Ultrasonic Machining (USM)

Ultrasonic machining or USM, Principle of Ultrasonic Machining, Working of Ultrasonic Machining, Advantages of Ultrasonic Machining, Limitations of Ultrasonic Machining, Applications of Ultrasonic Machining

               Ultrasonic waves are sound waves that have frequency above that of the upper frequency limit of the human ear [audible range] i.e., generally above 20 kHz. Ultrasonic machining [USM] is a modern metal removal process for brittle and hard materials which may be either conducting or non-conducting, by using high frequency oscillations of a shaped toot using abrasive slurry.

Principle of Ultrasonic Machining:

            In ultrasonic machining, a tool is made to vibrate or oscillate at ultrasonic frequency [20 to 30 kHz] in a direction normal to the surface being machined. The tool, while oscillating would be pressed against the workpiece and fed continuously. As the tool vibrates with a specific frequency, an abrasive slurry, usually a mixture of abrasive grains [boron carbide or silicon oxide] and water is made to flow under pressure through the tool-workpiece interface. The impact force arising out of vibration of the tool end and the flow of slurry through the work-tool interface, actually causes thousands of microscopic grains to remove the work material by abrasion or erosion. The tool has the same shape as the cavity to be machined. The limitation of USM is less material removal rate.

Working of Ultrasonic Machining:

                The workpiece is held in a fixture which is placed in a tank filled with abrasive slurry. The electronic oscillator is switched on, so that it converts the available electrical energy of low frequency to high frequency and supplies them to transducer. The transducer generates the high frequency vibrations in order of 20 to 30 KHz with an amplitude of the order of 0.02 mm. This vibration is transmitted to the tool through a tool holder. The tool shape is a close complementary shape of the final surface to be generated. The tool, while oscillating would be pressed against the workpiece and fed continuously. Simultaneously the abrasive slurry is pumped with the help of the pump between the tool and the work piece gap. Abrasive particles are driven into the work surface by the oscillating tool and removes material from the workpiece. As the material is removed, the tool is gradually advanced into the workpiece by a servomechanism, so that a constant gap is maintained between the tool and workpiece. Finally, the shape of the tool is impressed into the workpiece as shown below.

Advantages, Limitations & Applications of Ultrasonic Machining

Advantages of Ultrasonic Machining:

• Brittle materials can be machined.

• Both metals and non-metals can be machined.

• Both conductive and non-conductive materials can be machined.

• An accuracy of 0.003 mm can be obtained.

• The work piece is not subjected to heat and hence no thermal stresses.

• Tooling cost is less.

• The process is safe.

• Un-skilled labour can handle the machine.

Limitations of Ultrasonic Machining:

• Not useful for soft work materials.

• Low metal cutting rates.

• High power consumption.

• The depth of cylindrical holes is limited to 2.5 times the diameter of the tool.

Applications of Ultrasonic Machining:

• Production of hard alloy tools for upsetting, deep drawing etc.

• Manufacturing press tools.

• Production of watch bearings and jewels.

• Drilling holes in diamonds.

• Machining components made of glass, quartz, germanium, ceramics etc.

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