Method for magnetic control of plasma arc

A device for controlling a plasma arc is provided that includes a plurality of magnetic poles disposed around a distal end portion of a plasma arc torch. A plurality of electrical coils are wound around a proximal end portion of each of the plurality of magnetic poles, and a plurality of lead wires are connected to the plurality of electrical coils. A control system for controlling a current supplied to the plasma arc torch through the lead wires is also provided that changes at least one of a strength of a magnetic field produced by the magnetic poles, a polarity of the magnetic poles, and a movement of a magnetic force between the plurality of magnetic poles, such that a size and location of the plasma arc is controlled.

FIELD

The present disclosure relates to plasma arc torches or devices, and in particular, alternate methods and systems to control a plasma arc of such plasma devices.

BACKGROUND

Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in the tip, or nozzle, of the plasma arc torch. The electrode has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode during piloting. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch. In operation, a pilot arc is created in the gap between the electrode and the tip, often referred to as the plasma arc chamber, wherein the pilot arc heats and ionizes the gas. The ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece with the aid of a switching circuit activated by the power supply. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode.

A variety of devices and methods to control the plasma stream have been developed in order to improve cut quality and/or cut speed. Such methods include using a secondary gas that flows distally around the tip to stabilize the plasma stream. Shield caps that employ passageways to direct the secondary gas against/around the plasma stream are also known. Furthermore, a variety of current ramping techniques have been used, along with changing gas types and flow rates as a function of cutting parameters. Methods and devices to improve cut quality and cut speed are continuously desired in the art of plasma arc torches.

SUMMARY

In one form of the present disclosure, a device for controlling a plasma arc is provided that comprises a plurality of magnetic poles disposed around a distal end portion of a plasma arc torch, a plurality of electrical coils wound around a proximal end portion of each of the plurality of magnetic poles, and a plurality of lead wires connected to the plurality of electrical coils. A control system is also provided for controlling a current supplied to the plasma arc torch through the lead wires to change at least one of a strength of a magnetic field produced by the magnetic poles, a polarity of the magnetic poles, and a movement of a magnetic force between the plurality of magnetic poles, such that a size and location of the plasma arc is controlled.

In another form, a method of controlling a plasma arc is provided that comprises applying a current signal to a plurality of magnetic poles disposed around a plasma arc torch, controlling the current signal to change at least one of a strength of a magnetic field produced by the magnetic poles, a polarity of the magnetic poles, and a movement of a magnetic force between the plurality of magnetic poles, such that a size and location of the plasma arc is controlled.

In yet another form, a plasma arc torch is provided that comprises a torch head defining a proximal end portion and a distal end portion, a plurality of magnetic poles disposed around the distal end portion of the torch head, a plurality of electrical coils wound around a proximal end portion of each of the plurality of magnetic poles, and a plurality of lead wires connected to the plurality of electrical coils. A control system is also provided for controlling a current supplied to the plasma arc torch through the lead wires to change at least one of a strength of a magnetic field produced by the magnetic poles, a polarity of the magnetic poles, and a movement of a magnetic force between the plurality of magnetic poles, such that a size and location of a plasma arc is controlled.

DETAILED DESCRIPTION

Referring toFIG. 1, a device for controlling a plasma arc is illustrated and generally indicated by reference numeral20. The device20generally includes a plurality of magnetic poles22disposed around a distal end portion24of a plasma arc torch30as shown. The magnetic poles22define a body32extending axially along the plasma arc torch30, each of the bodies32having a distal end34defining a radial projection36, each of which extends inwardly towards the plasma arc.

In this form, there are four (4) magnetic poles that are equally spaced, radially around the plasma arc torch30, as shown in greater detail inFIG. 2. It should be understood that any number of magnetic poles may be employed, such as two (2) or six (6) or more, according to the principles of the present disclosure, and thus the illustration of four (4) is merely exemplary. Referring toFIG. 3, the projections36define a tapered end portion38in one form of the present disclosure. Additionally, the radial projections36lie in a common plane as shown. It should be understood, however, that the radial projections36may define a different geometry and lie in different planes while remaining within the scope of the present disclosure.

The magnetic poles22are illustrated as being disposed around the plasma arc torch30, and more specifically, a torch head. However, it should be understood that the poles may be integrated inside the plasma arc torch30while remaining within the scope of the present disclosure. Accordingly, in the form shown, the device may be employed as a retrofit kit to adapt to current plasma arc torches, while other integrated devices can be designed as a new system.

As further shown inFIG. 1, a plurality of electrical coils40are wound around a proximal end portion42of each of the plurality of magnetic poles22. A plurality of lead wires44are connected to the plurality of electrical coils40, and current is supplied to the plasma arc torch30through the lead wires44to change the strength of a magnetic field produced by the magnetic poles22, a polarity of the magnetic poles22, and/or a movement of a magnetic force between the plurality of magnetic poles, to increase constriction of the plasma arc, the plasma arc root footprint, and the plasma arc root movement. Accordingly, the size and location of the plasma arc may be controlled by a magnetic field.

To accomplish such control of the magnetics, a control system is employed to control both the current strength and the current waveform. An exemplary system is shown inFIG. 4with a circuit diagram corresponding to the four (4) magnetic poles22, and inFIG. 5with corresponding DC current waveforms. As shown inFIG. 5, the phases of the current waveform are offset 180 degrees from one magnetic pole to an adjacent magnetic pole, (poles are designated as P1, P2, P3, and P4), in one form of the present disclosure. It is also contemplated that pairs of magnetic poles22may be selectively energized in order to more precisely control the plasma arc, which is accomplished by the control system. More specifically, an inverter-based power supply with a stepper motor is used in one form of the present disclosure. The power supply produces a signal wherein the frequency of the current waveform controls a rotating magnetic field. The power supplied to each pole is switched from north to south, and the poles P1and P3are in series, while the poles P2and P4are in series. As the power is switched to each of the poles that are in series, a rotating magnetic field results. In one form, the power is switched at about 15 kHz, however, power can be switched as low as about 2 kHz while remaining within the scope of the present disclosure. In one form, the current magnitude can be about 5-10 amps, however other current levels may also be employed while remaining within the scope of the present disclosure. It is also contemplated that a modulated DC power signal, among other forms of current waveforms, is employed in accordance with another form of the present disclosure.

The magnetic poles22in one form are an iron steel, however, it should be understood that any ferromagnetic material may be employed while remaining within the scope of the present disclosure. Additionally, the number of windings for the electrical coils40is about 6-10 turns per inch for a 100 amp torch. It should be understood that the number of windings may be higher or lower and vary according to other amperages and other operating parameters while remaining within the scope of the present disclosure. For example, smaller coils may be employed with lower amperages. Accordingly, the values of windings and amperages set forth herein are merely exemplary and should not be construed as limiting the scope of the present disclosure.

It should be noted that the disclosure is not limited to the embodiments described and illustrated as examples. A large variety of modifications have been described and more are part of the knowledge of the person skilled in the art. These and further modifications as well as any replacement by technical equivalents may be added to the description and figures, without leaving the scope of the protection of the disclosure and of the present patent.