JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MACHINE TOOLS Previous Question Paper (February - 2022 - R13)

The Merchant Force Diagram represents the forces acting on a cutting tool during orthogonal machining. It is a circle diagram where the resultant force R is resolved into components acting at the tool-chip interface and the shear plane.

Key forces involved:

• F_c: Cutting force (horizontal)
• F_t: Thrust force (vertical)
• F: Friction force along the tool face
• N: Normal force to the tool face
• F_s: Shear force along the shear plane
• F_n: Normal force to the shear plane

The forces are related by the following geometric resolutions:

Where α is the rake angle and φ is the shear angle.

Chip formation occurs due to the plastic deformation of the work material as the cutting tool wedges into it. As the tool advances, the material ahead of the cutting edge is subjected to high compressive stress, causing it to undergo shear deformation along a specific plane. The material is compressed and pushed upward along the rake face of the tool, resulting in the formation of a chip.

Shear Plane: This is the theoretical plane extending from the cutting edge to the free surface of the work material, where the maximum shear stress occurs and the material undergoes plastic deformation to become the chip.

Shear Zone: In reality, the deformation does not occur along a single mathematical plane but within a narrow region of finite thickness. This region is known as the shear zone. Within this zone, the material transitions from its original state to the deformed state of the chip through intense shearing action.