WO2014151479A2

WO2014151479A2 - Method of removing a coating of a substrate

Info

Publication number: WO2014151479A2
Application number: PCT/US2014/025821
Authority: WO
Inventors: Faycal Benayad-Cherif; Christopher BAHNS
Original assignee: Videojet Technologies Inc.
Priority date: 2013-03-22
Filing date: 2014-03-13
Publication date: 2014-09-25
Also published as: WO2014151479A3

Abstract

A method of removing a coating of a substrate comprises a series of steps. A substrate is provided, the substrate including a feature on a surface of the substrate. The surface of the feature has a coating. The surface of the substrate is imaged to provide information about the feature. A portion of the coating is removed by a laser source. The surface of the substrate is imaged to provide information about a coating thickness of the coating of the surface of the feature. A boundary is calculated between a first area including the coating and a second area with the coating substantially removed. A portion of the coating in the first area within the boundary is removed using a laser source.

Description

METHOD OF REMOVING A COATING OF A SUBSTRATE

BACKGROUND

[0001] The present disclosure provides a method of removing a coating from a substrate with a laser. In particular, it provides a method for the removal of thermal barrier coatings from features of turbine blades.

[0002] Turbine blades are often coated with a thermal barrier coating (TBC) over a bond coat. To operate efficiently the slots on the turbine blade need to be cleared of TBC. Current processes typically use chemical etching process that provide adequate results when handling uniform coating over flat surfaces but little control over non uniform surfaces with complex shapes. When dealing with cavities or slots that have been coated, the thickness of the TBC can vary by several hundreds of microns depending on the shape of the slot as well as its location on the blade. Using a laser process without power or removal process control can either leave TBC material on the turbine blade or create damage that can require costly repairs.

BRIEF SUMMARY

[0003] The present disclosure provides a method of removing a coating from a substrate with a laser. In particular, it provides an accurate and adaptive process for the removal of thermal barrier coatings from features of turbine blades. The process, based on image processing techniques, guides a laser so it removes TBC material only where it is present without damaging the supporting layers. This process provides full removal of the TBC down to the bond coat.

[0004] In one aspect, a method of removing a coating of a substrate comprises a series of steps. A substrate is provided, the substrate including a feature on a surface of the substrate. The surface of the feature has a coating. The surface of the substrate is imaged to provide information about the feature. A portion of the coating is removed by a laser source. The surface of the substrate is imaged to provide information about a coating thickness of the coating of the surface of the feature. A boundary is calculated between a first area including the coating and a second area with the coating substantially removed. A portion of the coating in the first area within the boundary is removed using a laser source. [0005] The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a schematic view of a system for removing a coating of a substrate.

[0007] FIG. 2 is a flowchart showing the steps of an embodiment of the process.

[0008] FIG. 3 is a photo of the slot of the Example.

[0009] FIG. 4 is an embodiment of the laser pass generated from the image of FIG. 3

[0010] FIG. 5 shows the slot of FIG. 3 after a first laser pass.

[0011] FIG. 6 shows an embodiment of second laser pass generated from the processed image of FIG. 5.

[0012] FIG. 7 shows the slot of FIG. 5 after a second laser pass.

[0013] FIG. 8 shows an embodiment of a third laser pass generated from the processed image of FIG. 7.

[0014] FIG. 9 shows the substrate after the coating is fully removed.

DETAILED DESCRIPTION

[0015] The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings.

[0016] The present disclosure provides a method of removing a coating from a substrate with a laser. In particular, it provides an accurate and adaptive process for the removal of thermal barrier coatings from features of turbine blades. Turbine blades often have small channels or slots in them that are used for air cooling. When the blades are coated with a thermal barrier coating (TBC) over a bond coat, the TBC may partially plug these features and it desirable to remove the coating from the features. Additionally, the thickness of the coating tends to be uneven, so care has to be taken to remove only the TBC and not the underlying bond coat. The present process, based on image processing techniques, guides a laser so it removes TBC material only where it is present without damaging the supporting layers. This process provides full removal of the TBC down to the bond coat.

[0017] The process may be based on IMP (Intelligent Mark Positioning), used to accurately position the laser beam, to remove the TBC layer by layer while targeting only the remaining material left by the different steps of the process. IMP is disclosed in U.S. Patent No. 8,000,831 and U.S. Patent Application Nos.

20120170813 and 20110293907, the contents of all of which are incorporated by reference.

[0018] FIG. 1 illustrates an embodiment of a substrate 10 to be processed. The substrate 10 includes a feature 12, such as a channel, slot, or cavity in a turbine blade. The feature may have a length or dimension between 1 mm and 10 mm.

Imaging device 16 is capable of measuring and processing the structure of the substrate. Laser source 18 is capable of directing laser energy to the substrate to remove a portion of the coating. The laser source 18 may be any suitable laser source. In one embodiment, the laser is a YAG laser. The laser could also be a UV, C0₂, or any other suitable laser. The wavelength of the laser could be any suitable wavelength, including green (around 530 nm), UV (around 300 nm), or others.

[0019] In one aspect, the method includes multiple steps. As illustrated in FIG. 2, in a first step 20, a substrate is provided. The substrate includes a feature on a surface of the substrate. The surface of the feature has a coating. The surface of the substrate is imaged in step 30 to provide information about the feature. The information about the feature generally includes at least the location of the feature. Further information about the feature may also be used, such as the contour of the feature, X, Y, and yaw information about the feature, and Z and pitch and roll information about the feature. In one embodiment, the feature and substrate are first processed by a defined pattern or an extracted contour taken from an IMP system or any other imaging system. [0020] In step 40, a portion of the coating of the surface of the feature is removed by a laser source. In one embodiment, as the substrate is laser ablated, an IMP system monitors color changes that may change from light to dark or vice versa. For example, with a turbine blade, the color changes from dark to bright as the TBC thickness becomes thinner.

