Ultrasonic Machining (Non-Traditional Machining)

1. TSN, JSSATEB

2. INTRODUCTION
Ultrasonic machining (USM), sometimes called
ultrasonic impact grinding, employs ultrasonically
vibrating tool to impel the abrasives in a slurry at
high velocity against work piece.
The tool is fed into the part as it vibrates along an
axis parallel to the tool feed at an amplitude on the
order of several thousandths of an inch and a
frequency of 20 kHz.
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3. • USM is mechanical material removal process or an
abrasive process used to erode holes or cavities on
hard or brittle workpiece by using shaped tools, high
frequency mechanical motion and an abrasive slurry.
• USM is used to machining brittle materials such as
single crystals, glasses and polycrystalline ceramics
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4. • USM is used to machining complex and intricate
profiles.
• USM used extensively in machining hard and
brittle materials that are difficult to machine by
traditional manufacturing processes.
• Ultrasonic Machining abrasives contained in a
slurry are driven against the work by a tool
oscillating at low amplitude (25-100 μm) and
high frequency (15-30 KHz)
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5. Principle of USM
“When a tool vibrating at a very high frequency is
brought closer to the work piece with abrasive
particles between them, the vibrating energy of the
tool can propel the abrasive particles to strike the
work piece with a great velocity. The impact of the
abrasive particle fractures the hard work surface
resulting in the removal of material from the work
piece”
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6. TSN, JSSATEB

7. The tool is fed into the part as it vibrates along an axis
parallel to the tool feed at an amplitude on the order of
several thousandths of an inch and a frequency of 20
kHz.
 As the tool is fed into the work piece, a negative of the tool
is machined into the work piece.
 The cutting action is performed by the abrasives in the
slurry which is continuously flooded under the tool.
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8.  The slurry is loaded up to 60% by weight with abrasive
particles. Lighter abrasive loadings are used to facilitate the
flow of the slurry for deep drilling (to 5mm deep).
 Boron carbide, aluminum oxide, and silicon carbide are the
most common used abrasives.
Videos
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9. USM set up
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10. USM Process
1. Conversion of low frequency electrical power to high
frequency electrical signal and fed into transducer.
2. Transducer convert high frequency electrical signal into
high frequency mechanical motion(Vibration)
3. These mechanical vibration will be guide and amplified
and supplied to the tool tip through the horn.
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11. Cont..
4. The tool which is having the same shape as the cavity to
be machined, vibrates at a very high frequency .
5. During this time abrasive slurry will pumped between the
tool work interface.
6. The vibration of the tool transmits a high velocity to the
abrasive particles,
7. The abrasive particles strike the workpiece with great
force.
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12. Cont…
8. This impact fractures the hard and brittle work surface
resulting in the removal of material in the form of small
wear particles.
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13. Cont…
9. The abrasive slurry flowing at the cutting zone carries
away the fractured particles.
10. The tool is pressed against the work piece by applying a
slight force
11. The abrasive slurry is be pumped in at low pressure till
the operation is completed.
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14. Equipment
1. Power Supply
2. Transducer
3. Tool holder
4. Tool cone
5. Cutting tool
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15. Power Supply
• USM used very high power sine wave generator
that converts the low frequency electrical power
(60Hz) to a high frequency electric power (20KHz)
• The electrical signal is then supplied to the
transducer
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16. Transducer
•The high frequency electrical signal is transmitted to
traducer which converts it into high frequency low
amplitude vibration.
•Essentially transducer converts electrical energy to
mechanical vibration. There are two types of
transducer used
1. Piezo electric transducer
2. Magneto-stricitve transducer.
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17. Piezo electric Transducer
Piezoelectric transducer generate mechanical motion
through the piezoelectric effect of certain materials
like Quartz or Lead – Zirconate.
When an electric current is applied to one of these
materials the materials increases minutely in size
and when the current is removed, the material
instantly return to its original shape.
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18. Magneto-stricitve transducer
• In this type, transducer materials are constructed
from a laminated stack of nickel or nickel alloy
sheets
• Their conversion efficiency is about 20-30%.
• Such transducers are available up to 2000 Watts.
• The maximum change in length can be achieved is
about 25 microns.
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19. Tool Holder
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20. Tool Holder
• The tool holder holds and connects the tool to the
transducer. It virtually transmits the energy
• In some cases, amplifies the amplitude of vibration.
• Material of tool should have good acoustic
properties, high resistance to fatigue cracking.
• Due measures should be taken to avoid ultrasonic
welding between transducer and tool holder.
• Commonly used tool holders are Monel, titanium,
stainless steel.
• Tool holders are more expensive, demand higher
operating cost. TSN, JSSATEB

