A. Abrasive-flow machining:
In abrasive-flow machining, material removal occurs through the flow of a viscous abrasive media that is forced through the workpiece by hydraulic pressure. The abrasive particles in the media act as cutting tools, removing material from the workpiece surface. Thermal action is not involved in this process, as the material removal is primarily mechanical in nature.

B. Electrochemical grinding:
Electrochemical grinding is a process that combines the principles of electrochemical machining and conventional grinding. In this process, a grinding wheel is used as the cathode and a conductive fluid (electrolyte) is used as the anode. The grinding wheel is connected to a power supply, and when it comes into contact with the workpiece, a controlled electrochemical reaction occurs, which removes material from the workpiece. Thermal action is not the main mechanism of material removal in electrochemical grinding, as the process relies on electrochemical reactions.

C. Laser-beam machining:
Laser-beam machining is a non-contact thermal machining process that uses a high-energy laser beam to remove material from the workpiece. The laser beam is focused on the workpiece surface, causing localized heating and vaporization of the material. The vaporized material is expelled, resulting in material removal. Thermal action is the primary mechanism of material removal in laser-beam machining, as the intense heat generated by the laser beam causes the material to melt, vaporize, and be expelled.

D. Chemical machining:
Chemical machining is a process in which material removal occurs through the controlled chemical dissolution of the workpiece surface. A mask or stencil is applied to the workpiece, exposing only the areas that need to be removed. The workpiece is then immersed in a chemical etchant that selectively dissolves the exposed areas, leaving the masked areas untouched. Thermal action is not involved in chemical machining, as material removal is purely chemical in nature.

Conclusion:
Among the given options, laser-beam machining (option C) is the process in which material removal occurs primarily through thermal action. The intense heat generated by the laser beam melts, vaporizes, and expels the material from the workpiece surface. The other options, abrasive-flow machining, electrochemical grinding, and chemical machining, involve mechanical, electrochemical, and chemical mechanisms of material removal, respectively.

C