A topic of interest on Advance Machining Science & Technology. An unconventional machining process (or non-traditional machining process) is a special type of machining process in which there is no direct contact between the tool and the workpiece. In unconventional machining, a form of energy is used to remove unwanted material from a given workpiece

1. NON-CONVENTIONAL
MACHINING
 Ultrasonic Machining (USM)
 Electro Chemical Machining (ECM)
Sharath C M
BANGALORE

2. Ultrasonic Machining (USM)
■ USM is grouped under the mechanical group NTM processes. Fig. briefly depicts the
USM process

3. ■ In ultrasonic machining, a tool of desired shape vibrates at an
ultrasonic frequency (19 ~ 25 kHz) with an amplitude of around 15 –
50 μm over the workpiece.
■ Generally, the tool is pressed downward with a feed force, F.
■ Between the tool and workpiece, the machining zone is flooded
with hard abrasive particles generally in the form of a water based
slurry.
■ As the tool vibrates over the workpiece, the abrasive particles act
as the indenters and indent both the work material and the tool.
■ The abrasive particles, as they indent, the work material, would
remove the same, particularly if the work material is brittle, due to
crack initiation, propagation and brittle fracture of the material.

4. Mechanisms of Material Removal in USM
■ USM is generally used for machining brittle work material.
■ Material removal primarily occurs due to the indentation of the
hard-abrasive grits on the brittle work material. As the tool
vibrates, it leads to indentation of the abrasive grits.
■ due to Hertzian contact stresses, cracks would develop just
below the contact site, then as indentation progresses the
cracks would propagate due to increase in stress,
■ and ultimately lead to brittle fracture of the work material
under each individual interaction site between the abrasive grits
and the workpiece.

5. As the indentation proceeds, the
contact zone between the abrasive grit
and workpiece is established and the
same grows.
The contact zone is circular in nature and is characterised by its
diameter ‘2x’. At full indentation, the indentation depth in the
work material is characterised by δw.

6. Process Parameters and their Effects
During discussion and analysis as presented in the previous section, the
process parameters which govern the ultrasonic machining process have
been identified and the same are listed below along with material
parameters
Amplitude of vibration (ao) – 15 – 50 μm
Frequency of vibration (f) – 19 – 25 kHz
Feed force (F) – related to tool dimensions
Feed pressure (p)
Abrasive size – 15 μm – 150 μm

7. Abrasive material
– Al2O3
- SiC
- B4C
– Boronsilicarbide
- Diamond
Flow strength of work material
Flow strength of the tool material
Contact area of the tool – A
Volume concentration of abrasive in water slurry – C

8. Depicts the effect of parameters on MRR

9. Machine: The basic mechanical structure of an USM is very
similar to a drill press. However, it has additional features to
carry out USM of brittle work material.The workpiece is
mounted on a vice

10. The typical elements of an USM are
Slurry delivery and return system
Feed mechanism to provide a downward feed force on
the tool during machining
The transducer, which generates the ultrasonic
vibration
The horn or concentrator, which mechanically
amplifies the vibration to the required amplitude of 15 –
50 μm and accommodates the tool at its tip.

11. Stepped Machining of tapered or stepped horn is much easier as
compared to the exponential one. Fig. shows different horns
used in USM

12. Applications:
Used for machining hard and brittle metallic alloys,
semiconductors, glass, ceramics, carbides etc.
Used for machining round, square, irregular shaped holes and
surface impressions. Machining, wire drawing, punching or
small blanking dies.
Limitations:
Low MRR
Rather high tool wear
Low depth of hole

13. Electro Chemical Machining:
Introduction: Electrochemical Machining (ECM) is a non-
traditional machining (NTM) process belonging to
Electrochemical category.
ECM is opposite of electrochemical or galvanic coating or
deposition process.
Thus ECM can be thought of a controlled anodic dissolution at
atomic level of the work piece that is electrically conductive by
a shaped tool due to flow of high current at relatively low
potential difference through an electrolyte which is quite
often water based neutral salt solution

15. Process:
During ECM, there will be reactions occurring at the electrodes i.e. at
the anode or workpiece and at the cathode or the tool along with
within the electrolyte.
The electrolyte and water undergoes ionic dissociation as shown below
as potential difference is applied
NaCl ↔ Na+ + Cl-
H2O ↔ H+ + (OH)
the positive ions move towards the tool and negative ions move
towards the workpiece.
2H + + 2e- = H2↑ at cathode

16. The applied potential difference, however, also overcomes the
following resistances or potential drops.
They are:
The electrode potential
The activation over potential
Ohmic potential drop
Concentration over potential
Ohmic resistance of electrolyte shows the total potential drop
in ECM cell

17. Equipment:
The electrochemical machining system has the following
modules:
Power supply
Electrolyte filtration and delivery system
Tool feed system
Working tank

19. Material removal:
The first law states that the amount of electrochemical dissolution or
deposition is proportional to amount of charge passed through the
electrochemical cell, which may be expressed as:
m ∝ Q where m = mass of material dissolved or deposited
Q = amount of charge passed
The second law states that the amount of material deposited or
dissolved further depends on Electrochemical Equivalence (ECE) of
the material that is again the ratio atomic weigh and valency.
Thus

20. Power Supply
Type direct current
Voltage 2 to 35 V
Current 50 to 40,000 A
Current density
Electrolyte
0.1 A/mm2 to 5 A/mm2
Material NaCl and NaNO3
Temperature 20oC – 50oC
Flow rate 20 lpm per 100 A current
Pressure 0.5 to 20 bar
Dilution 100 g/l to 500 g/l
Working gap 0.1 mm to 2 mm
Overcut 0.2 mm to 3 mm
Feed rate 0.5 mm/min to 15 mm/min
Electrode material Copper, brass, bronze

21. ECM is used for
Die sinking
Profiling and contouring
Trepanning
Grinding
Drilling
Micro-machining
Applications:
ECM technique removes material by atomic level dissolution of the same by
electrochemical action. Thus the material removal rate or machining is not
dependent on the mechanical or physical properties of the work material.

23. Advantages:
ECM offers impressive and long lasting advantages.
 ECM can machine highly complicated and curved surfaces in a single pass.
 A single tool can be used to machine a large number of pieces without any loss in its
shape and size. Theoretically tool life is high.
 Machinability of the work material is independent of its physical and mechanical
properties. The process is capable of machining metals and alloys irrespective of their
strength and hardness.
 Machined surfaces are stress and burr free having good surface finish.
 It yields low scrap, almost automatic operation, low overall machining time, and
reduced inventory expenses.
 There is no thermal damage and burr free surface can be produced.

24. Disadvantages:
■ High capital cost of equipment.
■ Design and tooling system is complex.
■ Hydrogen liberation at the tool surface may cause hydrogen embrittlement of the
surface. Spark damage may become sometimes problematic.
■ Fatigue properties of the machined surface may reduce as compared to
conventional techniques (by 20%) 6. Non-conductive material cannot be machined.
■ Blind holes cannot be machined in solid block in one stage
■ Corrosion and rust of ECM machine can be hazard.
■ Space and floor area requirement are also higher than for conventional machining
methods.
■ Some additional problems related to machine tool requirements such as power
supply, electrolyte handling and tool feed servo systems