Ultrasonic Machining (USM) Working Principles

In this process the material of the workpiece is removed by the repetitive impact actions of abrasive particles. The erosion takes place by the abrasive particles which are carried by a liquid medium in the from of a slurry . A shaped vibrating tool is used to produce the impact. The term shaped is used to explain that the process is capable enough to create 3D profiles in correspondence to the tool shape which is not possible in AJM. The tool gets the vibrating motion from the vibrating mechanical horn.  Here is a schematic diagram of the basic system.   


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Ultrasonic Machining (USM) Principles

Working principle of Ultrasonic Machining  or Ultrasonic Impact Grinding is described with the help of a schematic diagram. The shaped tool under the actions of mechanical vibration causes the abrasive particles dipped in slurry to be hammered on the stationary workpiece. This causes micro-indentation fracture on th material. 

Small abraded particles are removed along the surface which is perpendicular to the direction of the tool vibration. When the material is removed a cavity of the same profile of the tool face is formed. The abrasive particles gradually erodes as the machining process continues. As a result fresh abrasive particles are needed to be supplied in the machining zone. Abrasive particles associated with the liquid is fed to the m/c zone and it ensures the removal of the worn out grains and material. 

Machining Time 

The machining time of the ultrasonic grinding depends on the frequency of the vibration, material properties and grain size.  The amplitude of the vibration may vary from 5 to 75 µm and frequency may vary from 19~25 kHz. Ample static force is also required to hold the job against the machining tool . A continues flow of abrasives suspension is also mandatory.

  

Advantages of USM:

1. It can be used to drill circular or non-circular holes on very hard materials like stones, carbides, ceramics and other brittle materials.
2. Non-conducting materials like glass, ceramics and semi precious stones can also be machined. 

Disadvantages of Ultrasonic Machining  :

1. It can be proved slower than the conventional machining processes. 

2. Creating deep holes is difficult because of the restricted movement of the suspension. 

3. It is arduous to select the perfect tool geometry for creating hole of certain dimension. The holes created may be of larger sizes because of side cutting.  

4. High tool wear because of continues flow of abrasive slurry. 

Applications:

1. Hard and brittle materials can be machined like tungsten carbide, diamond and glass. These are difficult to machine in conventional m/c-ing process.
2. Wire drawing dies of tungsten carbide can be drilled by this process.  

3. Circular as well as non-circular holes can  be done with straight or curved axes.
4. It has been proved successful in machining geranium, silicon quartz and synthetic ruby etc. 

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