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EP-4298006-B1 - HYBRID ROOF CROSS MEMBER FOR A CAR BODY AND METHOD FOR E-COATING A CAR BODY INCLUDING A HYBRID ROOF CROSS MEMBER

EP4298006B1EP 4298006 B1EP4298006 B1EP 4298006B1EP-4298006-B1

Inventors

  • ZHANG, FAN
  • GERHARDT, SVEN
  • STENGER, RALPH
  • BRAUNBECK, BARDO

Dates

Publication Date
20260506
Application Date
20210226

Claims (9)

  1. Hybrid roof cross member for a car body comprising at least one metal beam component (1) and at least one CFRP component (2), characterized in that the roof cross member is connectable to a car body such that tensile loads exerted by the car body on the roof cross member are carried predominantly or solely by the metal beam component (1), wherein the metal beam component (1) and the CFRP component (2) are connectable to the car body by the same connection means and the metal beam component (1) is connected to the CFRP component (2) only by the connection means.
  2. Hybrid roof cross member according to claim 1, characterized in that the connection means are the same fastener such as at least one bolted and/or riveted connection.
  3. Hybrid roof cross member according to any of the preceding claims, characterized in that it comprises at least one connecter (6), in particular a steel connecter (6), for connecting the roof cross member to the car body.
  4. Hybrid roof cross member according to claim 3, characterized in that the connecter (6), the metal beam component (1) and the CFRP component (2) are connected only by the connection means.
  5. Hybrid roof cross member according to any of the preceding claims, characterized in that the metal beam component (1) is positioned inside the CFRP component (2).
  6. Hybrid roof cross member according to any of the preceding claims, characterized in that the metal beam component (1) comprises at least two aluminium and/or magnesium beams, in particular two identical and/or exactly two and/or parallel and/or extrusion aluminium and/or magnesium beams.
  7. Hybrid roof cross member according to any of the preceding claims, characterized in that the CFRP component (2) comprises two, in particular exactly two, CFRP members, an upper member (4) and a lower member (5).
  8. Hybrid roof cross member according to claim 7, characterized in that the lower member (5) comprises a trough-shaped portion and that the metal beam component (1) is positioned inside the trough-shaped portion.
  9. Method for e-coating a car body including a hybrid roof cross member according to any of the preceding claims, characterized in that after a coating has been applied to the car body, the car body is heated in an oven, such that a temperature profile is kept constant and a maximum oven temperature is maintained without consideration of the Tg of the epoxy resin of the CFRP component (2).

Description

The present invention pertains to a hybrid roof cross member for a car body. The hybrid roof cross member comprises at least one metal beam component and at least one CFRP component. The roof cross member is connectable to the remainder of a car body such that tensile loads exerted by the remainder of the car body on the roof cross member during the e-coating drying process inside the oven are carried predominantly or solely by the metal beam component. The invention also pertains to a method for e-coating a car body including a hybrid roof cross member. Roof cross members (EP2878519) known from the art are connected to a car body or the remainder of a car body to form a car's body structure. The car's body structure may be understood to comprise components such as the roof cross member, pillars, spars, which are required for the car body construction. The roof cross member may be a part of the said body structure while at the same time being an integral part of the car roof. Once the car body structure is assembled during the manufacturing process of a car, the body structure will go through an oven process as part of an e-coating process and will be heated up to ca. 180 °C to dry or cure the paint applied during the e-coating process. The different materials used in the car body, e.g. aluminium, steel or CFRP, exhibit significant differences of thermal expansion coefficients that may lead to thermal deformations as well as joint and part failures during the oven process of an e-coating process. In particular, the roof cross member may be subject to tension loads and/or pressure loads due to the expansion and shrinking of the car body's side structures. Known CFRP roof cross members might exhibit permanent deformations after or during the e-coating or rather during or afterthe oven process of the e-coating process. This is because the oven temperature is much higher than the glass transition temperature Tg of standard epoxy resins. Therefore, the cross member may be softened and lose its stiffness to a significant degree. The loads applied to the cross member might then deform and/or destroy the structure of the cross member. Furthermore, joint failure may also occur if CFRP components of the roof cross member are joined to Al (aluminium) or steel structures of the car body in general or the roof cross member in particular. To integrate CFRP components in the car body structure, the existing manufacturing processes and especially the drying/curing processes or oven processes in the paint shop are adapted, such that a stepwise temperature profile and reduced maximum oven temperatures are applied. These changes are costly and require larger investments, including larger areas for ovens and overall longer process times. A cost effective integration of CFRP components in car body structures is therefore not possible or problematic. The aim of the present invention is to overcome these difficulties and to successfully integrate the CFRP roof cross member or roof bow into a car body i.e. in a car manufacturing body shop without changing the existing manufacturing parameters, in particular the oven or curing processes, and without using expensive epoxy resins. This aim is achieved by a hybrid roof cross member according to claim 1 and a method for e-coating a car body including a hybrid roof cross member according to claim 9. Preferable embodiments of the invention are subject to the dependent claims. According to claim 1, a hybrid roof cross member for a car body is provided. The hybrid roof cross member comprises at least one metal beam component and at least one CFRP component. The roof cross member is connectable to a car body, or the remainder of the car body, such that tensile loads exerted by the car body on the roof cross member are carried predominantly or solely by the metal beam component. Clearly, only tensile loads within a certain range may be carried predominantly or solely by the metal beam component, as excessive loads might lead to elongation of the metal beam component which in return could increase the proportion of the load carried by the CFRP component of the hybrid roof cross member. The tensile loads exerted by the car body on the roof cross member may occur during a curing or oven process, during which the hybrid roof cross member is heated together with the remainder of the car body to a temperature above the glass transition temperature Tg of the epoxy resin of the CFRP component. The heated components may experience varying expansions in dependence on the thermal expansion coefficients of their respective materials, such that the car body's side structures may exert a force on the hybrid roof cross member. In effect, a tensile load may be exerted on the hybrid roof cross member by the car body's side structures. According to the invention, the expansion of the body side structure of the car body is counteracted by the metal beam component of the roof cross member, while the CFRP compon