Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2002-04-29
2003-12-09
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S074000
Reexamination Certificate
active
06660958
ABSTRACT:
The invention relates to a process and apparatus for arc welding of a metallic component to a metallic structure. More particularly, the invention relates to the welding of a metallic stud or nut to a metallic sheet on which stud or nut is to be used as an anchorage.
The welding of metallic studs and nuts to a metallic structure by means of arc welding is a widespread process found in particular application in the automotive industry. The exact method of the welding process can be relatively varied but the general principal involves the formation of an electric arc between the stud and the metal sheet effecting relative melt of the metallic materials in the region of the arc so that the metal component can then be lowered into the melt which is formed in the fusion region to result in a strong welded connection being formed between the component and the metal structure on subsequent cooling.
One form of welding process is the so called drawn arc welding process which involves positioning the component to be welded to the metal sheet within a weld gun and bringing the component into electrical contact with the metallic surface to complete an initial circuit indicating that the metal component is in contact with the metal sheet. The weld cycle is then initiated whereby the stud is withdrawn from the work surface inducing a pilot arc which serves to help clean both the component and the work surface before a main welding current is initiated creating a weld arc between the raised component and the metal sheet. The weld arc serves to form a pool of molten metal on the sheet material and also on the metallic component. The welding apparatus then causes the component to be plunged into the molten metal whereby as the weld pool solidifies it forms a homogenous joint. The entire process takes less than a second and forms a joint which in fact is stronger than material that has actually been welded. Such a drawn arc welding process is standard within the welding industry and is used to attach both studs and nuts to metal sheets which allow further fastenings to be connected thereto. In this manner studs themselves may often be threaded to receive a co-operating threaded nut or a nut itself may be welded directly onto the sheet in order to receive a screw threaded connector. Usually such studs and nuts are to enable earthing connections to be made to the sheet metal and thus require good electric contact to be made between the stud or nut and the appropriate connector element fixed thereto. However, it has been found that even with the cleaning function of the pilot arc, the intense heat generated by the arc during the welding process results in the formation of vaporised carbon and other impurities which can result in a “smoke” emanating from the molten material. Condensation of this smoke and vaporised impurity on the threads above the welded nut or stud can serve to inhibit electrical contact with the subsequent connection and impair the threaded engagement between the component and threaded connector.
Furthermore, it has been found that due to the reactive forces generated by the formation of the arc itself and also by the driving of the component into the molten metal can result in the formation of splashes of molten metal whereby if such splashes land on the thread of the nut or the stud, then they again will solidify to inhibit the screw threaded operation of such nut or stud. It is therefore an object of the present invention to provide for an improved welding process and welding apparatus to alleviate the aforementioned problems in a manner which will not inhibit the speed or quality of the welding procedure.
According to one aspect of the present invention there is provided a method of welding a substantially metal component to a metal workpiece, comprising the steps of: creating a weld arc between said component and metal workpiece to create a weld pool of molten material and initiating a pressurised fluid flow over said component and the weld pool to deflect any airborne fluid residue of the weld pool away from said component during the displacement of the component into the weld pool.
Preferably, where the method is applicable to a component which comprises a metal weld region and a connector region, the weld arc is created between the metal weld region of the component and the metal workpiece to create a weld pool and the pressurised fluid flow is initiated so as to be disposed between the connector region of the component and the weld pool to deflect the fluid residue of the weld pool from the connector region. Usually the flow of pressurised fluid is initiated as least substantially simultaneously with the creation of the weld arc or before creation of the weld arc.
Where the connector region is threaded, the method will usually comprise the step of deflecting the fluid flow through a channel formed by the thread of the threaded region. In particular, where the component is a weld nut the pressurised fluid flow is directed through the central aperture of the nut to create a positive pressure within the aperture of the nut which prevent any splashes of molten weld material or gases from entering this region. The method will also preferably comprise the step of placing a solid cylindrical insert in frictional engagement with the internal threads of the nut in order to form sealed channels with the thread through which the fluid flow can then be directed. In this manner the pressurised fluid is further compressed through this threaded channel to create a high positive pressure which prevents any airborne particulate from the weld procedure from being thrown or drawn into the threaded region of the nut.
The pressurised fluid may be given a straight flow path prior to being directed through the nut. This flow path can be induced by passing the fluid through at least one longitudinally extending channel, usually formed within a solid control valve placed in the fluid path, and more usually the flow is induced by passing through six such channels, which are equally spaced angularly about the central axis of the fluid flow path.
The pressurised fluid may also be given a spiral flow path prior to being directed through the nut. Thus when the fluid flow engages with the spiral threads of the nut it has already partially aligned with such threads and therefore readily engages and enters the channels formed between the threads of the nut. This spiral flow path is preferably induced by passing the fluid through at least one spiral channel, usually formed within a solid control valve placed in the fluid path, and more usually the spiral flow is induced by passing through six such channels, which are equally spaced angularly about the central axis of the fluid flow path. The spiral channels are usually set to deflect the fluid flow at an angle of between 10 and 80° relative to a plane perpendicular to the direction of fluid flow and more particularly the angle of deflection generated is between 50 and 70°.
The pressurized fluid may also b allowed to expand after the spiral flow path is induced therein. Preferably, the fluid use in this method will be compressed air directed from a pressurized air source at a flow ate of between 5 and 30 liters per minute and preferably between 10 and 20 liters per minute.
Furthermore, according to a second aspect of the present invention there is provided apparatus for directing a pressurised fluid flow over a substantially metal component during arc welding, the fluid flow being directed by said apparatus so as to deflect any airborne fluid residue created by the welding process away from the component.
According to a further aspect of the present invention there is also provided welding apparatus for welding a substantially metal component to a metal workpiece, said component comprising a metal weld region and a connector region, said apparatus comprising a weld head having means for holding said weld region of said component adjacent said workpiece and inducing a weld arc between said weld region and workpiece to create a weld pool of molten materi
Eberling Richard L.
Harries Simon
Kurz Roland
Napierala Stefan
Elve M. Alexandra
Murphy Edward D.
Newfrey LLC
Tran Len
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