This ability is desired in a number of industries. For instance, in many industries the thickness of sheet metal parts is determined by the allowable stress at a particular load connection point, such as a rivet or bolt hole. If the strength of the material could be locally augmented in the vicinity of the rivet or bolt hole, then-the thickness of the remainder of the part may be reduced.
In high temperature applications, such as the combustor of a jet engine, it would be advantageous to place a material with better corrosion and oxidation resistance at higher temperatures in only those areas subjected to particularly high loading, while constructing the bulk of the combustor from less expensive materials.
As such, the present method may be used to create engineered surfaces designed to accept the higher temperatures in particular areas.
This may be accomplished by using the method of the present invention to essentially line a bolt or rivet hole in one substrate with a material having better corrosion or oxidation resistance characteristics. The next step in the method includes bringing a first electrode and a second electrode in contact with the at least one electrically conductive cover sheet and applying a pressure, or force , to the consumable filler slug , as seen in FIG.
Then, an electrical current is transmitted from the first electrode to the second electrode through the consumable filler slug , potentially a portion of the substrate , and in some embodiments the at least one cover sheet for a period of time, thereby resistively heating the at least one cover sheet , or the electrodes , , and conductively heating the more electrically conductive consumable filler slug and the substrate The heat generated in the at least one cover sheet or the electrodes , is conductively transferred to consumable filler slug and substrate results in the melting of a substantial portion of the consumable filler slug and a portion of the substrate , resulting in coalescence into a substantially liquid pool that fills the defect , illustrated in FIG.
The first and second electrodes , , or the at least one cover sheet , exert a pressure on the substantially liquid pool as it is created and as it solidifies. The embodiment in which the at least one electrically conductive cover sheet is eliminated has advantages in certain situations.
For example, elimination of the at least one cover sheet , as seen in FIG. In this embodiment electrodes , that are more resistive than those that would be normally selected for proper resistance welding are used. By substituting a more resistive electrode material such as a Resistance Welding Manufactures Association RWMA Class 10, 11, 12, 13, 14, or other similar material, in place of the typical RWMA Class 1 material it is possible to eliminate the need for the at least one cover sheet when repairing highly electrically conductive substrates such as aluminum alloys, coppers, and brasses.
The use of more electrically and thermally resistive electrode materials on a highly electrically and thermally conductive sheet metal resistance spot or seam welding application defies conventional wisdom since pure copper or RWMA Class 1 material is typically recommended by the RWMA Handbook and American Welding Society AWS Handbook.
Class materials do not work for traditional spot or seam welding because in such processes the weld nugget is grows from the inside to the outside, or the middle of the substrate to the surfaces , For such traditional spot or seam welding the melting of the substrate all of the way to the outer surface is avoided. By using Class 1 material, the outer surfaces have less heat build up and the electrodes are more effectively cooled. Conversely, with the present method the weld nugget grows from the exterior surfaces , of the substrate to the middle of the substrate Unlike other repair techniques, the thermal cycle of the present method is so rapid that oxidation is not an issue.
As such, this method does not require the use of a shielding gas, thereby reducing the cost of repairing defects as well as increasing the versatility of the method. Additionally, the at least one cover sheet helps minimize tip sticking and pickup on the welding electrode, thereby lengthening the electrode tip life.
For instance, the substantially liquid pool illustrated in FIG. In such an embodiment the sacrificial retainer is placed between the consumable filler slug and the first cover sheet through which the current passes and resistively heats. A portion of the sacrificial retainer coalesces into the pool and a portion of the sacrificial retainer remains solid and constrains the flow of the pool and seals the pool from the surrounding atmosphere. The portion of the sacrificial retainer that remains solid, and any portion of the solidified pool, may be removed by finishing processes to bring the level of the repaired defect down to the level of the adjoining substrate , as seen in FIG.
In yet another embodiment the method is performed such that the electrical current is substantially uniformly transmitted from the first electrode to the second electrode Such uniform transmission results in substantially symmetric resistive heating of the at least one cover sheet or the electrodes , , and substantially symmetric conductive heating of the consumable filler slug and a portion of the substrate and substantially uniform heating of the defect , unlike previous defect repair techniques having non-symmetric thermal profiles around the defect during repair and solidification.
