The document provides an overview of chemical machining, a non-traditional method for material removal that produces high-quality parts, including its definition, history, and various processes such as chemical milling, blanking, engraving, and photochemical machining. It details the chemistry involved in the process, including cleaning, masking, etching, and demasking, along with various masking techniques and their specific tolerances. Additionally, it highlights the etching process, including etchant selection and material removal rates, applicable mostly in the aircraft and electronics industries.

1. Chemical
Machining
The detail overview on how chemical machining removes
material to produce high quality parts and its different
processes

2. Content
• Definition & History
• Types of Chemical Machining
• Chemistry of Chemical Machining
• Masking Methods
• Etching Process
• Chemical Machining Processes

3. Definition & History
• It’s a non-traditional method
• Strong Chemical etchant
• After World War II
• Aircraft Industry

4. Types of Chemical Machining
• Chemical Milling
• Chemical Blanking
• Chemical Engraving
• Photochemical Machining
*use same mechanism to remove material

5. Chemistry of Chemical Machining
• Cleaning
• Masking
• Etching
• Demasking
*CM consist several steps with its unique sequence

6. Chemistry of Chemical Machining
• Cleaning:
It is the first step in which we clean material from any other pollutants
• Masking:
The protective layer is applied to the material which is resistive to our etchant*
• Etching:
This is the material removal step, converts work material into salt, wash the part
to stop further process
• Demasking:
The maskant is remove from the part
*(strong acid)

7. Masking Methods
Maskant material includes neoprene, polyvinylchloride, polyethylene
and other polymers. Masking can be achieved by any of following
three methods
1. Cut and Peel:
Apply maskant over entire part by dipping, spraying or painting, maskant
thickness (0.025 to 0.125 mm). After hardened maskant remove by hand using
scribing knife, usually with a template. It is used on large work parts and low
production where accuracy is not a critical factor. Maximum tolerance we can
achieved by it is (±0.125 mm).

8. Masking Methods
2. Photographic Resist:
Uses photographic techniques to perform the masking step. The masking
material contain photosensitive chemicals. Negative image of the desired areas to
be etched. Maskant can be remove through photographic developing techniques.
This process is normally applied where small parts are produced in high
quantities and close tolerance are required. Tolerance closer than (±0.0125 mm)
can be held.

9. Masking Methods
3. Screen Resist:
The maskant is applied by the means of silk screening method. In this maskant
is painted on the work part surface through a silk or steel mesh. Stencil protects the
area.
The screen resist method is generally used in applications that are between the
other two masking methods in terms of accuracy, part size and production
quantities. Tolerance of (±0.075 mm) can be achieved with this masking method.

10. Etching Process
• Etchant depends on work material, desired depth, rate of material removal and
surface finish requirements
• Etchant must also be matched with the type of maskant
• Material removal rate is CHM are generally indicated as penetration rates
(mm/min)
• The penetration rate is unaffected by surface area
• Depth of cut in CHM is 12.5 mm for aircrafts panels made out of metal plates
• There is also undercut
• Etch factor : Fe = d/u

11. Etching Process

12. Etching Process

13. Etching Process

14. Chemical Machining Processes
1. Chemical Milling
2. Chemical Blanking
3. Chemical Engraving
4. Photochemical Machining

15. Chemical Machining Processes
1. Chemical Milling
• It’s the first processes to be commercialized
• World War II, Aircraft Company, US, “chem-mill”
• Still used in Aircraft Industry for weight reduction
• Applicable large parts
• The cut and peel maskant method is used
• Surface finish varies with material removal rate
• Metallurgical damage is very small perhaps around (0.005 mm) into the work surface

16. Chemical Machining Processes
1. Chemical Milling

17. Chemical Machining Processes
1. Chemical Milling

18. Chemical Machining Processes
2. Chemical Blanking
• Uses Chemical erosion to cut very thin sheet metal parts – down to (0.025 mm)
• Conventional or punch die methods does not work
• Damage sheet metal, tool cost will be high
• Parts produce by this method is burr free
• Photoresist or Screen resist method
• For small or intricate we use photo resist
• Tolerance closes ±0.0025 mm can be held
• In screen resist the masking procedure provide accurate registration between two sides
• Limited to thin or intricate pattern, maximum stock thickness 0.75 mm
• Hardened and brittle materials can be processed

19. Chemical Machining Processes
2. Chemical Blanking

20. Chemical Machining Processes
3. Chemical Engraving
• Name plates and other flat panels
• Lettering and Artwork on other sides
• Either recessed or raised lettering
• Masking is done by either Photoresist or Screen Resist
• Except filling operation follows etching
• To apply paint ant other coating in recessed area
• The effect is to highlight the pattern

21. Chemical Machining Processes
4. Photochemical Machining
• Photoresist method of masking is used
• Applied to Chemical Blanking and Chemical Engraving when these metods use
Photographic resist method
• Used for close tolerance and intricate patterns
• Used in electronic industry to produce intricate circuit design
• There are various to photographically expose the desired image onto the resist
• Photoresist materials is sensitive to ultraviolet light
• No need to carry out procedure in the dark room
• In this procedure etch factor is known as anisotrophy

22. Chemical Machining Processes
4. Photochemical Machining

24. References

25. Thank you
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