The process utilizing mainly thermal energy for removing material is Laser Beam Machining.

Explanation:
Laser Beam Machining (LBM) is a non-contact machining process that utilizes a high-energy laser beam to remove material from a workpiece. It is a thermal-based machining process where the energy of a laser beam is used to melt or vaporize the material, resulting in material removal.

Working Principle:
LBM works on the principle of focusing a high-energy laser beam onto a small spot on the workpiece surface. The laser beam, which consists of highly concentrated photons, carries a significant amount of energy. When the laser beam interacts with the workpiece material, it rapidly heats up and melts or vaporizes the material.

Key Steps in Laser Beam Machining:
Laser Beam Machining involves the following key steps:

1. Generation of Laser Beam: A laser beam is generated using a laser source, such as a carbon dioxide (CO2) laser or a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. These lasers can produce high-energy beams with different wavelengths and power levels.

2. Focusing the Laser Beam: The laser beam is then focused using a lens system or mirrors to create a concentrated beam of light. The focused beam is directed towards the workpiece surface.

3. Material Interaction: The focused laser beam interacts with the workpiece material, which can be metal, ceramic, or even non-metallic materials like wood or plastic. The energy of the laser beam is absorbed by the material, causing it to rapidly heat up.

4. Material Removal: As the material heats up, it melts or vaporizes, and the high-pressure gas or vapor removes the molten or vaporized material from the workpiece surface. The material removal occurs due to the thermal energy of the laser beam.

5. Control and Precision: LBM offers high precision and control over the material removal process. The laser beam can be accurately focused and controlled to achieve the desired depth and shape of the machined feature.

Advantages of Laser Beam Machining:
- Non-contact process: LBM does not require direct contact between the tool and the workpiece, reducing the chances of tool wear and damage.
- High precision: LBM can achieve very high levels of precision and accuracy in material removal.
- Versatility: LBM can be used to machine a wide range of materials, including metals, ceramics, plastics, and composites.
- Minimal residual stress: Due to the localized heating and rapid cooling in LBM, it produces minimal residual stress on the workpiece.
- No tool wear: Since LBM does not involve physical contact between the tool and the workpiece, there is no tool wear, resulting in longer tool life.

Conclusion:
Laser Beam Machining is a thermal-based machining process that utilizes a high-energy laser beam to remove material from a workpiece. It offers high precision, versatility, and minimal residual stress.