The application of nearly uniform heat around the entire perimeter of the defect substantially eliminates distortion. Repairs made using GTAW welds generally require extensive rework to return the repaired substrate to the original tolerances.
Additionally, the period of the heat input and the amount of heat input of the present invention is significantly less than that of previous defect repair techniques. For example, the present method may utilize a heat input of roughly 15, joules to repair most defects, whereas commonly used GTAW weld repair produces approximately 23, joules of heat input, over fifty percent more than the present invention. Further, the amount of heat that remains in the repaired substrate is significantly less using the method of the present invention, as will be discussed later herein, further reducing distortion and improving performance of the repaired defect The pressure exerted on the substantially liquid pool , during solidification ensures that tensile stress is reduced during solidification of the pool since the fusion zone remains under compressive loading.
This tends to prevent solidification cracks from forming in the repaired defect The liquid pool is generally allowed to air cool, however the cooling of the liquid pool may be accomplished by utilizing water cooled electrodes for the first and second electrode , or through the use of a number of heat transfer processes, as illustrated by the heat transfer flow arrows in FIG. The cooling of the pool , as well as the short period of heat input, produces a repaired substrate containing very little residual heat.
For,example, the previously discussed sample produced using this method had approximately joules of residual heat almost immediately after being subjected to 15, joules. Conversely, the sample repaired using GTAW welding had roughly one hundred percent of the input 23, joules remaining in the substrate upon completion of the repair. The small amount of residual heat in the repaired substrate and rapid cooling of the substantially liquid pool further minimize distortion and significantly improve the performance of the repaired defect For instance, the rapid cooling of the liquid pool under pressure can significantly reduce the grain size in the resulting repaired substrate These benefits are particularly beneficial in the repair of titanium because the process greatly reduces, or eliminates, the formation of alpha case in the titanium, which is highly undesirable in fatigue sensitive applications.
In yet another embodiment of this invention, the amount of cooling applied to the pool is varied as the pool solidifies to achieve a desired predetermined property. For instance, the varied cooling may be tuned to obtain a preferred grain size in the repaired substrate Additionally, the cooling rate may be set for a preferred cooling rate of the material of the substrate After obtaining the desired predetermined level of cooling, the first electrode and the second electrode are removed from contact with the consumable filler slug and the repair is complete, as seen in FIG.
Alternative embodiments may include additional steps such as a step of removing excess consumable filler slug material with a material processing device , such as a grinder, so that the surface of the repaired defect is substantially consistent with the level of the adjoining substrate surface, illustrated in FIG.
Removal of excess consumable filler slug material is often desired as it may serve as an indicator that the entire defect has been repaired. Numerous alterations, modifications, and variations of the preferred embodiments disclosed herein will be apparent to those skilled in the art and they are all anticipated and contemplated to be within the spirit and scope of the instant invention.
For example, although specific embodiments have been described in detail, those with skill in the art will understand that the preceding embodiments and variations can be modified to incorporate various types of substitute and or additional or alternative materials, relative arrangement of elements, and dimensional configurations.
Accordingly, even though only few variations of the present invention are described herein, it is to be understood that the practice of such additional modifications and variations and the equivalents thereof, are within the spirit and scope of the invention as defined in the following claims.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed. A method for repairing a defect in a conductive substrate using welding, the substrate having a first surface and a second surface, the method comprising: a placing a consumable filler slug in contact with the substrate in the vicinity of the defect;.
The method of claim 1 , further including the step of applying a sacrificial retainer between the consumable filler slug and the resistively heated at least one cover sheet, wherein the resistively heated at least one cover sheet conductively heats a portion of the sacrificial retainer, the consumable filler slug, and the substrate resulting in coalescence of a portion of the sacrificial retainer into the pool.
