Patent Application
20160169056
The disclosure generally relates to a process for repairing a section of a rotatable shaft, and more particularly to a process of repairing a section of a rotatable shaft, such as a lobe or a journal utilizing welding processes.
Rotatable shafts having eccentric features formed on portions of their outer surfaces are commonly used in various machines requiring cyclically timed mechanical events or actuations of various components. For example, an internal combustion engine may use a rotating camshaft for timed actuation of intake or exhaust valves controlling the flow of air and exhaust into and out from one or more combustion chambers. Camshafts are typically unitary structures having lobes or eccentric features protruding therefrom. The lobes are arranged to periodically push a roller or follower connected to another engine component, where the roller or follower tracks an outer periphery or race of each lobe.
In a typical camshaft application, each lobe is typically continuously in contact with a roller or follower. The interface between the cam lobe and follower is subject to compressive forces and friction, causing wear and/or damage to the lobe during prolonged use, or when a defective condition is present. For example, in instances where inadequate lubrication of the interface is provided and/or situations when the follower is not properly aligned with its respective lobe, wear and/or damage to the lobe may occur. Prolonged extensive use will result in wear as well. A damaged and/or worn lobe may directly affect the motion of the follower and, hence, operation of the engine. Therefore, it is necessary to either replace or rebuild the camshaft.
One of the challenges associated with rebuilding camshafts is rebuilding the eccentric features, such as lobes and journals, on the shaft. These eccentric features commonly have portions that stand proud of the minor diameter of the feature creating raised, square-edged, stepped profiles. It is difficult to efficiently rebuild these features and, in particular to rebuild the square-edge original to the feature due to welding dynamics and weld bead surface tension. Economic considerations, however, dictate that it is usually more desirable to rebuild a worn camshaft instead of replacing the worn camshaft with a new one.
Different welding strategies have been employed to repair the worn portions of rotatable shafts and address issues associated with the repair such as downtime and material costs. For example, U.S. Pat. No. 5,172,475 (“Amos et al.”) issued Dec. 22, 1992 discloses a prior art method for repairing a rotor that entails severing the rotor into two or more segments, removing the crack from the rotor and depositing weld material onto the rotor until the removed portion is replaced with weld metal. Additional welding is performed to build up enough stock to machine a welding preparation, which is used to provide a surface to weld together the rotor body 14 and the stub end 18. See Col. 2, lines 24-55, and
While prior art methods of repairing worn rotatable shafts are useful to some extent, these methods do not specifically address the difficulties associated with welding eccentric features such as lobes and journals. Therefore, there remains a need to more efficiently repair rotatable shafts, including features such as lobes and journals while maintaining the square edge original to the feature. Accordingly, the disclosed process for repairing a section of a rotatable shaft is directed at overcoming one or more of these disadvantages in currently available repair methods.
In accordance with one aspect of the disclosure, a process for repairing a section of a rotatable shaft is disclosed. The section of the rotatable shaft includes a surface portion having a surface parallel to an axis of rotation of the rotatable shaft. The section of the rotatable shaft further includes axial ends perpendicular to the axis of rotation of the rotatable shaft. The process includes preparing a well region extending over a perimeter of the section and extending downward in the surface portion. The well region has a bottom portion that is substantially parallel to the axis of rotation and includes opposing sidewalls. Each sidewall extends proximate to the axial ends of the section and directly adjoins a remaining portion of the surface portion. The process further includes depositing material into the well region to fill the well region using a welding process and displacing a portion of the material that was deposited in the well region.
In accordance with another aspect of the disclosure, a process of repairing a section of a rotatable shaft is disclosed. The section extends eccentrically from the rotatable shaft and includes a surface portion having a surface parallel to an axis of rotation of the rotatable shaft. The section also includes axial ends perpendicular to the axis of rotation of the rotatable shaft. The process includes milling a well region extending over a perimeter of the section and extending downward in the surface portion. The well region has a bottom portion that is substantially parallel to the axis of rotation and includes opposing sidewalls. Each sidewall extends proximate to the axial ends of the section and directly adjoins a remaining portion of the surface portion. The process further includes depositing material into the well region to fill the well region by using laser clad welding and grinding a portion of the material that was deposited in the well region.
