Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2000-03-20
2001-04-17
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S091200
Reexamination Certificate
active
06218637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to weld tools for resistance spot welding a joint having two or more sheet metal members and more particularly to a method for sizing weld tools.
2. Discussion
Modern automotive development processes typically employ cross-functional teams having members with diverse backgrounds to review decisions related to the design and manufacture of various components. The diverse backgrounds provides a relatively small team with a broad understanding of almost all of the aspects that are relevant to the design, manufacture and use of the particular component. Accordingly, cross-functional teams have been instrumental in the shortening of the cycle times for developing and producing a vehicle in that the team is frequently able to identify problems and risks in proposed designs and processes prior to physical construction of the vehicle or any related tooling.
While cross-functional teams have made significant advancements, several drawbacks have been identified. One drawback concerns the need for a preliminary design having sufficient detail to properly convey the design concept of the component to team members or tooling suppliers. In the case of sheet metal fabrications, such as vehicle bodies, the design effort undertaken to sufficiently detail a given design for presentation to a cross-function team constitutes a majority of the overall effort required to completely design the sheet metal fabrication to completion. As such, the design of the sheet metal fabrication may be relatively mature prior to the disclosure of the design to the team members, eliminating or substantially impairing the option to introduce significant changes in the design should a notable problem be identified by the cross-functional team.
In particular, problems are routinely encountered with the sizing of weld tools for resistance spot welding the sheet metal members of a joint together. These problems arise when aspects of the design of the joint or the manufacturing process are not fully understood or compensated for in the design process. These aspects include, for example, the ability of the weld tool to equalize to the joint or the need to deflect one or more of the sheet metal members forming the joint into abutment prior to forming the spot weld. The additional force required in such situations often overstresses the weld tool and significantly reduces its useful life.
To avoid reducing the life of a weld tool, it would seem rather obvious to simply procure a larger weld tool for the operation. This alternative, however, is frequently not a viable option due to space constraints that result from the design of the sheet metal fabrication and to a lesser extent, machine tool capabilities. Even where a larger weld tool can be implemented, the machine tool used to orient the weld tool is frequently not sized to handle the additional weight of the larger tool and as such, this change negatively impacts the performance of the machine tool (due to increased inertia and weight) as well as its durability.
Accordingly, there remains a need in the art for a quick, efficient and accurate method for sizing weld tools for resistance spot welding a joint having a plurality of sheet metal members.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a method for calculating a weld force index for sizing a weld tool for resistance spot welding a joint.
It is another object of the present invention to provide a method for calculating a weld force index for sizing a resistance spot weld tool which utilizes a series of predetermined parameters for performing the calculation.
A method for mechanically sizing a weld tool for forming a resistance spot weld to fasten a joint having at least two sheet metal members is provided. The method includes the steps of providing a plurality of weld force curves, determining a governing metal thickness, determining a total thickness of the sheet metal members, determining a plurality of joint parameters, including a weld gap parameter, a thickness parameter, a strength parameter, an equalization parameter and a sheet stiffness parameter, using the plurality of joint parameters to select one of the plurality of weld force curves, and using the governing metal thickness and the selected weld force curve to calculate a weld force parameter.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5602341 (1997-02-01), Lee et al.
patent: 5652488 (1997-07-01), Rennau
patent: 5883355 (1999-03-01), Kaneshima
DaimlerChrysler Corporation
Lorelli Marc
Shaw Clifford C.
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