Patent Publication Number: US-2019176590-A1

Title: Hemming structure and hemming method for hybrid-type door

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2017-0168701, filed Dec. 8, 2017, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to a hemming structure and a hemming method for a hybrid-type door. More particularly, the present invention relates to a hemming structure and a hemming method for a hybrid-type door, in which it is possible to prevent deformation caused by difference in thermal expansion coefficient between an external panel of aluminum and an internal panel of steel. 
     Description of Related Art 
     Generally, a vehicle door has a structure composed of two or more panels connected to each other for weight reduction and rigidity maintenance. 
     For example,  FIG. 1  shows sectional views of a hemming structure and a problem of a conventional door. As shown in  FIG. 1 , the hemming structure of the conventional door may include an internal panel  10  disposed at the internal side of a vehicle body, and an external panel  20  disposed at the external side of the vehicle body. Here, at a junction area between the internal panel  10  and the external panel  20 , a flange  21  protruding more than the internal panel  10  by a predetermined length is disposed at an end portion of the external panel  20 , and a hemming structure is formed by being bent such that the flange  21  is brought into contact with an opposite surface of the internal panel  10  (a surface facing the internal of the vehicle). 
     Furthermore, a sealer  30  is applied onto the junction area between the internal panel  10  and the external panel  20  to prevent penetration of moisture and foreign matter. Here, the sealer  30  has an elongation property of about 10%, and an impact property of about 35 N/mm. The sealer  30  is cured as it passes through the oven during the painting process and maintains the impact property while increasing the bonding force between the internal and external panels. 
     Meanwhile, in recent years, to improve the physical properties of a door for weight reduction and rigidity maintenance, a hybrid-type door, in which the external panel may include aluminum material and the internal panel may include steel material, has been provided and used. 
     The sealer  30  is cured as it passes through an oven during the painting process and maintains the impact property while increasing the bonding force between the internal and external panels. 
     Meanwhile, in recent years, to improve the physical properties of a door for weight reduction and rigidity maintenance, a hybrid-type door, in which the external panel may include aluminum material and the internal panel may include steel material, has been provided and used. 
     However, the door of the hybrid type is subjected to the hemming process as shown in {circle around ( 1 )} of  FIG. 1 , and then passes through an oven during the painting process. Here, as shown in {circle around ( 2 )} of  FIG. 1 , due to the difference in thermal expansion coefficient between the internal panel  10  of steel and the external panel  20  of aluminum, the external panel  20  of aluminum is expanded more than the internal panel  10  of steel. Then, a sealer is cured as shown in {circle around ( 3 )} of  FIG. 1  with the external panel  20  expanded more than the internal panel  10 . During the process of cooling after the painting process with the external panel  20  and the internal panel  10  bonded together, the external panel  20  of aluminum contracts more than the internal panel  10  of steel as shown in {circle around ( 4 )} of  FIG. 1 , causing distortion. 
     Meanwhile, if the elongation of the sealer used in the hybrid-type door is improved, it is possible to prevent distortion caused by the difference in thermal expansion coefficient between different materials, but a sealer with high elongation cannot be used because of its low rigidity and bonding performance. 
     The information included in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and may not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY 
     Various aspects of the present invention are directed to providing a hemming structure and a hemming method for a hybrid-type door, in which it is possible to prevent deformation caused by difference in thermal expansion coefficient between an external panel of aluminum and an internal panel of steel. 
     According to various aspects of the present invention, there is provided a hemming structure for a hybrid-type door, in which the door may include an internal panel and an external panel made of different materials, the hemming structure being configured such that each of the internal panel and the external panel is provided with a contact area with end portions of the internal panel and the external panel being brought into contact with each other at the contact area, wherein the contact area may include a first contact area with a sealer applied onto a contact surface between the internal panel and the external panel, and a second contact area extending from the first contact area and being bent to be brought into contact with the internal panel at the first contact area, and the second contact area is provided with a bonding portion at which the internal panel and the external panel are mechanically bonded to each other. 
