Here is the detailed explanation of working principles and processes of chemical Machining

1. Atria Institute Of
Technology.
Under the Guidance Of
Anjan Kumar. D
Professor
Department of Mechanical Engineering.
Mallikarjun 1AT18ME027
Prabheek Prasad 1AT18ME035
Sam Prabhakar. S 1AT18ME038
Sanjay. B 1AT18ME039
Sanjay L N 1AT18ME040
PREPARED BY;

2. Chemical Machining.
 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 photo tools from a fully-
dimensional drawing or CAD file supplied by the customer.

3. Working Principle.
The chemical machining working
principle is chemical etching. The
part of the workpiece whose material
is to be removed is exposed to a
chemical known as enchant. The
enchantment removes the metal from
the chemical attack. The method of
making contact of material by the
enchant is masking.

4. Schematic setup and process.
There are two types of chemical
machining: chemical blanking, which is
used for cutting or stamping parts from
thin sheet materials, and the other,
chemical contour machining or chemical
milling used for selective or overall metal
removal from a thick workpiece material.
A brief description and characteristics of
both types of the process are discussed as
follows.

5. A) Chemical blanking is a process of producing a part from thin sheet metal or strip by
chemically etching the periphery of the desired shape. The material is removed by
chemical dissolution. Typical applications of chemical blanking include: burr-free
etching of printed-circuit boards, decorative panels, thin sheet metal stampings, as
well as the production of complex or small shapes in work-parts.
Process
Chemical blanking as shown in figure involves the processing steps as discussed
below.-
• Workpiece pre-cleaning process
• Masking
• Etching and
• Do-masking

6. (a) Workpiece pre-cleaning process The surface of the workpiece metal is cleaned
thoroughly, degreased and pickled by acid or alkalis. Pre-cleaning is of utmost importance in
order to remove oil, grease, din, rust, or any foreign substances from the work surface so as
to produce a good adhesion of the masking material. The material is allowed to dry.

7. (b) Masking: Masking involves covering the portions of the workpece metal where
material is not to be removedby the chemical action of the etchant. Refer figure 5.1(a). A
suitable maskant, say a polymer, rubber, or any other material is selected based on the
workpiece material. The maskant is applied on the work surface by various methods
like dip, brush, spray, roller, electro-coating, and as well as adhesive tapes.
(c) Etching Removal of material from the workpiece takes place by etching process.
The workpiece metal is either sprayed continuously with a selected etchant like Ferric
chloride, on those portions where the material is to be removed, or immersed in a tank
of agitated etchant, where the etchant chemically attacks those portions not masked.
Erosion of the work material takes place both inward and laterally from the exposed
(unmasked Surface as shown in figure 5.1 (b) to (d). The work materials converted into
metallic salt, which is then dissolved and carried away in the etchant solution.
(d) De-masking When etching is completed, the mask is removed either through
mechanical or chemical means. Any etchant on the work material is also removed with a
wash or clear, cold water. A deoxidizing bath may also be required in order to remove the
oxide films left on the surface of the work material.

8. B) Milling or Contour Machining Chemical milling is a process used to produce shapes by
chemically etching selective portion of material from the relatively large surface area of work metal.
The main purpose is to produce shallow cavities with complex profiles on plates, sheets, forgings,
generally for the overall reduction of weight. Chemical milling as shown in figure 5.2 involves the
processing steps as discussed below:
• Workpiece pre-cleaning process
• Masking and Scribing mask
• Etching
• De-masking
(a) Workpiece pre-cleaning process: The surface of the workpiece metal is cleaned thoroughly,
degreased and pickled by acid or alkalis. Pre-cleaning is of utmost importance in order to
remove oil, grease, dirt, rust, or any foreign substances from the work surface so as to
produce a good adhesion of the masking material. The material is allowed to dry.

9. (b) Masking & Scribing mask Masking involves covering the portions of the workpiece metal where
material is not to be removed by the chemical action of the etchant. Masking with adhesive tapes or paints
(maskants) is a common practice, although elastomers (rubber and neoprene) and plastics (polyvinylchloride,
polyethylene, and polystyrene) are also used. Since it is very difficult to apply maskants on small surfaces,
the maskant is initially applied on a large surface area and then scribed or cut with a sharp knife followed by
careful peeling of the mask from the selected areas to be etched as shown in figure 5.2(a) and (b)

10. (c) Etching The un-masked (exposed) surfaces of the work material are machined chemically
with selected etchants. Etching is carried out by immersing the work material in a tank of
agitated etchant as shown in figure 5.2(c). The process is carried out at higher temperatures
depending on the etched material. Temperature control and agitation (stirring) during
chemical milling is important in order to obtain a uniform depth from the material removed.
Erosion of the work material takes place from the exposed (unmasked) surface. The work
material is converted into metallic salt, which is then dissolved and carried away in the
eţchant solution.
(d) De-masking When etching is completed, the mask is removed either through
mechanical or chemical means. Any etchant on the work material is also removed by using
clean cold water. A deoxidizing bath may also be required in order to remove the oxide films
left on the surface of the work material.

11. Advantages.
• Components are produced burr-free.
• The process is relatively simple.
• Can be applied to almost any material.
• Thin sections.
• Several components can be produced simultaneously.
• The process does not distort the machined components.
• Most difficult to machine material can be processed.
• High surface finishing is possible.

12. Limitations.
• The metal removal rate is slow.
• Metal thicker than 2 mm can not be usually
machined.
• High operator skill is required.
• Corrosive etchant damages the equipment.
• Required the handling of dangerous chemicals.
• Disposal of potentially harmful byproducts.

13. Application of Chemical Machining.
• CHM has been applied in a number of usages where the depth of metal removal is crucial to a few microns, and
the tolerances are close.
• The surface finish obtained in the process is in the range of 0.5 to 2 microns.
• Besides, it removes metal from a portion of the entire surface of formed or irregularly shaped parts such as forgings,
castings, extrusions or formed wrought stock.
• One of the major applications of chemical machining is in the manufacture of burr-free, intricate stampings.

14. Reference Links.
https://youtu.be/f3MCrtCIHDE
https://youtu.be/KfJ85mjpWx4
https://youtu.be/2O1TyJGXuWY
https://youtu.be/qP3D-Ev6Ukc
https://youtu.be/4zK0QsbFE_Y