Ultasonic Machining Process

7/18/2019 Ultasonic Machining Process

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Chapter Ⅰ USMChapter Ⅰ USM



USM is able to efectively machine all hard materialwhether they are electrically conductive or not.



The process and cutting toolThe process and cutting tool

• The process is performed by a cutting tool, which oscillates athigh frequency, typically 20-40 kH, in abrasi!e slurry"

• The shape of the tool corresponds to the shape to be

produced in the workpiece"• The high-speed reciprocations of the tool dri!e the abrasi!e

grains across a small gap against the workpiece .

• The tool is gradually fed with a uniform force"

• The impact of the abrasi!e is the energy principallyresponsible for material remo!al in the form of small wearparticles that are carried away by the abrasi!e slurry"

• The tool material, being tough and ductile, wears out at amuch slower rate"



Ultrasonic MachiningUltrasonic Machining



Elements of ultrasonic machiningElements of ultrasonic machining

• The tool is oscillated by alongitudinal magnetostriction

• # magnetic field !ariation at

ultrasonic frequencies

• The length of a ferromagnetic

ob$ect changes



Material removalMaterial removal

• %ccurs when the abrasi!e particles, suspended in theslurry between the tool and workpiece, are struck by thedownstroke of the !ibration tool"

• The impact propels the particles across the cutting gap,hammering them into the surface of both tool and

workpiece" &ollapse of the ca!itation bubbles in the

abrasi!e suspension results in !ery high local pressures"

• 'nder the action of the associated shock wa!es on the

abrasi!e particles, microcracks are generated at the

interface of the workpiece"

• The effects of successi!e shock wa!es lead to chipping of

particles from the workpiece"



Material removalMaterial removal



The basic components to the cuttingThe basic components to the cutting

action are believed to beaction are believed to be



• (mall, tabletop-sied units to large-capacity machinetools,

• )ench units, and as self-contained machine tools"

• *ower range from about 40 + to 2" k+"

• The power rating strongly influences the materialremo!al rate"



Subsystems of USM SystemSubsystems of USM System

BB

EE

CC

DD

AA



• The power supply is a sine-wa!e generator

• The user can control o!er both the frequency and power of thegenerated signal"

• t con!erts low-frequency .0/0 H1 power to high-frequency.0- kH1 power

• (upply to the transducer for con!ersion into mechanical

motion"

AA



• Two types of transducers are used in '(3 to con!ert the

supplied energy to mechanical motion"• They are based on two different principles of operation

- 3agnetostriction

- *ieoelectricity

BB



• 3agnetostricti!e transducers are usually constructed from alaminated stack of nickel or nickel alloy sheets"

• 3agnetostriction is eplained in terms of domain theory "

BB



• 5omains are !ery small regions, of the order of l0-6 7 l0-8 cm9,

• n which there are forces that cause the magnetic moments of the

atoms to be oriented in a single direction"

• n each domain the atomic magnetic moments are oriented in one

of the directions of easy magnetiation

BB



• n the cubic-lattice crystals of iron and nickel there are

si directions of easy magnetiation"

• n unmagnetied material all these directions are

present in equal numbers, the magnetic moments of the

orderless, unorientated domains compensate oneanother

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• +hen the material is placed in a sufficiently strongmagnetic field, the magnetic moments of the domainsrotate into the direction of the applied magnetic fieldand become parallel to it"

• 5uring this process the material epands or contracts,until all the domains ha!e become parallel to oneanother"

BB



• #s the temperature is raised, the amount of

magnetostricti!e strain diminishes "

• 3agnetostricti!e transducers require cooling by fans or

water"

BB



• (uch as quart or lead,irconate,titanate, generate a small

electric current when compressed"

• &on!ersely, when an electric current is applied, the

material increases minutely in sie"

• +hen the current is remo!ed, the material instantlyreturns to its original shape"

