Abstract:
A method of joining a first body made of a first material to a second body made of a second material is disclosed. The method includes the steps of placing an adhesive between the first body and second body, moving the first body toward and into contact with the second body with the adhesive between the first body and the second body, pre-curing the adhesive, and curing the first body and second body in an oven. Pre-curing may be done by induction curing along a bonding line, pre-curing adhesive in a low temperature oven, or using a two-part adhesive.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional application No. 62/150,670, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    As temperature is applied to a material when a component is traveling through a cure oven, usually to cure an electrodeposition coating or electrostatic paint, the material will expand at a rate proportional the change in temperature. Different materials have different rates at which they expand. If the difference in thermal expansion is great enough between two bonded dissimilar materials, such as steel and aluminum, deformation can occur in either the joined materials or the mechanical joint. 
         [0003]    When adhesive is applied to these joints, the thermal expansion difference may also cause failure of the adhesive before it can fully cure to both surfaces. To account for this, adhesive suppliers have formulated adhesives to maintain flexibility during the curing process to account for this thermal expansion difference without failing. The challenge for the adhesive is to maintain enough flexibility to prevent failure when there is thermal expansion difference between the bonded surface, but then to maintain long term durability after cure. Typically increasing flexibility of the adhesive will compromise the shear strength. 
       APPLICATION SUMMARY 
       [0004]    The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. 
         [0005]    According to one aspect, a method of joining a first body made of a first material to a second body made of a second material is disclosed. The method includes the steps of placing an adhesive between the first body and second body, moving the first body toward and into contact with the second body with the adhesive between the first body and the second body, pre-curing the adhesive, and curing the first body and second body in an oven. 
         [0006]    According to another aspect, a vehicle component manufactured by the process of joining a first body made of a first material to a second body made of a second material is disclosed. The process includes the steps of placing an adhesive between the first body and second body, moving the first body toward and into contact with the second body with the adhesive between the first body and the second body, pre-curing the adhesive, and curing the first body and second body in an oven. 
         [0007]    According to yet another aspect, a method of partially curing an adhesive is disclosed. The method includes the steps of providing a first body and a second body, the first body and second body to be adhered together, placing the adhesive between the first body and second body, moving the first and second parts into contact, and pre-curing the adhesive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is schematic representation of a joint joining two dissimilar materials; 
           [0009]      FIG. 2  is schematic representation of a joint joining two dissimilar materials with an adhesive; 
           [0010]      FIG. 3  is schematic representation of an alternate embodiment joint joining two dissimilar materials with an adhesive; 
           [0011]      FIG. 4  is schematic representation of an alternate embodiment joint joining two dissimilar materials with an adhesive; 
           [0012]      FIG. 5  is schematic representation of a prior art embodiment joint joining two dissimilar materials with an adhesive; 
           [0013]      FIG. 5 a    is close-up schematic representation of a portion of the  FIG. 5  prior art embodiment joint joining two dissimilar materials with an adhesive; 
           [0014]      FIG. 6  is schematic representation of an alternate embodiment joint joining two dissimilar materials with an adhesive; 
           [0015]      FIG. 6 a    is close-up schematic representation of a portion of the  FIG. 6  embodiment joint joining two dissimilar materials with an adhesive; and 
           [0016]      FIG. 7  is schematic representation of an alternate embodiment joint joining two dissimilar materials with an adhesive. 
       
    
    
       [0017]    The figures depict various embodiments of the embodiments for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the embodiments described herein. 
       DETAILED DESCRIPTION 
       [0018]    The apparatuses and methods disclosed in this document are described in detail by way of examples and with reference to the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatuses, methods, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific techniques, arrangements, etc. are either related to a specific example presented or are merely a general description of such a technique, arrangement, etc. Identifications of specific details or examples are not intended to be, and should not be, construed as mandatory or limiting unless specifically designated as such. Selected examples of expandable adhesives for joining two vehicle components are hereinafter disclosed and described in detail with reference made to  FIGS. 1-7 . 
         [0019]    Two structural components of the vehicle can be coupled or joined together by forming a joint between the two structural components. The structural components can be joined together rigidly or can be joined together so as to permit relative motion between the two structural components. A vehicle, such as an automobile, can include a body that can be substantially supported by a frame, where the body can include a number of panels such as body panels and a hood. 
