Abstract:
A method for adhesively joining two members includes the steps of mixing non-compressible beads with an adhesive, applying the resulting mixture to one of the members and hemming one member over the other in overlapping relationship. Apparatus for performing this method includes a container for containing a mixture of an adhesive and a plurality of non-compressible beads, an applicator for applying the mixture to one of the members, and hemming means for hemming one member over the other in overlapping relationship. A metering device for dispensing adhesive fluid is constructed with a dispensing rod having a cooling means for facilitating operation of the metering device. The present invention finds particular utility in bonding together the inner and outer panels of an automotive door assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/708,121 filed on Nov. 7, 2000; which is a continuation of U.S. patent application Ser. No. 08/911,810 filed on Aug. 15, 1997, now U.S. Pat. No. 6,180,199; which is a continuation of U.S. patent application Ser. No. 08/486,694 filed on Jun. 7, 1995, now U.S. Pat. No. 5,783,298; which is a continuation of U.S. patent application Ser. No. 08/195,746 filed on Feb. 14, 1994, now U.S. Pat. No. 5,470,416; which is a continuation of U.S. patent application Ser. No. 07/869,649 filed on Apr. 16,1992, now abandoned. The disclosures of the above applications are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to adhesively bonding at least two members and, more particularly, to joining at least two members with a mixture of an adhesive and non-compressible beads.  
         BACKGROUND OF THE INVENTION  
         [0003]    [0003]FIGS. 1 through 4 show a method of making a hemmed joint for inner and outer sheet metal door panels. FIG. 1 shows a first member  10 , a second member  12 , and an amount of adhesive  14  which has been applied to second member  12 . In FIG. 2, first member  10  has been placed into proximity with second member  12 , and first and second members  10 , 12  have been squeezed together. The area where first and second members  10 , 12  overlap defines an adhesive joint  15 . Adhesive  14  has spread throughout the area of joint  15 . FIG. 2 further shows a hemming die  18  which is pressed downward to bend a portion of second member  12  into overlapping relationship with first member  10 . In FIG. 3, a second hemming die  20  is shown completing the hem by further folding down a portion of second member  12  to overlap first member  10 , such that a hemmed portion  22  of second member  12  is parallel with the portions of first and second members  10 , 12  in the area of joint  15 . Quite often, adhesive  23  is squeezed out of the area of joint  15  as a result of completion of the hemming operation. This squeezed-out adhesive  23  is unsightly and often requires removal in an additional. manufacturing step where aesthetics is important, such as in the making of an automobile door where inner and outer panels are hemmed together.  
           [0004]    Following formation of the hemmed joint  15 , the first and second members  10 , 12  tend to elastically relax and “spring back” toward their original. positions. FIG. 4 shows joint  15  subsequent to this “spring back” phenomenon, which tends to create an air-filled gap  26  between adhesive material  14  and first member  10 . Air-filled gap  26  results because adhesive  14  has been squeezed out of joint  15  and an insufficient amount remains to fill the void created by the “spring back” of first and second members  10 , 12 . This air-filled gap  26  reduces the area of joint  15 , resulting in a weakened joint.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a method and apparatus for adhesively joining at least two members in which a plurality of non-compressible beads are mixed with the adhesive, and one of the members is folded into overlapping relationship with the other in a hemming operation. The beads may be added to the adhesive in a preselected substantially uniform concentration. The apparatus for performing this method includes a container for containing a mixture of an adhesive and a plurality of non-compressible beads. An application gun applies this mixture to at least one of the members to be joined. A pump is employed for pumping the bead and adhesive mixture from the container through the application gun onto at least one of the members. A hemmer then hems one member into overlapping relationship with another.  
           [0006]    The present invention further provides a metering device having an improved displacement rod which includes a cooling means for cooling the rod and preventing the adhesive fluid from hardening, thus facilitating insertion of the displacement rod into the metering chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The various advantages and features will become apparent from the following description and claims in conjunction with the accompanying drawings:  
         [0008]    [0008]FIGS. 1 through 4 are sectional views showing steps in making a hemmed adhesive joint which illustrate the problem solved by the present invention;  
         [0009]    [0009]FIGS. 5 through 8 are sectional views of a hemmed adhesive joint formed according to the principles of the present invention;  
         [0010]    [0010]FIG. 9 is a perspective and partial cut-away view of an apparatus according to the principles of the present invention;  
         [0011]    [0011]FIG. 10 is a cut-away view of a metering device according to the principles of the present invention;  
         [0012]    [0012]FIG. 11 is a cut-away view of a displacement rod according to the principles of the present invention; and  
         [0013]    [0013]FIG. 12 is a cut-away view of an adhesive application gun according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention or its application or uses.  
