Jawaharlal Nehru Technological University Hyderabad B.Tech III METROLOGY AND MACHINE TOOLS Previous Question Paper (February - 2022 - R16)

The friction between the chip and the tool occurs at the tool-chip interface, specifically along the rake face of the cutting tool. This region is characterized by high pressure and temperature, leading to two distinct zones of contact: the sticking zone and the sliding zone.

In the sticking zone, which is located near the cutting edge, the pressure is so high that the chip material adheres to the tool surface, resulting in a shear strength equal to the shear strength of the work material. In the sliding zone, further along the rake face, the chip slides over the tool surface with a lower coefficient of friction. The total friction is a critical factor in metal cutting as it influences the cutting forces, the temperature at the tool tip, and the overall tool wear. High friction contributes to the formation of a Built-Up Edge (BUE) and increases the power consumption required for the machining process.

Heat in metal cutting is generated primarily through three sources: plastic deformation in the primary shear zone, friction at the tool-chip interface, and friction between the flank of the tool and the newly machined surface. The total heat generated is proportional to the energy consumed during the cutting process.

The dissipation of this heat occurs through three main paths:

1. Chip: The majority of the heat (often 60-80%) is carried away by the chip as it deforms and flows over the rake face.
2. Tool: A significant portion of the heat conducts into the cutting tool, which can lead to thermal softening and accelerated tool wear.
3. Workpiece: Heat is conducted into the bulk of the workpiece, potentially causing thermal distortion and changes in surface integrity.

Cutting fluids are typically employed to enhance heat dissipation by acting as a coolant, carrying heat away from the cutting zone through convection, and as a lubricant to reduce the heat generated by friction.