It's a presentation prepared by me on Chemical milling a type of non traditional machining process to help the students to know the key concept about it.

2. Chemical milling (chm)
By – Aditya sharma
Mech/67/15

3. Introduction
• Chemical Milling (CHM) is the controlled chemical
dissolution(CD) of the work piece material by contact with a
strong reagent
• Used to produce pockets & contours
• CHM consists of following steps-
• @ Preparing and precleaning the work piece surface
• @ Masking using readily strippable mask
• @Scribing of the mask, guided by templates
• @The work piece Is then etched and rinsed

4. Chm Setup

5. Etch Factor
Etch factor is the ratio of
the undercut (d) to the
depth of etch (t).
It must be considered when
scribing the mask using
templates.
A typical etch factor of 1:1
occurs at a cut depth of
1.27mm

6. Tooling for Chm
Four different types of
tools are required-
Maskants
Etchants
Scribing Templates
Accessories

7. Maskants
• Generally used to protect parts of work piece where CD action is
not needed.
• Properties;
• @ be tough enough to withstand handling
• @Adhere well to the work piece surface
• @scribe Easily
• @Be inert to the chemical reagent used

8. Etchants
• Etchants are acid or alkaline solutions maintained within a
controlled range of chemical composition and temperature.
• Main technical goals of etchants are-
• @ Good surface finish
• @Uniformity of metal removal
• @ Maintenance of air quality and avoid the environmental
problems
• @ ability to regenerate the etchant solution

9. Scribing TEmplAtEs
Scribing templates are used to define the areas for
exposure to the chemical machining action. The
most common work piece scribing method is to cut
the mask with a sharp knife followed by carefully
peeling of the mask from the selected areas.

10. Accessories

11. Process Parameters
• CHM process parameters include the reagent solution type,
concentration, properties, mixing, operating temperature and
circulation.
• These parameters will have the direct impacts on the work piece
as follows-
• @ Etch factor (d/t)
• @ etching and machining rate
• @ production tolerance
• @ surface finish

12. Material removal rate (mrr)
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13. CHM average roughness of some alloys after removing
0.25 to 0.4 mm

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15. Accuracy – surface finish of component achieved by machining
process
• In CHM, the metal is dissolved by CD action.
• The machining phase takes place both at individual grain surface
as well as grain boundaries.
• Fine grain size and homogeneous metallurgical structures are
necessary for fine surface quality of uniform appearance.
• Surface finished by CHM do not have regular lay pattern.
• Based on grain size, orientation, heat treatment and previously
induced stresses, every material has basic surface finish that
results from CHM for certain period of time.

16. • Surface imperfections will not be eliminated by CHM.
• Any prior surface irregularities, waviness, dents or scratches will
be slightly altered and reproduced in machined surface.
• The depth of cut tolerance increases when machining larger
depths at high rates.
• Aluminium and Magnesium alloys can be controlled more closely
than steel, Nikel or Titanium alloys.
• An etching rate of 0.025mm/min with tolerance of +10 or -10
percent of cut width can be achieved depending on workpiece
material and depth of cut.

17. Figure 3.7: Surface roughness and etch rate of some alloys
after removing 0.25 to 0.4mm.

18. FACTORS AFFECTING
SURFACE FINISHING OF
A COMPONENT

19. •Basically grain size and homogeneous
metallurgical structure are necessary for fine
surface quality.
•While surface imperfections will not be
eliminated by CHM but any prior surface
irregularities, waviness, dents or scratches
will be slightly altered.

20. FACTORS AFFECTING SURFACE FINISHING
ARE
• INITIAL WORKPIECE ROUGNESS
• PREVIOUS COLD WORKING PROCESS
• MACHINING RATE AND MACHINING
TEMPERATURE
• ETCHANT SOLUTION AND COCENTRATION

21. # INITIAL WORKPIECE ROUGNESS
It increases with the increase in the metal ion
concentration in the etchant.
# PREVIOUS COLD WORKING PROCESS
surface roughness decreases with the previous
cold working process and thus , we get good
surface finish

22. # MACHINING RATE AND MACHINING
TEMPERATURE
By increasing the machining rate, machining temperature
increases and thus we get surface roughness.
# ETCHANT SOLUTION AND CONCENTRATION
To get good surface finish we can decrease the temperature
by adding high pressure coolant to the echants. For
example: Triethanolamine.
etchant's specific gravity , oxidation reduction potential can
also effect surface finish.

23. Advantages,
Limitations and
Application of CHM

24. Advantages
• Weight reduction is possible on complex contours that are difficult
to machine using conventional methods.
• No burrs are found.
• Design changes can be implemented quickly.
• A less skilled operator is needed.
• Simultaneous material removal, from all surfaces, improves
productivity and reduces wrapping.

25. Limitations
• Handling and disposal of chemicals can be troublesome.
• Surface imperfections are reproduced in the machined parts.
• Deep narrow cuts are difficult to produce.
• Porous castings yield uneven etched surfaces.
• Material removal from one side of residually stressed material can
result in a considerable distortion.
• Welded areas frequently etch at rates that differ from base metal.

26. Applications
• CHM applications range from large aluminum alloy airplane wing
parts to minute integrate chips.
• CHM is used to thin out walls, webs, and ribs of parts that have
been produced by forging, casting, or sheet metal forming
• Shallow cuts in large thin sheets are the most popular application
especially for weight reduction of aerospace components
• Removal of sharp burrs from conventionally machined parts of
complex shapes.
• Elimination of the decarburized layer from low alloy steel
forgings.