The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one aspect of the disclosure in conjunction with the accompanying drawings, wherein:
The rotatable shaft 20 includes a section 10, which rotates as substantially one body with the rotatable shaft 20. The section 10 is, for example, affixed to or integral with the rotatable shaft 20. The section 10 includes a surface portion 30 with a surface that may be parallel to the axis of rotation A. The section 10 further may include axial ends 40 that are perpendicular to the axis of rotation A of the rotatable shaft 20.
The section 10 of the rotatable shaft 20 has a generally circular cross-section. The circular cross-section of the section 10, however, may be non-uniform. In some aspects, the section 10 is eccentric (i.e., non-concentric) relative to the axis of rotation A of the rotatable shaft 20. The profile of the section 10 depends on the particular application of the section 10 and the rotatable shaft 20.
In some aspects, the section 10 is a lobe for a rotatable shaft 20, such as a camshaft for an engine. In other aspects, the section 10 is a journal or other type of bearing for a rotatable shaft 20. The section 10 and the rotatable shaft 20 are composed of materials such as cast iron, cast steel, forged steel, aluminum or other materials suitable for their application.
During operation of the rotatable shaft 20, the section 10 may suffer wear and/or become damaged. For example, wear or damage may occur in situations when inadequate lubrication, misalignment, or another failure occurs that affects the working interface between the section and another component or in general, any follower component contacting the section. Excessive operation may result in a worn section 10 as well. Such conditions can require replacement and scrapping of the rotatable shaft 20. The rotatable shaft 20, however, may advantageously be repaired by the disclosed process as described below.
The disclosure provides various aspects for a process associated with repairing a section 10 of a rotatable shaft 20 that is worn or damaged to avoid scrapping the rotatable shaft 20 in favor of a new one.
Referring now to
At 120, the section 10 may be pre-weld heat treated to prepare the well region 50 and the section 10 for subsequent processes in the repair process 100. This pre-weld heat treatment occurs after preparing the well region 50 in the section 10 (process 110) and prior to depositing material into the well region 50 (process 130). The pre-weld heat treatment occurs at a high temperature for a specified period of time to ensure that the surface of the well region 50 is adequately prepared for depositing material in the well region 50. This pre-weld heat treatment process 120 is optional and depends on the welding process used in process 130, and the type of material deposited into the well region 50 as well as the material of the section 10 and the specific application of the section 10. Pre-weld heat treatment prior to welding may achieve better weld penetration and slow the cooling process after welding to allow for added stress relief, reduced material hardening and the like. Once process 120 is completed, the repair process 100 proceeds to process 130 (depositing material into the well region 50) as explained below. In lieu of process 120 or in addition to process 120, the well region may be cleaned and prepared for the next process. This process may include sanding, sandblasting, grease removal, grinding, coating removal, and the like.
At process 130 of the repair process 100, material is deposited into the well region 50 to fill the well region 50. The material deposited in process 130 replaces the material that was removed from the section 10 when the well region 50 was prepared in process 110. In general, the amount of material deposited in process 130 may be greater than the amount of material that was removed from the section 10 in process 110 to prepare the well region 50. The material deposited in process 130 may be the same or similar to the material that the section 10 is composed of and includes materials such as iron, steel, aluminum, stainless steel, titanium, nickel or other suitable materials for a section 10 of a rotatable shaft 20. The material deposited may also include titanium-based alloys, nickel-based alloys such as Inconel® and other alloys. Powder or wire feedstock may be used as the source of material to be deposited. In some aspects according to the disclosure, steel powder or steel wire is used as feedstock for the material deposited.
