Patent Application
20080253922
The invention relates generally to a method of roughening metal surfaces and an article manufactured thereby, and more particularly to an electrolytic process for etching a metal surface.
Aerospace and other industries often require surface preparation of metals prior to adhesive bonding. A large number of components, such as turbine blades, fan, compressor blades and other composite parts are adhesively bonded to each other to achieve the fabrication of a completed unit. To ensure obtaining a good metal-to-metal or metal-to-nonmetal adhesive bond, the surface of the metal is required to be as clean as possible, but many metals have a surface which is too smooth or uniform to provide an optimum bond subsequent to cleaning. In one known approach to providing better adhesion, the metal surfaces are chemically treated to provide an etched surface thereby producing more surface area, which contributes to achieving the bond. In this approach, chemical treatment involves application of a sacrificial, porous barrier layer (mask) and acid etchants to produce the desired roughening of metal surfaces. The etchant mixture may include combinations of nitric and hydrofluoric acids. The duration of the etching process is quite long and the etchant mixtures are difficult to handle. Moreover, etching has been limited in the degree of surface roughening which may be achieved.
Other roughening techniques have been used including mechanical means such as scratching or burr grinding. These techniques have drawbacks including distortion of the substrate, removal of excess material, inability or increased difficulty of roughening certain surfaces and inconsistent application. Moreover, with such techniques, it may be difficult to achieve increased levels of surface roughening desired for certain applications.
Accordingly, there is a need for an improved technique for roughening metal surfaces.
In accordance with one exemplary embodiment of the present invention, a method for surface roughening a metal work piece is provided. The method includes disposing the work piece proximate to a counter electrode. The work piece and the counter electrode are disposed in an electrolyte. An electric potential with current flow is applied between the work piece and the counter electrode to roughen the metal surface to a desired roughness.
In accordance with another exemplary embodiment of the present invention, a method for manufacturing a machined article is provided. The method includes disposing the work piece proximate to a counter electrode. The work piece and the counter electrode are, here again, disposed in an electrolyte. An electric potential with current flow is applied between the work piece and the counter electrode to roughen the metal surface to a desired roughness. The work piece is removed from the electrolyte and washed using a washing medium. The work piece is then bonded to a non-metallic substrate.
In accordance with yet another exemplary embodiment of the present invention, a machined article is provided. The machined article includes a work piece having a roughened metal surface having a desired roughness in the range of 90 to 400 microinches. The article also includes a composite substrate coupled to the roughened metal surface using a bonding material.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a method for surface roughening a metal work piece in which the work piece is disposed proximate to a counter electrode. The work piece and the counter electrode are disposed in an electrolyte bath. An electric potential is applied between the work piece and the counter electrode to roughen a surface of the work piece to a desired roughness. In certain other embodiments of the present invention, the work piece is removed from an electrolyte and then washed using a washing medium. The work piece is then bonded to one or more metal or non-metal components to form a machined article, for example a composite laminate component. In certain other embodiments, a machined article is disclosed. The machined article includes a work piece having a roughened metal surface with desired roughness in the range of 90 to 400 microinches and one or more proximate components coupled to the roughened metal surface using a bonding material. Embodiments of the present invention eliminate the use of masks and acid etchants while producing roughened surfaces suitable for subsequent processing, such as adhesive bonding. Specific embodiments of the present invention are discussed below referring generally to
Referring to
The present technique for surface roughening is described below with reference to one of the work pieces 12 of
Referring to
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In the illustrated embodiment, the work piece 12 and the counter electrode 28 are coupled to a power source 32. The power source 32 is configured to apply an electric potential (for example, an electric potential in the range of 5 to 30 volts) between the work piece 12 and the counter electrode 28 to roughen the internal surface 24 of the work piece by electrolytic etching process. The electric potential may be applied for duration approximately in the range of 0.5 to 30 minutes. In certain embodiments, a pulsed electric potential is applied between the work piece 12 and the counter electrode 28. In one example, the electric power is applied for 0.1 seconds, and then switched off for 0.12 seconds. The pulsed application of the electric potential may be varied to cause desired roughening of the surface depending on the application. The voltage, the duration and the pulse regime (if the source is pulsed) may be varied, of course, to obtain the desired degree of roughening.
When the electric potential is applied between the work piece 12 and the counter electrode 28, current flows between the work piece 12 and the counter electrode 28 through the electrolyte 30. The positive and negative ‘ions’ in the electrolyte solution are separated and are attracted to the plates of the opposite polarity. The positive ions are attracted to the counter electrode (also referred to as the “cathode”) and the negative ions are attracted to the work piece or positive plate (also referred to as the “anode”) causing oxidation and thereby corrosion of the surface 24 of the work piece 12. As a result, the surface 24 of the work piece 12 is roughened.
In the illustrated embodiment, the device 26 also includes a pump 34 configured to force a flow of fluid (electrolyte) through the bath so as to remove gas bubbles 36 from the electrolyte 30 during application of electric potential between the work piece 12 and the counter electrode 28. The pump 34 is provided with the suction lines 38, 40, 42, and a discharge line 44. Arrows 46, 48, illustrates the flow of electrolyte.
Referring to
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The method further includes applying an electric potential between the work piece and the counter electrode to roughen a desired surface of the work piece by electrolytic etching process as represented by the step 56. In certain embodiments, a pulsed electric potential is applied between the work piece and the counter electrode for a predetermined duration. The pulse parameters such as pulse duration, pulse interval, and pulse amplitude may be varied to cause desired roughening of the surface depending on the application.
In certain exemplary embodiments, the method also includes removing gas bubbles from the electrolyte during application of electric potential between the work piece and the counter electrode as represented by the step 58. The metal work piece is removed from the electrolyte bath after roughening process as represented by the step 60. The metal work piece with the roughened surface is washed using a washing medium as represented by the step 62. The material removed during the roughening process is cleaned using the washing medium. The metal work piece is then primed. The method includes bonding the work piece to a substrate, such as a composite laminate component as represented by the step 64. The work piece is bonded to the substrate using bonding material such as epoxy adhesive film.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