         [0015]    Referring to the drawings, in which like reference numerals refer to similar features, FIGS. 5 through 8 show a method of joining a first and second member  11 , 13  according to the present invention. By way of a non-limiting example, the first and second members  11 , 13  are edges of inner and outer sheet metal automobile door panels. FIG. 5 shows first member  11 , second member  13 , and an amount of adhesive  17  which has been mixed with a plurality of non-compressible beads  24 , and this mixture has been applied to second member  13 . In FIG. 6, first and second members  11 , 13  have been squeezed together to form a joint  16 , which has caused the adhesive  17  and bead  24  mixture to spread throughout the area of joint  16 . The non-compressible beads  24  maintain a specific distance  28  between the portions of first and second members  11 , 13  in the area of joint  16 . Hemming die  19  is shown folding a portion of second member  13  over a portion of first member  11 . FIG. 7 shows the joint  16  following completion of the hemming operation by second hemming die  21 . The non-compressible beads  24  prevent an excess amount of adhesive  17  from being squeezed out of the area of joint  16  and maintain the predetermined distance  28  between first and second members  11 , 13  throughout all the areas of joint  16 . The joint  16  does not require additional processing to remove the unacceptable squeezed-out adhesive as in the aforementioned prior art technique.  
         [0016]    [0016]FIG. 8 shows joint  16  following plastic relaxation of first and second members  11 , 13  toward their original positions. Because beads  24  ensure that most of adhesive  17  remains in the area of joint  16 , the joint  16  created by a method of the present invention tends to maintain its integrity and prevent creation of an air-filled gap in the area of joint  16 , resulting in a stronger bond between first and second members  11 , 13 .  
         [0017]    The beads  24  need not be spherical, although a spherical shape is preferable. Beads  24  are preferably made of glass and should be mixed with adhesive  17  in a concentration which is sufficiently high to prevent beads  24  from becoming partially embedded in the surfaces of the members  11 , 13  during the hemming operation, and should not show “read through” to the outer panel surface  25 . “Read through” is defined as an imperfect, uneven or bumpy outer surface  25  of second member  13 . The concentration of beads  24  in adhesive  14  should also be sufficiently low to provide a strong joint and not to damage apparatus for handling and pumping the bead and adhesive mixture. The adhesive in mixture  17  is preferably a blend of a two component acrylic/epoxy adhesive, such as Versilok 252 and Versilok 254 available from Lord Corporation. The concentration of beads  24  in the mixture range from about 5% to about 20% of the total weight of the mixture and about 10% by weight is preferable, which results in approximately 1000 beads per square inch of the adhesive mixture in the final joint.  
         [0018]    The beads  24  should preferably be made having a diameter sufficiently low to provide a strong joint and sufficiently high such that the beads  24  are effective spacers, without showing “read through” to the outer panel. Acceptable diameters for the beads  24  range from 0.003 to 0.030 inches, and 0.010 inches is preferable.  
         [0019]    [0019]FIG. 9 depicts apparatus  30  for forming an adhesive bond according to the method of the present invention. In the embodiment of FIG. 9, the adhesive is a two part adhesive consisting of a first component  32  and a second component  34 . The present invention may also be practiced with a one component adhesive. The proper amount of beads  24  are mixed in container  38  with the first component  32  to achieve the aforementioned concentration. The first component  32 , in this particular example, is Versilok 252 which contains acrylic and an epoxy curative. (Second component  34  contains epoxy resin and an acrylic curative). Beads  24  are mixed with first component  32  because it is more thixotropic than. second component  34 , thereby keeping the beads in suspension for longer periods of time. It is the understanding of the inventors that a pre-mixed bead/adhesive mixture is now available from Lord Corporation as Versilok 253. A second container  40  substantially similar to first container  38  contains second component  34 . First and. second containers  38 , 40  are preferably 55 gallon drums, as used in the art. First and second pumps  42 , 44  pump the first mixture  36  of first component  32  and beads  34  as well as the second component  34  from first and second containers  38 , 40  respectively. First mixture  36  is pumped through a first supply tube  46  into a first metering chamber  56  of a metering device  50  through a first inlet valve  52 . Second component  34  is pumped through a second supply tube  48  into a second metering chamber  58  of metering device  50  through a second inlet valve  54 .  
