Electric heating – Metal heating – By arc
Reexamination Certificate
2001-12-06
2003-09-09
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S130210, C219S130510
Reexamination Certificate
active
06617549
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the art of arc welding. More specifically, it relates to clearing a shorted arc while arc welding.
BACKGROUND OF THE INVENTION
Electric arc welding is well known, and is performed with a variety of processes using a variety of types of equipment. One electric arc welding process is a MIG process, which is typically performed using a system for welding including a wire feeder and a power supply (a source of gas may also be included); An example of a prior art system for welding used in MIG and pulse spray welding is a Miller S64M™ wire feeder used with a Miller XMT304™ power supply.
Typically, in a MIG process, power is provided from the power supply to the wire feeder, and the wire feeder provides the wire and power to the arc. The wire feeder typically includes a controller, which may be part of or separate from the wire feeder, and which controls the wire feeder. Additionally, the controller provides a command signal to the power supply which causes the power supply to output a current and voltage at a desired magnitude. The command is produced in response to a user-selected wire feed speed and
or output current or other parameters. Controller, as used herein, includes digital and analog, circuitry, discrete or integrated circuitry, microprocessors, DSPs, etc., and software, hardware and firmware, located on one or more boards, used to control devices such as power supplies, wire feeders, and used to control processes such as MIG, pulse-spray, TIG, etc.
MIG welding often is performed by cycling or pulsing between background current and a peak current (called normal operating currents). During a MIG process the arc will occasionally or frequently be shorted—wire will at times touch the workpiece (often during or at the end of the peak current), thus shorting the arc.
The controller receives feedback, such as output or arc voltage, and determines when a short occurs, for example by detecting when output voltage drops below a threshold. Prior art controllers then adjust the output current and or power to clear the short. A short is cleared When contact between the wire and the workpiece is eliminated, and or the arc is re-established. Clearing a short generally requires increasing the power provided to the arc to burn off the end of the wire (that is touching the workpiece).
There are two prior art methods of clearing a short, hard-restrike (or hard-clearing) and soft-restrike (or soft-clearing). Hard-restriking entails very rapidly increasing the current to above the peak current, typically, the maximum current output of the power supply (maximum current). A typical hard-restriking output is shown in FIG.
2
. Hard-restriking clears bigger or hard short circuits (when substantial contact is made between the wire and the workpiece) well because hard-restriking provides the needed power to clear hard short circuits. However, hard restriking clears small or whisker short circuits poorly, because the sudden increase in power increases stick-out and arc voltage, thus adversely affecting the weld. Hard-clearing a short, as used herein, includes providing a sudden and substantial increase in current to the final clearing magnitude, such as to or near the maximum current available.
Soft-restriking entails increasing the current from the normal operating current by a series of small steps or increments, such as 5 amps. After each incremental increase, the current is maintained at that level for a brief period, such as for 2 msec. Prior to increasing the current by the next increment, the controller determines if the short has cleared. If the short has not cleared, the controller causes the current to increase incrementally to the next level. A typical prior art soft-clearing waveform is shown in FIG.
1
. Soft-restriking clears bigger or hard short circuits poorly because soft-restriking doesn't provides the needed sudden increase in power to clear hard short circuits quickly enough. However, soft-restriking clears small or whisker short circuits well, because the incremental increases in power clear the short without adversely affecting the weld. Soft-clearing a short, as used herein, includes providing a gradual or incremental change in power, and determining if the short has cleared: prior to reaching the final clearing magnitude, and terminating the clearing routine if the short has cleared before the final clearing magnitude is reached.
Accordingly, a system for welding that clear both hard and soft shorts is desirable.
SUMMARY OF THE PRESENT INVENTION
According to a first aspect of the invention a method of clearing a short in a welding process includes increasing an output current from a first magnitude to a second magnitude and detecting if the short has cleared after the current has reached the second magnitude. The current is increased to a third magnitude, in the event the short hasn't cleared. The difference between the second and first magnitudes is less than the difference between the third and second magnitudes.
According to a second aspect of the invention a method of clearing a short in a welding process includes increasing an output current from a first magnitude to a second magnitude and detecting if the short has cleared after the current has reached the second magnitude. The current is increased to a hard clearing magnitude, in the event the short hasn't cleared, and the increase is completed even if the short clears when the current is increasing. The difference between the second magnitude and the first magnitude is less than the difference between the hard clearing magnitude and the second magnitude.
According to a third aspect of the invention a method of clearing a short in a welding process includes increasing an output current from a first magnitude to a second magnitude and detecting if the short has cleared after the current has reached the second magnitude, The current is linearly increased to a third magnitude, in the event the short hasn't cleared. The difference between the second and first magnitudes is less than the difference between the third and second magnitudes.
The current is increased from a fourth magnitude (which may be the normal operating magnitude) to the first magnitude in one embodiment. The difference between the first and fourth magnitudes is less than the difference between the third magnitude and the second magnitude. The current is increased to the second magnitude only if the short has not cleared after the current is increased to the first magnitude.
According to a fourth aspect of the invention a method of controlling a welding process includes detecting if a short is present and increasing an output current if the short is detected, This is repeated at least one more time. If the short is not cleared the current is increased to a second clearing magnitude. The last increase is greater than any earlier increase.
According to a third aspect of the invention a method of clearing a short in an arc welding process includes raising an output current by a first increment and then raising the current by a second increment if the short has not cleared. The current is raised by a third increment if the short has not cleared. The third increment is greater than the first and second increments.
The third magnitude is a maximum current output and or the first two increases are of the same magnitude in various embodiments.
According to a fifth aspect of the invention a method of clearing a short of an arc-welding process, includes increasing an output current to soft-clear the short and then increasing the current to hard-clear the short if the short did not clear from the soft-clear increase.
Increasing the current to soft-clear includes incrementing the current by at least two increments in another alternative.
According to a sixth aspect of the invention a system for welding includes a source of welding power a feedback module, and a controller, having a current command output connected to the control input on the source. The controller also includes a
Corrigan George R.
Illinois Tool Works Inc.
Shaw Clifford C.
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