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ULTRASONIC MACHINING(USM)

Presenters : Adeel Shehzad2009-MS-IME-07

Omer Asghar 2010-MS-IME-14

Presented to : Prof.Dr Nadeem A Mufti

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What is USM

USM is able to effectively machine all hard materials whether they are electrically conductive or not.

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Principle Of USM

The process and cutting tool• 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.

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Ultrasonic Machining

Principle Of USM

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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.

Principle Of USM

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Material removal

Principle Of USM

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Principle Of USM

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)

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The impact of the abrasive on the work2

Cavitation induced erosion3

Chemical erosion caused by slurry4

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USM System

1-Vibration Exciter2-Body Of Acoustic Head 3-Shoulder 4-Thin Walled Cup 5-Generator 6-Concentrator 7-Tool 8-Plate 9-Tray10-Workpiece 11-Base Guide

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Subsystems of USM System

USM System

USM System

B

E

C

D

APower supply

Transducer

Toolholder

Abrasive Tools

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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.

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USM System

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Transducer• The ultrasonic vibrations are produced by the transducer. The

transducer is driven by suitable signal generator followed by power amplifier. The transducer for USM works on the following principle – Piezoelectric effect – Magnetostrictive effect – Electrostrictive effect

• Among all the above types of transducers Magnetostrictive transducers are most popular and robust amongst all.

USM System

B

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Toolholder

• 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.

• The tool holder transfers the vibrations and, therefore it must have adequate fatigue strength

USM System

C

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Toolholder • Monel and titanium have good acoustic properties and are often used

together with stainless steel, which is cheaper. • However, stainless steel has acoustical and fatigue properties that are

inferior to those of Monel and titanium, limiting it to low amplitude applications.

• Amplifying toolholders have a cross section that diminishes toward the tool, often following an exponential function.

• An amplifying toolholder is also called a concentrator.

USM System

C

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• 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.

Tools

USM System

D

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- 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.

Tools

USM System

D

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• The criteria for selection of an abrasive for a particular application include hardness, usable life, cost, and particle size.

• Diamond is the fastest abrasive, but is not practical because of its cost.

• Boron carbide is economical and yields good machining rates. • Silicon carbide and aluminum oxide are also widely used.

Abrasives

USM System

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- Grain size

• Coarse grits exhibit the highest removal rates,when the grain size becomes comparable with the tool amplitude, cut more slowly.

• The larger the grit size, the rougher the machined surface.

Abrasives

USM System

E

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• The slury consists of small abrasives particles mixed with water or oil in concentration of 30% to 60% by weight.

• But thinner mixtures are used to promote efficient flow when drilling deep holes or when forming complex cavities.

- Abrasive concentration

Abrasives

USM System

E

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The ultrasonic vibration machining method is an efficient cutting technique for difficult-to-machine materials. It is found that the USM mechanism is influenced by these important parameters. Amplitude of tool oscillation(a0) ( 15 -50 µm) Frequency of tool oscillation(f) (19 KHz – 25 KHz) Tool material ( soft steel titanium alloy) Type of abrasive (Silicon carbide, aluminum oxide, Boron carbide ) Grain size or grit size of the abrasives – d (100- 800)Contact area of the tool – A Volume concentration of abrasive in water slurry – C Ratio of workpiece hardness to tool hardness; λ=σw/σt The machines have a power rating of 0.2-2.5 kW

Parameters of Ultrasonic Machining

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USM can be applied to machine nearly all materials; however it is not economical to use USM for materials of hardness less than 50 HRC. Generally the workpiece materials are of stainless steel, cobalt-base heat-resistant steels, germanium, glass, ceramic, carbide, quartz and semiconductors. It is highly useful in the machining of materials that cannot be machined by any conventional machining process that are ceramic and glass. Tool vibrations also affect the removal rate. The type of abrasive, its size and concentration also directly affect the MRR.

Material removal Rate

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Effect Of Different Parameters On Material Removal Rate

MRR vs Grain Size of abrasive MRR vs Frequency

MRR vs Ratio of Work piece MRR vs Concentration of Abrasivehardness to tool hardness

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UM effectively machines precise features in hard, brittle materials such as glass ,engineered ceramics , SiC- Chemical Vapor Deposition Silicon Carbide ,quartz , PCD - Polycrystalline diamond, ferrite, graphite, glassy carbon , composites ,piezoceramics .A nearly limitless number of feature shapes—including round, square and odd-shaped thru-holes and cavities of varying depths can be machined with high quality and consistency. Aspect ratios as high as 25-to-1 are possible, depending on the material type and feature size. USM machined surfaces exhibit a good surface integrity and the compressive stress induced in the top layer enhances the fatigue strength of the workpiece. The quality of an ultrasonic cut provides reduced stress and a lower likelihood of fractures.

Advantages

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Unlike other non-traditional processes such as laser beam, and electrical discharge machining, etc., ultrasonic machining does not thermally damage the workpiece or appear to introduce significant levels of residual stress, which is important for the survival of brittle materials in service. Unlike conventional machining methods, ultrasonic machining produces little or no sub-surface damage and no heat-affected zone.

This machining process is nonthermal, nonchemical, and nonelectrical. It does not change the metallurgical, chemical or physical properties of the workpiece.

Advantages

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Material removal rates is quite low, usually less than 50 mm3/min. The abrasive slurry also "machines" the tool itself, thus causing high

rate of tool wear , which in turn makes it very difficult to hold close tolerances .The machining area and the depth of cut are quite restricted .

Disadvantages

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Ultrasonic machining is ideal for certain kinds of materials and applications. Brittle materials, particularly ceramics and glass, are typical candidates for ultrasonic machining. Ultrasonic machining is capable of machining complex, highly detailed shapes and can be machined to very close tolerances (±0.01 mm ).Complex geometric shapes and 3-D contours can be machined with relative ease in brittle materials. Multiple holes, sometimes hundreds, can be drilled simultaneously into very hard materials with great accuracy.

Applications

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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

Various Work Samples Machined By USM