Patent Application
20070173907
The present disclosure relates to plasma arc torches and more particularly to electrodes for use in plasma arc torches.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
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, which heats and subsequently 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.
Plasma arc torches typically include several “consumable” components, which generally refer to components that require regular replacement due to wear under relatively extreme operating conditions. Among these consumable components is the electrode, which acts as the cathodic side of the power supply and the source of initiation for the plasma arc and often undergoes the most extreme operating conditions. As the electrode wears after extended periods of operation, the stability of the plasma arc begins to degrade and affects the wear of the other components such as the tip and the shield cap, and thus the quality of the cut correspondingly becomes worse. The more frequently consumable components have to be replaced, the more end users or operators are faced with decreased productivity and increased costs.
Accordingly, many approaches have been developed to improve the life of electrodes such as altering gas flow patterns, and incorporating geometry to enhance cooling, among many others. These approaches have resulted in better quality cuts and lower operating costs for operators, yet still, additional advancements in the art are always desired to further increase the life of consumable components, and especially electrodes, to provide even more cost savings and improved quality cuts for the end user. Many of these approaches used to date, however, have involved relatively expensive materials and manufacturing processes and thus more cost effective methods of manufacturing electrodes exhibiting improved life are still needed in the art of plasma arc torches.
In one form of the present invention, a method of fabricating an electrode for use in a plasma arc torch is provided that comprises forming an electrode body having a proximal end portion and a distal end portion, forming a recess within the distal end portion of the electrode body, brazing a slug within the recess of the electrode body, forming at least one face around the distal end portion of the electrode and a distal end face of the slug, creating a bore through the distal end face of the slug such that the bore extends through the slug and the electrode body, and securing an emissive element within the bore, the emissive element being in contact with the slug and the electrode body.
In another form, a method of fabricating an electrode for use in a plasma arc torch is provided that comprises forming an electrode body having a proximal end portion and a distal end portion, forming a cavity within the proximal end portion of the electrode body, forming a recess within the distal end portion of the electrode body, brazing a slug within the recess of the electrode body, machining the slug and the electrode body to form at least one face around the distal end portion of the electrode body and the slug, creating a bore through a distal face of the slug such that the bore is at least partially exposed to the slug and the electrode body, and fixedly mounting an emissive element within the bore, the emissive element being in contact with the slug and the electrode body and not with the cavity.
Additionally, another method of forming an electrode for use in a plasma arc torch is provided that comprises forming an electrode body defining a proximal end portion and a distal end portion, forming a recess within the distal end portion, securing a slug within the recess of the distal end portion, creating a bore through the slug and the distal end portion of the electrode body, and securing an emissive insert within the bore.
In yet another form, a method of forming an electrode is provided that comprises the step of coining a slug, the slug being adapted for attachment to an electrode body. Preferably, an emissive element is pressed within a bore of the slug to form an electrode subassembly, and the electrode subassembly is secured to a distal end portion of an electrode body to form the electrode.
In still another form, a hybrid electrode for use in a plasma arc torch is provided that comprises an electrode body defining a proximal end portion and a distal end portion. The electrode body comprises a cavity within the proximal end portion, and a secondary body is disposed at the distal end portion of the electrode body. The secondary body defines a distal face and a bore formed through the distal face, and an emissive element is disposed within the bore. The emissive insert is in contact with the secondary body and the electrode body, and the secondary body is not exposed to the cavity.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
In the various forms described herein, relatively low cost methods of manufacturing electrodes that exhibit increased life over conventional electrodes, as well as the other plasma arc torch components, are provided in accordance with the teachings of the present invention. Additionally, different electrode embodiments are also provided, which are produced from the relatively low cost manufacturing methods described herein.
Referring to
As shown, the hybrid electrode 20 comprises an electrode body 22 that defines a proximal end portion 24 and a distal end portion 26, wherein the distal end portion 26 further comprises a distal perimeter surface 28. The electrode body 22 also comprises a cavity 30 within the proximal end portion 24, which in general, accommodates a cooling fluid during operation of the plasma arc torch. As further shown, a secondary body 32 is secured to the distal end portion 26 of the electrode body 22 proximate the distal perimeter surface 28. The secondary body 32 defines a distal face 34 and a bore 36 formed through the distal face 34 and preferably all the way through the secondary body 32. An emissive insert 38 is disposed within the bore 36, and the electrode body 22 also includes a bore 37 that is formed conjointly with the bore 36. Accordingly, the emissive insert 38 preferably extends all the way through the secondary body 32 and at least partially through the electrode body 22. In this preferred form, the emissive insert 38 is not exposed to the cavity 30. Alternately, the emissive insert 38 could extend all the way through the electrode body 22 and be exposed to the cavity 30 (not shown) while remaining within the scope of the present invention.
The electrode body 22 is preferably a copper or copper alloy material that provides the requisite electrical conductivity as the electrode 20 comprises a part of the cathodic, or negative, side of the power supply (not shown). The secondary body 32 is preferably a silver or silver alloy material, however, other materials such as gold and gold alloys, among other materials, may also be employed while remaining within the scope of the present invention. The emissive insert 38 is preferably hafnium, however, other materials such as zirconium, tungsten, and tungsten alloys may also be employed while remaining within the scope of the present invention. Generally, the material for the secondary body 32 has a lower thermal emission of electrons than the material for the electrode body 22 such that a plasma arc that is attached to the emissive insert 38 during operation of the plasma arc torch remains attached to the emissive insert 38 and does not have a tendency to attach itself to the electrode body 22, or the secondary body 32, thus reducing overall wear and improving the life of the hybrid electrode 20, and other components of the plasma arc torch.
Referring now to
Preferably, the slug 42 is secured by brazing, however other methods such as mechanical press fitting and swaging, friction welding, mechanical threading, heat treatment, and adhesive bonding, among others, may also be employed while remaining within the scope of the present invention. Additionally, a brazing compound is preferably a silver solder paste, however other compounds such as a silver alloy solder paste, flux and silver solder paste, a flux, among others, may also be employed while remaining within the scope of the present invention.
Referring to
Although the emissive insert 38 is preferably secured within the bore 54 after the faces 50 and 52 are formed, it should be understood that the faces 50 and 52 can be formed after the emissive insert 38 is secured within the bore 54 while still remaining within the scope of the present invention. The specific steps of alternate manufacturing processes in accordance with the teachings of the present invention are illustrated in detail in
Referring more specifically to
In another form of the present invention, as illustrated in
In yet another form of the present invention, the slug 42 is formed by a coining process to further reduce costs of the manufacturing process. (Coining processes are known in the art and are not described in detail herein for purposes of clarity.) As shown in
In another form, the coining process as illustrated and described herein includes pressing the emissive element 38 into the slug 42 during the coining process, thereby resulting in an electrode subassembly 90 as illustrated in
Referring to
Accordingly, various low cost methods of forming hybrid electrodes that provide increased life are provided by the teachings of the present invention. It should be understood that the description of the invention is merely exemplary in nature and, thus, variations that do not depart from the substance of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
