What is ULTRASONIC MACHINING ?

 

What is meant by "ULTRASONIC"?

Ultrasonic is the science of sound waves of above the limits of human audibility.

OR

Ultrasound is a sound with a pitch so high that it can not be heard by the human ear.

Which normally starts from 20 KHz , and than exceeds.

Fact

The standard hearing range for humans is 20 to 20,000 Hz.

But

Some animals like dogs, dolphins, and frogs can hear ultrasonic sounds.

Pitch:

COMPARISON:

History:

v  The first useful description of technique of ultrasonic machining was given in the 1940’s (Balmuth 1945).

 

v   in 1964, first ultra-sonic machining tool was mostly on the basis of drilling and milling has been build up by Rosenberg.

v   The German company first used a diamond coated milling, boring and grinding tool.

Types of USM:

•       Chemical-Assisted USM: 

In this machining, a chemically reactive abrasive fluid is used for the machining process.

•       Rotary Ultrasonic vibration machining (RUM): 

In RUM, a vertically rotating tool is allowed to revolve about the axis of the sonotrode. The surface of the tool is impregnated with diamonds that is used to grind down the surface of the work-piece. Abrasive slurry is not used in this type of machine for material removal.

Introduction:

v  The tool oscillates at high frequency and is fed into the work piece by a constant force. An abrasive slurry comprising water and small abrasive particles is supplied between the tool tip and the work piece material removal occurs when the abrasive particles suspended in the slurry between the tool and work piece, impact the work piece due to the down stroke of the vibrating tool. 

Main Parts:

The ultrasonic machining machine consist of two main parts transducer and sonotrode (also called as horn), connected to an Electronic control unit with cables.

1. Transducer: The transducer mainly consists of a cylinder which is made up of piezoelectric ceramic. It converts electrical energy into mechanical vibration. Transducer then vibrates sonotrode at low amplitude and high frequency.

2. Sonotrode: It is made of low carbon steel. One end of it is connected with the transducer and other end contains tool. The sonotrode vibrates at low amplitude and high frequency and removes material from the w/p.

 3. Control Unit: The control unit consists of an electronic oscillator which produces an alternating current at high frequency. The frequency produced is usually in between 20 kHz to 40 kHz. (in ultrasonic range)

 

Working of USM

»      The electronic oscillator and amplifier also known as the generator.

»      It converted low frequency electrical energy in the high frequency power.

»      It is supplied to the transducer.

»      Transducer operate by magnetic friction

»      Transducer is connected to the tool

 

Fact

USM were considered as non traditional cutting machines because it wasn’t the tool which cut the metal actually abrasive particles were responsible for that.

 Abrasives

Abrasives Slurry:

»      Abrasives

                 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

»      Liquid

                               - Water most common

                               - Benzene

                               - Glycerol

                               - Oils

 Tool Characteristics:

˃     Tool material should be tough and ductile. Low carbon steels and stainless steels give good performance.

˃     Tools are usually 25 mm long ; width =twice the size of abrasives.

˃     Mass of tool should be minimum possible so that it does not absorb the ultrasonic energy.

Fact

A cutting tool being used in USM should be ductile.

Tool Samples:

Merits of USM:

»      Materials difficult to machine on conventional machine  can be machined with good accuracy and surface finish.

»      USM is suitable to precise machining brittle material.

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

»      Less stress because of its non-thermal characteristics.(stress free component)

»      Can drill circular or non-circular holes in very hard materials.

Fact

A drilled hole can either be circular or non-circular .

Demerits of USM:

»      Equipment is more costly than that of conventional machining process.

»      High tooling cost.

»      USM has low material removal rate. (3-15mm/min)

»      Tool wears fast in USM.

»      Abrasive slurry need be replaced periodically.

Applications: 

It is mainly used for

(1) drilling

(2) Surface grinding

(3) Profiling

(4) coining

(5) piercing of dies

(6) Threading,

(7) slot cutting

(8)    Used for machining round, square, irregular shaped holes and surface impressions.

       Etc.

Fact

We can perform Micro drilling of holes up-to 0.1mm diameter by using USM.