Metal founding – Process – Disposition of a gaseous or projected particulate molten...
Reexamination Certificate
2000-03-22
2002-10-15
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Disposition of a gaseous or projected particulate molten...
C164S131000
Reexamination Certificate
active
06463992
ABSTRACT:
The invention concerns a method of manufacturing a seamless self-supporting sheet metal part using the nickel carbonyl vapour deposition process to replace conventional sheet metal parts that are formed from flat blanks and welded or brazed together.
Conventional methods of forming sheet metal parts by various methods are well known in the art generally involving the use of flat sheet metal stock or coils of sheet metal which are flattened prior to cutting into various flat blank shapes.
Finished sheet metal components for various uses are conventionally bent, roll-formed, stamped and formed into shapes that are combined with other shapes and welded or brazed into a final sheet metal assembly.
In the production of aircraft engines in particular, the geometric complexity of sheet metal components and the accuracy required can be very demanding. The efficiency of an aircraft engine may depend heavily on the degree of shape accuracy of the fabrication of various sheet metal components. The surface finish of the components and finish of welds and other surface discontinuities can lead to aerodynamic inefficiencies, stress concentrations or possibly fatigue failure under thermal or dynamic loading.
As a consequence, the complex shapes constructed of sheet metal for aircraft engines involve a high degree of precision, skill, quality control, rework, part rejection and the necessary expenditure of time and money to produce acceptable results.
An example of a complex sheet metal component is an exhaust mixer for an aircraft engine. This component is an annular ring with a pleated or accordion-like skirt which serves to mix the cold engine bypass flow and hot engine exhaust gasses at the tail of the engine. Such complex shapes are generally fabricated by cutting and forming smaller segments in a sheet metal die press then assembling the components together in a complex welding jig. The fitting and assembly of multiple components inherently involves a degree of inaccuracy. As well, the introduction of heat to thin sheet metal components during welding introduces inaccuracies and heat distortion as the adjacent metal expands and contracts. Welding of aerodynamic shapes is less than ideal since the surface of welded areas must be ground, polished or finished to preserve the surface aerodynamic properties of the part. The heat from welding induces residual stresses which are locked into the structure and require heat treating to relieve these built-in stresses, that introduces distortion.
Where the accuracy of forming thin metal components is critical, the part may be machined from a casting or forging. However, machining involves relatively high expenses and labour as well as significant cycle time in manufacture. Accordingly, machining of very thin sheet metal components can be considered as the last resort that is only justified where the high cost of machining is necessary to ensure the accuracy and efficiency of the engine component. In some cases it is not possible to achieve the desired thickness.
U.S. Pat. No. 5,444,912 to Folmer shows a method of forming a flat blank into an exhaust mixer using hydraulic pressure and a complex forming jig. However, due to the complexity of this mechanism and the need to manufacture a separate jig for each different exhaust mixer configuration, this approach is of limited application.
A far greater disadvantage of conventional methods however is that the aerodynamic efficient design of the exhaust mixer and other sheet metal components are severely restricted by the method of manufacture.
The designers of aircraft engines may in theory design shapes for various components, that would result in increases in efficiency or optimize efficiency. However, these innovations are rendered impractical and uneconomical since the complex shapes that result would be prohibitively expensive to manufacture using conventional metal forming methods.
Therefore, the efficiency of an aircraft engine is severely restricted not by lack of technical design expertise but by the manufacturing methods used for economically producing the sheet metal components.
To date, the trade-off between efficiency of design and efficiency of manufacture has favoured manufacturing due to the high cost of producing complex sheet metal shapes.
The inventors have recognized that nickel vapour deposition may be utilized to produce complex sheet metal surfaces despite the relatively high cost involved and the long periods of time required to deposit pure nickel on a mould surface. In addition, the 99.9% pure nickel deposited in this process has limited capacity for heat resistance making it unsuitable for applications where operating temperatures exceed 900° F.
Despite these limitations and the generally high temperatures inside aircraft engines, the inventors have recognized that engine exhaust mixers can justify this slow and expensive process being complex sheet metal components exposed to relatively low temperatures of about 600° F. Cost/Benefit analysis will also reveal other sheet metal components for various low temperature applications where the invention can be justified within gas turbine engines and elsewhere to replace conventional sheet metal fabrications.
Nickel vapour deposition is commonly utilized for low temperature nickel plating of electrodes or other metal clad components as illustrated in the following U.S. patents: U.S. Pat. No. 4,687,702 to Monsees for applying a metal layer on one surface of a polyamide foam; and U.S. Pat. No. 5,362,580 to Ferrando et al. for a nickel coated lightweight battery electrode.
Another common application of nickel vapour deposition is in the manufacture of nickel plated moulds for plastic injection moulding. Various methods and apparatus for producing nickel plated moulds for plastic injection moulding are described in U.S. Pat. No. 5,591,485 to Weber et al. U.S. Pat, No. 5,470,651 to Milinkovic et al. and U.S. Pat. No. 5,570,160 to Weber et al.
In the prior art, the nickel deposition process is used to apply a thin very accurate plating or coating on a substrate. The nickel coating layer conventionally provides the properties of electrical conductivity or wear resistance as in U.S. Pat. No. 5,934,157 to Kobayashi et al. In the case of manufacturing plastic moulds, nickel deposition is used to provide an accurate mould surface that is rigid, wear resistant and accurately reproduces the shape and profile of a master part for reproduction in a plastic moulding.
In general, nickel vapour deposition is well known and will be described here only in general terms. U.S. Pat. No. 5,766,683 to Waibel describes a nickel deposition system with a carbon monoxide and vapour recovery system. Pure nickel on exposure to carbon monoxide produces nickel carbonyl vapour, which is contained within an enclosed deposition chamber. The substrate to be coated with a nickel layer is positioned within the chamber and exposed to the nickel carbonyl vapour. When the substrate is heated to a predetermined temperature, the nickel carbonyl vapour decomposes on the substrate. Elemental nickel is plated on the substrate and carbon monoxide gas is emitted. Nickel vapour deposition systems generally include means to withdraw the carbon monoxide gas and recycle the CO gas to produce a continuous supply of nickel carbonyl vapour for deposition.
Depending on the size of the mould or substrate to be coated, nickel vapour deposition generally progresses at a rate much greater than conventional plating to build up a thin plated layer on the substrate at a rate of up to 0.010 inches per hour. During the deposition process, it is critical to maintain the temperature of the substrate within a specified range to ensure that decomposition of the nickel carbonyl gas is maintained and deposition of nickel continues.
Where plastic moulds are produced using nickel vapour deposition, a negative mould surface with a nickel plating layer accurately reproduces the positive master. However, on the opposite surface where deposition occurs, the continuous addition of pure nickel on the surface e
Brand Joseph Horace
Dowhan Michael John
Eleftheriou Andreas
Waterston Andrew Robertson
Bachman & LaPointe P.C.
Elve M. Alexandra
Kerns Kevin P.
Pratt & Whitney Canada Corp.
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