process of Ultrasonic machining

1. Ultra Sonic Machining
G.H.PATEL COLLEGE OF ENGINEERING & TECHNOLOGY
2172003:Manufacturing Technology II

2. INTRODUCTION
• Ultrasonic machining (USM) is a mechanical material removal
process used to erode holes and cavities in hard or brittle
work pieces by using shaped tools, high frequency mechanical
motion, and an abrasive slurry.
• A relatively soft tool is shaped as desired and vibrated against
the work piece while a mixture of fine abrasive and water
flows between them. The friction of the abrasive particles
gradually cuts the work piece.

3. INTRODUCTION
• Materials such as hardened steel, carbides, rubies, quartz,
diamonds, and glass can easily be machined by USM.
Ultrasonic machining is able to effectively machine all
materials harder than 40HRC, whether or not the material is
an electrical conductor or an insulator.
• The tool, which is a negative of the work piece, is vibrated at
around 20KHz with and amplitude of between 0.013mm and
0.1mm in abrasive slurry at the work piece surface.

4. INTRODUCTION
• Ultrasonic machining, also known as ultrasonic impact
grinding. in which an abrasive slurry freely flows between the
work piece and a vibrating tool.
• It differs from most other machining operations because very
little heat is produced. The tool never contacts the work piece
and as a result the grinding pressure is rarely more than 2
pounds, which makes this operation perfect for machining
extremely hard and brittle materials, such as glass, sapphire,
ruby, diamond, and ceramics

5. INTRODUCTION
• The surface finish of ultrasonic machining depends upon the
hardness of the work piece/tool and the average diameter of
the abrasive grain used.
• this process simply utilizes the plastic deformation of metal
for the tool and the brittleness of the work piece. As the tool
vibrates, it pushes down on the abrasive slurry (containing
many grains) till the grains impact the brittle work piece.
• The work piece is broken down while the tool bends very
slightly. Commonly used tool material consist of nickel and
soft steels.

6. WORKING PRINCIPLES
• UM is a mechanical material removal process that can be used
for machining both conductive and non-metallic materials
with hardness of greater than 40 HRC.
• The UM process can be used to machine precision micro-
features, round and odd-shaped holes, blind cavities,
features.
• Multiple features can be drilled simultaneously, often
reducing the total machining time significantly

7. WORKING PRINCIPLES
• In the UM process, a low-frequency electrical signal is applied
to a transducer, which converts the electrical energy into high-
frequency (20 KHz) mechanical vibration.
• This mechanical energy is transmitted to a horn and tool
assembly and results in a unidirectional vibration of the tool
at the ultrasonic frequency with a known amplitude.
• The standard amplitude of vibration is typically less than
0.002in.

8. WORKING PRINCIPLES

9. WORKING PRINCIPLES
• The power level for this process is in the range of 50 to 3000
watts.
• Pressure is applied to the tool in the form of static load.
• A constant stream of abrasive slurry passes between the tool
and the work piece.
• Commonly used abrasives include diamond, boron carbide,
silicon carbide and alumina, and the abrasive grains are
suspended in water or a suitable chemical solution.

10. WORKING PRINCIPLES
• In addition to providing abrasive grain to the cutting zone, the
slurry is used to flush away debris.
• The vibrating tool, combined with the abrasive slurry, abrades
the material uniformly, leaving a precise reverse image of the
tool shape.
• Ultrasonic machining is a loose abrasive machining process
that requires a very low force applied to the abrasive grain,
which leads to reduced material requirements and minimal to
no damage to the surface.

11. MATERIAL REMOVAL MECHANISMS
Material removal during the UM process can be classified into
three mechanisms:
• mechanical abrasion by the direct hammering of the abrasive
particles into the work piece
• micro-chipping through the impact of the free-moving
abrasives
• cavitations-induced erosion and chemical effect

12. OPERATIONS OF ULTRASONIC MACHINING

13. • Function of the concentrators : The oscillation amplitude
obtained from the magnetostrictive transducer is usually around
5 microns, which is too small for removal of material from the
work piece. The function of the concentrator (also called
mechanical amplifiers, acoustic horn and tool cone) is to amplify
the amplitude of vibration of the magnetostrictive transducer
from 5 to 40–50 microns. Concentrator also concentrates the
power on a smaller machining area. To get the resonance
condition, like a transducer, the acoustic cone should be of half
wavelength of the resonator.

14. MATERIAL REMOVAL MECHANISMS
• Material removal rates and the surface roughness generated on the
machined surface depend on the material properties and process
parameters, including the type and size of abrasive grain employed
and the amplitude of vibration, as well as material porosity,
hardness and toughness.
• In general, the material removal rate will be lower for materials
with high material hardness (H) and fracture toughness.

15. PROCESS PARAMETERS
1. Amplitude of vibration ( 15 to 50 microns)
2. Frequency of vibration (19 to 25 kHz)
3. Feed force (F) related to tool dimensions
4. Feed pressure
5. Abrasive size
6. Abrasive material: boron silica carbide, diamond
7. Flow strength of the work material
8. Flow strength of the tool material
9. Contact area of the tool
10. Volume concentration of abrasive in water slurry
11. Tool (a) Material of tool
(b) Shape
(c) Amplitude of vibration

16. (d) Frequency of vibration
(e) Strength developed in tool
(g) Gap between tool and work
12. Work material (a) Material
(b) Impact strength
(c) Surface fatigue strength
13. Slurry
(a) Abrasive—hardness, size, shape and
quantity of abrasive flow
(b) Liquid—chemical property, viscosity,
flow rate
(c) Pressure
(d) Density

17. • Ultrasonic vibration machining physically operates by the
mechanism of micro chipping or erosion on the work piece's
surface. Since the abrasive slurry is kept in motion by high
frequency, low amplitude vibrations the impact forces of the
slurry are significant causing high contact stresses. These high
contact stresses are achieved by the small contact area
between the slurry's particles and the work piece's surface.
Brittle materials fail by cracking mechanics and these high
stresses are sufficient to cause micro-scale chips to be
removed from its surface. The material as a whole does not
fail due to the extremely localized stress regions. The average
force imparted by a particle of the slurry impacting the work
piece's surface and rebounding can be characterized by the
following equation:

18. • Where m is the mass of the particle, v is the velocity of the
particle when striking the surface and to is the contact time,
which can be approximated according to the following
equation:
Where r is the radius of the particle, co is the elastic wave velocity
of the work piece, E is the work pieces Young's Modulus and ρ is
the materials density.

19. • Pressure also has an effect on the MRR. Figure shows the effect of
the amplitude of vibration on MRR for different pressures.

20. Effect of Frequency on MRR
Frequency has a significant effect on
MRR . The frequency used for
machining process must be the
resonant frequency to obtain the
greatest amplitude at the tool tip and
thus achieve the maximum utilization
of the acoustic system. With increase in
the frequency of the tool head, the
MRR should increase proportionally.
However, there is a slight variation in
the MRR with frequency

21. ADVANTAGES OF UM
• Glass drilling.
• Glass machining.
• Mirror image machining.
• Machining of soft and ductile material.
• Machining of conductive and non conductive material.

22. DISADVANTAGES OF UM
• The hard abrasive grains suspended in the electrolyte cause
strain to the work piece.
• To control a pressure of the tool according to the thickness of
the work piece is difficult.

23. APPLICATIONS OF UM
• UM effectively machines precise features in hard, brittle
materials such as glass, engineered ceramics, CVD SiC, quartz,
single crystal materials, PCD, ferrite, graphite, glassy carbon,
composites and piezo ceramics.

24. Thank
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