Metal deforming – By deflecting successively-presented portions of work during... – By use of deflectors arranged to bend work longitudinally of...
Reexamination Certificate
2002-09-23
2004-11-23
Crane, Daniel C. (Department: 3725)
Metal deforming
By deflecting successively-presented portions of work during...
By use of deflectors arranged to bend work longitudinally of...
Reexamination Certificate
active
06820451
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to vehicle bumpers and methods for producing the same.
BACKGROUND OF THE INVENTION
Motor vehicles are typically provided with front and rear bumpers to protect the vehicle in the event of impact. Vehicle bumpers are typically formed from a strip of sheet steel that is shaped by roll forming in a roll forming assembly to have a predetermined transverse cross section that rigidifies the bumper and resists deformation during impact. Bumpers are also provided with a predetermined curvature in the longitudinal direction to provide a bumper that conforms to the shape of the vehicle in the “cross car” or side-to-side direction.
The degree of longitudinal curvature of the bumper is referred to as bumper “sweep” in the industry. The degree of bumper sweep is a general measure of the radius of curvature of the bumper. A basic commercial quantitative description of bumper sweep is obtained by measuring a chord length of 60 inches (1.524 m) along the bumper and determining the maximum distance between the bumper and the chord along a line perpendicular to the chord. The distance is measured in inches (centimeters) and converted to a sweep number by determining the number of eighths of an inch (0.3175 cm) in the measured distance.
Bumpers in commercial use typically have sweeps of approximately zero (i.e., a substantially straight bumper) up to approximately 50, although bumpers having a sweep as high as 80 are used in vehicle construction.
It is well known that the primary objectives of vehicle parts manufacturers is to produce high strength bumpers that resist deformation during impact, but that are also relatively light weight. The goal of minimizing weight can be achieved by reducing the thickness or gauge of the bumper, thereby using less metal to construct the bumper. Minimizing vehicle weight is important because lighter weight vehicles are easier to transport prior to sale and are more fuel efficient for the vehicle owner. The manufacturer can reduce metal thickness and still meet safety requirements by using higher strength steel to construct the bumper.
The type of metal used for bumper construction is thus a major determinant of bumper weight. Most commercial bumpers, however, are constructed of relatively mild grades of steel because mild steel grades are easier for the parts manufacturer to sweep form during manufacture. High strength low alloy (HSLA) grade steel is an example of such a grade of steel widely used commercially for bumper construction.
HSLA steel is available in grades having a KSI minimum yield strength of from 35 up to 80 (i.e., a MPa minimum yield strength of from 240 to 550). Grades of steel above HSLA are also commercially available, including dual phase and martinsitic grades of steel, but most parts manufacturers are generally not able to produce a satisfactory commercial bumper with a significant degree of bumper sweep using these higher steel grades.
Martinsitic steel having a tensile strength of up to 220 KSI (1516 MPa) is commercially available. Generally, any steel having a KSI greater than 80 (240 MPa) can be considered an ultra high strength steel. The rigidity and structural strength provided to the bumper by the transverse cross section makes the sweeping process difficult and limits the strength of the steel most manufacturers can use to construct the bumper.
More particularly, during manufacturing, a strip of sheet steel is roll formed in a series of pairs of roll forming rollers that gradually shape the steel in a transverse direction to provide the predetermined transverse bumper cross section. An initially shaped bumper structure emerges from a position of exit of the roll forming assembly as an elongated, longitudinally straight, continuous structure. Typically, the initially formed bumper structure is provided with the desired degree of longitudinal curvature (the terms “bumper sweep” and “longitudinal curvature” are used interchangeably in the present application) immediately after the roll forming operation in a separate sweep forming assembly positioned at the position of exit of the roll forming assembly.
The initially shaped bumper structure emerges from the sweep forming assembly as a finally shaped continuous bumper structure. By “finally shaped” it is meant that the desired degree permanent curvature has been imparted to the bumper structure in both the transverse and longitudinal directions so that the bumper structure has the predetermined transverse bumper cross section and the predetermined longitudinal curvature. The finally shaped bumper structure is then fed into a cutting assembly positioned immediately downstream of the sweep forming assembly. The cutting assembly cuts the finally shaped bumper structure into individual bumper members of predetermined length, each bumper member thus having the predetermined transverse bumper cross section and the predetermined longitudinal curvature.
Known prior art sweep forming assemblies are not commercially usable to provide a wide range of bumper sweep when high strength steel is used to construct the bumper because they use either what is effectively a form of extrusion or a bending operation to impart bumper sweep. One prior art method, for example, of providing bumper sweep uses a series of blocks, each block having a central opening that is generally the same size and shape as the transverse cross section of the bumper structure. The series of blocks is positioned so that the initially shaped bumper structure passes through the openings as it moves out of the roll forming assembly in the downstream direction. Selected blocks are raised so that the path formed by the openings is not straight, thereby requiring the bumper structure to deform in the longitudinal direction as it is forced through the openings. A degree of permanent curvature is thereby imparted to the bumper structure.
This method is, in effect, a form of extrusion and has several disadvantages. The metal-to-metal sliding engagement between the bumper structure and the sides of the openings in the blocks wears the metal of the bumper structure and the metal of the blocks. The metal-to-metal sliding engagement limits the speed at which the bumper structure can pass through the assembly line and thus limits the production capacity of a manufacturing plant. This method will provide only a limited degree of sweep and is not commercially feasible for high strength steel bumper manufacturing.
Another sweep forming assembly which has been used commercially in the past several years utilizes a series of longitudinally spaced movable upper rollers and a series of longitudinally spaced fixed lower rollers that cooperate to bend the bumper structure after it is roll formed. The lower rollers are disposed below the advancing bumper structure and support the same. The upper rollers are disposed above the advancing bumper structure and are vertically movable. The rollers are arranged so that one upper roller is vertically centered between two lower rollers. The sweep is imparted by moving the upper rollers vertically downwardly into engagement with an upper surface of the advancing initially shaped bumper structure. The upper rollers exert a downward force on the bumper structure sufficient to bend the bumper structure between an associated pair of lower fixed rollers, thereby imparting a degree of sweep to the bumper structure.
The method performed by this assembly is not effective when harder grades of steel are used in bumper structure construction because hard steel grades require forces of great magnitude to bend the steel. These high magnitude bending forces are undesirable because when a force of sufficient magnitude to bend the hard steel is applied by the upper rollers, the upper rollers tend to permanently deform the predetermined bumper cross section of the bumper structure. More particularly, the vertical sides of a hard steel bumper structure tend to pucker uncontrollably, crease or tear under the bending force of the upper rollers. Bending operations also do not pr
Bechtel Darrell A.
Harman Samuel
Renzzulla Edward
Crane Daniel C.
Magna International Inc.
Pillsbury & Winthrop LLP
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