Ultrasonic Machining USM Equipment Elements and Working

ultrasonic machining
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Ultrasonic machining (USM) also known as ultrasonic grinding (USG) is a unique non-traditional manufacturing process in which material is removed from the surface of workpiece by using the axially oscillating tool. The tool is vibrating at high frequency and low amplitude in the presence of fine abrasive particles. USM is used in precision machining of hard and brittle material. It can achieve dimensional accuracy up to ±0.005mm.

Construction or parts of ultrasonic machining equipment

The figure shows a schematic diagram of ultrasonic machining equipment. The main elements of this equipment are listed below

1. High-frequency generator
An electronic oscillator is used to generate high-frequency alternating current. The frequency is in the ultrasonic range (20-40KHz).

2. Transducer to generate vibration.
Transducer used in USM converts the electrical energy into mechanical vibration. There are mainly two types of transducer is used in USM; piezoelectric transducer or magnetostrictive transducer.

Piezoelectric transducer: Piezoelectric crystal such as barium titanate is vibrated when applying alternative current. It converts electrical energy to mechanical energy at high efficiency (above 90%) without any cooling.

Magnetostrictive transducer: Ferromagnetic material like nickel alloys place inside the coil of wire. The alternating current passes through the coil create an alternating magnetic field. Magnetostriction effect creates the vibrational movement. It requires water cooling to remove waste heat. The efficiency of this kind of transducer is low (25-30%).

3. Transformer or concentrator to amplify the vibration at the output of transducer.
The amplitude of vibration at the output of transducer is inadequate to the cutting process. Mechanical amplifier known as concentrator/ sonotrode is used to amplify the available vibration. Transformer is in taper shape, the reduction of crossectional area causes the amplification of vibration, and provide intense vibration of desired amplitude at cutting end. The amplitude may increase up to 600%.

4. Tool in a tool holder
Tool is made of ductile material like mild steel, brass to reduce the tool wear. They are fastened to the tool holder by brazing to reduce fatigue. The cavity produced in workpiece has the same geometry of tool.

5. Abrasive slurry feeding arrangement
A constant stream of abrasive suspension is flowed between to tool and workpiece. This slurry consists of abrasive material like boron carbide, silicon carbide, diamond dust, etc. mixed with water or oil. The abrasive grit size is usually in the range of 100-1000 mesh size. The smaller size gives smoother surface finish, larger grain results faster machining. The flow of slurry carried away the debris during the machining. The slurry is cooled down by a cooling system.

Working of ultrasonic machining equipment and working principle

An electronic oscillator used to produce an alternating current of high frequency at the ultrasonic range. This electrical energy then used to energize the transducer which converts electric energy into mechanical vibration. The small amplitude and high-frequency vibration produced in transducer then amplify using a mechanical amplifier that holds the tool, known as concentrator.

The abrasive slurry is pumped between the oscillating tool and workpiece. The slurry is continuously pumped to the tool-workpiece interface to efficient flushing of debris and to cool down the machining zone. Marching of soft material can be achieved without using slurry by using a chisel type tool tip. Then it is called dry ultrasonic machining. [What is the difference between dry ultrasonic machining and wet USM?]

🔗Factors affecting ultrasonic machining
🔗Applications, advantages and disadvantages of ultrasonic machining

The material removed by the abrasive action of slurry and impact force due to the vibration of tool. The ultrasonic oscillation of tool hammered the abrasive particle to the surface of the workpiece, it causes chipping of minute particles of the workpiece. The oscillating tool imposes a static pressure on abrasive slurry and feeds down to the workpiece to form a required shape.

In USM the material removal happened in three ways

1. Mechanical abrasion by the direct hammering of abrasive particle to workpiece. It is the dominant mechanism involved in USM.

2. Microchipping due to free impacting of particle that flies across during the machining and hit the workpiece at random location.

3. Erosion of workpiece due to cavitation of the slurry stream. Less than 5 percentage of material removed by cavitation.

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