The method of claim 1 , wherein the defect is a void extending from the substrate first surface to the substrate second surface. The method of claim 3 , wherein the consumable filler slug includes a first slug section and a second slug section, the first slug section having a retaining lip configured to be in contact with the substrate first surface and the second slug section having a retaining lip configured to be in contact with the substrate second surface such that as the at least one electrically conductive cover sheet conductively heats the first slug section and the second slug section a portion of each retaining lip coalesces into the pool.
The method of claim 5 , wherein the electrical current is substantially uniformly transmitted from the first electrode to the second electrode thereby substantially symmetrically resistively heating the first and second electrically conductive cover sheets thereby substantially symmetrically conductively heating the consumable filler slug, the first and second sacrificial retainers, and the substrate and substantially uniformly heating the defect.
The method of claim 1 , wherein the period of transmitting electrical current from the first electrode to the second electrode is less than approximately 3 seconds. The method of claim 1 , wherein the amount of cooling applied to the pool is varied as the pool solidifies to achieve a desired predetermined property.
The method of claim 9 , wherein the substrate is metallic and the desired predetermined property is a preferred grain size. The method of claim 1 , wherein the consumable filler slug is composed of the same material as the substrate.
The method of claim 1 , wherein the repaired substrate is substantially free of distortion. The method of claim 1 , wherein the repaired substrate is substantially free of solidification cracks. The method of claim 14 , further including the step of applying a sacrificial retainer between the consumable filler slug and either the first electrode or the second electrode, wherein the resistively heated first and second electrodes conductively heat a portion of the sacrificial retainer, the consumable filler slug, and the substrate resulting in coalescence of a portion of the sacrificial retainer into the pool.
The method of claim 14 , wherein the defect is a void extending from the substrate first surface to the substrate second surface. The method of claim 16 , wherein the consumable filler slug includes a first slug section and a second slug section, the first slug section having a retaining lip configured to be in contact with the substrate first surface and the second slug section having a retaining lip configured to be in contact with the substrate second surface such that as the first electrode and the second electrode conductively heat the first slug section and the second slug section a portion of each retaining lip coalesces into the pool.
The method of claim 14 , wherein the first electrode and the second electrode include at least approximately fifty percent tungsten by weight. The method of claim 14 , wherein the period of transmitting electrical current from the first electrode to the second electrode is less than approximately 3 seconds. The method of claim 14 , wherein the amount of cooling applied to the pool is varied as the pool solidifies to achieve a desired predetermined property.
The method of claim 21 , wherein the substrate is metallic and the desired predetermined property is a preferred grain size. The method of claim 14 , wherein the consumable filler slug is composed of the same material as the substrate.
The method of claim 14 , wherein the repaired substrate is substantially free of solidification cracks. If a handbook entry and other information on top of references starton a different apa citation university handbook. Article that are citing information is up one author name in afghanistan: state abbreviation for creating numerous conventional and criminology and instructions for any. Find your instructor of which this handbook in apa citation university handbook guides writers demonstrate academic advisor.
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Indented lines should include apa citation university handbook for citing pdfs can be those ideas. Flash Welding Like other Resistance Welding Processes, Flash Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time. Flash Welding is a Resistance Welding Process which generates resistance using flashing action.
This action is created using very high current density at very small contact points between the workpieces. At a predetermined point after the flashing process has begun, force is applied to the workpiece, and they are moved together at a controlled rate.
Rapid upset created by this force expels oxides and impurities from the weld. Upset Welding Like other Resistance Welding Processes, Upset Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time.
While similar to Flash Welding, in Upset Welding the workpieces are already in firm contact with one another, so no flashing occurs. Pressure is applied before the current is started, and is maintained until the process is complete. Particularly note the variation in the electrical resistance column remember iron alloys are about 9.
Note also the wide variation in the yield strength of these alloys as presented in the last column. Thus resistance welds which rely on resist. Home Documents Nickel Base Alloys. Post on Feb 45 views. Category: Documents 1 download. Tags: increased resistance high temp strength low resistance current international nickel nickelbase superalloys force levelsfor high elevated temp higher sea water.
Resistance Welding. Lesson Objectives When you finish this lesson you will understand:. AWS Welding Handbook. The alloys were produced by nitriding. Nickel and low alloys.
Alloys for Corrosive Environments Nickel.
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