Ultrasonic Machining

Maulana Azad National Institute of Technology

Topic : Ultrasonic Machining

By Name scholar No.

1. Aayush sharma 091116246

2. Palash gupta 091116248

3. Chetan chaudhary 091116249

4. Shreya majumdar 091116250

5. Govind yadav 091116256

6. Anandkumar singh 091116257

Concerned by : Prof. M.K Pradhan

Branch : PIESem : (V)Subject : Metal cutting (PI-305)

Content 1. Introduction of USM2. Schematic diagram 3. Principle & Working 4. Mechanism5. Mathematic Design for MMR6. Process parameter & effect7. USM system & subsystem 8. Application 9. Advantages & disadvantages 10. Summary 11. Quiz , Problem & solution 12. References

Ultrasonic machining

Introduction

Ultrasonic machining is a non-traditional mechanical means of uniform stock material removal process

It is applicable to both conductive and nonconductive materials.

Particularly suited for very hard and/or brittle materials such as graphite, glass, carbide, and ceramics.

Various work samples machined by USM

1- The first picture on the left is a plastic sample that has inner grooves that are machined using USM.

2- The Second picture (in the middle is a plastic sample that has complex details on the surface

3- The third picture is a coin with the grooving done by USM

Systematic diagram

Transducer

WorkpieceAcoustichead/toolholder

Force feed motion

Slurry to machining zone

Slurry pump

Slurry tank

Return slurry

Principal and working

The process is performed by a cutting tool, which oscillates at high frequency, typically 20-40 kHz, in abrasive slurry.

The shape of the tool corresponds to the shape to be produced in the workpiece.

The high-speed reciprocations of the tool drive the abrasive grains across a small gap against the workpiece .

The tool is gradually fed with a uniform force.

The impact of the abrasive is the energy principally responsible for material removal in the form of small wear particles that are carried away by the abrasive slurry.

The tool material, being tough and ductile, wears out at a much slower rate.

Mechanism

The basic components to the cutting action are believed to be

The direct hammering of the abrasive into the work by the tool (major factor)1

The impact of the abrasive on the work2

Cavitation induced erosion3

Chemical erosion caused by slurry4

2

3

Material removal• Occurs when the abrasive particles,

suspended in the slurry between the tool and workpiece, are struck by the downstroke of the vibration tool.

• The impact propels the particles across the cutting gap, hammering them into the surface of both tool and workpiece. Collapse of the cavitation bubbles in the abrasive suspension results in very high local pressures.

• Under the action of the associated shock waves on the abrasive particles, microcracks are generated at the interface of the workpiece.

• The effects of successive shock waves lead to chipping of particles from the workpiece.

Mechanism

material removal per abrasive grit is given as

If at any moment of time, there are an average ‘n’ of grits and the tool is vibrating at a frequency ‘f’ then material removal rate can be expressed as

Hemispherical materialremoved due to brittle

Mathematical design for MRR4.

1

indentation depth in the work material is characterised by

the impulse of force on the tool and work would be balanced. Thus total impulse on the tool can be expressed as

Again, if the flow strength of work material is taken as

If ‘A’ is total surface area of the tool facing the workpiece, then volume ofabrasive slurry of one grit thickness is

2

If n is the number of grits then the total volume of n grits is

Thus the concentration of abrasive grits in the slurry is related as follows:

3

Now it is expected that indentation would be inversely proportional to the flowstrength then,

Process Parameters and their Effects The process parameters which govern the ultrasonic machining process havebeen identified and the same are listed below along with material parameters

5.

Amplitude of vibration (a) - 15- 50 um

Frequency of vibration (f)-19-25kHz

Feed force (F)

Feed pressure (p)

Abrasive size-15-150um

Abrasive material – Al2O3 - SiC - B4C - Boronslicarbide - Diamond

Contact area of the tool - A

Volume concentration of abrasive in slurry - C

the effect of parameters on MRR.

USM System

B

E

C

D

APower supply

Transducer

Toolholder

Abrasive Tools

Subsystems of USM System

Power Supply

• The power supply is a sine-wave generator • The user can control over both the frequency and

power of the generated signal. • It converts low-frequency (50/60 Hz) power to high-

frequency (10-15 kHz) power• Supply to the transducer for conversion into

mechanical motion.

A

Transducer

• Two types of transducers are used in USM to convert the supplied energy to mechanical motion.