     The internal panel may include a steel material, the external panel may include an aluminum material, and the sealer may include a resin material with an elongation ratio of 20 to 40%. 
     The bonding portion may be formed by a method selected from the group consisting of clinching, self-piercing riveting (SPR), and resistance element welding (REW). 
     The bonding portion may be provided with a protruding surface protruding in a direction from the internal panel to the external panel. 
     Meanwhile, according to various aspects of the present invention, there is provided a hemming method for a hybrid-type door, in which the door may include an internal panel and an external panel made of different materials, the hemming method including: preparation of the internal panel and the external panel each provided with a contact area including a first contact area with a sealer applied thereto along end portions of the internal panel and the external panel while the end portions are brought into contact with each other, and a bent second contact area; application of the sealer onto the first contact area of the external panel; loading of disposing the internal panel onto the external panel such that the first contact areas thereof are brought into contact with each other; a first processing of forming a bonding portion in the second contact areas of the internal panel and the external panel being in contact with each other, with the internal panel and the external panel being mechanically bonded to each other at the bonding portion; and a second processing of hemming the second contact areas of the internal panel and the external panel. 
     In the preparation step, the internal panel may include a steel material and the external panel may include an aluminum material, and in the application step, the sealer may include a resin material with an elongation ratio of 20 to 40%. 
     In the preparation step, each of the internal panel and the external panel may be configured such that the first contact area and the second contact area are bent at an obtuse angle. 
     In the first processing step, the bonding portion may be formed by a method selected from the group consisting of clinching, self-piercing riveting (SPR), and resistance element welding (REW). 
     In the first processing step, a protruding surface provided at the bonding portion may be processed to protrude in a direction from the internal panel to the external panel. 
     The second processing may include: a first pre-hemming process of hemming the internal panel and the external panel such that the first contact areas and the second contact areas thereof are at right angles to each other; a second pre-hemming process of hemming the internal panel and the external panel such that the first contact areas and the second contact areas thereof are at acute angles to each other; and a main hemming process of hemming the internal panel and the external panel such that the first contact areas and the second contact areas thereof are brought into contact with each other. 
     In the main hemming process of the second processing, the bonding portion provided at the second contact areas of the internal panel and the external panel may be set to be an unpressurized portion. 
     According to an exemplary embodiment of the present invention, since in the case of hemming the external panel around the internal panel, which include different materials, the sealer with high elongation is used, it is possible to suppress distortion caused by difference in thermal expansion coefficient between the different materials. 
     Furthermore, since the mechanical bonding portion is formed at the internal panel and the external panel to compensate decrease in rigidity due to use of the sealer with high elongation, it is possible to manufacture a door which is lightweight and reduces cost by combining the advantages of steel material and aluminum material. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows sectional views of a hemming structure and a problem of a conventional door; 
         FIG. 2  shows a sectional view of a hemming structure for a hybrid-type door according to an exemplary embodiment of the present invention; and 
         FIG. 3  shows a view of a hemming method for a hybrid-type door according to an exemplary embodiment of the present invention. 
     
    
    
     It may be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as included herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particularly intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION 
     Reference will now be made more specifically to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments of the present invention, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the other hand, the invention(s) is/are intended to cover not only the exemplary embodiments of the present invention, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
       FIG. 2  shows a sectional view of a hemming structure for a hybrid-type door according to an exemplary embodiment of the present invention. 
     As shown in the drawing, a hemming structure for a hybrid-type door according to the exemplary embodiment of the present invention, various aspects of the present invention are directed to providing a hemming structure for a vehicle hybrid-type door which includes an internal panel  100  and an external panel  200  made of different materials. For example, the internal panel  100  includes steel material having a small thermal expansion coefficient and the external panel  200  includes aluminum material having a high thermal expansion coefficient. Herein, the steel material includes an iron-based alloy, and the aluminum material includes an aluminum-based alloy. 
