# Patent

## Title
Printed masking process

## Abstract

A method of chemically milling a workpiece includes depositing a masking material on portions of the workpiece according to a predefined masking pattern such that other portions of the workpiece that are desired to be milled are unmasked. Material from the unmasked desired milling areas of the workpiece is chemically removed.

## Background
This invention was made with government support under Contract No. N00019-02-C-3003 awarded by the United States Navy. The Government may therefore have certain rights in this invention.


BACKGROUND
This disclosure relates to milling, and more particularly to a printed masking process that may be used to perform chemical milling. Chemical milling is used performed to remove undesired material from a workpiece to form channels or patterns, for example. Chemical milling typically involves masking an entire workpiece, etching a pattern onto the masking, using a scalpel to manually remove portions of the masking according to the etching and dipping the workpiece in a chemical bath to remove material from the unmasked portions of the workpiece.
SUMMARY
A method of chemically milling a workpiece includes depositing a masking material on portions of the workpiece according to a predefined masking pattern such that other portions of the workpiece that are desired to be milled are unmasked. Material from the unmasked desired milling areas of the workpiece is chemically removed.
A system for milling a workpiece includes a computer having a storage module that stores at least one predefined masking pattern, and a three dimensional masking printer in communication with the computer. The masking printer is operable to apply masking material to portions of a workpiece according to the at least one predefined masking pattern such that other portions of the workpiece that are desired to be milled are unmasked.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a method of chemically milling a workpiece.
FIG. 2 schematically illustrates a system operable to perform the method of FIG. 1.
FIG. 3 schematically illustrates an example chemically milled workpiece.



DETAILED DESCRIPTION
FIG. 1 schematically illustrates a method 100 of chemically milling a workpiece, and FIG. 2 schematically illustrates a system 10 for performing the method 100. The method 100 may be used in conjunction with the system 10 to chemically mill or etch a workpiece to product an isogrid rib formation on a duct, or to produce raised lettering on a sign, for example.
The system 10 includes a computer 12 having a CPU 14, a storage module 16, and an input/output (“I/O”) module 18. The storage module 16 could include, for example, memory, hard drives, or any electronic, optical, magnetic or other type of computer storage. At least one predefined masking pattern is stored in the storage module 16. The at least one predefined masking pattern is retrieved from the storage module 16 (step 102). In one example the at least one predefined masking pattern includes one or more computer-aided design (“CAD”) models.
A three-dimensional masking printer 20 is in communication with the computer 12. The masking printer 20 deposits a masking material 22 onto portions of the workpiece 24 according to the at least one masking pattern (step 104). The masking printer 20 is movable in three dimensions, and is operable to deposit the masking material 22 onto the workpiece 24. In one example the masking material 22 is an elastomer dissolved in at least one organic solvent. In one example, the at least one organic solvent is selected from a group consisting of toluene, xylene, perchloroethylene, and combinations thereof. Of course, other masking materials could be used.
Once the predefined pattern has been formed on the workpiece 24, material from the unmasked desired milling areas 26 of the workpiece 24 is chemically removed (step 106). In one example, step 106 includes applying chemicals to the workpiece 24, such as in a chemical bath. In one example the chemicals applied to the workpiece in step 106 include an aqueous solution of acid such as ferric chloride. Of course, other milling chemicals could be used. An amount of material that is chemically removed from the workpiece 24 in step 106 may be controlled by adjusting the duration of the chemical bath.
Once a desired amount of material has been chemically removed from the unmasked areas, the masking material may be removed (step 108). In one example, step 108 includes a power washing process that sprays the masking material off.
Unlike masking an entire workpiece and then manually removing maskant by hand with a scalpel, which is a labor-intensive and error prone process, the method 100 facilitates removing the human error component, using less masking material, reducing cost and improving efficiency and accuracy.
The method 100 is widely applicable to many applications in which chemical milling or machining is desired. For example, as shown in FIGS. 2-3, the workpiece 24 is a duct for a gas turbine engine that may be used to contain high pressure gases within the gas turbine engine. The method 100 may be used to form an elevated isogrid 30 on the duct, with the elevated isogrid 30, an inside 34 of the duct, and flanges 36 corresponding to the masked areas of step 104. The elevated isogrid 30 pattern may be chosen because it can build structural strength on the duct. Of course, other patterns could be used.
Also, although a duct for a gas turbine engine has been illustrated, the method 100 is applicable to other types of workpieces or substrates. For example, the workpiece could be a sign, a medical device, a body of a component, a coating, a fuel cell, a heat sink, a sensor, or any other component that would benefit from precision chemical milling or machining.
Although embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A method of chemically milling a workpiece, comprising:
depositing a masking material on portions of a workpiece according to a predefined masking pattern such that other portions of the workpiece that are desired to be milled are unmasked, wherein the masking material is deposited using a masking printer that moves in three dimensions to deposit the masking material onto the workpiece; and
chemically removing material from unmasked desired milling areas of the workpiece, wherein the workpiece is a component of a gas turbine engine.

2. The method of claim 1, including:
removing the masking pattern from masked portions of the workpiece.

3. The method of claim 1, wherein said depositing a masking material on portions of the workpiece includes:
depositing the masking material on a curved surface of the workpiece.

4. The method of claim 1, wherein said depositing a masking material on portions of the workpiece includes:
depositing the masking material in an isogrid pattern on portions of the workpiece.

5. The method as recited in claim 1, wherein the component is a duct for the gas turbine engine.

6. The method as recited in claim 1, including:
removing the masking material from the portion of the workpiece by a power washing process that sprays the masking material off the workpiece.

7. The method of claim 1, wherein said depositing a masking material on portions of the workpiece includes:
depositing an elastomer dissolved in at least one organic solvent on portions of the workpiece.

8. The method of claim 7, wherein said depositing a masking material on portions of the workpiece includes:
depositing at least one organic solvent selected from a group consisting of toluene, xylene, perchloroethylene, and combinations thereof.

9. The method of claim 1, wherein said chemically removing material from the unmasked desired milling areas of the workpiece includes subjecting the workpiece to a chemical bath that includes an aqueous solution of acid.

10. The method of claim 9, wherein the acid includes ferric chloride.

11. A system for milling a workpiece, comprising:
a computer having a storage module that stores at least one predefined masking pattern; and
a masking printer in communication with the computer, the masking printer being operable to apply masking material to portions of a workpiece according to the at least one predefined masking pattern such that other portions of the workpiece that are desired to be milled are unmasked, wherein the masking printer moves in three dimensions to deposit the masking material onto the workpiece, wherein the workpiece is a component of a gas turbine engine.

12. The system of claim 11, wherein the component is a duct for the gas turbine engine.

13. The system of claim 11, wherein the at least one predefined masking pattern includes an isogrid pattern.

14. The system of claim 11, wherein the masking material includes an elastomer dissolved in at least one organic solvent.

15. The system of claim 14, wherein the at least one organic solvent is selected from a group consisting of toluene, xylene, perchioroethylene, and combinations thereof.

16. The system as recited in claim 11, including a power washer that removes the masking material from the portion of the workpiece by spraying the masking material off the workpiece.

17. The system of claim 11, including:
a milling chemical operable to remove portions of a surface of unmasked desired milling areas;
a chemical bath in which the milling chemical is applied to the workpiece, the chemical bath including an aqueous solution of acid.

18. The system of claim 17, wherein the acid includes ferric chloride.