         [0020]    In one example, schematically illustrated in  FIGS. 1-3 , a joint  10  can be formed between a first body  12  and a second body  14  with an adhesive  16  positioned between the first body  12  and the second body  14 . In one example, the first body  12  can be a hood panel and the second body  14  can be a body panel. In another example, the first and second bodies  12 ,  14  can be respective outer and inner panels of a rocker panel assembly. However, it will be understood that a joint can be formed from any of a variety of other vehicular components or other bodies in any of a variety of suitable configurations. As illustrated in  FIG. 1 , in preparation for forming the joint  10 , the first body  12  and the second body  14  can be placed adjacent to one another. As illustrated in  FIG. 2 , an adhesive  16  can be placed between the first body  12  and the second body  14 , and the first body  12  and the second body  14  can be moved towards one another so that the adhesive  16  comes into contact with both the first body  12  and the second body  14 . 
         [0021]    As illustrated in  FIG. 3 , a fastener  18  can be inserted through the first body  12 , second body  14 , and adhesive  16  to form the joint  10 . The fastener  18  can be inserted in a manner that facilitates a sustained connection between the first body  12  and second body  14 . In one example, the fastener  18  can be a rivet, but it will be understood that a fastener can be any of a variety of other types of suitable mechanical fasteners. The process of inserting the fastener  18  can apply a pressure such that the first body  12  and the second body  14  progressively move toward one another. Such movement of the first body  12  and the second body  14  can apply pressure on the adhesive  16  and result in the adhesive  16  flowing so as to move toward and past the edges of the first body  12  and second body  14 , as illustrated in  FIG. 3 . 
         [0022]    In another example, a joint can be formed without a fastener  18 . A temporary apparatus such as a clamp can be used to secure the first body  12  and second body  14  in relative position until the adhesive  16  is cured. Or the adhesive  16  can be at least partially cured early in the joint formation process so that the fastener  18  is not needed. 
         [0023]    As will be described below, the adhesive  16  can be arranged to provide a number of features or functions for the joint  10 . For example, the adhesive  16  can be arranged to be expandable when exposed to heat. Such an expandable adhesive  16  can spread along surfaces of the first body  12  and second body  14  so as to cover and protect surfaces that are otherwise uncoated and/or exposed. In another example, the adhesive  16  can include properties that upon partial curing of the adhesive  16  will secure the first body  12  and second body  14  in a proper relative alignment to accommodate additional processing steps of forming the joint  10  such as applying corrosive prevention layers or applying paint layers. In another example, the adhesive  16  can include insulating properties so that the first body  12  is insulated from the second body  14  so as to inhibit galvanic corrosion. 
         [0024]    Vehicle components such as body panels, hood panels, and other such components can be formed, for example, from a metal or metal alloy or another material, such as plastic or fiberglass. It will be understood that vehicle components can be formed from any of a variety of suitable materials. Thus, in certain examples, a joint can include a first body and a second body that are formed from similar or dissimilar materials. In one example, dissimilar materials can be used by forming the first body  12  of the joint  10  from steel, and forming the second body  14  of the joint  10  from aluminum. In such an example, the first body  12  and the second body  14  can have different physical and/or mechanical properties. In one example, the first body  12  and the second body  14  can have different coefficients of linear thermal expansion. 
         [0025]    When the materials are dissimilar, the joint  10  can be arranged such that the arrangement provides protection to the first body  12  and second body  14  against galvanic corrosion when the first body  12  and second body  14  come into contact with an electrolyte such as dissolved road salt. One arrangement that can offer protection against galvanic corrosion is the positioning of the adhesive  16  between the first body  12  and second body  14 . Such positioning of the adhesive  16  can provide physical separation between the first body  12  and the second body  14 . As described above, when the joint  10  is formed, the movement of the first body  12  toward the second body  14  can result in the adhesive  16  flowing so as to move toward and past the edges of the joint  10  to form a separation layer between the first body  12  and the second body  14 . Furthermore, when the adhesive  16  is formed so that it functions as an insulator, the adhesive  16  can facilitate isolation of the galvanic potential between the first body  12  and the second body  14 . Thus, the first body  12  and the second body  14  can be isolated and insulated by the adhesive  16  within a framework of the joint  10 . 
         [0026]    In addition to protection provided by the adhesive  16 , the joint  10  can be coated with a corrosion prevention layer. The corrosion prevention layer can be an epoxy-based coating. In one example, the coating can be applied by an electrodeposition coating process, also known as e-coating. In such example, e-coating can include any of a variety of suitable methods for e-coating, any of which can be used to apply a corrosion preventing layer to a joint  10 . 