Process 130 may be carried out using at least one of the following welding processes: Laser Beam (LB) Welding, Plasma Transfer Arc (PTA) Welding, Electron Beam (EB) Welding, Metal Inert Gas (MIG) Welding, Tungsten Inert Gas (TIG) Welding, or any other suitable welding processes. These welding processes can be carried out under an inert gas atmosphere, with inert gas shielding, or under vacuum to prevent excessive oxidation. For example, argon, carbon dioxide, helium gas or the like may be provided with some of aforementioned welding processes. In one aspect according to the disclosure, Laser Beam (LB) Welding is used in process 130 to deposit material into the well region 50. In yet another aspect, argon gas is used with Laser Beam (LB) Welding in process 130 to deposit material into the well region 50. Laser Beam (LB) Welding, however, may be performed with other protective gases such as carbon dioxide or helium. Of course, process 130 may be implemented without any specialized inert gas atmosphere.
Process 130 may be performed using multiple consecutive passes as necessary to fill the well region 50 with deposited material. Once process 130 has been completed, the repair process 100 may optionally proceed to process 140 (post-weld heat treatment) as explained below. Alternatively, the repair process 100 may omit process 140 and directly proceed to process 150 (displacing a portion of the deposited material) after process 130 is completed.
At process 140, the section 10 of the rotatable shaft 20 may be post-weld heat treated to relieve stress or the like. This post-weld heat treatment process 140 occurs after depositing material in the well region 50 (process 130) and prior to displacing a portion of the deposited material (process 150). The post-weld heat treatment process 140 is similar to a post-weld heat treatment that is well known to those skilled in the art. In the post-weld heat treatment process 140, the section 10 of the rotatable shaft 20 is typically heated at a high temperature for a specified period of time. This post-weld heat treatment process 140 is optional but in some instances may substantially reduce the risk that the section 10 and the rotatable shaft 20 will crack after welding. The post-weld heat treatment may have some other benefits as well. In some instances, this post-weld heat treatment process 140 depends on the welding process used in process 130, the specific application of section 10, and the type of material deposited into the well region 50. Once process 140 is completed, the repair process 100 proceeds to process 150 (displacing a portion of the deposited material) as explained below.
At process 150 of the repair process 100, a portion of the material deposited in the well region 50 is displaced. A grinding process can be used to displace a portion of the material deposited. Alternatively, a milling or machining process may be used to displace a portion of the material deposited in the well region 50. Process 150 is performed until all of the excess material that was deposited in the well region during process 130 is removed and the section 10 of the rotatable shaft 20 is returned to its original or desired shape. In some aspects, the section is polished after the grinding process. Once process 150 is complete, the repair process 100 is also complete and the section 10 of the rotatable shaft 20 is considered repaired and ready for use. It should be noted that process 140 may be implemented after process 150 as well.
The disclosure may find applicability in repairing sections 10 of a wide range of rotatable shafts 20. The process may be utilized, for example, in any engine or machine that performs some type of operation associated with industry such as mining, construction, farming transportation, or any other industry known in the art.
The process disclosed herein may be used in applications such as motor vehicles, machines, locomotives, marine engines, electrical power generators, small mechanical engines, work implements, pumps, etc. The rotatable shaft 20 may be used as a component for a turbine, a turbocharger, a starter, a motor, an alternator, a water pump, a hydraulic pump, a fuel pump, a coolant pump, an oil pump, a transmission, an auxiliary system for a vehicle, and a drivetrain. For example, the section 10 of the rotatable shaft 20 may be a lobe, a journal or a bearing configured on a rotatable shaft 20 for a camshaft, a crankshaft, a water pump shaft, a fuel pump shaft, a coolant pump shaft, etc.
The disclosed repair process may lead to more efficiently operating machines and engines because of the quality of the repair that is achieved. If the section 10 is repaired and the original shape and profile is restored then the rotatable shaft 20 will be able to operate in a more efficient manner, ultimately resulting in an increase operational savings. The disclosed repair process may also be useful to prolong the life of various rotatable shafts 20 as well as prolonging the life of the machines and engines that use the repaired rotatable shafts 20. As a result, the disclosed repair process may lead to concomitant savings in part costs as well as labor. The process may also result in reducing scrap and therefore, presenting a greener solution to rotatable shaft 20 repair.