     The internal panel  100  and the external panel  200  are parts constituting a vehicle door, and the shapes thereof may be variously changed depending on the shape of the vehicle door. 
     Herein, each of the internal panel  100  and the external panel  200  is provided with a contact area at which end portions thereof are brought into contact with each other. Herein, the end portions of the internal panel  100  and the external panel  200  refer to edge portions of the internal panel  100  and the external panel  200 . 
     Here, the contact area F of each of the internal panel  100  and the external panel  200  includes a first contact area F 1  where sealer  300  is applied onto a contact surface between the internal panel  100  and the external panel  200 , and a second contact area F 2  extending from the first contact area F 1  and bent to be brought into contact with the internal panel  100  at the first contact area F 1 . Accordingly, each of the internal panel  100  and the external panel  200  is provided with the first contact area F 1  with the sealer applied thereto along end portions of the internal panel and the external panel while the end portions are brought into contact with each other, and the second contact area F 2  which is bent while hemming. 
     Meanwhile, as the sealer  300  used in the exemplary embodiment of the present invention, a high temperature curing sealer is cured while exposed to a high temperature (180 to 200° C.) during the painting process after hemming the hybrid-type door. The high temperature curing sealer may be, for example, epoxy-type sealer. However, the internal panel  100  and the external panel  200  are attached to each other as the sealer  300  is cured in the state where the internal panel  100  and the external panel  200 , which are different materials having different thermal expansion coefficients, are expanded to different levels when exposed to the high temperature during the painting process, so it is exemplary to use the sealer  300  with high elongation property to prevent distortion which may occur during contracting to different levels as they are cooled in the present state. For example, the sealer  300  maintains the elongation of about 20 to 40%. 
     Meanwhile, since the sealer  300  with high elongation has a lower impact property than the sealer with low elongation, to complement this, in the exemplary embodiment of the present invention, the second contact areas F 2  of the internal panel  100  and the external panel  200  are provided with a bonding portion  400  at which the internal panel  100  and the external panel  200  are mechanically bonded to each other. The formation of the bonding portion is not limited to a particular method, but various methods may be applied to mechanically bond the internal panel  100  and the external panel  200  to each other. For example, the bonding portion  400  may be formed by a method selected from the group consisting of clinching, self-piercing riveting (SPR), and resistance element welding (REW). 
     Herein, when the bonding portion  400  is formed, a protruding surface  410  protruding in one direction is formed at the external panel  200 , and the protruding surface  410  formed in the bonding portion  400  protrude in a direction from the internal panel  100  to the external panel  200 . 
     In another exemplary embodiment of the presently claimed invention, the external panel  200  may include a receiving groove  420  at a lower surface of the protruding surface  410  and the bonding portion  400  may further include a protruding surface  430  protruding from the internal pane  100  such that the protruding surface  430  of the internal pane  100  may be mounted on the receiving groove  420  of the external panel  200 . 
     In another exemplary embodiment of the presently claimed invention, the internal pane  100  may further include a groove  440  formed at a bottom portion of the protruding surface  430  of the internal pane  100 . 
     Accordingly, after hemming the second contact areas F 2  formed with the bonding portion, it is possible to prevent undesired bending portion when the protruding surface  410  formed in the bonding portion  400  is brought into contact with the internal panel  100  at the first contact area F 1 . 
     As described above, in the exemplary embodiment of the present invention, since the sealer  300  with a high elongation coefficient is applied onto the first contact areas F 1  of the internal panel  100  and the external panel  200 , it is possible to prevent distortion caused by difference in thermal expansion coefficient between the internal panel  100  and the external panel  200  while being cooled after painting process of the door, and it is also possible to compensate rigidity (impact property) reduced by the sealer  300  with high elongation. 
     A hemming method for the hybrid-type door configured as described above according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 3  shows a view of a hemming method for a hybrid-type door according to an exemplary embodiment of the present invention. 