         [0020]    A first and second valve member (not shown) are operated by compressed air tubes  60 , 62  and  132 ,  134 . The operation of first and second valve  52 , 54  by compressed air tubes  60 , 62  and  132 ,  134  respectively will be explained below. First mixture  36  and second component  34  are then displaced from first and second metering chambers  56 , 58  through exit valves (not shown) identical to inlet valves  52 ,  54  and then into application tubes  114 ,  115  into an adhesive application gun  102  which is shown in greater detail in FIG. 12. Adhesive gun  102  has left and right halves (not shown) each containing a valve (not shown) operated by compressed air tubes  136 , 138  and  140 , 142 . Adhesive materials exit adhesive gun  102  and are mixed in an elongated mixing nozzle  118  and the resulting mixture is applied to a member  11 , 13  to be adhesively joined.  
         [0021]    Adhesive materials consisting of first mixture  36  and second component  34  flow through first and second valves  52 , 54  into a metering device  50  which is shown in greater detail in FIG. 10. Metering device  50  defines a first and a second metering chamber  56 , 58 . The first mixture  36  is pumped into first metering chamber  56  and second component  34  is pumped into second metering chamber  58 , with the exit valves being closed. The force of the fluids being pumped into the metering chambers causes rods  78 ,  78 ′ to be pushed upwardly. First and second valves  52 , 54  then close, preventing flow of first mixture  36  or second component  34 .  
         [0022]    First and second valves  52 , 54  are constructed substantially similarly having a valve seat  68 , 68 ′ and a valve member  70 , 70 ′ consisting of a spherical valve plug  72 , 72 ′ connected to a longitudinally extending valve shaft  74 , 74 ′ which is in turn connected to a plate-shaped piston member  76 , 76 ′. Inlet tubes  46 , 48  are connected to first and second valve  52 , 54  and allow fluid to enter valve chambers  116 , 116 ′. Compressed air hoses  60 , 62  and  132 , 134  are also connected to first and second valves  52 , 54 .  
         [0023]    Valve members  70 , 70 ′ are moved between open and closed positions by creating a pressure differential across pistons  76 , 76 ′ . To close the valve, the pressure in valve opening chamber  64 , 64 ′ is alleviated, and compressed air is forced into the closing chamber  66 , 66 ′ by closing compressed air tube  62 , 134  to increase the pressure therein. The resulting difference in pressure across piston  76 , 76 ′ causes the valve shaft  74 , 74 ′ to move axially and press spherical valve plug  72 , 72 ′ into place against the valve seat  68 , 68 ′ . To open valve, the pressures in opening and closing chambers  64 , 66  and  64 ′ , 66 ′ are reversed. When first and second valves  52 , 54  are open, first mixture  36  and second component  34  which are under pressure due to first and second pumps  42 , 44  enter first and second metering chambers  56 , 58  through valve chambers  116 , 116 ′ and from inlet tubes  46 , 48 .  
         [0024]    Valve plug  72 , 72 ′ must make full circular contact with valve seat  68 , 68 ′ to completely shut off flow. As a result, valve plug  72  and seat  68  are made of. a material sufficiently strong to resist damage by beads  24 , or strong enough to repeatedly crush any glass beads  24  without damage. As a result, valve plug  72  and seat  68  are preferably constructed of tungsten carbide or hardened steel. The same is true of the exit valve (not shown) which is connected to chamber  56 .  
         [0025]    Metering device  50  further has a first and second displacement rod  78 , 78 ′ which are assembled through a bearing  79 , 79 ′ and opposing seals  81 , 81 ′ formed with  0 -rings  82 , 82 ′ to retain them in place. Displacement rod  78  is preferably made of hardened steel to prevent damage by the beads. Displacement rods  78 , 78 ′ are adapted to be forced into first and second chamber  56 , 58  respectively, and thereby to displace first mixture  36  as well as second component  34  from first and second chamber  56 , 58 . As a result, first mixture  36  and second component  34  are forced by displacement rods  78 , 78 ′ through outlets  83 , 83 ′ and through a first and second application tube  114 , 115  into an application gun  102  and a mixing nozzle  118  which combines first mixture  36  and second component  34  into a second mixture of component  32 , second component  34 , and beads  24 . Gun  102  is used to apply second mixture to a member  11 , 13  to form an adhesive joint  16  according to the present invention. Rods  78 ,  78 ′ have different but constant cross-sections throughout their longitudinal lengths. Accordingly, rods  78 ,  78 ′ force a preselected volume flow ratio of first mixture  36  and second component  34  out of outlets  83  and  83 ′, respectively, in the proper proportion substantially equivalent to the cross-sectional ratio of the diameter of rod  78  to rod  78 ′ when they are moved downwardly by power head  77 .  
