Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2001-05-11
2003-01-14
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S109000
Reexamination Certificate
active
06506996
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system and method for performing preventative maintenance upon spot welding guns used in automotive vehicle assembly plants.
BACKGROUND OF THE INVENTION
The assembly and manufacture of automotive vehicles often requires multiple spot welds. Over time, the repetitive use of spot welding guns tends to wear and even cause failure of such guns, thereby slowing vehicle manufacture and/or causing downtime for automotive vehicle assembly. It is known to employ preventive maintenance programs such as testing or replacement of spot welding guns or components thereof at predetermined time intervals to avoid excessive wear or failure. However, such programs may cause waste by prematurely replacing guns or by allowing downtime if the guns fails prior to the predetermined time intervals established by the program.
In view of the foregoing, it should be appreciated that it would be desirable to provide a method and system that more accurately determines when preventative maintenance should be performed on spot welding guns. Furthermore, additional desirable features will become apparent to one of ordinary skill in the art from the foregoing background of invention and following detailed description of a preferred exemplary embodiment and appended claims.
SUMMARY OF THE INVENTION
The present invention provides a method and system for performing preventative maintenance on one or more spot welding guns.
According to the method, a plurality of C-factors is collected during a depreciation cycle of a spot welding gun. A plurality of C-factor averages (C
a
) is computed for the plurality of C-factors, wherein at least one of the plurality of C-factor averages (C
a
) is computed for each of a plurality of predetermined time intervals within the depreciation cycle. A lower limit is established for the plurality of C-factor averages (C
a
). A plurality of rates of depreciation (R
d
) are computed using the plurality of C-factor averages (C
a
). A threshold value is established for the plurality of rates of depreciation (R
d
). Preventative maintenance is performed on the spot welding gun if a comparison between at least one of the plurality of rates of depreciation (R
d
) and the threshold value for the rates of depreciation (R
d
) indicates an upcoming failure of the welding gun or if a comparison between at least one of the plurality of C-factor averages (C
a
) and the lower limit for the plurality of C-factor averages (C
a
) indicates the upcoming failure of the welding gun.
The system is comprised of a weld controller configured to calculate a plurality of C-factors during a depreciation cycle of a spot welding gun. A data collection system is configured to collect the plurality of C-factors calculated by the weld controller during the depreciation cycle of the spot welding gun. A data analysis system is configured to access the data collection system and compute a plurality of C-factor averages (C
a
) of the plurality of C-factors with at least one of the plurality of C-factor averages (C
a
) computed for each of a plurality of predetermined time intervals within the depreciation cycle such that preventative maintenance can be performed if a comparison between at least one of the plurality of C-factor averages (C
a
) and a lower limit for the plurality C-factor averages (C
a
) indicates an upcoming failure of the welding gun. The data analysis system is further configured to compute a plurality of rates of depreciation (R
d
) of the plurality of C-factor averages (C
a
) such that preventative maintenance can also be performed if a comparison between at least one of the plurality of rates of depreciation (R
d
) and a threshold value for the plurality of rates of depreciation (R
d
) indicates the upcoming failure of the welding gun.
REFERENCES:
patent: 3546421 (1970-12-01), Meyer et al.
patent: 4596917 (1986-06-01), Nied et al.
patent: 4634829 (1987-01-01), Okabe et al.
patent: 5493093 (1996-02-01), Cecil
General Motors Corporation
Sedlar Jeffrey A.
Shaw Clifford C.
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