Electric heating – Metal heating – By arc
Reexamination Certificate
2001-01-09
2002-11-19
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C361S117000
Reexamination Certificate
active
06483077
ABSTRACT:
BACKGROUND
Electric arc welding processes have become one of the most important welding techniques, particularly for joining steels. Electric arc welding generally involves the supplying of either direct or alternating current for creating an electric arc which generates enough heat to melt metal for the weld. Although arc welding produces welds having high join quality and join strength, arc welding has some drawbacks. For example, arc welding has traditionally resulted in distortion and spatter. Prior to the present invention, there was no cost effective or efficient way to control the electric discharges produced in arc welding technology.
It is known to control electric discharge by using high power laser sources which thermally ionize the local atmosphere. This process requires the use of ultraviolet lasers, which are strongly absorbed in the atmosphere, or very high power lasers which cause thermal breakdown in the local atmosphere. This approach tends to generate localized regions of ionization where the electric discharge is initiated. Guiding the electric discharge over a long path is difficult since both the ionization and the breakdown processes cause strong attenuation and scattering of the laser beam. Additionally, since breakdown requires a high field strength, the breakdown process tends to be localized at the laser focus rather than uniformly distributed along the path length of the laser beam itself.
The present invention discloses a new approach of controlling electric discharges by the production of excited molecules along the desired path of the discharge. More particularly, the invention discloses an approach to controlling electric discharges by the production of metastable molecules using a low power laser. The present invention is advantageous in that:
1.) a low power laser may be used to vibrationally excite predetermined molecules so as to guide an electric discharge;
2.) vibrational states of the molecules may be excited with little, if any, rotational or translational molecular energy conversion, i.e., the molecules do not experience generalized heating;
3.) the present invention may provide arc initiation, path stablilization and discharge constriction;
4.) the laser beam may be pulsed;
5.) the arc may be pulsed;
6.) both laser beam and arc may be pulsed;
7.) low powered, relatively inexpensive, lasers may be used to control electric discharges;
8.) rapid arc movement and accurate arc position are achieved;
9.) the discharge can be constricted to a very small cross section allowing constriction of an arc into a high power density heat source; and
10.) small area, high power density discharges may be controlled allowing for small welds (e.g., smaller than 3 mm wide) and deep penetration welding (e.g., where depth of penetration is greater that weld width).
SUMMARY OF THE INVENTION
The present invention includes a method of initiating an electrical discharge arc. This method preferably comprises the steps of: (a) providing a laser beam through a predetermined gas comprising molecules amenable to vibrational excitation by a laser beam so as to cause vibrational excitation of said molecules and to define a beam path in a direction of desired electrical discharge;
(b) propagating an electrical discharge arc so as to intersect said beam path, whereby said electrical discharge arc is directed along said beam path.
In other terms, the method of the present invention comprises the steps of: (a) providing a laser beam through an arc shielding gas, the gas comprising molecules amenable to vibrational excitation by the laser beam, so as to define a beam path comprising molecules vibrationally excited by the laser beam without substantially heating the gas; and (b) propagating an electrical discharge arc along the laser beam path and the vibrationally excited molecules.
The laser beam and the electrical discharge arc may be maintained substantially continuously, or laser beam and the electrical discharge arc may be pulsed. It is also possible that the laser beam is maintained substantially continuously while the electrical discharge arc is pulsed.
The arc shielding gas(es) may be one appropriate arc shielding gas or a mixture of two or more appropriate arc shielding gases, such as those known and used in the art. Such gases may include argon, helium, carbon dioxide or a mixture therein. Gas may be introduced into the shielding gas, these gases having molecules amendable to vibrational excitation by the laser of the present invention. Such gases may be selected from the group consisting of carbon monoxide, oxygen or nitrogen, for example.
The present invention includes a method of directing an electrical discharge arc along a first vector path. The method in broadest terms comprising the steps: (a) providing a laser beam through an arc shielding gas, the gas comprising molecules amenable to vibrational excitation by the laser beam, so as to define a beam path, the beam path directed along a first vector path comprising molecules vibrationally excited by the laser beam without substantially heating the gas; and (b) propagating an electrical discharge arc along a second vector path so as to intersect the first vector path, whereby the electrical discharge arc is directed along the first vector path and through the vibrationally excited molecules.
As in the method of initiating arcs, the laser beam and the electrical discharge arc may be maintained substantially continuously, or laser beam and the electrical discharge arc may be pulsed. It is also possible that the laser beam is maintained substantially continuously while the electrical discharge arc is pulsed. Where pulsed, the pulses of the laser beam typically range in duration from whole seconds to whole milliseconds, while the pulses of the electrical discharge arc typically range in duration from whole seconds to whole microseconds.
The arc shielding gas(es) may be one appropriate arc shielding gas or a mixture of two or more appropriate arc shielding gases, as described above.
Another aspect of the present invention includes a method of constricting an electrical discharge arc, the method comprising the steps: (a) providing a laser beam through an arc shielding gas, the gas comprising molecules amenable to vibrational excitation by the laser beam, so as to define a beam path, the beam path having a first cross-section area and comprising molecules vibrationally excited by the laser beam without substantially heating the gas; and (b) propagating an electrical discharge arc initially having a second cross-section area greater than the first cross-section area along the beam path and through the vibrationally excited molecules, whereby the electrical discharge arc is constricted so as to have a cross-section area less than the second cross-section area.
As in the methods of initiating and directing arcs, the laser beam and the electrical discharge arc may be maintained substantially continuously, or the laser beam and the electrical discharge arc may be pulsed. It is also possible that the laser beam is maintained substantially continuously while the electrical discharge arc is pulsed.
The arc shielding gas(es) may be one appropriate arc shielding gas or a mixture of two or more appropriate arc shielding gases, as described above.
The present invention also includes an apparatus for initiating an electrical discharge arc, the apparatus comprising: (a) a source of an arc shielding gas; (b) a laser adapted to provide a laser beam through the arc shielding gas, the gas comprising molecules amenable to vibrational excitation by the laser beam, so as to define a beam path comprising molecules vibrationally excited by the laser beam without substantially heating the gas; and (c) a source of an electrical discharge arc adapted to provide an electrical discharge along the laser beam path and through the vibrationally excited molecules.
The laser may be adapted to maintain the laser beam substantially continuously, and the source of an electrical discharge may be adapted to maintain the electrical discharge arc substan
Albright Charles E.
Lempert Walter R.
Macheret Sergy O.
Miles Richard B.
Rich Joseph W.
Shaw Clifford C.
Standley & Gilcrest LLP
The Ohio State University
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