Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-04-20
2001-05-15
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S086410
Reexamination Certificate
active
06232572
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spot welding control system and a spot welding control method for a high quality spot welding to be achieved by detecting time-dependent variations of inter-electrode displacement amount while welding.
A sureness or state of a spot welding is inspected by examining an attribute of a thermal expansion of a welding object during conduction of welding current or along a growth of a nugget: by a maximum displacement in Japanese Patent P48-41422 and Japanese Patent P53-4057, by a displacement rate in U.S. Pat. No. 3,400,242 and Japanese Patent P53-4057, and by a contracting state in Japanese Patent Application Laid-Open Publication No. 7-232279.
SUMMARY OF THE INVENTION
However, as an estimated nugget diameter constitutes a base for a decision on a conformity of a quality or sureness of an associated welding, it is difficult to know a quantitative conformity if welding electrodes are brought into irregular contact with workpieces to be welded, which may cause flash or expulsion while welding, or may have a varying initial contact resistance, or welding currents shunting to neighboring welded spots.
For example, as illustrated in
FIG. 2A
, if workpieces W to be welded are gapped to each other when welding, there may develop time-dependent variations of inter-electrode displacement amount such that, as illustrated in
FIG. 12B
, a maximum displacement hmax thereof is significantly smaller than a maximum displacement Hmax to be observed under a normal state (with electrodes perpendicular to workpieces and without gaps between the workpieces).
Further, as illustrated in
FIG. 13A
, if electrodes
1
are inclined to workpieces W when welding, i.e. in a case of inclined welding angle, there may also develop time-dependent variations of inter-electrode displacement amount such that, as illustrated in
FIG. 13B
, a maximum displacement hmax thereof is significantly smaller than a maximum displacement Hmax to be observed under a normal state.
In either example, there may well be given a smaller inter-electrode displacement rate dh/dt than the normal state.
In either case, or if workpieces are gapped or an inadequate welding angle appears while welding, the welding may be decided to be non-conforming, even when a conforming welding quality is finally achieved.
Further, as data on inter-electrode displacement amount sampled from a current welding are employed ex post facto for a decision on a conformity of a subsequent welding, a feedback of a result therefrom to any welding condition cannot be effective before the subsequent welding, thus resulting in a default decision of non-conformity up to the current welding, yielding one or more non-conforming products.
The present invention has been achieved with such points in view.
It therefore is a first object of the invention to provide a spot welding control system and a spot welding control method which allow, irrespective of a state of electrodes contacting on workpieces, for a nugget diameter (in terms of a quality or sureness of an associated welding) to be estimated from time-dependent variations of inter-electrode displacement amount, with a sufficient accurately for the result to be based in calculation for optimization of welding conditions, as necessary to achieve a conforming quality.
It is a second object of the invention to provide a spot welding control system and a spot welding control method which allow, irrespective of a state of electrodes contacting on workpieces, for optimal welding conditions to be set in real time on a basis of variations of inter-electrode displacement amount, as they are detected along with time.
To achieve the first object, an aspect of the invention provides a spot welding control system comprising a pair of electrodes pressing a welding object, conducting a current therethrough, an inter-electrode displacement amount detector detecting an inter-electrode displacement amount of the pair of electrodes substantially continuously from a reference position, and a welding state decision maker making a decision on a welding state of the welding object in dependence on inter-electrode displacement amounts detected by the inter-electrode displacement amount detector.
Another aspect of the invention provides a spot welding control system comprising a pair of electrodes pressing a welding object, conducting a current therethrough, a wear amount detector detecting a wear amount of the pair of electrodes, an inter-electrode displacement amount detector detecting an inter-electrode displacement amount of the pair of electrodes substantially continuously from a reference position, and a welding state decision maker correcting inter-electrode displacement amounts detected by the inter-electrode displacement amount detector in dependence on the wear amount detected by the wear amount detector and making a decision on a welding state of the welding object in dependence on corrected inter-electrode displacement amounts.
Another aspect of the invention provides a spot welding control method comprising pressing a welding object by a pair of electrodes, conducting a current therethrough, detecting an inner-electrode displacement amount of the pair of electrodes substantially continuously from a reference position during the conducting, and making a decision on a welding state of the welding object in dependence on detected inter-electrode displacement amounts
Another aspect of the invention provides a spot welding control method comprising detecting a wear amount of a pair of electrodes, pressing a welding object by the pair of electrodes, conducting a current therethrough, detecting an inter-electrode displacement amount of the pair of electrodes substantially continuously from a reference position during the conducting, and correcting detected inter-electrode displacement amounts in dependence on the wear amount detected and making a decision on a welding state of the welding object in dependence on corrected inter-electrode displacement amounts.
Further, to achieve the second object, an aspect of the invention provides a spot welding control system comprising a pair of electrodes pressing a welding object, conducting a current therethrough, an inter-electrode displacement amount detector substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes, a reference inter-electrode displacement amount memory having preset reference inter-electrode displacement amounts stored therein, a comparator comparing inter-electrode displacement amounts detected by the inter-electrode displacement amount detector with reference inter-electrode displacement amounts stored in the reference inter-electrode displacement amount memory, a welding condition setter setting a welding condition of the welding object in accordance with a result of comparison by the comparator, and a current conduction controller controlling a current conducting state of the pair of electrodes in dependence on the welding condition set by the welding condition setter.
Another aspect of the invention provides a spot welding control system comprising a pair of electrodes pressing a welding object, conducting a current therethrough, a wear amount detector detecting a wear amount of the pair of electrodes, an inter-electrode displacement amount detector substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes, a reference inter-electrode displacement amount memory having preset reference inter-electrode displacement amounts stored therein, a comparator correcting inter-electrode displacement amounts detected by the inter-electrode displacement amount detector in dependence on the wear amount detected by the wear amount detector, to compare with reference inter-electrode displacement amounts stored in the reference inter-electrode displacement amount memory, a welding condition setter setting a welding condition of the welding object in accordance with a result of comparison by the comparator, and a current conduction contr
McDermott & Will & Emery
Nissan Motor Co,. Ltd.
Shaw Clifford C.
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