• They are based on two different principles of operation - Magnetostriction - Piezoelectricity

B

- Magnetostriction

• When the material is placed in a sufficiently strong magnetic field, the magnetic moments of the domains rotate into the direction of the applied magnetic field and become parallel to it.

• During this process the material expands or contracts, until all the domains have become parallel to one another.

• very common magnetostrictive composite is the amorphous alloy Fe81Si3.5B13.5C2 with its trade name Metglas 2605SC

- Piezoelectric transducers

• Such as quartz or lead,zirconate,titanate, generate a small electric current when compressed.

• Conversely, when an electric current is applied, the material increases minutely in size.

• When the current is removed, the material instantly returns to its original shape.

Toolholder/ Acoustic head • Its function is to increase the tool vibration amplitude and to match

the vibrator to the acoustic load. • It must be constructed of a material with good acoustic properties

and be highly resistant to fatigue cracking.

C

Monel and titanium have good acoustic properties and are often used together with stainless steel, which is cheaper.

The acoustic head can be of different shape like

• Tapered or conical• Exponential• Stepped

Exponential tapered stepped

Different Horns used in USM

The acoustic head is the most complicated part of the machine.

It must provide a static force, as well as the high frequency vibration

• Tools should be constructed from relatively ductile materials. • The harder the tool material, the faster its wear rate will be. • It is important to realize that finishing or polishing operations on the

tools are sometimes necessary because their surface finish will be reproduced in the workpiece.

ToolsD

- The geometry of the tool• The geometry of the tool generally corresponds to the geometry of the cut

to be made, • Because of the overcut, tools are slightly smaller than the desired hole or

cavity • Tool and toolholder are often attached by silver brazing.

AbrasivesE

• liquid - water most common - benzene - glycerol - oils - high viscosity decreases MMR

• Abrasive Slurry - common types of abrasive - boron carbide (B4C) good in general, but expensive

- silicon carbide (SiC) glass, germanium, ceramics - corundum (Al2O3)

- diamond (used for rubies , etc) - boron silicon-carbide (10% more abrasive than B4C)

Applications

It is mainly used for (1) drilling (2) grinding,(3) Profiling(4) coining (5) piercing of dies (6) welding operations on all materials which can be treated suitably by

abrasives. (7) Used for machining hard and brittle metallic alloys, semiconductors,

glass, ceramics, carbides etc.(8) Used for machining round, square, irregular shaped holes and surface

impressions.

Advantages of USM

• Machining any materials regardless of their conductivity

• USM apply to machining semi-conductor such as silicon, germanium etc.

• USM is suitable to precise machining brittle material.

• USM does not produce electric, thermal, chemical abnormal surface.

• Can drill circular or non-circular holes in very hard materials

• Less stress because of its non-thermal characteristics

Disadvantages of USM

• USM has low material removal rate. (3-15mm3/min)

• Tool wears fast in USM.

• Machining area and depth is restraint in USM.

• Mechanics of material removal - brittle fracture caused by impact of abrasive grains due to vibrating at high frequency

• Medium - slurry • Abrasives: B4C; SiC; Al2O3; diamond; 100-800 grit size • Vibration freq. 15-30 KHz, amplitude 25-100 micro m• Tool material soft steel , ductile• Critical parameters - frequency, amplitude, tool material, grit size, abrasive

material, feed force, slurry concentration, slurry viscosity • Material application - metals and alloys (particularly hard and brittle),

semiconductors, nonmetals, e.g., glass and ceramics • Shape application - round and irregular holes, impressions • Limitations - very low mrr, tool wear, depth of holes, and cavities small.

Summary of USM

Quiz test

1. Which of the following material is not generally machined by USM (i) Copper (ii) Glass (iii) Silicon (iv) Germanium

2. Tool in USM is generally made of(i) Glass (ii) Ceramic (iii) Carbides (iv) Steel

4. USM can be classified as the following type of non-traditional process (i) Electrical (ii) optical (iii) mechanical (iv) chemical

3. Increasing volume concentration of abrasive in slurry would affect MRR inthe following manner (i) increase MRR (ii) decrease MRR (iii) would not change MRR (iv) initially

decrease and then increase MRR

1- (i)

2 – (iv)

3 – (i)

4 – (iii)

Problems

Soln. to Prob. 1

References

• Module 9 Non-conventional machining IIT Kharagpur

• http://nptel.iitm.ac.in/• http://

en.wikipedia.org/wiki/Ultrasonic_machining• www.youtube.com/watch?v=XXm4Cf_N9CA• http://www.bullentech.com/animation

Both of thank’s