         [0026]    [0026]FIG. 11 depicts displacement rod  78  as having a cooling system to prevent partial polymerization or hardening of the adhesive fluid located near the juncture of the rod  78  and housing of metering device  50  at the seal  81 . The displacement rod  78  is constructed of an upper and lower head block  80 , 82  which are each formed with vertical bores  84 , 86 . The bore  84  formed in upper head block  80  has a smaller diameter than bore  86  formed in lower head block  82 . Bore  84  formed in upper head block  80  carries the upper end of an inner flow tube  88  which has an inlet  90  and an outlet  92 . Upper head block  80  is formed with a horizontally extending inlet passage  94  which opens into the inlet  90  of inner flow tube  88 . Bore  86  formed in lower head block  82  carries the upper end of a displacement tube  96  which has an outlet  98  at one end and a cap  100  at the other end which allows no fluid communication. Inner flow tube  88  extends throughout a majority of the length of displacement tube  78 .  
         [0027]    In operation of the displacement rod  78  cooling system, cooling fluid such as water enters and flows through inlet passage  94  to inlet  90  of inner flow tube  88  as shown by the arrows in FIG. 11. Coolant fluid flows through inner flow tube  88  and exits through outlet  92 . Coolant fluid undergoes a flow reversal and proceeds upward through a gap  101  formed between the outer surface of inner flow tube  88  and the inner surface of displacement tube  96  and exits displacement rod  78  through outlet  98 .  
         [0028]    [0028]FIG. 12 shows the adhesive application gun  102 . Adhesive gun  102  is formed with side walls  104 , 104 ′, a rear panel  106 , a central longitudinally extending partition  108 , and a front nozzle portion  109 . Central partition  108  defines left and right symmetrical halves  110 , 112  of adhesive gun  102 . Each half  110 , 112  of adhesive gun  102  includes similar valves  128 , 130  constructed substantially similar to first and second inlet valves  52 , 54  and have a valve seat  144 , 144 ′ , valve plug  143 , 143 ′ valve member  146 , 146 ′, and application inlet tubes  114 , 115  which allow fluid to enter valve chambers  148 , 148 ′ . Valve seat  144  and plug  143  are made of tungsten carbide or other hardened materials to reduce bead damage. Compressed air hoses  136 , 138  and  140 , 142  operate valves  128 , 130  as described above. When the valves  128 , 130  are open, adhesive fluid under pressure due to displacement rods  78 , 78 ′ enters valve chambers  148 , 148 ′ through fluid inlet hoses  114 , 115  and proceeds out of adhesive gun  102  through nozzle  109 .  
         [0029]    An elongated mixing nozzle  118  is affixed to and extends from nozzle  109  formed on adhesive gun  102 . Mixing nozzle  118  is formed as an elongated tube  120  having an inlet  122  and an outlet  124  and contains a plurality of helical mixing elements  126 . The adjacent ends of successive helical elements  126  should not be aligned so that the adhesive fluids entering left and right sides  110 , 112  of adhesive gun  102  are thoroughly mixed. The resulting mixture exits mixing nozzle  118  through outlet  124 . Because first component  32  and second component  34  are mixed within mixing nozzle  118 , mixing nozzle  118  should be unscrewed and flushed or purged of old adhesive materials approximately every 15 to 20 minutes to prevent polymerization..  
         [0030]    Hemming apparatus as known in the art is used to fold one member  10  into overlapping relationship with a second member  12 . Hemming means preferably should apply local pressures in the range of 2000 to 10,000 pounds per square inch, but should be at least 1000 pounds per square inch. A typical hemming machine is commercially available from E. R. St. Dennis &amp; Sons Ltd. of Old Castle, Ontario, Canada.  
         [0031]    It should be understood that various modifications of the preferred embodiments of the present invention will become apparent to those skilled in the art after a study of the specification, drawings, and the following claims.