Nontraditional Machining Process:IM 527(selected Topic)

1. BENGHAZI UNIVERSITY
Industrial &Manufacturing Systems
Engineering Department
Nontraditional Machining
Process:IM527(selected Topic)
lecture 1:Chemical machining
Instructor : Omar Elmabrouk
Engineer : Rania.A. Elrifai
2011/2012 spring

2. Chemical machining

3. What is Chemical machining
(CHM)?
• Chemical machining that removes metal from a workpiece by
immersing it into a chemical solution.
• Chemical machining (also known as photo chemical machining or
PCM, photofabrication, or photo chemical milling) is a process
through which decorative metal items and precision metal parts are
formed.
• Chemical machining is a well known nontraditional machining
Photofabrication Engineering, Inc. (PEI) has perfected the Chemical
Machining process, starting with the creation of phototools from a
fully-dimensional drawing or CAD file supplied by the customer.

4. Cont…….(CHM)
• process is the controlled
chemical dissolution of the
machined workpiece
material by contact with a
strong acidic or alkaline
chemical reagent .
• the machining method is
widely used to produce
micro-components for
various industrial
applications such as micro
electromechanical
systems(MEMS) and
semiconductor industries.

5. History of the chemical
machining processs.
• machining method which is used to shape copper
with citric acid in the Ancient Egypt in 2300 BC .
• Until the 19th century this process was widely
used for decorative etching. The development of
photography provided a new dimension to
chemical machining .
• William Fox Talbot (1852) patented a process for
etching copper with ferric chloride, using a
photoresist .
• John Baynes, in1888, described a process for
etching material on two sides using aphotoresist
which was patented in the USA (US Patent No:
378423).
• The main industrial application of chemical
machining developed after the war.

6. Steps of chemical machining
Chemical machining process has several steps for producing
machine parts. These are given below:
1- Workpiece preparation:
The workpiece material has to be cleaned in the beginning of chemical
machining process.
• The cleaning operation is carried out to remove the oil, grease, dust, rust
or any substance from the surface of material.
• A good cleaning process produces a good adhesion of the masking
material.
• There are two cleaning methods:
 mechanical and chemical methods , the most widely used cleaning
process is chemical method due to less damages occurred comparing to
mechanical one.
 Ultrasonic cleaning machine is applied with using special cleaning
solution and heating is beneficial during the cleaning process.

7. 2. Coating with masking material:
• The next step is the coating cleaned
workpiece material with masking
material.
• The selected masking material should be
readily strippable mask,
• which is chemically impregnable and
adherent enough to stand chemical
abrasion during etching.

8. 3. Scribing of the mask:
This step is guided by templates to expose the areas that receive
chemical machining process.
The selection of mask depends on the size of the workpiece
material, the number of parts to be produced, and the desired
detail geometry. Silk-screen masks are preferred for shallow
cuts requiring close dimensional tolerances.

9. Etching (micro
fabrication)
4. Etching:
• This step is the most important stage to
produce the required component from
the sheet material.
• This stage is carried out by immerse
type etching machine.
• The workpiece material is immersed
into selected etchant and the
uncovered areas were machined.
• This process is generally carried out in
elevated temperatures which are
depended on the etched material. Then
the etched workpiece is rinsed to clean
etchant from machined surface.

10. 5. Demasking- Cleaning masking material( the maskant
is removed from the part):
• Final step is to remove masking material from etched part.
The inspections of the dimensions and surface quality are
completed before packaging the finished part.
• Masking material which is called maskant is used to
protect workpiece surface from chemical etchant.
• Polymer or rubber based materials are generally used for
masking procedure.

11. 1. Tough enough to withstand handling
2. Well adhering to the workpiece surface
3. Easy scribing
4. Inert to the chemical reagent used
5. Able to withstand the heat used during
chemical machining
6. Easy removal after chemical machining
etching

12. Types of masks used in CHM
• Cut and peel masks.
• Screen resist masks.
• Photo resist masks.

13. Cut and peel maskants
• Film of chemically resistant material is applied to
the work piece by dipping, spraying or flow coating.
• Vinyl, styrene and buta diene are used.
• Rubbery film is then cut & peeled away selectively.
• Manual scribing of mask material usually achieves
an accuracy of ±0.13 mm to ±0.75 mm.

14. Screen resist maskants
• Mask material is applied to the work piece
surface by printing, using stencils and a fine
polyester or stainless steel mesh screen.
• Relatively thin coatings with tolerances held
to ±0.05 to ±0.18 mm are obtained by
screen printing.
• Etching depths are restricted to about 1.5
mm because of thinness of the coating.

15. Photo resist maskants
• Photo resist mask is quite widely used & is often
referred to as photochemical machining.
• Produces intricate & finely detailed shapes using a
light activated resist materials.
• WP coated with photo resist material & a master
transparency is held against the WP, while exposure
to UV rays takes place.
• Light activates the photo resist material in those
areas corresponding to opaque parts.
• Tolerances of ±0.025 to 0.005 mm can be produced.

