m mm

1. Chemical Machining and Plasma
Arc Cutting

2. Chemical Machining/Chemical Milling
• Chemical machining is the material removal
process for the production of desired shapes
and dimensions. It is done by selective or
overall removal of material by a controlled
chemical attack with acids or alkalies.

3. Schematic Diagram of the process

5. Chemical Machining
• The metal is slowly converted into metallic salt
by chemical reaction and is finally removed in
this form. Areas from where the material is
not to be removed are protected by an
etching resistant material, known as ‘maskant
or ‘resist’.

6. Chemical Machining Process
• Almost all the materials, from metals to
ceramics, can be chemically machined. The
component to be machined is first cleaned in
trichloroethylene vapour or in a solution of
mild alkaline solution at 80 to 90 °C, followed
by washing in clean water. The cleaning
ensures good adhesion of the coating or
masking agent.

7. • After cleaning the component is dried and
coated with the maskant material which may
be cut and peel, photoresist or screen-print,
type. Finally, the metal is removed by etching.

8. The most commonly used etchant is;
• Ferric chloride (FeCl3) is a popular acidic
etchant, widely used in chemical machining
industry and known as universal etchant
suitable for most of materials.
• CuCl2 and Alkaline agents are also used.

9. The most commonly used masking
materials are;
• (a) Neoprene
• (b) Poly vinyl chloride
• (c) Polyethylene

10. Products

12. Advantages of Chemical machining
• Very close dimensions can be machined on
very thin to very thick components.

13. Photochemical Machining
• In photochemical machining the maskant film
is developed by the photocopy machine which
is then placed on the workpiece for etching.
• High precision Work can be done by
Photochemical Machining.

15. Plasma Arc Cutting
• The basic principle is that the arc formed
between the electrode and the workpiece is
constricted by a fine bore, copper nozzle. This
increases the temperature and velocity of the
plasma emanating from the nozzle. The
temperature of the plasma is in excess of 20
000°C and the velocity can approach the speed
of sound. When used for cutting, the plasma gas
flow is increased so that the deeply penetrating
plasma jet cuts through the material and molten
material is removed.

16. Plasma Arc Cutting

17. Dual gas plasma set up

18. Which Gases to be ionized
• Argon-H2 with Tungsten Electrodes
• Oxygen, air or Carbon Dioxide with Copper
Electrode
• Nitrogen gas is mostly used as a secondary
gas.

19. Uses:
• For cutting of thick metal plates with higher
feed rates because plasma gas is highly
penetrating gas.
• Plate must be a conductor

20. Disadvantages
• For Conductors only
• Poor surface finish is obtained
• Greater Heat Affected Zone as compared to
other processes