BB



• *ieoelectric materials are composed of small particles boundtogether by sintering"

• The material undergoes polariation by heating it abo!e the

&urie point"

• (uch transducers ehibit a high electromechanical con!ersionefficiency that eliminates the need for cooling"

BB



• The magnitude of the length change is limited by the

strength of the particular transducer material"

• The limit is approimately 0"02 mm"

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• ts function is to increase the tool !ibration amplitudeand to match the !ibrator to the acoustic load"

• t must be constructed of a material with good acousticproperties and be highly resistant to fatigue cracking"

CC



• 3onel and titanium ha!e good acoustic properties and are oftenused together with stainless steel, which is cheaper"

• Howe!er, stainless steel has acoustical and fatigue properties thatare inferior to those of 3onel and titanium, limiting it to lowamplitude applications"

• :onamplifying holders are cylindrical and result in the samestroke amplitude at the output end as at the input end"

• #mplifying toolholders ha!e a cross section that diminishestoward the tool, often following an eponential function"

• #n amplifying toolholder is also called a concentrator"

CC



• #mplifying holders remo!e material up to 0 times fasterthan the nonamplifying type"

• The disad!antages of amplifying toolholders includeincreased cost to fabricate, a reduction in surface finishquality, and the requirement of much more frequent runningto maintain resonance"

CC



• Tools should be constructed from relati!ely ductile

materials"

• The harder the tool material, the faster its wear rate will

be"

• t is important to realie that finishing or polishing

operations on the tools are sometimes necessary because

their surface finish will be reproduced in the workpiece"

DD



• The geometry of the tool generally corresponds to thegeometry of the cut to be made,

• )ecause of the o!ercut, tools are slightly smaller thanthe desired hole or ca!ity

• Tool and toolholder are often attached by sil!er braing"

DD



• The criteria for selection of an abrasi!e for a particular

application include hardness, usable life, cost, and particlesie"

• 5iamond is the fastest abrasi!e, but is not practical because of

its cost"

• )oron carbide is economical and yields good machining rates"

• (ilicon carbide and aluminum oide are also widely used"

EE



• &oarse grits ehibit the highest remo!al rates,when the grainsie becomes comparable with the tool amplitude, cut moreslowly"

• The larger the grit sie, the rougher the machined surface"

EE



• +ith an abrasi!e concentration of about 0; by weight

in water ， but thinner mitures are used to promote

efficient flow when drilling deep holes or when forming

comple ca!ities"

EE



EE



ExampleExample

• <ind the machining time for a hole mm in diameter in a

tungsten carbide plate cm thick"• The grains are 0"0mm in diameter, the feed force is 9:, and

the amplitude of oscillation is 20 micro m at a frequency of

2=H"

• The fracture hardness is approimately 800:/mm2"

• The slurry is mied in equal parts water and abrasi!e"



ExampleExample

The acoustic head is the

most complicated part of

the machine"

t must pro!ide a static

force, as well as the highfrequency !ibration



- Basic machine layout- Basic machine layout

ExampleExample

3agnetostricti!e materials should ha!e a good coupling of

magnetic and mechanical energy



Basic machine layoutBasic machine layoutExampleExample





• f a tool is designed to increase flow, better cutting speeds willoccur"

• Tools

- hard but ductile metal

- stainless steel and low carbon

- aluminum and brass tools wear near to 0 times faster

• #brasi!e (lurry

- common types of abrasi!e

- boron carbide .)4&1 good in general, but epensi!e- silicon carbide .(i&1 glass, germanium, ceramics

- corundum .#l2%91

- diamond .used for rubies , etc1

- boron silicon-carbide .0; more abrasi!e than )4&1



• liquid- water most common

- benene

- glycerol

- oils• high !iscosity decreases mrr

• typical grit sie is 00 to 600

>ittle production of heat and stress, but may chip at eitside of hole"

(ometimes glass is used on the back side for brittle

materials"



