When a resistance welding machine starts but then does not complete the cycle there is ussually and I/O signal missing back to the controller/timer. There are several Inputs that could cause this to happen. The problem is even more complex to troubleshoot when a PLC or other controls are interfaced with the RW unit or controller. We'll go over just the RW timer/controller.
First, if it comes down and then goes back up it could be one of 2 things. Either the squeeze-weld-hold cycle was too short (or the cylinder too slow) and the unit thinks it just made a weld or the latch for the welding (foot pedal switch, palm buttons etc.) was released and should not have been causing the machine to go back up for possible safety reasons due to initiation release prior to completion. On some controllers this could cause a weak weld if the number of weld cycles is not enough.
You may also experience the machine coming down and stopping or coming down and "locking up" and needs to be reset. This is most often a problem with a water flow switch, pressure switch, zero-cross-over-detection, temperature switch for the TX or the SCR or something like that. In this case the error codes in the unit should lead you to the correct wires to check. If there is PLC redundancy then the issue is even more complex. Most of the time it's a pressure switch. Basically the input needs to be there when the timer wants to see it. Sometimes if the input is not there then the unit will timeout and stop in the down position.
Sometimes timers/controllers are set up for checking things after the weld has been made. This is a quality issue or possible more PLC I/O. Often seperate weld checkers will "pull out" an Input signal to lock up what might be a bad weld. There might also be interal current control montoring that if not satisfied then the machine "stays down to signal a bad part" even though the part may be good. This is a weld checker problem and depends upon how it is interfaced with the robot, machine or controller/timer.
There are many different manufactures' controller/timers for resistance welding. There are also many different models from these companies and many additional ways to program and set up different I/O functions. Your controller/timer manual should be available if the machine is less than 10 years old. To go to our controller links page click here.
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