         [0027]    E-coating can be preceded by cleaning and/or treating the exposed surfaces of the first body  12  and the second body  14 , which can provide sufficient phosphatability to facilitate proper coating formation. As illustrated in  FIG. 4 , a surface conditioner  20  can be applied to the exposed surfaces of the first body  12  and the second body  14  to facilitate the coating of the joint  10 . Generally, e-coating can include submerging the joint  10  into an electrodeposition bath in an e-coating tank, which can include, a binder resin, a synthetic resin, and optionally, a pigment and other additives dissolved or dispersed in a solvent. In an example, an epoxy resin can be used, along with any of a variety of other suitable resins. 
         [0028]    Upon immersion into the e-coating tank, the joint  10  can come into contact with electrodes such that a voltage can be applied between the cathode and an anode to provide current through the electrodeposition bath resulting in the application of a protective coating  22  on the joint  10 . Such a protective coating  22  is illustrated in  FIGS. 5 and 6 . In one example, the joint  10  can undergo electrodeposition one or more times, and in some embodiments, the joint  10  can be washed between coatings, post-coating, or both. 
         [0029]    When the process of applying a protective coating  22  as described herein is performed with prior art adhesives  24 , portions of the first body  12  and second body  14  can remain unprotected after the protective coating  22  has been applied to the joint  10 . As illustrated in  FIGS. 5 and 5A , the use of a prior art adhesive can result in the first body  12  including an unprotected section  26 . In one example, as will be described below, the joint  10  undergoes one or more heating processes during the application of the protective coating  22  and any subsequent applications of paint. Some prior art adhesives  24  can shrink during heating processes. As illustrated in  FIG. 5A , such shrinkage can result in a gap G between the prior art adhesive  24  and the protective coating  22  that exposes a section  26  of the first body  12  to potential corrosion. As is also illustrated in  FIGS. 5 and 5A , the second body  14  can include a similar exposed section. The exposed section  26  can result in corrosion of the joint  10 . In another example, if the surface conditioner  20  is not effective at the interface of the first body  12  and second body  14 , a similar gap G can result and a section  26  of the first body can be exposed. 
         [0030]    The adhesive  16  can be an expandable adhesive, and in certain examples, partial curing can cause the adhesive  16  to expand to cover the exposed section  26  of the first body  12  as illustrated in  FIGS. 6 and 6A . In other examples, the adhesive  16  can be expandable upon fully curing. The adhesive  16  can also expand to cover the exposed section of the second body  14 . In certain arrangements, such as a rocker panel assembly, expansion of the adhesive  16  can extend over sections of an interior that might otherwise remain exposed using the prior art adhesives. When the interior is then e-coated, the e-coating can be more complete and thus enhance the overall integrity of the rocker panel assembly. An example of the effects of the expandable adhesive is shown in Appendix A. 
         [0031]    In some examples, partial curing can be effected by one or more chemical processes and/or preliminary and localized heating of the adhesive  16  such that any effects of thermal expansion of the first body  12  and/or second body  14  can be minimized. In one embodiment, the adhesive  16  can be partially cured with an induction cure of the bond line (e.g., localized heating) prior to introduction into an e-coating oven (for curing the e-coat). In another embodiment, the adhesive  16  can be partially cured by passing the joint  10  through a “pre-cure” oven that prior to the e-coat oven. The pre-cure oven can be smaller than, and operate at a lower temperature than, the e-coating oven. In yet another embodiment, the adhesive  16  can be partially cured by incorporating a secondary chemical reaction into the adhesive formulation that achieves some initial strength buildup prior to introduction into the e-coating oven. However, it will be appreciated that any of a variety of suitable methods can be employed alone or in combination with other methods to effect sufficient partial curing of an adhesive. 
         [0032]    In one example, the adhesive can be an adhesive as described and disclosed in WIPO Patent Application WO/2006/128722, entitled Toughened Epoxy Adhesive Composition, and filed on Jun. 2, 2006, which is incorporated herein by reference. In another example, the adhesive can be the adhesive described and disclosed in WIPO Patent Application WO/2006/128722 and further including a foaming agent. 
         [0033]    After the protective coating  22  is formed, the protective coating  22  can be cured by baking the joint  10  in an oven. In certain examples, the oven can be heated to about 150° C. or greater; in other examples, the oven can be heated to about 180° C. or greater; and in other embodiments, the oven can be heated to about 195° C. or greater. 
