Patent Application
20160280048
The present disclosure relates to a vehicle-body structure constructed from multiple materials.
Current government regulations and fuel costs have increased the importance of producing motor vehicles that are fuel efficient. This increased emphasis on fuel efficiency has increased demand for lightweight-vehicle components, such as aluminum-alloy vehicle components. Aluminum alloys typically have a higher strength to weight ratio than steel alloys. Consequently, replacing steel with aluminum offers potential for weight reduction. Steel alloys and aluminum alloys may have different material properties. For example, aluminum alloys have a different coefficient of thermal expansion than steel alloys. These differences require unique design solutions in addition to material substitution.
According to one embodiment, a method of assembling vehicle-body components includes positioning a first component on a second component. The first component has a different coefficient of thermal expansion than the second component and one of the first and second components defines a slot. The method also includes loosely installing a bolt though the slot and the first and second components, and creating a joint in the first and second components. The method further includes heating the first and second components, which causes the first and second components to move relative to each other due to thermal expansion in response to the heating. This movement causes the joint to fail. The method also includes tightening the bolt.
According to another embodiment, a method of assembling a vehicle-body assembly includes positioning a first component on a second component. The first component has a different coefficient of thermal expansion than the second component, and one of the first and second components defines a slot. The method also includes installing a fastener assembly through the slot to join the first and second components. At least a portion of the fastener assembly is configured to disintegrate when exposed to a surface-treatment solution. The method further includes dipping the first and second components in the surface-treatment solution causing the at least a portion of the fastener assembly to disintegrate and the first and second components to thermally expand. The method also includes retightening the fastener.
According to yet another embodiment, a door-in-white assembly includes an inner panel having a mounting surface and a beam attached to the mounting surface by a fastener assembly. The beam has a lower coefficient of thermal expansion than the panel. The fastener assembly has at least one component configured to disintegrate during electro-coating such that the fastener assembly loosens allowing relative movement between the panel and beam resulting from thermal expansion during the electro-coating.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Referring to
The door-in-white assembly 20 also includes a beam 44, such as an anti-intrusion beam, disposed within the cavity 26 and attached to the exterior side 36 of the inner panel 22. The beam 44 includes a first end 46 and a second end 48. The first end 46 is attached to a first mounting surface 50 of the inner panel 22 at a first joint 52. The second end 48 is attached to a second mounting surface 54 of the inner panel 22 at a second joint 56. The beam 44 may extend longitudinally from the front of the door (i.e. the hinge face) to the rear of the door (i.e. the latch face), and acts as a passive safety device. As such, door beams are typically made of high-strength materials, such as steel.
Many of the door components, including the inner and outer panels, and the beam, are stamped separately and are assembled into a door-in-white assembly in a plurality of stages. In one stage, the beam 44 is attached to the inner panel 22. In a subsequent stage, commonly referred to as “door setting” the inner and outer panels 22, 24 are joined together by a hemming process. For example, the outer panel 24 is larger than the inner panel 22 and includes a flange 28 that is typically bent at 90 degrees relative to the main body of the outer panel 22. During hemming, an outer portion 30 of the inner panel 22 is placed against the outer panel 24 near the flange 28. The flange is folded over the outer portion 30 creating the hem 32, which holds the panels together. Adhesive may be applied to the hem 32 for increased strength and corrosion resistance. During the door-setting stage, the joints 52, 56 between the inner panel 22 and the beam 44 may be tight to help ensure a proper geometry of the door. After the door is set, the door may undergo painting stages. The term painting generally denotes a series of consecutive stages that may include applying one or more surface-treatment solutions to the components and passing the components though one or more ovens. The surface-treatment solutions may include cleaning, phosphorus coating, electro-coating (E-coating), and painting. The painting stages typically subject the door to heat. For example, the E-coating oven may have a temperature between 150° C. and 190° C. The various door components thermally expand when subjected to the painting stages and contract when cooled. Therefore, the door components may expand and contract several times throughout the assembly process.
To reduce vehicle weight, some components of the door 20 may be made of lightweight metal alloys. For example, the inner and outer panels 23, 24 may be an aluminum alloy. But, the door beams 44 typically remain steel. Having a bimetal door assembly 20 creates many manufacturing challenges. Heat exposure during painting causes the components of the door 20 to thermally expand. The amount of thermal expansion is a function of the coefficient of thermal expansion (CTE), which is an inherent property of the material. Different metals typically have different CTEs. For example, a typical CTE for steel is 12×10−6/C.° and a typical CTE for aluminum alloy is 23.6×10−6/C.°. Because the CTE is higher for aluminum, the aluminum components will expand more than the steel components. This can cause distortion, breakage, cracking and other problems. Thus, in an example door assembly 20 that has aluminum alloy panels 22, 24 and a steel beam 44, the panels will expand approximately 50% more than the beam 44, which can cause any of the above identified problems.
These problems can be mitigated by allowing relative movement between the mounting surfaces 50, 54 and the beam 44 during high-heat stages of assembly. But simply leaving one end of the beam 44 loose is not an optimum solution because the beam needs to be adequately attached to the inner panel 22 during other stages of assembly. For example, the beam needs to be adequately attached on both ends to set the geometry of the door. Thus, the loose-end technique requires the beam to be tightly attached, loosened, and retightened during door construction. This may be labor and time intensive, and may be ill suited for mass production.
To prevent damage to the door 20 during painting, one of the joints 52, 56 may be configured to allow relative movement between the beam 44 and the inner panel 22.
The amount or status of the components of the joint 42 may vary throughout the door construction process.
Referring to
The fastener 82 may be tightly attached during initial installation to adequately secure the joint 80 during the door-setting stage. The fastener assembly 82 includes at least one temporary component that is configured to disintegrate during painting. For example, the fastener assembly 82 may include a bolt 84, a temporary washer 86, and a nut. During one of the painting stages, the temporary washer 86 disintegrates, which causes the fastener assembly 82 to loosen, allowing the inner panel 22 and the beam 44 to move relative to each other via the slot 58 as they thermally expand. The temporary washer 86 may be made out of cardboard, wax, or compacted dirt. The temporary washer 86 includes properties that are configured to disintegrate upon contact with the surface-treatment solutions of the painting stages. For example, if cardboard or dirt, the washer is configured to dissolve. Or, if wax, the washer is configured to melt. The fastener 82 may be retightened after all heated stages are complete to secure the joint 80. The temporary component is not limited to a washer and maybe or any type of component that is designed can be designed to disintegrate during painting.
The joining techniques described above with respect to the door assembly 20 are not limited to door construction and may be used on other vehicle-body structures having bimetal construction.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
