ULTRASONIC MACHINING

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Ultrasonic machining(USM) is one of the non-traditional machining process.

Working principle: In this process,abrasives contained in a slurry are driven at high velocity against the work piece by a tool vibrating at low amplitude and high frequency. Amplitude is kept of the order of 0.07 mm and frequency is maintained at approximately 20,000 Hz. The work piece material is removed in the form of extremely small chips. Normally, very hard particle dust is included in the slurry like, Al₂O₃,silicon carbide, boron carbide or diamond dust. Working principle of USM is same as that of conventional machining that is material of work piece is removed by continuous abrasive action of hard particles vibrating in the slurry. Abrasive slurry acts as a multi point cutting tool and does the similar action as done by a cutting edge.

Process Details: USM process is indicated in line diagram as shown in the figure:

Abrasive Slurry: Abrasive slurry consists of dust of very hard particles. It is filled into the machining zone.Abrasive slurry can be recycled with the help of pump.

Work piece: Work piece of hard and brittle material can be machined by USM. Work piece is clamped on the fixture I the setup.

Cutting Tool: Tool of USM does not do the cutting directly but it vibrates with small amplitude and high frequency. So it is suitable to name the tool as vibrating tool rather than cutting tool. The tool is made of relatively soft material and used to vibrate abrasive slurry to cut the work piece material. The tool is attached to the Arbor (tool holder) by brazing or mechanical means. Sometimes hollow tools are also used which feed the slurry focusing on to machining zone.

Ultrasonic Oscillator: This operation uses high frequency electric current which passes to an ultrasonic oscillator and ultrasonic transducer. The function of the transducer is to convert electric energy into mechanical energy developing vibrations into the tool.

Feed Mechanism: Tool is fed to the machining zone of work piece. The tool is shaped as same to the cavity of be produced into the work piece. The tool is fed to the machining area. The feed rate is maintained equal to the rate of enlargement of the cavity to be produced.

Applications of USM: This process is generally applied for the machining of hard and brittle materials like carbides, glass, ceramics, precious stones, titanium, etc. It is used for tool making and punch and die making. The work piece material is normally removed in the form of very find chips, so generated surface quality is extremely good. It is widely used for several machining operations like turning, grinding and milling, etc. It can make hole of round shape and other shapes.

Advantages of USM:

(a) Its main advantage is that work piece after machining is free from any residual stresses.

(b) Extremely hard and brittle materials can be machined, whose machining is very difficult by conventional methods.

(c) Very good dimensional accuracy and surface finish can be obtained.

(d) Operational cost is low.

(e) The process is environmental friendly as it is noiseless and no chemical and heating is used.

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‍Disadvantages of USM:

(a) Its metal re movalrate (MRR) is very low and it can not be used for large machining cavities.

(b) Its initial setup cost and cost of tool is very high, frequently, tool replacement is required a stool wear takes place in this operation.

(c) Not recommended for soft and ductile material due to their low ductility.

(d) Power consumption is quite high.

(e) Slurry may have to be replaced frequently.

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