Method of elongated bumper bar with sections twisted rotationally about the axis of elongation
A bumper system for an automotive vehicle includes a rolled steel tube having a box or C-shaped cross section fixed to the forward ends of the side rails of the vehicle so as to extend transversely to the vehicle's longitudinal axis. The forward surface of the vehicle is formed by a plastic fascia which may have sloped surfaces for styling or aerodynamic reasons. The space between the forward end of the bumper bar and the fascia is filled with foam intended to absorb energy in an impact. To better match the sloped sections of the fascia, certain sections of the bumper bar are twisted about the longitudinal axis of the bar to create surfaces inclined relative to the vertical. The bars are formed by roll forming a steel web into an elongated member having generally vertical opposed faces. A section of the rolled member is heated above a metallurgical transition temperature. Then sections to be inclined are twisted about the longitudinal axis of the bumper bar in a die forming station and are then quenched to form a hardened steel member.
1 . The method of forming a bumper bar for use in a bumper system for a vehicle having a frame with forward projecting side members which are secured to the rear face of the bumper bar, and a fascia extending forward of the bumper bar and having certain sections inclined forwardly and downwardly relative to the central section of the vehicle, comprising:
roll forming sheet steel into a section having generally vertical opposed sidewalls;
heating at least certain portions of said rolled section above a metallurgical transition temperature;
twisting at least certain portions of said roll formed heated section to provide at least the forward section of the bumper bar with a forward and downward inclination at said twisted section; and
quenching the bumper bar.
2 . The method of claim 1 , wherein the roll formed section is formed as a box section, further including the step of joining the proximate edges of the box section to form a closed box section.
3 . The method of claim 1 , wherein the sheet steel is rolled as a “C” section.
4 . The method of claim 1 , wherein the metallurgical transition temperature constitutes its austenizing temperature.
5 . The method of claim 1 , including the step of bending the bar about its longitudinal axis while it is heated above its metallurgical transition temperature, to provide a sweep to the bumper.
6 . The method of claim 1 , wherein the step of twisting at least certain portions of said rolled section about an elongated axis of the bumper bar to provide at least the forward section of the bumper bar with a forward and downward inclination at said twisted section comprises engaging the bar, while heated above its metallurgical transition temperature, with a forming tool which engages the selected sections of the bar and twists the selected sections about the longitudinal axis of the bar.
7 . The method of claim 6 , wherein the forming tool additionally bends the bar about the longitudinal axis to provide it with a sweep to accommodate the fascia.
8 . The method of forming a bumper bar, comprising:
roll forming steel into a section having generally vertical opposed sidewalls and generally horizontal top and bottom walls;
heating at least portions of said roll formed section above its metallurgical transition temperature;
engaging certain portions of the heated section with a forming tool, which twists said certain sections about the longitudinal axis of the bar, to provide at least certain portions of the forward section of the bumper bar with a forward and downward inclination relative to the vertical and horizontal surfaces of the bar; and
quenching the section.
9 . The method of claim 8 , wherein the metallurgical transition temperature comprises the austenitic temperature of the metal.
10 . The method of claim 8 wherein the twisted section constitutes the center of the bar, leaving the two ends with substantially vertical forward walls.
11 . The method of claim 8 , wherein the twisted section has forward and rear walls inclined relative to the vertical.
12 . The method of claim 8 , wherein the twisted section has forward walls inclined relative to the vertical.