Ultra Sonic Machining by G.Venkatesh

1. Ultrasonic Machining (USM)
1.Components(Elements of USM)
2.MR mechanisms
3.Advantages
4.Disadvantages and Limitations
5.Applications
6.Process Parameters
7.Effect of Process Parameters on MRR
8.Design Considerations in Tool
9.Tool Feed mechanisms
10.Process Capabilities

2. Started way back in 1927-------------accidently investigated during
ultrasonic grinding of abrasive powders
What is ultrasonic???

3. Elements of USM (Components)
1. High Power Sine Wave generator (Ultrasonic Wave Generator)
2. Acoustic Head (Transducer)
3.Horn or Sonotrode
4.Form Tool
5.Abrrasive Slurry
6.Work material

6. • It converts low frequency (60Hz) electrical power to high frequency
(Greater than 16 KHz) electrical power.
• The main requirements of a generator are reliability, efficiency,
simplicity in design and low cost.
• USM is usually employed with Vacuum tube generators.
Ultrasonic Sine Wave Generator

7. Transducer
Converts the high frequency output
of Generator into linear vibrations
a. Piezo-Electric (Low power)
b. Magneto strictive (High power)
c. Electro-strictive effect
One form of energy into other

8. • Piezoelectric transducer: When an electric current is passed through the
piezoelectric crystal (quartz) it expands, when the current is removed the
crystal attains its original size. This effect is known as piezoelectric effect.
These are available up to 900W power supply &95% efficiency.
• Magneto-strictive transducer: When an object made of ferromagnetic
materials (Nickel & Nickel alloy sheets) is placed in the continuously changing
magnetic field, a change in its length takes place.
• These are available up to 2.4KW power supply & 20% - 30% efficiency.
• For this transducer cooling is essential to remove the waste heat.

10. Horn or Sonotrode (Trunk or amplifier or Concentrator)
Very critical or Important link in USM
 The horn holds and connects the tool to the transducer
 It amplifies and focuses vibrations of transducers of the required intensity
necessary for driving tool
 Commonly used tool holders are Monel, titanium, stainless steel
 Tool holders are more expensive, demand higher operating cost.

11. Form Tool
1. Tool is designed to provide maximum amplitude of vibrations at the free end
2. Selection of Tool material is very important -----not to fail due to wear (Tough)
HSS
MS
SS
TC
Brass
Silver

12. Design considerations for tool in USM
1. The tool is made up of a strong but ductile metal.
2. Stainless steels and low carbon steels are used for making the tools.
3. Aluminium and brass tools wear is ten and five times faster than steel tools respectively.
The geometrical features are decided by the process.
1. The diameter of the circle circumscribed about the tool should not be more than 1.5–2.0
times the diameter of the end of the concentrator.
2. The tool should be as short and rigid as possible.
3. When the tool is made hollow, the internal contour should be parallel to the external one
to ensure uniform wear.
4. The thickness of any wall or projection should be atleast five times the grain size of the
abrasive.
5. In the hollow tool, the wall should not be made thinner than 0.5–0.8 mm.
6. When designing the tool consideration should be given to the side clearance which is
normally of the order of 0.06–0.36 mm, depending on the grain size of the abrasive.

13.  Alumina is used for machining ceramics, glass and germanium. Alumina wears out
very fast and loses its cutting power very fast.
 Diamond and rubies are cut by diamond powder. Good surface finish, accuracy and
cutting rates are possible with diamond dust.
Selection of abrasive particles depends on:
• Particle size
• Hardness
• Cost of abrasives
• Durability of abrasives
Abrasive Slurry:
 Commonly used abrasives are Al2O3, Sic & B4C (Boron Carbide).
 Vibrating Abrasives attain K.E. and strike the work piece surface with a force much
higher than their own weight.

14. Work Material:
USM usually is employed to machine hard and/or brittle materials but there is
no limitation to the range of materials that can be machined, except that they
should not dissolve in the slurry media.
 The metal removal rate and surface finish depend on size of abrasive particles. Coarse
grains give higher MRR, but lower surface finish. Fine grains give good surface finish, but
MRR is low.
 The abrasive slurry is circulated by pumping, and it requires cooling to remove the
generated heat to prevent it from boiling in the gap and causing the undesirable
cavitation effect.

15. MR mechanisms
 Material removal primarily occurs due to the indentation of the
hard abrasive grits on the brittle work material.
 During indentation, 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.
 The tool material should be such that indentation by the abrasive grits does not lead
to brittle failure.

16. 4 mechanisms of MRR
1. Mechanical abrasion
2. Impact
3. Erosion
4. Chemical

17. ECONOMIC CONSIDERATIONS:
• The USM process has the advantage of machining hard and brittle
materials to complex shapes with good accuracy and reasonable
surface finish. Considerable economy results from the USM
of hard alloy press tools, dies and wire drawing equipment.
• The power consumption of USM is 0.1 W-h / mm3 for glass and
about 5 W-h / mm3 for hard alloys.

