another, rather than being parallel as shown in the preferred embodiment. Either of these alternatives can be advantageous due to space constraints in a particular equipment layout within a plant. This can be the case, for example if it is desired to place the machine near a corner or a wall. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.