     As shown in the drawing, a hemming method for a hybrid-type door according to an exemplary embodiment of the present invention is a hemming method for a vehicle hybrid-type door having the internal panel  100  and the external panel  200  made of different materials. As described above, the internal panel  100  may include steel material having a small thermal expansion coefficient and the external panel  200  may include aluminum material having a high thermal expansion coefficient. 
     Firstly, the internal panel  100  and the external panel  200  are prepared, each of which is provided with the contact area F including the first contact area F 1  with the sealer  300  applied thereto along end portions of the internal panel and the external panel while the end portions are brought into contact with each other, and the bent second contact area F 2  (preparation step). 
     Here, each of the internal panel  100  and the external panel  200  is configured such that the first contact area F 1  and the second contact area F 2  are bent at an obtuse angle. Accordingly, in the following first processing, it is possible to prevent a tool gun B used to form the bonding portion  400  from interfering with the internal panel  100  and the external panel  200 . 
     When the internal panel  100  and the external panel  200  are prepared, the sealer  300  is applied onto the first contact area F 1  of the external panel  200  by use of an application tool A (application step). Here, the applied sealer  300  may be made of resin material with an elongation ratio of 20 to 40%. Furthermore, the sealer  300  may be high temperature curing sealer which is cured while exposed to a high temperature (180 to 200° C.) during the painting process. 
     After applying the sealer  300 , the internal panel  100  is disposed onto the external panel  200  such that the first contact areas F 1  thereof are brought into contact with each other (loading step). In the loading step, the internal panel  100  is disposed onto the external panel  200  such that the second contact areas F 2  thereof are brought into contact with each other as well as the first contact areas F 1 . 
     Then, the bonding portion  400  with the internal panel  100  and the external panel  200  mechanically bonded to each other is formed at the second contact areas F 2  of the internal panel  100  and the external panel  200  (first processing). 
     Here, the bonding portion  400  may be formed by a method selected from the group consisting of clinching, self-piercing riveting (SPR), and resistance element welding (REW) used for bonding different materials. Herein, when the bonding portion  400  is formed, the protruding surface  410  protruding in one direction be formed to protrude in a direction from the internal panel  100  to the external panel  200 . 
     After forming the bonding portion  400 , the second contact areas F 2  of the internal panel  100  and the external panel  200  are hemmed such that the second contact area F 2  of the internal panel  100  and the first contact area F 1  of the internal panel  100  are brought into contact with each other (second processing). 
     The second processing may include: a first pre-hemming process of hemming the internal panel  100  and the external panel  200  such that the first contact areas F and the second contact areas F 2  thereof are at right angles to each other; a second pre-hemming process of hemming the internal panel  100  and the external panel  200  such that the first contact areas F and the second contact areas F 2  thereof are at acute angles to each other; and a main hemming process of hemming the internal panel  100  and the external panel  200  such that the first contact areas F and the second contact areas F 2  thereof are brought into contact with each other. Thus, a hemming tool C is used in the first pre-hemming process, the second pre-hemming process, and the main hemming process, wherein the first pre-hemming process, the second pre-hemming process, and the main hemming process are sequentially performed by controlling the operation of the hemming tool C. 
     Meanwhile, in the main hemming process, the bonding portion  400  formed at the second contact areas F 2  of the internal panel  100  and the external panel  200  is set to be an unpressurized portion. Herein, the unpressurized portion refers to a portion which is free from being pressurized by the hemming tool while the main hemming process is performed by use of the hemming tool C. The reason for setting the bonding portion  400  to an unpressurized portion is to prevent undesired deformation of the portion, preventing loss of the function of the bonding portion  400  or deterioration of the surface quality. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “internal”, “outer”, “up”, “down”, “upper”, “lower”, “upwards”, “downwards”, “front”, “rear”, “back”, “inside”, “outside”, “inwardly”, “outwardly”, “internal”, “external”, “internal”, “outer”, “forwards”, and “backwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described to explain certain principles of the present invention and their practical application, to enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the present invention be defined by the Claims appended hereto and their equivalents.