Electric heating – Metal heating – For bonding with pressure
Patent
1988-11-30
1991-05-14
Shaw, Clifford C.
Electric heating
Metal heating
For bonding with pressure
2191171, 21913021, B23K 1124
Patent
active
050158155
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention proceeds from a process for regulation of resistance welding operations in which by measuring the current strength of the welding current and the voltage at the welding electrodes, the dynamic resistance or resistance index of the workpiece to be welded is determined during the welding operation, stored and evaluated in comparison with an empirically determined correcting or command variable.
In process and apparatuses with measurement of the dynamic resistance during the welding operation, the resistance of the workpiece is repeatedly determined and related to the quality of the joint to be expected. Due to the low measuring technology expenditure, only physical quantities (voltage and current) being measured, which drop in spot welding, this process is preferably used for spot welding control. In all other known control methods of this type particularly distinguished quantities are determined in a respective half or whole welding period, for example the resistance at the instant of the current maximum or a resistance-similar quantity which results from the quotient of the integrated voltage with respect to the integrated current (MIACHY method). The variation of these distinguished quantities is determined over the entire welding time and when a switch-off criterion is reached the welding is terminated. The switch-off criteria are determined empirically.
These known processes use for the regulation the welding time or the number of welding periods per welding spot as the controlling variable. The energy introduced into the weld spot, which can be varied by the phase angle of the primary voltage, can be employed as additional controlling variable. DE-OS No. 3,301,039 discloses a process in the work integral introduced at the welding point is determined and within each mains half period the energy supply to the welding point is switched off after reaching a work integral corresponding to a desired value for the respective mains half period. To control the electrical work, thyristors which can be switched off are preferably employed.
In the known process due to inadequate information density or information evaluation, an advance recognition of a disturbance in the welding process is not possible.
SUMMARY OF THE INVENTION
In the process according to the invention, the variation of current strength and electrode voltage of a welding current half period is measured with high resolution, stored error-corrected and by mathematical processing, the effect of the welding influencing parameter power
______________________________________ or/and energy
or/and charge amount
or/and electrode voltage
or/and current strength
______________________________________
with high resolution (e.g. measuring point interval 10 microsec.) and is
evaluated on-line comparison with the corresponding correcting or command
variable. Preferably, the effects of several welding influencing
parameters are determined quantitatively and employed individually or in
combination with each other and compared with empirically determined basic
values of the correcting and command variable.
In the process according to the invention the assessment of the quality of the weld spots is made immediately during a welding half period or cycle, i.e. on-line. Since the quantitatively acquired effects of the welding influencing variables are collected as correcting or command variables in high density or resolution and investigated for their characteristics, each welding operation can be controlled in such a manner that any impending disturbance is avoided.
The occurrence of disturbances, such as spattering, is indicated by characteristic basic values of the evaluated measured quantities which are compared with the stored correcting or command variables early enough to avoid the disturbance by changing the current strength or voltage or by changing the phase angles and thus changing the power supply, and the welding operation is terminated in optimum manner.
The apparatus necessary for carrying o
REFERENCES:
patent: 4302653 (1981-11-01), Denning et al.
patent: 4403132 (1983-09-01), Sugimoto
patent: 4419560 (1983-12-01), Zurek
Matuschek Ulrich
Zimmermann Martin
Shaw Clifford C.
Striker Michael J.
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