Electric arc welder using high frequency pulses

Details Electric arc welder using high frequency pulses Electric arc welder using high frequency pulses

2001-05-29

2003-02-04

Shaw, Clifford C. (Department: 1725)

Electric heating

Metal heating

By arc

C219S130310, C219S130500, C219S1370PS

Reexamination Certificate

active

06515259

ABSTRACT:

The present invention relates to the art of electric arc welding using a GMAW process and more particularly to a GMAW electric arc welder that creates a high frequency chain of current pulses to form a series of weld cycles constituting a weld process.
INCORPORATION BY REFERENCE
Electric arc welding of aluminum and aluminum alloy has created a dilemma for manufacturers to obtain a weld having a pleasing outer appearance. It was often necessary to use TIG welding. This welding process does produce a desired weld bead; however, it is costly and relatively slow compared to other types of welding. Consequently, over the years manufacturers of electric arc welders have attempted to develop an electric arc welder that would perform a pulse welding process on aluminum without the disadvantages associated with TIG welding and prior, less than satisfactory pulse welding processes. An early effort in this regard is shown in Tabata U.S. Pat. No. 4,994,646 wherein high frequency pulses are created in a series separated by a quiescent duration to control the weld puddle. This disclosure involves complex combination of various pulses having different frequencies and heights, as well as intentional period delays. This patent is incorporated by reference herein as an early attempt to use MIG welding for aluminum. This is background information relating to the present invention. In a like manner, Ueyama U.S. Pat. No. 5,667,709 is incorporated by reference herein. This patent discloses several prior art MIG welding methods for use in welding of aluminum and aluminum alloy. To overcome the alleged disadvantages of the MIG processes, this patent teaches a MAG welding process using high frequency current pulses, or groups of pulses, having different frequencies or other selected pulse characteristics. This is additional background information that need not be repeated in explaining the present invention. Another patent illustrating background technology is Lloyd U.S. Pat. No. 5,643,479. This patent illustrates a high frequency process using pulses, wherein the individual pulses have controlled pulse shapes determined by ramp up, ramp down, peak current and time durations. Of course, these pulses are formed on a fixed background current. This patent is incorporated by reference herein to show that well known technology exists for adjusting the profile, or shape of high frequency pulses. The present invention relates to a concept wherein the profile or pulse shape is changed for a purpose not contemplated by the Lloyd patent; however, the Lloyd patent is incorporated by reference herein as background technology relating to high frequency pulses for electric arc welding. The area of the individual pulses is changed by modifying ramp up, ramp down, peak current, and/or pulse amplitude. Japanese patent 58-176074 is also incorporated by reference as showing an electric arc welder apparently using high frequency output pulses with changes in the amplitude along the pulse train. All of these patents show background information regarding known technology for using high frequency current pulses for welding. The systems are highly complex and still present certain difficulties with respect to controlling the actual weld process, especially when welding aluminum.
The present invention is used to control a Power Wave electric arc welder sold by The Lincoln Electric Company of Cleveland, Ohio, and disclosed generally in Blankenship U.S. Pat. No. 5,278,390. This patent is incorporated by reference herein as illustrative of an electric arc welder having a waveform generator to control the contour, profile or shape of high frequency pulses generated to perform a pulse welding process.
BACKGROUND OF INVENTION
In welding aluminum and aluminum alloy, substantial research and development work has been directed to the use of a pulse welding process either MIG or MAG, where high frequency pulses direct metal from aluminum weld wire to a molten metal puddle or pool on the workpiece. It is advantageous to coordinate each pulse with a molten ball of aluminum for propulsion to the workpiece. Each pulse should correspond to a given droplet of molten metal. However, such processes generate a substantial amount of heat and agitate the molten aluminum puddle formed during the welding process. To prevent this agitation of the puddles and the resultant deterioration of the appearance of the weld, the pulse welding processes have been used where there are successive delay periods or a reduction in the size of the pulses periodically. In accomplishing this objective, the frequency of the pulses is often drastically reduced. The molten metal in the puddle generally resumes its surface tension configuration where it hardens and does not produce the desired appearance obtainable by TIG welding. High frequency is designed to transfer metal with good arc stability, typically at a one drop per pulse rate, with. the drop diameter close to the wire diameter. Heat input designed for arc stability is the same beat input that controls the puddle heating, cooling, and solidification rate, and thus bead appearance and penetration profile. Heat input optimized for wire melting may not be optimized for puddle melting. Thus, prior pulse control systems sacrificed weld quality or bead appearance by employing a pulse delay or drastically changed pulse spacing. Consequently, prior art high frequency pulse welding for aluminum has not resulted in high quality outer appearance of the resulting weld bead without substantial modification of the pulses, discontinuation of the pulses or otherwise periodic disruption of the weld process, with the resultant degradation of the weld process. Consequently, there is a need for a system to create high frequency pulses that overcome difficulties experienced in electric arc welding of aluminum and aluminum alloy.
THE INVENTION
The present invention overcomes the disadvantage of prior efforts to use high frequency pulse welding for aluminum by creating a series of high frequency pulses having a frequency in the range of 50-400 Hz so that each pulse can generally correspond to a deposition globular of aluminum in the pulse welding process. This use of separate and distinct pulses for droplet transfer in the pulse welding process has the advantage of efficient transfer of molten metal and thus high deposition rate. The high frequency pulses are continuous to maximized efficiency and heat for the weld process. However, the high frequency pulses, in accordance with the invention, are modulated at a frequency scaled to the size of the weld puddle, depending upon the wire feed speed, travel speed, and plate thickness. The smaller the puddle, the higher the low frequency used for modulation. This frequency is between about ¼ Hz to 40 Hz. By compromising “one droplet per pulse” design rule, individual high frequency pulse energy is modulated based upon the low frequency puddle formation. A weld bead having distinct and equally spaced ripple and uniform fusion line is obtained. While the instantaneous melt-off rate and arc length indeed alternates between high and low values at low modulation frequency, the average arc length and average melt-off rate is still maintained. By the technique of merely modulating high frequency pulses with a low frequency factor, there is no need for complex digital processing to form quiescent periods and/or complex weld profiles that cannot be coordinated with the frequency for transfer of globulars.
The shaped individual high frequency current pulses are produced by the pulse width modulator at a frequency in the range of 50-400 Hz. They are individually profiled by the wave shaper. Indeed, this profiling of the pulses creates high energy current pulses for the high energy portion of the weld cycle and low energy current pulses for the low energy portion of the weld cycle. The integrated shape is the heat energy of a pulse. Shaping of the pulses is made possible by the use of a high speed switching power supply with a wave shape to generator or wave shaper.
In one aspect of the invent

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