Metal working – Method of mechanical manufacture – Work holding
Reexamination Certificate
2000-11-13
2003-10-07
Hong, John C. (Department: 3726)
Metal working
Method of mechanical manufacture
Work holding
C029S281100, C029S721000, C269S071000
Reexamination Certificate
active
06629354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method and apparatus for establishing a net datum position of a framing structure. More specifically, this invention relates to a method and apparatus that finds reference surfaces of an automotive vehicle frame that has been assembled within an acceptable tolerance range, and despite the within-tolerance variation of the reference surfaces on the frame, the frame is immobilized in its free state so that work can be subsequently performed on the frame to fabricate a net datum locating feature in its original design-intent location on the frame.
2. Description of the Related Art
In the manufacturing of automobiles and trucks, a chassis frame typically includes an underbody, a pair of side frames, and front and rear headers wherein such chassis frame usually undergoes a progressive series of positioning and welding steps before a rigid chassis frame is produced. Though vehicle bodies are still manually assembled and welded, emphasis on automated assembly and welding operations has generated numerous automated and semi-automated framing systems.
Generally, in such prior art processes it is a common object of a framing system to accurately locate the body components relative to each other and maintain such location throughout later welding operations, until the structural rigidity of the body is sufficient to preserve the desired geometric configuration throughout the assembly line. A further object for most framing systems is to provide sufficient flexibility to accommodate more than one body style, so as to enhance the versatility of the assembly line and reduce the tooling cost per assembly unit.
Chassis frames, however, have not received as much attention as vehicle bodies with respect to automated assembly techniques and accordingly, are currently still being assembled on fixtures built to design-intent, wherein a pair of rail members are clamped in place with a series of cross members therebetween and subsequently welded together to permanently fasten the rails and cross members.
Unfortunately, the heat generated from welding operations causes the chassis frame to warp or twist out of its design-intent geometry and position. Such warping is problematic because the individual components of the chassis frame include locating surfaces or holes that are relied upon for locating other features produced in subsequent operations. Unfortunately, due to warpage of the chassis frame from the welding operation, such locating surfaces or holes are intolerably displaced from their design-intent position, and thereby negatively effect the location of the other features produced during subsequent operations.
There are at least two well-known attempts to solve this problem. First, many manufacturers use a frame straightening process in an attempt to correct the warping. The frame straightening process, however, tends to be an exercise in futility since the process introduces additional built-in stress to the chassis frame and can lead to further displacement of the rails and cross member structure. Such frame straightening processes are rarely, if ever, capable of reliably straightening the entire chassis frame back into its exact design-intent geometry.
A second solution involves welding the components of the chassis frame together, then forcibly clamping the chassis frame from its free state back into its exact design-intent geometry, then producing holes and other features, and finally unclamping the chassis frame. This solution is performed with the expectation that the holes and other features will remain positioned within a certain tolerance relative to the design-intent geometry of the chassis frame when the part is unclamped. Unfortunately, however, the chassis frame tends to spring back to its warped free state when unclamped and thus, the holes and other features of the chassis frame are carried away from their design-intent position, in some cases out of the acceptable tolerance range.
In addition to the above-mentioned general approaches, several other locating or positioning devices associated with processing vehicle chassis frames have been proposed in the prior art. For example, U.S. Pat. No. 4,976,026 to Dacey, Jr. addresses the problems associated with locating a datum reference on a partially assembled structural object such as an automobile chassis frame. As a solution, Dacey, Jr. teaches an apparatus having a probe portion thereof for detecting pre-established surfaces and features on the vehicle body to establish a datum position. Tooling attached to the apparatus subsequently references the datum position established by the probe portion, and performs work on the vehicle body in relation thereto.
Dacey, Jr. discloses the apparatus as having a base rigidly mounted to a floor, and having a transfer platform attached to the base with guideposts to ensure freedom of movement of the transfer platform in a first horizontal direction toward the vehicle body. A support platform is attached to the transfer platform using guideposts to ensure freedom of movement relative thereto in a second horizontal direction that is perpendicular to the first horizontal direction. A vertical platform is attached to the support structure and is moveable therewith along guideposts in a vertical direction. A form and pierce device is attached to a lower portion of the vertical platform for performing work on the vehicle body. A pair of hydraulic work supports interpose each of the platforms, at clamping plate locations, for locking horizontal and vertical movement of the apparatus. A series of probes are attached to an upper end of the vertical platform for detecting the pre-established surfaces and features of the vehicle body from which the datum position is established. For example, one of the probes includes a tapered surface to permit the probe to climb vertically onto a fender rail, and another probe is tapered to guide it into a preformed orifice in the vehicle body. Once the probes locate the pre-established surfaces and features of the vehicle body, fluid pressure is introduced to the work supports so that push rods of the work supports exert an equal clamping force on either side of the positioning plates for locking the transfer, support, and vertical platforms in place. The datum position of the pre-established surfaces and features is thereby established to permit the form and pierce tool to perform work upon the chassis frame in relation to the datum position.
As discussed above, Dacey, Jr. provides an apparatus having a sub-assembly for forming and piercing a vehicle body panel or sub-frame in direct relation to a datum position established by detecting pre-established surfaces and features of the vehicle body by another sub-assembly of the same apparatus. Unfortunately, however, Dacey, Jr. requires that a preformed orifice and specific body panels be located on the vehicle body prior to immobilizing the tooling device for subsequent forming and/or piercing operations. Additionally, Dacey, Jr. does not teach or disclose that the apparatus is capable of rigidly immobilizing the entire vehicle body by itself, not just proximate the datum location, thereby enabling work to be performed anywhere on the vehicle body. Finally, the piercing operation disclosed in Dacey, Jr. is performed by a tooling device, relative to a datum location established by probing various predefined features that have pre-existing tolerance variation. The positions of the various predefined features on the vehicle body, such as the top of the fender rail and the preformed orifice, have size and locational tolerance variations. Further, the apparatus including the probes, platforms, and piercing tooling have size and locational tolerance variations also. Therefore, the piercing operation is performed relative to specific features of the vehicle body that have tolerance variation, rather than performed directly relative to a net datum position of the entire vehicle body frame.
U.S. Pat. No. 5,987,726 to Akeel iden
Hong John C.
Utica Enterprises Inc.
VanOphem & VanOphem P.C.
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