21. Tool /Tool cone
• Tools are made of relatively ductile materials like
Brass, Stainless steel or Mild steel so that Tool
wear rate (TWR) can be minimized.
• The value of ratio of TWR and MRR depends on
kind of abrasive, work material and tool
materials.
• The size of the tool is slightly smaller than that of
the desired shape in the work piece.
• The tool is attach to the tool holder by silver
brazing, soft soldering, or by means of screws
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22. Abrasives/ Cutting tool
• Abrasives are usually suspended in liquid and
supplied to the cutting point during the operation.
• The liquid will help in the
– Removal of materials due to cavitations effect.
– Uniform distribution of abrasive particles into the gap.
• Selection of abrasive is depends on the hardness
of the workpiece materials
• The abrasive slurry is stored in reservoir and
pumped to the tool work interface through the
nozzle.
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23. Abrasives/ Cutting tool
• The slarry apart from fracturing the workpiece, it
also carries away the fractured particle of the
work materials.
• Eg: Boron carbide, silicon carbide and aluminum
oxide.
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24. Material Removal Models / Mechanism in
USM
The following are the Material Removal Models
used in USM
1. Throwing of abrasive grains.
2. Hammering of abrasive grains.
3. Cavitations in the fluid medium arising out of
ultrasonic vibration of tool.
4. Chemical erosion due to micro –agitations.
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25. Tool feed Mechanism
1. Counter weight type mechanism
2. Spring loaded feed mechanism system
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26. Counter weight type mechanism
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27. Cont..
• The feed force being the difference between the
weight of transducer + tool holder and counter
weight
• Counter weight attached through a lever system
using pulley
• The force is adjusted through weights
• This mechanism is insensitive to change in cutting,
it is inconvenient to adjust the weights.
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28. Spring loaded feed mechanism system
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29. Cont…
• This system uses piston cylinder arrangement
with a suitable liquid or air as working fluid
• Through the working fluid required force is
applied to the tool
• This mechanism is sensitive to changes in cutting
conditions.
•
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30. Process parameters in USM
Process parameters affects the metal removal
rate(MRR), surface finish and accuracy of the
machined surface.
a. Amplitude and frequency of vibrations of the tool
b. Slurry ( Abrasive water mixture)
c. Tool and work material
d. Type of abrasive
e. Abrasive size
f. Effect of applied static load (Feed force)
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31. Amplitude and frequency of vibrations of the
tool
• MRR increases with increase in both Amplitude
and Frequency
• F and a0 determines is affects on velocity of
abrasive particles.
• High amplitude tend to increase the surface
roughness, however the effect is minimum
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32. Slurry ( Abrasive water mixture)
• MRR increases with slurry concentration.
• Slurry saturation occurs at 30 to 40%
abrasive/water mixture.
• Material Removal rate drops with increasing
viscosity.
• The pressure with which the slurry is fed into the
cutting zone affects MRR .
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33. Cont..
• In some cases MRR can be increased even ten
times by supplying the slurry at increased pressure.
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34. Tool and work material
• The shape of the tool affects the MRR.
Narrower rectangular tool gives more MRR
compared to square cross section.
• Conical tool gives twice MRR compared to
cylindrical tool.
• The brittle behavior of material is important in
determining the MRR.
• Brittle material can be cut at higher rates than
ductile materials.
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35. Cont..
• Tool has to withstand vibration, it should not fail
or wear out quickly.
• Harder the tool material, the faster the wear rate
• Tough malleable materials such as alloy steel and
stainless steel are more suitable
• Hardness ratio is tool / workpiece hardness
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36. Type of abrasive
• The abrasive used be should be harder than the
workpiece material being machined.
• If the abrasive is softer than the workpiece leads to
poor surface finish during the subsequent
machining
• Boron carbide is used for high MRR and hard
workpiece like tungsten carbide, tool steel and
precious stones. TSN, JSSATEB