• 3echanics of material remo!al - brittle fracture caused by impact ofabrasi!e grains due to !ibrating at high frequency

• 3edium - slurry

• #brasi!es? )4&@ (i&@ #l2%9@ diamond@ 00-600 grit sie

• Aibration freq" -90 =H, amplitude 2-00 micro m

• Tool material soft steel

• 3aterial/tool wear B " for +& workpiece, 00 for glass

• Cap 2-40 micro m

• &ritical parameters - frequency, amplitude, tool material, grit sie,abrasi!e material, feed force, slurry concentration, slurry !iscosity

• 3aterial application - metals and alloys .particularly hard and brittle1,

semiconductors, nonmetals, e"g", glass and ceramics

• (hape application - round and irregular holes, impressions

• >imitations - !ery low mrr, tool wear, depth of holes, and ca!ities small"



" # cylindrical impression with a diameter of 0mm and a depthof mm has to be made on a tungsten carbide surface" Thefeed force is constant and equal to :" The a!erage diameterof the grains in the abrasi!e slurry is 0"0mm" The tooloscillates with an amplitude of 90 micro m at 20 =H" Theslurry contains part of abrasi!e to about part of water" Thefracture hardness of tungsten carbide workpiece may betaken as D000 :/mm2" Estimate the machining time"



2" # square through hole of mm by mm has to be drilled in amm thick tungsten carbide sheet" The slurry is made of part of 0 micro m radius boron carbide grains mied with "parts of water" The feed force is 4:" The tool oscillates with an

amplitude of 0"0mm at 2=H" #ssuming that only 20; ofthe pulses are effecti!e, calculate the time required tocomplete the $ob"

9" n an E&3 operation, a pure copper block is being machined"f a current of 000# is used, determine the !olume rate of

material remo!al from the copper block"



4" The composition of a :imonic alloy turbine blade is 6;

cobalt, 2; :i, and 20; chromium" t is being machined

electrochemically with a current of 00#" <ind out the !olume

remo!al rate if the density of the alloy is 6"9g/cm9" The

dissolution !alency of chromium is , whereas that for both

nickel and cobalt is 2"

" The composition of a monel alloy workpiece undergoing

electrochemical machining is as gi!en here? 9; :i, 9"D; &u, 2"; <e, 2; 3n, 0"; (i, 0"9; &

if the machining current is 000#, estimate the !olume

remo!al rate"



" The equilibrium gap when machining .electrochemically1 iron,

using :a&l solution in water as the electrolyte, is found to be

0"2mm" The current density is 200#/cm2, the operating

!oltage being 2A" ron dissol!es at a !alency 2, the density ofiron is D"6 g/cm9, and the specific resistance of the electrolyte

is 2"6 ohm cm" &alculate the metal remo!al rate/unit work

surface area" The o!er!oltage may be taken as "A"



D" n an electrochemical trepanning operation on a flat ironsurface, an electrode in the form of a tube .with an outerdiameter of cm1" # laser beam with a power intensity of

2 F 0 +/mm2 is used to drill a 0"2mm diameter hole in atungsten sheet of 0"4mm thickness" f the efficiency of theoperation is only 0;, estimate the time required"

6" TG'E / <#>(E - +ater is the main cutting tool in 'ltra

(onic machining"

8" +hy are the !ibrations in '(3 so small



0" '(3 will be used to add the following pattern to an ob$ect,

f the tool is Tungsten carbide, and the work is &u, with an

amplitude of oscillation of 0 Im, at 90=H, how long will the

operation take .:ote? the grain diameter is 20Im, and thehead has a static force of :1



" +hen is the abrasi!e added into the flow for the !arious

abrasi!e $et machining processes

2" +hy is the depth of material remo!ed by abrasi!e $etmachining so !ariable

9" 5escribe the ability of the abrasi!e processes to

produce sharp corners"

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Ultasonic Machining Process