[0021] Thus, after each of the several laser processing steps, dark surfaces represent areas of TBC left to be removed and shiny areas represent areas that have the coating fully removed. Shiny areas should not be further ablated by the laser during the next steps to prevent damage to the underlying bond coat.

[0022] In step 50, the surface of the substrate is imaged to provide information about a coating thickness of the coating of the surface of the feature. In step 60, a boundary between a first area with the coating and a second area with the coating substantially removed is calculated. The boundaries are used to determine which areas of the substrate to further subject to the laser for removal. The boundaries may be determined by difference in color between the first and second areas. The method may include calculating a contour of the feature, wherein the contour includes information about the boundary between the first area and the second area, and aligning the contour with the substrate before removing a portion of the coating in the first area within the boundary using a laser source. In an embodiment, the contours of the dark and white areas are extracted using an edge detection technique. The contrasted image is processed by an image processing filter used to detect the edge of the remaining contours.

[0023] In step 70, a portion of the coating in the first area within the boundary is then removed using a laser source. The steps 50, 60, and 70 are repeated until the coating of the feature is substantially removed. The steps 50, 60, and 70 may be repeated between 5 and 10 times until the coating of the feature is substantially removed. During the lasing process only areas imaged as still including the coating are subjected to the laser, therefore removing only the remaining coating.

[0024] In an embodiment, imaging the surface of the substrate is entirely done by laser or other light source and does not require contact with the substrate. Although the process is described for the process of one slot, more than one slot can be processed simultaneously.

EXAMPLE

[0025] An example of the inventive process is shown in FIGS. 3-9. The process was performed on a ceramic turbine blade with slots. The blade was first processed by a defined pattern or an extracted contour taken from an IMP system or any other imaging system. FIG. 3 is a photo of the slot and FIG. 4 is the laser pass generated from the image. The slot was subjected to a YAG laser to remove a portion of the coating. The lasers used were a DP50 diode pumped laser and a DP 20F fiber laser, both available under the FOBA brand from Alltec GmbH. As the blade surface was laser ablated, the IMP system monitored color changes that are expected to change from dark to bright as the TBC thickness becomes thinner. FIG. 5 show the slot after the first laser pass. FIG. 6 shows the second laser pass generated from the processed image. The bright area 22 was not subjected to further laser ablation.

[0026] After each of the several laser processing steps, dark surfaces represented areas of TBC left to be removed and shiny areas represented areas that have the coating fully removed. Shiny areas were not touched by the laser during the next steps to prevent damage to the bond coat. The contours of the dark and white areas were extracted using an edge detection technique. The contrasted image was processed by an image processing filter used to detect the edge of the remaining TCB contours.

[0027] The extracted edge components were chained using a predefined contour of the surface to process to prevent removal outside the surface boundaries of the feature to process. The generated contour was imported to the laser marker software where it was closed and filled with a hatch pattern that provided a uniform removal laser process. A combined fill was applied to the joined contours to create the next laser pattern to apply to the slot, as shown in FIG. 6.

[0028] Using the vision alignment tool built in the laser marker, this new contour was aligned to the blade so the contour aligns to surface to process. FIG. 7 shows the substrate after a second pass of laser ablation. During the lasing process only areas imaged as TBC were hit by the laser, therefore removing only the remaining material. After laser ablating, a new image of the part was taken as shown in FIG. 8 and the process of imaging, creating a boundary, and laser ablating was repeated. FIG. 9 shows the substrate after the coating is fully removed.

[0029] The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and

embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

Claims What is claimed is:

1. A method of removing a coating of a substrate, comprising:

a) providing a substrate, the substrate comprising a feature on a surface of the substrate, wherein the surface of the feature has a coating;

b) imaging the surface of the substrate to provide information about the feature;

c) removing a portion of the coating of the surface of the feature by a laser source;

d) imaging the surface of the substrate to provide information about a coating thickness of the coating of the surface of the feature;

e) calculating a boundary between a first area comprising the coating and a second area with the coating substantially removed;

f) removing a portion of the coating in the first area within the boundary using a laser source; and

repeating the steps of d), e), and f) until the coating of the feature is substantially removed.

2. The method of claim 1 further comprising using the boundaries to determine which areas of the substrate to subject to laser.

3. The method of claim 1 where information about the feature includes a location of the feature.

4. The method of claim 1 where information about the feature includes a contour of the feature.

5. The method of claim 1 where information about the feature includes X, Y, and yaw information.

6. The method of claim 5 where information about the feature further includes Z and pitch and roll information

7. The method of claim 1 wherein the boundaries are determined by difference in color between the first and second areas.

8 The method of claim 1 wherein the substrate is a turbine blade.

9. The method of claim 1 wherein the coating comprises a thermal barrier layer coating.

10. The method of claim 1 wherein the laser source is a YAG laser.

11. The method of claim 1 further comprising calculating a contour of the feature, wherein the contour include information about the boundary between the first area and the second area, and aligning the contour with the substrate before removing a portion of the coating in the first area within the boundary using a laser source.

12. The method of claim 1 wherein the feature is a slot or cavity.

13. The method of claim 12 wherein the feature has length of between 1 mm and 10 mm.

14. The method of claim 1 wherein imaging the surface of the substrate does not require contact with the substrate.

15. The method of claim 1 wherein the steps of d), e), and f) are repeated between 5 and 10 times until the coating of the feature is substantially removed.

16. The method of claim 1 where the imaging is performed by a laser.

17. A turbine blade subjected to the method of claim 1.