         [0034]    The joint  10  can be arranged to rely on the adhesive  16  to facilitate maintaining an alignment of the first body  12  and the second body  14 . In such embodiments where the first body  12  and the second body  14  are formed from dissimilar materials, the properties of the materials can be considered. For example, dissimilar materials, such as steel and aluminum, can expand at different rates when heated to temperatures associated with the e-coat bake (i.e., first body  12  and the second body  14  can include different coefficients of linear thermal expansion). Uneven expansion during thermal loading as well as uneven contraction during thermal relaxation can create stress on the joint  10  and particularly on the adhesive  16  when the adhesive  16  is fully cured thus causing the adhesive to undergo plastic deformation or failure which can result in poor long term durability and/or performance. To account for this, the adhesive  16  applied to the joint  10  can be partially cured prior to the e-coat bake to fix the first body  12  with respect to the second body  14  before coating the joint  10 . Such an arrangement can facilitate maintaining functionality of the adhesive  16  through an e-coat process. The adhesive  16  can be partially cured such that it can facilitate sustaining the connection between the first body  12  and the second body  14  during the e-coat and can retain sufficient flexibility to endure the uneven thermal expansion of the first body  12  and the second body  14  (i.e., distribute stress) during the subsequent e-coat bake. Thus, the adhesive  16  can cooperate with the first body  12  and second body  14  to maintain alignment through both the coating and subsequent baking of the joint  10  after partially curing the adhesive  16 . In certain examples, the adhesive  16  can be fully cured in the oven, along with the coating  20 , during the e-coat bake. 
         [0035]    Thus, in certain examples, the joint  10  can include an adhesive  16  that can be effective where the first body  12  has a first coefficient of linear thermal expansion and the second body  14  has a second coefficient of linear thermal expansion, such that the first and second coefficients of linear thermal expansion are different. In one example, when partially cured, the adhesive  16  can withstand a pressure of 10 MPa. 
         [0036]    The adhesive  16  can undergo the expansion described herein while fully curing in the oven during the e-coat bake. In one example, in arrangements where the adhesive  16  expands during partial curing, the adhesive  16  can undergo additional expansion while fully curing. 
         [0037]    In some example, a foaming agent can be combined with a base resin composition to provide an adhesive with a desired expanding effect. It will be appreciated that a joint can include any of a variety of suitable adhesives, foaming agents, and combinations thereof such that sufficient expansion can be affected to provide desired protection. 
         [0038]    According to one example, a method of making a joint  10  can include providing the joint  10  including the first body  12 , the second body  14 , and the expandable adhesive  16  therebetween. The method can further include coating the joint  10  and expanding the adhesive  16  to cover at least a portion of the coating  20  on each of the first and second bodies  12 ,  14 . In some embodiments, the method can further include partially curing the adhesive  16  to fix the first body  12  with respect to the second body  14 . And in such embodiments, the method can further include fully curing the adhesive  16  by baking the joint  10  in an oven, wherein the adhesive  16  can expand to cover at least a portion of the coating  22  on each of the first and second bodies  12 ,  14  and the adhesive  16  can cooperate with the first and second bodies  12 ,  14  to maintain an alignment of the joint  10  established during partially curing the adhesive  16 . 
         [0039]      FIG. 7  illustrates a panel  110  according to another embodiment. The joint  110  can be similar to, or the same in many respects as, the joint  10  of  FIGS. 1-6 . For example, the joint  110  can include a first body  112 , a second body  114 , an adhesive  116 , and a plurality of fasteners  118 . The adhesive  116  can be positioned between the first body  112  and the second body  114 . The fastener  118  can be inserted through the first body  112 , the second body  114 , and the adhesive  116  to form the joint  110 . However, during manufacture of the joint  110 , the adhesive  116  can be deposited onto the first body  112  or the second body  114  in segments that are spaced from each other (e.g., a stitch bead application) such that the adhesive  116  defines a plurality of gaps  130 . Each of the fasteners  118  can extend through respective ones of the gaps  130  to prevent interference between the adhesive  116  and the fasteners  118 . 
         [0040]    Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment. The appearances of the phrase “in one embodiment” or “an embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0041]    In addition, the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the embodiments, which is set forth in the claims. 
         [0042]    While particular embodiments and applications have been illustrated and described herein, it is to be understood that the embodiments are not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatuses of the embodiments without departing from the spirit and scope of the embodiments as defined in the appended claims.