Electric heating – Metal heating – By arc
Reexamination Certificate
2002-03-06
2004-04-06
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06717107
ABSTRACT:
The invention relates to the art of electric arc welding and more particularly to an electric arc welder having two stage or two mode operation and the method performed by this two stage electric arc welder.
INCORPORATION BY REFERENCE
As background information, prior pending application Ser. No. 866,358 filed on May 29, 2001 together with references incorporated by reference in that application are hereby incorporated by reference. Kawai U.S. Pat. No. 4,889,969 shows a switch to shift between DIP welding and pulse welding and is incorporated by reference as background technology.
BACKGROUND OF INVENTION
Electric arc welders of the GMAW type are often powered by a high speed switching power supply or power source with a controller for controlling the current waveform of the welding process. The Lincoln Electric Company of Cleveland, Ohio has pioneered the concept of an electric arc welder with a wave shaper to control the shape of the current waveform during each cycle by the use of high frequency current pulses, the magnitude of each pulse being controlled by a pulse width modulator. In such welders, the wave shape of the current is accurately controlled to perform such diverse welding processes as pulse welding, constant voltage welding, spray welding, pulse welding, short-arc CV welding and STT welding. In such processes, the wave shape for each weld cycle is controlled by the pulse width modulator to produce a series of welding cycles that perform a designated process. Such arc welders are quite versatile; however, they are operated in selected mode by controlling the pulses created by the waveform shaper.
THE INVENTION
The present invention relates to an electric arc welder, of the type mentioned above, where the controller is shifted between two separate and distinct welding processes or welding modes. In accordance with the invention, the pulse shaper or pulse generator shapes a series of pulses forming a first welding process. The controller is shiftable to then perform a second welding process by implementing a series of different pulse shapes constituting a different mode of operation. By counting the cycles in the first mode of operation, the first process is terminated and the second process is initiated. Thereafter, the cycles of the next process are counted until they reach a set number, which indicates that the welder is to be shifted back to the first welding process. Thus, the electric arc welder has the capability of performing two separate welding processes by switching the controller from one mode of operation to another mode of operation. By this unique two stage or two state operation of an electric arc welder, the welder can perform a welding operation alternately using a first process and then a second process. For instance, a high energy process is performed for a short time and then the welder is converted to a low energy weld process. If the two processes are STT, low energy STT cycles are implemented followed by implementation of high energy STT cycles. Thus, in one embodiment, the first process is a high energy process and the second is a low energy process. A counted number of cycles of each process are used in the welding process to perform a total welding operation by implementing in series the first and second welding processes. As an example, in one specific embodiment the first process is a constant voltage spray process with high heat. The second process is a pulsed GMAW or low heat welding process. In the welding operation, the controller first implements the first process for a number of cycles and then the second process for a number of cycles. In another embodiment of the invention, the first process is a pulse welding process where the pulses have high energy or high heat. This is used in sequence with a low heat STT weld process for a number of cycles. By alternating between the pulse cycles and the STT cycles, a desired total welding operation is performed. In another embodiment, the first process is a pulse welding process having high heat. This process is alternated with a second weld process, which is a short-arc, constant voltage welding process. In a still further embodiment, the first weld process is a pulse process for high heat. The second weld process is a series of pulses where the energy of the pulses are determined by a closed loop feedback of the power exerted. A still further example of the invention is an embodiment where the first series of pulses in the pulse welding operation are electrode positive to give high heat. The second series of pulses is a pulse welding process are negative, comprising electrode constant voltage pulses. By shifting between these welding processes, the actual welding operation is controlled to optimize the performance of the welder.
In accordance with still another aspect of the invention, the first weld process of this two stage or two state electric arc welder is a pulse welding process. This process is continued until the arc voltage indicates a short circuit Then, the two stage welder is shifted to a short clearing weld process, such as an STT weld cycle. In the preferred embodiment, the signal to shift from the pulse welding process is not only dependent upon the indication of a short by a plunge in the arc voltage, but also on the time of a timer. The arc welder control shifts from the first weld process of the pulse mode into a short clearing process only when the short is sustained for a set time. The timer is preferably set to indicate that the short is maintained for at least 1.0 ms and preferably greater than a set time in the range of at least 0.2 to 0.5 ms. Consequently, only when there is an actual short, instead of an incipient short, does the electric arc welder shift into the second weld process for clearing the detected short circuit.
In accordance with the present invention there is provided an electric arc welder including a high speed switching power supply with a controller for creating a first and second weld process across the gap between a workpiece and a welding wire advancing toward the workpiece. The first process uses a first current waveform and the second process uses a second current waveform. A circuit is used to shift between the first and second weld processes, wherein the circuit includes a counter for counting the waveforms in the first and second processes. The welder shifts from the process being processed to the other weld process when the waveform count of the weld process being processed reaches a preselected number for each weld process. By using this two stage welder, the arc welder can be shifted between two separate and distinct welding processes in accordance with the count or other parameter.
In accordance with another aspect of the invention, there is a two stage arc welder of the type including a high speed switching power supply with a controller for creating a pulse wave weld process and a weld process to clear a detected short. A circuit is activated to create a short signal when the arc voltage is below a value indicative of a short and there is a switch to shift the controller from the pulse wave process to the short clearing process by a process shift signal created upon creation of the short signal. In an aspect of the invention, the two stage welder includes a timer to create the shift signal only when the short signal is held for a given time which is defined as greater than about 1.0 ms and preferably greater than a set time in the general range of 0.2 to 0.5 ms. Consequently, when the short is maintained for a preselected time, the two stage welder is shifted from the pulse mode of operation to a short clearing mode of operation. In the preferred embodiment, the short clearing mode of operation is an STT weld process.
In accordance with yet a further aspect of the invention, there is provided a method of operating an electric arc welder of the type including a high speed switching power supply with a controller. This controller creates a first and second weld process across a gap between the workpiece and the welding wire advancing
Fay Sharpe Fagan Minnich & McKee
Lincoln Global Inc.
Shaw Clifford C.
LandOfFree
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