Metal working – Method of mechanical manufacture – Structural member making
Reexamination Certificate
2000-08-29
2003-02-18
Vidovich, Gregory M. (Department: 3726)
Metal working
Method of mechanical manufacture
Structural member making
C029S421100, C029S425000
Reexamination Certificate
active
06519855
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to methods for manufacturing body and frame assemblies for vehicles. More specifically, this invention relates to an improved method for manufacturing a vehicular body and frame assembly including a pair of side rails, wherein each of the side rails has a central portion that is enlarged relative to the ends portions thereof.
Many land vehicles in common use, such as automobiles, vans, and trucks, include a body and frame assembly that is supported upon a plurality of ground-engaging wheels by a resilient suspension system. The structures of known body and frame assemblies can be divided into two general categories, namely, separate and unitized. In a typical separate body and frame assembly, the structural components of the body portion and the frame portion of the vehicle are separate and independent from one another. When assembled, the frame portion of the assembly is resiliently supported upon the vehicle wheels by the suspension system and serves as a platform upon which the body portion of the assembly and other components of the vehicle can be mounted. Separate body and frame assemblies of this general type are found in most older vehicles, but remain in common use today for many relatively large or specialized use modem vehicles, such as large vans, sport utility vehicles, and trucks. In a typical unitized body and frame assembly, the structural components of the body portion and the frame portion are combined into an integral unit that is resiliently supported upon the vehicle wheels by the suspension system. Unitized body and frame assemblies of this general type are found in many relatively small modern vehicles, such as automobiles and minivans.
One well known example of a separate type of vehicular body and frame assembly is commonly referred to as a ladder frame assembly. A ladder frame assembly includes a pair of longitudinally extending side rails that are joined together by a plurality of transversely extending cross members. The cross members connect the two side rails together and provide desirable lateral, vertical, and torsional stiffness to the ladder frame assembly. The cross members can also be used to provide support for various components of the vehicle. Depending upon the overall length of the vehicle and other factors, the side rails of a conventional ladder frame assembly may be formed either from a single, relatively long structural member or from a plurality of individual, relatively short structural members that are secured together. For example, in vehicles having a relatively short overall length, it is known to form each of the side rails from a single integral structural member that extends the entire length of the vehicle body and frame assembly. In vehicles having a relatively long overall length, it is known to form each of the side rails from two or more individual structural members that are secured together, such as by welding, to provide a unitary structural member that extends the entire length of the vehicle body and frame assembly.
Traditionally, the side rails of known vehicle body and frame assemblies have been formed exclusively from open channel structural members, i.e., structural members that have a non-continuous cross sectional shape (U-shaped or C-shaped channel members, for example). Thus, it is known to use a single integral open channel structural member to form a side rail that extends the entire length of the vehicle body and frame assembly, as described above. Additionally, it is known to secure a plurality of such open channel structural members together to form the individual sections of a unitary side rail for a vehicle body and frame assembly, as also described above. However, the use of open channel structural members to form the side rails and cross members for vehicle body and frame assemblies has been found to be undesirable for several reasons. First, it is relatively time consuming and expensive to bend multiple portions of the side rails to conform to a desired final shape, as is commonly necessary. Second, after such bending has been performed, a relatively large number of brackets or other mounting devices must usually be secured to each of the side rails to facilitate the attachment of the various components of the vehicle to the body and frame assembly. Third, in those instances where the side rails are formed from a plurality of individual sections, it has been found difficult to maintain dimensional stability throughout the length of the side rail when the individual side rail sections are secured together.
More recently, it has been proposed to form the side rails and the cross members from closed channel structural members, i.e., structural members that have a continuous cross sectional shape (tubular or box-shaped channel members, for example). In vehicle body and frame assemblies of this type, it is known that the closed channel structural member may be deformed to a desired shape by hydroforming. Hydroforming is a well known process that uses pressurized fluid to deform a closed channel structural member into a desired shape. To accomplish this, the closed channel structural member is initially disposed between two die sections of a hydroforming apparatus that, when closed together, define a die cavity having a desired final shape. Thereafter, the closed channel structural member is filled with a pressurized fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid is increased to a magnitude where the closed channel structural member is expanded or otherwise deformed outwardly into conformance with the die cavity. As a result, the closed channel structural member is deformed into the desired final shape.
Hydroforming has been found to be a desirable forming process because portions of a closed channel structural member can be quickly and easily deformed to have a complex cross sectional shape. In those instances where the perimeter of the closed channel structural member is essential the same as the perimeter of the die cavity, the cross sectional shape of the closed channel structural member is changed during the hydroforming process. However, at least ideally, the wall thickness of the closed channel structural member should remain relatively constant throughout the deformed region. Hydroforming has also been found to be a desirable forming process because portions of a closed channel structural member can be quickly and easily expanded from a relatively small perimeter to a relatively large perimeter. In those instances where the perimeter of the closed channel structural member is somewhat smaller than the perimeter of the die cavity, not only is the cross sectional shape of the closed channel structural member changed during the hydroforming process, but the wall thickness thereof is decreased. However, at least ideally, the wall thickness of the closed channel structural member should decrease uniformly through the expanded region.
Such variations in the wall thickness of the closed channel structural member are usually considered to be undesirable because they can result in undesirable weaknesses in the formed closed channel structural member. One solution is to increase the wall thickness of the entire closed channel structural member such that the most extreme reductions in the wall thickness thereof would not adversely affect the overall strength of the member for its intended use. However, such over-designing undesirably increases the overall weight and cost of the closed channel structural member and the resultant vehicle frame component. An alternative solution is to employ a process known as end feeding. End feeding involves applying a mechanical force against one or both end portions of the closed channel structural member simultaneously as the interior portion is expanded. As a result, some of the metallic material of the end portions flows into the interior portion being expanded, thus minimizing the reduction in the wall thickness thereof. End feeding has been found to function s
Dana Corporation
MacMillan Sobanski & Todd LLC
Nguyen T.
Vidovich Gregory M.
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