16. Chemical Machining Processes
• Chemical milling
• Chemical blanking
• Chemical engraving
• Photochemical machining

17. Chemical milling
1. In chemical milling, shallow cavities are
produced on plates, sheets, forgings and
extrusions.
2. The two key materials used in chemical
milling process are etchant and maskant.
3. Etchants are acid or alkaline solutions
maintained within controlled ranges of
chemical composition and temperature.
4. Maskants are specially designed
elastomeric products that are hand
strippable and chemically resistant to the
harsh etchants.
5. Chemical milling is used in the aerospace
industry to remove shallow layers of
material from large aircraft components
missile skin panels extruded parts for
airframes.

18. Chemical blanking
• Chemical blanking is used to etch entirely through a
metal part.
• In chemical blanking, holes and slots that penetrate
entirely through the material are produced, usually
in thin sheet materials.
• Used to produce fine screens, flat springs, etc…
• Very cheap but efficient.

19. Figure 2 : parts profiled by chemical
blanking process

20. Chemical Engraving
Chemical Engraving is the practice of incising a design on
to a hard, usually flat surface, by cutting grooves into it.
The result may be a decorated object in itself, as when
silver, gold, steel or glass are engraved, or may provide
an printing plate, of copper or another metal, for printing
images on paper as prints or illustrations; these images.
Types of engraving
• Wood Engraving
• Copper and Steel Engravings
• Laser engraving

21. Photo Chemical Machining (PCM)
Process steps for photochemical
machining
• Photochemical machining (PCM), also
known as photochemical milling or
photo etching, is the process of
fabricating sheet metal components
using a photo resist and etchants to
corrosively machine away selected
areas.
• PCM can be used on virtually any
commercially available metal or alloy,
of any hardness. It is limited materials
0.0005 to 0.080 in (0.013 to 2.0 mm)
thick. Metals include aluminium,
brass, copper, inconel, manganese,
nickel, silver, steel, stainless steel,
zinc and titanium

22. Applications
• Thin gauge (under 0.050 in (1.3 mm)) parts in a broad range of alloys
are candidates for photo etching.
• Industrial applications include fine screens and meshes.
• Battery grids
• fuelcell components
• sensors,
• springs
• pressure membranes
• RF and microwave circuits and components, semiconductor
• leadframes

23. Characteristics Of Chemical Machining
• Shallow removal of material (up to 12mm)
• Blanking of thin sheets.
• Low tooling and equipment cost.
• Suitable for low production runs.
• Material removal rate(0.1mm/min)

24. The Benefits of Chemical
Machining
• No effect on the metal properties
• Burr free metal parts
• Low cost tooling
• Quick turnaround & Affordable short runs

25. Conclusion
• Chemical machining is widely used to
produce complex
• machine parts for various application as
well as decorative parts.
• The machining operation should be carried
out carefully to
• produce a desired geometry.

26. Video shows (PCM)

27. Important parameters in (CHM)
(a) MRR= C×A
,(mm³/min)
(b)C: penetration rate(
mm/min).
(c) Time of etch (Tm)
=d/c , (hr)
(d)Fe(factor etch)=d/u,
d: depth (mm), under
cut(mm)

28. Solve the problems about (GHM)
• What is a photoresist in chemical machining?
Photoresist is the masking material that is sensitive to light . When exposed , it chemically
transforms and can be removed from the surface of the work, leaving the desired surface
• chemical milling is used in which of the following applications
.(a) drilling holes with high depth – to- diameter ratio
(b) Making intricate patterns in the sheet metal
© removing material to make shallow pocket in metal
(d) removing material from aircraft wing panels
(e) Cutting of plastic.
26.15: A= 200×400-4(15x15- ¼ π(15)²= 79806.5mm²
(a) MRR= C×A= 0.024X79806.5= 1915.4mm³/min
(b) Time of etch (Tm) = 12/0.024= 500 min
(c) Fe(factor etch) =1.75,Fe=d/u → u=d/Fe =12/1.75=6.86mm
Maskant opening length = 400- 2(6.68)=386.28mm
Maskant opening width = 200-2(6.68)= 186.28mm, radius corner 15-2(6.68)= 8.14mm

29. • 26.16: area of ellipse A= π×a xb =3.14×9×6=1696.5.in²,
d=0.4in,pentration rate=0.001inlmin
• (a) MRR= 0.001X1696.5=1.6965 in³/min=101.179in³/hr
• (b) Tm= 0.4/0.001=400 min=6.67hr
• © Fe= 2, undercut (u)= d/Fe= 0.4/2= 0.2 in,
• maskant opening a = a-2u= 9-2(0.2)= 8.6 in
• maskant opening b = b- 2u= 6- 2(0.2)= 5.6 in
• 26..17: because the Tolerances of ±0.025 to 0.005 mm can be
produced so, it should have been used in the case.
• 26.18: Fe= 1.75 , in chemical blanking, etching will occur on two
sides hol4ndepth on each side = 0.015/2= 0.0075 In , undercut u=
0.0075/1.752= 0.0043 in
• Diameter opening =0.001- 2(0.0043)= 0.0914 in