In ultrasonic machining, the material is removed by mechanical action. This process involves the use of high-frequency vibrations generated by an ultrasonic generator. These vibrations are then transmitted to a tool called a sonotrode, which is pressed against the workpiece. The vibrations of the sonotrode cause the abrasive particles present in a slurry to impact the workpiece, resulting in the removal of material.

Here is a detailed explanation of the material removal process in ultrasonic machining:

1. High-frequency vibrations: An ultrasonic generator produces high-frequency vibrations, typically in the range of 20 kHz to 50 kHz. These vibrations are transmitted to the sonotrode.

2. Sonotrode: The sonotrode is a specially designed tool made of a high-strength material such as titanium or steel. It is brought into contact with the workpiece surface.

3. Slurry: A slurry is a mixture of abrasive particles and a liquid medium. The slurry is continuously supplied to the machining zone between the sonotrode and the workpiece. It acts as a medium for transmitting the vibrations and carrying away the debris.

4. Material removal: When the sonotrode vibrates at high frequency, the abrasive particles in the slurry start impacting the workpiece surface. The repeated impacts of the abrasive particles cause the removal of material from the workpiece. The material removal rate depends on factors such as the vibration amplitude, the slurry composition, and the applied pressure.

5. Debris removal: As material is removed, debris is generated. The slurry helps in carrying away the debris from the machining zone. It also acts as a coolant, reducing the heat generated during the machining process.

6. Precision machining: Ultrasonic machining is capable of achieving high precision in the machined surface. The vibrations can be controlled to produce intricate shapes and fine details.

Advantages of ultrasonic machining:
- Can be used for a wide range of materials, including hard and brittle materials.
- Does not generate heat, minimizing the risk of thermal damage to the workpiece.
- Can machine complex shapes with high precision.
- Does not require high cutting forces, reducing the risk of workpiece deformation.

In conclusion, ultrasonic machining is a process in which material is removed by the mechanical action of high-frequency vibrations. These vibrations cause abrasive particles in a slurry to impact the workpiece surface, resulting in material removal. This process is particularly useful for machining hard and brittle materials with high precision.