37. cont..
• Aluminum oxide wears out fast and loses its cutting
power
• Silicon carbide is best suited
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38. Abrasive Size
• The size of the abrasive particle varies between
240 – 800 grit
• Coarse grades are suitable for high metal removal
rates, but result in rough surface finish
• Coarse grades are used for roughing operation
• finer grades 750-800 grit are used for fine
surface finish btr MRR is less
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39. Cont.
Note: A higher grit number indicates a
smaller abrasive grain and a finer
abrasive product.
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40. Effect of applied static load (Feed force)
• Initially with increase in static load on the tool,
the depth of penetration of the abrasive particle
on the work surface is more lading to increase
in MRR
• However there is a limit to the applied static
load, beyond this limit the depth of penetration
is found to decrease leading to low MRR
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41. Cont…
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42. Process capabilities ( Characteristics) of USM
Following are the process capabilities of USM
process
– Metal Removal Rate (MRR)
– Surface Finish
– Accuracy
– Drilling hole capacity
– The corner radius obtained is limited to 0.025mm
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43. Metal Removal Rate (MRR)
• Brittle non metallic materials can be cut at
higher rates than ductile materials
• USM work satisfactorily only when workpiece
hardness greater than HRC40
• It gives excellent results for workpiece with
hardness greater than HRC 60.
• USM is more suitable for hard and brittle
materials
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44. Sl No Work Material MRR(mm3/Min)
1 Glass 425
2 Ceramic 185
3 Mica (glass
Bonded)
390
4 Tungsten Carbide 40
5 Tool Steel
(Hardened)
30
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45. Cont…
 Stainless steel, cobalt-base heat resistant steels,
germanium, glass, ceramic, carbide, quartz and
semiconductors are machined.
Material removal rate per unit time is inversely
proportional to the cutting area of the tool, provided
the circulation of the slurry and other operating
conditions are held constant.
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46. Cont…
 Tool vibrations also affect the removal rate. The type
of abrasive, its size and concentration of the slurry also
directly affect the material removal rate. Boron carbide
is the hardest and has the highest material removing
capability.
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47. Surface Finish
The size of the abrasive grit has a major influence
of the surface finish
Larger the grit size the finer will be the surface
finished
Surface finish may rang from 0.2 to 0.6 micron
Finer abrasive results in slower metal removal rate.
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48. Accuracy
The process accuracy is measured through the
overcut (over size) produced during drilling of
holes
The term over size measures the difference between
the hole diameter, measured at the top of the
surface , and tool diameter.
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49. Cont..
 The clearance between the tool and machined
hole is necessary to enable the abrasive to flow
in to machining zone under oscillating tool.
 Grain size of the abrasive represents the main
factor, which affects the overcut produced.
 The over cut is about two to four times greater
than the mean grain size in case of glas and
tungsten carbide
 The accuracy level in USM is of about
±25micron TSN, JSSATEB

50. Drilling Hole Capacity
• Hole as small as 76 Micrometer can be drill in
USM
• Hole depth up to 51 mm have been easily drill
• 152 mm deep hole has also been drilled using
special flushing technique.
• Aspect ratio of 40:1 has been achieved
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51. Advantages of USM
• Ability to machine non conductive materials Like
Glass, ceramics etc.
• It is capable to machine intricate cavities in single pass
in fragile or /and hard materials.
• In USM, there is no direct contact between the tool and
workpiece hence it is a good process for machining very
thin and fragile components.
• A brittle material can be machined more easily than a
ductile one. TSN, JSSATEB

52. Cont..
• It is considered as a very safe process because it does
not involve high voltage, chemicals, mechanical forces
and heat.
• It is non thermal, non chemical, creates no change in the
microstructure, chemical or physical properties of
workpiece material.
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53. Limitations of USM
• Low metal removal rates.
• Depth of holes and cavities produced are small.
Usually the depth of hole is limited to 2.5 times
the diameter of the tool.
• Tool wear is more.
• Not suitable for soft work piece materials.
• Abrasive slurry has to be periodically replaced for
efficient machining
• It is costlier for complex shapes
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54. Applications Of USM
• Drilling and machining cavities or holes in
conductive and non-conductive materials like
glass and ceramics etc.
• Threading of various glass and ceramic
materials.
• Hard materials and precious stones such as
synthetic ruby for the preparation of jewels to
watch and timer movements are successfully
machined by this method.
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55. Cont..
• Ultrasonic machining is useful in micro-drilling
hole up to 0.1mm.
• Enabling a dentist to drill a hole of any shape
without creating any pain.
• Casting and welding of metals.
• Measurement of hardness and grain size
determination of metals.
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