18. Advantages
1. No PHYSICAL ,THERMAL,CHEMICAL changes occurs to work piece.
2. No physical contact is required.
3. No structural changes
4. Free from burrs and distortions
5. Good surface finish obtained
6. No electricity conductivity is required
 No residual stress
 No thermal stress
 No damage to work piece

19. Disadvantages and Limitations
1. Soft materials like lead, plastics are not suitable for machining.
2. Consumes higher power and lower material removal rates.
3. Tool wear is high when compared to other NTM.
4. While producing blind holes there ineffective slurry circulation leads to presence
of fewer active grains under the tool face.
5. It is difficult to drill deep holes, as slurry movement is restricted

20. Applications
1. Machining Brittle and fragile Metallic alloys
2. Advanced ceramic components in auto engine components
3. Used for machining round, square, irregular shaped holes and surface impressions.
4. Machining, wire drawing, punching or small blanking of dies.
5. Used for machining round, square, irregular shaped holes and surface impressions.
6. USM enables a dentist to drill a hole of any shape on teeth without any pain
Glass
Sapphire
Quartz
Silicon carbide
Ceramic matrix composites

21. USM process Capabilities
1. Can machine the workpieces harder than 40 HRC to 60 HRC like carbides,
ceramics, tungsten glass that cannot be machined by conventional
methods. USM is not applicable to soft and ductile materials such as
copper, lead, ductile steel and plastics, which absorb energy by
deformation.
2. Tolerance range: 7 to 25 microns.
3. Holes up to 76 microns have been drilled. Hole depths up to 51 mm
have been achieved easily. Hole depth of 152 mm deep is achieved by
special flushing techniques.
4. Aspect ratio 40 : 1 has been achieved.
5. Linear material removal rate: – 0.025 to 25 mm/min.
6. Surface finish: – 0.25 micron to 0.75 micron.
7. Non-directional surface texture is possible compared to conventional
grinding.

22. Process Parameters
1. Amplitude of vibration (ao) – 15 – 50 μm
2. Frequency of vibration (f) – 19 – 25 kHz
3. Feed force (F) – related to tool dimensions
4. Feed pressure (p)
5. Abrasive size – 15 μm – 150 μm
6. Abrasive material – Al2O3 - SiC - B4C - Boronsilicarbide - Diamond
7. Flow strength of work material
8. Flow strength of the tool material
9. Contact area of the tool – A
10. Volume concentration of abrasive in water slurry – C

23. Effect of Amplitude on MRR
 (ao) has greatest effect of all process variables.
 MRR increases with increases in amplitude and then
decreases.
 The magnitude of amplitude decides the velocity of
abrasive particles at interface between tool and work
piece.
 As the amplitude increases the K.E rises of abrasive
particles increases which enhances the mechanical
chipping action consequently i.e the removal rate
finally increases.
 At greater vibration amplitude it may lead to occurrence
of splashing of particles which causes a reduction of
number of active abrasive grains and results in decrease
in MRR

24. • MRR should also rise proportionately with the mean grain diameter.
• An increase in abrasive grain size results in higher MRR but poorer surface finish.
• Maximum MRR is achieved when the abrasive grain size is comparable with an
amplitude of vibration of the tool. The hardness of the abrasives and method of
introducing the slurry also has effect on MRR.
Effect of Abrasive Grain Size

25. Effect of Abrasive slurry Viscosity on MRR
As the viscosity of medium increases the
MRR decreases because the abrasive particles
are ceased to move because of viscous forces
between particles and medium. As the particle
are ceased the number of cutting edges available
for machining decreases this reduces MRR.

26. Effect of Frequency on MRR
Frequency has significant effect on MRR. The
frequency used for machining process must be
resonant frequency to obtain greatest amplitude
at the tool tip.
With in increase in frequency of tool head the MRR
Increases.

27. Effect of slurry Concentration on MRR
Concentration of abrasives directly controls
number of grains producing per cycle.
As the concentration increases the number of
cutting edges available for machining
increases which increases the chipping rate
and consequently the overall MRR.
In practice 30-35% concentration of abrasives
is recommended in case of USM.

28. Tool Feed mechanisms
The feed mechanism of an ultrasonic machine must perform the following functions:
1. Bring the tool slowly to the workpiece to prevent breaking.
2. The tool must provide adequate cutting force and sustain it during the machining
operation.
3. The cutting force must be decreased when the specified depth is reached.
4. Overrun a small distance to ensure the required hole size at the exit.
5. The tool has to come back to its initial position after machining is done.
There are four types of feed mechanism which are commonly used in USM:
1. Gravity feed mechanism
2. Spring loaded feed mechanism
3. Pneumatic or hydraulic feed mechanism
4. Motor controlled feed mechanism.

29. 1. Gravity feed mechanism
Figure shows the operation of the gravity tool feed mechanism.
 In this mechanism counter, balance weights are used to apply the required
load to the head through pulley and rope arrangement.
 In order to reduce friction ball, bearings are used.
 Gravity feed mechanisms are simple in construction, but this mechanism is
insensitive and inconvenient to adjust.

30. 2. Spring loaded feed mechanism
 In this mechanism spring pressure is used to feed the tool during the machining
operation.
 This type of mechanism is quite sensitive and easy to adjust.

31. 3. Pneumatic or hydraulic feed mechanism
 In this mechanism, hydraulic cylinder is used to give a linear motion of the
tool.
 High feed rate and accurate positioning are possible with hydraulic feed
mechanism.

32. 4. Motor controlled feed mechanism
Figure 2.8 shows the operation of the motor controlled feed mechanism.
This mechanism is used for precise control of the tool feed movement.